溶解氧对A~2/O工艺脱氮除磷效果的影响及解决方法

溶解氧对微生物生长的影响很大,通过溶解氧对硝化、反硝化、除磷的影响试验,详细论述了溶解氧对A2/O工艺脱氮除磷的效果影响.试验结果表明,在保证足够好氧泥龄的前提下,提高曝气池的溶解氧,可以改善硝化效果.在好氧段末端设置20～30 min的非曝气区,可以使内回流中的DO降低2～3 mg/L,当内回流比为400%时可节约碳源28～41 mg/L.曝气段中过度曝气会造成生物除磷能力下降.因此,必须通过自动控制维持好氧段的溶解氧在合理水平,并通过设立非曝气区和预缺氧区,消除内外回流中溶解氧过高造成的缺氧区和厌氧区氧化还原电位的提高,从而保证进水中碳源有效用于脱氮除磷.     

内外回流比对A2/O工艺生物脱氮的影响

针对内外回流比对A2/O工艺生物脱氮效率的效果及其局限性进行了中试研究。结果表明,通常缺氧段出水NO3-—N不为零,使TN理论去除率>反硝化理论脱氮率>TN实际去除率,并进一步分析了此时TN的理论去除率变化。当内外回流比之和为300%和500%时,出水TN稳定,分别小于20mg/L和15mg/L。当内回流比由200%上升到400%时,缺氧出水NO3-—N由1.3mg/L上升到3.8mg/L,但是反硝化速率由0.036kgNO3-—N/(kgVSS.d)上升到0.044kgNO3-—N/(kgVSS·d)。MLVSS中TN约占9.8%,通过剩余污泥排放去除TN比例随着泥龄的增加而减少,当好氧SRT为14d、8d、5d时,其均值分别为7.1%、26.2%、37.1%。     

溶解氧对低碳源污水一体化处理工艺脱氮除磷的影响

通过试验对比,研究了溶解氧对低碳源污水一体化工艺脱氮除磷效果的影响。结果表明,平均溶解氧为0.18mg/L时,系统出水可以稳定达到GB 18918—2002一级A标准,溶解氧过高或过低都会降低系统脱氮除磷效果。在平均溶解氧为0.18mg/L的工况下,系统存在反硝化吸磷、同时硝化反硝化及全程反硝化3种脱氮方式,且反硝化吸磷和同时硝化反硝化脱氮量占氮总去除量的66.7%,可以较大程度降低脱氮除磷过程所需碳源量并节省耗氧量,提高低碳源污水脱氮除磷效果。     

多级生物滤池工艺脱氮效能研究

为实现BAF工艺的高效稳定脱氮,采用了外加碳源的后置反硝化三级BAF工艺(C+N+DN).研究了水温、污染物负荷、硝化液回流等条件下低碳氮比生活污水的脱氮效果.结果表明,在无硝化液回流的条件下,水温高于23℃时,系统具有高效稳定的脱氮效果,出水NH3-N稳定低于5 mg/L;水温低于23℃时,系统出水NH3-N明显升高.当水温为12～23℃时,采取50%硝化液回流并降低负荷后,硝化和反硝化效果明显提高,C柱和N柱对NH3-N和TN的去除率分别提高了19%和22%,最终出水中NH3-N与TN稳定达到<城镇污水处理厂污染物排放标准>(GB18918-2002)一级A标准.     

清潭污水处理厂一级A提标改造工程脱氮除磷特性分析

结合清潭污水处理厂一级A提标改造工程实例,通过全流程生产性测试和主要功能单元的模拟试验,对回流污泥内源反硝化强化环沟型改良A2/O工艺的脱氮除磷特性进行了分析。结果表明,回流污泥内源反硝化池HRT为3.2h时,内源反硝化NO-3—N去除量为9.6mg/L,污泥内源反硝化速率为0.68mgNO-3—N/(gVSS·h);在进水COD/TN为3.3的条件下,工艺脱氮能力高达35mg/L,回流污泥内源反硝化池、缺氧池和生物同化作用对工艺脱氮的贡献率分别为27.4%、44%和28.6%。通过将初沉池改造为回流污泥内源反硝化池,工艺脱氮能力提高37.8%;在进水PO3-4浓度均值为3.22mg/L时,好氧池出水PO3-4可达0.3mg/L以下,厌氧池厌氧释磷作用显著,PO3-4释放量高达8.3mg/L,污泥厌氧释磷速率为9.68mgPO3-4/(gVSS·h)。     

