Anaerobic treatment of highly concentrated aniline wastewater using packed-bed biofilm reactor

The performance of packed-bed biofilm reactor (PBBR) with self-floating bio-carriers was investigated to treat highly concentrated organic nitrogenous aniline wastewater with a COD value as high as 24,000 mg/L. With 45 vol% of carrier charge inside the reactor, the aniline wastewater can be effectively treated with 94% of COD removal efficiency at a low organic loading rate (OLR) of 0.9 kg COD/(m3 d). The removal efficiency decreased gradually down to 75% when OLR increased to 12.27 kg COD/(m3 d) that corresponded to 1 day of HRT. Separate tests with biofilm alone showed that the conversion contribution of the biofilm was about half of the overall COD conversion by the biofilm plus sludge system at the same OLRs of 3–4 kg COD/(m3 d), and that the biofilm had higher activity than suspended sludge. Ammonium released from decomposed aniline was increased gradually from 500 to 1700 mg/L with the OLR increase from 0.9 to 12.27 kg COD/(m3 d), which resulted in inhibitory effect to the microorganism due to the toxicity of free ammonia. Batch anaerobic toxicity tests showed that the biofilm was less sensitive to toxic compounds than suspended sludge and could tolerate higher concentration of free ammonia.