Waterborne engineering (csu) design report

Waterborne Engineering (CSU)

2010 WEFTEC Student Design Competition:

Rocky Mountain Region

Cristian Robbins

Asma Hanif

Ashwin Dhanasekar

Jenna Reaves

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TABLE OF CONTENTS

I. Executive Summary II. Introduction

III. Team Members’ Roles and Responsibilities

IV. Decision Criteria

V. Design Alternative Analysis VI. Cost Analysis

VII. Decision Analysis

VIII. Preliminary Design (BioWin Modeling) IX. Conclusion

X. Appendices

Appendix A: Treatment Train Schematics for Alternatives

Appendix B: Decision Analysis Graph and Table of Results Appendix C: Cost Analysis Tables

Appendix D: Energy Costs Associated with Phosphorus Removal

Appendix E: Refined Cost Estimation for Selected Alternative Appendix F: BioWin Modeling

Appendix G: Review of the DynaSand Filter

Appendix H: Review of the Hydrotech Discfilter Appendix I: Effects on Hydraulic Profile of Plant

Appendix J: Depiction of Process on Site Plan

Appendix K: Wastewater Safety Regulations for Chemical Addition

Appendix L: Possible Aluminum Health Effects Appendix M: Phosphorus Effects on Water Bodies

Appendix N: Phosphorus Recycling Post Removal

Appendix O: Autonomous Micro Fluidics Based Analyzer for Sensing Phosphorus In Waste Water

Appendix P: Relevant CDPHE Design Criteria

Appendix Q: Works Cited

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I. EXECUTIVE SUMMARY

Waterborne Engineering began this project by analyzing the existing Littleton and Englewood

Wastewater Treatment Plant. This plant is very unique and offered the opportunity to learn about the

individual processes in depth and the purpose that each serves. After analyzing the current plant and the

options for phosphorus removal techniques Waterborne Engineering decided on the following 4

phosphorus removal alternatives:

Alternative 1: Addition of a coagulant prior to the final clarifier and a second addition

after the nitrification trickling filters

Alternative 2: Addition of an anaerobic tank prior to the solids contact tank and chemical

feed of a coagulant after nitrification

Alternative 3: Addition of a coagulant after denitrification and addition of filtration for

phosphorus removal after chemical addition

Alternative 4: Addition of alum prior to the final clarifier and a second addition of

phosphoric acid (H3PO4) after nitrification

After completing a thorough analysis of all four alternatives using decision analysis software and an

initial cost analysis, Waterborne Engineering decided that alternative 3 consisting of adding a coagulant,

alum, after denitrification and adding filtration designed for phosphorus removal, Parkson DynaSand

granular filters, after the chemical addition offered the greatest benefits with an acceptable cost. This

alternative does not disturb the plant’s biological processes and also the filtration system has been proven

to work within current wastewater treatment plants to remove phosphorus well below the proposed level

of 0.135 mg/L. Utilizing BioWin modeling software, Waterborne Engineering simulated this alternative

and obtained a value of 0.04 mg/L of phosphorus in the final effluent.

II. INTRODUCTION

This project serves to evaluate options for adding phosphorus removal to the existing

Littleton/Englewood Wastewater Treatment Plant process. The Water Quality Control Division is

developing a proposal for numeric criteria for total phosphorus for rivers and streams to be considered in

June 2011 that could lead to regulatory guidance for phosphorus in the final effluent from wastewater

treatment plants. Various phosphorus removal technologies were evaluated and the most effective

alternative was selected that would best integrate into the existing treatment scheme. Various phosphorus

removal technologies were researched and the best phosphorus removal process capable of meeting both a

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30-day and 7-day average permit limit for total phosphorus was chosen. Flexibility within the design

proved to be a key consideration in choosing the best alternative. Other key criteria for selecting an

alternative were performance, treatment residuals, and integration into existing system. These will be

discussed in detail along with other criteria used in the design criteria section of the report. The proposed

stream standard for phosphorus was 0.135 mg/L and this is what the design criteria are for this project.

However, CDPHE raised the limit to 0.16 in October 2010 (October 13 WQCD work group meeting) and

it is possible that it could be increased further.

Additionally, the best location for the phosphorus removal process within the existing plant site was

chosen and infrastructure requirements for the process were evaluated. In order to best select an

alternative, cost estimation was completed on all options to analyze overall capital construction and

operating costs. A decision analysis was conducted utilizing a decision criteria matrix to recommend the

most effective phosphorus removal alternative to the Littleton / Englewood Wastewater Treatment Plant

to implement within their existing treatment scheme based on relative costs and benefits of each

alternative. After selecting the alternative, a preliminary design was completed using BioWin 3.1

modeling software to determine the level of phosphorus removal achieved and specific design parameters.

III. TEAM MEMBERS’ ROLES AND RESPONSIBILITIES

The Waterborne Engineering Group (Colorado State University) was divided into four functional areas

to best address the problem. Each team member will be the lead for their respective area, but everyone

will assist where needed to determine the best option for phosphorus removal.

Integration (Cristian Robbins) – The integration team lead will be responsible for cost estimation for each

alternative, scheduling of tasks and milestones, decision analysis, and report coordination.

Process (Jenna Reaves) – The process team lead will be responsible for the overall design of the process

of phosphorus removal within the existing treatment process. Within this role, the process team lead will

conduct a literature review to better understand the phosphorus removal process background and various

techniques along with understanding permit limits and guidelines associated with phosphorus removal.

Design (Asma Hanif) – The design team lead will be responsible for the more detailed technical aspects of

phosphorus removal within the treatment train. This involves clearly understanding the various

phosphorus removal technologies along with the effectiveness of each in removing phosphorus. The

design team lead will be in communication with vendors to best select the appropriate phosphorus

removal technology to best suit the needs of the Littleton / Englewood Wastewater Treatment Plant. Also,

this team member will knowledgeable with CDPHE design criteria.

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Hydraulics/Plant Layout (Ashwin Dhanasekar) – The hydraulics/plant layout team lead will be

responsible for applying the chosen phosphorus removal technology within the existing plant treatment

train. This team member will fully understand the existing plant treatment train and find locations within

the plant to best optimize phosphorus removal. Also, this person will understand the L/E WWTP’s

SCADA system and how our recommended phosphorus removal technology will integrate into the

existing SCADA system.

IV. DECISION CRITERIA

Four phosphorus removal alternatives were identified and they were analyzed using Criterium

Decision Plus software (student version manufactured by InfoHarvest). The alternatives include two stage

chemical addition, enhanced biological nutrient removal, chemical addition (post precipitation) with

additional filtration, and chemical addition with phosphoric acid addition. These alternatives are discussed

in detail in the alternative analysis section of this report. The criteria and weights (maximum is 100) are

described below.

Performance (100)

Performance received the maximum weight of 100 because of the importance to this project to have an

effective phosphorus removal technique. Due to changing regulatory guidance for nutrient removal in

wastewater, the technique that will be chosen will need to remove phosphorus to a level possibly as low

as <0.135 mg/L. The alternative that will receive the highest rating will need to provide the best

performance in regards to removing phosphorus and provide the lowest level of phosphorus in the

effluent. Questions that will be asked when rating the alternatives for this criterion will be:

Does this alternative perform at a rate of <0.135 mg/L?

Will this alternative perform effectively and efficiently?

Does not affect the nitrification/denitrification processes?

Risk of Technology (60)

If an alternative is selected that is not widely used, there may be some risk of failure of that technique

due to it either being a relatively new technique or not used regularly. A newer technique may prove to be

very effective at phosphorus removal in at lab or pilot scale but when applied in a full scale treatment

plant it may not be as effective. Phosphorus removal techniques that are widely used and been effective in

operation will receive a high rating for this criterion. Techniques that have not been widely used and

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where only minimal data has been collected at a full scale will receive a lower rating. Questions that will

be asked while rating the alternatives for risk of technology:

Is the alternative widely used in full scale treatment plants and has it been proven to be effective

based on operational data?

If the alternative is relatively unknown and not widely used, how much data and research

supports the effectiveness of the technique?

Safety (80)

Safety always is of the utmost importance and needs to be factored into everything that occurs within

the plant. Ensuring that the chosen phosphorus removal technique is safe will reduce the overall cost of

the selected alternative by reducing the risk of accidents and days lost on the job for workers at the plant.

Questions that will be asked when rating safety for the alternatives are:

Will this alternative pose any unsafe working conditions for those operating the removal process?

If so, what? How will it affect the operators?

Maintenance (70)

A technique that requires minimal maintenance and also possesses durability over time will receive the

highest rating for this criterion. A technique that requires a large amount of maintenance will greatly

affect the operating and maintenance (O & M) costs and will be factored into the cost estimation for each

alternative. If the alternative receives a high rating for maintenance it will result in lower overall O & M

costs. Questions that will be asked when maintenance is rated for each alternative:

Will this alternative require a lot of maintenance?

How long will this alternative last?

Integration into Existing System (80)

It is important to ensure that the alternative that has the highest rating is complimentary of the existing

processes within the plant. The selected alternative needs to fit within the existing treatment train for the

plant without adversely affecting other processes within the plant. It is crucial to the success of the

treatment plant that the alternative chosen does not decrease the efficiency of the existing plant and the

processes that are already functional. Also, it is vital to the cost analysis to know whether the alternative

can fit into the existing plant with minimal addition of infrastructure which would increase cost.

Questions that will be asked when rating integration into existing system:

Can this alternative be implemented quickly and effectively into the existing plant?

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Can this alternative be placed directly into this plant or does it require additional infrastructure

and a change in the current plant?

Flexibility of Design (70)

With the proposed standard for phosphorus in effluents from wastewater treatment plants still in a draft

status, there exists a high probability that the proposed standard of 0.135 mg/L will change. Most

information gathered from correspondence from the Colorado Nutrient Coalition, wastewater treatment

plants, and other entities point to the standard moving more towards 0.5 mg/L of phosphorus in the

effluent. Due to this, an alternative needs to be flexible in responding to a change in the standard of

phosphorus in the effluent. An alternative that allows for modifications to be easily implemented as a

response to a change in the standard will receive the highest rating as it will be able to optimize

performance and cost for the plant in removing phosphorus to meet the standard. Questions that will be

asked while rating the flexibility of design criterion:

How easily can the alternative be modified to adjust to a change in the phosphorus removal

standard?

How can the alternative be modified to either remove more or less phosphorus?

Treatment Residuals (80)

It is important to analyze the production of treatment residuals for alternatives. An alternative that

produces a large amount of treatment residuals may cause a stress on the current processes of dealing with

residuals that could lead to costly additions to infrastructure. An alternative that produces a small amount

of treatment residuals that can easily be handled with the existing plant processes will receive a high

rating. Alternatives that produce a large amount of residuals will receive a lower rating, because it may

cause addition to infrastructure or increase in costs to dispose of the residuals. Questions that will be

asked while rating the treatment residuals criterion:

Will the alternative produce a significant amount of treatment residuals?

Will the current plant’s processes to handle treatment residuals be affected by the alternative

increasing the amount of residuals?

V. DESIGN ALTERNATIVE ANALYSIS

In this section, the four alternatives will be analyzed and rated using the decision criteria discussed

earlier. Each alternative will be scored based on how well each alternative meets the criteria.

