Potential Application and Performance of Methanotrophic Mixed Culture Under Main Stream Condition in Wastewater Treatment Plant

Wastewater treatment plants (WWTP) produce significant amount of biogas during sludge digestion in anerobic digestion (AD). Biogas is mainly methane gas which is a potent greenhouse gas (GHG) causing global warming. Direct use of biogas as fuel is an unattractive option due to its low efficiency, storage and transportation difficulty. There is an attractive option to convert methane gas biologically into more desirable forms like methanol and bio polymer. It has been proven through researches that the bio-conversion of methane can be done with the help of a biocatalyst called methanotrophs with higher efficiency and requires no or less energy input. The application of methanotrophs into WWTP has been challenged by its capability to grow under main stream conditions with Chemical Oxygen Demand (COD) along with diverse microbial community. In this study the growing capability of methanotrophic mixed culture was examined under varying COD in synthetic feed. The experiment was done in repeated batch for fifty cycles to obtain the stable behavior of the microbial consortium. In addition, the nitrogen utilization mechanism was investigated to figure out whether the nitrogen is used only for cell synthesis or cell synthesis along with nitrification/ denitrification. The results show that the best microbial performance was attained at COD of 360 mg/L. The average Specific Growth Rate (day-1) was 0.490.05, average Biomass Yield (mg-VSS/mg-CH4) was 0.490.04 and the average methane uptake rate (mg/hr) was 2.500.36. In addition, average COD consumption was 895 % at COD 540mg/L and the average ammonia consumption was around 99.720.48 %. The percentage of ammonia utilized for cell synthesis was 61-72% and 28-39% of ammonia was converted to a gaseous form of nitrogen. These results demonstrate the feasibility of integrating methanotrophic cultures within the mainstream of existing WWTPs.