am-pro-wwt-wwt 1.3 screens and screenings handling-sec3 issue 1.1

THAMES WATER Asset ManagementInternal Company and Partners Asset Standards

Technical Lead: Des Monger Issue 1.1

AM-PRO-WWT-WWT 1.3 Screens and Screens Handling-SEC3 Page 1 of 20

UNCONTROLLED WHEN PRINTED

Asset Management Asset Standard Section 3 of 5 Operating Standard Wastewater Non-Infrastructure WWT 1.3 Screens and Screens Handling

Document Reference AM-PRO-WWT-WWT 1.3 Screens and Screenings Handling-SEC3

Version Issue 1.1

Data Owner Sarah Shipsey

Data Steward Kevin Kelleher

Technical Lead Des Monger

Document Author Tim Wheatley

Authorised by Asset Standards

Document Location AM Lotus Notes Best Practice Database on LNAPP01

Date of Issue December 2012

Reason for Issue Conversion and validation of old BOP into new Standard format

Next Review December 2012





Contents:- 3.0 Operating Standard..................................................................................................................... 3

3.1 Screens and Screenings Handling Performance Measures ................................................... 3 3.2 Operator Activities ................................................................................................................... 5

3.2.1 Process Checklist SCREENS ....................................................................................... 5 3.2.2 Process Checklist SCREENINGS HANDLING - MECHANICAL UNITS ...................... 8 3.2.3 Process Checklist SCREENINGS HANDLING - MANUAL UNITS............................. 10 3.2.4 Process Checklist KEY................................................................................................ 10 3.2.5 Process Checklist Notes ................................................................................................ 11

3.3 Troubleshooting Guide .......................................................................................................... 12 3.3.1 Dos and Donts ............................................................................................................... 14

Appendices .......................................................................................................................................... 15 3.4 Operation ............................................................................................................................... 15

3.4.1 Screen Operation and Control........................................................................................ 15 3.4.2 Quantities of Screenings ................................................................................................ 15 3.4.3 Impact on Secondary Treatment Processes .................................................................. 15 3.4.4 Odour.............................................................................................................................. 17 3.4.5 Screen Optimisation ....................................................................................................... 17 3.4.6 Contingency Planning .................................................................................................... 18 3.4.7 Plant Release / Taking out of and Bringing into service ................................................ 18

Health and Safety................................................................................................................................. 20





3.0 Operating Standard

3.1 Screens and Screenings Handling Performance Measures Performance measures provide a means to understand and characterise the screens and screenings handling process. The data collected, along with understanding the process, can be used for monitoring performance and problem solving.

Measure Why Frequency Method of Collection

Screened Sewage Flows

The peak instantaneous flow treated by a screen should be measured and compared against its rated capacity where possible. Flow profiles are also considered useful to ensure correct velocities are maintained in screen channels to prevent grit build up and settlement. Flows can also be used to estimate the screenings load to the process.

Continuous

SCADA, Onsite documentation, Flow Readings

Screen Inlet and Outlet Levels

Inlet and outlet levels provide a visual indication of headloss across a screen. High inlet levels may be associated with a blinded screen, high flows or a downstream blockage. The consequences may include unscreened sewages bypassing to treatment, litter in sludge liquids and cake, early discharge to storm, onsite flooding or flooding in the network.

Continuous, Daily or Per Visit

SCADA and alarm calls, Onsite Level Readings, Process Checklist and Logbooks, visual inspections.

Screenings Carryover

Screenings carryover indicates there may be a problem with a screen. This may be as a consequence of screen panel damage, worn collection bars or teeth, ineffective cleaning systems, or lip or labyrinth seal failure.

Daily or Per Visit

Process Checklist and Logbook, visual inspections.

Screen Operational Hours run (where applicable)

Screen operational hours are generally associated with loadings on a screen. However, high operational hours may indicate other factors such as, an overloaded screen, inefficient washing or worn brush cleaning systems, loss of adequate washwater pressure, faulty control systems, blinded screens or other problems.

