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 degrees C, while it was about 2 1 % at 80 degrees C. The average protein solubilization reached to 31% at 80 degrees C. Methane conversion efficiency following the acidification was around 85% in average at 55 degrees C, but decreased with increasing temperature and methane gas was not produced over 73 degrees C. The upper temperature limits for growth of microbes were secondly observed and shown to be 73 degrees C for acetate oxidizers, 65 degrees C for propionate oxidizers, 70 degrees C for iso-butyrate oxidizers, 80 degrees C for lactate oxidizers and 65 degrees C for protein degrading bacteria in the methane fermenter. As well as, microbes affiliated with methanogens dominated the population below the 65 degrees C, while those affiliated with acidogens were predominant over the 73 degrees C. These results indicated that the hyperthermophilic processes have considerable benefits to treat wastewater or waste containing high concentration of protein. (C) 2008 Elsevier Ltd. All rights reserved.