| Description |
About 5% of global methane is emitted through wastewater treatment processes. The majority of methane emission in wastewater treatment plant originates from anaerobic processes such as anaerobic digestion (AD) of biomass. Due to an equilibrium between the liquid phase and gaseous phase, some of the total methane generated in digesters is lost in the AD effluents in the dissolved form. During further handling of the AD effluents, methane is subsequently released into the atmosphere. This loss of dissolved methane (D-CH4) in AD effluent not only represents a loss of potential energy source but also contributes to the total emission of greenhouse gas (GHG). With modern technologies, it is possible to capture methane produced in gaseous form, but not much research has been conducted to handle D-CH4. One of the cost-effective ways to manage D-CH4 from AD effluents is by utilizing microbial-mediated methane oxidation either in aerobic or in anaerobic conditions. In this research, three different management strategies were proposed, and experimental conditions were established for managing D-CH4. The first strategy was aerobic methane oxidation (AMO) carried out by methanotrophic bacteria. In this strategy, a packed-bed column was utilized as a posttreatment biological process. Maximum methane removal rate (MRR) was observed to be 1.75 Kg COD m-3d-1 at 37˚C and residence time of 0.5 h. The second strategy employed a sequencing batch reactor enriched with denitrification coupled with anaerobic methane-oxidizing (DAMO) bacteria, which oxidizes methane with simultaneous reduction of nitrate/nitrite to dinitrogen gas in anoxic conditions. The iv combined NO2-N and NO3-N removal rate in this strategy was 0.82±0.14 mmol d-1 with the MRR of 0.31±0.11 Kg COD m-3d-1. The third strategy employed was aerobic oxidation of methane to methanol by mixed culture of ammonia-oxidizing bacteria (AOB) to support the implementation of the circular economy in wastewater treatment plants. An attached growth reactor was utilized in this strategy where the bio-carriers were enriched with AOBs. Our results show an average MRR of 0.73±0.03 Kg COD m-3d-1 with the average methanol production rate of 31.5±0.19 g COD m-3d-1. Our results indicate that using these bioengineered strategies as a posttreatment process to AD can make the anaerobic process eco-friendlier and sustainable by oxidizing dissolved methane along with the simultaneous removal of nitrogen and production of a chemical commodity, methanol, which can be used further for denitrification. |