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ALTERNATIVE 1: PHOSPHORUS REMOVAL USING TWO STAGE CHEMICAL ADDITION

In Figure 1 in Appendix A, the location for two stage chemical addition within the existing Littleton

and Englewood Wastewater Treatment Plant is shown. Phosphorus is commonly removed with chemical

precipitation and it is a common process to use two chemical application points within the treatment train

to optimize the dose of chemical for phosphorus removal.

The removal of phosphorus using chemical addition involves the mixing of a coagulant and the

wastewater. Calcium, iron and aluminum are all common coagulants used in this process. In current

practice, this process removes up to 90% of the phosphorus within the wastewater, but the amount of

coagulant added is in direct relation with the amount of phosphorus needing to be removed. With the

addition of a coagulant in two locations, this alternative should provide low levels of phosphorus in the

effluent to meet the proposed standard for total phosphorus of 0.135 mg/L.

After the solids contact tank, a coagulant will be added to form precipitates that can be removed in the

final clarifier. Nitrification and denitrification requires a certain amount of phosphorus to function. The

Water Environment Research Foundation (WERF) recommend 0.04 g P/ g NOx-N removed while other

research suggests that the threshold for phosphorus limitation on tertiary denitrification occurs at a filter

influent ortho-P/NOx-N ratio of approximately 0.01.1 This alternative will be designed to not affect the

nitrification and denitrification processes. After nitrification takes place an additional dose of chemical

will be added. The denitrification filters located after this addition will remove phosphorus by solids

separation.

Performance (95/100)

Chemical addition in two different locations within the existing treatment train will provide the ability

to remove phosphorus to below the proposed limit of 0.135 mg/L and can achieve a lower effluent TP

concentration.2 An example of multi-point chemical addition with filtration in use is at the Milford

WWTP in Milford, MA. A chemical is added prior to secondary clarification and prior to filtration and

they achieve an average effluent phosphorus concentration of 0.07 mg/L3 which would easily meet the

proposed phosphorus effluent limit for Colorado. This alternative will provide a high level of phosphorus

removal to meet the proposed standard.

1 Littleton/Englewood Wastewater Treatment Plant. 2010/2011 Student Design Competition – Supplemental Information Document #1: 2010.

2 George T. Moore. Scientific, Technical, Research, Engineering, and Modeling Support

(STREAMS). Environmental Protection Agency. Nutrient Control Design Manual. MA: 2010.

3 Water and Watersheds. Environmental Protection Agency. Advanced Wastewater Treatment to

Achieve Low Concentration of Phosphorous. Seattle: 2007.

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Risk of Technology (60/60)

Chemical precipitation for phosphorus removal is a reliable, time-tested wastewater treatment method

that has not drastically changed over the years.4 The risk of technology for this alternative is low so this

alternative will receive the maximum score for this criterion.

Safety (70/80)

When dealing with chemicals, there are always inherent risks. These risks can be mitigated by

practicing sound safety procedures. Maintaining a storage facility with restricted access and proper

signage will help mitigate the risk. Also, ensuring that anyone operating around the chemicals uses proper

personal protective equipment (PPE) will also mitigate the risk. These are all practices that have been

implemented at the L/E WWTP for dealing with chemicals on site and since this alternative is widely

used with no major accidents reported this alternative can be deemed to be relatively safe.

Maintenance (40/70)

With this alternative, there will be an increase in regards to maintenance of the filters. The addition of

a chemical prior to denitrification will cause increased solids accumulation on the denitrification filters.

This will cause frequent backwashes of the filters due to the addition of the chemical and the formation of

precipitates that will be removed using the solids separation process. An in-depth analysis will need to be

conducted to determine whether the existing filters would be overburdened. With the addition of the

chemical occurring without any clarification prior to filtration, it can be safely assumed that the filters

will need to be backwashed regularly.

Integration into Existing System (50/80)

A chemical feed system will need to be installed and possibly a new storage facility for the chemical

used for precipitation. These are common practices within wastewater treatment plants and have been

widely utilized so it should not be an issue integrating the chemical addition into the existing system. As

discussed in the beginning of this summary, some amount of phosphorus needs to be available prior to

denitrification or this process will be negatively affected. This will make this alternative more difficult to

integrate as it will require additional design and engineering to optimize this alternative. Additionally,

chemical phosphorus removal consumes alkalinity that can affect nitrification.5 More specifically, if the

chemical is added before the secondary clarifier (co-precipitation) then alkalinity will be removed within

the biological nitrification process that can lower pH and inhibit nitrification.6 Since the first stage of

chemical addition occurs prior to nitrification and prior to the secondary clarifier, this will need to be



5 Ibid.

6 Ibid.

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addressed. Based on these drawbacks and the increased operational complexity, integration into the

existing system will be somewhat difficult.

Flexibility of Design (65/70)

Chemical addition in multiple locations provides flexibility to the amount of phosphorus that needs to

be removed.7 This alternative provides the ability to optimize the chemical dose to meet lower

requirements and a good control point at final dosing.8 More chemicals can be added in order to decrease

the phosphorus levels more and can be decreased according to regulations and nitrification needs

Treatment Residuals (35/80)

The addition of chemical precipitation of phosphorus will significantly increase the sludge production

for this facility.9 An additional consideration is that the use of metal salts can lead to large increases in

inorganic solids in the sludge, which can result in increased organic salts (salinity) in sludge and the

effluent. Salinity can create problems when biosolids are land applied or when the effluent is returned to

existing water supply reservoirs10

Overall, the increased sludge production will increase cost and require

further engineering to best apply the treatment residuals beneficially.

ALTERNATIVE 2: ENHANCED BIOLOGICAL NUTRIENT REMOVAL (EBNR)

The second alternative, shown in Figure 2 in Appendix A, involves Biological Nutrient Removal

(BNR) that requires the addition of an anaerobic tank along with chemical addition similar to the Pho-

redox process (A/O). In this process, an anaerobic zone is added at the head of the aeration basin.11

The

benefit of this removal process is a lower level of sludge production, as well as the likelihood of reaching

levels of phosphorus <0.1 mg/L. The issue that needs to be addressed with this alternative is the

complication with cold weather, the functionality of this alternative, and the construction of an additional

basin before the solids contact tank.


An EBNR treatment system promotes the production of phosphorus accumulating organisms that

utilize more phosphorus in their metabolic processes than a conventional secondary biological treatment

process. The average total phosphorus concentration in raw domestic wastewater is usually between 6 to 8

mg/l and the total phosphorus concentration in municipal wastewater after conventional secondary

treatment is routinely reduced to 3 or 4 mg/l. For the L/E WWTP, the average influent TP concentration

7 Ibid. 8 Ibid.

9 Mackenzie L. Davis. Water and Wastewater Engineering. (New York: McGraw-Hill, 2010), 19-4.



11 Ibid.

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for August 2010 was 4.54 mg/L and the average TP concentration after secondary treatment in August

2010 was 2.73 mg/L. EBNR incorporated into the secondary treatment system can often reduce total

phosphorus concentrations to 0.5 mg/l or less.12

Facilities using EBNR significantly reduced the amount

of phosphorus to be removed through the subsequent chemical addition and tertiary filtration processes.

This improves the efficiency of the tertiary process and can significantly reduce the costs of chemicals

used to remove phosphorus. An example of this process in use is at the Durham Advanced WWTP in

Tigard, OR.13

They utilize BNR, chemical addition, and filtration within their treatment train. They

reported a monthly average of 0.07 mg/L TP.14

This alternative has been demonstrated to achieve a TP

concentration lower than the proposed standard of 0.135 mg/L.


Biological phosphorus removal is a widely used and trusted technique. Adding an anaerobic tank prior

to a solids contact tank is not a commonly used technology. The addition of the tank will create the

anaerobic/aerobic process similar to an A/O process, but the tank addition may have issues. Since this

retrofitting is not common there is a risk associated with implementing this alternative.

Safety (80/80)

In regards to the effluent water being released into the environment, recent studies report finding that

WWTPs using EBNR also significantly reduce the amount of pharmaceuticals and health care products

from municipal wastewater, as compared to the removal accomplished by conventional secondary

treatment. The same procedures discussed in the safety paragraph in alternative 1 for dealing with

chemicals will need to be implemented for this alternative.

Maintenance (60/70)

Maintenance is not going to be affected by the addition of an anaerobic tank. A high internal recycle

rate of about 4:1 is maintained to provide adequate contact time for wastewater treatment through EBNR.

This recycle rate means that for every 10 MGD of wastewater influent treated about 50 MGD is routed

through the treatment system. The mixed liquor suspended solids concentration is maintained at about

1800 mg/l in the contact basins. This represents a solids retention time of about 20 days. The addition of

the anaerobic tank will not require frequent maintenance. With this alternative, there will be an increase in

regards to maintenance of the filters due to chemical addition. Filtration increases maintenance when the

12 Ibid.



14 Ibid.

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chemical addition application point is during tertiary treatment only.15

This will lead to more frequent

backwashes of the filters due to the addition of the metal salt prior to filtration. An in-depth analysis will

need to be conducted to determine whether the existing filters would be overburdened.


The addition of this alternative will require construction and addition to the infrastructure. An

anaerobic tank will have to be built in the current footprint prior to the aeration zone of the solids contact

tank. The chemical addition of this alternative should integrate into the system relatively easily. A

chemical feed system will need to be installed and possibly a new storage facility for the chemical. These

are common practices within wastewater treatment plants and have been widely utilized so it should not

be an issue integrating the chemical addition into the existing system. Overall, this alternative should

integrate into the existing system relatively well but will require extensive infrastructure addition.


It has been shown in the performance paragraph that this alternative can remove phosphorus at a level

well below the proposed standard. Similar to other chemical addition alternatives, in this alternative, if the

proposed standard is increased the amount of chemical added can be reduced to meet the change and

optimize the use of chemicals. However, if the biological phosphorus removal does not perform well, then

it will require an increase in chemicals which reduces the flexibility of this design.


The addition of an anaerobic tank will not increase the sludge production for this facility as much as

the chemical precipitation alternatives but since chemical precipitation occurs prior to denitrification to

polish the effluent there still will be an increase in sludge production. The results of adding chemical

addition with regards to increased sludge production is discussed previously in the alternative 1 summary.

ALTERNATIVE 3: POSTPRECIPITATION WITH ADDITIONAL FILTRATION

The third alternative, shown in Figure 3 in Appendix A, involves utilizing chemical addition

(commonly known as post precipitation) and filtration. This alternative adds two to eight filters to the

existing DENIT filtration gallery to achieve low levels of phosphorus and nitrogen. This alternative is

extremely effective in obtaining low levels of phosphorus in the effluent and also will not affect any of

the existing biological processes that occur in the plant’s treatment train.

15 George T. Moore. Scientific, Technical, Research, Engineering, and Modeling Support (STREAMS).

Environmental Protection Agency. Nutrient Control Design Manual. MA: 2010.