NOTE 1 SCADA, Site Panels, visual inspections

Screenings Handling Operational Hours (where applicable)

Screenings handling operational hours are generally associated with loadings. High operational hours may indicate blocked washwater filter systems, loss of adequate washwater pressure, worn cleaning systems, worn brushes or other problems.

NOTE 1 SCADA, Site Panel, visual inspections





Measure Why Frequency Method of Collection

Screenings Quality

Gives an indication of performance of the screen or screenings handling operations. Wet screenings with a high faecal content may indicate issues with either excessive loading and or mechanical failure.

Daily or Per Visit

Visual inspections or third party reports.

Screenings Quantities

Quantity of screenings removed will give an indication of high or low screenings capture by the screens and screens handling units.

As per skip movements

Duty of Care Tickets

NOTE 1: Operational hours are not currently collected on a regular basis. When considered necessary operational hours should be obtained to aid performance measurement.

THAMES WATER Asset Management rs Asset Standards




Internal Company and Partne

3.2 Operator Activities 3.2.1 Process Checklist SCREENS Any of the following checks that result in faulty operation needs to be logged and reported for maintenance / repair ABBREVIATIONS: MR = MANUALLY RAKED SCREEN DRU = DRUM OR CUP SCREEN BAR = BAR SCREEN

B&S = BAND AND STEP SCREENS DS = D SCREEN RBI = ROTATING BAR INTERCEPTOR SCREEN ESC = ESCALATOR SCREEN ROT = ROTARY SCREEN DB = DISPOSABLE BAG SCREEN

NOTE: Where screening and screenings handling is combined in one unit the task lists for screenings handling must also be completed. Task Task Applies To Low PE

(10-1000)

Low-Med (1000-5000)

Med PE (5000-20,000)

High PE (20,000-350,000)

Manned (350,000+)

SCREEN - CHECK INLET CHANNEL LEVEL IS NORMAL ALL SCREENS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK FOR ANY GRIT BUILD UP IN FRONT OF SCREEN ALL SCREENS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - VISUALLY CHECK UNIT AND ITS ASSOCIATED EQUIPMENT FOR SECURITY AND FREE FROM EXCESSIVE NOISE, VIBRATION OR OVERHEATING AND THERE IS NO EXTERNAL DAMAGE, LEAKS, MISSING FIXINGS AND ALL GUARDS ARE SECURE AND IN GOOD CONDITION. WHERE APPLICABLE ENSURE MAIN AND BRUSH DRIVES TURN AND THAT BRUSHES ARE SPINNING.

ALL SCREENS

OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK SCREEN OPERATION AND CHECK FOR SCREENINGS CARRYOVER, LOG EXCEPTIONS TO NORMAL OPERATION

ALL SCREENS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK PRODUCT QUALITY AND QUANTITY

ALL SCREENS EXCEPT RBI TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK & CLEAN ACCUMULATION OF SCREENINGS AND FAT FROM DEBRIS DISPOSAL MECHANISM


THAMES WATER Asset Management Internal Company and Partners Asset Standards


Task Task Applies To Low PE Low-Med Med PE High PE Manned (10-1000)

(1000-5000) (5000-20,000)

(350,000+) (20,000-350,000)

SCREEN - CHECK & CLEAN ANY OBSTRUCTIONS IMPEDING THE OPERATION OF SCREEN RAKING MECHANISM

ALL SCREENS EXCEPT DB, RBI, B&S TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - INSPECT DEBRIS DISPOSAL MECHANISM FOR CORRECT OPERATION AND VERIFY SCREENINGS ARE BEING REMOVED

ALL SCREENS EXCEPT DB & RBI TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK & CLEAN SCREEN PANELS ALL SCREENS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK & CLEAN LAUNDER CHUTES AND CHANNELS FOR ACCUMULATION OF GRIT, SAND, RAG, FAT, ETC.


