Full-Scale investigation of the influence of flow equalization and prefermentation on nitrification

This article presents the findings on the effects of flow equalization and prefermentation on nitrification in a full-scale municipal plant. Existing primary clarifiers in one process train were modified for diurnal flow equalization and for a low-rate volatile fatty acid production. The performance of the biological process was compared with the parallel reference process train operated with conventional primary clarification. Only a few reports on the effects of equalization on nitrification have been published, but based on this limited knowledge, diurnal flow equalization was presumed to improve the nitrification performance. However, more constant flow conditions could not fully explain the improvements of autotrophic activity. The authors suggest that increased readily biodegradable organic matter played indirectly a role in nitrification performance. Moreover, stable flow conditions were reflected in improved sludge characteristics and offered, in addition to a levelling out of diurnal variations, a long-term buffer capacity against high hydraulic loadings.