Methanogenic capacity and robustness of hydrogenotrophic cultures based on closed nutrient recycling via microbial catabolism: Impact of temperature and microbial attachment.

A biological methanation system based on nutrient recycling via mixed culture microbial catabolism was investigated at mesophilic (37 °C) and thermophilic (55 °C) temperatures. At mesophilic temperatures, the formation of biofilms on two different types of material was assessed. Results showed that with intense mixing the biofilm reactors presented methanogenic capacities (per working volume) 50% higher than the ones operated with suspended cultures. Gas feeding rates of 200 L/L/d were achieved at a H2/CO2 to CH4 conversion efficiency of above 90% by linking two reactors in series. Furthermore the robustness of the cultures was assessed under a series of inhibitory conditions that simulated possible process interferences at full scale operation. Full recovery after separate intense oxygenation and long starvation periods was observed within 2-5 days.

Enhancement of microbial density and methane production in advanced anaerobic digestion of secondary sewage sludge by continuous removal of ammonia.

Ammonia inhibition mitigation in anaerobic digestion of high solids content of thermally hydrolysed secondary sewage sludge by the NH4+ affinitive clinoptilolite and a strong acid type ion-exchange resin S957 was investigated. Continuous NH4+-N removal was achieved through ion-exchanging at both temperatures with average removals of 50 and 70% for the clinoptilolite and resin dosed reactors, respectively. Approximate 0.2-0.5unit of pH reduction was also observed in the dosed reactors. The synergy of NH4+-N removal and pH reduction exponentially decreased free NH3 concentration, from 600 to 90mg/L at 43°C, which mitigated ammonia inhibition and improved methane yields by approximately 54%. Microbial community profiling suggested that facilitated by ammonia removal, the improvement in methane production was mainly achieved through the doubling in bacterial density and a 6-fold increase in population of the Methanosarcinaceae family, which in turn improved the degradation of residual volatile fatty acids, proteins and carbohydrates.

Closed nutrient recycling via microbial catabolism in an eco-engineered self regenerating mixed anaerobic microbiome for hydrogenotrophic methanogenesis.

A novel eco-engineered mixed anaerobic culture was successfully demonstrated for the first time to be capable of continuous regeneration in nutrient limiting conditions. Microbial catabolism has been found to support a closed system of nutrients able to enrich a culture of lithotrophic methanogens and provide microbial cell recycling. After enrichment, the hydrogenotrophic species was the dominating methanogens while a bacterial substratum was responsible for the redistribution of nutrients. q-PCR results indicated that 7% of the total population was responsible for the direct conversion of the gases. The efficiency of H2/CO2 conversion to CH4 reached 100% at a gassing rate of above 60v/v/d. The pH of the culture media was effectively sustained at optimal levels (pH 7-8) through a buffering system created by the dissolved CO2. The novel approach can reduce the process nutrient/metal requirement and enhance the environmental and financial performance of hydrogenotrophic methanogenesis for renewable energy storage.