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Envirolink 1225-GSDCC103

An Assessment of the Gisborne Biological Trickling Filter

Report CSC13001

April 2013

Institute of

Environmental

Science & Research

Limited

jmm

Text Box

Appendix IV

Cover image: Courtesy of Peter McConnell

Institute of Environmental Science & Research Limited

Christchurch Science Centre

Location address: 27 Creyke Road, Ilam, Christchurch

Postal address: P O Box 29 181, Christchurch, New Zealand

Website: www.esr.cri.nz

For further information please contact

Name: Brent Gilpin

Email: [email protected]

Suggested Reference:

Gilpin BJ, Wood D and McKay J (2013) An Assessment of the Gisborne Biological Trickling Filter. Envirolink 1225-GSDCC103, ESR Report FW013001.

An Assessment of the Gisborne

Biological Trickling Filter

Envirolink 1225-GSDCC103

ESR Client report FW013001

April 2013

Report Authors

Brent Gilpin

ESR

David Wood

ESR

John Mackay

dnature

Peer Reviewed by: Authorised by:

Wendy Williamson

ESR

John Wright

Water Programme Manager

DISCLAIMER

This report or document ("the Report") is given by the Institute of Environmental Science and Research Limited ("ESR") for the benefit of the Gisborne Wastewater Treatment Advisory Group as defined in the respective Contracts between ESR and above parties, and is strictly subject to the conditions laid out in those Contracts.

Neither ESR nor any of its employees makes any warranty, express or implied, or assumes any legal liability or responsibility for use of the Report or its contents by any other person or organisation.

TABLE OF CONTENTS

1 EXECUTIVE SUMMARY ............................................................................................... 7

2 INTRODUCTION ........................................................................................................... 9

2.1 SCOPE ....................................................................................................................................... 12

2.2 EXCLUSIONS AND LIMITATIONS .................................................................................................... 12

3 MONITORING DATA FROM OPERATION OF THE TREATMENT PLAN ................... 13

3.1 RESOURCE CONSENT ................................................................................................................. 13

3.2 REMOVAL RATES ........................................................................................................................ 14

3.3 DATA FROM GISBORNE WASTEWATER TREATMENT PLANT ........................................................... 15

3.3.1 Flow ................................................................................................................................. 16

3.3.2 pH .................................................................................................................................... 17

3.3.3 TSS .................................................................................................................................. 18

3.3.4 TOG (Total Oil and Grease) ............................................................................................ 19

3.3.5 Biochemical Oxygen Demand (BOD)/Chemical Oxygen Demand (COD) ...................... 20

3.3.6 Enterococci ...................................................................................................................... 23

3.3.7 Relationships between monitored parameters ................................................................ 24

3.3.8 dnature PCR testing ........................................................................................................ 26

4 INVESTIGATION OF BTF ........................................................................................... 28

4.1 MICROBIAL ANALYSIS ................................................................................................................. 28

4.1.1 Interpretation of microbial analysis results ...................................................................... 30

4.2 ANALYSIS OF EFFLUENT BY PCR ................................................................................................. 31

4.2.1 Interpretation of PCR analysis results ............................................................................. 32

4.3 FAECAL STEROL ANALYSIS .......................................................................................................... 31

4.3.1 Interpretation of sterol results .......................................................................................... 35

4.4 FLUORESCENT WHITENING AGENT ANALYSIS ................................................................................ 37

4.4.1 Interpretation of FWA results ........................................................................................... 37

5 DISCUSSION AND CONCLUSIONS........................................................................... 38

5.1 CONTAMINANT REMOVAL BY THE BTF .......................................................................................... 38

5.1.1 The extent of micro-organism reduction achieved by the BTF plant ............................... 38

5.2 BIOTRANSFORMATION OF HUMAN FAECAL MATERIAL ..................................................................... 41

6 CONCLUSIONS .......................................................................................................... 43

7 REFERENCES ............................................................................................................ 45

TABLE OF TABLES

Table 1. Consent limits for specified parameters .................................................................................. 14

Table 2. Summary of sewage composition before and after the BTF................................................... 16

Table 3. Likely number of exceedences of TSS under current and proposed limits ............................ 19

Table 4. Comparison of average BOD and COD levels ....................................................................... 23

Table 5. Correlation matrix (Spearman) of TSS with other variables ................................................... 25

Table 6. PCR Markers Detected before and after the BTF, February 2011 ......................................... 26

Table 7. Levels of microorganisms before and after the BTF ............................................................... 29

Table 8. Levels of Campylobacter jejuni (and E. coli) before and after the BTF .................................. 29

Table 9. Percentage removal rates of microorganisms through BTF ................................................... 29

Table 10. Log Removal rates of microorganisms through BTF ............................................................ 30

Table 11. Levels of PCR markers in samples before and after the Gisborne BTF............................... 31

Table 12. Percentage removal rates of PCR markers through Gisborne BTF ..................................... 31

Table 13. Log removal rates of PCR markers through Gisborne BTF .................................................. 32

Table 14. Reduction in proportion of human bacteriodes ..................................................................... 32

Table 15. Faecal sterol ratios ................................................................................................................ 33

Table 16. Sterol levels measured (parts per trillion, adjusted to 100 mL volume) ................................ 34

Table 17. Percentage removal rates of sterols through Gisborne BTF ................................................ 34

Table 18. Log Removal rates of sterols through Gisborne BTF ........................................................... 35

Table 19. Ratio analysis of sterols before and after the Gisborne BTF ................................................ 35

Table 20. Levels and removal rates of FWAs through Gisborne BTF .................................................. 37

Table 21. Removal rates of microorganisms in trickling filters reported in literature ............................ 40

Table 22. Typical removal rates of sewage treatments ........................................................................ 40

TABLE OF FIGURES

Figure 1. Gisborne Biological Trickling Filter (BTF) ................................................................................ 9

Figure 2. BTF media after about 2 months of biofilm growth. ............................................................... 10

Figure 3 Locations 1, 2, 3 and 4 at the Gisborne Plant where sampling is required. ........................... 13

Figure 4. Flow rate per day through BTF .............................................................................................. 17

Figure 5. Concentration of TSS at outlet of the BTF ............................................................................. 18

Figure 6. Concentrations of Total oil and grease at the outlet of the BTF ............................................ 20

Figure 7. Daily BOD Loading of BTF .................................................................................................... 22

Figure 8. Enterococci before and after the BTF .................................................................................... 24

Figure 9. Relationship between BOD load and enterococci removal ................................................... 25

ESR Report: Gisborne Biological Trickling Filter, April 2013 Page 7

1 EXECUTIVE SUMMARY

In late December 2010 Gisborne City Council commissioned a new domestic wastewater treatment plant. The main treatment element is an 8 m high biological trickling filter (BTF). A Wastewater Technical Advisory Group (WTAG) was established and one task of this group was to investigate the extent of biotransformation being achieved by the BTF.

The WTAG agreed on the following definition of biotransformation:

"A biological process by living organisms which remove and/or breakdown harmful contaminants into safe non-toxic components that can be recycled back into the environment".

This report presents the analysis of monitoring data supplied by Gisborne City Council on the quality of the effluent before and after commissioning of the BTF. In addition, to understand wastewater biotransformation through the BTF in more depth, the authors undertook wastewater and effluent characterisation before and after the BTF by measuring: the amounts of a range of microorganisms, the presence of DNA markers by PCR and the concentration of several chemical markers.

Two key aspects of the assessment of biotransformation are:

(a) Identification of hazardous contaminants in sewage and the measurement of the degree to which they are removed or broken down by passage through the BTF; and

(b) Measurement of indicators of human waste and the measurement of the degree to which they are removed or broken down.

Pathogenic microorganisms are a key hazard in wastewater. However, the diversity and concentration of different pathogens in wastewater varies with time depending on the amount of disease in the community. While we tested for the pathogen Campylobacter, we examined the levels of a range of other non-pathogenic microorganisms which can be used to provide evidence of the BTF’s operational capacity to remove human pathogens from wastewater.

We found that:

The BTF achieved a reduction in microorganisms (Escherichia coli, enterococci, Clostridium, Campylobacter, fRNA phage) of between 90-99% (1 - 2 log10).

Passage of wastewater through the BTF was insufficient to reduce the levels of enterococci to below the consent initial conditions of 1,000 CFU/100 mL; average observed level of enterococci after BTF was 67,000 CFU/100 mL.

