Water Services Training Group WRc FOG Project Engineering/Operations Issues

Andy Drinkwater/Frank Moy FOG Team WRc

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)

Engineering/Operations Issues  Grease separator selection  Products database  Jetting and cleaning of FOG from sewers  Sewer design  Pumping station design

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

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

 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 Grease separator selection

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

 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. Grease separator standard

Grease separator standard (2)  The standard (EN 1825)  Does not consider hybrids – Dosing and separators  Most separator suppliers don’t 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 of the separator

EN 1825 separator

Active separator (skimmer)

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

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

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

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

Inadequate grease separators Examples of two small and poorly maintained separators

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

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

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

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

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

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 1. General purpose jet to remove soft debris 2. Plough to remove hard sediments, 3. Spinning jet to remove FOG 4. Survey with a camera

Jetting heads

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

Jetting and cleaning Before and after using recommended procedure

Jetting and cleaning practice (4)  Should the dislodged FOG be:  Removed at the manhole: or  Passed forward ?  No evidence of significant problems if:

Jetting and cleaning practice (5)  Break fragments into small pieces, remove large fragments  Remove large quantities  Remove if FOG is mixed with sediment

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

Jetting and cleaning practice

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

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

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

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)

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

New sewer design to avoid FOG  Also:  Avoid flow control devices  If tanks are necessary, use off-line systems

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

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

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

Problem pumping station

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

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

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

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