am-pro-wwt-wwt 1.4 grit removal, treatment and skip management-sec3 - issue 1.1

THAMES WATER Asset ManagementInternal Company and Partners Asset Standards

Technical Lead: Andy Waghorn Issue 1.1

AM-PRO-WWT-WWT 1.4 Grit Removal, Treatment and Skip Management-SEC3 Page 1 of 14

UNCONTROLLED WHEN PRINTED

Asset Management Asset Standard Section 3 of 5 Operational Standard Wastewater Non Infrastructure WWT 1.4 Grit Removal, Treatment and Skip Management

Document Reference AM-PRO-WWT-WWT 1.4 Grit Removal, Treatment and Skip Management-SEC3

Version Issue 1.1

Data Owner Sarah Shipsey

Data Steward Kevin Kelleher

Technical Lead Andy Waghorn

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

Review Date December 2014





Contents:- 3.0 Operational Standard .................................................................................................................. 3

3.1 Grit Removal & Treatment and Skip Management Performance Measures........................... 4 3.2 Process Checklist: Operator Tasks ......................................................................................... 5

3.2.1 Operator Tasks Grit Removal and Treatment ............................................................... 5 3.2.2 Operator Tasks Skip Management ............................................................................... 6

3.3 Troubleshooting Guide ............................................................................................................ 8 3.3.1 Troubleshooting Guide Grit Removal and Treatment ................................................... 8 3.3.2 Troubleshooting Guide Skip Management.................................................................... 9

3.4 Operation ............................................................................................................................... 10 3.4.1 Operation and Control .................................................................................................... 10 3.4.2 Impact on Downstream Processes................................................................................. 11 3.4.3 Odour.............................................................................................................................. 12 3.4.4 Process Start up and Shut down Procedures ................................................................ 12

3.5 Health and Safety .................................................................................................................. 14 Glossary of Terms ............................................................................................................................ 14





3.0 Operational Standard This document defines the Performance Targets for the Grit Removal & Treatment and Skip Management processes. It also includes operational procedures and associated tasks and a troubleshooting guide. Comprehensive background information on the Grit Removal & Treatment and Skip Management processes and the waiver and ARC process is detailed in Section 1. The types of processes discussed in this document include:

Vortex Separator Powered or Unpowered Cross Flow Grit Separator (Detritor) Constant Velocity Channel Aerated Grit Chamber Stone Pits Detritus Tanks Inclined Rake Classifier Inclined Screw Classifier Hydrocyclone Skip Management

THAMES WATER Asset Management n Asset Standards




3.1

Inter al Company and Partners

Grit Removal & Treatment and Skip Management Performance Measures

Measure Why Frequency Method of Collection

Wastewater Flowrate

Grit is removal is completed through settlement. The key parameter for settlement is the velocity of the flow through the grit removal process. In some processes the velocity is kept constant through use of multiple channels or shape of the channel while in others it will vary with the flowrate. In general terms a lower flowrate will result in lower velocities and greater removal of grit and organics. A higher flowrate will result in higher velocities and less removal of grit and organics.

Continuous Inlet Flow

SCADA, Onsite documentation, Flow Readings

Grit Quantity Quantity of grit removed will give an indication of high or low grit capture by the removal and treatment processes or changes in catchment characteristics. As per Skip Movements

Duty of Care Tickets

Grit Quality Gives an indication of the performance of the grit removal and treatment processes. Wet grit with a high organic content may indicate issues with excessive loadings, low flows, poor performance of classifier, mechanical failures or other operational issue.

Daily or Per Visit Visual Inspection

Grit Carryover Grit carryover indicates there may be a problem with the grit removal processes. This may be as a consequence of mechanical failures, insufficient grit removals, bypasses operating or other reason. The level of grit carryover can be difficult to ascertain as grit is often removed with sludge.

Daily or Per Visit Site Logbook, Visual inspections, Pump Overhauls

THAMES WATER Asset Management Internal Company and Partners Asset Standards

3.2




Process Checklist: Operator Tasks Any of the following checks that result in performance of the process outside of the limits defined in the following table or a fault being detected will require an operator to change the process to bring the plant back into acceptable limits or the fault needs to be logged and reported for maintenance/repair. 3.2.1 Operator Tasks Grit Removal and Treatment

Task Details Notes Low PE (10-1000)

Low-Med (1000-5000)

Med PE (5000-20,000)

High PE (20,000-350,000)

Manned (350,000+)

GRIT REMOVAL - CHECK INFLOW AND OUTFLOW FOR NORMAL RATE OF FLOW AND CORRECT DISTRIBUTION

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

GRIT REMOVAL - CHECK MANUALLY DEGRITTED CONSTANT VELOCITY CHANNELS FOR BUILD-UP OF GRIT

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

GRIT REMOVAL - CHECK MECHANICAL PLANT IS OPERATING CORRECTLY Note 2 OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - CHECK VOLUME, DRYNESS AND QUALITY OF GRIT PRODUCED Note 1 OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - REMOVE RAG FROM THE AREAS Note 1 OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - LOG MANUAL DE-GRITTING OPERATIONS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - LOG ABNORMAL GRIT VOLUMES OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - CLEAN GRIT CHANNEL Note 1 OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

