Cultivation of anaerobic ammonium oxidizing bacteria (AnAOB) using different sewage sludge inoculums: process performance and microbial community analysis

BACKGROUND: This study explores the feasibility of three different inoculum sources (anaerobic, aerobic, and anoxic sludge from conventional sewage treatment plants) together with the potential of biomass carrier for Anaerobic ammonium oxidation bacteria (anammox) cultivation. Fed-batch reactors were operated with synthetic medium at different temperatures. RESULTS: The reactor inoculated with anaerobic sludge and biomass carrier showed close to stoichiometric nitrite to ammonia utilization (1.2:1) and the highest ammonia removal (12.2 mg NH₄⁺·g VS⁻¹·day⁻¹), followed by the reactor inoculated with activated sludge without carrier (4.3 mg NH₄⁺·g VS⁻¹·day⁻¹), which also showed close to stoichiometric nitrite to ammonia utilization. Anammox development was recorded by higher nitrogen removal, gradually increasing gas production rate, and the presence of Brocadiaceae anammox family bacteria. All batch reactors revealed significant phosphorus removal (>80%), which was attributed to the co-existence of anammox bacteria (Brocadiaceae) with denitrifying polyphosphate accumulating organisms (flavobacterium sp.). CONCLUSION: The results of this study revealed that anaerobic sludge and activated sludge from sewage treatment plants with biomass carriers for microbial immobilization were suitable for anammox bacteria enrichment. The co-existence of anammox bacteria with denitrifying polyphosphate accumulating microorganisms reveals new possibilities for simultaneous nitrogen and phosphate removal.