20 WWG PSG DSG ProcessSelectionGuideWW

8/6/2019 20 WWG PSG DSG ProcessSelectionGuideWW

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PROCESS SOLUTION &MINIMUM ASSET STANDARDSWastewater Treatment

DETAILS OF DOCUMENT CONTROL DATE:

AUTHOR: Risk & Value Project Manager

NAME: Owen James

Document Reviewer:

Name:

Document Authoriser:

Name:

REV DATE Who REASON FOR CHANGE1.0 29/07/08 OJames First Issue1.1 03/11/08 PGreen Clarification of P-removal descriptions

62905319.doc Page 1 of 15 Revision: 1.1Last Saved: 24/11/2008 09:04:00 AM


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CONTENTS

1 INTRODUCTION & OVERVIEW ........................................................... 3

2 PROCESS SELECTION ....................................................................... 4

2.1 PROCESS SELECTION MATRIX ..................................................................... 63 MINIMUM STANDARDS .................................................................... 8

3.1 PRINCIPLE......................................................................................................... 83.2 WHOLE LIFE COST EVALUATION (NPC ANALYSIS) .......................................................... 83.3 GENERAL REQUIREMENTSFOR ALL SITES..................................................................... 83.4 SPECIFIC REQUIREMENTS PROCESS DEPENDENT............................................................ 8

1 DEVIATION PROCESS ..................................................................... 15



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1 INTRODUCTION & OVERVIEW

The purpose of this document is to define the starting point for process selectionand define high level minimum asset standards for those processes and toexplain how they fit in the process of capital appraisal and delivery.

The document is intended for use by various parts of the business. Thematrices in this document define what you need rather than what you want.

There will be circumstances when deviations will be required however, thesedeviations will be justified through risk economics.

Asset Planners Provides a high level guide to asset needs that can beused in asset plans and workbook submissions.

Operational Manager Provides a baseline of process selection & minstandards

Capital delivery engineers (ops cap & major capital delivery) Provides afirst point of reference in the capital delivery process and also provides

the baseline of asset requirements.

The application of Minimum Standards is an integral part of an essential processof identifying the right solution to risks & issues in the business.

The key steps in the process are:

Quantify riskUsing the business impact matrix and R&V riskAssessment.

Identify Rootcause

An approach of root cause analysis should be used to

methodically understand factors that are out ofcontrol. See R&V HAWK pages for moreinformation . . . )

Reviewoperationalsolutions

To manage or resolve risk. Check root causesagainst trouble shooting guides available via HAWK(seehttp://hawk/Vol_Eng/DG/WWProcessTroubleShootingGuides.xls).

Review against

process selectionmatrix

Where there is no further operational solution or only

high cost operational solutions, what is the least costcapex solution? (Table 1 in this document)

UnderstandMinimumStandard

High level Minimum Standards for process solutionsselected. For more detailed descriptions, seeengineering standards pages on HAWK. (Table 2 inthis document

Document andjustify any

requireddeviations

It is important to understand the rationale for anydeviation from process selection standard or assetstandard. This will be documented in the R&V report.

http://hawk/Vol_Eng/DG/WWProcessTroubleShootingGuides.xlshttp://hawk/Vol_Eng/DG/WWProcessTroubleShootingGuides.xlshttp://hawk/Vol_Eng/DG/WWProcessTroubleShootingGuides.xlshttp://hawk/Vol_Eng/DG/WWProcessTroubleShootingGuides.xls


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2 PROCESS SELECTION

The process selection matrix below indicates desired processes for new works ornew streams. In any option evaluation phase the solution indicated inthis table needs to be the first consideration and any deviations fromthis need to be justified in terms of risk economics and or NPVanalysis. While this table provides general guidance all solutions mustbe chosen on the basis of whole life costs balancing capex, opex andcarbon footprint to obtain the optimum balance between risk and cost.

1. Site specific circumstances will dictate that deviations from this matrixare required. This includes sludge treatment requirements where processselection may be influenced by where and how sludge is treated.

2. The boundaries to the population equivalent bandings should be taken asa guide. For example where a PE is just below a banding threshold (e.g.4500 PE) then an assessment may need to be considered on therequirement for process selection in the next banding.

3. Further information on the content of each process is indicated in section6 on minimum standards.

4. The processes indicated in bold indicate the first choice / minimumstandard. Further options are provided if first choice is ruled out. Therationale for this will still need to be documented.

5. The consents indicated in the table are indicative only. There may beintermediate consent limits or site specific consents that require specialconsideration.

