We don’t stop to think about what happens to the leftover cooking fat we tip down our kitchen sinks. But when it gets into the sewerage system it can create enormous blockages called ‘fatbergs’. They have become so common that a definition has been added to the Oxford English Dictionary.
Fatberg: ‘A very large mass of solid waste in a sewerage system, consisting especially of congealed fat and personal hygiene products that have been flushed down toilets’.
Argent Energy made the news when it volunteered to turn the largest fatberg ever found, into biofuel. A 250-metre long monster weighing 130 tonnes had to be dug out of an east London sewer in September 2017. Some of it was taken to Argent Energy’s Ellesmere Port plant in the UK where it was processed to biodiesel.
In the ISCC system, fatbergs are classed as ‘grease trap fat’, which is certifiable as a sustainable feedstock for biodiesel. ‘FOG’ – Fats, Oils and Grease, specifically originating in sewage systems and treatment plants, encompass fatbergs and are included in the same category.
Dickon Posnett, Director of Corporate Affairs at Argent Energy, says, “ A lot of waste fat ends up in sewers and gets carried to sewage treatment plants. We have invested extensively in new treatment plant to cope with this material, as it is a valuable source of renewable fuel. We are the only people in the UK with the facilities to convert the London fatberg into biodiesel, so we stepped in.”
The fatberg material was delivered by lorries to the Argent Energy plant, where solids and liquids were separated out and then the congealed fat was heated and further cleaned before being turned into FAME (fatty acid methyl ester), a form of biodiesel which can be blended with mineral oil diesel. The yield of biodiesel from the fatberg is normally between 25% and 40% of the weight. The biodiesel saves over 80% of greenhouse gas emissions compared with normal diesel.
Argent energy has been certified with ISCC since 2011 for conversion of all types of waste oils to biodiesel. Dickon again “ISCC, with its clear approach to waste materials, allows us to show customers that our biofuels are sustainably produced with audited greenhouse gas savings.”
The new Argent Energy plant will be able to produce up to 90 million litres (80,000 tonnes) of biodiesel from FOG a year when it is fully operational. This compares with the 700 million litres of biodiesel blended into UK road transport fuel in the year 2016/17. Posnett estimates there could be between 300,000 and 400,000 tonnes of grease and fat in the UK’s sewers and water treatment works each year. So there is a huge untapped potential for renewable transport fuel from this source alone.
Innovative technology was developed to cope with the impurities within the FOG. Argent Energy also has the only sites in the UK to use continuous distillation technology to ensure that the quality of the final biodiesel meets European and British Standards.
Flushed with success from the fatberg, the company is on the lookout for more hard-to-treat wastes to turn into biofuel. In the past they have used waste mayonnaise, soup and ghee. Their latest endeavour is producing biofuel from waste coffee grounds from shops and restaurants. As Dickon says, “Coffee grounds oil bring its own challenges but at least it smells good”.
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