Abstract: A method for treating wastewater that generates a supernatant having a concentration of volatile fatty acids (VFAs) that falls within a specified range and a sludge that has percent total solids. The method includes the steps of providing a fermentation tank and a gravity thickener, operatively connected to the fermentation tank. The wastewater is permitted to flow continually or intermittently into the fermentation tank and a portion of the wastewater overflows the fermentation tank, thereby defining an overflow rate. The fermentation tank is subjected to anaerobic conditions and the wastewater in the tank is permitted to stratify so that sludge forms at the bottom of the tank. In addition the sludge is continually pumped from the bottom of the fermentation tank so that each stratification level within the fermentation tank corresponds to a sludge residence time that in turn corresponds to a range of VFA concentrations.