SCREEN - CHECK OPERATION OF WASH WATER SYSTEM FOR SCREENS

ALL SCREENS EXCEPT MR, DB, RBI & BAR TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - WASH DOWN SCREEN ALL SCREENS T1/1M T1/1M T1/1M T1/1M T1/1M

SCREEN - CHECK SCREEN ELEMENTS FOR DAMAGE OR MISALIGNMENT ALL SCREENS T1/1M T1/1M T1/1M T1/1M T1/1M

SCREEN - BEFORE FROST SETS IN CARRY OUT CHECKS ON COLD WEATHER OPERATION SYSTEM

ALL SCREENS EXCEPT MR & DB TYPE OP/12M OP/12M OP/12M OP/12M OP/12M

SCREEN - CHECK AND CLEAN INSTRUMENTATION PROBES AND FLOATS (WHERE APPLICABLE)

ALL SCREENS EXCEPT MR & DB TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - ENSURE PRESSURE OF SPRAY BAR IS CORRECT. CHECK AND CLEAN THE INLINE FILTER FEEDING THE SPRAY BARS (WHERE APPLICABLE)






Task Task Applies To Low PE Low-Med Med PE High PE Manned (10-1000)

(1000-5000) (5000-20,000)

(350,000+) (20,000-350,000)

SCREEN - CHECK AND CLEAN THE SPRAY BAR NOZZLES


SCREEN - CHECK THE LIP, LABRYNTH OR OTHER SEALS BETWEEN THE SCREEN AND THE CHANNEL WALL ARE MAKING AN EFFECTIVE SEAL

B&S ESC, DRU, DS & ROT TYPES ONLY OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK FOR RAG ROLLING OR RAG BALLS UPSTREAM OF THE SCREEN AND REMOVE WHERE NECCESSARY

ALL SCREENS EXCEPT MR, DB, RBI & ROT TYPE OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK FOR HAIRPINNING ON SCREEN PANELS AND REMOVE WHERE NECESSARY

B&S & DRU TYPES ONLY OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - CHECK (VISUAL) THE SCREENINGS REMOVAL BRUSHES FOR BLINDING AND WEAR. CLEAN THE BRUSHES. ENSURE THE BRUSHES ARE IN CORRECT CONTACT WITH THE SCREEN AND THAT SCREENINGS ARE BEING REMOVED

B&S, ESC, DS & ROT TYPES ONLY OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - (COPA TYPE SAC AND TRAWL SCREENS) WHERE INSTALLED CHECK BAG REMOVAL LIFTING APARATUS CONDITION AND OPERATION

DB TYPE ONLY T1/1M T1/1M T1/1M T1/1M T1/1M

SCREEN - CHECK FOR SCREENINGS CAPTURE AND REMOVE AS NECCESSARY. RBI TYPE ONLY

OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREEN - INSPECT GREASE POTS AND FILL THEM WHEN LEVEL IS BELOW THE STANDARD. USE GREASE NIPPLES TO LUBRICATE REQUIRED PARTS OF SCREEN.

ALL SCREENS EXCEPT MR & DB TYPE OP/1W OP/1W OP/1W OP/1W OP/1W

SCREEN CLEAN AREA AROUND SCREEN ALL SCREENS

OP/1W OP/1W OP/1W OP/1W OP/1W




3.2.2




Process Checklist SCREENINGS HANDLING - MECHANICAL UNITS Compactors, Washpactors, LISEPs and other Screening Handling Plant

Any of the following checks that result in faulty operation needs to be logged and reported for maintenance / repair Task Low PE

(10-1000) Low-Med (1000-5000)

Med PE (5000-20,000)

High PE (20,000-100,000)

Manned (100,000+)