GRIT REMOVAL - CHECK OPERATION OF WASH WATER SYSTEM AND CHECK AND CLEAN THE INLINE FILTER (WHERE APPLICABLE)


GRIT REMOVAL - CHECK AERATED GRIT CHANNELS FOR AIR FLOW AND BUBBLE PATTERN


GRIT REMOVAL - CHECK STONE PITS, DIP, AND CLEAN OUT IF NECCESSARY Note 1 OP/1W OP/1W OP/1W OP/1W OP/1W/7D

GRIT REMOVAL CHECK GRIT BUILD UP IN INLET CHANNELS AND CLEAN OUT IF NECCESSARY

Note 1 Note 2



3.2.2




Operator Tasks Skip Management

Task Details Notes Low PE(10-

1000)

Low-Med (1000-5000)

Med PE (1000-20,000)

High PE (20,000-100,000)

Manned (100,000+)

SKIP - ENSURE ONLY PRESCRIBED MATERIAL IS IN THE SKIP. REMOVE ANY MATERIALS NOT PRESCRIBED TO THE SKIP

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

SKIP - RAKE SKIP Note 1 OP/1W OP/1W OP/1W OP/1W/5D OP/1W/7D

SKIP - REMOVE EXCESS WATER IF THERE IS A FACILITY TO DO SO OP/1W OP/1W OP/1W OP/1W/5D OP/1W/7D

SKIP CHECK SKIP CAPACITY IS ADEQUATE AND INFORM CONTRACTOR WHEN SKIP IS FULL


SKIP - LOG SKIP MOVEMENTS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SKIP - RETAIN ANY WASTE TRANSFER NOTES FOR A MINIMUM OF TWO YEARS OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

SKIP - WHERE PRACTICABLE, ON COLLECTION SIGN DUTY OF CARE CERTIFICATE Notes 4, 5, 6 OP/1W OP/1W/3D OP/1W/5D OP/1W/5D OP/1W/7D

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



Process Checklist Notes

1. Any manual handling of grit or screenings must be completed with the correct PPE and wherever possible tools should be used for manual handling. This is because grit can contain sharp objects such as needles.

2. Guards, covers and other restrictions must not be breached until isolation has been completed and proved. 3. Ensure that the contents of the skip are not mixed with unauthorised materials. Recycling of skip contents is regularly practised and hence skip contents must be

monitored and controlled. 4. Each skip removed from site must comply with Duty of Care. 5. In most cases, transfer of waste is through a Framework Agreement, in which case a single transfer note, or Season ticket, will have been signed between the Carrier and

Thames Water management to cover that series of transfers. 6. Once a year an Audit Trail of the disposal operation should be carried out. The date, time and any deviations must be logged. 7. Ensure grit and silt build up in channels does not cause hydraulic back-up or other issues.




3.3




Troubleshooting Guide 3.3.1 Troubleshooting Guide Grit Removal and Treatment

Symptom Possible Cause Action Risk/Consequence

Odour complaints Grit in the system too long Poor or incorrect operation of the grit classifier or rake

Review grit removal frequency and time of day Rectify problem

Increased risk of more complaints. Poor Public Relations

High amount of organics in the grit

Organics return not operating correctly Washwater problem Grit not being treated correctly Low flows

Repair Check washwater system Check treatment system

No guaranteed disposal route for the grit.

Grit pump or transfer equipment blocked

High amount of grit received High amount of screenings received High flows Equipment worn and prone to blockages

Increase grit removal rate Check inlet screens Repair

Grit forwarded to downstream processes

Abnormal grit volumes (HIGH)

High flows Storm flows Catchment issues Classifier/ detritor malfunction

Ensure grit system operation is normal after high flow event

Check and rectify Grit forwarded to downstream processes

Abnormal grit volumes (LOW)

Grit plant not working Bypass in operation Pump problem Classifier/ detritor malfunction

Check and rectify Grit forwarded to downstream processes


3.3.2




Troubleshooting Guide Skip Management

Symptom Possible Cause Action Risk/Consequence

Product quality not correct

Plant overloaded Plant not set up correctly Plant blocked Unauthorised material dumped in skip

Investigate and rectify Contractor will not take product from site. Prosecution

Excessive water in skip Feed too wet Catching spillages Weather

Process improvement Use Guzzler or other skip drain Consider use of covered skip Adjust location of skip Reconsider frequency of emptying.

Contractor will not take product from site. Prosecution





3.4 Operation The operation of grit removal and treatment 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.

For sites with SCADA (Supervisory Control And Data Acquisition) the key parameters are monitored. The parameters monitored may include incoming flowrate, incoming level and starts, stops and run times for motorised equipment including paddles, scrapers, air blowers, pumps, rakes and screws.