Collated data and examination of the literature suggests that the Gisborne BTF is functioning at least as well as could be expected and additional improvement in the BTF removal rates of microorganisms are probably unrealistic.


Replacing enterococci with any other indicator would not “solve the problem”, as other possible indicators exhibited similar behaviour through the BTF.

Meeting the consent conditions for enterococci will require additional treatment steps either before and/or after the BTF.

Whether the limit of 1,000 CFU/100mL is appropriate or not is beyond the scope of this report. Any alteration to this limit would require a public health risk assessment to be carried out.

There was no simple relationship between the BTF plant biological oxygen demand (BOD) loading and microorganism reduction. BOD loading could not be used to estimate or predict microorganism reduction.

To evaluate indicators of human waste, we considered, in addition to microorganisms from human faeces, PCR-based markers for human specific microorganisms, a PCR-marker for mitochondrial DNA from human cells, and both natural (faecal sterols) and man-made (fluorescent whitening agents (FWAs)) chemicals.

We found that:

The BTF reduced levels of bacterial DNA markers by 90-97%, faecal sterols by 80%, and FWAs levels were unaltered.

The most direct indicator of human-source in the effluent is the presence of human mitochondrial DNA. In this study we found removal of up to 99% of the human DNA through the BTF (2 log removal).

In all cases the human indicative markers were detected after the BTF, albeit at reduced levels.

Our overall conclusions are that the BTF is functioning at least as well as could be expected for this type of wastewater treatment. The BTF achieves about the same treatment effectiveness as oxidation pond treatment, but it does so with a much smaller footprint and it does so with a much shorter retention time. Therefore, BTF may be a technological consideration for communities where increasing the capacity of ponds or managing ponds susceptible to flooding is a problem.

However, as the primary wastewater treatment element, the BTF is unlikely to treat sewage to a level that will meet New Zealand expectations for microbial removal or community expectations for biotransformation. Additional treatment steps, either before or after the BTF, are required to increase the removal rates and the levels of biotransformation.


2 INTRODUCTION

In late December 2010, the Gisborne City Council commissioned a new domestic wastewater treatment plant. Domestic wastewater is screened by a rotating drum screens (1 mm mesh size), and then passed through a vortex grit removal chamber. The screenings and grit removed from these stages are bagged and trucked to a landfill at Paeroa.

The screened and de-gritted wastewater gravitates into a biological trickling filter (BTF) pump station before being pumped up through the tank’s central column to a height of 8m, and is then distributed through 6 rotating arms to trickle slowly through many different channels in 10 layers of large plastic media blocks. The resulting treated wastewater is pumped via a marine outfall 1.8km out to sea.

Traditionally, the BTF process is preceded by a primary sedimentation stage and followed by a secondary sedimentation stage. Both stages produce sludge which must be dewatered and transported to landfill or disposed of elsewhere. Rather than installing primary settlement tanks and having an ongoing operational cost, the Gisborne Plant was designed to apply sewage to the BTF at a very low rate. It was

Figure 1. Gisborne Biological Trickling Filter (BTF) (http://www.gdc.govt.nz/wastewater-biological-trickling-filter/)

http://www.gdc.govt.nz/wastewater-biological-trickling-filter/


intended that organic material that would normally be separated in the primary tank would instead be transformed in the BTF filters.

The plant was built as required by a condition of the resource consents granted in September 2007. There are 61 clauses of the resource consent including establishment of Wastewater Technical Advisory Group (WTAG), and requirements for a BTF Plant Monitoring and Investigation Study. Clause 4(d) of the resource consent refers to the study and states that:

The BTF Plant Monitoring and Investigation Study shall:

Investigate the extent of biotransformation achieved by the Single BTF plant, including the disinfection plant once it is installed:

o Define biotransformation o Determine the relevance of BOD as a measure of biotransformation o Determine the relationship between Suspended Solids and

biotransformation of wastewater o Determine through monitoring, data analysis and research, relevant

parameters to be used in assessing biotransformation.

Investigate the extent of micro-organism reduction achieved by the BTF plant and wastewater disinfection plant.

Investigate through surveys, literature reviews and research the importance of social, cultural and environmental components of biotransformation in the treatment of wastewater.

Determine the relationship if any between the BTF plant BOD loading and micro-organism reduction.

Figure 2. BTF media after about 2 months of biofilm growth.


Investigate the relationship between wastewater treatment processes and their carbon footprint.

The above work will feed into the third annual report from the WTAG which as specified in clause 4a(c)(iv) must report and provide recommendations on:

a) Summaries of monitoring results of the BTF Plant Monitoring and Investigation Study.

b) The extent of biotransformation being achieved by the BTF Plant. c) Appropriate parameters and a monitoring programme for ongoing assessment

of biotransformation d) Appropriate parameter limits to ensure biotransformation is being achieved. e) Review of - existing permit conditions: 37 (BOD), 42 (enterococci) and 43

(Suspended Solid, Total Oil and Grease) and recommend any changes to these.

f) Recommend what additional treatment steps (if any) are required to achieve biotransformation and other requirements that may be necessary to improve the quality of the discharge to avoid adverse effects.

The WTAG have agreed on the following definition of biotransformation:

"A biological process by living organisms which remove and/or breakdown harmful contaminants into safe non toxic components that can be recycled back into the environment".


2.1 Scope

This report is a component of the BTF Plant Monitoring and Investigation Study. The work within is intended to inform debate by the WTAG on:

The extent of microorganism reduction achieved by the BTF plant.

The relationship, if any, between the BTF plant BOD loading and microorganism reduction.

Relevant parameters to be used in assessing biotransformation.

The extent of biotransformation being achieved by the BTF Plant.

The relevance of BOD as a measure of biotransformation.

The relationship between suspended solids and biotransformation of wastewater.

Appropriate parameters and a monitoring programme for ongoing assessment of biotransformation.

Appropriate parameter limits to ensure biotransformation is being achieved.

We have used the definition of biotransformation formulated by the WTAG, but with additional focus on the degree to which the BTF treatment process transforms human waste into organic matter.

We have reviewed monitoring data supplied by the WTAG, and we have undertaken additional investigations of biotransformation using alternative parameters.

2.2 Exclusions and Limitations

This report does not attempt to address cultural aspects of biotransformation. We hope the information in this report will contribute to, and inform future discussions on biotransformation from a cultural viewpoint, of which the data provided in this report is just one component.


3 MONITORING DATA FROM OPERATION OF THE TREATMENT PLAN

3.1 Resource Consent

The plant was built as required by a condition of the resource consents granted in September 2007. The consent includes a number of monitoring requirements, including specifications for sampling sites at the plant. These locations are described as Locations 1, 2, 3 and 4, and are shown in Figure 3.

Location 1 is the domestic flow influent after screening, and immediately prior to BTF. In this report we refer to this also as Before BTF.

Location 2 is the discharge after the BTF and before it mixes with industrial flow. In this report we refer to this also as After BTF.

Location 3 is the separate industrial flow after it is screened and before it is mixed with municipal discharge from the BTF.

Location 4 is the combined effluent from domestic and industrial flows as discharged at the outfall.

Figure 3 Locations 1, 2, 3 and 4 at the Gisborne Plant where sampling is required.

This report only addresses sampling data from the location 1 (Before BTF) and location 2 (After BTF) sites.

Clause 36 specifies that the permit holder shall sample, analyse and record from a composite flow proportional samples at Location 1 and Location 2 the following parameters:

Floatable oil and grease in terms of g/m and kg/day.


Total oil and grease in g/m3 and kg/day.

Suspended solids in g/m3 and kg/day

5-day carbonaceous BOD and COD in g/m3

and kg/day.

Enterococci in cfu/100 mL.

Further parameters as agreed in the BTF Plant Monitoring and Investigation Study.

Location 1 was also required to monitor particles retained by screen and sieve (in g/m3 and kg/day).

Concentration limits and maximum daily loads are specified in the consent for some of these parameters at Locations 1 or 2, while other limits are only given at either Locations 3 (Industrial flow) or Location 4 (combined discharge, Table 1).

