Efficient nitrogen removal and partial elemental sulfur recovery by combined nitrite-Anammox and sulfate-Anammox: A novel strategy for treating mature landfill leachate

The application of anaerobic ammonia oxidation (Anammox) is of great significance due to its eco-friendly potential. Besides conventional nitrite-dependent Anammox (N-Anammox), sulfate can also serve as an electron acceptor for ammonia oxidation under anaerobic conditions (S-Anammox). For the first time, an innovative process integrating partial nitrification, N-Anammox, and S-Anammox (P-NA/SA) in one single system, was applied herein to treat mature landfill leachate (1079.6 mg/L NH4+-N, 1584.4 mg/L SO42--S) with oxic/anoxic operation mode. After 180 days of continuous operation, the nitrogen and sulfate removal efficiencies of 95.7% and 24.3%, respectively, were obtained. Importantly, valuable elemental sulfur was recovered with an average efficiency of 21.9%. Isotope analysis confirmed that N-Anammox and S-Anammox contributed to 65.6% and 27.5% of total inorganic nitrogen removal, respectively. Furthermore, S-Anammox was identified as a step-wise bioprocess, with biologically generated NO2--N and S2- as intermediates. With enhancement of S-Anammox, partial nitrification pretreatment-step for nitrite generation in oxic stage became less necessary, leading to a remarkable 44% saving in aeration energy consumption. The Anammox bacteria gene (hydrazine synthase, HzsB) was highly abundant (1.2-2.5 x 10(8) copies/g center dot SS), with the dominant Anammox genus transforming from Candidatus_Kuenenia (4.6%-> 2.1%) to Candidatus_Brocadia (0.3%-> 3.2%). Anammox-mediated biotechnology by coupling N-Anammox and S-Anammox offers new insights into sustainable treatment of ammonia- and sulfate-containing wastewater.