Patent ID: 6387264
Filing Date: 2002-05-14
Classification: C02F,Y10S

Abstract:
A method for treating wastewater that generates a supernatant having a concentration of volatile fatty acids (VFAs) that fall within a specified range and a sludge that has specified percent total solids independent of VFA production, said method comprising the steps of:(a) providing a fermentation tank and a gravity thickener, operatively connected to said fermentation tank; (b) permitting primary sludge to flow continually or intermittently into said fermentation tank and permitting a portion of said wastewater to overflow said tank, thereby defining an overflow rate; (c) subjecting said fermentation tank to anaerobic conditions; (d) allowing said wastewater in said tank to stratify so that a sludge forms at the bottom of said tank; (e) continually pumping said sludge from the bottom of said fermentation tank so that each stratification level within said fermentation tank corresponds to a sludge residence time that in turn corresponds to a range of VFA concentrations; (f) combining overflow liquids from said fermentation tan with said sludge from said fermentation tank in said gravity thickener, permitting VFAs to be separated from said sludge and mixed into said overflow to form a supernatant rich in VFAs; and (g) setting the rate of said pumping of said sludge from said bottom of said fermentation tank to a proportion of said overflow rate, said proportion being set such that said supernatant has a concentration of VFAs that falls within said range of concentrations and so that said sludge has said percent total solids.