采用UCT工艺的复合式MBR脱氮除磷影响研究

采用UCT工艺的复合式MBR(HMBR)系统进行污水脱氮除磷试验研究,探讨进水C/N比、系统内回流比r、硝化液回流比R和污泥停留时间对系统脱氮除磷效果的影响。试验结果表明,上述4个因素对采用UCT工艺的HMBR系统的脱氮除磷效果均有影响,在C/N=5～8、r=200%、R=300%、SRT=28 d的条件下,系统脱氮除磷效果最佳,TN平均去除率79.17%,膜出水平均浓度11.78 mg/L;TP平均去除率86.68%,膜出水平均浓度0.71 mg/L。     

薛城焦化厂废水的A/O处理工艺

内循环A/O生物脱氮工艺是一种改进的A/O法,它通过内回流,使硝化和反硝化菌处于最佳生长环境,菌种活性强.该工艺在山东薛城焦化厂运行以来,效果良好:进水氨氮319mg/L,出水低于10mg/L,去除率达80%以上,其他各项指标也均达到了排放要求.本文还讨论了氨氮、COD、硝态氮负荷、碱度,碳氮比等因素对生物脱氮的影响.并介绍了该工艺的推荐参数.     

双污泥回流A~2/O工艺在低温下的脱氮除磷效果

在温度为9~16℃的低温条件下,考察了双污泥回流A2/O工艺系统处理低C/N城市污水的脱氮除磷特性。试验结果表明:在低温处理低C/N城市污水时,将A2/O工艺改良为双污泥回流系统,通过富集反硝化除磷菌(DPB)和强化缺氧吸磷等方法,取得了良好的同步脱氮除磷效果。当水温为12~16℃,缺氧池DO为0.2~0.4mg/L时,进水TN、NH3—N和TP平均分别为47.44mg/L、37.50mg/L和6.01mg/L时,系统出水TN、NH3—N和TP平均分别为12.81mg/L、2.75mg/L和0.37mg/L,去除率分别为72.99%、92.66%和93.90%,当水温为9~12℃时,系统对TN、NH3—N和TP去除效果下降,不能达到预定的去除目标。系统对COD去除效果良好,进水COD平均为253.59mg/L,出水为26.85mg/L,平均去除率为89.41%。     

基于响应面法的推流式耦合工艺深度脱氮优化研究

为了解决污水处理厂提标改造过程中面临的场地、投资受限,实施提标改造期间难以减产等实际问题,总结前期工作成果,建立了推流式固定载体生物与活性污泥耦合工艺。为了进一步研究测试,建立了处理规模为120m~3/d的推流式耦合工艺中试试验装置,选取好氧区溶解氧值、混合液内回流比、污泥浓度和缺氧区机械搅拌强度为自变量,利用响应面分析法对推流式耦合工艺的运行参数进行优化。优化研究结论如下:响应面法分析得出的最佳工艺参数为好氧DO值3.9mg/L,内回流比200%,污泥浓度为4 900mg/L,缺氧搅拌强度为140w/t;根据响应面法预测,推流式耦合工艺运行最佳工艺参数,各项污染物去除率分别为CODcr去除率97.28%,TN去除率87.22%,NH_4~+-N去除率98.18%;推流式耦合工艺中试试验装置依照最佳工艺参数运行,试验得出实际CODcr出水约为15mg/L,去除率为95.47%;TN出水约为8mg/L,去除率为85.66%;NH_4~+-N出水约为0.3mg/L,去除率为99.11%。     

