Evaluation of anaerobic co-digestion of para-grass and pig manure on methane production efficiency and microbial community

Abstract

The study was focused on the co-digestion of para-grass and pig manure, which was divided into 3 parts. The first part was to evaluate the biochemical methane potential of para-grass conducted at 35oC at various inoculum to substrate ratio (ISR). The maximum methane yields derived were 332.4, 475.0, 519.5 and 521.9 mL/gTSadded from pig farm digester inoculum at ISR 1, 2, 3, and 4, respectively. It suggested the use of ISR higher than 3 for BMP assay of this substrate. In the second part, anaerobic single-stage mesophilic 35°C, and temperature-phased anaerobic digestion (TPAD) system (thermophilic 55oC – mesophilic 35°C) were compared under different solid loadings from 0.10-3.76 gVS/L/d (0-8% dry para-grass mixing ratios, PG). Results showed the highest methane yield of 158.6 mLCH4/gVSadded was obtained from TPAD at 4 %PG with a methane content of around 55%. The highest biogas yield in terms of grass addition was 66.3 m3biogas/tonfresh at 4 %PG. Analysis of microbial communities by DGGE indicated that an addition of para-grass had shifted the domination of bacteria while achaea were rather stable. Third part was the investigation of effects of digester feeding scheme. Anaerobic sequencing batch reactor (ASBR) was operated at 35°C under increasing solid loadings in a regular ASBR feeding (RF) and a periodic feeding (PF) patterns. Results showed the highest methane yield of 169.8 mLCH4/gVSadded was obtained from periodic feeding at 2 %PG with a methane content of 53.3%. PF pattern could be advantageous since it could save time and labor to operate.