The effect of pre-hydrolysis of D-stage filtrate on the biotreatability of chlorinated organic compounds in bleached kraft mill effluents

The influence of pre-hydrolysis of D-stage filtrate on the biotreatability of bleached kraft mill effluent was investigated at the bench scale using four continuous aerated “lagoons” operated in parallel. In comparison to non-hydrolyzed effluent, pre-hydrolysis of D-stage filtrate at pH 11 and 60°C for an hour reduced the AOX inlet to the treatment system by 40% and the outlet AOX discharge after biological treatment by 13%. Overall, pre-hydrolysis followed by biological treatment resulted in a 63% AOX removal, which was significantly higher, at the 95% confidence level, than the 58% removal achieved by biological treatment alone. COD and BOD5 removals for both feeds were 45 and 99%, respectively, and were not significantly affected by the pretreatment. Studies on the pre-hydrolysis effect on known non-biodegradable organochlorine model compounds showed that pre-hydrolysis was effective in improving the biodegradability of a monomeric model, but not the dimeric model compound.