Table 1. Consent limits for specified parameters

Location Parameter Limit Maximum daily load Clause

Flow 33,000m3/day 2

1 5-day carbonaceous BOD 400 g/m3

of media 37

2 Suspended solids 30 g/m3

43a

2 Total oil and grease 10 g/m3

43a

3 Enterococci 1000 cfu/100 mLb 44

3 Suspended solids 600 g/m3

45b


45b


1080 kg/day 33b

4 Floatable oil and grease 20 g/m3

360 kg/day

33b

4 Suspended solids until wastewater

disinfection commissioning 900 g/m3

16,200 kg/day 33b

4 Suspended solids after wastewater

disinfection commissioning 600 g/m3

10,800 kg/day 33b

4 Enterococci 1000 cfu/100 mLb 42

ano more than 16 exceedances in 26 samples

bno more than 3 exceedances in 26 samples

3.2 Removal rates

This report quantifies the reduction or changes of a number of measured analytes. The degree of removal or reduction can be expressed as percentage removal, or in some cases log10 removal rates or fold reduction.


While percentage reduction is familiar to the public, performance of treatment processes is often measured in terms of log10 removal (log removal) for indicator and pathogenic microorganisms because these organisms are initially present in sewage at very high concentrations and consequently, the required removal rates are high, over 90%.

A 1 log removal corresponds to 90% removal or a 10-fold reduction.

A 2 log removal corresponds to a 99% removal or 100-fold reduction.

Log removal is mathematically calculated as:

Log removal = -log10(N/N0)

Where N is the concentration remaining after treatment and N0 is the pathogen concentration prior to treatment.

While removal rates are important, these must also be considered along with the total level of parameter or load in the effluent after the BTF. We would recommend that log removal rates are reported for enterococci and other microorganisms.

3.3 Data from Gisborne Wastewater Treatment Plant

Gisborne Plant provided the following monitoring data from the plant from locations 1 and 2.

pH

TSS g/m3

Total oil and grease (TOG) g/m3

BOD g/m3 and BOD load kg/m3/day for the BTF

Chemical oxygen demand (COD) g/m3

Enterococci colony forming units (CFU’s)/100mL

Flow in m3/d was also provided. Following is a brief explanation of each of these parameters and an analysis of the last 12 months of data. The data set included 48 weekly measurements, from 30/11/2011 through to 28/11/2012. No data were reported for July.

A summary of the composition before and after the BTF as well as reduction is given in Table 2.


Table 2. Summary of sewage composition before and after the BTF

Before BTF After BTF % reduction

Flow m3/d 18,137

Enterococci cfu/100mL 9.1 x 105 6.4 x 10

4 91

pH 7.4 7.4

TSS g/m3 305 178 40

TOG g/m3

39 16 53

BOD g/m3

275 98 56

BOD load on BTF g/m3 media per day 0.86

COD conc gms/m3 506 266 41

Where: TSS = total suspended solids; TOG = total oil and grease; BOD = biological oxygen demand;

COD = chemical oxygen demand

No information was provided to ESR on floatable oil and grease.

3.3.1 Flow

Flow is a measure of the volume of effluent treated per day. The consent indicated the inflows to the plant should be limited to a maximum of 33,000 m3/day, with an exception of extreme events.

Flows coming into the plant come from domestic and industrial flows. The BTF only handles domestic flows. The average (mean) flow through the BTF was 18,100 m3/day. The maximum flow was 39,300 m3/day and the flow was recorded as exceeded the maximum volume of 33,000 on three sampling occasions between 1st and 15th August 2012. This suggests that the maximum flow into the plant was greater the limit set out in the consent.

Combining the flow information with the concentration of analytes provides an estimate of the daily load.

Flow is an important factor for consideration when designing a waste treatment system. The greater the flow the larger the potential impact on the receiving environment. Also removal rates may be a function of flow.


Figure 4. Flow rate per day through BTF

3.3.2 pH

pH is a measure of the concentration of free hydrogen ions in water. pH is measured on a logarithmic scale, an increase of one unit indicates an increase of ten times the amount of hydrogen ions. A pH of 7 is considered to be neutral, with most waters having a pH of 7-7.5. Acidity increases as pH values decrease, and alkalinity increases as pH values increase. The pH of water affects the solubility of many toxic and nutritive chemicals; therefore, the availability of these substances to aquatic organisms is affected. As acidity increases, most metals become more water soluble and more toxic, as does the toxicity of cyanide increase as acidity increases (pH decreases). In contrast, ammonia becomes more toxic with only a slight increase in pH. pH is easily measured, and large changes in pH are a warning of potentially toxic inputs, or other detrimental impacts.

Before and after the BTF

The average pH of untreated New Zealand wastewater pH 7.5 (NZ Municipal Wastewater Monitoring Guidelines 2002). The average pH of the Gisborne influent was 7.4, which is within a normal range for wastewater. Transit through the BTF did not appear to change the pH of the effluent from that of the influent.


3.3.3 TSS

Total Suspended Solids (TSS) is a measure of fine organic or inorganic material suspended in the water. High levels of suspended solids can overload treatment in various ways, including reducing the performance of UV disinfection. Suspended solids also have the potential for negative impacts on the receiving environment and aesthetic impacts such as plumes.

The typical TSS level in New Zealand influent ranges from 50-800 gm-3 (= to mg/L) with an average of 300 gm-3 (NZWERF, 2002). Overseas data from Bitton (2011) describes a range of TSS from 100 gm-3 for weak domestic wastewater up to 350 gm-3 for strong domestic wastewater.


The influent contained on average 300 gm-3 TSS with a minimum of 100 and a maximum of 560 gm-3. The daily inflow contained, on average, 4,200kg of TSS. The average concentration of the outflow was 178 gm-3 with a minimum of 29 and a maximum of 400 gm-3

On average, 40% of TSS was removed by the BTF, ranging from -14% (where higher TSS were observed in the effluent than the influent) to 71%. The BTF removes, on average, 2,600kg of TSS per day.

Figure 5. Concentration of TSS at outlet of the BTF

The average concentration of TSS at location 2, the outlet of the BTF, was 178g/m3. TSS levels after BTF are shown in Figure 5. The current limit is 30 g/m3 with a


provision that there should be no more than 16 exceedances out of 26 consecutive samples. The 30 g/m3 limit was exceeded 48 out of 49 sampling occasions.

The resource consent describes a proposal to increase the TSS limit at Location 2 from 30 g/m3 to between 170 and 210 g/m3 (see 16.4.2 of the consent variation). If these new limits were adopted then the average number of breaches would be 7.7 and 4.5 times per 26 samples for a limit of 170 and 210g/m3 respectively.

Table 3. Likely number of exceedences of TSS under current and proposed limits

Current limit Potential future limits

< 30 g/m3 < 170 g/m

3 < 210 g/m

3

No of exceedances out of 48 sample 47 19 14

Average number of exceedances per 26

samples (current target not more than 16)

25.0 7.1 4.7

3.3.4 TOG (Total Oil and Grease)

Fats, oils and grease in domestic wastewater come mainly from food including butter, margarine, meat, nuts and even some fruit. Kerosene and lubricating and road oils can also be found in domestic wastewater. These compounds are relatively stable and are not rapidly decomposed by bacteria. High levels of oils and grease can be problematic for sewers and treatment plants. High quantities of oil and grease in the final discharged effluent can result in various adverse environmental impacts including surface water slicks, reduction of dissolved oxygen for fish and other aquatic life, and damage to periphyton.


The influent into the BTF contains on average 39 gm-3 TOG with a minimum of 10 and a maximum of 100 gm-3. On average 620 kg of oil and grease are received by the BTF per day.


Figure 6. Concentrations of Total oil and grease at the outlet of the BTF

After the BTF, the average concentration of TOG observed was 16 gm-3 of effluent with a minimum of 5 gm-3 and a maximum of 30 gm-3. TOG levels after BTF are shown in Figure 6. On average 270 kg of TOG are discharged from the BTF each day.

The current consent conditions of 10 gm-3 comes with the proviso that this level should not be exceeded more than 16 times in 26 samples. The standard of 10 gm-3

was met on seven occasions out of 48 samples (15% of the time).

On average 54% of TOG is removed by the BTF, ranging from 14% to 83%. The BTF removes, on average, 350 kg of TOG per day. In order to meet the consent conditions, the removal rate required would be 63%.

The consent also mentions floatable oil and grease, but no data were available on this parameter.

