The continuous anaerobic treatment of pulping wastewaters

The anaerobic treatability of thermomechanical pulping (TMP) effluents and soda pulping liquors was evaluated in this study. Continuous experiments were conducted in laboratory scale UASB reactors inoculated with anaerobic granular sludge at 30±2°C. TMP wastewaters were found highly suitable for anaerobic treatment. The application of high organic loadings (31 g COD·l^-1·d^-1) was feasible by the end of the continuous experiment with TMP wastewaters, with 68 and 98%, total COD and blodegradable COD elimination efficiencies, respectively. Unlike TMP effluents, soda pulping wastewaters were highly inhibitory to methanogenic bacteria and they contained important fractions of recalcitrant organic matter. Wood resin constituents were shown to be responsible for most of the methanogenic inhibition in these wastewaters. Nonetheless, anaerobic wastewater treatment was feasible for removing the biodegradable substrate in soda pulping wastewaters if the wastewaters were diluted to subtoxic levels or detoxified by pretreatment with the adsorbent Amberlite XAD-2 prior to biological treatment. Low COD removal efficiencies were observed during the continuous experiment (45 to 50%) with soda pulping liquors, due to the high amounts of recalcitrant lignin in these wastewaters. The elimination of UV280 absorbance (15 to 20%) indicated partial removal of some lignin components by anaerobic treatment. The lignic fraction removed or biotransformed anaerobically corresponded to low molecular weight lignin derivatives as confirmed by gel chromatography results.