Discharge of aniline to the environment must be controlled as aniline is toxic to aquatic life and also exerts additional oxygen demand due to nitrification reaction involved during its biodegradation. Organic carbonaceous removal by heterotrophs during aniline biodegradation releases NH4+ which is the substrate for autotrophic nitrifying bacteria. However, aniline is toxic to nitrifying bacteria and severely inhibits their activity. Accordingly, batch and continuous studies were conducted to assess the biodegradation of aniline and its inhibitory effect on nitrification. Synthetic wastewater was used as feed with aniline as sole carbon source for mixed microbial population.

Experiments were conducted at ambient temperatures of 30–32°C. An aerobic activated sludge Unit was operated at an HRT of about 13 hours and SRT of about 12 days. Biomass from aerobic activated sludge process treating domestic wastewater was acclimatized to synthetic wastewater Containing aniline. Removal efficiencies more than 95% were obtained for feed aniline concentrations upto 350 mg/l with insignificant inhibition of nitrification due to aniline. Ammonia oxidation rates of about 20–115 mgNH4N/l/d were observed.

Batch tests were carried out to test the inhibitory effects of high initial aniline concentrations on nitritication. Carbonaceous removal by heterotrophs proceeded rapidly within 4–6 hours with nitrification picking up as soon as aniline concentration dropped below 3–4 mg/l. For higher initial aniline concentration more than 250 mg/l, complete nitrification did not take place even after aniline Concentration dropped below 3–4 mg/l.