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Clearing the FOG

Peter Jennings, Technical Director for ACO Building Drainage, looks at the problems caused by the disposal of fats, oils and greases and looks at what the drainage industry can do to help address the problem.

The disposal of fats, oils and greases into public sewers is a growing concern for local councils and water authorities. In fact, it is generally estimated that fats, oils and greases are responsible for 75% of the 200,000 drain blockages throughout the UK every year, resulting in approximately £15million being spent annually on reactive blockage clearance nationwide, not to mention the additional costs associated with the clean up process following flooding incidents.

However, it is not hard to understand why this has become a problem as the production of fats, oils and greases for cooking has more than trebled since the 1960s, with hundreds of thousands of litres now being used every week. Although a percentage of this material is recycled or disposed of through waste collection services, the major volume is generally flushed straight down sink wastes and drains directly into public sewers. Over time, these waste materials will coagulate into a solid mass that steadily builds up, trapping other solids in the drainage system to gradually restrict the flow. This problem is worse in towns and cities, where there is typically a far higher concentration of catering establishments, including fast food outlets, restaurants, schools and hospitals.

Although there is clearly defined legislation governing the disposal of fats, oils and greases from industrial scale food processing and production operations, the control of smaller catering businesses is less obvious. Prosecution can be in some instances be carried out under local bylaws or national legislation such as the Water Industry Act 1991, Water Resources Act 1991 and Building Regulation Part H1 (2. 21). In general, however, it is left to each business to take a responsible approach to the problem.

An effective solution is, however, relatively straightforward and involves a combination of good practice, sensible recycling or waste disposal and the use of appropriate technology. To meet the demand and help alleviate the problem, leading manufacturers, such as ACO Building Drainage, have developed an innovative range of advanced, reliable and easy to use grease separators, which allow fats, oils and greases to be separated from wastewater, and then safely passed to waste.

These devices offer a number of important advantages, both to catering establishments and to drainage engineers, as they can be supplied alongside existing services, with the potential for ongoing maintenance contracts.

In essence, this technology relies on the relative density differentials naturally present in kitchen waste water. While the density of fats, oils and greases vary from one product to the next, they will always be less dense than water and will float on the surface of the water within the separator unit. Similarly, solid particulates common to most cooking processes are typically denser than water and sink to the base of the separator. It is therefore possible to retain separated fats, oils, greases and solids within the body of the unit, while allowing a relatively clean wastewater stream to pass through the separator via a submerged outlet. Periodic maintenance or cleaning is then carried out to remove the entire contents of the separator, which is normally sent for processing at a sewage treatment plant by a specialist waste contractor.

In order for catering companies to realise the full benefits of this latest technology, it lays in the hands of the specifiers and installers to establish the size of grease separator required in relation to the application for which it is to be used. This can be determined according to the methodologies given in BS EN 1825 Part 2, which considers either the type of kitchen equipment in use or assesses throughput. As a result, it is essential for designers to know the nature and number of the kitchen appliances, for example how many sinks and dishwashers. If this information is unobtainable then the specifier must instead consider the establishment type, how many meals are produced each day and the number of hours the kitchen is operational each day, or in the case of abattoirs, the volume of meat produced.

Once the required size of grease separator has been established, specifiers need then to consider the type of grease separator to be installed; either for external ground installation or for free standing installation within the building. For example, ACO offers two types of below ground grease separators, both of which satisfy BS EN 1825 with Load Class D400 access covers to BS EN 124. The economical Liputec model features a separator body structure that is non-load bearing and where the cover load is borne by the surrounding structural detail. The ECO-FPI is a fully load bearing structure in its own right, significantly reducing installation time and cost.

Similarly, free standing grease separators come in a variety of formats to suit the application and project budget. In particular, this range includes split design models, which separate into three lightweight components, making them ideal for use in areas where access is limited, for example in basements, stairwells and narrow corridors. Designed and tested in accordance with BS EN 1825, these units are easy to transport and assemble, as well as being easy to maintain.

Finally, specifiers need to evaluate if there is a need for any ancillary equipment. The latest generation of grease separators offer increasing levels of sophistication, including notably a disposal pump to assist the disposal contractor remove waste where the separator is located more than 6m below street level, and various degrees of self cleaning using high pressure internal pumps.

It is clear that the growing trend for using of fats, oils and greases in recent years is placing a huge strain on the sewerage infrastructure. By specifying and installing the appropriate grease separator technology, combined with responsible practices, this problem can be overcome, protecting not only our environment but also many businesses in the catering and food process and production industries.

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