Abstract

The objective of this study was to evaluate the performance characteristics of a hyperthermophilic digester system that consists of an acidogenic reactor operated at hyperthermophilic (70 °C) conditions in series with a methane reactor operated at mesophilic (35 °C), thermophilic (55 °C), and hyperthermophilic (65 °C) conditions. Lab-scale reactors were operated continuously, and were fed with co-substrates composed of artificial kitchen garbage (TS 9.8%) and excess sludge (TS 0.5%) at the volumetric ratio of 20:80. In the acidification step, COD solubilization was in the range of 22–46% at 70 °C, while it was 21–29% at 55 °C. The average protein solubilization was 44% at 70 °C. The double bond fatty acid removal ratio at 70 °C was much higher than at 55 °C. These results suggested that the optimal operation conditions for the acidogenic fermenter were about 3.1 days of HRT and 4 days of SRT at 70 °C. Methane conversion efficiency and the VS removal percentage in the methanogenic step following acidification was around 65% and 64% on average at 55 °C, respectively. The optimal operational conditions for this system are acidogenesis performed at 70 °C and methanogenesis at 55 °C. The key microbes determined in the hyperthermophilic acidification step were Anaerobic thermophile IC-BH at 6.4 days of HRT and Thermoanaerobacter thermohydrosulfuricus DSM 567 at 2.4 days of HRT. These results indicated that the hyperthermophilic system provides considerable advantages in treating co-substrates containing high concentrations of proteins, lipids, and nonbiodegradable solid matter.

Keywords: Hyperthermophilic process; Co-digestion; Excess sludge; Kitchen garbage; Microbial diversity

Article Outline

1. Introduction

2. Methods

2.1. Reactor and operation

2.2. Inoculums and substrate

2.3. Chemical analysis

2.4. Molecular biological analysis

2.4.1. DNA extraction

2.4.2. PCR amplification and gel extraction

2.4.3. Cloning of 16S rDNA

3. Results and discussion

3.1. Solubilization of kitchen garbage and excess sludge

3.2. Best design for methane fermentation

3.3. Diversities of microbes in acidogenesis

4. Conclusions

Acknowledgements

References