Inhibitory effect of azo dyes on ammoni-n oxidation by nitrtosomonas

The potential inhibitory effect of five azo dyes on ammonia-N oxidation was investigated. Ammonia-N oxidation was inhibited by the dyes: Mordant Black 17, Direct Red 2, Reactive Red 4, Reactive Yellow 2 and Direct Blue 14 at the concentrations (0.01mgL-1 to 100mgL-1) tested. Inhibition of ammonia-N oxidation increased with increasing concentration of the toxicants. The EC50 values obtained were; 0.208 (Mordant Black 17), 1.813 (Direct Red 2), 7.926 (Reactive Yellow 2), 50.174 (Direct Blue 14) and 332.208 (Reactive Red 4). The results obtained were attributed to any/or all of the following factors: molecular size, impurities in the toxicants and metallic ions. The potential adverse ecological impact of the azo dyes on the productivity of ecosystems is discussed.