3.3.5 Biochemical Oxygen Demand (BOD)/Chemical Oxygen Demand (COD)

In domestic wastewater, approximately 60% of organic matter occurs as particulate organic carbon (POC), with the other 40% occurring as dissolved organic carbon (DOC). Most of this organic matter is easily and rapidly biodegradable, and consists of carbohydrates, amino acids, peptides, proteins, volatile acids, fatty acids and their esters. Three main tests are used to measure levels of organic matter in wastewater - biochemical oxygen demand (BOD), total organic carbon (TOC), and chemical oxygen demand (COD). These tests are useful for measuring the effectiveness of the wastewater treatment plant and for assessing the potential impact of effluent on


receiving waters. One adverse environmental impact of high organic matter in effluent is on dissolved oxygen (DO) levels. Fish require dissolved oxygen levels in water in excess of 2- 8 mg/L (Brown & Caldwell, 2001). High levels of organic matter in effluent discharged into water (as measured by high BOD), can stimulate microbial activity to biodegrade this organic matter - a process which uses up oxygen in the water. This can reduce DO in water to levels below that which fish and other aquatic animals need to survive. The increase in bacterial and protozoan biomass may also be undesirable.

Biochemical oxygen demand is a measure of the amount of oxygen that bacteria will consume while decomposing organic matter under aerobic conditions. Biochemical oxygen demand is determined by incubating a sealed sample of water for five days and measuring the loss of oxygen from the beginning to the end of the test. Typical levels of BOD in domestic waste water range from 150 to 800 gm-3 and have an average of 250 gm-3 (NZWERF, 2002).

Chemical oxygen demand does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. Chemical oxygen demand values are always greater than BOD values.

BOD Before and After the BTF

The influent levels before the BTF contained on average 270 gm-3 BOD with a minimum of 59 and a maximum of 1100 gm-3. On average 4,200kg of BOD is received by the BTF per day.

After the BTF, the average concentration of BOD observed was 97 gm-3 of effluent with a minimum of 40 gm-3 and a maximum of 240 gm-3. On average 1,600kg of BOD are discharged from the BTF each day.

On average 56% of BOD is removed by the BTF, ranging from 5% to 88%. The BTF removes, on average, 2,600 kg of BOD per day.

There are no consent conditions for the BOD concentration in the influent or effluent, but there are consent conditions for the BOD load of 0.4 kg/m3 of media.

BTF has a nominal value of approximately 5000 m3 of media. The average daily loading was 0.86 kg/m3 media. The consent condition of not exceeding 0.4kg/m3

media per day was met only twice. It has been proposed that the consent condition should be set at 0.8 kg/m3 per day, and this level was met 31 times.


Figure 7. Daily BOD Loading of BTF

COD Before and After the BTF

The influent contains on average 500 gm-3 COD with a minimum of 160 and a maximum of 1450 gm-3. On average 8,200 kg of COD is received by the BTF per day.

After the BTF, the average concentration of COD observed was 260 gm-3 of effluent with a minimum of 100 gm-3 and a maximum of 520 gm-3. On average 4500kg of BOD are discharged from the BTF each day.

On average 41% of COD is removed by the BTF, ranging from 0% to 80%. The BTF removes, on average, 3,700 kg of COD per day.

There are no consent conditions for the COD levels.

Table 4 compares average BOD and COD levels from Gisborne wastewater influent and effluent with levels published wastewater influent and effluent in the literature (Bitton, 2011). The decrease in BOD/COD ratio indicates an increase in the proportion of organic compounds that are not easily or rapidly biodegraded. The levels of BOD and COD present after the BTF are consistent with levels of organic carbon in the wastewater that further treatment could biodegrade.


Table 4. Comparison of average BOD and COD levels

BOD COD BOD/COD

Gisborne Before BTF 270 500 0.54

After BTF 97 260 0.37 Domestic Sewage*

Raw 300 500 0.60

After biological treatment 10 50 0.20 Slaughterhouse* Wastewater 2000 3500 0.57

*Data from Bitton, 2011

3.3.6 Enterococci

Enterococci bacteria are a subgroup of the faecal streptococci, and include Streptococci faecalis and S. faecium. Enterococci are found in the guts of humans, animal and birds and therefore are an indicator of faecal waste. Studies in the USA and NZ have found strong positive correlations between the levels of enterococci and swimming-associated gastrointestinal and respiratory illness in marine waters. The US EPA has set health-based national recreational water quality standards of 35 colony forming units (CFU) per 100 mL of beach water sampled (30-day average) or 104 CFU per 100 mL (single sample standard).

In New Zealand the MfE/MoH Microbial Water Quality Guidelines for Marine and Freshwater Areas (2003), specify enterococci as the most suitable water quality indicator. Surveillance uses a green/amber/red criteria, with single samples with less than 140 enterococci/100 mL meeting green criteria.

Before and After the BTF

Enterococci levels before and after the BTF are shown in Figure 8. The influent contained an average of 862,000 enterococci per 100 mL with a minimum of 84,000 and maximum of 3.2 million CFU/100 mL.

After the BTF, the average enterococci observed was 67,000 CFU/100 mL, with minimum of 4,000 and maximum of 340,000.

Consent conditions of 1,000 CFU/100 mL were not meet on any occasion. Average log removal of 1.2, with range of 0.3 to 1.7.

A further 1 log removal would result in meeting consent conditions 4% of the time, a 2 log removal would meet consent conditions 83% of the time, a 2.5 log removal would result in meet consent conditions 90% of the time, while a 3 log removal would meet consent conditions 100% of the time. These assume no change to the influent quality.


Figure 8. Enterococci before and after the BTF

3.3.7 Relationships between monitored parameters

Generally the removal rate of TOG, TSS, BOD and COD are strongly positively correlated to one another (P<0.001). That is, as one is removed, others are removed. However, the removal rates of these analytes through the BTF are not simply related to enterococci removal.

Based on the information collected over a one year period there is no evidence of a simple relationship between the BOD loading and enterococci reduction (p=0.611 Pearson correlation coefficient). Enterococci removal rates appear to be independent of the BOD loading on the BTF (Figure 9). If the assumption is that lower BOD load results in greater enterococci reduction, then the data above do no support that hypothesis.

There is some evidence of a positive correlation between BOD loading and removal rates of BOD, COD, TSS and TOG (P<0.05). Implying higher removal rates of all these analytes is achieved at higher loading of the BTF. However, further investigation identified the fact that this relationship, with the exception of BOD removal, was driven by a few outliers when the loading of the BTF was greater than 0.8 kg of BOD per m3 media per day. Therefore, we conclude that during normal operation there is no simple relation between the BOD loading of the BTF and the removal rates of COD, TSS and TOG.


Figure 9. Relationship between BOD load and enterococci removal

Table 5 suggests that there is some correlation between the levels of TSS entering or leaving the plant with reductions in the level of analytes, the only exception being no correlation with enterococci reduction. Higher levels of TSS entering the BTF are associated with higher levels of BOD and COD reduction. Inversely, higher levels of TSS leaving the plant are associated with lower reductions in TSS, TOG and COD during passage through the BTF.

Table 5. Correlation matrix (Spearman) of TSS with other variables

TS

S loa

d into

BT

F

TS

S loa

d o

ut

of B

TF

log r

eduction

Ente

rococci

% T

SS

reductio

n

% T

OG

reductio

n

% B

OD

reductio

n

% C

OD

reductio

n

TSS load into BTF 1 0.41 0.057 0.212 0.164 0.440 0.373

TSS load out of BTF 0.411 1 -0.114 -0.764 -0.453 -0.261 -0.453

Values in bold are significantly different from 0 with a significance level alpha=0.05


3.3.8 dnature PCR testing

dnature diagnostics and research Ltd have undertaken analysis of samples before and after the BTF. Below is data from reports dated 28 February 2011 and 7th December 2011. A range of published assays were used which were able to detect nucleic acids from:

Enterococci – general faecal indicator (but some non faecal sources)

Esp gene – human indicative marker of enterococci

Bacterioides - general faecal indicator (but some non faecal sources)

Human DNA marker (detail)

Polyomavirus – human virus shed in faeces and urine

Faecalibacterium

28 Feb 2011

The five PCR assays were applied to influent and effluent samples collected 8-9 February 2011.

Table 6. PCR Markers Detected before and after the BTF, February 2011

Before BTF After BTF

Percent

removal Log removal

Enterococci 440,000 50,000 88.6% 0.9

Esp gene 775 550 29.0% 0.2

Bacterioides 1,450,000 650,000 55.2% 0.4

Human DNA marker 19,000 2,000 89.5% 1.0

Polyomavirus not detected not detected - -


28 Feb 2011

This report included analysis of large number of samples. For simplicity, below we have reproduced results from last two sampling periods, with percent reduction and log removal rates.