SCREENINGS HANDLING - WHERE INSTALLED CHECK OPERATION OF MACERATOR OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - WHERE INSTALLED CHECK AND EMPTY STONE TRAP OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - CHECK CONTROL SYSTEM AND AMPS ON PANEL FOR NORMAL LEVELS / OPERATION OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - CHECK OPERATION OF AUTO DRAIN T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CHECK FOR GRIT BUILD-UP IN TROUGH - HOSE OUT AS NECESSARY T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CHECK THAT THE WASHWATER SYSTEM IS OPERATING CORRECTLY T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CHECK (VISUAL) CONDITION AND OPERATION OF BRUSHES (ENSURE TROUGH IS BEING CLEANED) IF BLINDING OCCURS REGULARLY HAVE WEAR ON SCREW BRUSHES CHECKED. T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CHECK SCREW CONVEYOR AND BRUSHES FOR WEAR AND CENTRAL RUNNING. T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CLEAN AND CHECK MESH FOR BLINDING AND HAIRPINNING T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - CHECK MOTOR MOUNTING PLATE FOR EVIDENCE OF LEAKAGE PAST MECHANICAL SEAL (ROD-OUT GROOVE IN BEARING HOUSING - IF SEAL IS WORN EXCESSIVE WATER WILL BE PRESENT) T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING - REMOVE DEBRIS WHICH MAY BE OBSTRUCTING NOZZLES (AS NECESSARY) T1/1W T1/1W T1/1W T1/1W T1/1W



Task Low PE Low-Med Med PE High PE Manned (10-1000) (1000-5000) (5000-20,000) (100,000+) (20,000-

100,000) SCREENINGS HANDLING - CHECK FOR SIGNS OF WEAR OR DAMAGE ON IMPELLER FACE T1/1M T1/1M T1/1M T1/1M T1/1M

SCREENINGS HANDLING - CHECK AND CLEAN THE INLINE FILTER FEEDING THE SPRAY BARS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - CHECK AND CLEAN THE SPRAY BAR NOZZLES OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - WHERE INSTALLED CHECK OPERATION OF THE TROUGH DELUGE SYSTEM OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SCREENINGS HANDLING - BEFORE FROST SETS IN CARRY OUT CHECKS ON COLD WEATHER OPERATION SYSTEM OP/12M OP/12M OP/12M OP/12M OP/12M

SCREENINGS HANDLING - CLEAN AREA AROUND SCREENINGS HANDLING UNITS AND SKIPS OP/1W OP/1W OP/1W OP/1W OP/1W

SCREENINGS HANDLING - CHECK LEVEL OF SCREENINGS IN SKIP AND CHANGE WHEN FULL OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D




3.2.3




Process Checklist SCREENINGS HANDLING - MANUAL UNITS Disposable Bag (COPA type sac and trawl) and Manually Raked Screenings

Any of the following checks that result in faulty operation needs to be logged and reported for maintenance / repair Task Low PE

(10-1000) Low-Med (1000-5000)

Med PE (1000-20,000)

High PE (20,000-100,000)

Manned (100,000+)

SCREENINGS HANDLING - CLEAN AND CHECK MESH FOR BLINDING T1/1W T1/1W T1/1W T1/1W T1/1W

SCREENINGS HANDLING REMOVE AND SAFELY DISPOSE OF CONTAMINATED SCREENINGS AND WHERE APPLICABLE THE CONTAMINATED DISPOSABLE BAG T1/1W T1/1W T1/1W T1/1W T1/1W

3.2.4 Process Checklist KEY

OP = OPERATOR T1 = TECH 1

1W = 1 TIME PER WEEK 1M = 1 TIME EVERY MONTH 1W/2D = 2 TIMES PER WEEK 3M = 1 TIME EVERY 3 MONTHS 1W/3D = 3 TIMES PER WEEK 6M = 1 TIME EVERY 6 MONTHS 1W/5D = 5 TIMES PER WEEK (EVERY WEEKDAY) 12M = 1 TIME EVERY YEAR 1W/7D = 7 TIMES PER WEEK (EVERYDAY) 48M = 1 TIME EVERY 4 YEARS





3.2.5 Process Checklist Notes

What to check Action / What to check for on deviation Frequency of Checks

Where a task frequency is stipulated as weekly, this should be completed per visit with a maximum frequency of one week between visits.

