Two pilot-scale two-stage anoxic/oxic membrane bioreactors were operated at different dissolved oxygen (DO) levels to evaluate nitrogen removal performances for treating landfill sludge dewatering liquid. Under either high (5.0-6.0 mg/L) or conventional DO (2.0-3.0 mg/L) conditions, partial nitrification (PN)-denitrification was both achieved, and high-concentration free ammonia (FA) ensured stable PN. The high DO system exhibited higher nitrite accumulation (98.5 %) and nitrogen removal (98.0 %), and its nitrogen removal was mainly ascribed to PN-denitrification (53.8 %). Kinetic inhibition tests and microbial sequencing results demonstrated that high DO condition improved the abundance and ability of ammonia-oxidizing bacteria (AOB) rather than nitrite-oxidizing bacteria under the FA inhibition. Pseudomonas, Thauera, and Soehngenia were characteristic genus in the high DO system, and Nitrosomonas was only AOB. Metagenomic analysis confirmed the important role of PN on nitrogen removal in high DO system. This provides valuable references for the efficient and economic treatment of ammonia-rich wastewater.

The municipal solid waste (MSW) with high water content can be pre-treated by the mechanical dewatering technology to significantly decrease the leachate generation in sequential landfill treatment or to improve the efficiency for solid waste incineration, which has attracted great concerns recently. However, the generated mechanical dewatering wastewater (MDW) containing high organics and nitrogenous content has been one of the big challenges for the sustainable treatment of MSW. In this study, a pilot-scale integrated system composed of physiochemical pretreatment, anaerobic sequencing batch reactor (ASBR), partial nitrification SBR (PN-SBR), denitrification SBR (DN-SBR), and UV/O3 advanced oxidation process, with a capacity of 1.0 m3/d to treat MDW containing over 34000 mg-chemical oxygen demand (COD)/L organics pollutant and 850 mg/L NH4+-N, was successfully developed. By explorations on the start-up of this integrated system and the process conditions optimization, after a long-term system operation, the findings demonstrated that this integrated system could reach the removal efficiency in the COD, NH4+-N and total nitrogen (TN) in the MDW of 99.7%, 98.2% and 96.9%, respectively. Partial nitrification and denitrification were successfully obtained for the TN removal with the nitrite accumulation rate of over 80%. The treatment condition parameters were optimized to be 800 mg/L polyaluminum chloride (PAC) and 2 mg/L polyacrylamide (PAM) under a pH of 9 for pretreatment, 36 h hydraulic retention time (HRT) for ASBR, 24 h for PN-SBR, and 2 h for UV/O3 unit. The organic sources in the MDW were also found to be feasible for the DN-SBR. Consequently, the resulting final effluent was stably in compliance with the discharge standard with high stability and reliability.

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

The anoxic/multi-aerobic process is widely applied for treating landfill leachate with low carbon to nitrogen ratio. In this study, the effect of two aeration modes in the aerobic phase, i.e. decreasing dissolved oxygen (DO) and increasing DO, on nitrogen removal and N2O emission in the process were systematically compared. The results demonstrate that the aerobic phase with increasing DO mode has a positive effect on improved total nitrogen removal (78 %) under the COD/N ratio as low as 3.45 and minimized N2O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N2O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N2O emission. Under efficient nitrogen removal stage, N2O emission factor was 2.4 ± 1.0 % of the total incoming nitrogen. Microbial analysis revealed that increasing DO mode increased the abundance of ammonia oxidizing bacteria and denitrifiers.

Poor nitrogen removal from municipal sewage is mainly due to insufficient carbon source and low C/N ratio. The A2/O pilot plant was established to investigate the accumulation rate of nitrous nitrogen and the removal of nitrogen pollutants by adjusting the ratio of anoxic/aerobic zoning and dissolved oxygen levels in the aerobic zone. The results showed that when DO is 2.0-2.5 mg·L-1, changing the ratio of anoxic to aerobic zoning had little effect on the reaction system, and it was difficult to realize partial nitrification. When DO is 0.5-0.8 mg·L-1, VAnoxic:VAerobic=1:1, this is the best working condition of the system. The accumulation rate of nitrous nitrogen at the end of aerobic zone is stable at more than 62%, and the total nitrogen of effluent is reduced to 9.0 mg·L-1, which can achieve the goal of deep denitrification. Analyzing the apparent activity of nitrifying bacteria, it was found that the SAOR and SNOR (according to N/VSS calculation) were 0.14 g·(g·d)-1 and 0.04 g·(g·d)-1, respectively, under the optimum conditions. The difference between them was more obvious than that in other stages of the experiment, that is, the higher inhibition of NOB activity was the direct reason for the increase of nitrite accumulation rate. Illumina MiSeq sequencing showed that the number of NOB in this stage was significantly lower than that in other stages. Intermittent OUR method was used to analyze the composition of carbon sources at the inlet and outlet of the anoxic zone. The results showed that short-cut nitrification and denitrification could save 27.3% of the carbon sources under the optimal operating conditions. The biodegradable COD consumption in the anoxic zone was 63.6%, which was much higher than that in other stages.

A simultaneous nitrification, denitrification and organic matter removal (SNDOR) process in sequencing batch biofilm reactor (SBBR) was established to treat saline mustard tuber wastewater (MTWW) in this study. An average COD removal efficiency of 86.48% and total nitrogen removal efficiency of 86.48% were achieved at 30gNaClL-1 during 100days\' operation. The underlying mechanisms were investigated by PacBio SMRT DNA sequencing (V1-V9) to analyze the microbial community structures and its variation from low salinity at 10gNaClL-1 to high salinity at 30gNaClL-1. Results showed elevated salinity did not affect biological performance but reduced microbial diversity in SBBR, and halophilic bacteria gradually predominated by succession. Despite of high C/N, autotrophic ammonia-oxidizing bacteria (AOB) Nitrosomonas and ammonia-oxidizing archaea (AOA) Candidatus Nitrososphaera both contributed to ammonium oxidation. As salinity increasing, nitrite-oxidizing bacteria (NOB) were significantly inhibited, partial nitrification and denitrification (PND) process gradually contributed to nitrogen removal.