Achieving stable partial nitritation using endpoint pH control in an SBR treating landfill leachate

The feasibility of using endpoint pH control to achieve stable partial nitritation (PN) in an SBR for landfill leachate treatment was investigated. By imposing a fixed-time anoxia followed by variable-time aeration in an SBR cycle, successful partial nitritation was maintained for 182 days at a nitrogen loading rate of 0.30–0.89 kg/m3/day. The effluent NO2−-N/NH4+-N ratio and the effluent NO3−-N concentration were 1.30 ± 0.22 and 16 ± 9 mg/L, respectively. High free ammonia (FA) and low dissolved oxygen (DO) concentrations were inhibition factors of nitrate formation. The termination of aeration at a suitable endpoint pH was the key to achieve an effluent NO2−-N/NH4+-N ratio close to the stoichiometric value. This endpoint pH control strategy represents practical potentials in the engineered application of combined PN–ANAMMOX processes.

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► Endpoint pH control was reliable to achieve stable partial nitritation performance.
► An effluent NO2−-N/NH4+-N ratio close to 1.32 was achieved.
► High FA and low DO concentrations were the main causes for inhibition of nitrate formation.
► Nitrogen loss was observed in both the air-off and air-on phases, possibly due to denitrification.