| Excess emissions of nitrogen to the natural water will led to depletion of oxygen in the liquid and cause eutrophication which seriously threaten to the water quality and seafood. Nowaday, the discharge of municipal wastewater is increasing year by year. The effluent discharge standards are becoming strict, but the conventional biological nitrogen removal process are often not regarded as suitable treatment options because of the high-energy requirements, low efficiency and unstable operation. So to develop new nitrogen removal process, reducing operation cost and improving performance efficiency, is very important to the steady development of wastewater treatment.Single-stage autotrophic biological nitrogen removal process was considered as sustainable development wastewater treatment process which partial nitritation and anammox occur simultaneously in one reactor. the ammonium oxidizers consume oxygen and produce a suitable amount of nitrite for the anammox organisms. This way the anammox organisms are protected from oxygen, consume ammonium and nitrite at the same time. Compared with the conventional nitrogen removal process, the single-stage autotrophic nitrogen removal process can develop in one reactor which can apparently save the land area and equipment cost. It also involves lower energy consumption and the need for carbon addition is omitte. Now most studies about partial nitritation/anammox process were focused on ammonium rich wastewater treatment such as sludge digester supernatant and landfill leachate treatment, the studies about municipal wastewater treatment via the single-stage process were very limited. This study was conducted with raw municipal wastewater, firstly, enrichment of anammox bacteria and ammonium oxidizer was investigated. The feasibility of pulse dosing sulfide to inhibit NOB and achieve single-stage autotrophic biological nitrogen removal is also discussed. At last, nitrogen removal efficiency of the single-stage process under non aeration and the effect of HRT on it are estimated.After30days of enrichment, the partial nitritation biomass performed well in removing nitrogen. At the end of enrichment phase, the mean effluent ammonia and nitrite were measured as2.1and26.1mg/L, respectively. The effluent nitrate was mostly below detection limit with a nitrite accumulation rate of97.7%. A large amount of protozoa was observed with microscope. At the stable anammox enrichment phase, ammonium and nitrite removal efficiency were90.7%and96.1%, respectively. The ratio of NH4+-N removal:NO2--N removal:NO3--N generation was1:1.31:0.39. In the combination period of anammox and partial nitritation biomass, a complete nitrification dominated in reactor because growth of nitrite oxidizers (NOB) is not prevented, with a nitrate concentration of15.34mg/L in the effluent, and the molar ratio of produced NO3--N to consumed NH4+-N was more than0.9.To inhibit the NOB activity in the external circulation sequencing batch reactor (ECSBR), Pulse dosing sulfide to ECSBR was applied. The NOB activity was inhibited immediately after pulse dosing sulfide and the single-stage autotrophic biological nitrogen removal was achieved. The results showed that the NH4+-N concentration of effluent was below3.78mg/L and the removal efficiency was88.4%; the total nitrogen removal rate reached66.8g/m3/d. Before dosing sulfide, a complete nitrification dominated in reactor with a nitrate concentration of13～22mg/L in the effluent, and the molar ratio of produced NO3--N to consumed NH4+-N was more than0.9. After sulfide was pulse dosed to reactor, the NOB activity was efficiently inhibited and the effluent NO3-N was reduced to4.18mg/L. The molar ratio of produced NO3--N to consumed NH4+-N was decreased to0.17. Most of the influent N was removed in the form of N2, which accounted for65.4%of the influent N. A partial nitrification associated with anammox process became the dominant reaction after pulse dosing sulfide. It was also found that NOB inhibition caused by sulfide was reversible that the NOB activity could recover when the sulfide was no longer exposure. The pulse sulfide application can ensure the inhibitory effect of sulfide on NOB during operation.To maintain long-term stable performance and save operation cost by reducing aeration power consumption, the oxygen supply to the reactor is decreasing gradually.As a result, the single-stage micro-aerobic autotrophic biological nitrogen removal without aeration was achieved.The NH4+-N and NO2--N concentration of effluent was0.9mg/L and2.9mg/L, respectively. The mean ratio of NO3--Nproduction/NH4+-Nremove was0.27.HRT determine the key parameters of the reaction structures in the actual project size, water quality and operation of energy-consuming,In stable period of the micro-aerobic process, the effect of HRT on the nitrogen removal efficiency was investigated. For HRT=8h,6h and4h, the NH4+-N concentration of effluent were0.8,0.8and9.9mg/L, respectively. The effluent NO2--N and NO3-N were6.0and2.5mg/L for HRT=6h, and2.9and11.2mg/L for HRT=8h, respectively. When the HRT was set at4h, no oxidation nitrogen was detected. The mean ratio of NO3--Nproduction/NH4+-Nremove with HRT being changed from8h to4h were0.26,0.05and0.03, respectively. Some unexpected biological reaction such as sulfate dependent anammox and desulfurization-denitrification might exist in the current system. The concertation of NH4+-N remained high in the effluent when HRT was set at4h while8h was not regarded as suitable treatment option because of the energy wastage associated with too long of running time.The HRT of6h was the better treatment option since it depleted ammonium in a shorter time. But a small portion of nitrite was still in the effluent in that HRT. So further research will be conducted for optimizing. |
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