13


Chemical addition post secondary treatment with additional filtration will provide the lowest

phosphorus content in the effluent out of all possible locations for chemical addition.16

Thus, it will

optimize performance in regards to removing phosphorus and should easily meet a minimum standard of

0.135 mg/L TP in the effluent. A general example of this alternative in use is at the Walton Wastewater

Treatment Plant in Walton, NY.17

After secondary clarification, aluminum chloride is added for

flocculation and then filtration through two-stage DynaSand filters occurs. This plant produces a total

phosphorus range of monthly averages of <0.005 to <0.06 mg/l.18

Also, it has been noted that the key to

achieving low TP limits is the solids separation process. Typically, conventional clarification is not

sufficient in many cases and low target limits require advanced clarification processes or effluent

filtration.19

For this alternative, there will be additional effluent filtration that will achieve low target

limits for TP.


As noted in the performance paragraph, this process is documented in textbooks and utilized by

wastewater treatment plants throughout the country. Chemical precipitation for phosphorus removal is a

reliable, time-tested wastewater treatment method that has not drastically changed over the years.20

The

risk of technology for this alternative is low so this alternative will receive the maximum score for this

criterion.

Safety (75/80)

When dealing with chemicals, there are always inherent risks. These risks can be mitigated by

practicing sound safety procedures. Maintaining a storage facility with restricted access and proper

signage will help mitigate the risk. Also, ensuring that anyone operating around the chemicals uses proper

personal protective equipment (PPE) will also mitigate the risk. These are all practices that have been

implemented at the L/E WWTP for dealing with chemicals on site and since this alternative is widely

used with no major accidents reported this alternative can be deemed to be relatively safe.

16 Takashi Asano, et al., Water Reuse: Issues, Technologies, and Applications (New York: Metcalf

& Eddy, 2007) 329.

17 Water and Watersheds. Environmental Protection Agency. Advanced Wastewater Treatment to Achieve Low Concentration of Phosphorous. Seattle: 2007.

18 Ibid.



20 Ibid.

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Maintenance (50/70)

With this alternative, there will be an increase in regards to maintenance of the filters. Filtration

increases maintenance when the chemical addition application point is during tertiary treatment only.21

With the addition of the chemical occurring without any clarification prior to filtration, it can be safely

assumed that the filters will need to be backwashed regularly. Frequent maintenance of the new filters

will need to occur increasing the maintenance requirements for the plant.


A chemical feed system will need to be installed and possibly a new storage facility for the chemical.

Additional filtration added to the treatment train could make the integration and implementation a little

more difficult. Additional infrastructure may be needed to add on to the current filtration gallery.

However, since all of this occurs after denitrification disruption to the plant’s existing processes will be

minimal which makes the integration easier.


An important aspect of this project is selecting an alternative that can respond to a change in the

proposed effluent phosphorus limit of 0.135 mg/L. It has been shown in the performance paragraph that

this alternative can remove phosphorus at a level well below the proposed standard. In this alternative, if

the proposed standard is increased the amount of chemical added can be reduced to meet the change and

optimize the use of chemicals. This would be relatively easy to implement utilizing the SCADA system

and would lower the amount of precipitate formed along with lessening the burden on the filters.

Additionally, the precipitant can be recycled to the headworks for added P removal which provides

additional flexibility.22

This alternative is very flexible to respond to changes in regulatory guidance.


As discussed in previous alternative 1, the addition chemical phosphorus precipitation will greatly

increase the sludge production for the facility.23

If the only chemical application point occurs during

tertiary treatment, there will be a need for separate sludge handling which can add to the complexity of

the process.24

The sludge will be removed via the additional filters and will be the only location where

increased sludge production will occur.

21 Ibid.

22 Ibid.

23 Mackenzie L. Davis. Water and Wastewater Engineering. (New York: McGraw-Hill, 2010), 19-4.



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ALTERNATIVE 4: CHEMICAL ADDITION WITH PHOSPHORIC ACID ADDITION

This alternative involves chemical addition similar to alternative 1 but in order to not affect the

nitrification and denitrification processes, phosphoric acid will be added if needed to ensure that enough

phosphorus is remaining in the effluent prior to this process. In order for denitrification to be effective,

this process needs available phosphorus and if too much phosphorus is removed in order to meet the

standard defined earlier for phosphorus, then issues will occur during denitrification. To prevent these

issues, the use of phosphoric acid will add enough phosphorus to the flow prior to denitrification when

needed to allow for this process to occur without issue.


The effectiveness of phosphorus removal by chemical addition is highly dependent on the solids

separation process following chemical precipitation.25

Chemical addition prior to secondary clarification

will remove phosphorus to a low level. This alternative will require a large dose of chemical since it is a

single point chemical addition process. If phosphorus is not removed during secondary treatment, then the

removal of phosphorus will be limited through the nitrification and denitrification processes based on the

current plant effluent data for total phosphorus. Due to this, the performance of this alternative will not be

as high as the other alternatives.


The addition of phosphoric acid to aid in the denitrification process is not commonly practiced. This

will require more attention to detail than other alternatives and add risk on whether the process will be

effective since it is not widely used. This will make the risk of technology high for this alternative.

Safety (65/80)

The safety risks for this alternative are similar to those in alternative 1. The major difference is the

handling of phosphoric acid which is a more dangerous chemical than a metal salt and will require

additional training on the safe handling of this acid.

Maintenance (65/70)

In this alternative, most of the phosphorus will be removed during secondary clarification. Thus, there

will not be an increase in solids accumulation on the filters so there will not be added maintenance to the

filters. The effect of phosphoric acid on the filters may be an issue which may result in increased

maintenance for the filters.

25 Ibid.

16


This alternative will have similar issues as discussed earlier for alternative 1. The major difference is

that the addition of phosphoric acid will help to mitigate the effects on the biological processes, but it will

greatly add to the operational complexity. This alternative will be relatively difficult to implement.


Chemical addition adds flexibility to the amount of phosphorus removed. However, a single point

chemical addition process will limit the optimization of chemical dosage as compared to a multi-point

chemical addition process. In general, this alternative will not provide much flexibility as other

alternatives.


This alternative will be similar in increased sludge production to alternative 1. This will increase cost

and require further engineering to best apply the treatment residuals beneficially.

VI. COST ANALYSIS

In order to complete the decision analysis between the four alternatives an initial cost analysis was

made using information from the “Environmental Protection Agency: Biological Nutrient Removal

Processes and Costs” as well as the “Arlington County Water Pollution Control Plant-Master Plan 2001

Update.” The costs are shown in Tables 2 and 3 in Appendix C. The latter document gave specific

information on costs such as building a chemical storage facility, additional chemical feed points, and

construction of a tank. These costs are reflected in Table 3 in the breakdown of the costs used in the

analysis.

Due to alternatives 1, 2, and 4 all requiring lime prior to nitrification to increase the alkalinity that was

consumed with the metal salt the chemical costs will be higher than for alternative 3 which will not add a

chemical until after denitrification. Additionally, for alternative 4 there will be the additional cost of

phosphoric acid to increase the amount of phosphorus prior to denitrification. In Table 2, information

regarding the complete capital and operation and maintenance costs of each alternative is shown. Table 3

breaks these costs into sections.

Assumptions were made in regards to the energy and maintenance costs. It was assumed that the

energy costs would equate to 5% of the capital cost of each alternative and that the maintenance costs

would equate to 20% of the capital cost of each alternative. This does not account for the possibility of

more frequent backwashes on the denitrification filters for alternatives 1, 2, and 4 due to the metal

addition prior to this process. It can also be safely assumed that this additional loading onto the

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denitrification filters could result in a shorter operational lifespan that could result in higher lifecycle

costs for alternatives 1, 2 and 4.

Contingency and engineering costs were assumed to be 15% of the capital cost for each alternative.

Various documents used that number as a good value for these costs. The costs associated with additional

sludge production did not get factored into the initial cost analysis. The cost for additional sludge

production will be determined for the chosen alternative based on the amount of chemical added in the

BioWin simulation model and is shown in Appendix E.

VII. DECISION ANALYSIS

Waterborne Engineering utilized Criterium Decision Plus software to determine the best alternative

based on benefits from our decision criteria. In Figures 5 and Table 1, the results of the decision analysis

are presented in a bar graph and in tabular format. The highest rated alternative was alternative 3,

chemical addition after denitrification with additional filtration, with a score of 0.663 out of 1. Alternative

2, EBNR, came in second with a score of 0.649 and alternative 4, chemical and phosphoric addition, came

in last with a score of 0.554. Based on the results, it can be determined that solely based on benefits and

before a cost analysis has been completed that alternative 3 would be the recommended alternative. After

getting the results of the decision analysis from Criterium Decision Plus, a cost analysis was completed

for all four alternatives so that a relative costs versus benefits analysis would be able to provide a

recommended alternative.

Alternative 2 due to the addition of an anaerobic tank prior to the solids contact tank proved to be the

costliest alternative. The next costliest alternative was alternative 2 due to addition of addition filtration

designed for phosphorus removal. Alternatives 1 and 4 had the lowest costs due to these options not

requiring much addition to infrastructure besides chemical feed systems and chemical storage facilities.

As discussed in the cost analysis, there exists other factors for alternatives 1, 2, and 4 in regards to adding

a chemical prior to nitrification and denitrification which could significantly increase the up front costs

and lifecycle costs.

When comparing the alternatives, the main factor considered was not disrupting the nitrification and

denitrification processes of the plant. As discussed earlier, chemical addition prior to these processes will

consume alkalinity resulting in increased chemical costs because lime will need to be added and also there

exists the possibility of having too little phosphorus prior to nitrification and denitrification which could

starve the processes and create issues in regards to nitrogen removal. To avoid these issues, the best

course of action will be to add alum after denitrification and add a solids separation process to remove the

18

precipitate. To best remove the precipitate, additional filtration designed specifically for phosphorus

removal will provide the best results. Even though alternative 3 has a higher cost than alternative 1 (multi-

stage chemical addition), the benefits of placing the chemical addition and filtration after denitrification

outweigh the difference in cost. The issues, such as consuming alkalinity and starving the

nitrification/denitrification processes, that could arise with adding chemicals prior to these biological

processes could result in these processes being ineffective at nitrogen removal or requiring a level of

phosphorus higher than the proposed standard prior to denitrification which could result in not achieving

the proposed standard if these filters are unable to remove the phosphorus.

An additional factor to consider is that the denitrification filters are not designed for phosphorus

removal. Also, they may not be designed to handle the additional precipitate that will be loaded on to the

filters. This could degrade the filters in regards to denitrification and will require more frequent backwash

that will increase the energy costs. Also, the operational lifespan of the denitrification filters will more

than likely be reduced due to the additional loading of precipitate onto the filters. These additional costs

are hard to quantify until pilot testing occurs but would more than likely greatly increase the cost of the

multi-stage chemical addition alternative. In the future, regulations will include limits on nitrogen that

will require the denitrification process to perform effectively.

Based on the relative cost and benefits analysis and the issues discussed in the previous paragraphs,

Waterborne Engineering recommends alum addition post denitrification followed by filtration to optimize

phosphorus and nitrogen removal within the Littleton / Englewood WWTP.

