Water Services Training Group

1
Water Services Training Group

• WRc FOG Project
• Engineering/Operations Issues

2
Engineering/Operations Issues

• Andy Drinkwater/Frank Moy
• FOG Team
• WRc

3
WRc FOG Project

• Work Package 1 Legal
• Work Package 2 Sociological
• Work Package 3 Biological/chemical
• Work Package 4a Engineering designing FOG out
  (sewers/ pumping stations, grease separators)
• Work Package 4b Operations cleaning techniques
  etc (sewers/ pumping stations)

4
Engineering/Operations Issues

• Grease separator selection
• Products database
• Jetting and cleaning of FOG from sewers
• Sewer design
• Pumping station design

5
FOG Work Package 4 - Deliverables

• Reports
• Operational Problems caused by FOG
• Guidance document on Sewer Cleaning and Blockage
  Removal Techniques
• Factors that Influence FOG Accumulation on Sewer
  Pipes
• Design to Minimise FOG Deposition and Associated
  Operational Disruption
• Review of Use of Grease Separators
• Grease Separator Advice

6
FOG Work Package 4 - Deliverables

• FOG Strategy various advice sheets and
  leaflets, including
• Grease separator advice
• Operational guidance improved cleaning
  procedures
• Design guidance for sewers and pumping stations
• Guidance for improving existing sewer systems and
  pumping stations

7
Grease separator selection

• Large number of different types of separator are
  now commercially available
• Many are not of the traditional design and, as
  such, are not covered, by a standard
• However, many of the new designs show promise and
  deserve further investigation

8
Grease separator selection (2)

• When considering new types of separator, look at
• Their practicality - ease to install, where to
  install, ease to maintain/clean etc
• Their overall effectiveness
• Guidance given by manufacturers/ suppliers etc
  size/installation etc

9
Grease separator standard

• The standard (EN 1825)
• Difficult to understand (information spread
  between Part 1 and Part 2)
• Only considers conventional large underground
  separators Not practical for most town centre
  catering outlets
• No consideration of more recent separator
  designs, including skimmers.

10
Grease separator standard (2)

• The standard (EN 1825)
• Does not consider hybrids Dosing and separators
• Most separator suppliers dont understand EN 1825
• Suppliers have a variety of sizing methods
• Seems to be little standardisation but plenty of
  confusion
• Often, sizing is only for the food trap part
  ofthe separator

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EN 1825 separator
12
Active separator (skimmer)
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Grease separator selection

• Three main issues to consider
• Location/access
• Size
• Maintenance
• Each property is unique
• Selection is an iterative process
• may need combination of separator/ biological
  solution

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Grease separator selection

• Location
• Close to source connect all sources
  (dishwashers issue)
• Far enough away for effluent cooling
• Upstream of other inputs (rainwater and foul
  water)
• Outside units preferable - Consider internal
  units at properties with no external space
• Enable access for cleaning/maintenance

15
Grease separator selection

• Size
• To provide adequate retention time for separation
  to take place - determined by
• Flow rate to the separator
• Volume of FOG in discharge
• Maintenance frequency v size

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Grease separator selection

• Maintenance
• By whom
• Staff small separators, easy access, cleaning
  record, storage of wastes
• Contractor for larger underground separators,
  less frequent visits, vactor units remove wastes
  from site
• Frequency determined by storage capacity of the
  separator

17
Inadequate grease separators

• Examples of two small and poorly maintained
  separators

18
Products database

• Database including details of
• Grease separators and Biological treatments
• Product/company name
• Contact details for products
• Basic product information
• Guidance on appropriate applications
• Available to contributors and their agents
  through password access

19
Jetting and cleaning

• The most frequent symptom of FOG in the sewer
  system is a blockage
• Sewer blockages may occur at any point on the
  sewer system, from the point of source to the
  wastewater treatment works
• Sewer blockages can be categorised as a primary
  or secondary blockage

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Jetting and cleaning

• Primary FOG related blockages are due to natural
  deposition of FOG at a specific location as a
  result of the combination of
• a source and appropriate type of FOG,
• concentration of FOG in the flow,
• the natural processes of separation, and
• hydraulic conditions

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Jetting and cleaning

• Secondary FOG blockages are those that occur as a
  direct result of a previous blockage or severe
  flow restriction.
• Flow velocity upstream of the original blockage
  will reduce - FOG that would otherwise remain in
  the flow will separate out.
• FOG will be high on the pipe wall or in the crown
  of the upstream pipe, due to the increased depth
  of flow
• Sewer debris, (sanitary towels and other sewage
  debris) then sticks to the FOG on the crown of
  small pipes, a secondary blockage subsequently
  develops

22
Jetting and cleaning practice

• The following may seem obvious BUT experience
  often shows otherwise !
• All FOG related blockages must be effectively
  cleared and the upstream pipe effectively cleaned
  to prevent repeat incidents
• A recommended procedure has been proposed to
  ensure effective cleansing