6. Descriptive consents dont generally have numeric limits set to themhowever there is a growing acceptance that they will treat to a numericequivalent of 60mg/l of solids, 40mg/l of BOD and in some cases 20mg/lof ammonia. This should be taken into consideration when using the linefor descriptive consents.

7. Trickling filters will always require primary and humus settlement inaddition to the filter beds.

8. An activated sludge plant will always require final settlement (clarifiers)however the inclusion of primary settlement should be on the basis of

whole life costs balancing the energy and sludge disposal costs againstand other opex against the capital cost. Modifications of the activatedsludge process may also be considered that include internal clarification(eg SBRsetc) but only on the basis of lowest whole life cost and riskmitigated as above.

9. A removal of Iron to


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should be provided. However, the requirement for odour control must beminimised as far as possible.

12.



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2.1 PROCESS SELECTION MATRIX

Table 1 - Process Selection MatrixNote: A clear idea of the sludge disposal route is essential before selecting the main process streams.

Ref

indicativeconsent

standard

population equivalent (see note 2 above)

20;

BOD >15)or

UWWTR consentinc 75%COD

removal

Balancing tank/Septic tankReedbed storm handling above 250pe

Aerated LagoonorRBC or SAFOr trickling filter7

screening & gritStorm tank

TF7

Or ASP(see note 8)


TF7

Or ASP(see note 8)


+TF7 or

ASP (carbonaceous)(see note 8)


+ASP (carbonaceous)

(see note 8)

S1Sludge handling

(TF works)Co-settled primary & humus

Storage to 3,000PE

Co-settled primary & humusGravity thickening

Storage

Co-settled primary & humusGravity thickeningSludge treatment

S2Sludge handling

(ASP typeworks)

Storage only to 3000 peSeparate primary & SAS sludge

SAS: Drum thickeningBlending & Storage

Separate primary & SAS sludgePrimary sludge: PFT

SAS: Drum thickeningBlending & sludge treatment

P3

Ammonia down

to 5 mg/l(SS / BOD as

above)

Balancing tankSAF / RBC

Also consideraerated lagoon

Balancing tank+ Storm separation +

TF (nitrifying)7

or SAF / RBC

Also consider SBR oraerated nitrifying

lagoon

screening & gritstorm tank

TF (nitrifying)7

orASP (nitrifying)8

or SBR


or TF (nitrifying)7

ASP (nitrifying)8

or SBR


ASP (nitrifying)8

Or add tertiary nitrification to existing plant plastic media filterornitrifying sand filter or SAF or BAF

P4Ammoniaconsent Ferrous chloride to aeration tankAs P7e

OrBiological P removal if

sufficient VFA in crude /Fermenter.

(model required)P8 P consent to 1mg/l

As above (P7)Plus backup dosing (see design guide)

Note: on critical sites where processproblems exist tertiary solids separation maybe required, if so backup dosing is located in

this positionNo tertiary Separation is required for

Activated Sludge

As above (P7)Plus backup dosing (see design guide)

Note: on critical sites where process problems exist tertiary solidsseparation may be required, if so backup dosing is located in this

positionNo tertiary Separation is required for Activated Sludge

P9Fe consent

3mg/l(see note 9)

As above (P3) for TF plus Tertiary Reedbeds / lagoons orother tertiary solids separation

No tertiary Separation is required for Activated Sludge

As above (P3) for TF plusTertiary solids separation

No tertiary Separation is required for Activated Sludge

Other consents including the requirement for N removal or disinfection are not covered by this matrix but should be consideredon a case by case basis.

Notes for this table are on Page 4 of this document.



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3 MINIMUM STANDARDS

3.1 Principle

For each process above these standards will detail what you get as part of that processin terms of standby & contingency and ancillary type assets (e.g. lighting , access,

building, duty / standby etc.)

3.2 Whole Life Cost Evaluation (NPC analysis)

In all schemes the NPC of all options, including operational solutions must be evaluatedand considered. Whole life period should be taken as 40 yrs.The guidelines in this document are for new additional process units and thusapplication of the guidelines to existing works should only be considered if final effluentcompliance and works serviceability are at risk

3.3 General Requirements for All Sites

1. Health and Safety is a primary concern and where possible simple access arrangements shouldbe arranged. Elevated access to process units should be avoided if possible on the basis of both

H&S and cost.2. Sockets to be provided for mobile generators for equipment necessary to maintain final effluent

compliance. Fixed generators to be considered on sites above 30,000 PE.

