Lurking in darkness under our city’s streets is a silent and growing threat to human health. Cooking fats and grease tipped down the sink in homes and businesses are mixing with solids in our sewers and forming giant lumps of solid fat, sometimes the size of cars, sometimes hundreds of metres long. They cause a media frenzy when photos of them appear online, but in their most extreme form, ‘fatbergs’ can damage or block or sewers, causing serious disruption. Earlier this year a fatberg running the length of an entire sewer was found in Cheltenham, where it took eight hours to unblock. They’re a particular problem in older systems, such as the 1940s-era sewers th at had to be completely replaced when a vast, 10-tonne fatberg the size of a London bus led to the replacement of 100 feet of tunnels, costing Thames Water £400,000. Even that berg was smaller than the 15-tonne Kingston fatberg that resulted in the formation of Thames Water’s crack fatberg hit squad, a team of sewage treatment experts specialised in their removal. In practice, the removal of fat and grease deposits from the capital’s sewers relies on relatively basic techniques, blasting the solid waste with high-pressure hoses, and scraping off the remnants. “We clear a sewer blockage caused by fatbergs every seven-and-a-half minutes and spend more than Â£1m a month clearing them,” says Lawrence Gosden, head of wastewater at Thames Water. “Annually, there are around 366,000 sewer blockages in the UK,” he adds. “Eight times every hour, a Thames Water customer suffers a blockage caused by sewer abuse. As well as being costly in terms of money, there is also a human cost of these fatbergs, as we often have to close a road to dig down and clear them, often causing delays and inconveniences.” As destructive as they are, utility companies are beginning to take advantage of some surprising opportunities to be found by reprocessing fatbergs. At a site on England’s North-west coast, Argent Energy has started turning fatbergs from wastewater facilities around the country into a biodiesel. In a simplified version of the process the untreated fats, oils and greases – FOG – arrives at the plant, gets heated to separate oil and grease, has excess solids removed and becomes biodiesel with the addition of a few chemicals, polished off with distillation.
Independent 17th Aug 2017 read more »