Control factors of partial nitritation for landfill leachate treatment

Anaerobic ammonium oxidation (ANAMMOX) technology has potential technical superiority and economical efficiency for the nitrogen removal from landfill leachate, which contains high-strength ammonium nitrogen (NH4(+)-N) and refractory organics. To complete the ANAMMOX process, a preceding partial nitritation step to produce the appropriate ratio of nitrite/ammonium is a key stage. The objective of this study was to determine the optimal conditions to acquire constant partial nitritation for landfill leachate treatment, and a bench scale fixed bed bio-film reactor was used in this study to investigate the effects of the running factors on the partial nitritation. The results showed that both the dissolved oxygen (DO) concentration and the ammonium volumetric loading rate (N(v)) had effects on the partial nitritation. In the controlling conditions with a temperature of 30 +/- 1 degrees C, N(v) of 0.2-1.0 kg NH4(+)-N/(m3 x d), and DO concentration of 0.8-2.3 mg/L, the steady partial nitritation was achieved as follows: more than 94% partial nitritation efficiency (nitrite as the main product), 60%-74% NH4(+)-N removal efficiency, and NO2(-)-N/NH4(+)-N ratio (concentration ratio) of 1.0-1.4 in the effluent. The impact of temperature was related to N(v) at certain DO concentration, and the temperature range of 25-30 degrees C was suitable for treating high strength ammonium leachate. Ammonium-oxidizing bacteria could be acclimated to higher FA (free ammonium) in the range of 122-224 mg/L. According to the denaturing gradient gel electrophoresis analysis result of the bio-film in the reactor, there were 25 kinds of 16S rRNA gene fragments, which indicated that abundant microbial communities existed in the bio-film, although high concentrations of ammonium and FA may inhibit the growth of the nitrite-oxidizing bacteria and other microorganisms in the reactor.