Wastewater Treatment Plant Optimization En

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1/53Wastewater Treatment Plant Optimization No vemb er 2003 1

Wastewater Treatment PlantOptimization

This document is the fifth in a series of bestpractices that deal with buried linear infrastructureas well as end of pipe treatment and managementissues. For titles of other best practices in this andother series, please refer to www.infraguide.ca.

StormandWastewater

National Guide toSustainable Municipal

Infrastructure


2/532 Wastewater Treatment Plant Optimization Nove mb er 2003

Wastewater Treatment Plant Optimization

Issue No. 1.0

Publication Date: November 2003

2003Federation of Canadian Municipalities and National Research Council

ISBN 1897094329

The contents of this publication are presented in good faith and are intended as general

guidance on matters of interest only. The publisher, the authors and the organizations towhich the authors belong make no representations or warranties, either express or implied,

as to the completeness or accuracy of the contents. All information is presented on the

condition that the persons receiving it will make their own determinations as to the

suitability of using the information for their own purposes and on the understanding that the

information is not a substitute for specific technical or professional advice or services. In no

event will the publisher, the authors or the organizations to which the authors belong, be

responsible or liable for damages of any nature or kind whatsoever resulting from the use

of, or reliance on, the contents of this publication.


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Why Canada Needs InfraGuide

Canadian municipalities spend $12 to $15 billionannually on infrastructure but it never seems to be

enough. Existing infrastructure is ageing while demand

grows for more and better roads, and improved water

and sewer systems responding both to higher

standards of safety, health and environmental

protection as well as population growth. The solution

is to change the way we plan,

design and manage

infrastructure. Only by doing

so can municipalities meet

new demands within afiscally responsible and

environmentally sustainable framework, while

preserving our quality of life.

This is what the National Guide to Sustainable

Municipal Infrastructure (InfraGuide) seeks to

accomplish.

In 2001, the federal government, through its

Infrastructure Canada Program (IC) and the National

Research Council (NRC), joined forces with the

Federation of Canadian Municipalities (FCM) to createthe National Guide to Sustainable Municipal

Infrastructure (InfraGuide). InfraGuide is both a new,

national network of people and a growing collection of

published best practice documents for use by decision

makers and technical personnel in the public and

private sectors. Based on Canadian experience and

research, the reports set out the best practices to

support sustainable municipal infrastructure decisions

and actions in six key areas: municipal roads and

sidewalks, potable water, storm and wastewater,

decision making and investment planning,environmental protocols, and transit. The best

practices are available on-line and in hard copy.

A Knowledge Network of Excellence

InfraGuides creation is made possible through$12.5million from Infrastructure Canada, in-kind

contributions from various facets of the industry,

technical resources, the collaborative effort of

municipal practitioners, researchers and other

experts, and a host of volunteers throughout the

country. By gathering and synthesizing the best

Canadian experience and

knowledge, InfraGuide

helps municipalities get the

maximum return on every

dollar they spend oninfrastructurewhile

being mindful of the social and environmental

implications of their decisions.

Volunteer technical committees and working

groupswith the assistance of consultants and other

stakeholdersare responsible for the research and

publication of the best practices. This is a system of

shared knowledge, shared responsibility and shared

benefits. We urge you to become a part of the

InfraGuide Network of Excellence. Whether you area municipal plant operator, a planner or a municipal

councillor, your input is critical to the quality of

our work.

Please join us.

Contact InfraGuide toll-free at 1-866-330-3350or visit

our Web site atwww.infraguide.ca for more

information. We look forward to working with you.

Introduction

InfraGuide

Innovations and

Best Practices

Wastewater Treatment Plant Optimization No vemb er 2003 3

INTRODUCTION

InfraGuide Innovations and Best Practices



The InfraGuide Best Practices Focus

Transit

Urbanizat ion places pressure on an eroding,

ag eing infrastructure, a nd raises concerns about

declining a ir an d w at er q uality. Transit systems

contribute to reducing traffic gridlock and

improving roa d sa fet y. Transit be st practices

address the need to improve supply, influence

demand and make operat ional improvements

w i th the least environmenta l impact , w hi le

meeting social and business needs.

Storm and Wastewater

Age ing buried infrastructure , d iminishing f ina ncial resources, str icter

legisla t ion f or eff luent s , increa sing pub lic aw arene ss of en vironme nta l

impa c t s d u e t o w a s t e w a t e r a n d con t a min a t e d s t o r mw a t e r a r e ch a llen g e stha t munic ipa l i t ies have to dea l wi th . Events such as w a t er conta mina t ion

in Walkerton a nd North Ba t t le f ord, a s w ell as the recent CEPA

classi f ica t ion o f amm onia , roa d sa l t a nd chlor ina ted orga nics as toxic

subs tances, ha ve ra ised t he ba r for m unicipa l it ies. Storm and w as tew a t er

best pract ices dea l with b uried linea r infra structure a s w ell as end o f pipe

t rea tm ent a nd m ana gement issues. Examples include w ays to cont ro l and

reduce in f low and in f il t ra t ion ; how to secure re levant a nd cons istent da ta

sets; how to inspect and a ssess condit ion a nd perfo rman ce of collect ions

systems ; t rea t ment p lant opt imiza t ion ; and m ana gement o f b iosol ids .

Decision Making and InvestmentPlanning

Elected o fficials an d senior mu nicipal

administrators need a framework for

art iculat ing t he va lue of infrastructure planning

and maintena nce, whi le ba lancing social ,

environmental and economic factors. Decision-

making a nd investment planning best pra ct ices

transform complex and technical ma terial into

non -technical principles an d g uidelines fo r

dec is ion making, an d fac i li t a te the rea l iza t i on

of a deq uate f unding over the li fe cycle of the

infrastructure. Exam ples include prot ocols for

determining costs and benefi ts associated

w ith desired levels of service; an d strat eg ic

benchmarks, indicators or reference points

for investment policy and planning decisions.

Potable Water

Potab le w ater best practices add ress various

approaches to enhan ce a municipalitys or w ater

utilitys ability to manage drinking water delivery

in a w ay tha t ensures public health and safet y at

best value a nd o n a susta inable b asis. Issues such

as w ater a ccounta bility, w ater use a nd loss,

deterioration and inspection of distribution

systems, renew al planning a nd t echnologies for

rehabilitation of potable water systems and water

quality in the distribution systems are examined.

Municipal Roads and Sidewalks

Sound decision ma king and preventive maintena nce are essent ial to mana ging

municipal pavement infrastructure cost effectively. Municipal roads and

sidew alks best practices ad dress tw o priorities: front-end planning a nd de cision

making to ident i fy and manage pavement infrastructures as a component of the

infrastructure system; a nd a preventive approa ch to slow the d eteriorat ion of

existing roa dw ays. Example topics include t imely preventa tive mainten an ce of

municipal roads; construction and rehabilitation of utility boxes; and progressive

improvement o f a sphal t and concrete pa vement repair pract ices.

Environmental ProtocolsEnvironmental protocols focus on the interaction

of na tural systems and their effects on huma n

qua l ity of l ife in relat ion t o municipal

infrastructure delivery. Environmental elements

an d systems include land (including flora), w at er,

air (including noise an d light ) and soil. Examp le

pract ices include how to factor in environmental

considerations in establishing the desired level

of municipal infra structure service; a nd

definition of local environmental conditions,

chal lenge s and opportuni t ies w i th respect to

municipa l infrastructure.


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Acknowledgements. . . . . . . . . . . . . . . . . . . . . . 7

