Development of a horizontal reactor with radial agitation to synthesize bio-methane from biomass waste and domestic sewage sludge

Abstract

Aiming to produce clean energy from biomass, we devised an anaerobic horizontal reactor for the production of biomethane from an innovative combination of agricultural and livestock residues with domestic sewage sludge. Differently from conventional reactors, the horizontal reactor was designed with a radial agitator with finned rectangular blades and a gas chamber to ease CH4 capture. Moisture content in biomass was nearly 90% in acclimation and co-digestion processes. In addition, the pH varied as the substrate was added from 8.5 to 7.55 (fruit and vegetable residue pH was 4.80) and during the digestion process the pH dropped to 5.70 by a Hydraulic Retention Time of 30 days. The reaction system had alkalinized without the use of chemicals, at a pH of 7.60 by the end of the experiment. The acclimated inoculum was processed for a period of 120 days, and produced 254.35 NL of biogas in the anaerobic horizontal reactor. Moreover, the reactor produced 965.55 NL of biogas with the mixture of Acclimated Inoculum, Solid Organic Residue and Domestic Sewage Sludge. The maximum methane concentration of 86% was observed after 73 days, whilst the final methane content was 82% (after 120 days). The reaction process resulted in a biogas production of 0.47 Nm3/kgVS and 0.39 Nm3CH4/kgVS (normalized cubic meters of methane per kilogram of volatile solids). In addition, the net biogas production of the horizontal reactor was 711.20 NL with a rate of 27.59 (NL/day). Finally, a reduction in H2S concentration was observed after the methane concentration had reached about 65%.