TMP wastewater treatment, including a biological high-efficiency compact reactor - Toxicity reduction and removal of extractives

Removal of extractable material in the effluent from an integrated newsprin t mill in a full-scale treatment plant with primary clarifier and activated sludge HCR (High-efficiency Compact Reactor) has been studied. Of the 193 mg/L identified lipophilic extractives (free and bound fatty acids, sterols and resin acids) in the TMP mill effluent, 95% were attached to particulat e material and 70% were removed by a primary clarifier. The lignan concentr ation in the effluent showed no reduction in this part of the treatment pla nt. After the primary clarifier the pH was adjusted from 5 to 7, giving an increase in the concentrations of the identified lipophilic extractives in both the colloidal and dissolved phases. The lignans and resin and fatty ac ids were removed by >99 % in the bioreactors, with 1.5 hours retention time s in each of the two reactors in series, beta-Sitosterol, the only sterol q uantified was removed by 96%. The calculated unidentified methyl tert-butyl ether (MTBE) extractable material was only removed by 37%, and the residua ls were found mainly in the dissolved phase. The resin acids were almost co mpletely biodegraded (98%), showing that resin acids in the dissolved, coll oidal and particulate phases of the effluent had sufficient accessibility t o the microorganisms in these reactors. For beta-sitosterol the removal mec hanisms were both biosorption (46%) and biodegradation/transformation (50%) . The acute toxicity of the wastewater, measured by the Microtox test, was completely removed by the biological treatment.