DESIGN CONSIDERATIONS ON PRIMARY SLUDGE HYDROLYSIS UNDER PSYCHROPHILIC CONDITIONS

Wastewater readily-biodegradable COD concentration is a critical param eter affecting biological nutrient removal efficiencies. Primary sludg e hydrolysis has been recognized as a viable alternative to increase s uspended solids degradability and provide biomasses with an extra load of available substrate. However, fermentation performance strongly de pends on both feed sludge characteristics and process conditions. The aim of this paper is to evaluate the applicability of the process to r eal wastewater treatment plants operating under psychrophilic conditio ns. After a short review of previous research, some results of an expe rimental work are reported in order to explain some of the assumptions made. Then, a simple design procedure for primary fermentation system s is outlined and applied to a general situation. Results indicate tha t primary sludge hydrolysis at low temperatures (16-20 degrees C) and recirculation of the separated liquid supernatant allows for little im provements in denitrification efficiencies. Maximum increase in nitrat e reduction was estimated to be less than 3% as referred to the total influent nitrogen.