Evaluation of recycled paper mill effluent digestion in a modified anaerobic hybrid baffled (MAHB) reactor: reactor performance & kinetic studies

Recycled paper mill effluent (RPME) consists of various organic and inorganic compounds. In this study, modified anaerobic hybrid baffled (MAHB) bioreactor has been successfully used to anaerobically digest RPME. The anaerobic digestion was investigated in relation to methane production rate, lignin removal, and chemical oxygen demand (COD) removal, with respect to organic loading rate (OLR) and hydraulic retention time (HRT). The analysis using kinetic study was carried out under mesophilic conditions (37 ± 2 °C) and influent COD concentrations (1000-4000 mg L^-1), to prove its practicability towards RPME treatment. First-order kinetic model was used to clarify the behavior of RPME anaerobic digestion under different OLRs (0.14-4.00 g COD L^-1 d^-1) and HRT (1-7 d). The result shows that the highest COD removal efficiency and methane production rate were recorded to be 98.07% and 2.2223 L CH₄ d^-1, respectively. This result was further validated by evaluating the biokinetic coefficients (reaction rate constant (k) and maximum biogas production (y_m)), which gave values of k = 0.57 d^-1 and y_m = 0.331 L d^-1. This kinetic data concludes that MAHB presented satisfactory performance towards COD removal with relatively high methane production, which can be further utilized as on-site energy supply.