Executive Summary. . . . . . . . . . . . . . . . . . . . . . 9

1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .11

1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

1.3 Health and Safety . . . . . . . . . . . . . . . . . . . . . .11

1.4 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

2. Rationale. . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . .15

2.2 Expected Benefits ofWWTP Optimization . . . . . . . . . . . . . . . . . . . .15

2.2.1 Improved Plant Performance,Reliability, Flexibility,and Efficiency . . . . . . . . . . . . . . . . . . .15

2.2.2 Reduced Capital Costs ofExpansion/Upgrading . . . . . . . . . . . . .16

2.2.3 Reduced Operating Costs . . . . . . . . .16

2.2.4 Improved Operating Practices . . . . .16

3. Work Description. . . . . . . . . . . . . . . . . . . . 17

3.1 Elements of a WWTP OptimizationProgram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

3.2 Establish Objectives . . . . . . . . . . . . . . . . . . . .19

3.3 Plant Evaluation Tools . . . . . . . . . . . . . . . . . .19

3.3.1 Self-Assessment Report . . . . . . . . . .20

3.3.2 Historical Data Review . . . . . . . . . . .20

3.3.3 Unit Process Capacity Chart . . . . . . .21

3.3.4 Sludge Accountability Analysis . . . .22

3.3.5 Benchmarking Operating Costsand Staffing . . . . . . . . . . . . . . . . . . . . .22

3.3.6 Flow Meter Assessment . . . . . . . . . .22

3.3.7 Continuous Monitoring . . . . . . . . . . .23

3.3.8 Off-Line Monitoring . . . . . . . . . . . . . .24

3.4 Process Analysis Tools . . . . . . . . . . . . . . . . .243.4.1 Aeration System Capacity and

Efficiency Analysis . . . . . . . . . . . . . . .24

3.4.2 Hydraulic Modelling . . . . . . . . . . . . . .25

3.4.3 Analysis of Recycle Streams . . . . . .25

3.4.4 Stress Testing . . . . . . . . . . . . . . . . . . .25

3.4.5 Clarifier Hydraulic Tests . . . . . . . . . .27

3.4.6 Other Clarifier Diagnostics Tests . . .27

3.4.7 Mixing Tests . . . . . . . . . . . . . . . . . . . . .27

3.4.8 Process Modelling and Simulation .28

3.5 Optimization Approaches . . . . . . . . . . . . . . .28

3.5.1 Improved Operations andMaintenance . . . . . . . . . . . . . . . . . . . .28

3.5.2 Instrumentation, Control andAutomation . . . . . . . . . . . . . . . . . . . . . .29

3.5.3 Treatment Process Modifications . .31

3.5.4 Achieving Resource Cost Savings . .32

3.6 Document Benefits . . . . . . . . . . . . . . . . . . . .34

3.7 Optimization Task Flow Sheet . . . . . . . . . . .34

4. Applications and Limitations. . . . . . . . . . 354.1 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . .35

4.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Appendix A: Selected Case Histories. . . . . . 37

Appendix B: Optimization Opportunities

Through Process Modifications . . . . . . . . . . 43

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

TABLESTable 31: Performance limiting

factors at a WWTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Table 32: Examples of historical data reviewimpacts on subsequent optimization tasks . . . . 20

Table 33: On-Line process variables. . . . . . . . . 23

Table 34: Summary of typical unit processdesign parameters and evaluation criteria . . . . 26

Table 35: Automation applicationsat WWTPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Table 36: Potential treatment processoptimization approaches . . . . . . . . . . . . . . . . . . . . 31

FIGURESFigure 31: Elements of WWTP optimization. . . 17

Figure 32: Example of a processcapacity chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 33: Representation of optimizationtask flow sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table of Contents


TABLE OF CONTENTS


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The dedication of individuals who volunteered their

time and expertise in the interest of the National Guide

to Sustainable Municipal Infrastructure (InfraGuide) is

acknowledged and much appreciated.

This umbrella best practice for wastewater treatmentplant optimization was developed by stakeholders

from Canadian municipalities and specialists from

across Canada based on information from a scan of

municipal practices and an extensive literature

review. The following members of InfraGuides Storm

and Wastewater Technical Committee provided

guidance and direction in the development of this

document. They were assisted by the Guide

Directorate staff and by XCG Consultants Ltd.

J ohn Hodgson, Chair

City of Edmonton, AlbertaAndr AubinCity of Montral, Quebec

Richard BoninCity of Qubec, Quebec

David CalamCity of Regina, Saskatchewan

Kulvinder DhillonProvince of Nova Scotia, Halifax, Nova Scotia

Tom FieldDelcan Corporation, Vancouver, British Columbia

Wayne GreenCity of Toronto, Ontario

Claude OuimetteOMI Canada Inc., Fort Saskatchewan, Alberta

Peter SetoNational Water Research Institute,Environment Canada, Burlington, Ontario

Timothy A. TooleTown of Midland, Ontario

Bilgin BuberogluTechnical Advisor, NRC

In addition, the Storm and Wastewater Technical

Committee would like to thank the following

individuals and institution for their participation in

working groups, peer reviews, and support.

Susheel K. AroraMunicipality of the County of Colchester,Nova Scotia

Vince CorkeryCity of Edmonton, Alberta

Paul DoCity of Calgary, Alberta

Graeme FarisRegional District of Comox-Strathcona,British Columbia

Andr MarsanCentre dpuration Rive-Sud de Longueuil, Quebec

Gatan MorinRoche Lte, Groupe-Conseil, Quebec

Mark RupkeCity of Toronto, Ontario

Peter SetoNational Water Research Institute,Environment Canada, Burlington, Ontario

J ames ArnottOntario Ministry of the Environment, Hull, Quebec

Tony HoMinistry of Environment, Toronto, Ontario

Debbie MaceyCanadian Association for Environmental AnalyticalLaboratories (CAEAL), Ottawa, Ontario

Vince PileggiOntario Ministry of the Environment,Toronto, Ontario

Serge ThriaultDepartment of Environment and Local Government,New Brunswick

A. Warren WilsonWPC Solutions Inc., Calgary, Alberta

Great Lakes Sustainability Fund,

Environment Canada

Acknowledgement


ACKNOWLEDGEMENTS



This and other best practices could not have been

developed without the leadership and guidance of

the Project Steering Committee and the Technical

Steering Committee of the National Guide to

Sustainable Municipal Infrastructure (InfraGuide),

whose memberships are as follows:

Project Steering Committee:Mike Badham, ChairCity Councillor, Regina, Saskatchewan

Stuart BriesePortage la Prairie, Manitoba

Bill CrowtherCity of Toronto, Ontario

J im DOrazioGreater Toronto Sewer and WatermainContractors Association, Ontario

Derm FlynnMayor, Appleton, Newfoundland and Labrador

David GeneralCambridge Bay, Nunavut

Ralph HaasUniversity of Waterloo, Ontario

Barb HarrisWhitehorse, Yukon

Robert HiltonOffice of Infrastructure, Ottawa, Ontario

J oan LougheedCity Councillor, Burlington, OntarioStakeholder Liaison Representative

Saeed Mirza

McGill University, Montral, QuebecRen MorencyRgie des installations olympiquesMontral, Quebec

Lee NaussCity Councillor, Lunenburg, Nova Scotia

Ric RobertshawRegion of Halton, Ontario

Dave RudbergCity of Vancouver, British Columbia

Van SimonsonCity of Saskatoon, Saskatchewan

Basile StewartMayor, Summerside, Prince Edward Island

Serge ThriaultDepartment of Environment and Local Government,New Brunswick

Alec WatersAlberta Transportation, Edmonton, Alberta

Wally WellsDillon Consulting Ltd., Toronto, Ontario

Technical Steering Committee:

Don BrynildsenCity of Vancouver, British Columbia

Al CepasCity of Edmonton, Alberta

Andrew CowanCity of Winnipeg, Manitoba

Tim DennisCity of Toronto, Ontario

Kulvinder DhillonProvince of Nova Scotia, Halifax, Nova Scotia

Wayne GreenCity of Toronto, Ontario

J ohn HodgsonCity of Edmonton, Alberta

Bob LorimerLorimer & Associates, Whitehorse, Yukon

Betty Matthews-MaloneHaldimand County, Ontario

Umendra MitalCity of Surrey, British Columbia

Anne-Marie ParentCouncillor, City of Montral, Quebec

Piero SalvoWSA Trenchless Consultants Inc., Ontario

Mike SheflinFormer CAO, Regional Municipality ofOttawa-Carleton, Ontario

Konrad SiuCity of Edmonton, Alberta

Carl Yates

Halifax Regional Water Commission,Nova Scotia

Founding Member:

Canadian Public Works Association (CPWA)

Acknowledgements


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Wastewater treatment plants (WWTPs) aretypically designed to conservative designguidelines and are operated based on historicpractices. Generally, experience has shownthat such facilities often have considerableadditional capacity that can be realizedthrough optimization. Improvements in effluentquality and reductions in operating costs canalso be realized. This best practice providesan overview of the approach that should betaken to optimize an existing WWTP. It alsodescribes a set of tools that can be used toachieve the specific objectives of anoptimization program. By applying this bestpractice, the capacity of the existing

infrastructure can be maximized, theperformance of the works enhanced, and theoperating and maintenance costs reduced.

WWTP optimization should become anoperating philosophy for the municipality thatis championed by management, supported bycouncil and staff at all levels, and has theoverall objective of continuous improvement.The best practice for WWTP optimizationincludes the following elements.

Establish the objectives of optimization. Evaluate the WWTP to establish or

benchmark conditions, prioritizeopportunities for optimization, anddetermine performance or capacity limitingfactors.

Identify and implement operational orprocess changes to address performanceor capacity limiting factors.

Conduct follow-up monitoring to documentthe benefits.

A WWTP optimization program is iterative, andclear objectives should be established beforeeach iteration. Depending on the objectivesestablished, the outcome of WWTP optimizationmay include any or all of the following:

an increase in the capacity of the existingworks without the major capital costsassociated with a plant expansion;

an improvement in process without themajor capital costs associated with a plantupgrade; and

a reduction in operating costs through moreefficient use of power, chemicals, or labour.

