Thailand has a large numbers of cassava pulp residues from agro-industries. Though it is rich in carbohydrate, their utilization is limited due to the low content of protein and poor digestibility resulting to low methane production rate. To improve the utilization efficiency of cassava pulp residues for methane production, this study investigated effect of rumen fluid (RF) and synergisms between rumen fluid and enriched fatty acid degrading consortium (RFAD) on cassava pulp utilization under batch condition. The cassava pulp residues used in this study had a VS/TS ratio of 0.89 with cellulose, hemicellulose, and lignin contents of 50.1%, 17.5%, and 14.3%, respectively. After incubated for 90 days, the cumulative methane production of both RF and RFAD reached 440 mL-CH4/gVS, which was 37% higher than that of non-RFAD addition. However, RFAD showed the shorten lag phase of methane production (0.12 day), whereas RF showed the longest lag phase 27.6 days. The methane production rate of the RFAD was 26.8 mL-CH4/g-VS/day, which was 39-45% higher than that of RF (15.5 mL-CH4/g-VS/day) and control (17.3 mL-CH4/g-VS/day). Volatile solid reduction of RF and RFAD was also higher than control.
Microbial diversity of each condition was analyzed by 16S rRNA sequencing. The result showed that the relative abundance of Methanobacterium and Methanosaeta were observed 3.5% and 20% in control digester, 18.5% and 2.6% in RFAD addition digester, respectively. Which was higher than RF addition digester. However, Rikenellaceae (4.9%), Lysinibacillus (13.6%) and Clostridium (10%) were high dominated in RF addition digester. Also, Rikenellaceae was observed 3.4% in RFAD addition digester. Those are among the important hydrolytic and acidogenic bacteria in the AD process. The addition of RFAD consortium is thus a promising strategy to achieve higher methane yields and higher biodegradation efficiency without any additional energy input.
