The Acid-Phase Anaerobic Digestion of Primary Sludge and Its Role in the Biological Phosphorus Removal Process

Abstract

Abstract The effects of certain operational and environmental parameters on the acid-phase anaerobic digestion of primary sludge have been investigated using a series of bench-scale, continuous-flow experiments. Short-chain volatile fatty acids (VFA), the main products of the process, are preferred substrates for the bacteria involved in the biological removal of phosphorus. Results show that the net volatile fatty acid generation improves with an increase in hydraulic retention time (up to 12 hours) as well as in solids retention time. Although acid production is not affected by a decrease in pH from 5.1 to 4.5, the production is significantly lower (25 to 30%) at pH of about 6.0. The use of different feed sources influences to some extent the amount of product formation. Moreover, lipid and carbohydrate degradation patterns are dependent on reactor configuration, whereas protein utilization appears to be independent of the reactor regime. The amount of VFA produced, in most cases, is high enough to support biological phosphorus removal processes.