Effect of recycle ratio on methanogenic anaerobic digestion of palm oil mill effluent (POME) in a stirred tank reactor assisted by ultrafiltration membrane into biogas in transition conditions

Abstract

The purpose of this study is to increase the conversion of biogas production using digester type CSTR by recycling the effluent through ultrafiltration membrane at transition conditions (45°C). In this research was investigated the effect of recycle ratio on the pH profile, alkalinity, production, and biogas composition produced. Initially, the suitable loading up was determined by varying HRT at 25, 15, 10, and 6 days in 2 L CSTR with agitation rate 250 rpm, pH 7 ± 0.2, and at temperature of 45°C. Furthermore, the effect of the recycle ratio was determined by varying the recycle ratio, i.e. 0, 15, and 25%. Analysis of total solids (TS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), and chemical oxygen demand (COD) were carried out to study the changes of organic compounds that were converted into biogas. Gas analysis is also carried out by measuring the volume and composition of the biogas produced. The highest total biogas production was achieved at 25% recycle ratio of 33.15 x 10-2 L/g.VS.day, with the composition of methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S) were 79; 19; and 0.006% respectively.