3. Where fixed generators are installed consideration must be given to triad avoidance and peaklopping.

4. Energy use must be minimised where possible through use of high efficiency motors etc.

5. Telemetry to be provided in accordance with MTPC version 9.2.

6. Need for a water supply to be investigated and if necessary has to comply with AW byelawrequirements. In addition, use of final effluent for wash-water use needs consideration.

7. Access road length to be minimized and finished appropriate for usage with no curbs ordrainage.

8. Septic tank / RBC sites consider permanent pipeline for removal of sludge rather than road to

site.9. Fencing to be provided as appropriate-

o No fencing if possible

o Low risk areas (where vandal and safety ok)-wooden post/rails

o Medium risk-Weld Mesh

o High risk areas- Security fencing

10. Control equipment to be housed in kiosks rather than buildings unless shared with process plant.

11. Site areas to be minimized and finished with cost and low maintenance surfaces. Accesspathways also to be considered.

12. Consider insulation requirements on exposed sludge & wash water pipelines & valves.

13. Sludge pipelines to be 150mm or greater.

14. Site entrance signage to be provided to include AW contact details.15. Site lighting should be avoided as much as possible however lighting is required for key plant

items and on H&S basis.

16. Washroom and toilet facilities to be provided at permanently manned sites and by evaluation onsmaller sites.

17. Auto-emptying of storm tanks must be justified by a business case linked to compliance

18. TSFR Flow meters & other instrumentation will be in accordance with POSWASTES

19. Sampling chambers and equipment will be in accordance with POSWASTES

3.4 Specific Requirements Process Dependent

For specific requirements relating to individual processes selected refer to the tablesbelow. For more detailed specific standards refer to Engineering Standards on HAWK.



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Table P1 Descriptive works

ID Descriptive Works

D1 Septic tank GRP vessel & tanker connection point

D2 Flow balancing If lagoon then part of lagoon otherwise septic tank

D3 Aerated lagoon2 lagoons earth banked, butyl rubber lined.Floating wind powered aerator.

D4 SAF Package Plant (as per Design guide)

D5 RBC Package RBC

Table P2 No Ammonia Consent (SS>20, BOD >15mg/l)

ID ProcessPopulation Equivalent

< 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

SB1 Balance tankGRP vessel with flowregulatorTanker connection point

Tank with flow regulatorMethod of flushing /cleaning.

Tank with flow regulatorMethod of flushing /cleaning.

n/a n/a

SB2 Septic tankGRP vessel & tankerconnection point

n/a n/a n/a n/a

SB3 ScreeningMesh bags above 250PE.Other screening only ifconsent requires.

duty combined screen withhydraulic bypass(manually raked 25mm)

duty fine screen (6mm 2d)with hydraulic bypass(manually raked 25mm)

Duty / standby fine screen(6mm 2d) & hydraulicunscreened bypass

Duty / Assist / standby(6mm 2d) Band Screensfor 6DWF & unscreenedbypass

SB4Screeningshandling

Only if consent requiresscreen

Duty compactor Duty washer compactor duty / standby washercompactor

duty / standby washercompactor

SB5 Grit Removal n/a n/a Mechanical Grit TrapCrossflow detritor - dutyonly

crossflow detritors

SB6Reedbed StormHandling

Single plot with basicdistributor & collectorchannels

Single plot with basicdistributor & collectorchannels

n/a n/a n/a

SB7Storm Handling(See note 15above)

If consent requires.Storm plot / tanksIf storm tanks then requirestorm return mechanism &high level & overflow alarm

If consent requires.Storm plot / tanksIf storm tanks then requirestorm return mechanism &high level & overflow alarm

Storm tank with auto drain& return.Basic Cleaning facilities(eg hydrant).

Storm tank with auto drain& return downstream offlow recording & UWWTRsample point / upstream ofPST.Cleaning facilities.

Storm tank with auto drain& return downstream offlow recording & UWWTRsample point / upstream ofPST.Cleaning facilities.



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Table P2 No Ammonia Consent (SS>20, BOD >15mg/l) (Continued)

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

SB8Aeratedlagoon

2 lagoons in series earthbanked, butyl rubber lined.Floating wind poweredaerator.

n/a n/a n/a n/a

SB9 SAFPackage Plant (as perDesign guide)

Package Plant (as perDesign guide) up to 2500pe

n/a n/a n/a

SB10 RBC

Package Plant (as per

DSG) n/a n/a n/a n/a

SB11PrimarySettlement

1 circular radial GRP tank.No scraper.With manual desludge.

