NITRIFICATION INHIBITION AT LOW TEMPERATURE BY THE AZO DYE ACID BLACK 1

A municipal wastewater treatment plant (WWTP) receiving industrial dyeing discharge containing acid black 1 (AB1) failed to meet discharge limits, especially during the winter. Dyeing discharge was mixed with domestic sewage in volumetric ratios reflecting the range received by the WWTP and fed to sequencing batch reactors at 22°C and 7°C. Analysis of the various nitrogen species revealed complete nitrification failure at 7°C with more rapid nitrification failure as the dye concentration increased; slight nitrification inhibition occurred at 22°C. Dye-bearing wastewater also reduced COD removal at 7°C and 22°C and increased effluent TSS at 7°C. Activated sludge quality at 7°C deteriorated, as indicated by excessive foaming and the presence of filamentous bacteria and by decreased endogenous and exogenous oxygen uptake. Decreasing AB1 loading led to partial nitrification recovery. Eliminating the dye-bearing discharge to the full-scale WWTP resulted in improved performance bringing the WWTP into compliance with discharge limits.