Marker Reduction

Date Before After % log

Bacteroides (all) 22/09 895,450 2,084 99.8% 2.6

27/10 5,535,000 176,397 96.8% 1.5

Enterococci 22/09 60,340 3,093 94.9% 1.3

27/10 80,980 11,738 85.5% 0.8

Polyomavirus 22/09 285 9 96.8% 1.5

27/10 99 47 52.5% 0.3

Sheep 22/09 27,754 2,648 90.5% 1.0

27/10 372,980 23,911 93.6% 1.2

Bovine 22/09 4,661 281 94.0% 1.2

27/10 3,240 184 94.3% 1.3

Conclusions

A range of levels of markers were observed. A reduction of all markers was observed, with an average removal of just over 1 log. Further discussion of these results included with analysis of PCR markers during the October 2012 sampling.


4 INVESTIGATION OF BTF

To shed further light on the possible biotransformation in the BTF, we collected and analysed samples from before the BTF (Location 1) and after the BTF (Location 2). These samples were composites collected as follows:

A 3 hour composite of samples collected at 9am, 10am, and 11am on the 16th October 2012.

A 3 hour composite of samples collected at 12pm, 1pm, and 2pm on the 16 th October 2012.

A 24 hour composite, as per the consent conditions, collected over 16th-17th October 2012.

Samples were analysed for a range of microorganisms, for presence of DNA markers by PCR, and for chemical markers.

A fourth set of 24 hour composite samples were collected over the 30th- 31st October 2012, and analysed for just Escherichia coli and Campylobacter.

4.1 Microbial Analysis

Monitoring of the BTF to date has focussed on the levels of enterococci. Enterococci are only one of thousands of different microorganisms present in sewage, most of which we do not have the technology to be able to culture. There are however a number of microorganisms which we can culture. We enumerated in these samples numbers of enterococci, E. coli, Clostridium perfringens, Campylobacter, and f-RNA phage.

E. coli are bacteria used to monitor freshwater quality. Non-pathogenic strains of E. coli are present in high numbers in faecal material.

Clostridium perfringens are anaerobic bacteria which represent up to 0.5% of the faecal microflora. They produce resting spores that are quite resistant to many environmental degradation stresses. C. perfringens has been suggested as an indicator for protozoa such as Cryptosporidium.

Campylobacter are bacteria that cause the largest number of notified bacterial disease in New Zealand.

F-RNA phage are single stranded viruses which infect bacteria. They have been suggested as possible indicators for viral contamination in the marine environment (Bitton, 2011).

Quantification of these bacteria in the BFT is shown in Table 7 and Table 8. Initial analysis of Campylobacter was unsuccessful due to microbial overgrowth, and was repeated on a subsequent sample collected on the 31st October. E. coli were enumerated in this later sample as well. The percentage removal and log removal rates are listed in Table 9 and Table 10, respectively.


Table 7. Levels of microorganisms before and after the BTF (Sampled 16-17/10/2012)

3hr AM 3hr PM 24 hr composite

Before After Before After Before After

CMB814 CMB815 CMB816 CMB817 CMB818 CMB819

Enterococci 2,300,000 38,000 1,260,000 119,000 1,010,000 58,000

E. coli 12,100,000 175,000 25,000,000 590,000 10,300,000 400,000

Clostridium 245,000 270,000 785,000 115,000 240,000 260,000

Phage 98,000 17,700 211,000 21,000 144,000 13,800

All results colony forming units (CFU)/100mL

Table 8. Levels of Campylobacter jejuni (and E. coli) before and after the BTF (Sampled 31/10/2012)

24 hr composite

Before (CMB834) After (CMB835)

E. coli 4,850,000 215,000

Campylobacter jejuni 4,300 <300

E. coli are colony forming units (CFU)/100 mL, while Campylobacter are Most Probable Number

(MPN)/100 mL. The detection limit for the Campylobacter assay is 300 CFU/100 mL.

Table 9. Percentage removal rates of microorganisms through BTF

3 hr AM 3 hr PM 24 hr 24 hr Average

16/11/12 16/11/12 17/11/12 31/11/12

Enterococci 98.3% 90.6% 94.3% - 94.4%

E. coli 98.6% 97.6% 96.1% 95.6% 97.0%

Clostridium -10.2% 85.4% -8.3% - 22.3%

Phage 81.9% 90.0% 90.4% - 87.5%

Campylobacter - - - 96.5% -

Campylobacter removal based on half the detection limit (ie 150 CFU/100 mL)


Table 10. Log Removal rates of microorganisms through BTF

3 hr AM 3 hr PM 24 hr 24 hr Average

16/11/12 16/11/12 17/11/12 31/11/12

Enterococci 1.8 1.0 1.2 - 1.4

E. coli 1.8 1.6 1.4 1.4 1.6

Clostridium -0.04 0.8 -0.03 - 0.3

Phage 0.7 1.00 1.0 - 0.9

Campylobacter - - - 1.5 -

Campylobacter removal based on half the detection limit (ie 150 CFU/100 mL)

4.1.1 Interpretation of microbial analysis results

The influent levels of enterococci were within the normal range observed from monitoring at this plant, with the log removal rate of 1.3 for the 24 hour composite only slightly above the 12 month average of 1.2 log removal. The enterococci results are suggestive that the samples analysed for this project are not unusual with regard to this plant.

E. coli were an average of ten-fold higher than enterococci. While removal rates were slightly higher than for E. coli, there was still less than a 2 log removal, and large numbers of E. coli were detected in all the samples after the BTF.

Clostridium appears to have undergone little change through the BTF, with the levels observed probably reflecting fluctuations in the inputs at different times. This suggests that protozoa are also unlikely to be removed through the BTF.

Bacteriophage removal rates were around 1 log.

Campylobacter were only enumerated in one 24 hour composite sample, with the levels in the post BTF samples below the assay’s detection limit of 300 MPN/100 mL. To calculate the removal rate, we used a post-BTF level of 150 MPN/100 mL (half the detection limit), which gives a removal rate of 1.5 log. While higher removal may have been achieved, Campylobacter levels in the influent will depend on the level of disease in the community, which can fluctuate significantly. Hence, this removal rate provides a conservative removal estimate.

Future analysis of samples from this plant should use MPN enrichment analysis of Campylobacter using 5 x 3 MPN test, with analysis of volumes of 10 mL, 1 mL, 0.1 mL, 0.01 mL and 0.001 mL to improve the sensitivity of the assay at low concentrations of the pathogen. This would give a MPN detection range between less than 3 MPN/100 mL up to greater than 110,000 MPN/100 mL.


4.2 Analysis of effluent by PCR

The samples were analysed by PCR for the presence of a range of DNA markers. Analysis of all markers was performed by John Mackay, dnature. The extracted DNA was also sent to ESR, and analysis undertaken using PCR assay which targets human mitochondrial DNA.

The makers examined by dnature were an enterococci marker specific for the DNA of enterococci, and DNA markers targeting bacteroides bacteria. For bacteroides, first a general marker for all bacteroides was assayed (Layton et al., 2006), then markers specific for bacteroides from human (Lee et al., 2010), rumen, and sheep sources (Mieszkin et al., 2009). The Polyomavirus marker is human specific and shed in human faeces and urine (McQuaig et al., 2009). The marker for Campylobacter DNA was also assayed. Levels of each marker are given in Table 11, with percent removal and log removal rates in Tables 12 and 13.

Table 11. Levels of PCR markers in samples before and after the Gisborne BTF.




Enterococci 344599 24438 237749 36408 459925 20721

Bacteroides (all) 21298951 3566472 13074284 6054657 45677412 5499187

Bacteroides (Human) 48927 5691 10493 2618 54615 1882

Polyomavirus (Human) 2882 2002 2044 1093 3284 1640

Bacteroides (Rumen) 214 70 496 347 4235 690

Sheep 1895 426 2728 786 6013 238

Campylobacter 84 Trace 23 Trace 214 Trace

Human mitochondrial 295612 12403 529766 29491 85464 2008

Table 12. Percentage removal rates of PCR markers through Gisborne BTF

3 hr AM 3 hr PM 24 hr Average

Enterococci 92.9% 84.7% 95.5% 91.0%

Bacteroides (all) 83.3% 53.7% 88.0% 75.0%

Bacteroides (Human) 88.4% 75.1% 96.6% 86.7%

Polyomavirus (Human) 30.5% 46.5% 50.1% 42.4%

Bacteroides (Rumen) 67.3% 30.0% 83.7% 60.3%

Sheep 77.5% 71.2% 96.0% 81.6%

Campylobacter >90% >90% >90% >90%

Human mitochondrial 95.8% 94.4% 98.9% 96.4%


Table 13. Log removal rates of PCR markers through Gisborne BTF


Enterococci 1.2 0.8 1.4 1.1

Bacteroides (all) 0.8 0.3 0.9 0.7

Bacteroides (Human) 0.9 0.6 1.5 1.0

Polyomavirus (Human) 0.2 0.3 0.3 0.2

Bacteroides (Rumen) 0.5 0.2 0.8 0.5

Sheep 0.7 0.5 1.4 0.9

Campylobacter >1.0 >1.0 >1.0 >1.0

Human mitochondrial 1.4 1.3 2.0 1.5

4.2.1 Interpretation of PCR analysis results

All the markers that were looked for were found in the raw and treated sewage. Removal rates of between 30 and 99% were observed (Table 12). The highest removals were of human mitochondrial DNA, while the lowest were of polyomavirus.