1 circular radial GRP tank.No scraper.With manual desludge.

2 tanks Radial flowAutodesludge whereapplicableRotation sensor to telemetry

2 tanks Radial flowAutodesludgeRotation sensor totelemetry

Multiple radial flow tankswith auto desludge.Rotation sensor totelemetry

SB12TricklingFilter

Single Conventional singlepass filter. Media to choiceinfluencing retaining walls.Syphon / drive. No sensor.

Conventional single passfilter. Media to choiceinfluencing retaining walls.Syphon / drive. Rotationsensor

Two Conventional singlepass filter. Media to choiceinfluencing retaining walls.Syphon / drive. Rotationsensor

Minimum of 2 Filters Minimum of 2 Filters

SB13 ASP(carbonaceous)

n/a n/a n/aCompare type based on NPCIf blowers then D(A)S blowers.

Aerated selector. DO control, Telemetry / SCADA

SB14HumusSettlement

Single tank with manualdesludge.

Single tank with manualdesludge.

Two tanks with autodesludge

As PST (SB11) As PST (SB11)

SB15Final Tanks(after ASP)(Clarifiers)

Radial flow FST with sludgeblanket detectors & rotationsensor.Manual RAS control.

Radial flow FST withsludge blanket detectors &rotation sensors.Manual RAS control.

Radial flow FST with sludgeblanket detectors & rotationsensors.Auto RAS control.

Radial flow FST withsludge blanket detectors &rotation sensors.Auto RAS control.

Radial flow FST with sludgeblanket detectors & rotationsensors.Auto RAS control.

SB16 General>50m3/d TSFR to meetMCERTS.Agreed sample points.

>50m3/d TSFR to meetMCERTS.Agreed sample points.






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Table S1/S2 Sludge Handling

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

SH1 Sludge StorageSludge storage - onemonth or tanker loadwhichever is smaller.

Glass coated steel tankwith thickening facility with7 days storage.

Glass coated steel tankswith thickening facility with14 days storage.

Sludge tanks withthickening facility with 14days storage.

Sludge tanks with picketfence thickening with 14days storage. & separateMechanical SASthickening (eg aqua belt).

SH2 Thickener

SH3 Blending

Table P3 Ammonia down to 5mg/l (SS >20 & BOD>15)

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

A1Balance tank /septic tank

Septic tank as above.Only if necessary and thenbalance tank as above

Only if necessary and thenbalance tank as above

none none

A2Aerated nitrifyinglagoon

2 lagoons earth banked,butyl rubber lined.Floating wind poweredaerator + forced aerationon timer control.Floating SAF.

n/a n/a n/a n/a

A3 Screening As above As above As above As above As above

A4 Grit Removal See Grit matrix See Grit matrix See Grit matrix See Grit matrix See Grit matrix

A5 Storm Handling As above As above As above As above As above

A6 SAF


Design guide)


Design guide) up to 2500pe n/a n/a n/a

A7 RBCPackage Plant (as perDSG)

n/a n/a n/a n/a

A8PrimarySettlement

1 radial flow withNo scrapermanual desludge.

2 radial flow.No scraperManual desludge

2 tanks Radial flowAutodesludge whereapplicableRotation sensor totelemetry

Two tanks Radial flow PSTAutodesludgeRotation sensor totelemetry

Multiple radial flow tankswith auto desludge.Rotation sensor totelemetry

Table P3 Ammonia down to 5mg/l (SS >20 & BOD>15) Continued



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ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

A9Trickling Filter(nitrifying)

As above but withrecirculation



n/a n/a

A10ASP (OxidationDitch)

Oxidation ditch as simpledlined structure . Timercontrol. DO Alarm

Oxidation ditch as linedpuddled clay . DO controlbasic feedback. 2 probesto average.

A11 ASP (nitrifying) Package plant ASP Package plant ASP

Conventional ASP withtapered aeration & integral

anoxic zone.Single lane DO &ammonia control.Duty / Standby blowers*.


anoxic zone.Single lane DO &ammonia control.Duty / Standby blowers*.


anoxic zone.Single lane DO & ammoniacontrolDuty / /Standby blowers.

A12 SBR SBR as package SBR as package

SBR as package upto7000PE. Process SBR athigher PE.3 units min. Must haveclarifier/ humus tank.