Cold weather checks

Cold weather checks should be completed in the 9th month of the calendar year

Manually removed screenings and disposable bag screens.

Check that manually raked screenings and contaminated disposable bags (i.e. Copasac and Copatrawl type) are removed immediately and disposed of safely to prevent nuisance caused by odour and vermin. For health and safety reasons associated with manual handling, disposable bags must be removed at part capacity, normally approximately 50% for the Copa Sac type.

Duty Cycling Checks should be made that automatic cycling (where appropriate) is operating correctly for screens and screening handling plant. This can be indicated by assessing hours run meters where installed on multiple units.

Isolations Checks should be made with regard to the correct operation and safety of all isolations. Penstocks, stop-logs, gates and valves should all be exercised regularly in accordance with the site operating manual and the required method statements and risk assessments.

Screenings carryover

Check downstream process units for screenings capture, pump blockages and litter carryover. Baffles, weirs and launders often capture screenings. Primary sludge flows are also likely to contain solids that pass the screens. An increase in screenings observed downstream may indicate screening problems which should be investigated.

Washwater Check the washwater supply system and also any delivery points to screens and the screenings handling plant. Inline filters and spray bar nozzles should be checked and cleaned to ensure washing efficiency is maintained. Regularly check washwater pressure gauge indicators where fitted.

Skip Integrity The integrity of the final screenings disposal container or skip should be monitored on a regular basis, It is important to ensure skips are filled correctly to reduce cost. Skips must not be overfilled and loads must be level. Skips should not contain water. Thames Water has a duty of care to comply with waste transfer legislation to avoid overloading of vehicles.

Cleaning and Wash Down

With reference to Task 360 and other tasks associated with cleaning of the screens, screenings handling units and surrounding areas. Where hot-jet equipment is available this should be used to aid fat and grease removal. Where a hot-jet is not available other means such as high pressure wash water may be used.