The human indicative markers were detected in the effluent following passage through the BTF, with 99% removal of the human mitochondrial DNA, 90% removal of the bacterial human indicator (Bacteroides) and 40% removal of the human viral indicator (Polyomavirus). The human bacteroides is a subset of the total bacteroides, allowing an additional calculation to be made (Table 14). If the initial sewage is assumed to be 100% human, then based on proportions, the final effluent has potentially reduced its human proportion by up to 71% (Table 14). Combined together with the overall reduction in total bacteroides, based on the levels of bacteroides, the reduction could be up to 97%.

Table 14. Reduction in proportion of human bacteroides before and after the Gisborne BTF.




Human bacteroides as

proportion of the total

bacteroides

0.23% 0.16% 0.08% 0.04% 0.12% 0.03%

Reduction in human % 31% 46% 71%

% human remaining 70% 54% 29%


4.3 Faecal sterol analysis

Sterols are lipids that have important biological functions, in plants and animals, including maintenance of cell wall structure. The subgroup of "faecal" sterols is found mainly in human and animal faeces, and the sterol "fingerprint" can be quite distinctive between species. In particular, human faeces have high levels of the sterol coprostanol and the analysis of ratios of sterols generates a fingerprint that is able to discriminate human faeces from other sources (Table 15). Biotransformation of sterols occurs in the large intestine, where microbial populations convert digested sterols such as cholesterol to a range of other sterols.

Table 15. Faecal sterol ratios

Ratios indicative of faecal pollution (either human or animal)

F1 coprostanol/cholestanol. >0.5 indicative of faecal source of sterols

F2 24ethylcoprostanol/ 24-ethylcholestanol. >0.5 indicative of faecal source of sterols.

Human indicative ratios

H3 coprostanol/ 24-ethylcoprostanol Ratio >1 suggests human source

H1 % coprostanol Ratio >5-6% suggests human source

H2 coprostanol/(coprostanol+cholestanol) Ratio >0.7 suggests human source

H4 coprostanol/(coprostanol+24-ethylcoprostanol) Ratio >0.75 suggests human source

Ruminant indicative ratios

R3 24-ethylcholesterol/24-ethylcoprostanol Ratio <1 suggests ruminant source

R1 % 24-ethylcoprostanol Ratio >5-6% suggests ruminant source

R2 coprostanol/(coprostanol+24-ethylcoprostanol) Ratio <30% suggests ruminant source

Avian indicative ratios

A1 24-ethylcholestanol/(24-ethylcholestanol+24-

ethylcoprostanol+24-ethylepicoprostanol)

A1 Ratio >30% AND A2 Ratio >67%

suggests avian source

A2 cholestanol/(cholestanol+coprostanol+epicoprostanol)

Plant indicative ratios

P1 24-ethylcholesterol/24-ethylcoprostanol Ratio >4 suggests plant decay

Samples were analysed for sterols, with the level of each sterol given in Table 16, with percent removal and log removal rates in Tables 17 and 18. In Table 19 sterol ratio analysis is given.


Table 16. Sterol levels measured (parts per trillion, adjusted to 100 mL volume)



Sterol CMB814 CMB815 CMB816 CMB817 CMB818 CMB819

Coprostanol 121940 27524 305276 18272 167824 27118

24-ethylcoprostanol 31424 9756 104452 8854 70212 13389

Epicoprostanol 1232 899 49008 733 4148 1859

Cholesterol 104956 20535 171036 20210 130504 27524

Cholestanol 6388 4044 39944 3555 8956 7118

24-methylcholesterol 12516 3069 24756 2943 19672 3932

24-ethylepicoprostanol 240 239 6916 172 732 536

Stigmasterol 1648 2502 4088 745 3872 1032

24-ethylcholesterol 22844 3774 41352 3793 36928 4792

24-ethylcholestanol 3212 736 12528 526 6448 1002

Total sterols 306400 73079 759356 59802 449296 88301

Actual volumes analysed were 25 mL per sample from before the trickling filter and 250 mL post BTF. Some overloading of the column occurred with levels of coprostanol, 24-ethylcoprostanol and cholesterol exceeding calibration limits in most of the samples. Future analysis should use 5 mL of sample from before the trickling filter, and 25 mL post the trickling filter.

Table 17. Percentage removal rates of sterols through Gisborne BTF


Coprostanol 77.4% 94.0% 83.8% 85.1%

24-ethylcoprostanol 69.0% 91.5% 80.9% 80.5%

Epicoprostanol 27.0% 98.5% 55.2% 60.2%

Cholesterol 80.4% 88.2% 78.9% 82.5%

Cholestanol 36.7% 91.1% 20.5% 49.4%

24-methylcholesterol 75.5% 88.1% 80.0% 81.2%

24-ethylepicoprostanol 0.5% 97.5% 26.7% 41.6%

Stigmasterol -51.8% 81.8% 73.3% 34.4%

24-ethylcholesterol 83.5% 90.8% 87.0% 87.1%

24-ethylcholestanol 77.1% 95.8% 84.5% 85.8%

total sterols 76.1% 92.1% 80.3% 82.9%


Table 18. Log Removal rates of sterols through Gisborne BTF


Coprostanol 0.6 1.2 0.8 0.9

24-ethylcoprostanol 0.5 1.1 0.7 0.8

Epicoprostanol 0.1 1.8 0.4 0.8

Cholesterol 0.7 0.9 0.7 0.8

Cholestanol 0.2 1.1 0.1 0.5

24-methylcholesterol 0.6 0.9 0.7 0.7

24-ethylepicoprostanol 0.0 1.6 0.1 0.6

Stigmasterol -0.2 0.7 0.6 0.4

24-ethylcholesterol 0.8 1.0 0.9 0.9

24-ethylcholestanol 0.6 1.4 0.8 0.9

total sterols 0.6 1.1 0.7 0.8

Table 19. Ratio analysis of sterols before and after the Gisborne BTF



Ratio and threshold CMB814 CMB815 CMB816 CMB817 CMB818 CMB819

Faecal F1 >0.5 19.09 6.81 7.64 5.14 18.74 3.81

Ratios F2 >0.5 9.78 13.25 8.34 16.85 10.89 13.37

Human

Indicative

H3 >1 3.88 2.82 2.92 2.06 2.39 2.03

H1 >5% 39.8% 37.7% 40.2% 30.6% 37.4% 30.7%

H2 >0.7 0.95 0.87 0.88 0.84 0.95 0.79

H4 >75% 80% 74% 75% 67% 71% 67%

Ruminant

Indicative

R3 <1 0.73 0.39 0.40 0.43 0.53 0.36

R1 >5% 10.3% 13.3% 13.8% 14.8% 15.6% 15.2%

R2 <30% 80% 74% 75% 67% 71% 67%

Wildfowl A1 >30% 9% 7% 10% 6% 8% 7%

Indicative A2 >67% 5% 12% 10% 16% 5% 20%

Plant P1 >4 0.73 0.39 0.40 0.43 0.53 0.36

4.3.1 Interpretation of sterol results

As expected there were high levels of sterols in all samples, with in particular levels of coprostanol exceeding 30% in all samples. There was a reduction all sterols after the BTF (with exception of stigmasterol in the 3 hour morning composite, which is probably a reflection of variability in influent), of approximately 80%.


Ratio analysis of influent was all consistent with human sewage. The elevated ruminant R3 and R1 ratios are in fact not, in this case, considered to be indicative of ruminant sewage, but an artefact of the high levels of human sterols. Ruminant faecal matter would not have the elevated human sterol ratios observed. The human indicative ratios are all lower after the BTF, but all still clearly indicate human faecal material. There has been a reduction in sterols and some change in composition of sterols, but they remain indicative of human faecal material.