Furthermore, Waterborne Engineering after comparing two different filters designed for phosphorus

removal (Appendices G & H) recommends purchasing Parkson DynaSand continuous, upflow, deep bed

granular filters. The other filter considered was the HydroTech Discfilter but it does not have the proven

track record of DynaSand filters and did not provide as many benefits. DynaSand filters are a proven

method for phosphorus removal utilized by numerous wastewater treatment plants around the United

States as shown in the EPA’s 2007 study ‘Advanced Wastewater Treatment to Achieve Low

Concentration of Phosphorus.’ These filters will provide the L/E WWTP with a solids separation process

that is low energy and low maintenance and that is been proven to remove phosphorus to low levels.26

It

is recommended that the modular concrete design for DynaSand filters be built due to it being able to

handle larger flows. 32 DynaSand 80” deep bed filters should be purchased with each filter being able to

treat 1 MGD flow each. The filters should be configured in 8 cells with 4 filters per cell. The DynaSand

filter loading rate for phosphorus removal will be 3-5 gpm/ft2 per filter.

27 The estimated cost for these

26 DynaSand Continuous, Upflow, Granular Media Filter (Parkson, 2009).

27 Ibid.

19

filters is provided in Appendix E and a diagram of the DynaSand filter is shown in Figure 8 of Appendix

G.

VIII. PRELIMINARY DESIGN (BIOWIN MODELING)

The preliminary design of the recommended alternative was completed using BioWin 3.1 modeling

software (Appendix F). BioWin 3.1 is utilized worldwide to accurately model wastewater treatment plants

processes and provided Waterborne Engineering with a powerful tool to predict the effluent phosphorus

level. Due to the recommended alternative occurring after denitrification, Waterborne Engineering was

able to simplify the model and only needed to model the plant treatment train after denitrification through

phosphorus filtration. The BioWin model is shown in Appendix F along with explaining how BioWin can

be used to model treatment trains.

In order to do this, the values for the denitrification effluent were inputted into BioWin as the initial

values for the model (these values are shown in Table 7 in Appendix F). In BioWin, the microscreen icon

is utilized to model granular media filters but a volume is not inputted for microscreens. BioWin required

that an icon with a volume be inputted to run a simulation and due to this a media bioreactor with a

volume of 1 cubic meter was added (labeled Null Bioreactor). This media bioreactor did not have any

effect on the denitrification effluent as all values remained the same coming out of the media bioreactor.

Alum addition was inputted next in the model. To optimize phosphorus removal, an alum dose of 150

mg/L was added which equated to 45.42 kg per day of alum (100 lbs of alum per day). This equates to

roughly a 0.05 ton of alum needed per day to optimize phosphorus removal. This cost related to this

output will be discussed and calculated in the refined cost analysis in Appendix E.

Filtration was modeled next utilizing the microscreen icon. This resulted in 362.12 kg per day of

additional sludge being produced that will be factored into the alternative cost and possibly by reclaiming

phosphorous for beneficial uses that could mitigate some of the costs of the increased sludge production.

After simulation of the model, the final effluent value for phosphorus was 0.04 mg/L. This value

corresponds to the phosphorus effluent values for plants in the United States currently utilizing DynaSand

filtration for phosphorus removal and also is a significant amount below the proposed standard of 0.135

mg/L for phosphorus in WWTP effluent in Colorado.28

Due to the flexibility of this design, the amount of

alum used can be reduced to optimize the chemical cost while meeting the standard for phosphorus in the

plant’s effluent. When an alum dose of 109 mg/L was applied, the amount of alum was reduced to 33 kg

per day and the effluent phosphorus level was 0.13 mg/L. This still meets the proposed standard and if the



20

standard moves to 0.50 mg/L of phosphorus, then an alum dose of 77 mg/L, which is 23 kg per day of

alum used, can be applied to meet that standard. Clearly, chemical addition after denitrification with

filtration provides the flexibility to optimize phosphorus removal in the L/E WWTP without affecting any

of the current processes within the plant.

IX. CONCLUSION

The best alternative for the Littleton / Englewood Wastewater Treatment Plant to optimize phosphorus

removal without disturbing the nitrification and denitrification processes of the plant is to add alum post

denitrification and add DynaSand filters for phosphorus removal after chemical addition. If chemicals are

added prior to nitrification and denitrification, there exist numerous issues that could result in these two

processes being detrimentally affected. Also, the denitrification filters would face increased loading from

the chemical precipitate which could degrade the filter media rapidly resulting in more frequent

backwashes and a shorter operational lifespan.

A refined cost estimation for our selected alternative was completed and the results are shown in

Appendix E. The other alternatives by adding chemicals prior to nitrification and denitrification greatly

increase the high likelihood of disruption to the plant’s biological processes. With chemical addition post

denitrification and the proven effectiveness of tertiary filtration for phosphorus removal utilizing

DynaSand filters makes the additional filtration alternative the most desirable. Due to this, Waterborne

Engineering recommends this alternative to be implemented in the Littleton / Englewood Wastewater

Treatment Plant.

21

APPENDIX A: TREATMENT TRAIN SCHEMATICS FOR

ALTERNATIVES

Figure 1. Possible Phosphorus Removal using Two Stage Chemical Addition disinfection

Figure 2. Second Alternative: Enhanced Biological Nutrient Removal (EBNR)

Figure 3. Third Alternative: Chemical Addition with Added Phosphorus Removal Filters

Figure 4: Fourth Alternative: Chemical Addition with Phosphoric Acid Addition

22

APPENDIX B: DECISION ANALYSIS GRAPH AND TABLE OF RESULTS

Figure 5: Bar Graph of Decision Analysis Results

Lowest Level Chemical Precip

(2 Locations) EBNR Chem Precip w/ Filtration

Chem Precip w/ Phos.

Acid Model

Weights

Performance 0.95 0.9 1 0.8 0.185

Risk of Technology 0.6 0.4 0.55 0.3 0.111

Safety 0.7 0.8 0.75 0.65 0.148

Maintenance 0.4 0.6 0.5 0.65 0.13

Integration into Existing System 0.5 0.55 0.7 0.45 0.148

Treatment Residuals 0.35 0.6 0.4 0.45 0.148

Flexibility of Design 0.65 0.55 0.6 0.45 0.13

Results 0.608 0.649 0.663 0.554

Table 1: Table of Decision Analysis Results

23

APPENDIX C: COST ANALYSIS TABLES

Table 2: Complete Alternative Costs

Costs Divided Alternative #1 Alternative #2 Alternative #3 Alternative #4

Chemicals: $750,000 $350,000 $250,000 $850,000

Feed and Storage

Facility: $762,500 $381,250 $381,250 $762,500

Additional Feed

Points: $250,000 $125,000 $125,000 $250,000

Energy: $100,625 $430,313 $300,313 $100,625

Sludge Pump: $1,000,000 $750,000 $1,000,000 $1,000,000

Maintenance: $552,250 $251,250 $351,250 $572,500

Additional

Anaerobic Tank: N/A $7,000,000 N/A N/A

Additional Filters: N/A N/A $4,500,000 N/A

Table 3: Costs Breakdown

Alternative Capital Cost O & M Cost ENG/CONT Costs Total Costs

#1 $2,012,500 $1,403,125 $603,750 $4,019,375

#2 $8,606,250 $681,563 $2,476,875 $11,764,688

#3 $6,006,250 $901,563 $1,801,875 $8,709,688

#4 $2,012,500 $1,523,125 $603,750 $4,139,375

24

APPENDIX D: ENERGY COSTS ASSOCIATED WITH PHOSPHORUS

REMOVAL

According to research completed by the University of Georgia, energy costs can be broken into three

categories: aeration, pumping, and mixing energy. These costs are all associated with chemical feed

systems to remove phosphorus. Below are the standard operation and maintenance costs by various

factors including the annual costs per total phosphorus removal percentage. This information along with

other information gathered during our literature review helped us conduct our initial cost analysis for all

four alternatives.

Factor Estimation

Maintenance 4 per cent of total capital cost Taxes and insurance 2 per cent of total capital cost

Labor $28.21/hr

Electricity $0.0499/ kwh Chemicals Al2(SO4)3•12H2O $80/ton

Ca(OH)2 $80.8 /ton

Polymer $3780/ton

Residuals Management Disposal costs $0.27/ kg solids for biological sludge and $1.24/ kg solids for a blend of chemical and biological

sludge.

Table 4: Cost Factors and Estimation

25

Figure 6: O & M Costs versus Total P Removal %

26

APPENDIX E: REFINED COST ESTIMATION FOR SELECTED

ALTERNATIVE

The amount of alum used to achieve an effluent phosphorus level of 0.04 mg/L was 43.5 kg per day.

To meet an effluent phosphorus level of 0.13 mg/L, 33 kg per day of alum was used. In the refined cost

estimation, 43.5 kg per day of alum will be used to provide what the highest chemical cost for this

alternative. An estimate of how much on the cost of alum is $400 per wet ton. Based on the BioWin

modeling discussed previously in the BioWin modeling section, 0.05 tons of alum will be used per day to

achieve an effluent phosphorus level of 0.04 mg/L. The cost associated for using alum per year will be

$7300 based on these results. This is significantly lower than what was estimated in the cost analysis

which will bring down the cost of the alternative.

With an alum usage of 0.05 tons per day, the amount of additional sludge produced will be 362.12 kg

per day (796 lbs per day). An estimate of O & M costs for alum sludge handling is $600 to $800 per dry

ton dry solids29

0.4 tons of alum will be produced on a daily basis which equates to a yearly O & M cost

of $116,800. This cost was not calculated in the initial cost analysis but will be added to the refined cost

estimation.

For updating the cost estimation for filtration, it is assumed that 32 DynaSand filters will be used that

each can treat 1 MGD of flow. These would be configured in eight cells with four filters per cell which is

a scaled up version of what is used at the Aurora Sand Creek Wastewater Reuse Plant.30

Due to the

difficulty on getting estimates for these filters, it is assumed that each filter will cost $300,000. This

estimate is based on costs of other filters such as the cost of a Severn Trent denitrification filter sized for

2.25 MGD for the Oldsmar, FL Wastewater Treatment Plant. Severn Trent submitted a bid proposal of

$728,00031

Those these filters serve different purposes it is a good starting point to refine the cost

estimate for added filtration. The updated cost of added filtration is $9,600,000 based on these revised

numbers. The summary of the revised cost estimation is provided below.

29 John McGee (Loveland, CO WWTP), e-mail, 8 Dec 2010. 30 Water and Watersheds. Environmental Protection Agency. Advanced Wastewater Treatment to


31 John Mulvihill (Director of Public Works, Oldsmar, FL), B-10-05: Water Reclamation

Facility (WRF) Filter Replacment. FL: 28 July 2010.

27

Table 5: Refined Cost Estimation for Alternative 3

Costs Divided Alternative #3

Chemicals: $7,300

Feed and Storage Facility: $381,250

Additional Feed Points: $125,000

Energy: $555,313

Sludge Pump: $1,000,000

Maintenance: $302,710

Alum Sludge Handling: $116,800

Additional Filters: $9,600,000

Table 6: Cost Breakdown

Alternative Capital Cost O & M Cost ENG/CONT Costs Total Costs

#3 $11,106,250 $982,123 $3,331,875 $15,420,248

28

APPENDIX F: BIOWIN MODELING

BioWin 3.1 modeling software provided Waterborne Engineering with a proven tool in determining

effluent values utilizing our chosen alternative based on data for the L/E WWTP. BioWin 3.1 contains

the best default parameters from the latest research publications which helped modeling the alternative if

data for a parameter in BioWin could not be found in the L/E WWTP plant data32

BioWin 3.1 offered

many different process icons that allowed for Waterborne Engineering to accurately reflect our process.