3.3 Troubleshooting Guide WWT 1.3 Troubleshooting Guide Screens and Screenings Handling

Symptom Possible Cause Action Risk / Consequence Screenings carryover

Screen mesh/panels damaged

Removal system needs adjusting

Screens out of service Screen seal failure Screen blinded and

bypass channel operating

Inspect mesh/panels for damage and repair

Check screenings removal system

Check seal between screen and channels

Check screen not blinded

Screenings carry over Consent failure Damage to down stream

processes Sludge contamination

Low flow through screen

Screen Blinded Rag balls and/or

hairpinning No, or reduced,

washwater Blocked in line filters on

spray bar systems Blocked spray bar jets Cleaning brushes

damaged or worn Excessive loadings onto

screen Loss of power or motor

tripped Launder blocked or

damaged Screenings handling

plant fault Assist and/or standby

screen(s) not available Build up of fat/grease on

screen mesh Other Screen damaged Incorrect operation of the

screen Blockage upstream or

downstream of screen Flow control issues

Inspect and clear blinding and/or blockages

Check washwater system, spray bars, filters

Check brushes Observe loadings

not excessive Check flow control

settings Repair screen

damage Monitor operation

and correct Check for

obstructions upstream and downstream and clear

Hot wash/steam clean screen

Premature flow to storm Flooding upstream of

screen Pollution Illegal discharge Not passing flow to

treatment

Screen not Cleaning

Loss of power or motor tripped

No, or reduced, washwater

Blocked in line filters on spray bar systems

Blocked spray bar jets Screenings handling

plant fault Cleaning brushes

Monitor operation Observe loadings

not excessive Check washwater

system, spray bars, filters

Check brushes Check screenings

handling plant Check power supply


screen Pollution Illegal discharge Not passing flow to

treatment





WWT 1.3 Troubleshooting Guide Screens and Screenings Handling

Symptom Possible Cause Action Risk / Consequence damaged or worn

Excessive loadings onto screen

and motor faults

Screenings launder or chute blocked

Launder deluge system not working

Excessive screenings load

Solids blockage

Inspect and clear Repair Monitor loadings


screen Launder flooding Pollution Screenings back up in

system and ultimately carry over to treatment

Contaminated screenings

Screenings handling plant blocked

No, or reduced, washwater

Blocked in line filters on spray bar systems

Blocked spray bar jets Launder blocked or

damaged Screenings handling

plant fault Cleaning brushes

damaged or worn Incorrect and intermittent

screen operation causing surges in screenings volume into conditioning plant

Inspect and clear Repair Monitor operation

and correct


screen Contaminated

screenings Pollution Illegal discharge Failure to comply with

Duty of care Damage and high repair

costs to plant and equipment

Contaminated or wet screenings

Plant inadequate No washwater Incorrect settings Damaged or worn

brushes and cleaning equipment


and correct

Odours Loss of disposal outlets Failure to comply with

Duty of Care Customer complaints Vermin infestation

Screenings handling plant running with high amps and possibly excessive audible noise

Blockage Fault Worn impellors,

gearboxes and motors


and correct

Potential plant failure Possible back-up to

screen and subsequent failure.

Screenings handling plant experiencing excessive brush wear

Stones and grit in plant Lack of routine flushing

of grit and stone traps No provision for grit and

stone protection

Install grit trap Develop case for

grit and stone trap addition

Poor product High maintenance





3.3.1 Dos and Donts

Dos Donts

Regularly check screens and screenings handling unit operation in-line with task lists, site operating manual and the process checklist and logbook.

Become complacent over task list and checklist items.

Ensure all frost stats and cold weather protection equipment is tested prior to the winter season

Ignore the screen and conditioning plants, as they are the primary means of protecting the entire Sewage Treatment Process

Ensure all screens and conditioning plant are fully operational and available prior to the winter season and high flow conditions

Allow standby and or broken equipment to remain out of service.

Regularly check screen cleaning mechanisms be it brushes, rakes and/or washwater supply

Operate screen or screenings handling plant without washwater supply, or cleaning systems.

Observe plant operation in all conditions.

Plan plant shutdowns during high flow or load conditions

Encourage high standards of housekeeping and cleanliness in and around screen and conditioning plant installations

Handle screenings without correct equipment and PPE. Leave screenings or used disposable bags where they can cause nuisance or attract vermin.

Inform your line manager and ask for additional support if problems persist. When assessing problems try to quantify the issues. This will aid in future decision making regarding the assets.

Ignore issues hoping they will resolve themselves.

Encourage annual manufacturers refresher training for all staff operating and maintaining this type of plant and equipment. Pass on site specific good practice to new starters and inexperienced team members

Have visual indication adjacent to level controllers, pressure gauges, ammeters etc, as this will help inexperienced staff and team members to quickly assess the normal operational settings and operating limits for the equipment being monitored.

Ensure you have a comprehensive inventory of critical spares, e.g. brushes, filters, lip and labyrinth seals etc





Appendices 3.4 Operation The operation of Screens and screenings handling equipment must be in accordance with the design. Effective operation will ensure the protection of downstream treatment processes, reduce unnecessary operational cost and damage and thus reduce the whole life cost of those assets against rag accumulation and debris. Effective operation also means discharge consent requirements for final effluent and storm flows will be met so that flows do not contain a significant quantity of solid matter having a size greater than 6mm in more than two dimensions.

For sites with SCADA (Supervisory Control And Data Acquisition) the key areas for screen and screenings handling operation are controlled and monitored. These areas of control are normally screen run/stop and screenings handling run/stop as based on water levels, timer, flow or other parameter.