This best practice provides WWTP owners

and operators with a description of some ofthe state-of-the-art tools available to evaluateand optimize their WWTP and the individualunit processes that comprise it, such as:

oxygen transfer testing;

hydraulic modelling;

clarifier hydraulic testing;

stress testing; and

process modelling and simulation.

Available tools to optimize through improvedoperations and maintenance practices;instrumentation, control, and automation; andprocess modifications are described in thedocument, along with opportunities to achieveresource cost savings.

A key element of the WWTP optimization bestpractice that is often ignored is the follow-upmonitoring needed to document the level ofsuccess achieved. Communication of thebenefits of the optimization program is

essential to build support for future initiatives.This support is the key to ensuring the iterativeprocess of optimization is sustained and anenvironment conducive to optimization isfostered within the municipality.

As a guide to conducting WWTP optimization,a step-wise approach is illustrated thatsuggests the type of testing that could be doneto meet various optimization objectives.

Executive Summar


EXECUTIVE SUMMARY


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1.1 Introduction

Wastewater treatment plants (WWTPs) havetraditionally been designed to conservative

design guidelines and standards that weredeveloped based on historic design practices.Procedures are often passed from operatorto operator without consideration for newapproaches that might improve performanceor reduce costs. Generally, experience hasshown that WWTPs often have considerableadditional capacity beyond the rated capacitythat was assigned at design. Furthermore,improvements in performance and reductionsin operating costs can often be achievedthrough optimization approaches.

This best practice provides an overview ofan iterative approach to optimization of anexisting WWTP that will allow theowner/operator to maximize the capacity ofthe existing infrastructure, enhance theperformance of the facility, and reduce theoperational costs.

1.2 Scope

This best practice has been developed by theNational Guide to Sustainable Municipal

Infrastructure: Innovation and Best Practices.It is one of more than 50 aspects identified bythe Guides Storm and Wastewater TechnicalCommittee relating to linear infrastructure,wastewater treatment, customer interaction,and receiving water issues.

This best practice applies to the optimizationof municipal wastewater treatment plants.

WWTP optimization is considered to be a step-wise process that results in the maximum useof the existing infrastructure at a competitiveoperating cost consistent with principles ofsustainability. Depending on the objectives ofthe optimization program, the outcomes mayinclude any or all of the following:

increasing the capacity of the existingworks without the major capital costsassociated with a plant expansion;

improving process performance without themajor capital costs associated with a plantupgrade; and

reducing operating costs through moreefficient use of power, chemicals, or labour.

This best practice covers the processing ofthe most common liquid and sludge treatmentprocesses that typically comprise a WWTP.The liquid treatment processes includepreliminary, primary, secondary, and tertiarytreatment, and the disinfection of the treatedeffluent. The sludge treatment processesinclude thickening, dewatering and digestion(aerobic and anaerobic). Management of thebiosolids stream produced by the WWTP isnot addressed in this best practice. A bestpractice for biosolids management has beendeveloped by the National Guide toSustainable Municipal Infrastructure:

Innovation and Best Practices.The reader isreferred to that best practice for information

specific to biosolids management.1.3 Health and Safety

Some of the test procedures described in thisbest practice involve using hazardouschemicals or working in hazardous areas of aWWTP around electrical and mechanicalequipment. Appropriate safety measuresshould be taken before undertaking any of thetesting described, including reference tomanufacturers safety data sheets (MSDSs) on

chemicals that might be used during testingand adherence to occupational health andsafety standards.

1. General

1.1 Introduction

1.2 Scope

1.3 Health and S


1. General



1.4 Glossary

Biochemical oxygen demand (BOD)

The quantity of oxygen consumed, usuallyexpressed in mg/L, during the biochemicaloxidation of organic matter over a specifiedtime period (i.e., five day BOD or BOD5) at atemperature of 20C.

Biological nutrient removal (BNR)

Processes that remove nitrogen and/orphosphorus by biological rather than chemicalor physical means.

Chemical oxygen demand (COD) Thequantity of oxygen required in the chemicaloxidation of organic matter under standardlaboratory procedures, expressed in mg/L.

Dissolved oxygen (DO) The concentration

of oxygen dissolved in water usuallyexpressed in mg/L. Dissolved oxygen isimportant for aerobic (with air) biologicaltreatment. An adequate DO concentration ina wastewater effluent is important for theaquatic life in the receiving stream or river.

Endogenous Oxygen Demand Oxygendemand for the basic respiration of the micro-organisms, independent from the currentwastewater loading.

Food-to-micro-organismratio (F/M) The ratio of the influent mass loading (usuallyexpressed in kg/d) of BOD or COD to the massof volatile suspended solids concentration in awastewater treatment aeration tank. The unitsof F/M are typically d-1.

Hydraulic retention time (HRT) A measureof the length of time a volume of liquid isretained in a tank or vessel, calculated bydividing the tank or vessel volume (L) by theliquid flowrate (L/d) and is presented in either

days or hours.

Inflow and infiltration (I/I) Inflow is waterentering the sanitary sewer during wetweather events from such sources as roofleaders, foundation drains, manhole covers orstorm sewer interconnections. Infiltration is

water entering the sanitary sewer system fromthe ground through defective pipes, pipejoints, connections, or manhole walls.

Mixed liquor suspended solids (MLSS)

The concentration of dry solids in mg/L ofmixed liquor biomass in the aeration tank ofa suspended growth (activated sludge orextended aeration) WWTP.

Oxidation-reduction potential (ORP)

A measure of the net potential of all oxidantsand reducing agents in a solution usuallyexpressed in mvolts.

Return activated sludge (RAS) That portionof the activated sludge separated from themixed liquor in the secondary settlementtanks, which is returned to the aeration tanks.

Sequencing batch reactors (SBR) A treatment process characterized by theinterruption of flow to the reactor during thesedimentation and decanting phase oftreatment.

Sludge loading rate (SLR) The mass loadingrate in kg/d of mixed liquor suspended solids(MLSS) per unit area of the secondary clarifierIt is typically expressed as kg/m2.d

Sludge volume index (SVI) A measure of

the settling characteristics of biomass definedas the volume in mL occupied by 1 g of settledsludge after settling for 30 minutes in a settlingcolumn, typically a 1 litre graduated cylinder.SVI is usually expressed in mL/g.

Solids retention time (SRT) A measure ofthe theoretical length of time the averageparticle of mixed liquor suspended solids hasbeen retained in the biological reactor sectionof the treatment plant. It is usually presentedin days, and is also referred as mean cell

residence time (MCRT) or sludge age.

Specific Oxygen Uptake Rate (SOUR)

Also known as the oxygen consumption orrespiration rate, is defined as the milligramof oxygen consumed per gram of volatilesuspended solids (VSS) per hour.

1. General

1.4 Glossary


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Step-feed aeration A modification ofconventional plug-flow process in which thesettled wastewater is introduced at severalpoints in the aeration tank to equalize F/Mratio, thus lowering peak oxygen demand.

Stirred Sludge Volume Index (SSVI)

A measure to determine the settling propertiesof an activated sludge. It is expressed in mL/g.

Supervisory control and data acquisition

(SCADA) A computer-monitored sensing,alarm, response, control, and data acquisitionsystem used in WWTPs to monitor theiroperations.

Total Kjeldahl nitrogen (TKN) The sum ofthe organic and ammonia nitrogen in a watersample usually expressed in mg/L.

Total Phosphorus (TP) Total amount ofphosphorus present in the wastewater (orwater) either in soluble or insoluble forms, inorganic and inorganic (orthophosphates,metaphosphates or polyphosphate)compounds, expressed in mg/L.

Total suspended solids (TSS) Solidspresent in a water sample that are retainedon the filter paper after filtering the sample,usually expressed in mg/L.

Volatile Suspended Solids (VSS) The amountof total suspended solids burned off at 550 50Cexpressed normally as mg/L. It indicates thebiomass content of the mixed liquor.

Waste activated sludge (WAS) The excessportion of the activated sludge separated fromthe biological treatment process.

1. General

1.4 Glossary



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2.1 Background

In the 1980s and early 1990s, WWTPoptimization first gained recognition as a cost-effective way to achieve improved performance,reduce costs, and maximize the use of existinginfrastructure. Early efforts at optimization in theUnited States were initiated by the recognitionthat considerable capital dollars had been spenton new facilities, but these facilities were notperforming to expectations. The CompositeCorrection Program (CCP) was developed toidentify the major causes of poor performancein these plants (Water Pollution ControlFederation, 1985).