BioWin 3.1 allowed us to run a steady state simulation which gave us a very accurate prediction for

phosphorus removal with a very small error (given error in BioWin of results was approximately .001).

Also, BioWin 3.1 provided us with the flexibility to change alum doses to achieve different levels of

phosphorus removal. This can be a valuable asset to optimize chemical costs for phosphorus removal.

DENIT Effluent

Alum Addition

EffluentNull Bioreactor DynaSand Filters

Filter Sludge

Figure 7: BioWin Model of L/E WWTP with Alum Addition and DynaSand Filtration after

Denitrification

Element name DENIT Effluent

Flow 37854.12

Total Carbonaceous BOD mgBOD/L 2.00 Volatile suspended solids mgVSS/L 2.00 Total suspended solids mgTSS/L 2.75 Total Kjeldahl Nitrogen mgN/L 1.40

Total P mgP/L 2.70 Nitrate N mgN/L 15.00 pH 7.40

Alkalinity mmol/L 6.00 Calcium mg/L 80.00 Magnesium mg/L 15.00

Table 7: Denitrification Effluent Values

APPENDIX G: REVIEW OF THE DYNASAND FILTER

32 EnviroSim. BioWin Version 3.1. Canada: 2009.

29

The DynaSand® filter is an upflow, deep bed, granular media filter with continuous backwash. The

filter media is cleaned by a simple internal washing system that does not require backwash pumps or

storage tanks. The absence of backwash pumps means low energy consumption. The DynaSand filter’s

deep media bed allows it to handle high levels of suspended solids. This heavy-duty performance may

eliminate the need for pre-sedimentation or flotation steps in the treatment process in some applications.

Principles of Operation:

Influent Filtration (refer to Figure 8 for filter diagram)

Influent feed is introduced at the top of the filter (A) and flows downward through an annular section

(B) between the influent feed pipe and airlift housing. The feed is introduced into the bottom of the sand

bed through a series of feed radials (C) that are open at the bottom. As the influent flows upward (M)

through the downward moving sand bed (D), organic and inorganic impurities are captured by the sand.

The clean, polished filtrate continues to move upward and exits at the top of the filter over the filtrate weir

(J) and out through the effluent pipe (E).

Sand Cleaning

The sand bed containing captured impurities is drawn downward into the center of the filter where the

airlift pipe (F) is located. A small volume of compressed air is introduced at the bottom of the airlift,

drawing the sand into the airlift pipe. The sand is scoured within the airlift pipe at an intensity of 100-150

SCFM/ft2. The effectiveness of this scouring process is vastly greater than what can be expected in

conventional sand filtration backwash. The scouring dislodges any solid particles attached to the sand

grains. The dirty slurry is pushed to the top of the airlift (G) and into the reject compartment (H). From

the reject compartment, the sand falls into the sand washer (I) and the lighter reject solids are carried over

the reject weir (K) and out the reject pipe (L). As the sand cascades down through the concentric stages

of the washer, it encounters a small amount of polished filtrate moving upward, driven by the difference

in water level between the filtrate pool and the reject weir. The heavier, coarser sand grains fall through

this small countercurrent flow while the remaining contaminants are carried back up to the reject

compartment. The clean, recycled sand is deposited on the top of the sand bed where it once again begins

the influent cleaning process and its eventual migration to the bottom of the filter.

The DynaSand® Filter is available as either stand alone package units or in a modular concrete design.

Concrete modules are frequently used for high flow capacity systems by placing multiple modules into a

30

common filter cell. The modules in a filter cell share a common filter bed where cones at the bottom of

each module distribute sand to their respective airlifts and sand washers. The DynaSand Continuous

Contact Filtration process is better suited to remove small floc, which can help reduce chemical

requirements by 20-30% over conventional treatment.

The following are the benefits of using the DynaSand Filter:

• No shutdown for backwash cycles • Elimination of ancillary backwash equipment

• No flow control valves, splitter boxes, or backwash controls

• No short-circuiting • Optimum sand-washing efficiency

• Superior filtrate quality

• Reduced operator attention

• Minimizes overall pressure-drop • Reduces potential for pluggage

• Significantly reduces wear/maintenance

• Can be easily maintained without filter shutdown • Up to 70% less compressed air vs. other self-cleaning filters

Applications: • Algae removal

• Potable water (turbidity and color)

• Oil removal

• Process water • Brine filtration

• Metal finishing

• Cooling tower blowdown • Steel mill scale

• Chemical processing

• Phosphorus removal

• Product recovery • Denitrification

• Cryptosporidium and Giardia removal

• Surface water • Ground water

• Arsenic removal

• Effluent reuse

31

Figure 8: DynaSand Filter Diagram

32

APPENDIX H: REVIEW OF THE HYDROTECH DISCFILTER

The ACTIDisc process train for tertiary treatment is composed of two successive processes: the

ACTIFLO® high-rate ballasted flocculation, and the HYDROTECH Discfilter cloth filtration. The

ACTIFLO process is a patented technology based on a high-rate settling process that combines the

advantages of ballasted flocculation and lamella clarification. The HYDROTECH Discfilter is a

mechanical, self-cleaning filter, specially designed for achieving high performance in systems where it is

essential to prevent coagulated flocs from fragmenting. The cloth filter works without pressure. Effluent

to be treated flows by gravity, or through pumping, into the filter segment from the centre drum. The

media mounted on both sides of the partially-submerged discs separates solids from the effluent. The

effluent flows through the disc media (microscreen cloth) into the collection tank. Once solids have

accumulated on the inside of the media, the discs are cleaned by the counter-current backwash system.

Treatment objectives for final effluent turbidity were to be less than 2 NTU, less than 5 mg/L of TSS,

and less than 0.1 mg/L total phosphorus. Tests showed that, at the optimal coagulant dose in the

ACTIFLO and in the discfilter, the final effluent rates were 1.68 NTU turbidity, 3 mg/L TSS, and 0.075

mg/L TP.

Throughout the pilot testing program, overall TP removal achieved by the high rate ballasted

flocculation clarifier alone was 85%. Clarifier efficiency was not affected significantly by variations in

the condition of the raw water. Effluent from the ballasted flocculation process was partly sent to the cloth

filter, where coagulant and polymer were added. The combination with the cloth filter was able to

produce effluent with turbidities in the range of 1.5 - 2.0 NTU. TP removed by the cloth filter approached

40%, which corresponds to an average effluent concentration of 0.0235 mg/L TP.

There were two pilot tests taken using the flocculation and filter process. The results were quite good.

Recent research and development efforts have made it possible to extend the phosphorus removal

capacity of the high-rate ballasted clarification process by linking it with cloth disc filtration. The

ACTIDisc process is aimed at achieving an effluent with a low level of total phosphorus and suspended

solids discharge. Both pilot tests have confirmed the efficiency of this combination of technologies, to

achieve discharge values as low as 0.023 mg/L in total phosphorus, turbidities of 1.6 NTU, and 5 mg/L in

suspended solids.33

33 Martine Lanoue, et al. “Novel Processes for Reducing Phosphorus and SS Levels Down to

Tertiary Discharge Standards.” Environmental Science and Engineering Magazine March

2010: 18-22.

33

APPENDIX I: EFFECTS ON HYDRAULIC PROFILE OF PLANT

The driving head elevation from the denitrification filters clearwell is 65.5 feet based on the L/E

WWTP hydraulic profile diagram. The head elevation at the control weir of the chlorine contact basins is

61.6 feet based on the hydraulic profile diagram. The DynaSand filters will be installed prior to the

chlorine contact basins. The typical head loss through DynaSand filters is 0.6 to 0.8 meters at full flow,

but it is recommended to allow 1.2 m (3.9 feet) in designing pumping systems.34

There is 3.9 feet of

available head from the denitrification filters to the control weir of the chlorine contact basins, so no

additional pumping will need to be added to move the flow through the filters. The DynaSand filters will

fit within the chlorine disinfection system and will not require pumping.

34 “Frequently Asked Questions,” 2010 < http://www.hydro-international.biz/wastewater/

dynasand_faq.php>.

34

APPENDIX J: DEPICTION OF PROCESS ON SITE PLAN

In the below figure, the selected alternative is depicted on the scale site plan drawing. The proposed

location for the chemical storage facility is between the centrate storage building and the sludge

dewatering building. The chemical feed system will be connected from the chemical storage facility to a

feed point located along the flow pipe before the proposed location of the DynaSand filters. The

DynaSand filters’ proposed location is between the sludge dewatering building and the disinfection

building. Based on the scale drawing, there appears to be adequate space to emplace the filters and

enough available head to not require pumping from the denitrification filters to the DynaSand filters.

Figure 9: Overlay of Selected Alternative on Site Plan Drawing

Alum

Storage Facility

Alum

Addition DynaSand

Filters

35

APPENDIX K: WASTEWATER SAFETY REGULATIONS FOR

CHEMICAL ADDITION

Although the addition of chemicals is widely used and has been successful in many wastewater

treatment plants throughout the country, there are several hazards associated with handling chemicals.

The majority of chemical feed systems is SCADA friendly and is reliable when it comes to turning off the

system or adjusting the amount of chemicals that are being added.

The hazards associated with chemical feed systems are storing and transporting chemicals to the

system. Below are the common chemical safety rules. These should be observed while first testing the

chemical addition feed system as well as when using the system.

Aluminum

Precautions: Do not ingest. Wear suitable protective clothing. If ingested, seek medical advice

immediately and show the container or the label. Keep away from incompatibles such as oxidizing agents,

acids, alkalis.

Storage: Keep container tightly closed. Keep container in a cool, well-ventilated area. Moisture sensitive.

Engineering Controls: Use process enclosures, local exhaust ventilation, or other engineering controls to

keep airborne levels below recommended exposure limits. If user operations generate dust, fume or mist,

use ventilation to keep exposure to airborne contaminants below the exposure limit.

Personal Protection: Safety glasses. Lab coat. Gloves.

Personal Protection in Case of a Large Spill: Safety glasses. Lab coat. Gloves.

For more information please refer to the following website: http://www.sciencelab.com/xMSDS-

Aluminum-9922844

Ferric Chloride

Precautions: Keep locked up. Keep container dry. Do not ingest. Do not breathe gas/fumes/ vapor/spray.

In case of insufficient ventilation, wear suitable respiratory equipment. If ingested, seek medical advice

immediately and show the container or the label. Avoid contact with skin and eyes.

Storage: Keep container tightly closed. Keep container in a cool, well-ventilated area. Do not store above

24°C (75.2°F).

Engineering Controls:

Provide exhaust ventilation or other engineering controls to keep the airborne concentrations of vapors

below their respective threshold limit value.

http://www.sciencelab.com/xMSDS-Aluminum-9922844

http://www.sciencelab.com/xMSDS-Aluminum-9922844

36

Personal Protection:

Face shield. Full suit. Vapor respirator. Be sure to use an approved/certified respirator or equivalent.

Gloves. Boots.