城市污水处理厂表曝氧化沟脱氮改造工程设计

针对某污水处理厂转碟曝气氧化沟存在的充氧不足、脱氮效率低和转碟噪声较大等问题,提出了取消曝气转碟,配套微孔曝气系统,将氧化沟改造为前置缺氧区的A/O反应池,增加缺氧池搅拌系统和好氧池硝化液内回流系统,在好氧区和缺氧区之间设置调节段,以及在好氧区末端设置脱气区等改造措施。工程实践表明,改造工程出水NH3—N、TN及TP平均浓度分别为1mg/L、6.45mg/L以及0.1mg/L,有效提高了系统的硝化、反硝化及生物除磷效果。     

Nitrogen removal in an upflow sludge blanket (USB) reactor combined by aerobic biofiltration systems.

A new nitrogen removal process (up-flow sludge blanket and aerobic filter, USB-AF) was proposed and tested with real sewage. In the USB reactor, the larger part of influent organic and nitrogen matters were removed, and ammonia was effectively oxidized in the subsequent aerobic filter. The role of the aerobic filter was to convert ammonia into nitrate, an electron acceptor that could convert soluble organic matters into volatile suspended solid (VSS) in the USB. The accumulated as well as influent VSS in the USB was finally degraded to fermented products that were another good carbon source for denitrification. Total COD, settleable COD and soluble COD in the raw sewage were 325, 80 and 140 mg/l, respectively. Most unsettleable COD as well as some SCOD in the influent was successfully removed in the USB. TCOD removal in the anoxic filter was by denitrification with the recycled nitrate. Low COD input to the aerobic filter could increase nitrification efficiency, reduce the start-up period and save the aeration energy in the USB-AF system. About 95% of ammonia was nitrified in the aerobic filter with no relation to the influent ammonia concentration. Denitrification efficiency of the recycled nitrate in the anoxic filter was about 85, 83, and 72% at recycle ratios of 100, 200, and 300%, respectively. T-N removal efficiency was 70% at recycle ratio of 300%.     

Automatic control strategy for biological nitrogen removal of low C/N wastewater in a sequencing batch reactor.

To establish an automatic control system of external carbon addition in biological nitrogen removal, a bench-scale sequencing batch reactor with real-time control strategy was designed in this study. An oxidation-reduction potential (ORP) profile was used for automatic control of external carbon addition. The mean removal efficiency of total organic carbon was over 98%. Complete denitrification in an anoxic phase and complete denitrification and nitrification in anoxic and oxic phases were accomplished, respectively, because the oxic and anoxic periods were also appropriately controlled with ORP and pH profiles, respectively. Mean removal efficiency of total nitrogen was over 95%. When concentration of influent wastewater was changed, volume of additional carbon was automatically changed with the influent fluctuation, and flexible hydraulic retention time was achieved in this system.     

Effect of internal recycle rate on the high-strength nitrogen wastewater treatment in the combined UBF/MBR system.

An anaerobic/aerobic system combining an anaerobic upflow-sludge bed filter (UBF) and an aerobic membrane bioreactor (MBR) was operated to enhance organic and nitrogen removal efficiency. The internal recycle rate, which is one of the most important operation factors that affects overall removal efficiency, was varied from 100% to 300% of the influent flow. Under these conditions, the overall removal efficiencies of organic and nitrogen and characteristics of membrane fouling in the combined system treating the synthetic wastewater including high concentration of organics and nutrients were studied. As a result, nitrogen removal efficiency was increased to 67% when the internal recycle rate was 300% of influent flow rate. As the internal recycle ratio increased from 100% to 200%, protein content decreased by 17% and carbohydrate content increased by 12%. However, there was no remarkable difference in total extracellular polymeric substances (EPS) content. At the high recycle rate of 300%, the surface charge of sludge was decreased while hydrophobicity (specific ultraviolet absorbance, SUVA) was increased. The differences in SUVA and surface charge were 11% and 1%, respectively. It is concluded that SUVA and EPS composition were important parameters affecting membrane fouling in the combined system.     

Two-stage entrapped mixed microbial cell process for simultaneous removal of organics and nitrogen for rural domestic sewage application.