Rising energy prices in the 1980s led to a focuson energy conservation in WWTPs throughoptimization techniques. The process audit wasdeveloped based on work undertaken at theTillsonburg, Ontario WWTP, primarily as a meansto reduce process energy use at these facilities(Speirs and Stephenson, 1985). Experience withthe tool showed it could also be applied toevaluate plant capacity and identifyopportunities to obtain additional capacity in an

existing works at lower capital costs.Case histories showing substantial capital andoperating cost savings as a result ofoptimization of WWTPs began to appear in thetechnical literature. Guidance manuals wereprepared describing the benefits of, andavailable approaches for, WWTP optimization(WEAO, 1996). By the mid-1990s, WWTPoptimization had become a well-establishedpractice. In some jurisdictions, optimization ofthe existing works became a prerequisite forobtaining grants for plant expansion.

Specific goals of WWTP optimization mayinclude any or all of the following:

improved plant performance, reliability,flexibility, and efficiency;

reduced capital costs of expansion orupgrading;

reduced operating costs associated withenergy use, chemical use, and labour; and

improved operating practices.

2.2 Expected Benefits of WWTPOptimization

2.2.1 Improved Plant Performance,

Reliability, Flexibility, and Efficiency

Applying this best practice will result inimproved plant performance, and reduce therisk of noncompliance with either effluentquality requirements or biosolids qualityregulations.

The Regional Municipality of Halton, ownerand operator of the Burlington Skyway WWTP,used the Composite Correction Program (CCP)as an optimization tool, together with otheroptimization tools, to improve the performanceof this facility significantly. This was inresponse to a need to achieve enhancedeffluent quality requirements. The CCPapproach is described in Section 3.5 of thisbest practice. Through a comprehensiveperformance evaluation (CPE), non-technicalor management and human resources relatedlimitations are identified as performancelimiting factors. As a result of improvementsachieved during the follow-up comprehensivetechnical assistance (CTA), significantimprovements in plant performance wereachieved, allowing the plant to attain bothphosphorus and ammonia limits notconsidered achievable without major capitalexpenditures. At the same time, substantialsavings in capital costs for future plantexpansion were deferred as a result of theadditional capacity realized at the plant. Thetotal savings in capital costs were estimatedat about $50 million. A more detailed casehistory of the Burlington Skyway WWTPoptimization project accomplishments ispresented in Appendix A (Case History 1).

2. Rationale

2.1 Background

2.2 Expected Ben

WWTP Optim


2. Rationale

I n some

j u r i sd i ct i ons,

op t imiza t ion o

the ex is t ing

w o r k s b e c a m

a prerequ is i te

ob ta in ing g ra

fo r p lan t

expans ion .



2. Rationale

2.2 Expected Benefits of

WWTP Optimization

2.2.2 Reduced Capital Costs of

Expansion/Upgrading

Through WWTP optimization, significantcapital cost savings can be realized bymaximizing the capability and capacity of theexisting infrastructure.

The Regional Municipality of Waterloo, ownerand operator of the Ayr WWTP, was able to re-rate this facility from a nominal rated capacityof 1,181 m3/d to a new rated capacity of 1,500m3/d after applying some of the optimizationtools described in this best practice. A historicdata review and production of a processcapacity chart identified additional availablecapacity in the major unit processescomprising the packaged extended aerationplant. This review also questioned the

accuracy of the plant flow metering. Stresstesting of the secondary clarifiers, oxygentransfer testing, and biological simulationmodelling were used to confirm the findingsof the desktop evaluation. As a result, theregulator issued a new certificate of approvalfor the plant for the increased capacity andwith more stringent effluent limits for ammoniaand phosphorus, allowing further developmentin the community. The 27 percent increase incapacity was realized after minor upgrades to

the aeration system, the raw sewage pumpingstation, and the return sludge pumping system.No new aeration or clarification tankage wasrequired to allow the increased capacity. Amore detailed case history of the Ayr WWTPproject is presented in Appendix A (CaseHistory 2). Another example of optimizationleading to reduced capital costs for expansionof the Montral WWTP is also presented inAppendix A (Case History 4).

2.2.3 Reduced Operating Costs

The operating costs associated with energyuse, chemical use, and labour can be reducedthrough WWTP optimization.

A demonstration of optimized aeration modeoperation was conducted at the Tillsonburg

WWTP to determine the impact of on-offaeration on energy costs. The plantconfiguration allowed for a direct comparisonof parallel activated sludge aeration basins(also known as bioreactors) operated inthe on-off mode and in the conventionalcontinuous aeration mode. Aeration energysavings of between 16 and 26 percent wereachieved at the plant depending on whetherone of the two aeration cells or both aerationcells were cycled. Operation in the on-off

mode also resulted in denitrification atthe plant, reducing the total nitrogenconcentration in the plant effluent. A moredetailed case history of the on-off aerationdemonstration is presented in Appendix A(Case History 3). Another example ofoptimization resulting in reduced chemicalcosts at the Montral WWTP is also includedin Appendix A (Case History 4).

2.2.4 Improved Operating Practices

Improved operating practices will result inbenefits in all the areas outlined above.

An enhanced understanding of thefundamentals of sewage treatment processesthrough operator training and appropriateapplication of these concepts to processcontrol will improve plant performance andreliability, and allow operating staff torecognize opportunities to reduce costs.Through the use of techniques likecomprehensive technical assistance (CTA), itis possible to transfer the knowledge and skillsthat will lead to sustained WWTP optimizationand continuous improvement, as illustrated bythe optimization work undertaken at theBurlington Skyway WWTP.

An enhanced

understanding of

t he fundamenta ls

o f sewage

t rea tment

p r o ce ss e s

t h r ough ope r a t o r

t r a in ing and

app r op r ia t e

app l i cat i on o f

t hese concep t s t o

p ro ce ss con t ro l

w i l l im p r ove p lant

p e r f o r m a n ce a ndre l iab i l i t y .



3.1 Elements of a WWTP OptimizationProgram

WWTP optimization is not a one shot project

conducted by a contractor on behalf of theWWTP owner. Rather, it is an operatingphilosophy that is sustained with the overallobjective of continuous improvement. Someof the tools used to optimize the WWTPdescribed in this best practice can beundertaken by a contractor on behalf of themunicipality, but the overall optimizationprogram must be championed by themunicipality and supported by staff at all levelsof the organization. The elements of the best

practice for WWTP optimization apply to anysize or type of treatment plant; however, thetools used may vary. Those applied at a smallWWTP may be different than those applied ata larger WWTP, because the costs and thepotential return from some approaches maynot be justified at smaller facilities.

The best practice for WWTP optimizationincludes the following elements.

Establish the objectives of optimization.

Evaluate the WWTP to establish thebaseline or benchmark conditions, prioritizeopportunities for optimization, anddetermine performance or capacity limitingfactors.

Identify and implement operational orprocess changes to address performanceor capacity limiting factors.

Conduct follow-up monitoring to documentthe benefits.

The level of improvement achieved and thebenefits realized from implementing this bestpractice will depend on the starting point.Initial corrective measures may be neededto bring operating staff to a basic level ofknowledge and plant performance to anacceptable level. Subsequently, furtherenhancement to the performance of thefacility can be targeted. Thus, the processis iterative, and clear objectives should beestablished before each iteration.

The Composite Correction Program (CCP)was developed by the U.S. EnvironmentalProtection Agency (EPA, 1985) to identifyfactors that prevent a WWTP from achievingcompliance with its effluent requirements andto mitigate operational problems at suchfacilities. Through the CCP, the problemscausing poor plant performance can beresolved with minimal capital expenditure. Theapproach has been modified for application at

Canadian WWTPs (MOEE, 1996).

3. Work Descriptio

3.1 Elements of a

WWTP Optim

Program

Figure 31

Elements of WWTP

optimization

W W TP i s a n

o p e r a t i n g

ph i l osophy t h

sus t a ined w i t

the overa l l

ob jec t i ve

o f con t i nuous

impr ovemen t

3. Work Description

Figure 31:Elements of WWTP optimization


18/53

The CCP is a two-step process that followsa fairly rigorous format. The first stage, theComprehensive Performance Evaluation (CPE),is conducted to evaluate the potential of theWWTP to achieve the desired performancelevels. The evaluation focuses on four majorareas: plant design, operation, maintenance,

and administration. During the evaluation,performance limiting factors, typically five tofifteen, are identified and prioritized. Someof the factors that can limit performance orcapacity are identified in Table 31.

The methodology of conducting a CPE canbe summarized as follows.

Identify performance limiting factors.

Prioritize performance limiting factors.

Assess the approach to improveperformance.

Produce a CPE report.

Based on the results from the evaluation,the WWTP is classified as capable (Type 1),marginal (Type 2), or not capable (Type 3), interms of its ability to achieve compliance atits current flow. The causes of the problemsare identified and grouped into three prioritycategories.

Priority A factors have a major effect onplant performance on a continuous basis.

