Batch Mode of Anaerobic Digestion of Macroalgae and Bacterial Community Analysis

Abstract

Four sets of anaerobic batch reactors provided with two different macroalge Laminaria Japonica and Ulva pertusa were studied. To access how process performance and microbial community could be change with time in each reactor, the volatile fatty acids (VFAs) and methane production profiles with bacterial community shifts were investigated. In the anaerobic reactors with BES (2-bromoethanesulfonic acid) which is methanogenic inhibitor, the ratio of acetate to total VFAs presented 72% for L (L. japonica)-reactor and 56% for U (U. pertusa)- reactor. On the other hand, the ratio of propionate to total VFAs counted for 18% for L-reactor, and 32% for U-reactor, respectively.In the overall A.D reactors, the degradation of VFAs showed different profiles depends on the substrates. In the L-reactor, methane production was mainly originated from the rapid degradation of acetate, but in case of U-reactor, methane produced in twice when each acetate and propionate was consumed. Methane yields for L-reactor and U-reactor were 0.22 and 0.17 L/g VS add, respectively. Several band sequences were detected using DGGE analysis. Clostridium sp., Enterobacter sp. and Aeromonas sp. were commonly identified during the initial acidogenesis period in four sets of reactors. It means these groups might play an important role as predominat acidogens in acidogenesis of anaerobic fermentation using macroalgae. Desulfovibro vulgaris popularly known as sulfate-reducing bacteria (SRB) was isolated only in the U-reactors. It is assumed that the high portion of protein and the sulphated glucuronorhamnoxyloglycan in U. pertusa lead to appearance of this SRB which known to compete with methanogens. When compared DGGE band profiles and quantitative PCR results of anaerobic reactors with and without BES, there is no difference of the bacterial population in terms of quality between two types of reactors. However, 16S rRNA gene concentrations of bacteria were higher in the acidogenic reactors than overall A.D reactors. Therefore, it is suggested that the classic methanogenic inhibitor had an effect on the bacterial community qualitatively, not quantitatively.