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Jetting and cleaning practice (2)

• General purpose jets are a compromise
• Removal of FOG from a sewer should be carried out
  as a staged and incremental process
• General purpose jet to remove soft debris
• Plough to remove hard sediments,
• Spinning jet to remove FOG
• Survey with a camera

24
Jetting heads
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Jetting heads
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Jetting and cleaning practice (3)

• Analysis shows that the correct cleaning practice
  will be beneficial in terms of
• Reducing the number of operational disruptions
• Improving customer satisfaction
• Cost effectiveness

27
Jetting and cleaning

• Before and after using recommended procedure

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Jetting and cleaning practice (4)

• Should the dislodged FOG be
• Removed at the manhole
• or
• Passed forward ?
• No evidence of significant problems if

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Jetting and cleaning practice (5)

• Break fragments into small pieces, remove large
  fragments
• Remove large quantities
• Remove if FOG is mixed with sediment

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Jetting and cleaning practice (6)

• Remove if downstream problems may occur
• Notify operators of pumping stations and works of
  the possibility of dislodged FOG being passed
  downstream

31
Jetting and cleaning practice
32
Sewer design

• Greater likelihood of FOG deposition/ adherence
• Higher concentration of FOG
• Lower the temperatures of the pipe surfaces
• Slower the velocity of flow/movement of effluent

33
Existing sewer improvements (1)

• First option control FOG at source
• Good kitchen practice
• Install grease separators and/or
• Biological treatment systems
• Modest improvements to drainage system to reduce
  areas with low velocity
• Other measures
• Improve sewer cleaning/blockage practice
• Consider off line, as opposed to on-line tanks

34
Existing sewer improvements (2)

• Modest improvements to drainage system to reduce
  areas with low velocity
• Removal of Buchan traps
• Relay pipes with sags, to enable positive
  gradient
• Removal of tree roots
• Make good intruding laterals (use of saddle
  connections etc)
• Improve benching/pipe layout in manholes
• Install drop pipes to high level connections

35
Existing sewer improvements (3)

• Where existing systems need to be altered to
  reduce CSO spills etc, ensure that the
  improvement will not result in areas of low
  velocity/tranquil flow where serious FOG
  deposition could occur.
• Similarly, where storage needs to be added to
  reduce sewer flooding
• (These may seem obvious, but they have happened)

36
New sewer design to avoid FOG

• The following should be done as good practice, to
  ensure there are no areas with very low velocity
• Pipe velocity, 0.6 m/s or greater
• Use minimum number of pipe joints (joints
  dissipate energy in small flows)
• Use easier to clean pipe materials
• Good detailing of connections (saddles etc)
• Good detailing in manholes

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New sewer design to avoid FOG

• Also
• Avoid flow control devices
• If tanks are necessary, use off-line systems

38
Pumping station design

• Greater likelihood of FOG build up with
• Higher concentration of FOG
• Low velocity/movement in the wet well
• More tranquil the effluent in the wet well
• If there are dead zones in the wet well

39
Existing pumping station improvements (1)

• Where possible, remove dead zones
• Remove redundant/non essential equipment
• Remove baffles from incoming flows
• Consider re-profiling wet well floor
• Ensure effluent is mixed at start of pump down

40
Existing pumping station improvements (2)

• Refit with easy clean materials
• Replace fouled float switches with ultrasonics
  (located clear of the effluent)
• Use varying pump on/off levels , to avoid FOG
  shelves at pump on level
• Improve access to wet wells, for cleaning
  purposes
• Review pump regimes to reduce FOG deposition in
  rising mains

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Problem pumping station
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Problem pumping station
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Problem pumping station
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Problem pumping station
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New pumping station design (1)

• Greater likelihood of FOG build up
• Higher concentration of FOG
• Low velocity/movement in the wet well
• Ensure wet well does not have dead zones

46
New pumping station design (2)

• Avoid dead zones
• Use circular wet wells
• Use deep/small diameter wet wells better mixing
• Avoid excessive use of equipment in the wet well
• Minimise use of dividing walls
• Make use of energy/turbulence caused by incoming
  flow
• Use of non stick materials

47
FOG Work Package 4 - Deliverables

• Reports
• Operational problems caused by FOG
• Guidance document on Sewer Cleaning and Blockage
  Removal Techniques
• Factors that Influence FOG Accumulation on Sewer
  Pipes
• Design to Minimise FOG Deposition and Associated
  Operational disruption
• Review of Use of Grease Separators
• Grease Separator Advice

48
FOG Work Package 4 - Deliverables

• FOG Strategy various advice sheets and
  leaflets, including
• Grease separator advice
• Operational guidance improved cleaning
  procedures
• Design guidance for sewers and pumping stations
• Guidance for improving existing sewer systems and
  pumping stations