4.4 Fluorescent whitening agent analysis

Fluorescent whitening agents (FWAs) are common constituents of washing powders used to brighten clothing. Most household plumbing systems mix effluent from toilets with ‘grey water’ from washing machines. Consequently, FWAs are usually associated with human faecal contamination in both septic tanks and community wastewater systems. The presence of FWAs indicates human effluent, and is used as an indicator of human effluent.

Samples were analysed for FWAs, with the concentration of FWA in each sample given in Table 20, along with percentage removal and log removal rates.

Table 20. Levels and removal rates of FWAs through Gisborne BTF




FWA (µg/L) 5.0 5.1 9.9 7.8 3.0 4.0

% removal -2% 21% -33%

log removal -0.01 0.10 -0.12

4.4.1 Interpretation of FWA results

FWA levels ranged between 3.0 and 9.9 µg/L. We believe that the variation observed in each sample reflects variation of the amount of FWAs in the influent. The higher levels in the afternoon samples and may reflect increase in laundry activities during the morning (time taken for this wastewater to physically reach the wastewater treatment plant). We believe these results show no degradation or removal of FWAs in the BTF. FWAs are broken down by sunlight exposure, or absorb to solids, neither of which is likely to be significant in the BTF.


5 DISCUSSION AND CONCLUSIONS

This report seeks to contribute to the question of what is “The extent of biotransformation being achieved by the BTF Plant”.

The WTAG have agreed on the following definition of biotransformation:

"A biological process by living organisms which remove and/or breakdown harmful contaminants into safe non toxic components that can be recycled back into the environment".

Through discussion with WTAG, we have added to this the notion of the extent with which the BTF transforms human waste into organic matter, ie something no longer recognisable as human in nature. Assessment of biotransformation could therefore include the following two components.

Identification of harmful contaminants in sewage, and measurement of the degree to which they are removed or broken down by the BTF.

Measurement of indicators of human waste, and measurement of the degree to which they are removed or broken down.

5.1 Contaminant removal by the BTF

The major contaminants in wastewater are biodegradable organic compounds, volatile organic compounds (VOCs), recalcitrant xenobiotics, toxic metals, suspended solids, nutrients (nitrogen and phosphorous) and microbial pathogens and parasites. A sewage treatment process needs to reduce or remove the contaminants sufficiently that the discharge from the wastewater plant is environmentally acceptable for disposal. Separate strands of work not covered in this report are targeting the toxic or carcinogenic trace organics and toxic metals.

The degree to which organic content and nutrients need to be reduced, depends on the nature of the receiving environment and its ability to assimilate organic content and nutrients and the activities that take place in the receiving environment (such as swimming/surfing or food gathering). This is not an issue we have addressed closely, but we note that previous investigations of the impacts of raw sewage discharge found little evidence of detrimental impacts on the environment.

The key issue that we addressed in this project was the extent of microorganism reduction achieved by the BTF plant. The level required of discharge of <1,000 enteroccocci per 100 mL and is a target of many plants in NZ.

The extent of micro-organism reduction achieved by the BTF plant

Monitoring of the BTF to date has focussed on the level of the microorganism enterococci. We have supplemented these data with enumeration of E. coli, C. perfringens, Campylobacter, and f-RNA phage.

The influent to the plant contains an average of 862,000 enterococci per 100 mL. The BTF is able to reduce this by an average of 1.2 log, resulting in average level of enterococci after the BTF of 67,000 CFU/100 mL. The consent condition of 1,000 CFU/100 mL was not meet on any occasion. Even using the maximum observed


reduction in the BTF (1.7 log), this limit would still be exceeded on every occasion (see section 3.3.6).

The removal rates of other microorganisms tested were within the range observed for enterococci (E. coli, Campylobacter, and f-RNA phage), or in the case of C. perfringens much less (See section 4.1). This would suggest that enterococci is a suitable indicator of bacterial removal through the BTF, although it may overestimate removal rates of more hardy organisms such as protozoa (eg. the pathogens Cryptosporidium and Giardia).

A number of previous studies have investigated the effectiveness of trickling filters (Table 21). It is likely none of these examples are directly comparable with Gisborne, because each system has unique construction, type and size of media, treatment steps before the trickling filter, environment conditions (notably temperature) and to a degree type of sewage treated. The removal rates observed in the Gisborne BTF are at the higher end of removal rates reported previously. The large size of the Gisborne BTF, the use of high surface area plastic media, and moderate loading rates probably all contribute to this better than average performance by the Gisborne BTF compared to the examples.

While this is positive in reflecting that the BTF is functioning at least as well as could be expected, it also suggests that additional improvement in the BTF removal rates are probably unrealistic and to further reduce the concentration of indicator microorganisms additional treatment is required before or after the BTF These published removal rates also support the lower removal rates in the Gisborne BTF for bacteriophage (type of virus) and Clostridium (surrogate indicator for protozoa).

Therefore, it is reasonable to expect a well-managed BTF to achieve a reduction in microorganisms of between 1 and 2 log (or 90-99%). This is equivalent to that achieved with primary septic tanks or oxidation ponds (Table 22).


Table 21. Removal rates of microorganisms in trickling filters reported in literature

Country Organism Removal Rate Reference

Bacte

ria

Poland Enterococci/ faecal coliforms

70% Filipkowska and Krzemieniewski, 1998

UK Salmonella 75-95% Feachem et al. 1983, reported in Bitton, 2011

UK Enteric bacteria 20-80% Feachem et al. 1983, reported in Bitton, 2011

USA Faecal coliforms 95% Moore et al. 1981, reported in Bitton, 2011

New Zealand Faecal coliforms >90% Lewis et al. 1986

Viruses

USA

enteroviruses 59-95% Moore et al. 1981, reported in Bitton, 2011

Sweden noroviruses 0.1 log Nordgren et al., 2009

Unknown Bacteriophage 40-90% Kott et al. 1974, reported in Bitton, 2011

New Zealand Viruses 0-20% Lewis et al. 1986

Pro

tozo

a

India Entamoeba histolytica

74-91% Panikcer and Kristhnomorthi, 1978, reported in Stott 2003.

UK Helminth eggs 60%

(range 5-90%)

Gerba, 2008

UK Protozoan cysts 77%

(range 5-93%)

Gerba, 2008,

France Cysts and oocysts

10-99% Schwartzbrod et al. 2002

Table 22. Typical removal rates of sewage treatments1

Treatment method Removal rates

primary septic tank 90% 1 log

oxidation pond primary effluent 99% 2 log

modified primary septic tank 99% 2 log

secondary-treated municipal effluent 99.99% 4 log

oxidation pond tertiary effluent 99.99% 4 log

improved secondary septic systems 99.999% 5 log

advanced tertiary septic systems 99.9999% 6 log

tertiary treated municipal effluent 99.9999% 6 log

1 Data extracted from: (a) Removal of microbial pathogens in Christchurch City Council’s Bromley Wastewater

Treatment Plant, M. Leonard, 2002. ESR Report CSC0210; (b) Opus material on Principles & Trends of

Wastewater Treatment; (c) WHO http://www.who.int/water_sanitation_health/bathing/bathwatchap9.pdf.

http://www.who.int/water_sanitation_health/bathing/bathwatchap9.pdf


5.2 Biotransformation of human faecal material

Obviously the main human component of sewage is human faeces. Pathogenic organisms within faeces and the potential for these to be spread by the faecal oral route, are a key reason why the treatment of sewage to keep these out of drinking and recreational waters has had the greatest public health impact in reducing mortality and morbidity, of any action taken. Using the pathogens assayed here as indicators of human sewage, may both over- and under-estimate the human component.

It may over-estimate human component as these organisms are also found in a range of different animals including cows, sheep, dogs and wildfowl. Some of these pathogens can survive outside of the human host for some time, particularly in the case of protozoa, and may at various points not be directly associated with recent inputs of human faeces.

Pathogens may also under-estimate human component as they will only be present if there are people sick with these pathogens. Usually only a small number of people are sick with any one pathogen type at any one time, therefore levels of individual pathogens in sewage can be relatively low. For these reasons, and also for ease of analysis, we tend to use indicator organisms such as enterococci or E. coli as indictors of faecal pollution in water. These indicator bacteria are usually present at higher levels than pathogens in faeces, and are cheaply and quickly measured. The absence of enterococci or E. coli in water usually correlates with absence of bacterial pathogens. However, like pathogens, enterococci and E. coli are found in other animals, and can also be found outside animal host.

