Too good to waste?Reports that sludge from sewage plants is routinely used to fertilise edible crops have caused outrage. Is this simply a prudent use of so-called 'biosolids' or a grave threat to our health? Rose George investigates
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The Guardian, Friday 29 August 2008
Sewage treatment plant in London A sewage treatment plant in London. Jason Hawkes / Getty
It is my first and last day at sewage school. The premises are nothing much to look at, consisting of a Portakabin in the car park of Barston, a small sewage-treatment works near Birmingham. This classroom is one of five run by Severn Trent, one of the 10 utilities that supply clean drinking water and remove dirty water for the people of England and Wales. The education programme is fully funded by the utility in an attempt to reveal its vital job to a public that doesn't pay it mind. They think it's a good investment.
Today's class comes from a nearby primary school. After a brief trot through the water cycle and some green lessons - washing a car with a hosepipe uses nine litres of water a minute, children, so use buckets - the sewage pupils put on their wellies for the tour. First, the influent, brown water rushing in from the sewers, visible through a hole in the ground. Then the compactor that crunches up objects screened by grills. It's not moving, sir, they say, but it is, spitting out in slow-motion rags and pen caps and hundreds of the yellow sweetcorn kernels that humans can't digest, prized by picnicking birds.
Wastewater treatment is much-tinkered-with - 1,000 works will have 999 different processes, a worker tells me - but the basics are unchangeable. Solids are removed from sewage first by filtering and letting them sink. This is primary treatment. Secondary treatment involves micro-organisms, bolstered by added oxygen, that break down any organic content still in the wastewater. The bacteria-cleaned effluent...