Title: Water Services Training Group
1Water Services Training Group
- WRc FOG Project
- Engineering/Operations Issues
2Engineering/Operations Issues
- Andy Drinkwater/Frank Moy
- FOG Team
- WRc
3WRc 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)
4Engineering/Operations Issues
- Grease separator selection
- Products database
- Jetting and cleaning of FOG from sewers
- Sewer design
- Pumping station design
5FOG 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
6FOG 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
7Grease 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
8Grease 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
9Grease 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.
10Grease 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
11EN 1825 separator
12Active separator (skimmer)
13Grease 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
14Grease 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
15Grease 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
16Grease 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
17Inadequate grease separators
- Examples of two small and poorly maintained
separators
18Products 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
19Jetting 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
20Jetting 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
21Jetting 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
22Jetting 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
23Jetting 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
24Jetting heads
25Jetting heads
26Jetting 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
27Jetting and cleaning
- Before and after using recommended procedure
28Jetting and cleaning practice (4)
- Should the dislodged FOG be
- Removed at the manhole
- or
- Passed forward ?
- No evidence of significant problems if
29Jetting and cleaning practice (5)
- Break fragments into small pieces, remove large
fragments - Remove large quantities
- Remove if FOG is mixed with sediment
30Jetting 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
31Jetting and cleaning practice
32Sewer 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
33Existing 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
34Existing 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
35Existing 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)
36New 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
37New sewer design to avoid FOG
- Also
- Avoid flow control devices
- If tanks are necessary, use off-line systems
38Pumping 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
39Existing 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
40Existing 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
41Problem pumping station
42Problem pumping station
43Problem pumping station
44Problem pumping station
45New 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
46New 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
47FOG 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
48FOG 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