Personal Protection in Case of a Large Spill:

Splash goggles. Full suit. Vapor respirator. Boots. Gloves. A self contained breathing apparatus should be

used to avoid inhalation of the product. Suggested protective clothing might not be sufficient; consult a

specialist BEFORE handling this product.

For more information please refer to the following website:

http://www.sciencelab.com/msds.php?msdsId=9925886

Lime

Potential Health Effects: Eye: Causes severe eye burns. May cause irreversible eye injury. May cause

temporary corneal clouding. Skin: May cause severe skin irritation or burns. May be harmful if absorbed

through the skin. Ingestion: Causes severe digestive tract burns with abdominal pain, vomiting, and

possible death. May cause circulatory system failure. May cause perforation of the digestive tract.

Inhalation: May cause severe irritation of upper respiratory tract with coughing, burns, breathing

difficulty, and possible coma.

Handling:

Wash thoroughly after handling. Use with adequate ventilation. Do not allow water to get into the

container because of violent reaction. Do not breathe dust, vapor, mist, or gas. Do not get in eyes, on skin,

or on clothing. Use only in a chemical fume hood.

Storage:

Store in a cool, dry area. Store in a tightly closed container. Keep away from strong acids.

Engineering Controls:

Facilities storing or utilizing the material should be equipped with an eyewash facility and a safety

shower. Use adequate general or local exhaust ventilation to keep airborne concentrations below the

permissible exposure limits.

Personal Protective Equipment

Eyes: Wear appropriate protective eyeglasses or chemical safety goggles as described by OSHA's eye and

face protection regulations in 29 CFR 1910.133.

Skin: Wear appropriate protective gloves to prevent skin exposure.

Clothing: Wear appropriate protective clothing to prevent skin exposure.

For more information please refer to the following website: http://www.labchem.net/msds/75458.pdf

http://www.sciencelab.com/msds.php?msdsId=9925886

http://www.labchem.net/msds/75458.pdf

37

APPENDIX L: POSSIBLE HEALTH EFFECTS OF ALUMINUM

According to the Environmental Protection Agency, aluminum is listed as a non-priority pollutant that

may cause concern for healthy wildlife. Due to the potential risks for wildlife, the use of alum can be a

concern if not limited when discharging into a water source from a wastewater treatment plant.

Aluminum is mined and used in a broad range of metals. Currently, the metal can be recycled and

reused which saves energy and money. When used as a coagulant to rid water of phosphorus, aluminum

should also be monitored to ensure that low levels of both aluminum and phosphorus are achieved.

Currently, the USEPA recommends that the acute level of aluminum in fresh water not exceed 750 g/L

and that the chronic level of aluminum not exceed 87 g/L.

In our recommended alternative, alum will be used as the coagulant to precipitate phosphorus out of

the wastewater effluent. Based on our BioWin model, it can safely be assumed that most of the alum

coagulant will be removed after it precipitates via the DynaSand filters. When using alum, the level of

aluminum should be monitored after filtration to ensure that the level of aluminum does not exceed an

acceptable level for the effluent. Based on our preliminary design and analysis, the use of alum will not

increase the amount of aluminum in the plant’s effluent to an unacceptable level.

38

APPENDIX M: PHOSPHORUS EFFECTS ON WATER BODIES

Phosphorus is a multivalent nonmetal in the nitrogen group that is a component of all phospholipids,

which means that it is crucial in the formation of cell membranes and is essential for all living cells. Like

nitrogen, phosphorus bonds tetravalent to hydrogen and therefore thrives in moist areas.

Below in figure 1, the common way that phosphates enter a body of water through agriculture

fertilization is shown. Phosphates enter waterways from human and animal waste, phosphorus rich

bedrock, laundry, cleaning, industrial effluents, and fertilizer runoff.

Figure 10: Fertilizer, Phosphorus runoff

After phosphate enters the water it begins to promote algae and weed growth. These in turn use the

oxygen in the water to survive depriving the water life and water of oxygen. Phosphates in high levels can

be harmful towards wildlife and human life. In order to keep phosphates in low doses the Environmental

Protection Agency (EPA) suggests a dose of no higher than 0.05mg/L when discharging into reservoirs.

39

APPENDIX N: RECYCLING PHOSPHORUS POST REMOVAL

Phosphorus is currently used for agricultural purposes to promote growth in plants. Phosphorus is

mined and placed into fertilizers but in the future this resource could be depleted without recycling

efforts. Some research indicates that biological phosphorus sludge may be a viable alternative to replace

fertilizers for agricultural purposes.

Phosphorus rich sludge may have undesirable impurities such as zinc and copper. These metals would

not be beneficial if this sludge is used as fertilizer and may deter some from using it for this purpose. In

order to assure quality control, this sludge can be measured for impurities so that it will be beneficial to

agriculture growth.

The Littleton Englewood Wastewater Treatment Plant is an ideal location for sludge phosphorus

recycling. Colorado has a broad range of farmland surrounding the city that can utilize this sludge. The

heavy metals are already regulated and removed during the final clarifier and denitrification filtration

system. If sludge is collected before and after the additional phosphorus filtration, the sludge can be

recycled and sold to the nearby farmers. This provides benefits for both the L/E WWTP and the farmers

in a financial aspect as well as an environmental aspect.

40

APPENDIX O: AUTONOMOUS MICRO FLUIDICS BASED ANALYZER

FOR SENSING PHOSPHORUS IN WASTE WATER

A portable sensor for the analysis of phosphorus in aqueous samples has been developed. The sensor

incorporates micro fluidic technology, colorimetric detection, and wireless communications into a

compact and rugged portable device. The detection method used is the molybdenum yellow method, in

which a phosphate-containing sample is mixed with a reagent containing ammonium metavanadate and

ammonium molybdate in an acidic medium. A yellow-colored compound is generated and the absorption

of this compound is measured using a light emitting diode (LED) light source and a photodiode detector.

The absorption is directly proportional to the phosphate concentration in the original sample. This type of

sensor has been applied for phosphorus analysis in wastewater at a municipal wastewater treatment plant

in Co. Kildare, Ireland.

Design and Operation Of The Analyzer:

Sensing Principle:

The analyzer is based on the molybdenum yellow method. This method involves mixing the sample

with an equal volume of a reagent containing 7.143 g of ammonium molybdate and 0.357 g of ammonium

in an acidic medium (95 mL of H2SO4) in 1 L of deionized water (DIW). Vanadomolybdophosphoric

acid is formed, which is yellow in color and absorbs strongly below 400nm. The absorbance is measured

using a LED light source (370 nm) and a photodiode detector, and is directly proportional to the

concentration of phosphate in the original sample. The major advantage of this detection scheme is the

excellent stability of the reagent, which allows the same solution to be used for over 1 year without

significant loss of activity, thus allowing long deployments to be carried out without the need for

replacing the reagent solution.

41

Analyzer Design and Operation:

Figure 11: Sensor Schematic

This is a schematic of the system and its mode of operation. The system contains bottles for storing the

reagent, calibration solutions and cleaner, a sample port for collecting the water sample to be analyzed,

and an array of solenoid pumps for pumping the required liquids through the microfluidic chip. The

microfluidic chip allows for the mixing of the reagent and sample. The chip also presents the reacted

sample to a photodiode and LED for an absorbance measurement. The analyzed sample is then pumped to

the waste storage. All of the fluid handling and analytical components are controlled by a microcontroller

that also performs the data acquisition and stores the data in a flash memory unit. A GSM modem is used

to communicate the data via the SMS protocol to a laptop computer. The microcontroller used to control

the system is the MSP430F449 (Texas Instruments). This was chosen for its low power consumption

during operational and sleep mode. A 2 megabyte SPI flash chip mounted on the PCB with the

microcontroller allows for 16,384 data points to be logged. The solenoid pumps and the power to the

GSM modem are controlled via an array of field effect transistors (FETs). Power is provided by a 12 V,

7Ah lead acid battery. A and a 370nm LED) are used for the absorbance measurement. A transimpedance

amplifier circuit based around a TLV2772 operational amplifier (Texas Instruments) is used to condition

the signal from the photodiode. This circuit is built on a separate board close to the microfluidic chip,

thereby limiting the noise on the signal from the photodiode. The entire system is enclosed within a

robust and portable case which is water- and air tight when closed. The complete integrated system is

shown in Figure 12 below.

42

Figure 12: This is the prototype phosphate analyzer system. (1) Electronics board. (2) GSM modem. (3)

Microfluidic chip / detector assembly. The battery, storage bottles, and solenoid pumps are contained

within the lower part of the case.

Microfluidic Chip Design:

A micro fluidic chip is used as a platform for the phosphate measurement. This allows for small volumes

of reagent and sample (22 μL of each solution) to be used per measurement. The reagent and sample are

mixed in a T-mixer which leads into a cylindrical optical curette (5 mm length × 1 mm diameter) where

the resulting solution is presented to the emitter and photo-detector for the absorbance measurement. Each

side of the T-mixer has three inlet channels leading into them. On one side are the two phosphate standard

solutions for a two point calibration. A third inlet channel is for the water sample. On the other side of the

T-mixer there is an inlet for the reagent and two inlets for cleaning solution. All channels are of 200μm in

width and depth. The micro fluidic channels are milled into the sheet using the CAT-3D-M6 micromill

using a 200μm end mill. The 35×20 mm chip layers are bonded using a pressure sensitive adhesive.

PEEK tubes are inserted into the inlet and outlet ports and are held in place using epoxy adhesive. The

completed microfluidic chip is shown in Figure 13 below.

Figure 13: Completed Microfluidic Chip

43

APPENDIX P: RELEVANT CDPHE DESIGN CRITERIA

The attached "design criteria" for domestic wastewater treatment facilities are a composite of parts of

previous criteria published June, 1973, the revised portions of the "Criteria used in the Review of Wastewater

Treatment Facilities" approved by the Water Quality Control Commission on January 2, 1979 and updated in

1996, and modifications based on the outcome of a stakeholder process including the Water Quality Control

Division, consulting design engineers and facility owners conducted from September 2001 to March 2002. The

document allows the design engineer to be familiar with the criteria the State utilizes to review wastewater

treatment facility designs.

The General Assembly of the State of Colorado has enacted certain laws relating to the pollution of streams

and waters within the State of Colorado and has granted specific and general powers to the Colorado Water

Quality Control Commission. The Commission, after public hearings, adopts and promulgates reasonable quality

standards for State waters to prevent, control, and abate pollution. It is the responsibility of the operating agency

to provide treatment facilities as required to meet the discharge permit limits which are based on the adopted

water quality standards.

The Colorado Department of Public Health and Environment, Water Quality Control Division (Division), by

review of plans and specifications, assumes no responsibility for the successful operation of the facility so

reviewed. It is the primary responsibility of the professional engineers designing such facilities as well as the

agency constructing and operating such facilities to see that they will operate satisfactorily. The Colorado Water

Quality Control Division must and will strictly enforce the provisions of State laws and regulations and

discharge permit requirements.

This publication provides technical guidance to Division staff on which to base the official review of plans

and specifications involving wastewater treatment facilities designs. This document lists and suggests limiting

values for items upon which the Division will make an evaluation of such plans and specifications.