3.4.1 Screen Operation and Control Some screens are called to operate by a timer. This is usually only practicable when the quantity of screenings and incoming flow can be accurately predicted. It is not suitable therefore on works serving a combined sewerage system. Differential Head relies on the blinding effect of the screen when rags collect and restrict the flow through it. A clean screen will produce very little difference in level upstream and downstream whereas a ragged screen will produce a significant difference and possible overloading of downstream conditioning plant. The 3 main methods of detecting this difference are:

Floats Ultrasonic Transducers Probes

Electrical circuitry within the control panel compares the upstream and downstream levels and calls for the screen to start when the difference reaches a predetermined figure. 3.4.2 Quantities of Screenings At the National Screen Evaluation Facility (Chester Le Street) Screening Capture Ratio (SCR) is calculated. The best screens remove. 70 to 80% while some common makes struggle to remove 60%. More than 20% of screenings get through, over, under or around the screen. These tend to be finer materials that represent a low risk to downstream plant and equipment. 3.4.3 Impact on Secondary Treatment Processes The following figure details the potential impacts of poor screening on all aspects of the wastewater treatment process.

Internal Co

Tech

AM-PRO

THAMES WATER Asset Management

mpany and Partners Asset Standards

nical Lead: Des Monger Issue 1.1

-WWT-WWT 1.3 Screens and Screens Handling-SEC3 Page 17 of 20


u V scree the scree Insufficie p

3.4.4 Odour Screens and screenings handling operations have very high potentials for odour release. There aremany reasons including;

- screening may be one of the first points where odorous gases generated in the collection systems can be released

- the process may receive anaerobic wastewater - there are often areas of turbulence where odorous gases are released from the liquid phase - decomposable matter may be removed from the flow - odorous flows from septic tankers, storm tanks, sludge processing or filter backwashing may

all return to the screening process

Odour management at the screens and screenings handling processes is therefore very important.At many sites screening operations will be completely contained in buildings or smaller structures andodour removal and treatment equipment utilised to minimise the impacts. The site Odour Management Plan should detail any maintenance measures to ensure odour containment in line with the sites requirements. This may be audited by the local authority. Further details of odour management are not within the scope of this asset standard. 3.4.5 Screen Optimisation Maintaining sufficient channel velocities and distribution to the screens is critical to good performanceof screen units operating singularly and in parallel. These factors may be optimised where controlcan be used to bring standby screens online to maintain channel velocities and good distribution. Generally the screen optimisation is completed during the design phase. Routine maintenancehowever must be completed to ensure the efficient operation of the screen units. Ensuring grit deposition ahead of the screen is minimal, obstructions and debris build-up are removed, the washwater system is operating effectively and oiling and greasing is completed will aid optimal screen performance. In addition regular logging of hours run and maintenance completed is important. Running of all units regularly helps reduce corrosion and build up of grit and stones in front of standbynits.

isual checks of downstream processes (detritor inlet baffles, settling tank launders) can indicatenings carryover from the process and that further investigation is required. The seals between

n and channel walls are a common area that must be checked for screenings passing. nt washing and thus screenings being carried over into downstream flow is another regular

roblem resulting in screenings carryover.





3.4.6 Contingency Planning Screenings shock load (first flush) This can occur at any time but often occurs during the first rain following a dry period. Quantities may be far in excess of normal and therefore may cause problems for screens and screen handling equipment. In these circumstances contingency plans are required to ensure all screenings are removed from the flow and processed without causing flooding or damage to downstream processes. In the event of a screenings shock load to a plant then performance of the screens and screenings handling units should be closely monitored. Where necessary manual intervention may be performed, this may include:

Removing solids build up or blockages in launders Manually running of equipment to ensure continuous operation Reducing load on screenings handling by diverting screenings for processing at a later stage Where applicable regular or continuous raking of manually raked screens Diversion of the main flow or the screenings flow to be treated at a later stage Tankering of the areas ahead of screens and of the screenings removed

