INCREASING SUBSTRATE FOR POLYPHOSPHATE-ACCUMULATING BACTERIA IN MUNICIPAL WASTE-WATER THROUGH HYDROLYSIS AND FERMENTATION OF SLUDGE IN PRIMARY CLARIFIERS

The possibility of improving enhanced biological phosphorus removal (E BPR) by increasing the level of substrate for biological polyphosphate -accumulating bacteria in influent wastewater, achieved through enhanc ed hydrolysis and fermentation of primary sludge in the primary clarif iers, was studied at a Cull-scale University of Cape Town plant for mo re than 1 year. The sludge level in the clarifiers was increased to cr eate anaerobic conditions and to increase the solids retention time in the clarifiers. Recirculation of sludge from the bottom to the top of the clarifiers was begun to wash out the fermentation products formed in the sludge phase into the water leaving the clarifiers. The perfor mance of the EBPR plant improved considerably after enhanced hydrolysi s and fermentation were established in the primary clarifier. Daily an alyses at the treatment plant and laboratory-scale fermentation experi ments on sludge from the clarifiers showed that the soluble chemical o xygen demand (GOD) in the wastewater increased by up to 10 mg COD/L. M easurements of volatile fatty acid potential (VFA-potential) yielded a n increase of 5 to 10 mg/L VFA-COD. Long-term fermentations in the lab oratory showed that another 15 to 20 mg/L of VFA-COD could be derived from the sludge, should the hydrolysis and fermentation be prolonged a nd optimized; if applied to a full-scale wastewater treatment plant, t his process would require the use of a separate reactor.