A range of new indicators of faecal material have been developed, three of which we have used in this study. PCR-based DNA technologies target other groups of microorganisms found in faeces, or the DNA of humans themselves. Molecular assays targeting other microorganisms in faeces, include assays that target certain species of bacteroides, or types of polymavirus that are only found in human faeces. Human cells are sloughed off into faeces from bowel, and skin cells washed into sewage from bathing. Detection of human mitochondrial DNA from human cells is indicative of human cells being present. Other chemical indicators such as faecal sterols, are present in human faeces in specific combinations. Conversion of these to forms no longer typical of human faeces should be reflective of degree of biotransformation. The third indicator of human sewage we have used is FWA analysis. FWAs are added to washing powder to brighten clothing and as greywater, becomes an integral component of most human sewage.

The human indicative markers were detected in the effluent following passage through the BTF. Of the human specific microorganisms, an average of 10% of the bacterial human indicator (Bacteroides) and 60% of the human viral indicator (Polyomavirus) remained in the effluent.

The BTF resulted in no degradation or removal of FWAs in the BTF. FWAs are broken down by sunlight exposure, or absorb to solids. Sedimentation tanks typically remove significant amounts of FWAs. The high levels of FWAs in sewage make them a potentially good indicator of the fate of other recalcitrant chemicals that may be present at much lower levels that are difficult or very expensive to detect.


In contrast, faecal sterols readily undergo microbial biotransformation. The BTF reduced total level of sterols by 80%, but ratio analysis indicates the sterols remaining were still typical of human faecal material.

The most direct indicator of human-source in the effluent is the presence of human DNA. In this study we found removal of up to 99% of the human DNA through the BTF (2 log removal).

Therefore, the BTF does achieve some biotransformation of the sewage. It reduces microorganism levels by 90-99% (1 to 2 logs), and reduces the human indicative characteristics of the sewage. Whether this is sufficient to satisfy Gisborne’s definition of biotransformation is something for the local community to decide.

A health risk assessment taking into account potential exposures of the receiving water (ocean outfall), and tides and flows would be required to assure public health agencies (and the public), that the BTF is achieving sufficient microbial reduction.

Biotransformation of the sewage to no longer be human is only partially achieved. Again, whether the transformation is sufficient is not something the report authors can answer. However, to aid discussion, we briefly mention the approach taken in the fields of genetically modified (GM) foods and verification of authenticity of foods. The later is well illustrated by the recent scandals with horse meat in food products that were labelled as beef. It is not possible to say that a food of mixed or unknown origin has no horse meat, rather assay methods result in detection limits of 1% or 0.1% (assay-dependent). Therefore “horse meat-free” food is one with less than 0.1% or 1% horse meat in it (assay-dependent). GM foods tend to use a similar detection limit, for acceptance of GM free. In both cases, some additional assurance can be obtained by tracking all components. Using a similar logic, one could argue that if effluent is less than 1% or 0.1% human signature, then it has been biotransformed and may no longer be thought of as human.

If the influent is classed as 100% human, then these thresholds could be met by a reduction of 99% or 99.9% of the biotransformation indicators. The data in this reports shows that microorganisms reduced 90-99%, microbial DNA markers 90%, sterols by 80%, and human mitochondrial DNA by 99%. While the human mitochondrial DNA reduces by 99%, in all cases human markers can still be detected after the BTF.

An alternative view would be: is the treated effluent less than 1% or 0.1% human? The only markers that can be used in this type of calculation are the PCR markers. Human indicative markers were detected in the effluent following passage through the BTF, with 90% removal of the bacterial human indicator (Bacteroides) and 40% removal of the human viral indicator (Polyomavirus). A reduction in human bacteroides as a proportion of the total bacteroides is also evident. So the effluent has reduced by 90% level of bacteroides and if the initial sewage is assumed to be 100% human, the final effluent has potentially reduced also reduced its human proportion by up to 70%, to be only 30% human. Combined together the reduction could be up to 97%.

The consent poses a number of additional issues or questions which we will address together:

Relevant parameters to be used in assessing biotransformation.


Appropriate parameters and a monitoring programme for ongoing assessment of biotransformation.

Appropriate parameter limits to ensure biotransformation is being achieved.

The relevance of BOD as a measure of biotransformation.

The relationship between Suspended Solids and biotransformation of wastewater

As the levels of BOD, microorganisms and TSS are reduced by the BTF, so the degree of biotransformation accomplished will increase. These are useful measures of the BTF function, and of biotransformation. Several additional parameters are described in this report. DNA-based methods offer an opportunity to measure specific microorganisms and cells specific to human faecal sources. Faecal sterol analysis also offers human specific indicators. These are perhaps best used for assessing the potential of additional treatment measures, or for calibrating the effect of any changes in BTF which are observed on the basis of the currently monitored parameters. FWA analysis may also be a good surrogate for recalcitrant contaminants, which in themselves are difficult to measure, and present at only low or intermittent levels.

6 CONCLUSIONS

This report presents the analysis of monitoring data supplied by Gisborne City Council on the quality of the effluent before and after commissioning of the BTF. In addition, to understand wastewater biotransformation through the BTF in more depth, the authors undertook wastewater and effluent characterisation before and after the BTF by measuring: the amounts of a range of microorganisms, the presence of DNA markers by PCR and the concentration of several chemical markers.

Two key aspects of the assessment of biotransformation are:

(a) Identification of hazardous contaminants in sewage and the measurement of the degree to which they are removed or broken down by passage through the BTF; and

(b) Measurement of indicators of human waste and the measurement of the degree to which they are removed or broken down.

Pathogenic microorganisms are a key hazard in wastewater. However, the diversity and concentration of different pathogens in wastewater varies with time depending on the amount of disease in the community. While we tested for the pathogen Campylobacter, we examined the levels of a range of other non-pathogenic microorganisms which can be used to provide evidence of the BTF’s operational capacity to remove human pathogens from wastewater.

We found that:

The BTF achieved a reduction in microorganisms (Escherichia coli, enterococci, Clostridium, Campylobacter, fRNA phage) of between 90-99% (1 - 2 log10).


Passage of wastewater through the BTF was insufficient to reduce the levels of enterococci to below the consent initial conditions of 1,000 CFU/100 mL; average observed level of enterococci after BTF was 67,000 CFU/100 mL.

Collated data and examination of the literature suggests that the Gisborne BTF is functioning at least as well as could be expected and additional improvement in the BTF removal rates of microorganisms are probably unrealistic.

Replacing enterococci with any other indicator would not “solve the problem”, as other possible indicators exhibited similar behaviour through the BTF.

Meeting the consent conditions for enterococci will require additional treatment steps either before and/or after the BTF.

Whether the limit of 1,000 CFU/100mL is appropriate or not is beyond the scope of this report. Any alteration to this limit would require a public health risk assessment to be carried out.

There was no simple relationship between the BTF plant biological oxygen demand (BOD) loading and microorganism reduction. BOD loading could not be used to estimate or predict microorganism reduction.

To evaluate indicators of human waste, we considered, in addition to microorganisms from human faeces, PCR-based markers for human specific microorganisms, a PCR-marker for mitochondrial DNA from human cells, and both natural (faecal sterols) and man-made (fluorescent whitening agents (FWAs)) chemicals.

We found that:

The BTF reduced levels of bacterial DNA markers by 90-97%, faecal sterols by 80%, and FWAs levels were unaltered.

The most direct indicator of human-source in the effluent is the presence of human mitochondrial DNA. In this study we found removal of up to 99% of the human DNA through the BTF (2 log removal).

In all cases the human indicative markers were detected after the BTF, albeit at reduced levels.

Our overall conclusions are that the BTF is functioning at least as well as could be expected for this type of wastewater treatment. The BTF achieves about the same treatment effectiveness as oxidation pond treatment, but it does so with a much smaller footprint and it does so with a much shorter retention time. Therefore, BTF may be a technological consideration for communities where increasing the capacity of ponds or managing ponds susceptible to flooding is a problem.

However, as the primary wastewater treatment element, the BTF is unlikely to treat sewage to a level that will meet New Zealand expectations for microbial removal or community expectations for biotransformation. Additional treatment steps, either before or after the BTF, are required to increase the removal rates and the levels of biotransformation.


7 REFERENCES

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