Priority B factors have a major effect onplant performance on a periodic basis, ora minor effect on a continuous bases.

Priority C factors have a minor effect onplant performance.

18 Wastewater Treatment Plant Optimization Nove mb er 2003

3. Work Description

3.1 Elements of a

WWTP Optimization

Program

Table 31

Performance Limiting

Factors at a WWTP

Table 31:Performance Limiting Factors at a WWTP

Category Factors

Operation

Design

Maintenance Scheduling and recording

Equipment malfunction

Availability of equipment

Skilled manpower

Age of equipment

Knowledge/training of staff

Administration Level of staffing

Support from administrative bodies

Financial

Policies

Record keeping

Operator training

Process monitoring

Sludge wasting and disposal

Knowledge of operating staff

Manual and technical support

Availability of equipmentProperchemical selection and use

Hydraulic load

Organic load

Oxygen transfer Inflow and infiltration (I/I)

Instrumentation and control (I&C)

Industrial load

Lack of flexibility

Sludge treatment capacity

Sludge storage capacity

Sludge disposal capacity Process equipment

Non-modular design

Configuration of process tankage


19/53

To achieve long-term performanceimprovements, all the factors contributingto poor performance at a facility must beaddressed in the next stage of optimization.

The second stage of the CCP, termedComprehensive Technical Assistance (CTA),is normally undertaken at a Type 1 or Type 2WWTP and involves systematically addressingthe performance limiting factors identified inthe CPE that do not involve capital works.A major component of the CTA is hands-onoperator training and support to implementprocess control techniques and standardoperating procedures (SOPs) to improveprocess performance. In addition,empowerment of operating staff in prioritysetting and problem-solving skills isaccomplished with the result that performanceis improved. WEAO has published guidancemanuals comprising an instructors manualand a student workbook (Training Operatorson Problem Solving Skills). The manuals canbe obtained by contacting WEAO [email protected].

Within the context of this best practice, theCPE phase of the CCP would be considered tobe a plant evaluation tool (refer to Section 3.3)and generally involves such components as a

historical data review (Section 3.3.2) and unitprocess capacity charts (Section 3.3.3).However, the CPE also includes a broaderevaluation of administrative factors that canlimit plant performance.

The CTA phase of the Composite CorrectionProgram is the actual optimization phase and isdiscussed in this best practice in Section 3.5.1.

3.2 Establish Objectives

The tools used for WWTP optimization willdepend on whether the objectives are:

reduced energy costs;

reduced chemical costs;

improved reliability by eliminatingoperational problems and upsets;

improved effluent quality;

improved biosolids quality;

increased treatment plant capacity;

reduced labour costs;

reduced sludge production or biosolidsmanagement costs;

reduced capital costs for plant upgradingor expansion; or

reduced odour production.

Clear objectives should be established anddocumented before WWTP optimization isinitiated. The objectives may be qualitative (i.e.,fewer upsets, fewer effluent exceedances) orquantitative (15 percent reduction in energycosts, 25 percent increase in plant capacity).This will allow the success of the measurestaken to be compared to the objectives.

3.3 Plant Evaluation Tools

During the WWTP evaluation stage, performanceis evaluated, capacity limiting factors areidentified and prioritized, and the approach tooptimizing the WWTP is developed. In doing thisevaluation, various tools can be used.


3. Work Descriptio

3.2 Establish Obj

3.3 Plant Evaluat


20/53

3.3.1 Self-Assessment Report

A self-assessment report, prepared by aqualified operational staff, allows the WWTPto evaluate its performance, and identify andprioritize areas for optimization by collectinginformation on the condition, quality, andcapacity of the treatment system.

The report should be done annually andrepresents a report card on the facility formunicipal managers and councillors. Thereport is used to evaluate the status of:

effluent compliance and plant performance;

plant capacity (current and five-yearprojections);

combined sewer overflows and plantbypasses;

biosolids handling, storage, and disposal; effluent sampling and analysis;

equipment maintenance;

operator training and certification; and

budgets for current operation andmaintenance, as well as for future facilityreplacement and growth.

A sample self-assessment report has beendeveloped by the Ontario Ministry of theEnvironment (MOE) based on the model whichhas been successfully used for many years bythe Wisconsin States Department of NaturalResources. The report can be obtained fromthe MOE Web site

3.3.2 Historical Data Review

A historical data review is an essentialcomponent of the evaluation stage of a WWTPoptimization program. The review definesthe current loadings on the facility, theperformance of each unit process, and thekey process operating parameters. It alsoidentifies data gaps that need to be filledthrough additional monitoring and can be usedto determine the representativeness of the

historical data.The detailed historical data review can alsobe used to redefine the project. Table 32provides examples of possible impacts ofthe historical data review on subsequentoptimization tasks.


3. Work Description

3.3 Plant Evaluation

Tools

Table 32

Examples of historical

data review impacts on

subsequent optimizationtasks

Table 32:Examples of historical data review impacts on subsequent optimization tasks

Source: Adapted from WEAO (1996).

Historical Data Review Finding Impact on Optimization Tasks

Mass balance cannot be completed Obtain required information

Mass balance does not close within 15 percent Complete flow meter assessment and/or review of off-line sampling accuracy

Effluent BOD5 and/or nitrogenous compoundsconcentrations exceed criteria

Conduct aeration capacity analysis

Return stream flows/concentrations not available Include sampling of recycle streams in off-linemonitoring program

Effluent SS higher than design values Conduct stress tests and hydraulic analysis (dye tests)to determine capacity and performance limits


21/53

3. Work Descriptio

3.3 Plant Evaluati

Tools

Figure 32

Examples of a proce

capacity chart


3.3.3 Unit Process Capacity Chart

One outcome of a historical data review is aprocess capacity chart based on the results ofa process capacity assessment of the key unittreatment processes at the WWTP. Theprocess capacity chart is used to identifybottlenecks that need to be addressed toincrease the capacity of the facility. The unitprocess capacity chart should cover both theliquid and sludge treatment processes as

either could be the limiting factor inmaximizing overall WWTP capacity. Figure 32provides an example of a process capacitychart. Full-scale stress testing is oftenperformed following a process capacityassessment to confirm the capacity suggestedby this analysis, especially for borderline

cases. It should be noted that the chart isbased on typical design guidelines orstandards which are often conservative.

Figure 32:Example of a process capacity chart

Source: XCG Consultants Ltd. (2002).


22/53

3. Work Description


Tools


3.3.4 Sludge Accountability Analysis

An output of the historic data review is asludge accountability analysis. This isbasically a solids mass balance across unitprocesses (e.g., clarifiers) or the overall plantto account for solids within the treatmentprocess. In general, mass balances will notclose exactly. A discrepancy from about 10 to15 percent is considered acceptable; however,a discrepancy of more than 15 percentindicates the need for further assessment toresolve the cause of the inconsistency. Thecommon sources of discrepancies in solidsmass balance analysis include:

non-representative samples (analyticalaccuracy, sampling techniques);

inaccurate flow monitoring;

the impact of periodic recycle streams (theboundaries of the balance must be clearlydefined and all inputs/outputs must beaccounted for in the mass balance); and

assumptions made concerningaccumulations.

A sludge accountability analysis should beperformed on a routine basis by plantoperating staff to verify the accuracy of flowmeasurements and analytical data.

3.3.5 Benchmarking Operating Costs andStaffing

If an objective of the optimization programis to reduce operating costs, the historicaloperating and maintenance costs for thefacility should be compared to those of othersimilar plants of similar size. This will identifythe magnitude of the cost reductionopportunity for energy, chemicals, sludgedisposal, and labour that represent the largest

components of the operating costs.Benchmarking information for resource costs(energy, chemicals, water) is available in theGuide to Resource Conservation and Cost

Savings Opportunities in the Water and

Wastewater Sector(MOEE, 1997). Moredetailed benchmarking data are available inBenchmarking Wastewater Operations:

Collection, Treatment and Biosolids

Management(WERF, 1997).

3.3.6 Flow Meter Assessment

Field evaluation and calibration of plant flowmeters are important since evaluation ofhistorical data and unit process capacity isbased on the assumption that recorded flowsare representative of the historical plantoperation. As a first step in any evaluation, aphysical inspection should be done to confirmthat the flow meters are installed according tosound engineering practices. Any questionsregarding flow meter installation and flowdata should be verified before proceedingfurther with other investigations. Sludgeaccountability imbalance can be an indicatorof inaccurate flow meters.

A number of different methods can be used inflow metering assessment and calibration,

including: recording run times on pumps and

estimating flow based on the pump capacityor pump curve;

injecting a tracer material into the flowstream at a constant and known rateupstream of the flow meter and determiningthe concentration of the tracer in samplescollected downstream;

drawing down the liquid level in a basin ortank and filling it back up while recordingthe meter reading;

flow measurement from a redundant meterto calibrate a suspected meter over a rangeof flow; and

hydraulic modelling to develop the headversus flow relationship for non-standardflume and weir installations.