The official Division review is limited to the review of plans and specifications of new interceptors (greater

than or equal to 24 inches in diameter), all domestic wastewater treatment facilities and wastewater pumping

stations (Ref: 25-8-702 C.R.S.). An official review of plans and specifications for new collection systems,

extensions, and replacement sewers is done only when designed in conjunction with a request for State funding.

Wastewater Treatment Facilities: Site Approval for new or expanding (existing) domestic wastewater treatment

plants shall be obtained prior to completing the review of the design and plans and specifications for

construction. Any increase in organic or hydraulic capacity of the facility is considered an expansion. Site

approval is also needed for significant process changes or if new treatment processes are being added to comply

with updated permit limits. Site applications for new or expanding domestic wastewater treatment plants shall

44

contain signatures from all required reviewing entities prior to being submitted to the Division (Ref: 5 CCR

1002-12).

Process Design Report Technical Elements: Enough process design information must be submitted to

demonstrate how the design was developed and its conformance with applicable design criteria. A facility layout

drawing shall be submitted showing the wastewater treatment plant in relation to the remainder of the collection

system. The Process Design Report shall also include:

a. Size and location of plant structures.

b. Schematic flow diagram showing the flow through various unit processes including a preliminary hydraulic

profile.

c. General piping arrangements including any by-pass of individual units, materials handled and direction of flow

through pipes.

d. Flow and solids balance showing the flows of raw wastewater, supernatant liquor, all return flows and sludge

flows at average and peak design conditions.

e. Pump location, type and size.

f. Type of Treatment: Careful consideration should be given to the type of treatment before making a final

decision. A few of the important factors that should influence the selection: the location and topography of the

plant site; the effect of industrial wastes likely to be encountered; operating costs, flexibility, level of treatment

required, the probable type of supervision and operation which the plant will have and ultimate costs to the users.

New treatment processes, methods and equipment will be reviewed in accordance with the procedure given in

Section 1.6.

g. Design Flow Rate: Unless satisfactory justification can be given for using a lower or higher per capita flow,

plans for wastewater treatment plants to serve new sewer systems should be designed on the basis of an average

daily per capita (gpcd) wastewater flow of not less than 70 gallons (265 liters) nor greater than 100 gallons (380

liters), to which industrial and commercial wastewater flows must be added. Plans for wastewater treatment

plants to serve existing collection systems will be examined on the basis of gauging the present flow in the

system plus allowances for infiltration and the estimated future increase in population, commercial and industrial

contributions.

h. Industrial waste contributions or other special factors requiring special treatment processes or other

contributions that may impact raw wastewater strength and volume in the design of the facility.

i. Calculations showing average, maximum month, and peak flows and organic loads (and for nutrient loads,

when applicable due to permit limits) for present and design conditions, for each treatment unit.

j. Process design parameters for each treatment unit process referencing the applicable design criteria.

45

k. Oxygen transfer calculations and data used for oxygen transfer equations. Include blower or aerator sizing and

air flow requirements for treatment and mixing.

DESIGN

4.2.1 Flow Metering/Measuring: The Division will require, as part of the basis of design of any treatment

facility, a list of the locations where flow metering and/or measuring devices will be provided. Flow metering

requires recording whereas flow measuring does not require recording.

The monitoring of the various flows throughout a wastewater treatment facility as well as the behavior of the

plant under various flow and organic loading conditions provides an audit of plant performance. Additionally,

flow records provide an aid in forecasting the need for additional treatment capacity. Therefore, the design of any

new or expanded wastewater treatment facility shall include adequate flow metering and/or measuring of all

pertinent liquid and sludge flow streams.

a. Influent and Effluent Flow Metering: As a general rule, flow metering at the headworks area of any

treatment facility should (see 4.2.1.c below) be provided. The metering device shall be equipped with a local

flow indication instrument and a flow recording-totalizing device suitable for providing permanent flow records.

The recording-totalizing device should be located in the plant control building when practical. Where influent

flow metering is not practical and the same results may be obtained from metering at the effluent end of the

treatment facility, this type of flow metering arrangement will be considered. Effluent metering will be required

in cases where it is required by the CDPS permit. For lagoon systems both influent flow metering and effluent

flow measuring capability shall be provided.

b. Metering Accuracy: In locating flow meters, adequate attention shall be directed to the upstream and

downstream hydraulic conditions at each metering device to ensure that flow metering accuracies within + 10%

can be maintained as close to the actual flows as possible during the full range of anticipated flow variations.

c. In-plant Flow Measuring: Where multiple treatment units are proposed, such as two or more clarifiers or two

or more aeration basins, provision shall be included for flow splitting and for measuring capability to control

flows to each treatment unit in proportion to the loading requirements. The pacing of chlorine feed and other

equipment associated with treatment performance by flow pattern variations is recommended and should be

controlled by signals from the flow metering equipment such that the paced unit varies the chemical, etc. in

proportion to the flow variations.

d. Flow Measuring Devices: The following types of equipment are commonly used for flow measurement

applications and are acceptable:

46

Parshall Flumes Differential Meter

Weirs (various types) Magnetic Meter

Propeller Meter Kennison Nozzle

Venturi Meter Dall Tube

In some cases the use of elapsed time clocks or plunger pump stroke length and frequency counter will be

adequate for measuring pumped flows. Where hour meters are used on pumps, a method must be specified to

periodically calculate pump flow capacity. Other flow measuring devices will be considered on an individual

basis related to the proposed application.

e. General Flow Measuring Capability: The following locations within a treatment facility are

required/recommended for flow metering/measuring capability:

Metering:

Raw sewage influent (Recommended if not required in the CDPS permit)

Re-circulated flows (Recommended)

Waste activated sludge flows (Recommended)

Return activated sludge flows (Recommended)

Recommended measuring:

Humusreturnflows

Raw sludge

Digester liquid level

Digester gas

Pumpedflows

Other significant in-plant wastes

Additionally, it is desirable to measure the in-plant use of air, oxygen, gas (natural or methane), electrical energy

and water.

Design Loading:

a. Hydraulic Loading: Certain treatment units within a wastewater treatment plant are designed based on the

average wastewater flow rate per 24 hours. However, other components should be designed based on peak

monthly, weekly or even daily flows.

Where large seasonal variations in loadings occur, the design shall be based on peak season loads.

Where the duration of loading is less than 24 hours per day (i.e. schools, subdivisions, recreational facilities,

etc.) treatment units and equipment shall be increased in size by the factor of 24/loading duration (hours) or

appropriate equalization facilities shall be provided.

47

The design engineer must provide the rationale for the selected design flow rate for each unit process in the

Process Design Report. Additionally, the flow characteristics from most commercial and industrial developments

are usually much more critical than that of a municipality; therefore, the design flow rate for commercial and

industrial developments should be based on the period of significant waste discharge. The following

considerations should be included in determining design flow:

1. Peak rates of flow, which adversely affect the detention time of treatment units or the flow characteristics of

conduits.

2. Data from similar municipalities, in the case of new systems.

3. Wet weather flows.

4. Re-circulation flows.

b. Organic, Solids and Nutrient Loadings: The design organic loading in terms of BOD5, solids loading in terms

of total suspended solids and nutrient loadings are usually computed in a manner similar to hydraulic loading and

must include re-circulation flows and loads. Designs should be based on maximum month mass loadings (and

should account for any variation in monthly, weekly, or daily effluent limits) to ensure that all effluent limits can

be met all the time. Loadings for lodges, motels, etc., should be computed for the maximum possible occupancy.

The unit of usage, such as number of meals served for a restaurant, is recommended for computation of total

organic loading. The shock effect of high contribution for short periods of time should also be considered.

Conduits: All piping and channels shall be designed to carry the maximum expected flows. The incoming sewer

should be designed for free discharge. Bottom corners of the channels should be filleted. Pockets and corners

where solids can accumulate should be eliminated. Suitable gates should be placed in channels to seal off unused

sections, which might accumulate solids. The use of shear gates or stop planks is permitted where they can be

used in place of gate valves or sluice gates. In larger facilities, fillets may be waived if it can be shown solids

accumulation in corners can be minimized without them.

4.2.4 Arrangement and Reliability of Units: Component parts of the plant should be designed and arranged for

greatest operating convenience, flexibility, economy, and so as to facilitate routine maintenance and installation

of future units. Consideration should be given to providing at least two treatment units of each type to allow

maintenance or repairs while maintaining CDPS permit compliance. Plant piping and valving should be designed

to allow bypassing of individual units while still providing the maximum practical level of treatment.

48

4.2.5 Critical Environmental Conditions: The various unit processes and equipment should be designed and sized

for the most critical environmental conditions to which they will be exposed at the proposed plant site. Such

factors as low and high wastewater temperatures, air temperature, altitude, etc., should be considered, especially

when predicting the treatment efficiency to be obtained. The treatment units must be designed to meet any

seasonal effluent permit limits.

ACTIVATED SLUDGE FACILITIES

The activated sludge process may be used where the wastewater is amenable to biological treatment. All of the

activated sludge processes require a higher degree of attention and operating supervision compared to lagoon

systems. These requirements must be evaluated when proposing this type of treatment.

5.14.1 Classification: Activated sludge plants may be classified by flow pattern and organic loading. There are

many variations of the activated sludge process including: High Rate Processes, Conventional, Step Aeration,

Contact Stabilization Extended Aeration and Sequencing Batch Reactors. Several do not require primary

clarification, but it should be evaluated for all classifications.

5.14.2 Unusual Installation: Plans for plants contemplating abnormal BOD5

concentrations, unusual aeration

periods, significant amounts of industrial wastes or special equipment or arrangements will be reviewed on a

case-by-case basis.

5.14.3 Loading Considerations: All calculations shall be based on a maximum month loading except as follows:

a. Seasonal Variations: Where large seasonal variations in loadings occur, the design shall be based on peak

season loads.

b. Short Term Variations: Where the duration of loading is less than 24 hours per day (i.e., schools, subdivisions,

recreational facilities, etc.) treatment units and equipment shall be increased in size by the factor of 24/loading

duration (hours) or appropriate equalization facilities shall be provided.

5.14.4 Aeration Basins:

a. Multiple Units: Total aeration tank volume shall be divided among two or more units, capable of independent

operation where design average flows exceed 0.25 MGD (1.0 x 103

m3

/day). Multiple units should be considered

for smaller facilities. Selection of the number of units should include an evaluation of projected growth rates,

ultimate projected aeration basin size, and they type of aeration being installed.

b. Freeboard: All aeration basins shall have a freeboard of not less than 18 inches (0.5 meters) at peak flow.

49

c. Basin Geometry: Aeration basin geometry shall be arranged to provide optimum oxygen transfer and mixing

for the type aeration device proposed.

d. Flexibility: Facilities for flexible operation, such as variation in wastewater and sludge loading points to

incorporate several of the activated sludge process variations, should be incorporated into the design of aeration

basins.

e. Design Parameters: Aeration basins (including “Package Plants) used in the activated sludge process shall

generally be designed in accordance with the criteria shown in Table 5 at the end of this document.

