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

- NH3 inhibition was mitigated by continuous NH4+ removal using ion-exchangers.
- CH4 yields improved by 54% when NH3 reduced from 630 to 92 mg/L.
- Population density of MSC and MBT increased by over 6 and 5 times.
- Total bacterial density increased by over 2 times facilitated by ammonia reduction.
- Enhanced carbohydrates and proteins hydrolysis was achieved with ammonia removal.

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 0.2-0.5 unit 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 90 mg/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.

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