NOTES: Any manual handling of screenings must be completed with the correct PPE and wherever possible tools should be used for manual handling. This is because screenings can contain sharp objects such as needles. Guards, covers and other restrictions must not be breached until isolation has been completed and proved. Screen or screenings handling failure In the event of a screen or screenings handling failure a contingency plan is required over and above any designed in standby or bypass arrangements. Diversion of flows to spare tanks and/or tankering of flows or screenings are short term measures which can be instigated quickly once a failure occurs. Relocation of existing units or Installation of temporary replacement units are longer term solutions which may take considerable time to effect. Running equipment in hand, utilising manually raked equipment or tankering wet screenings are other contingencies which can be used on a case by case basis. 3.4.7 Plant Release / Taking out of and Bringing into service Taking out of service - Planned When Screen(s) are being taken out of service the Plant Release procedure needs to be followed together with site process risk assessment and plant availability. If a Screen cannot be taken out of service due to process risk then this needs to be highlighted in the Risk Register for potential investment / capital delivery purposes. The frequency for removing Screens from service must be set at a level that ensures the performance of the Screen is maintained and inspection of the Screen can be made prior to any damage occurring.





Taking out of service - Unplanned The following points must be taken into account when taking a Screen out of service to maintain site operation, maintenance and compliance. Always protect effluent quality. Review operation of upstream processes, i.e. screens which may be causing problems Plan flow diversion needs i.e. Tanker, pumping station etc. Health & Safety Inspections required Monitor downstream processes Alarms that could lead to needless Call Outs, i.e. not temporarily disabled during outage. Odour

This is not an exhaustive list and a site specific process risk assessment and method statement must be drawn up. Bringing into service Check Screen(s) alarms before leaving site. Check that all Screen(s) have equal flow distribution to ensure optimal operation. More than one Screen on site Ideally a clear out of the upstream channel should have been completed. Dependant on configuration flow may be gradually or wholly diverted to the screen to ensure correct velocities and running depths. Level sensors or probe settings should be validated. Where high level is existing in the screen channel when the screen is to be brought online, an in hand operation mode may be used initially until levels are reduced. One Screen only on site Ideally a clear out of the upstream channel should have been completed. Flow may be wholly diverted to the screen to ensure correct velocities and running depths. Level sensors or probe settings should be validated. Where high level is existing in the screen channel when the screen is to be brought online, an in hand operation mode may be used initially until levels are reduced. General It is advisable that an inspection of the Screen and its Screen Handling system is carried out within a few days of being put back in service. Learning Points Small sites with duty only processes may benefit from increased inspection and maintenance visits.





Health and Safety The Thames Water H&S management system has been designed to ensure effective risk control, and a key aspect of this system is risk assessment and the safe undertaking of activities conducted by the business. External suppliers using this Operational Standard must utilise a H&S process that is equal to the Thames Water approach to managing risk Thames Water managers must identify via the completion of the SHE 1 document activities to be undertaken and how they are to be controlled via the adoption and implementation of relevant key procedures (HSPs) and risk assessment guidelines (RAGs). Thames Water employees must be provided with the necessary information, resources and training to perform these tasks, and prior to completion they must confirm that they can comply with these procedures and guidelines. However, if an employee believes that compliance will require additional resource, the task should be reviewed using the SHE 5 form and if necessary curtailed. Thames Water managers must be trained in this system, and be in receipt of a controlled copy of a H&S manual which is supported by information posted on the company portal.

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3.0 Operating Standard3.1 Screens and Screenings Handling Performance Measures3.2 Operator Activities3.2.1 Process Checklist SCREENS 3.2.2 Process Checklist SCREENINGS HANDLING - MECHANICAL UNITS3.2.3 Process Checklist SCREENINGS HANDLING - MANUAL UNITS 3.2.4 Process Checklist KEY 3.2.5 Process Checklist Notes

3.3 Troubleshooting Guide 3.3.1 Dos and Donts

Appendices3.4 Operation3.4.1 Screen Operation and Control3.4.2 Quantities of Screenings3.4.3 Impact on Secondary Treatment Processes3.4.4 Odour3.4.5 Screen Optimisation3.4.6 Contingency Planning3.4.7 Plant Release / Taking out of and Bringing into service

Health and Safety

am-pro-wwt-wwt 1.3 screens and screenings handling-sec3 issue 1.1

Documents

process checklist screens

screens handlingsec3

monger issue

process checklist notes

process checklist key

issue conversion

quantities of screenings

lnapp01 date of issue