Effects of temperature, light, coexistent microbes, and dissolved matter on the growth of cyanobacteria Aphanothece clathrata and Microcystis wesenbergii were discussed using a batch incubation system in this research for microbial biomass production in wastewater. As a result, water temperature in the effluents from the municipal wastewater treatment plants in Tokyo was suitable for the growth of these cyanobacteria, though preheating of wastewater may be required for M. wesenbergii in winter. The dissolved matter in the treated wastewater did not affect the growth of A. clathrata and enhanced the growth of M. wesenbergii. However, the microbes in the treated wastewater attacked the cyanobacteria and inhibited their growth. Therefore, pretreatment of microbes might be required for biomass production in the treated wastewater. The maximum methane production potentials of A. clathrata and M. wesenbergii in the treated wastewater were estimated to be 13.5 and 2.12 L-CH4•m-2•day-1, respectively, when the depth of the bioreactor was set at 4.8 m for A. clathrata and 0.7 m for M. wesenbergii. The potential of A. clathrata was higher than that of grasses. Consequently, cyanobacteria, especially A. clathrata, may become a good biomass for bioenergy production.
Keywords: biomass; growth characteristic; methane production potential; microalgae; wastewater.