TOXICITY REDUCTION OF WASTEWATERS BY ACIDOGENIC BIOTREATMENT PROCESS

Abstract

A laboratory investigation was carried out to reduce the toxicity of a synthetic industrial wastewater containing organic priority pollutants by an acidogenic culture. The effects of environmental pnrnrnetcrs such as SRT and pH were studied to obtain an enriched acidogenic culture. The effect of an easily degradable compound on the degradation of 2-nitroaniline was observed at different F/M ratios. The stimulatory and inhibitory effects of 2-, 3-, and 4-nitroaniline and nitrophenol were studied by serum bottle tests. An extended exposure period test was conducted for these toxic compounds at 50 mg/L and 200 mg/L.

The investigation was carried out in a SBR system which is a fill-and-draw process. Two bench scale reactors were operated at 35° C. Anaerobic sludge was collected from the Ulu Pandan Sewage Treatment Plant and screened using a 600 Lm sieve. The HRT was 24 hours and the targeted MLVSS was 4000 rng/L and 8000 mg/L for non-toxic and toxic reactors respectively.

SRT and pH were varied from 6 days, 4 days to 2 clays, and 6.0, 5.5, 5.0 to 4.0, respectively to obtain an enriched aciclogenic culture. A viable SRT and pH for suppression of rnethanogenic bacteria were 4 days and 4.0 respectively. Operation of the acidogenic reactors under these conditions resulted in the highest acid production which offered a favourable substrate to a downstream treatment process such as a methanogenic or aerobic reactor. F/M ratios such as 2.2, 1.5 and 1.0 did not show significant effect on the degradation of 15 mg/L 2-nitroaniline. Removal efficiencies of 88%, 84% and 95% were achieved by the enriched acidogenic culture at F/M ratios of 2.2, 1.5 and 1.0 respectively.

Moderate inhibition in the enriched acidogenic cultures was observed at 200 mg/L of either toxicants. Toxicity of the 2-, 3-, 4-nitroaniline and nitrophenol was in the order: 3-nitroaniIine>4-nitroanniline>2-nitroaniline and 4-nitrophenol>2-nitrophenol>3-nitrophenol. It was observed during the extended exposure period test that nitrophenols required less time for acclimation than nitroanilines. 3-nitroaniline was found more toxic than 2-and 4-nitrnaniline in ncidogenic enriched culture.