Digestion of sewage sludge

摘要

Collected sewage passes through a preliminary treatment stage provided by an in-line pumping station 4, a treatment works pumping station 5, a screening unit 6 and a grit removal unit 7. The sewage then passes through a primary treatment stage provided by a settlement tank 10, as well as a secondary treatment stage, provided by a biological filtration unit 11 and a humus tank unit 13. Sludge from the primary and secondary treatment stages is collected by a digester 27, where the collected sludge is raised in temperature by heat input provided by a heat pump unit 40, using a duct 44. The heat, which is obtained from a warmer source, namely a solar heat-harvesting unit 42, causes thermophillic action to take place within the body of sludge 36, which action disinfects the sludge. Methane gas produced by the thermophillic action is used to drive the heat pump unit 40, by way of duct 43 and gas engine 41.