The objective of this study was to investigate and monitor changes of microbial diversity using PCR-DGGE and metagenimic sequencing in order to provide the alternative solution for enhancing the system efficiency and achieving a better system control and operation of biogas production from anaerobic co-digestion processes between septage and waste from agroindustry. Also, the relationship between microbial communities and changes of operating conditions such as organic loading rate (OLR ), influent characteristics, temperature and gas production efficiency was evaluated using an artificial neural network analysis.
In this work, Temperature-Phased Anaerobic Digester reactors (TPAD)were operated with continuous mode. Each TPAD had 2 systems connected in series that are thermophilic reactor and mesophilic reactor. Different types of substrates that are septage as a single substrate (TPAD 1), septage co digested with wastewater from dried longan process (TPAD 2), septage co-digested with longan peel (TPAD 3) were used in this study. In order to investigate the system performance, waste and wastewater samples from influent and effluent were collected for physical and chemical analysis and biogas yield from each reactor was also measured. Moreover, microbial sludge from both reactors of three TPAD systems were collected for microbial community analysis using PCR-DGGE and metagenomic sequencing analysis.
Results showed that the co digestion process between septage and longan peel gave the highest gas production and system stability. Moreover, microbial community structure appeared to be diverse and change along with different influent characteristics and operating conditions, especially different operating temperatures. Bacteroidetes Firmicutes Proteobacteria Verrucummicrobia Tenericutes Verrucummicrobia and Chloroflexi were dominant species found from all TPADs which had different ratios andquantities between systems. The dominance and microbial community obtained from thermophilic system and mesophilic system from TPAD 1 were similar. Interestingly, Firmicutes and Proteobacteria were found from both tanks, while higher amount of Bacteroidetes and Cloacimonetes were found only from mesophilic reactor. However, it was found that microbial community structures obtained from both systems from TPAD 2 were significantly unique. Firmicutes and Thermotogae were found from thermophilic reactor, while the latter could not be detected from the mesophilic reactor. Interestingly, Cloacimonetes was only found from Mesophilic reactor. In TPAD 3, high percentage of Firmicutes and Chloroflexi were detected from mesophilic tank, while Bacteroidetes and Cloacimonetes were found from thermophilic reactor. However, approximately 1-5% of microorganisms found from the system were methanogens and Methanosarcina and Methanothermobacter were dominance obtained from both systems.