Comparative Study of Biogas Production from Cassava Pulp in a Sequencing Batch Reactor and a Continuous Stirred Tank Reactor

Abstract

Abstract Thai cassava starch industry generates solid waste or pulp approximately of 9.5 Mt/y (with a moisture content of 70–80%). Biogas production technology has been introduced for several decades in Thailand. However, the implementation of biogas production using cassava pulp as a feedstock is still limited due to the complex lignocellulosic structure, which diminishes hydrolysis. This work investigated biogas production from cassava pulp in a 50-m3 pilot-scale sequencing batch reactor (SBR) and continuous stirred tank reactor (CSTR). Both reactors were fed with cassava pulp, under the organic loading rate (OLR) of 8 kg-COD/m3-d and the average hydraulic retention time (HRT) of 7 d. Under the batch operation, more than 60% of the starch content was utilized within the first three days. The SBR achieved methane production of 1.87 m3-CH4/ton-pulpfresh-d and acids production of 2.19 kg-TVA/ton-pulpfresh-d while the CSTR had methane production of 0.22 m3-CH4/ton-pulpfresh-d and acids production of 7.07 kg-TVA/ton-pulpfresh-d. The methane production was higher in the SBR because the settling process helped microorganisms remain in the system. In CSTR, acids rather than methane were produced due to the washout of methanogenic microorganisms. This work revealed that the SBR yielded higher biogas production, while the CSTR produced intermediate acids, which could be supplied to the biochemical industry.