ORGANIC AND AMMONIUM NITROGEN AND OXYGEN IN RELATION TO GRANULAR SLUDGE GROWTH IN LAB-SCALE UASB REACTORS

Laboratory studies of in-reactor granular-sludge yield (Y-gram) were c arried out to investigate the effect of substrates rich in proteins. B oth lab-scale upflow anaerobic sludge blanket (UASB) and shake-flask s ystems were used to monitor the behaviour of the sludge. Influent base d on molasses with a COD to N ratio of 100:2.5-3.0 gave good Y; increa sing substitution of the carbohydrate COD by protein COD resulted in a deterioration of the sludge characteristics. The negative effects app ear to be related to the protein rather than to the NH4+ formed. Of th e various environmental parameters examined, the surface tension of th e mixed liquor was the main deviating factor. At a proper range of oxy genation i.e., by means of monitoring of both the input COD to oxygen ratio (gCOD gO(2)(-1)) and the daily oxygen loading rate (mgO(2) OVSS- 1.d(-1)), the UASB reactors treating the nitrogen-rich wastewater show ed enhanced Y-gran with only a minor reduction in methanogenesis. A ra nge of working conditions in which this principle can be applied to de crease fluffy growth to the advantage of granular increase is proposed .