Bespoke designed system Bespoke designed system

A13HumusSettlement

Radial flow tank.Manual desludge.

Radial flow tank.Manual desludge

Radial flowManual desludgeRotation sensor totelemetry

n/a n/a

A14Final Tanks(after ASP)

radial flow dependent onFixed rate RAS return withno controlD/S RAS pumps.

Single radial flowFixed rate RAS return withno controlD/S RAS pumps.

Single (2x at higher pe)radial flow, RAS returnwith flow controlD/ S RAS pumps.

2 x radial flow with RASreturn with flow control.D/A/S RAS pumps.

2 or more radial flow withRAS return with individualtank flow control.D/A/S RAS pumps.

A15 BAF n/a

BAF as GRP tank dutyonly in split tankconfiguration. Box sparefor blower & pump.

BAF as GRP tank dutyonly in split tankconfiguration. D/S blower& pump



Note * - Ensure that blower capacity is matched appropriately to the flow and load conditions.



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Table P4 Ammonia less than 5mg/l

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

AA1 ASP (nitrifying) As above (A11) plus FE monitoring (inc Turbidity & Amm)

AA2 SAF As above (A6)

AA3 SBR As above (A12)

AA4 TertiaryNitrification

n/a As above (A15)

Table P5/P6 Solids < 20mg/l

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

SS1TertiaryReedbed

Twin plots of nominalloading area. Distributor &collector channels.



n/a n/a

SS2Short RetentionLagoon

Single lagoon. 4 dayscapacity.

2 lagoons in series. 4 dayscapacity total + by pass to2nd lagoon

n/a n/a n/a

SS3ContinuousBackwashSandfilters

Single Duty unit onlyunless no other storage ofeffluent avialable. D/Spumps & compressors.(See MAS on HAWK)

Duty only units singleunit to 2,000PE & lagoon /storage availableotherwise multiple units.D/S pumps in Pumps, D/Scompressors (See MAS)

Duty only multiple units.D/S pumps & compressors(See MAS)

Duty only multiple units.D/S pumps & compressors(See MAS)

n/a

SS4

Batch typesandfilter(rectangular rapidgravity type)

n/a n/a n/a TBD TBD



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Table P7/P8 Inclusion of P consent

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

Phosphorous Consent to 2 mg/l

PP1Ferric Sulphatedosing on TFonly

Single point dosing to Primary tank inlet chamberD/S Dosing lines & pumpsFlow control(See Detailed MAS for further information for sites to 25,000pe)

Single point dosing to Primary tank inletchamberD/S Dosing lines & pumpsFlow control

PP2Ferrous ChlorideDosing

As above (PP1) except dosing to settled sewage or RAS or pre aeration if crudeAs above (PP1) except dosing to settledsewage or RAS or pre aeration if crude

PP3Biological Premoval

Bespoke design

Phosphorous Consent to 1 mg/l

PP4 DosingAs PP1 or PP2 above but with backup dosing (see design guide for more information).Common chemical storage tank for both main dosing and backup (trim) dosing.Dedicated duty only dosing lines & pumps for the backup dosing.

Table P9 Iron Consent < or = 3mg/l Trickling Filters

ID Process < 1,000 1,000 5,000 5,000 10,000 10,000 50,000 50,000 100,000

(a) (b) (c) (d) (e)

FE1TertiaryReedbed

As SS1 above As SS1 above As SS1 above As SS1 above As SS1 above

FE2 Lagoons As SS2 above As SS2 above As SS2 above As SS2 above As SS2 above

FE3TertiaryClarification

TBD TBD TBD TBD TBD

FE4Tertiary SandFilters

As SS3 & SS4 above As SS3 & SS4 above As SS3 & SS4 above As SS3 & SS4 above As SS3 & SS4 above



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1 DEVIATION PROCESS

Changes and deviations will be managed within the existing governance asoutlined in the diagram below.

Other p

(e.g.

Regulatory

change

Notes:a) A standard will need to be submitted to the ASF if:

i) It is a new standard that has an implication on operating or maintenance risk.ii) There is a capex or opex implication associated with that standard.

b) A standard will need to be submitted to CIG if:

i) There is an associated significant increase in Capex or Opex (> approx 50k AMP4implication).

ii) There is an associated significant increase in residual risk (> approx. 50k per yearprogramme implication)

c) A deviation approval will need to be submitted to CIG in a highlight report if it leads to achange in time, cost or quality (see the process for highlight & exception reporting).


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20 WWG PSG DSG ProcessSelectionGuideWW