A two-stage entrapped mixed microbial cell ((2S)EMMC) process which separates nitrification and denitrification phases by the installation of the anoxic and oxic EMMC reactors packed with EMMC carriers was operated with 6, 4, 3, and 2 hours of hydraulic retention time (HRT) using simulated domestic wastewater. The activated sludge was immobilized using cellulose acetate for the EMMC carriers. Similar soluble chemical oxygen demand (SCOD) removal efficiencies of 90-97% were observed for all HRTs (SCOD loading rate of 0.84-2.30 g/L/d) applied. In order to achieve more than 80% of TN removal efficiency, the HRT should be maintained higher than 4 hours (less than 0.24 g/L/d of TN loading rate). Denitrification was a rate-limiting step which controlled overall TN removal efficiency at TN loading rate of 0.15-0.31 g/L/d although nitrification efficiencies achieved 97-99%. The effluent TSS of less than 25 mg/L in the (2S)EMMC process was maintained at the SCOD loading rate of less than 1.23 g/L/d with back-washing intervals of 5 and 10 days in the anoxic and oxic EMMC reactors, respectively. The minimum HRT of 4 hours is required for high removal efficiencies of organics (average 95.6%) and nitrogen (average 80.5%) in the (2S)EMMC process with 3 times of recirculation ratio.     

A pilot-plant study of a moving-bed biofilm reactor system using PVA gel as a biocarrier for removals of organic carbon and nitrogen.

A pilot-plant study was conducted to evaluate the performance of a moving-bed biofilm reactor process using PVA-gel beads as a biocarrier. Real primary-settled wastewater was fed to the pre-denitrification system and removals of nitrogenous and organic contaminants were evaluated over a 1-year period. The results demonstrated that at a total nitrogen (TN) loading of 18 mg/L.h, a TN removal efficiency in keeping with and even exceeding the theoretical maximum efficiency based on the level of internal recycle, was possible and a nitrification rate of 15 mg/L.h was sustained with a HRT of only 2.5 h at 15 degrees C. Furthermore, soluble COD and BOD5 in the effluent of the pilot plant were reduced to levels well below most regulatory discharge limits. In addition, the possibility of using this biocarrier in a system, including the elimination of waste organic sludge, was discussed.     

Automatic control of external carbon source addition for nitrogen removal in sewage with low C/N ratios.

For cost-effective nitrogen removal from sewage with low C/N ratios, an automatic control system for the addition of external carbon based on oxidation-reduction potential (ORP) data in an anoxic reactor has been developed. In this study, it was carried out with a pilot-scale modified Bardenpho process. This consisted of anoxic1, aerobic1, anoxic2 and aerobic2 stages with an external recycle ratio of 150% (Q/Qinf), and a media packing ratio of 2.4%-2.9% (v/v) in the aerobic reactor. As a result of applying the automatic control system for the minimization of the external carbon source dosage, the dosage was decreased by about 20%. This estimate was based on ORP compared with a stable dosage of 75 mg/L based on the C/NOx-N ratio of the anoxic influent. It was necessary that the ORP set-value be regulated from -120 mV to -80 mV because influent NH4+-N concentration varied from 12 to 15 mg/L due to rainfall. Correspondingly, the demanded dosages were decreased. Drift of the the real-time value in control system was more stable after changing the ORP set-value from -120 mV to -80 mV.     

Total nitrogen removal from high-strength ammonia recycle stream using a single submerged attached growth bioreactor.

An experimental study investigating the nitrogen removal efficiency from the recycle stream generated in the dewatering facility of the anaerobically digested sludge at the Deer Island wastewater treatment plant (WWTP) in Boston was conducted using a single submerged attached growth bioreactor (SAGB), designed for simultaneous nitrification and denitrification. The applied nitrogen loading to the reactor ranged from 0.7 to 2.27 kg-N/m3xd, and the corresponding total nitrogen (TN) removal rate ranged from 0.38 to 1.8 kg-N/m(3)xd. The observed nitrification rates varied from 0.42 kg-N/m3-d to 1.45 kg-N/m(3) xd with an ammonia load of 0.5 kg-N/m3-d and 1.8 kg-N/m(3)xd, respectively. An average nitrification efficiency of 91% was achieved throughout the experiment. Denitrification efficiency varied from 55%/o, obtained without any addition of carbon source, to 95% when methanol was added in order to obtain a methanol/nitrate ratio of about 3 kg methanol/kg NO3- -N.     

