Comparative evaluation of sludge-bed anaerobic membrane bioreactor (SB-AnMBR) treating prehydrolysis liquor at mesophilic and thermophilic conditions

Dissolving pulp mill wastewater called prehydrolysis liquor (PHL) obtained from steam (@150-170°C) treatment of wood had a total chemical oxygen demand (COD) of approximately 100 g/L contains mainly sugars, furfural, lignin, and acetic acid, poses a considerable wastewater disposal problem. Replacement of the current energy intensive disposal method (evaporation and use of recovery boiler) is a requirement of dissolving pulp industry. The bioreactors were fed with PHL at organic loading rates (OLR) ranging from 0.8 to 5 kg-COD/m3-d to study the performance with respect to the COD removal, methane (bio-energy) production, effluent characteristics, and membrane fouling. Average COD removal of 91% and specific methane yield of 0.36 m3/kg-CODremoved/day were achieved during the pseudo-steady period of the continuous mesophilic operation at each loading rate. Whereas, in thermophilic conditions, methane yield of 0.38 m3/kg-CODremoved/day was observed. There was no sugar and furfural found in the effluent of the SB-AnMBR at both temperatures (35°C and 55°C) during the pseudo-steady period. High effluent COD can be attributed to lignin in effluent (0.2 to 1.6 g/L). Flat-sheet membranes used in the SB-AnMBRs did not show significant fouling based on monitoring of temporal variations in the trans-membrane pressure at a sustained flux of 0.1 m3/m2/d during the 550 days of the continuous operation.