As a f i r s t s tep in

any eva lua t ion , a

p hys i ca l

i nspec t i on shou ld

be done t o

conf i r m t ha t t he

f l o w m e t e r s ar e

ins ta l led

a c co r d i n g t o

s o u n d

e n g i n e e r i n g

p r a c t i c e s .


23/53

3. Work Descriptio

3.3 Plant Evaluati

Tools

Figure 33

On-Line process var


3.3.7 Continuous Monitoring

Typical data collection at a WWTP involves acombination of grab and composite sampling.This type of sampling will not identify dynamicconditions occurring in the plant. On-linecontinuous monitoring involves the use oftemporarily or permanently installedinstrumentation to measure the processloading and performance parameters, and adata acquisition system to collect real-timeprocess data. The real-time process dataallow for the identification of various dynamicrelationships in the plant, such as:

the impact of hydraulic surges on processperformance;

floc shear caused by extreme variation inprocess air flow;

effluent quality deterioration caused bydiurnal loadings;

return activated sludge concentrationvariations and;

process upsets or instabilities caused byreturn streams from sidestream solidsprocesses such as digester supernatantor biosolids dewatering.

On-line monitoring data have also been used

to identify potential energy and chemicalsavings at WWTPs. Primary clarifier sludge,return activated sludge (RAS) and wasteactivated sludge (WAS) flows are useful on-line process variables, and are important forsolids accountability. Measurement of theflows of internal recycle streams such asdigester supernatant, dewatering filtrate orcentrate, and thickener overflow is alsobeneficial. Table 33 identifies some processvariables typically measured with on-lineinstrumentation (WEAO, 1996).

Table 33:On-Line process variables

Category Measurements

Process flow rates Influent/effluent wastewater

Primary clarifier sludge

RAS

WAS

Biosolids flow

Process air flow

Chemical metering rates

Process variables MLSS concentration

RAS/WAS suspended solidsconcentration

Dissolved oxygen concentration

Effluent suspended solids concentration

Sludge blanket height

pH

Ammonia-nitrogen

Nitrite/nitrate-nitrogen

Orthophosphate

Conductivity

UV transmissivity

M easu r emen

t he f l ow s o f

i n t e r na l r ecy

s t r eams such

d iges t e r

supe r na t an t ,

dew a t e r i ng f i

o r cen t r a t e , a

t h i ckene r ove

is a lso benef


24/53

3. Work Description


Tools

3.4 Process Analysis

Tools


Wherever possible, on-line monitoring isencouraged, because of the benefit real timedata provide to operating staff; however, it isrecognized that on-line monitoring may not befeasible for some WWTPs, depending on sizeand available resources. These plants are stillencouraged to monitor their operation by

conducting sampling and analysis on a regularbasis. A sampling and analysis scheduleshould be developed, including a list of theparameters to be analyzed daily or weekly.For example, mixed liquor and effluentsuspended solids concentrations can beanalyzed by obtaining daily grab or compositesamples. For parameters that do not changerapidly, such as sludge quality data (e.g.,solids concentrations in digested sludge),sampling can be performed on a daily or

weekly basis. Grab samples can also beobtained to monitor variations in processparameters throughout the day. It is goodpractice to conduct on-line monitoring ofthose parameters with more rapid fluctuationssuch as dissolved oxygen concentrations inaeration basins (also referred to asbioreactors), or process flows.

3.3.8 Off-Line Monitoring

Off-line monitoring is conducted to supplement

plant historical data, or to obtain data nothistorically collected at the plant but importantfor plant evaluation purposes. These mayinclude analytical parameters or internalstreams within the plant not routinelymonitored by plant staff.

Microscopic examination of the biological masscan be performed to determine the general stateof the system, and to identify potential problemssuch as bulking sludge due to filamentousorganisms. J ar testing is generally performed toevaluate and optimize coagulant or chemicaladdition to wastewater for improved settleabilityor precipitation of some element in thewastewater (e.g., phosphorus removal).Additional laboratory/field tests can beperformed to assess the performance of a

particular unit process such as settling columntests, dissolved oxygen monitoring and profiling,oxygen uptake rate, sludge volume index (SVI),and sludge blanket monitoring.

3.4 Process Analysis Tools

Various tests can be used to optimize a

WWTP. These process analysis tools are usedto identify cost-effective ways to increaseplant capacity and meet more stringenteffluent limits or improve biosolids quality,without major capital works. They can also beapplied at those facilities identified by a CPE tobe incapable of meeting compliance limits atthe current flow due to design deficiencies.

This toolbox of tests is often referred to as aprocess audit. When applied at a WWTP, the

audit can lead to an optimized facility in termsof capacity, operating cost, and performance.The Water Environment Association of Ontario(WEAO) has published the Guidance Manualfor Sewage Treatment Plant Liquid Train

Process Audits(WEAO, 1996), an invaluableresource for any WWTP owner/operatorembarking on a WWTP optimization program.Unfortunately, no similar guidance manual hasbeen developed as yet that is specific tosludge treatment unit processes.

3.4.1 Aeration SystemCapacity andEfficiency Analysis

Aeration is one of the most fundamental andcostly processes in aerobic biologicalwastewater treatment, representing as muchas 75 percent of total plant energy use.Inadequate oxygen transfer may result inthe deterioration of effluent quality due toinsufficient oxygen to meet the biologicaloxygen demand and the endogenous oxygen

demand of the biological mass. Aerationsystem capacity analysis is conducted toevaluate the aeration system capacity, andto identify opportunities for energy savings.

A e r a t i o n i s o n e

o f t h e m o st

f undamen t a l and

cos t l y p r ocesses

in aerobic

biological

was t ewa t e r

t reatment,

represent ing as

much as 75

perce nt of t ot a l

p lant energy use.



The two most common techniques for testingin-situ oxygen transfer efficiency (OTE) are theoff-gas analysis and hydrogen peroxide tests.The results of these tests are used to comparethe existing aeration capacity with currentand future (or potential) oxygen demands.This comparison is then used to evaluate the

capacity of an aeration system for increasedloadings and further treatment capabilities(e.g., nitrification), and to evaluate the energysavingpotential for a plant. For more informationon oxygen transfer testing and test protocols,readers are referred to American Society ofCivil Engineers Standard Guidelines for In-Process Oxygen Transfer Testing(ASCE, 1997).

3.4.2 Hydraulic Modelling

Hydraulic modelling involves developing the

head loss versus discharge relationships forthe hydraulic control sections and performingbackwater calculations for the open channelsections between control sections. Thecalibrated hydraulic model can be used to:

determine the hydraulic capacity of anexisting facility;

identify hydraulic bottlenecks andinvestigate alternative strategies forreducing the hydraulic limitations identified;

determine flow imbalances and investigatemethods of improving the flow distributionbetween parallel unit processes; and

determine velocity gradients and identifyoptimum locations for chemical addition.

3.4.3 Analysis of Recycle Streams

Sludge treatment recycle streams are oftenresponsible for problems in the liquid trainof a WWTP. These streams can increase theorganic loading by five to fifty percent,depending on the type and number of solidstreatment processes used. The following arepossible solutions to minimize or eliminate theimpact of sludge handling recycle streams onthe liquid train.

Modify the solids handling processes toimprove the quality of the recycle streams.

Change the timing, return rate or return pointof the recycle streams to minimize the impact.

Modify the liquid train to handle the recyclestreams.

Provide separate treatment for the solidsrecycle streams.

Analysis of recycle streams from sludgeprocessing (digester supernatant, dewateringcentrate, or filtrate) can also provide anindication that these processes would benefitfrom optimization.

3.4.4 Stress Testing

Stress testing is conducted to identifythe loading rate at which the process

performance approaches the design value.Diurnal and/or wet weather flow increasesmay be used to stress unit processes that areaffected by hydraulics, such as clarifiers.Hydraulic, organic and solids loading ratesto the unit processes can be increased byvarying the number of units in service, biasingthe flow to the test unit.

Stress testing is generally not conducted untilprocess failure occurs due to the potentialimplications on compliance. Prior to undertaking

stress testing, a plan should be developed thatidentifies the possible impacts of stressing aspecific unit process, the monitoring that willbe done to evaluate the performance of theprocess, and the steps that will be taken if itappears that process failure is imminent. Theneed to inform the pertinent regulatory agencyabout the test must also be considered.

3. Work Descriptio

3.4 Process Anal

Tools



Table 34 summarizes typical unit processdesign parameters and evaluation criteria thatwould be applied during a stress test.

Stress testing is seldom conducted on sludgedigestion processes due to the long responsetime to changing conditions and the longrecovery time if stress testing results in aprocess upset.

