Abstract The pulp and paper industry (PPI) produces various lignocellulosic wastes, including paper sludge, which is rich in cellulose and suitable for biofuel production. Anaerobic digestion (AD) has emerged as a promising treatment technology due to its environmental and economic benefits. Biochemical methane production (BMP) assays were performed at different food-to-microorganisms (F/M) ratios: 1.0, 1.5, 2.0, 2.5, and a control (Inoculum). Among the four different F/M ratios, F/M 1.5 achieved the highest methane yield of 272 mL CH 4 /g VS, followed by 2.0 > 1.0 > 2.5 with methane yield of 250 > 247 > 227 mL CH 4 /g VS over a period of 42 days. The effect of the F/M ratio on specific methanogenic activity (SMA) was evaluated to support the interpretation of BMP assay results. Further effects of substrate biodegradability and methane production rate were also evaluated in a kinetic study using two simplified models, among them the modified Gompertz model provided the best fit (R 2 = 0.997) to the experimental data. Statistical analysis using one-way ANOVA revealed that the F/M ratio significantly affected methane yield (p < 0.05). Fourier Transform Infrared Spectroscopy (FTIR) analysis confirmed the presence of active organic functional groups, which highlights the lignocellulosic degradation pattern before and after digestion. A phytotoxicity assay using Vigna radiata L. (mung bean) revealed a concentration-dependent decline in seed germination, shoot and root length, and biomass after digestion relative to the control. This study uniquely integrates F/M ratio optimization, biodegradability assessment, kinetic modeling, and statistical analysis to provide a complete understanding of methane production from PPI sludge. It also links process performance with environmental safety through phytotoxicity evaluation, offering a comprehensive waste-to-energy framework.
Haq et al. (Mon,) studied this question.