Upgrading upflow anaerobic sludge blanket (UASB) reactors with rice straw biochar: a smart pathway for rural sanitation, bioenergy recovery& agricultural reuse

Abstract

Rural sanitation in Egypt faces critical challenges due to the high costs associated with conventional wastewater treatment systems. This study explores a low-cost, sustainable solution by integrating rice straw biochar, a locally available agricultural byproduct, into Upflow Anaerobic Sludge Blanket (UASB) reactors. Two pilot-scale reactors were operated at the Faculty of Veterinary Medicine, Suez Canal University: a standard UASB (R4) and a modified UASB (R3) amended with 2 g L⁻¹ of rice straw biochar. Both systems treated buffalo cattle shed wastewater under identical conditions. The biochar-amended reactor (R3) significantly outperformed the conventional system, improving chemical oxygen demand (COD) removal from 79.9% to 86.0%, total suspended solids (TSS) removal from 74.0% to 81.6%, color removal from 72.7% to 81.8%, and turbidity from 75.7% to 81.9%. Biogas production also increased substantially, from 800 mL per day to 1500 mL per day, achieving a biogas yield of 0.050 L per g COD removed—an 80% improvement over the control. These enhancements are attributed to biochar's conductive and porous structure, which promotes microbial colonization and efficient electron transfer during anaerobic digestion. The study further demonstrates the agricultural reuse potential of the treated effluent, showing positive impacts on the growth of drought-tolerant plants and improvements in soil fertility. Rice straw biochar serves as a sustainable, locally sourced alternative to synthetic additives, aligning with circular economy principles. This integrated approach addresses sanitation, renewable energy production, and agricultural reuse, contributing directly to UN Sustainable Development Goals 6 (clean water), 7 (clean energy), 12 (responsible consumption), and 13 (climate action).