METHOD OF ANAEROBIC DIGESTION OF SEWAGE SLUDGE

摘要

The present invention relates to a method of anaerobic digestion of sewage sludge, comprising the steps of subjecting surplus sludge to preliminary heat treatment at 60 DEG C or higher, dewatering the surplus sludge to make dewatered sludge of 10 to 25 % by weight, mixing the dewatered sludge with digested sludge which is taken out from a methane fermentation vessel of dewatered sludge, and supplying the resulting mixture to the methane fermentation vessel of dewatered sludge while discarding digested sludge whose amount is equal to that of the dewatered sludge supplied. According to the invention, the sewage sludge containing a large quantity of surplus sludge is subjected to preliminary heat treatment, and then the heat-treated sludge is dewatered to permit a nitrogenous component to be transferred to eliminated water whereby the nitrogenous component in the dewatered sludge can be reduced. The resulting dewatered sludge can stably undergo methane fermentation even at a high concentration of 10 to 25% by weight.