Autotrophic ammonia removal from landfill leachate using anaerobic membrane bioreactor

Abstract

Anaerobic Membrane Bioreactor (AnMBR) is an innovative high cell density system having complete biomass retention, high reactor loading and low sludge production and suitable for developing slow growing autotrophic bacterial cultures such as ANAMMOX. The Anaerobic Ammonium Oxidation (ANAMMOX) process is an advanced biological nitrogen removal removes ammonia using nitrite as the electron acceptor without oxygen. The NH₄⁺-N in the landfill leachate that is formed due to the release of nitrogen from municipal solid waste (MSW), when discharged untreated, into the surface water can result in eutrophication, aquatic toxicity and emissions of nitrous oxide (N₂O) to atmosphere. Besides, NH₄⁺-N accumulation in landfills poses long term pollution issue with significant interference during post closure thereby requiring its removal prior to ultimate disposal into inland surface waters. The main objective of this study was to investigate the feasibility and treatment efficiency of treating landfill leachate (to check) for removing NH₄⁺-N by adopting ANAMMOX process in AnMBR. The AnMBR was optimized for Nitrogen Loading Rate (NLR) varying from 0.025 to 5 kg NH₄⁺-N/ m³/ d with hydraulic retention time (HRT) ranging from 1 to 3 d. NH₄⁺-N removal efficacy of 85.13 ± 9.67% with the mean nitrogen removal rate (NRR) of 5.54 ± 0.63 kg NH₄⁺-N/ m³/ d was achieved with nitrogen loading rate (NLR) of 6.51 ± 0.20 kg NH₄⁺- N/ m³/ d at 1.5 d HRT. The nitrogen transformation intermediates in the form of hydrazine (N₂H₄) and hydroxylamine (NH₂OH) were 0.008 ± 0.005 mg/L and 0.006 ± 0.001 mg/L, respectively, indicating co-existence of aerobic ammonia oxidizers (AOB) and ANAMMOX. The free ammonia (NH₃) and free nitrous acid (HNO₂) concentrations were 26.61 ± 16.54 mg/L and (1.66 ± 0.95) x 10-5 mg/L, preventing NO₂^--N oxidation to NO₃^--N enabling sustained NH₄⁺- N removal.