FEASIBILITY OF USING PRIMARY-SLUDGE MESOPHILIC HYDROLYSIS FOR BIOLOGICAL, REMOVAL OF NITROGEN AND PHOSPHORUS FROM WASTE-WATER

This work was suggested by the general lack of information regarding p ractical design aspects of a process widely studied at both theoretica l and experimental levels, primary-sludge hydrolysis. The availability of sufficient amounts of readily biodegradable organic substrates is a crucial aspect of biological nutrient-removal processes. These subst rates can be provided to biomasses either by dosing chemicals, or by e xploiting internal carbon sources of the system. Hydrolysis allows for the conversion of particulate and soluble, slowly degradable fraction s of primary sludge into readily biodegradable substrates, such as sho rt-chain fatty acids. In order to evaluate the technical and economica l feasibility of the process under mesophilic conditions, the general case of a medium-size wastewater treatment plant (100 000 PE) was cons idered. Given a typical domestic savage, the production of readily bio degradable COD (RBCOD) via primary sludge hydrolysis was assessed unde r two different conditions. The effects of hydrolysate addition on nut rient removal efficiencies were also evaluated. Results show potential substrate productions of about 250-600 kgRBCOD day(-1) depending on p rocess conditions. Denitrification efficiency after addition of this i nternal carbon source was found to increase by 4-10% with respect to t he influent total nitrogen. Cost is competitive with respect to curren t Italian costs for reagents.