3.4.1 Operation and Control Grit removal processes are generally operated on a continuous run basis. This applies to rotating paddles in vortex separators, grit scrapers in cross flow grit separators and air blowers for aerated grit channels. This is detailed further in the Section 2 Design Standard. The grit removal and treatment equipment is generally controlled on a timer basis. This includes ancillary rakes, grit pumps, airlift units, washwater supply and classifiers. The frequency and time of operation will be operator adjustable. This is detailed further in the Section 2 Design Standard.

Grit plants are normally provided with a full flow bypass or will have multiple units such that maintenance can be completed while passing full flow. It must be noted that removing a unit for service may impact grit removal as will bypassing flow, so plant should be returned to service as soon as possible. The impacts of poor grit removal are discussed in the next section.





3.4.2 Impact on Downstream Processes The following figure details the potential impacts of poor grit removal and treatment on many aspects of the wastewater treatment process.

SCREENING PRIMARY SETTLEMENTAERATION

PLANT SLUDGEBLOCKAGES

WEAR & DAMAGE

Grit wear on moving parts

Damage and wear to

scrapers

Damage to aeration

systems and pipework

Loss of volume and

treatment due to build up of

grit

Settlement of grit in tanks, pipes and chambers

Increased screen

maintenance costs

Increase in sludge

volumes

Loss of volume and increased

dead areas due to grit

Reduced biogas

production and loss of CHP

income

Increased odour due to

septicity

Damage to screens

Damage to de-sludge pumps

Damage to mixers

Increased wear on

thickening and dewatering

plant

Damage and wear to

pumps and mechanical

plant

Reduced screen lifetime

Blockages of de-sludge pipework

Impacts on diffusers (greater

headloss and energy use)

Damage to mixers and

heat exchangers

Increased cost of callouts,

cleanups and overtime

IMPACTS OF POOR GRIT REMOVAL

Figure 3.1 Example of Grit Accumulation in an Aeration Tank





3.4.3 Odour Grit removal and treatment operations have high potentials for odour release. There are many reasons including;

- Grit removal and treatment is at the head of the treatment plant where odorous gases generated in the collection systems can be released

- the process may receive anaerobic wastewater - 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 head of the works - grit removed from the wastewater will contain a level of organic material which has the

potential to degrade and produce odour

Odour management at the grit removal processes is very important. At many sites grit removal and treatment operations will be completely contained in buildings or smaller structures and odour 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. 3.4.4 Process Start up and Shut down Procedures When grit removal plants are being taken out of service the Plant Release procedure needs to be followed together with site process risk and plant availability assessments. If a grit removal plant 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 grit removal plants from service must be set at a level that ensures the performance of the plant is maintained and inspection of the plant can be made prior to any damage occurring. Taking Out Of Service The following points must be taken into account when taking a grit removal plant out of service:

Health and safety Always protect effluent quality Hazardous areas Grit load to downstream processes Flow diversion requirements i.e. Storm tank, tanker, pumping station, bypass etc. Isolation; upstream, downstream, washwater, air and drainage valves Impact on upstream processes Hydraulics and impact on upstream levels Alarms that could lead to needless Call Outs, i.e. not temporarily disabled during outage. Odour





Cleaning requirements potential for solidified grit Maintenance requirements Monitoring of flows and downstream plant performance Weather predictions and monitoring Skip management will it be impacted?

Bringing Into Service In addition to those outlined above the following points must be taken into account when bringing a grit removal plant into service:

Check that correct flow distribution is achieved to ensure optimal operation. Check frequency and runtime settings of timers Check inlet baffles are set to provide a uniform flow pattern through cross flow separators Check mechanical equipment is operating as expected Oiling and greasing requirements For aerated grit channels check air flow and bubble pattern Check washwater system is operating correctly Check skip levels are sufficient Check grit quality Check grit plant alarms before leaving site. It is advisable that an inspection of the grit system is carried out within a few days of being

put back in service. This is not an exhaustive list and a site specific process risk assessment and method statement must be drawn up.





3.5 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 an 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 an H&S manual which is supported by information posted on the company portal.

Glossary of Terms

TERM DESCRIPTION

PPE Personal Protective Equipment

SCADA Supervisory Control And Data Acquisition (a process control system)

----- End of Section 3 -----

3.0 Operational Standard 3.1 Grit Removal & Treatment and Skip Management Performance Measures3.2 Process Checklist: Operator Tasks3.2.1 Operator Tasks Grit Removal and Treatment3.2.2 Operator Tasks Skip Management

3.3 Troubleshooting Guide3.3.1 Troubleshooting Guide Grit Removal and Treatment3.3.2 Troubleshooting Guide Skip Management

3.4 Operation3.4.1 Operation and Control3.4.2 Impact on Downstream Processes3.4.3 Odour3.4.4 Process Start up and Shut down Procedures

3.5 Health and SafetyGlossary of Terms

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