| Eutrophication is increasingly serious, caused heavy direct economic losses to human being and negative effects on social harmonious development. In China, the discharge of municipal wastewater is increasing year by year. Considering nitrogen and phosphorus in municipal wastewater is in enormous amount, is major reasons of eutrophication and of destruction of water ecological balance. Currently, the conventional biological nitrogen removal process of municipal wastewaters often have the disadvantages of high-energy requirements associated with low efficiency and high operation cost. Now, as the energy crisis is increasing seriously, is very important to develop new nitrogen removal process, reduce operation cost and improve performance efficiency.The combining anaerobic ammonium oxidation (anammox) process with partial nitrification can achieve a reduced oxygen demand, whilst producing less surplus sludge, and is considering as sustainable technologies of wastewater treatment. In conventional nitrogen removal process, organic matter was used as carbon source of denitrification, so lots of organic matter can’t be used to produce biogas. Anammox bacteria don’t need organic carbon source during their normal metabolism. So the organic matter could used for energy production by using anammox technology. Now most studies about anammox were focused on ammonium rich wastewater treatment under high temperature, the studies about sewage treatment via anammox at at moderately low temperatures were very limited.In this study, the combination of direct anaerobic treatment and anammox/partial nitrification process was develop to a novel municipal wastewater treating process base on anammox ror energy production and autotrophic nitrogen removal. To estimate the nitrogen removal performance of the combined system, the degradation pathway of organic matter as well as the feasibility of the new strategy to achieve partial nitrification in municipal wastewater treatment, while the nitrogen removal activities of the anammox reactor at low temperatures and microbial community structure were also investigated.First, the combined process was started up with synthetic wastewater. The result indicated that it was feasible to treat low-strength wastewater by the combined process. Effluent NH4+-N of the combined treatment process was below detection limit while NO3--N, NO2--N and were less than0.5mg/L,3.6and mg/L respectively. COD in the effluent was10mg/L and the COD removal rate of98%was achieved. More than80%COD was removed by the up-flow anaerobic sludge fixed bed(UAFB) and anaerobic gas production was3.3L/d with the methane yield of0.3L/g. About39.2%of influent COD was removed in form of methane and about6.52%was transferred to VFAs. Partial nitritation with high nitrite accumulation efficiency of97%was realized in a Sequencing Batch Reactor (SBR). Ammonium was partly oxidized to nitrite with an ammonium:nitrite ratio of1:1.13,which was suitable for the sub-sequent ANAMMOX reaction. In terms of N balance, The N convert rate of SBR was36.59%while anaerobic ammonium oxidation (ANAMMOX) reactor, the major system in nitrogen removal,which removed56.91%of N. TN removal rate of ANAMMOX reactor was0.62kg/m3/d and the ratio of NH4+-N removal:NO2--N removal:NO3--N generation in was1:1.18:0.25.The synthetic influent was gradually replaced by raw municipal wastewater during moderately low temperatures.The concentrations of ammonia, nitrite,TN and COD in effluent were below1mg/L,0.1mg/L,7mg/L and30mg/L, respectively, which match the emission standard A of municipal wastewater in China.Methane reclaim from low-strength wastewater was achieved with a volumetric methane producing rate of325.2mg/L d under moderately low temperatures.The methane production efficiency of UAFB were estimate under different temperatures. In the UAFB, there was no obvious change observed in the total methane production at temperatures of35℃,28℃,24±3℃and17±3℃, accounting for28.8%,27.2%,28.0%and28.3%of the influent COD, respectively. Obvious accumulation of VFAs was observed in the effluent as the temperature dropped.A new control strategy with a flexible aeration period that depend on the temperature and the influent characteristics was firstly proposed in this study to achieve partial nitrification in municipal wastewater treatment. A stable effluent with equimolar concentrations of nitrite and ammonium, coupled with high nitrite accumulation (>97%) was achieved in the SBR at moderately low temperatures.High nitrogen removal efficiency was achieve in the anammox reactor in municipal wastewater treatment. In the anammox reactor, the HRT was as low as0.96h and the nitrogen removal rate of0.83kg/m3/d was achieved at12～15℃. At low temperatures, the corresponding FISH image revealed a high amount of anammox bacteria.The effect of several kinds of inhibitors to anammox were estimated. Urea of low concentration (5mg/L) can be used by the system while high concentration (39.8mg/L) has a bad effect on the system which would break the balance of electron donor and electron acceptor. Urea hydrolysis would be limited in the system without the addition of organic carbon. However, small portion of urea still be converted to ammonium. Concentrations of50mM of sulfate resulted in60%inhibition percentage in both ammonium and nitrite conversion rates. When sulfate reach100mM, ammonium increased with time which might due to cell lysis and a loss of ammonium remove ability. Concentrations of50mM of chlorine resulted in45%inhibition percentage in ammonium conversion rates and20%in nitrite conversion rates. A chlorine concentration of100mM caused an inactivation of the anammox organisms.5mM phosphate could reduce ammonium conversion rates and nitrite conversion rates by30%and37%, respectively. When phosphate reach10mM,34%of ammonium conversion rates lose.20mM phosphate could almost completely inhibit the activity of Anammox bacteria. |
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