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Biological pretreatment enhances biogas production in the anaerobic digestion of pulp and paper sludge

High efficient resource recovery from pulp and paper sludge (PPS) has been the focus of attention. The objective of this research was to develop a bio-pretreatment process prior to anaerobic digestion of PPS to improve the methane productivity. Active and inactive mushroom compost extracts (MCE) were used for pretreating PPS, followed by anaerobic digestion with monosodium glutamate waste liquor (MGWL). Laboratory-scale experiments were carried out in completely mixed bioreactors, 1-L capacity with 700 ml useful capacity. Optimal amount of active MCE for organics’ solubilization in the step of pretreatment was 250 A.U./gVS sludge. Under this condition, the PPS floc structure was well disrupted, resulting in void rate and fibre size diminishment after pretreatment. In addition, SCOD and VS removal were found to be 56% and 43.6%, respectively, after anaerobic digestion, being the peak value of VFA concentration determined as 1198 mg acetic acid L-1. The anaerobic digestion efficiency of PPS with and without pretreatment was evaluated. The highest methane yield under optimal pretreatment conditions was 0.23 m3 CH 4/kgVSadd, being 134.2% of the control. The results indicated that MCE bio-pretreatment could be a cost-effective and environmentally sound method for producing methane from PPS.