Aerobic and anaerobic ammonium-oxidising bacterial enrichment from municipal solid waste

Leachate from the municipal solid waste (MSW) landfills contains high concentration of ammoniacal nitrogen that is a major toxic pollutant that has a great threat to environment. Among the processes available for the removal of ammoniacal nitrogen, one process is a combination of partial nitrification and anaerobic ammonium oxidation (anammox) process. It requires aerobic ammonium-oxidising bacteria (AOB) and anaerobic ammonium-oxidising bacteria (AnAOB). This paper presents the feasibility of enriching the AOB and AnAOB in 100-mL and 2.5-L batch reactors from fresh and mined MSW and leachate under aerobic and anaerobic conditions with varying feed-to-seed ratio. The AOB and AnAOB activity was monitored by measuring the intermediates such as hydroxylamine and hydrazine along with variations in ammoniacal nitrogen, nitrite nitrogen, and nitrate nitrogen concentrations in the reactor contents. The formation of intermediates such as hydroxylamine and hydrazine and ammoniacal nitrogen transformation data confirmed the enrichment of AOB and AnAOB. Further, AOB and AnAOB were validated by most probable number test and scanning electron microscopy analysis, respectively. DNA extraction, polymerase chain reaction amplification, and sequencing analysis authenticated the AnAOB as Candidatus Brocadia anammoxidans.

Keywords
Bacterial enrichment; Ammoniacal nitrogen removal; Aerobic ammonium-oxidising bacteria; Anammox bacteria; Feed-to-seed ratio; Candidatus Brocadia anammoxidans