Cutting through the FOG
Kim Littlewood discusses WRc Group's project to examine the problem of fats, oils and greases (FOG) in sewers
FOG cause problems for sewerage utilities and customers from the beginning to end of the sewer system. In the small pipes near the customer’s house, they cause drain blockages and sewer flooding, in the larger pipes they cause flow inefficiencies, sewer cleaning costs, and more blockages and flooding.
Other assets are affected, and there will be a build up of FOG at pumping stations, inlet works and treatment works, and finally FOG may cause problems with digestion processes, and may lead to breaches of the discharge consent. All of these issues have cost and serviceability consequences. FOG cause other problems throughout the sewerage system such as odours, and can encouraging rats and flies.
FOG problems in the sewer network can be broken down into four main areas: legal and political issues, operational issues; biological and chemical issues and sociological issues. However, these are all interlinked, and the most important aspect is the interaction between them.
The interaction between the effect of legislation, sociological and biological or chemical aspects of FOG disposal is poorly understood. And, the role these issues play in any engineering or operational solution is far from clear. For example, the Landfill Directive effect people’s disposal habits in the home, as local authorities strive to meet landfill reduction targets, which may impact on how people dispose of FOG.
These interlinkages are likely to mean that there will be a significant increase in disposal to sewer of both FOG and associated substances such as food waste, so exacerbating the problem.
There is a need for a co-ordinated investigation of FOG issues, and concentrating on one aspect of the problem will not make a significant difference. The WRc project therefore considers the wider issues.
The WRc project
The WRc project is wide-ranging and intended to develop a suite of solutions to the FOG problem, from trying to stop the problem at source, providing alternatives to sewer disposal to design and operation aspects of controlling FOG. It is divided into four work packages, each examining one of the four main themes of FOG control. However, as discussed, these aspects cannot be considered in isolation. The current legal situation is not clear. Some issues that need to be clarified are:
- Can customers reasonably be fined for putting FOG down the sewer?
- What are the impacts of current and possible future waste disposal regulations?
- What are the alternate disposal routes, and what impact will future legislation have on these?
- What is the potential impact of individual pieces of legislation such as the Streetworks Act?
We are already seeing a link between recent changes in waste disposal legislation and the likely impact on FOG problems in the sewer system. To create a win-win situation, WRc will need to investigate whether there are alternatives to current disposal, and whether legislation will have an impact on these. An example of a win-win situation may be the biodiesel market, which may be able to mitigate against FOG disposal problems. However, there may be legislative and fiscal barriers to increasing the biodiesel market, which may block its potential for mitigation of the FOG problem.
There has been a significant body of work carried out on people’s flushing behaviour, which can also be applied to their FOG disposal habits. People flush because it is:
- Removes the storage problem before disposal
- There are limited alternatives
- There are no barriers to flushing. While flushing could be considered illegal, legal action against repeat offenders is unknown
All of these issues will also be applicable to the sink-side disposal of domestic and commercial FOG. People will continue to dispose of FOG down the sink until there is a safe, practical and convenient alternative.
The sociological work package will examine this issue, along with the sources of FOG, and in particular the drivers and tensions that make the sewer the easier place to dispose of FOG. In order to change people’s behaviour, we need to examine alternatives, and how these can be made more attractive. There are a number of key questions associated with public behaviour:
- What is the public perception of disposal of FOG to the sewer?
- What drivers can be used to reduce the disposal of FOG to sewers? Drivers are likely to include the provision of economic alternatives, such as collection for recycling, or developing ways to make the reuse of oils economic, for example the biodiesel approach
- What are the drivers for the catering industry on reduction or redirection of FOG disposal? This could include dealing with the proper disposal of fats in catering and food hygiene courses
- Is there potential for a framework for national leafleting campaigns and coordinated efforts at changing behaviour? For example, a significant aspect of this could be the development of material for schools and encouraging the inclusion of such issues in environmental awareness related education. This would build on successful national campaigns such as Bag It and Bin It
Biological / chemical Issues
Utilities have been seeking a solution to the problem of FOG for many years, and there are a number of biological and chemical compounds on the market which claim to break down FOG. Some of these have been tested by utilities but with mixed results. In this aspect, there is a need for understanding of these solutions, including how they work, and whether there are biological or chemical solutions that really will break down FOG, and under what circumstances these compounds will work best. The key issues here are:
- Fundamental research into the components of FOG. Does it contain, or is it affected by, road salts or dishwasher salts? Does it change by area? For example, are there ethnic effects on composition? Does it contain starch, gelatine or washing powder compounds? How far down the drain does it start to solidify? What temperature does it solidify at? This part of the project will be carried out as an EPSRC studentship, see http://www.jobs.ac.uk/jobfiles/EJ092.html for further details
- Examination of the biological solutions. This should include examining the range of solutions currently being marketed
- Ascertaining the operation constraints and requirements for biological solutions, including understanding which solutions work best in which parts of the sewers
- A review of chemical solutions. However, it is unlikely many of these will gain widespread use because their impact on biological processes is considered too great. A greater understanding of by-products will be necessary
There is already a range of operational solutions to clearing FOG but these may be affected by legislation such as the Streetworks Act, making them uneconomical. There is a need to examine their effectiveness and how these may interact with chemical and biological solutions. This will include the design of sewers, wet wells, detention tanks and inlet works. The effect of different types of construction materials will also be taken into account. Are clay pipes less susceptible to FOG build up than concrete pipes, for example, or are brick structures a particular problem? Some key operational issues are:
- What is the scope for operational solutions, including working with contractors to ascertain best practices for cleaning and removal? This will include looking at new methods of applying biotech solutions in the sewer system or pumping station or inlet works
- What could be done to improve operational practices to reduce fat build up in wet wells and inlet works?
- What will be the impact of food macerators and rubbish grinders on the composition of wastes and their effect on fat in the sewers
- What is the potential for the use of fat traps on lateral drains or sewers serving high-risk FOG sites (for example in catering)
All of these impact on each other, so people’s habits will be linked to changes in legislation, as well as provision of alternatives. And sources of FOG change over time. The potential benefits of a co-ordinated FOG reduction programme will be wide-ranging. Firstly, there will be a drop in the volume of sewer cleaning and blockage clearance, with a cut in OPEX. There will be a lower risk of sewer blockages, customer complaints and risk of flooding.
However, a key issue will be to ensure solutions are implemented and that work carried out within the industry gains momentum. This project is currently being supported by seven utilities, so there is a significant level of gearing on it because more testing can be carried out and the results can be shared across the contributors.
Also, an approach to user behaviour may be more effective if it is co-ordinated, with best practice from each utility being combined to give a united message. This means that the WRc project has scope to make significant changes across the industry as a whole.
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