Enhanced Biomethane Recovery From Source‐Separated Cow Urine via Co‐Digestion With Waste Paper

ABSTRACT In this study, the biogas potential of source‐separated cow urine (CU) was evaluated through anaerobic co‐digestion with waste paper (WP) under mesophilic conditions (37°C ± 1°C) in batch mode. Anaerobic digestion performance was assessed in terms of biogas‐biomethane yields, total (TS) and volatile solids (VS) removal, pH, volatile fatty acids (VFA), soluble chemical oxygen demand (sCOD), and carbon‐to‐nitrogen (C/N) ratios and compared with WP mono‐digestion. Five different blends were prepared in duplicate with an inoculum‐to‐substrate ratio of 1:1. The proportions were: 100% WP (CU 0 control), 90% WP + 10% CU (CU 10 ), 80% WP + 20% CU (CU 20 ), 70% WP + 30% CU (CU 30 ), and 50% WP + 50% CU (CU 50 ) operated over a 66‐day hydraulic retention time. The CU 50 bioreactor showed the highest efficiency, achieving 86% TS and 87% VS removal, and yielding 92.5% and 150% higher biogas and biomethane yields, respectively, compared with the control. The pH values and VFA concentrations of the bioreactors ranged from 5.395 to 7.83 and 1615.46 to 7280.02 mg L −1 , respectively. Effluent sCOD values in CU 30 , CU 20 , CU 10 , and CU 0 increased by 80.05, 111.07, 154.41, and 293.94 mg sCOD g −1 VS, respectively, relative to influent values, whereas CU 50 achieved 47.2 mg sCOD g −1 VS removal. Comparison of C/N ratios showed a 14.35% decrease in the control, whereas CU 50 achieved an optimal C/N ratio of 25.1312, facilitating biogas production. Co‐digesting source‐separated cow urine with waste office paper effectively enhanced biogas production.