Effect of temperature on performance and microbial diversity in hyperthermophilic digester system fed with kitchen garbage

The objective of this study was to evaluate the performances and microbial diversities for development of the effective hyperthermophilic digester system that consists of hyperthermophilic reactor and hyperthermophilic or thermophilic reactor in series. Lab-scale reactors were operated continuously fed with artificial kitchen garbage. The effect of temperature on the acidification step was firstly investigated. Results indicated that 43.1% of COD solubilization was achieved at 70 °C, while it was about 21% at 80 °C. The average protein solubilization reached to 31% at 80 °C. Methane conversion efficiency following the acidification was around 85% in average at 55 °C, but decreased with increasing temperature and methane gas was not produced over 73 °C. The upper temperature limits for growth of microbes were secondly observed and shown to be 73 °C for acetate oxidizers, 65 °C for propionate oxidizers, 70 °C for iso-butyrate oxidizers, 80 °C for lactate oxidizers and 65 °C for protein degrading bacteria in the methane fermenter. As well as, microbes affiliated with methanogens dominated the population below the 65 °C, while those affiliated with acidogens were predominant over the 73 °C. These results indicated that the hyperthermophilic processes have considerable benefits to treat wastewater or waste containing high concentration of protein.