Comparative Study on the Optimisation of the Hydrolysis Step During Biogas Production from Typha Grass Using Conventional Microbiology and Metagenomics Tools

Abstract

The impact of climate change has increased by many orders of magnitudes in recent years. These changes have necessitated a global drive towards alternative sources of energy. Biogas has been re-echoed as one form of renewable energy that is sustainable because of the possibility of using several biomass sources to produce biogas. To date, two major factors hindered biogas production, the first been the biomass (having the appropriate C: N ratio) secondly enhanced hydrolysis to boost and sustained the yield of the biogas. The present study explored Typha grass as biomass for biogas production. The proximate composition was determined by the AOAC method. The biogas produced in the reactor was measured using water displacement method. The bacteria were isolated using standard bacteriology method and characterised by PCR amplification of the 16S rDNA gene. The metagenomics microbial community was determined by the Illumina amplicon sequencing method. The percentage of acid-insoluble lignin was determined using TAPPI (T222) method. The holocellulose content was determined according to DIN 2403. The a- Cellulose content of the substrate was determined in the 17.5% NaOH solutions using TAPPI 203 om-93 method. Typha grass had low lipid value of 2.05% and fiber 2.3% and an appreciable amount of lignin 47.05%, followed by holocellulose of 40.55%, hemicellulose 29.5% and cellulose was 11.5%. Biogas production started after 6 days and was optimum after 8 days with mean gas yield of 180 mL and decreased to 25 mL after 12 days. The reactor had a bacterium count of 1.33E+08 CFU/g at day 8. The result of the PCR amplification indicates the presence of bacterial species such as Acinetobacter sp., Pseudomonas putida, Pseudomonas veronii, Citrobacter species and Delftia sp, in the reactor. The metagenomics data revealed that bacteria were the major microbial community detected within the reactor and the inoculum and it accounted for more than 99%. At the phyla level, unknow bacteria, Firmicutes, Bacteroidetes and Proteobacteria were the major group within the reactor and in the inoculum. Uncultured bacterium, unclassified, rumen, Bacteroidetes and Archaeon constitute the major genera in the reactor. The results suggest that Typha grass can be exploited as biomass for biogas production and the complex microbial especially uncultured bacterium are important in the production process.