Effects of dilution and fungal pretreatment on anaerobic biodegradability of oxygen delignification process spent liquor

The effects of several pretreatment techniques, including dilution, fungal pretreatment and addition of hydrogen peroxide on the enhancement of anaero bic biodegradability of spent liquor (SL) of the oxygen delignification pro cess of recycled fibers, were evaluated. A 14% COD removal efficiency and a 37% acidification were obtained by the untreated effluent, indicating its low degree of biodegradability. After pretreatment, the efficiency of COD r emoval and the overall yield of methane production were increased by 24% to 246% and by 26% to 396%, respectively, compared to the untreated liquor. T he acidification of spent liquor also increased to more than 70% following the pretreatment. Kinetics analysis of methane production and COD removal i mplied the production of inhibitory metabolites during the anaerobic biodeg radation. The optimal dilution factor for the spent liquor sample under stu dy, to reduce toxicity while maximizing the specific rates of COD removal a nd methane production, was predicted to be less than five times.