5.14.5 Air Supply (General):

a. Dissolved Oxygen Concentration: The design should provide for the introduction of air in sufficient volume

and in sufficient manner to maintain at least 2 mg/L of dissolved oxygen under all conditions of loading, in all

parts of the aeration tanks except immediately beyond the inlet. This criterion does not apply to anaerobic zones

specifically designed for phosphorus removal or anoxic zones used as selectors or for nitrate removal.

b. Minimum Air Supply Rates: Aeration systems should provide a minimum of 1.2 pounds of oxygen per pound

of BOD5 (0.5 kg O

2/kg BOD

5) applied to the aeration basins for the extended aeration process.

c. Mixing: The design shall provide for the introduction of air or provide mechanical mixing to bring sludge

particles into intimate contact with all portions of wastewater. The aeration system and other mixing equipment

used shall provide sufficient mixing to prevent deposition of mixed liquor suspended solids under any flow

condition.

d. Air Supply Control: Adequate facilities to vary the amount of aeration with the incoming organic loading must

be provided. Preference will be given to facilities that allow continuous aeration and yet also allow variation in

the amount of aeration. Possible ways of accomplishing this are (1) variable speed or multiple contact speed

blowers, or (2) automatic variation in over-flow level of aeration tank to change mechanical aerator cone

exposure.

5.14.6 Diffused Air Systems:

a. Multiple Units: Blowers shall be provided in multiple units, so arranged and in such capacities as to meet the

maximum air demand with the single largest unit out of service. In facilities not staffed 24 hours per day, the

blower/compressor units should be equipped with automatic reset and restart mechanisms to place

the units back in operation after periods of power outage. In facilities staffed 24 hours per day, alarms may be

installed in place of automatic reset and restart mechanisms.

b. Design Approach: Air filters, maximum air and/or wastewater temperatures, and elevation must be evaluated

when calculating process air requirements and specifying blower requirements.

c. Diffuser System Capacity: The air diffuser system, including piping, shall be capable of delivering 150 percent

of average air requirements without undue pressure losses.

50

d. Maintenance Considerations: Devices should be provided for removing and replacing diffusers without

dewatering the tank. If redundant tanks are provided, fixed diffuser systems may be considered. Non-clog

diffusers shall be provided for all systems using intermittent aeration.

e. Air Control Valves: Individual diffuser header assemblies with air control valves should be provided. These

valves are basically for open or closed operation but should be of the throttling type.

5.14.7 Mechanical Aeration Systems: The oxygen transfer capability of mechanical surface aerators shall be

calculated by the use of a generally accepted formula and the calculations presented in the Process Design

Report.

5.14.8 Other Aeration Systems: Other types of aeration systems (i.e., pure oxygen, turbine aeration, jet aeration,

combination systems, etc.) shall meet the applicable mixing criterion outlined in Section 5.14.5.c above. Specific

design characteristics of each of these systems will be reviewed on a case-by-case basis.

5.14.9 Process Control Equipment:

a. Return Sludge Equipment:

1. Pumps and Piping: Devices shall be provided on the return sludge lines and/or pumps for observing, sampling,

and controlling the return sludge flow. Sludge shall be returned continuously and flow rates shall be variable to

any rate within the limits of Table 5.

2. Flow Measurement: Provisions shall be made for measuring return sludge flow rates in all plants utilizing the

activated sludge process.

b. Waste Sludge Equipment:

1. Pumps and Piping: Devices should be provided on the waste sludge lines and/or pumps for observing,

sampling, and controlling the waste sludge flow.

2. Flow Measurement: Provisions shall be made for measuring waste sludge flow rates in all plants utilizing the

activated sludge process.

5.14.10 Polishing Ponds: Polishing ponds or some other means of suspended solids removal shall be provided

following all treatment plants where the average daily flow is less than 250,000 gallons per day (1,000 3

/day)

unless adequate redundancy is provided in the activated sludge treatment process with respect to both solids

separation and removal (clarification) and aeration to remove BOD. This must be discussed in the Preliminary

Plan of Operation. Polishing ponds should be evaluated for plants where the average daily flow is in the range of

250,000 to 500,000 gallons per day (1,000 to 2,000 m3

/day) especially with respect to the redundancy for solids

51

separation and removal (clarification) and aeration to remove BOD provided in the activated sludge design.

Specific design criteria for polishing ponds are provided in Section 5.5.4.

Provision shall be made to by-pass the polishing ponds and/or suspended solids removal unit for all plants

utilizing the activated sludge process. This will allow effluent from the activated sludge facilities to be

discharged directly when the quality meets or exceeds permit requirements.

5.14.11 Sludge Holding Facilities: Where digestion facilities are not included in the design, an aerated

sludge/scum holding tank shall be provided. As a minimum, enough oxygenation capability shall be provided to

maintain detectable dissolved oxygen within the tank contents. It shall also be designed to concentrate sludge and

decant clear supernatant back to the aeration system. Sizing calculations, a description of how, where, and when

final disposal of sludge will be accomplished shall be included in the Process Design Report.

Phosphorus Removal: Aluminum salts or iron salts can be used for phosphorus removal. Doses required

are based on the level of phosphorus removal required. Flocculation and clarification requirements may

be different depending on where the flocculating salts are added.

Nitrifying Trickling Filters: Nitrifying trickling filters (NTF) are designed the same as trickling filters (Sec.

5.7.1). NTF's should have a minimum media depth of 20 feet (6 m). However, the variability of ammonia

loading and nitrification rate at low temperature must be considered in the design. Forced ventilation should be

provided and a rate of 50 lbs. of O2

supplied per lb. O2 used (22.5 kg O

2/kg O

2) should be considered. pH should

be controlled, if necessary based on alkalinity calculations, and re-circulation rates should be minimized. Design

considerations for the WWTP preceding the NTF should include a BOD5:TKN ratio less than 1.0

ANAEROBIC DIGESTION FACILITIES

8.2.1 Gas Collection, Piping, and Appurtenances:

a. General: All portions of the gas system, including space above the tank liquid, storage facilities and piping

must be so designed that under all normal operating conditions, including sludge withdrawal, the gas will be

maintained under pressure. All enclosed areas where any gas leakage might occur, should be adequately

ventilated.

b. Safety Equipment: All necessary safety facilities shall be included where gas is produced. Pressure and

vacuum relief valves and flame traps, together with automatic safety shutoff valves, are essential.

c. Gas Pipe and Condensate: Gas pipe shall be of adequate diameter and should slope to condensation traps at

low points. Float control condensate traps are not permitted unless allowed by local plumbing codes. If float

52

control condensate traps are allowed, provisions shall be made to properly and safely vent the gas to the

atmosphere.

d. Gas Utilization Equipment: Gas burning boilers, engines, etc., should be located at ground level and in well-

ventilated rooms. Gas lines to these units must be provided with suitable flame traps.

8.2.2 Boiler or Heat Exchanger Controls: The controls provided must automatically shut off the main gas supply

in the event of pilot burner or electrical failure.

8.2.3 Waste Gas Burner: This burner must be located at least 25 feet (7.5 meters) away from any plant structure,

if placed at ground level, or may be located on the roof of an adjacent building, if sufficiently removed from the

tanks.

8.2.4 Electrical Fixtures: Electrical fixtures in enclosed places where gas may accumulate, must comply with the

National Board of Fire Underwriters' specifications for hazardous conditions.

8.2.5 Ventilation: Any underground enclosures connecting with digestion tanks-or containing sludge, gas piping

or gas equipment, shall be provided with forced ventilation, in accordance with the requirements given in

Chapter 3, or local codes, whichever is more stringent.

8.2.6 Maintenance Provisions: Non-sparking tools, rubber soled shoes, safety harnesses, gas detectors for

inflammable and toxic gasses, and gas masks approved by the United States Bureau of Mines should be

provided.

REFERENCES

References that may also be helpful to users of this document are:

- Design of Municipal Wastewater Treatment Plants, MOP 8, 4th

Edition, Water Environment Federation (WEF), 1998

- Wastewater Engineering, Metcalf and Eddy, 3rd

Edition, 1991

- Municipal Wastewater Stabilization Ponds, EPA 625/1-83-015, October 1983, http://www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:epa-cinn:3911;&rank=1&template=epa

- Alternative Wastewater Collection Systems, EPA 625/1-91/024, October 1991, http://www.epa.gov/cgi-

bin/claritgw?op-Display&document=clserv:epa-cinn:2752;&rank=4&template=epa

- Constructed Wetlands Treatment of Municipal Wastewaters, EPA 625/R-99/010, September 2000, http://www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:epa-cinb:1123;&rank=4&template=epa

- Hammer, Donald, A., Constructed Wetlands for Wastewater Treatment: Municipal, Industrial and

Agricultural, December 1989 - Land Treatment of Municipal Wastewater: Process Design Manual, EPA 625/1-91-013, October 1981,

http://www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:epa-cinn:2542;&rank=1&template=epa

- Wastewater Treatment/Disposal for Small Communities, EPA 625/R-92/005, September 1992, http://www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:epa-cinn:2754;&rank=4&template=epa

53

- Rich, Linvil Gene, High-Performance Aerated Lagoon Systems, American Academy of Environmental

Engineers, December 1998

- Tchobanoglous, George (Editor), Wastewater Engineering: Treatment and Reuse, 4th

Edition, 2002

WEF, Alexandria, Virginia, Biological and Chemical Systems for Nutrient Removal, 1998

- Henze, M., Herremoes, P., La Cour Jansen, J. and Arvin, E., Wastewater Treatment - Biological and

Chemical Processes, 3rd

Edition, 2002

- Oswald, William J., Wastewater Treatment with Advanced Integrated Wastewater Pond Systems and

Constructed Wetlands - ASCE (A syllabus on Advanced Integrated Pond Systems), 1996

54

APPENDIX Q: WORKS CITED

“Alternatives Comparison and Recommendations." Arlington County Water Pollution Control Plant - Master Plan 2001 Update 16 (2002): Nov. 2011

Asano, Takashi, et al., Water Reuse: Issues, Technologies, and Applications (New York: Metcalf & Eddy, 2007).

Davis, Mackenzie L. Water and Wastewater Engineering (New York: McGraw-Hill, 2010).

DynaSand Continuous, Upflow, Granular Media Filter (Parkson, 2009).

EnviroSim. BioWin Version 3.1. Canada: 2009.

“Frequently Asked Questions,” 2010 < http://www.hydro-international.biz/wastewater/

dynasand_faq.php>.

Lanoue, Martine, et al. “Novel Processes for Reducing Phosphorus and SS Levels Down to

Tertiary Discharge Standards.” Environmental Science and Engineering Magazine March 2010: 18-22.

Littleton/Englewood Wastewater Treatment Plant. 2010/2011 Student Design Competition –

Supplemental Information Document #1: 2010.

McGee, John (Loveland, CO WWTP), e-mail, 8 Dec 2010.

Moore, George T . Scientific, Technical, Research, Engineering, and Modeling Support


Mulvihill, John M. (Director of Public Works, Oldsmar, FL), B-10-05: Water Reclamation Facility (WRF) Filter Replacement. FL: 28 July 2010.

United States Environmental Protection Agency. Biological Nutrient Removal Processes and Costs. Washington, D.C.: 2007.

Water and Watersheds. Environmental Protection Agency. Advanced Wastewater Treatment to Achieve Low Concentration of Phosphorous. Seattle: 2007.

Documents

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