3. Work Description


Tools

Table 34

Summary of typical unit

process design parameters

and evaluation critieria

Table 34:Summary of typical unit process design parameters and evaluation criteria

Unit Process Design Parameter Evaluation Criteria

Primary clarifier Surface overflow rate Removal efficiencies

Sludge blanket depth

Real detention time

Secondary clarifier Surface overflow rate

Solids loading rate

Effluent quality criteria

Sludge blanket depth

Activated sludge(Including aeration)

HRT/SRT

Organic/nitrogenous loading rate

F/M ratio

Recycle ratio

Effluent quality

Dissolved oxygen concentration

SVI/SSVI

SOUR

Effluent filter Hydraulic and solids loading rate Effluent quality

Head loss

Backwash solids concentration

Disinfection(chlorination/UV)

Cl2 dosage

Retention time

Effluent solids

UV dosage/transmissivity

Residual Cl2

Bacterial concentrations(total/fecal coliform, E. coli)

Sludge Thickening and

Dewatering

Hydraulic and solids loading rate

Chemical dosage (if applicable)

Sludge concentration

Recycle stream quality

Sludge Digestion(Aerobic or Anaerobic)

Hydraulic retention time

Solids retention time

Gas production (anaerobic digestion)

Volatile solids destruction

Pathogen destruction

Supernatant quality

Biosolids concentration

Source: Adapted from WEAO (1996).



3.4.5 Clarifier Hydraulic Tests

Clarifier hydraulic tests are conducted toevaluate the hydraulic characteristics within aclarifier and to determine possible methods toincrease the hydraulic capacity of the clarifier.The clarifier dye test, also called the CrosbyDye Test, is a qualitative test that uses dye totest the hydraulic flow pattern of clarifiers(Crosby, 1987). The test has two components:the dispersion test and the flow pattern/solidsdistribution test.

The dispersion test involves an instantaneousinjection of tracer upstream of the clarifier andsampling the effluent over a period of time.The test is used to determine the actualhydraulic residence time, estimate the degreeof hydraulic short circuiting, and determine

sampling times for the flow pattern test.The flow pattern/solids distribution testinvolves injecting dye continuously at aconstant rate into the flow entering theclarifier. Samples are then collected atmultiple depths and locations in the body ofthe clarifier to provide snapshots of themovement of dye. TSS concentrations aremonitored at each position and depth. Flowpattern tests are used to evaluate the spatialdistribution of flow through the clarifierincluding the location of dead zones, densitycurrents, and the possible effect of bafflearrangements.

Sophisticated hydrodynamic models can alsobe used to simulate the hydraulic patterns inclarifiers, and to assess the effect of variousphysical modifications to the clarifier (inletbaffles, weir baffles, etc.) on clarifierperfomance or to predict the impact of highflows, high solids loading rates or poor

settleability. Two-dimensional and complexthree-dimensional models have beensuccessfully used to improve clarifierperformance (Ekama et al., 1994).

3.4.6 Other Clarifier Diagnostics Tests

While SVI and SSVI are the most commontools used to determine the settleability ofbiological sludges, other diagnostic tools suchas State Point Analysis (Keinath, 1985) andDispersed Suspended Solids (DSS)/Flocculated Suspended Solids (FSS) testing(Wahlberg et al, 1995) can provide insight intothe causes of poor secondary clarifierperformance. State Point Analysis (SPA) willprovide information on whether a clarifier isoperating in an overloaded condition anddirection on operational steps that can betaken to eliminate the problem. DSS/FSStesting will indicate whether poor secondaryclarifier performance is related to poor solidsflocculation or poor clarifier hydraulics.

3.4.7 Mixing Tests

Mixing tests are conducted to evaluate thehydraulic characteristics of unit process tankswhen mixing problems are suspected, and arealso used to evaluate mixing equipment,equipment layout, and geometry. The resultsof the mixing test can be used to:

identify hydraulic short circuiting;

define mixing characteristics;

identify dead zones within the fluid volume;

evaluate the effectiveness of bafflingarrangements; and

determine the predominant flow patternswithin the unit process.

Mixing tests are particularly valuable indigestion tanks because scum, grit, and othermaterials can accumulate causing a loss ofactive reactor volume and short-circuiting.Improving mixing can often result in increasedvolatile solids destruction and improved

biosolids quality.

While fluorescent dyes can be used effectivelyin mixing tests in clarifiers or chlorine contactchambers, lithium chloride is the preferredtracer in digesters. Test procedures and dataanalysis methods are outlined in Monteith andStephenson, 1984.

3. Work Descriptio

3.4 Process Anal

Tools



3.4.8 Process Modelling and Simulation

Process models are efficient tools to determineoptimum operating conditions. This can includehydraulic retention time (HRT) and solidsretention time (SRT), and the capacity of thesystem to meet specified performance criteria.Process models are available for many of thecommon biological processes, such as activatedsludge, extended aeration, sequencing batchreactors (SBRs), rotating biological contactors(RBCs), and trickling filters.

Process modelling and dynamic processsimulation can be used for:

process capacity estimation;

bottleneck identification;

hydraulic load change analysis;

optimization of aeration system operation; optimization of sludge recycle and wastage;

optimization of the operational sequence ofSBR systems;

bypass impact reduction;

evaluation of alternate design strategies;

management of wet-weather flow;

sludge production estimation; and

design of reactor configurations for

biological nutrient removal (BNR).A dynamic model simulates variationsthroughout the diurnal and seasonal cyclesand tracks the effects of these variations onprocess performance. Process simulationmodelling is also employed to establish thecapacity of biological components of thewastewater treatment plant and model theeffects of process changes on plant capacityor performance. Recent work has focused onlinking dynamic models with supervisorycontrol and data acquisition (SCADA) andlaboratory information management systems(LIMSs) to further improve the accuracy andvalue of their predictions (Irrinki et al., 2002).

3.5 Optimization Approaches

3.5.1 Improved Operations and Maintenance

Improved process control procedures tailoredfor the particular WWTP can both improveprocess performance and save money. Aprocess control testing schedule to monitor

control parameters, including but not limited tosludge settling, sludge mass, sludge wasting,sludge return concentration and flow, volatilesolids destruction in digesters, dewateringperformance, and aeration basin dissolvedoxygen should be established as a first step inWWTP optimization. On-the-job training shouldalso be provided for the operators in specificprocess control sampling and testingrequirements, as well as process controlcalculations.

Formalizing record keeping will generallyimprove maintenance practices. The followingfour-step procedure is suggested fordeveloping a maintenance record keepingsystem:

Inventory all equipment.

Gather manufacturers maintenanceinformation and schedules on all equipment

Complete equipment information summarysheets for all equipment.

Develop a time-based preventivemaintenance schedule.

The list of equipment should be updated whenequipment is added or removed from thefacility. The maintenance schedule shouldinclude daily, weekly, monthly, quarterly, semi-annual, and annual checklists of requiredmaintenance tasks.

For larger facilities, a computerizedmaintenance management system (CMMS)can cost effectively optimize the maintenancefunction. Through information technology (IT),process control information, SCADA, CMMS,laboratory data and other information can belinked so all key information is available tostaff on-line and in real time.

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A staffing plan (Daigger and Buttz, 1992)should be developed to determine if a facilityis properly staffed. Benchmarking informationis available from various sources to assessstaffing needs (WERF, 1997).

Staff training can help improve plantperformance (as it relates to poor operationalpractices), address safety issues, and improvestaff morale. Staff training should recognizethat on-site training is the most effective wayto develop an operators capability to applywastewater treatment concepts properly toprocess control. Operating personnel shouldalso be encouraged to improve sewagetreatment understanding through budgetsupport for off-site training and certification.Comprehensive technical assistance (CTA) is asystematic approach to eliminate those factorsthat inhibit performance in existing WWTPs.CTA facilitators work with plant operators andmanagers to develop process control activitiesand to transfer skills and knowledge.

3.5.2 Instrumentation, Control, And

Automation

Opportunities to reduce costs and improveoperational performance and reliability arepotentially available through the on-lineinstrumentation and/or automation ofwastewater treatment operations. By addingprocess measurements, the operator also hasmore information on which to base judgmentsand implement control decisions. Efficientoperation can be maintained using automatedcontrols. Optimization of processes throughthe use of on-line measurement and feedbackcontrol can significantly reduce the amount of

chemical, energy, and water use as well asreduce the production of waste residualsrequiring treatment and disposal (WEF, 1997).Higher savings potential occurs in facilitieswith high variability in wastewater quality andflow. Examples of best practice automationapplications are summarized in Table 35.

