PRIMARY SLUDGE HYDROLYSIS FOR BIOLOGICAL NUTRIENT REMOVAL

Primary sludge hydrolysis can enrich primary effluent with the soluble organics which in turn can be a valuable carbon source to subsequent nutrient removal processes. By controlling hydraulic retention time an d temperature it is possible to confine the anaerobic digestion of the primary sludge to the acidogenic and acetogenic phase (hydrolysis/fer mentation process), and take advantage of the soluble organics produce d. This paper presents the results of a research involving bench and p ilot scale experiments related to primary sludge hydrolysis. The pilot scale sedimentation tank (4.10 m in diameter, 3.20 m in depth) operat ed over an expended period of 21 months as a conventional clarifier an d following this as a fermenter unit employing sludge recirculation. P arallel to the pilot scale experiments, several batch and continuous f low bench scale experiments were conducted in order to determine the f actors controlling the production of soluble organics and the effect o f the tatter on the denitrification process. The conclusions drawn wer e that a) a soluble COD production of the order of 5-6% in terms of sl udge TCOD can be expected in a batch fermenter operating with HRT cong ruent to 2 days at T less than or equal to 20 degrees C, b) in a conti nuous flow fermenter, combinations of T > 20 degrees C and SRT > 2 sho uld be applied in order to achieve a production of the order of 10%, c ) significant soluble carbon production can be achieved in primary sed imentation tanks (over 30% in terms of influent SCOD) when relatively increased SRTs (4 to 5 days) in combination with sludge recirculation are employed, under T > 22 degrees C, and d) increased denitrification performance of the order of 9 mgNOx/g MLSS.hr, can be achieved with h ydrolysate as a carbon source. Copyright (C) 1996 IAWQ.