Achieving and maintaining of short-cut nitrification in a cyclic activated sludge system

A lab-scale Cyclic Activated Sludge Technology (CAST) system was operated more than 5 months to evaluate the effects of the operation mode on nitrogen removal performance and investigate a feasible method for achieving short-cut nitrification in the system. Results showed that nitrogen was removed by conventional biological nitrification and denitrification in traditional operation mode (fill/aeration 2 h, settle 1 h, decant 1 h), whereas short-cut nitrification and denitrification was the main nitrogen removal pathway in modified operation mode and the nitrogen removal performance was enhanced. Short-cut nitrification was successfully achieved in CAST system at 17 ± 1 °C by adjusting operation conditions and the average total nitrogen removal efficiency increased by 11.4% compared to traditional mode. It was assumed that low dissolved oxygen (<1.0 mg/L) limitation combined with free ammonia (0.28-0.34 mg/L) inhibition on nitrite-oxidizing bacteria caused nitrite accumulation in modified mode. During maintaining period of short-cut nitrification, preset aeration time enhanced ammonium-oxidizing bacteria dominance. It was also found that low DO could result in overgrowth of filamentous microorganisms and poor sludge settleability. The pH variation could provide effective information for controlling aeration duration in modified mode. However, no evident breakpoint appeared on pH and DO profiles in traditional mode.     

Feasibility study on the removal of nitrous compounds with a hollow-fiber membrane biofilm reactor.

The objective of this study was to develop an integrated nitrogen treatment system using autotrophic organisms. A treatment system consists of an aerobic hollow-fiber membrane biofilm reactor (HfMBR) and anaerobic HfMBR. In the aerobic HfMBR, a mixture gas of air and O2 was supplied through the fibers for nitrification. Denitrification occurred in the anaerobic HfMBR using H2 as the electron donor. The treatment system was continuously operated for 190 days. NH4-N removal efficiencies ranging from 95% to 97% were achieved at NH4-N concentrations of influent ranging from 50 to 100 mg N/L. When glucose was added to the influent, the simultaneous nitrification and denitrification occurred in the aerobic HfMBR, and nitrogen removal rates were changed according to the COD/NH4-N ratio of influent. In the anaerobic HfMBR, autotrophic denitrification using H2 occurred and the removal rates achieved in this study were 23-58 mg N/m2 d. In this study, the achieved removal efficiency was lower than other study findings; however, the result suggested that this hybrid HfMBR system can be used effectively for nitrogen removal in oligotrophic water.     

Nitrification and denitrification in partially aerated biological aerated filter (BAF) with dual size sand media.

A 104-mm (4-inch) diameter pilot-scale biological aerated filter (BAF) with a media depth of 2.5 m (8.3 feet) was operated with an anaerobic, anoxic and oxic zone at a temperature of 23 degrees C. The medium for the anaerobic and anoxic zones was 10 mm diameter sand while the medium for the oxic zone was 5 mm diameter sand. The influent sCOD and total nitrogen concentrations in the feedwater were approximately 250 mg/L and 35 mg N/L, respectively. sCOD removal at optimum hydraulic retention time (HRT) of 3 h with recirculation rates of 100, 200 and 300% in the column was above 96%. Nitrification was found to be more than 96% for 3 h HRT at 200 and 300% recirculation. Total nitrogen removal was consistent at more than 80% for 4 and 6 h HRT at 300% recirculation. For 3 h HRT and 300% recirculation, total nitrogen removal was approximately 79%. The ammonia loading rates for maximum ammonia removed were 0.15 and 0.19 kg NH3-N/m3-day for 100 and 200% recirculation, respectively. The experimental results demonstrated that the BAF can be operated at an HRT of 3h with 200-300% recirculation rates with more than 96% removal of sCOD and ammonia and at least 75% removal of total nitrogen.