Instrumentation and Control (I&C) at a WWTPcan provide information to the operator onthe status of equipment, provide real timemeasurements of process parameters, allowfor automatic control of equipment (e.g.,turning equipment on and off), and signalalarm conditions. Various parts of the I&Csystems can be upgraded. For example,primary elements can be upgraded by addingprocess measurements, and control hardwareand software can be upgraded by addingalarms that automatically switch to a backupwhen equipment fails. The overall processcontrol system can be improved for WWTPswith outdated I&C systems. In emergencies,automatic controllers can switch to a backup.All critical control functions should have amanual control backup. Proper staffingsupport to calibrate and maintaininstrumentation is critical to attain thebenefits provided by automation.

Automated process control strategies forspecific unit processes are discussed in detailin the WEF special publication AutomatedProcess Control Strategies(WEF, 1997) and inthe recent WERF report Sensing and ControlSystems: A Review of Municipal and Industrial

Experiences(WERF, 2002).


3. Work Descriptio

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Opera t ing

personne l sh

a lso be

encou r aged t

imp r ove sew a

t rea tment

unders tand in

th rough budg

suppor t for o

t ra in ing and

cer t i f icat ion.



3. Work Description

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Table 35

Automation applications

at WWTPs

Table 35: Automation applications at WWTPs

Source: WERF (2002).

Process/Unit Application

Preliminary treatment Automatic screen cleaning based on head loss, total flow treated and/or timers

Primary and chemicallyenhanced primarytreatment

Flow proportional chemical dosage control

On-line effluent suspended solids/turbidity monitoring

Automated sludge density control of sludge pumping

Automated sludge blanket height control of sludge pumping

Biological treatment On-line respirometry

On-line measurement of BOD load

Automated sludge age (SRT) control

Automated biological sludge wasting control

Automated ORP control in the control of biological nutrient removal processes

On-line measurement of MLSS concentration

On-line dissolved oxygen monitoring and control

On-line measurements of NH3-N, NOx-N and PO4-P concentrations

Secondary clarifiers On-line effluent TSS or turbidity analysis

Tertiary filters On-line monitoring of turbidity and/or phosphorus concentration

On-line monitoring of head loss

Aeration system Automated blower control based on on-line dissolved oxygen sensors

On-off aeration control

Variable speed control of mechanical aerators

Disinfection

(i) Chlorination/dechlorination

(ii) UV irradiation

Flow proportional chemical dosage

Automated chlorine residual control

Automated ORP control

UV intensity monitoring and control

Flow pacing of UV lamps

Initiation of automatic self-cleaning

Sludgethickening/dewatering

Automatic flow pacing of chemical addition

Automatic mass dosage control of chemical addition

Automatic monitoring of solids content of liquid stream

Automatic chemical dosage control based on flocculation properties

Digestion Automated control of sludge distribution between multiple reactors based on flowor solids mass load

On-line monitoring of supernatant quality



3.5.3 Treatment Process Modifications

A variety of modifications are possibledepending on the unit process underconsideration and the specific performancelimiting factor identified during the plantevaluation stage. Table 36 summarizes, on aunit process by unit process basis, some ofthe optimization opportunities that could beconsidered to increase capacity, improveefficiency, or reduce the costs associatedwith chemical or energy use.

More detailed discussions of how these andother optimization opportunities might beimplemented in each specific unit process areprovided in Appendix B. Readers should referto Appendix B for a discussion of potentialapproaches to optimize the particular unitprocesses that make up their WWTP, or for

those unit processes that have been identifiedduring the plant evaluation stage to limitperformance or reduce overall plant capacity.

3. Work Descriptio

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Table 36

Potential treatment p

optimization approac

Table 36: Potential treatment process optimization approaches

Note: More detailed discussion of these optimization approaches is provided in Appendix B

Process Optimization Approach

Plant hydraulics Eliminate surges due to pump station operation

I/I control

System storage and real-time control

Preliminary treatment Upgrade screens and improve control

Improve hydraulics in grit tanks

Improve grit removal and handling

Primary treatment

Biological treatment

Secondary clarifiers

Tertiary filtration Optimize chemical use

Optimize backwash

Disinfection Improve mixing

Implement automatic control

Sludge Thickening/Dewatering

Optimize chemical dosage or chemical type

Manage primary sludge and WAS separately

Aerobic Digestion

Anaerobic Digestion

Improve process flexibility

Optimize BOD5 removal

Optimize nitrification

Implement BNR

Optimize oxygen transfer

Implement step feed

Implement foam/scum controlmeasures

Optimize chemical use

Improve hydraulics

Improve scum/sludge removal

Eliminate co-settling of wasteactivated sludge

Improve flow splitting

Eliminate hydraulic surges

Improve hydraulic patterns

Control sludge bulking

Improve RAS/WAS flexibility

Optimize oxygen transfer

Optimize settling to increase sludgethickness or improve supernatantquality

Improve mixing

Increase raw sludge concentration

Improve mixing

Increase temperature to improvevolatile solids destruction

Improve load distribution betweenmultiple tanks

Increase raw sludge concentration

Use biogas for energy value


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3.5.4 Achieving Resource Cost Savings

Energy usage in wastewater treatment can bea major portion of the annual operating costs.Much of the information presented in this sub-section is adapted from the Guide to ResourceConservation and Cost Savings Opportunities

in the Water and Wastewater Sector(MOEE,1997). Readers are referred to this documentfor more detail on opportunities for resourcecost savings in WWTPs.

High Efficiency Motors/Variable Speed Drives

Many facilities operate using inefficient pumpsand motors designed and installed years agowhen system constraints and requirementswere very different than today. Motorefficiencies are now much higher than whatwas available even 10 years ago. As a result,

significant energy savings can be realized byreplacing old motors in existing equipment.Using variable speed drives, facilities canoptimize pump operation by matching energyrequirements with pumping requirements.

The most attractive lifecycle payback occurswhen existing motors need replacement, andhigh-efficiency motors or variable speeddrives are appropriate for that application.It must also be noted that relative cost of

maintenance and replacement of variablespeed drives (variable frequency drives (VFDs)in most cases) needs to be considered in theevaluation of payback expected from suchdevices. Higher energy savings will also occurin facilities with high peak demand ratios thatare pumping outside of the efficient range ofthe existing pumps. The plant operator shouldensure that pumps operate at the mostefficient point on their operating curve.

Off-Peak Operation

During peak demand periods, energy demandand consumption charges may be higher thanduring off-peak demand periods. Wherepossible, moving the operation of existingprocesses to off-peak periods can significantlyreduce energy costs. Shifting demands to off-peak periods requires operational changesonly (i.e., no capital investment) and, as aresult, payback can be immediate. Although

the energy cost is reduced, the amount ofenergy used during off-peak operation is notalways reduced. Energy use reductions willonly be achieved if the operating ranges ofthe process equipment are better suited forlower intensity/longer duration operationsimplemented by transferring operation to

off-peak periods.This technique is applicable throughout afacility. The potential benefit varies with thetype of process, available storage and thedesign of the specific facility under review.It should be noted that small plants do notnecessarily have hydro demand meters or off-peak rates available. Therefore, this techniquewill not offer any savings in energy use or costin these instances.

Flow Measurement

Accurate flow metering equipment forwastewater flows, sludge flows, effluent andbackwash water, and chemical dosing ratesensures optimized resource usage withsignificant effects on chemical usage, filterruns, backwashes, and sludge productionrates. For example, if flow measurement isinaccurate in a flow-paced disinfectionprocess, then unnecessary wastage of energyand chemical use can occur by overpumpingand overchlorinating.

Biological Treatment System

When nitrification is not required, controllingsolids retention time and/or reducing dissolvedoxygen levels will reduce oxygenrequirements significantly, which can reducerun time for mechanical aerators or blowers,resulting in reduced energy use, preventingunnecessary nitrification. The addition ofcoagulant during primary treatment improvesthe removal of particulate matter beforeaeration. This reduces aeration energyconsumption. Although energy use is reduced,chemical use and primary sludge productionare increased during primary treatment, andtrade-offs must be investigated.


3. Work Description

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The mos t

a t t r ac t i ve

l i f ecyc le payback o c c u r s w h e n

ex i s t i ng mo t o r s

n e e d

r ep lacemen t , and

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mo t o r s o r

va r i ab le speed

d r i v e s a r e a p p r op r i a t e f o r

t h a t a p p l i c a t i o n .



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By switching to an on/off aeration mode,blowers or mechanical aerators can beoperated for short periods (e.g., 30 minutes) andthen shut down for equal or smaller periods.This reduces energy usage significantly. Thisapproach should not be used for aerationsystems that would foul if the air supply is shut

off (i.e., ceramic, fine pore, or some coarsebubble diffusers). Aeration devices will need tobe retrofitted with some form of ramp startingequipment to protect them from the wearassociated with an increased number of start-ups. Soft start devices can be used to reducethe peak demand.

By optimizing the solids retention time (SRT),biomass production can be r

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