the dumping of sludge in the sea ended in 1998, following a european community directive, and the remaining sludge boats were sold. the sludge pipeline was used to transfer sludge to shell green, near widnes, where it is turned into ash, or used in agriculture. parts of the old secondary beds became the davyhulme millennium nature reserve in 2000, and low-profile geodesic domes were built over the primary settlement tanks in 2003, as part of a £20 million odour control scheme. the works continues to be innovative. in 2013, the world's largest thermal hydrolysis plant was commissioned. sludge is heated to 165 degrees celsius under pressure, and the pressure is then released in a flash tank. this process breaks up complex organic substances, allowing it to be digested more easily. large volumes of methane are a by-product, which enables the site to be self-sufficient for gas and electricity. a £200 million upgrade to the second activated sludge plant began in 2014, and is expected to be completed in 2018. the works now handles sewage for a population of 1.2 million people, most of which is water. income is generated from the processing of trade effluent, which accounts for 70 percent of the organic load. its output forms around 40 percent of the ship canal below barton locks.