Wastewater Research & Industry Support Forum

WASTEWATER RESEARCH AND INDUSTRY SUPPORT FORUM

Latest meeting 6^th March 2008

Jo Lambert from WRc, Technical Director of the FOG research programme, described progress to date.  FOG (fat, oil and grease) is a major contributor to problems for sewer performance.  This three-year research is due to complete in autumn 2008.  Daughter projects are expected to follow.  An EPSRC-funded PhD studentship into the chemistry of FOG will continue at Southampton University until 2009.

Figure 1: 4-foot brick sewers half blocked with FOG - it can form from the roof or the floor; roots can initiate FOG formation. 

Sewer blockages typically occur in smaller diameter pipes (<225 mm diameter) around the property. However, larger sewers may also be affected, particularly in town centre “hot spot” locations where there are high concentrations of food catering establishments.

Indirectly sewer blockages are responsible for many cases of sewer flooding, leading to property damage and pollution incidents.  Water Companies suffer the fines and clean-up costs, even though FOG is probably the result of somebody’s negligence.  They estimate the cost of dealing with FOG related problems in the UK is approximately £15-20 million each year on clearing blockages; plus further expenditure on cleaning up flooding incidents.  This is nearly £1 per customer per year.  Contractors might not report the causes of blockages accurately but 55-75% of sewer blockages are thought to be caused by FOG.  Before and after CCTV is not done routinely.  The origination of the blockage might be tree roots around which of material gathers and it is the conglomeration that blocked the sewer, but it would not have happened if there had been no roots.   Sewer maintenance contracts do not necessarily specify reporting requirements. 

FOG can build up at wastewater pumping stations; it can accumulate around the edge of wet wells and often fouls pump controls. In severe cases a thick crust of solid FOG can build up on the surface of the wastewater. Pumping stations can also suffer from the accumulation of fat/FOG balls; FOG can obstruct/impede float-switches. FOG accumulations can block pumps, especially the cooling chambers. Often the blockages are not due to FOG alone but a combination of FOG and rags, the reduction in one or other of these materials may help to alleviate the situation.  Similar problems exist at wastewater treatment works, with FOG build up manifesting itself at various points including the terminal pumping station, inlet works and the primary settlement tanks. At the inlet works FOG can blind the screens, and fat balls may accumulate in the flow channels, however, these can be removed easily. FOG build up in the primary tanks is often on the scum boards and around the edges of the tanks. Large lumps of FOG (boulder-sized) are often found in the bottom of the tanks when they are drained for cleaning.

The different problems were investigated during the first year. Many of them split very nicely into the different topics of the four work packages. However, it became apparent that many spanned several different areas.  The second year was spent developing an understanding of the actual issues and a range of solutions. Where the issues are confined to a specific area the solution may be quite straight forward, however, where different areas are involved the solution becomes more complex and more difficult to determine.  The final year of the programme will be spent finalising the solution and developing the final tools. The information gained from ongoing Case Studies and trials will be invaluable in developing appropriate solutions.

The FOG project comprises four inter-related work packages:

1. Legal aspects, which reviews the legislation (domestic, non-domestic, building regs, nuisance) and considers how local authorities and sewerage operators could work together better
2. Sociological Aspects: which looks at domestic and non-domestic behaviour with regard to FOG and how these can be influenced positively, for example, targeted awareness campaigns and providing alternatives such as collection for biodiesel production.
3. Biological / Chemical Aspects: which includes reviewing systems for removing preventing or reducing grease, i.e. grease separators and biological dosing systems.  Grease separators must be fitted in new developments, but there is nothing to prevent them being removed later and there is no obligation to maintain them; there is no power to require installation of grease separators in existing kitchens.  There have been some successes with biological dosing, but also some failures.  A Ph.D. student is researching the chemistry of FOG, its composition, structures and formation reactions.
4. Engineering & Operations Aspects which has reviewed current sewerage design and operational practices in the different companies, investigated grease separator requirements and problems with their use and developed good practice for design, installation and operation of sewerage.

The main output from the FOG project will be detailed recommendations for dealing with FOG.  The outputs will be specific to the requirements of each work package but the information from each of the work packages will be used to develop an overall strategy for dealing with FOG issues.  It is expected that, whilst one solution will not fit all circumstances, a single overall strategy (using the toolbox of measures) should be applicable.

The solutions need to be practicable and convenient.  It should be possible to oblige commercial kitchens that generate FOG to have and to maintain grease traps, which will require an extension to the current legal requirement, but it has been found to be effective in the USA.  There then needs to be practicable facilities for the grease trap maintainers to get rid of the material they have collected, such as anaerobic digestion at WwTW for “dirty” FOG or biodiesel conversion for “clean” FOG.

It is necessary to design out points of accumulation for FOG, or move the FOG to places on the network where it is less problematic.  A legal anachronism is that discharges from restaurants are regarded as “domestic” because cooking a meal for consumption is considered to be a "domestic" activity and therefore the wastewater is considered to be domestic, but take-aways are considered to be “trade” dischargers.  Anglian Water had success with dosing by Environmental Biotech at a persistent problem site. The perception of costs attributable to FOG and therefore the financial viability of solutions varies from company to company; whether they look at costs over 1 year, 2 years or 5 years and whether they do sewer cleaning in-house or by contract.

 One outcome is that some sites that were known as notorious FOG sites have turned out to be prone to blockages for other reasons.  Blockages due to tree roots have, in some cases, been attributed to FOG.  Work in Thames Water found that tree roots are not attracted to sewers per se but that roots proliferate where there is moisture, i.e. if there is moisture at a sewer joint roots [fine] will proliferate that can get around O-ring seals, etc.  FOG and litter can accumulate on the tree roof curtain.  If sewer cleaning operations (contract or in-house) do not require CCTV before and after cleaning [non-man-entry] sewers, it is difficult/impossible to know the cause of blockage.

Undoubtedly there is need for education and awareness-raising so that more people have a better understanding of wastewater conveyance and treatment.  It is pointless complaining these functions are “out of sight, out of mind” when so little is done to enable people to understand this vital function for modern society

One possibility is to apply “Method Based Consents” to commercial premises, i.e. requiring them to have appropriate facilities (grease traps) in place and to maintain them.  It is currently possible to use Method Based Consents in Scotland, Northern Ireland and Republic of Ireland but in England and Wales it requires a commencement order under Section 89 of the Water Act 2003. 

The next meeting of the Forum will be on 2^nd July 2008.