A Complete System for Renewable Utilization of Cassava to Biohydrogen Coupled with Biomethane as Zero-Waste Management

Abstract

A novel system of a two-phase bioenergy production was successful in producing pure H2 with a complete utilization of cassava and separately obtained CH4 as a value added product. The system composed of two sequential anaerobic processes. The first process for H2 was performed in a 6.0 L-patented photobioreactor containing 10 g/L cassava starch provided electron donor for Rubrivivax gelatinosus SB24. The biogas was proved to compose of 100% H2. High yield of H2 at 11.0 L was produced in 10 days at the rate of production 15.8 mL/L culture/h. Starch was 97% utilized with 192 mL H2/g substrate H2. The second process in a 6.0 L acetogenesis-methanogenesis reactor aimed to further utilize the suspended wastewater of the former reactor. Successful conditions for operation were when a loading rate was 0.73 L every 4 days at a hydraulic retention time 30 days. Organic loading rate was 1,650 g×COD/L/4 days. Within 3.5 months 97% COD was reduced and 99% COD was removed after 6 months which eliminated 94 and 99% protein and starch, respectively. The condition was bufferized and stable, resulted continuous production of ignitable methane of 4 L/4 days for 14 months. Effluent consisted clear solution with low COD and sediment remained N, P and K 77-105, 672-695 and 688-782 mg/L, respectively. Properties of the sediment suggested further usable as fertilizer or soil amendment. The waste of the system could be managed to be zero.