不同NO3-浓度An/A/O-SBR系统PAOs-GAOs竞争及N2O释放特性

采用厌氧/缺氧/好氧运行的序批式生物反应器（An/A/O-SBR）,经不同NO₃^-浓度（10,20,30和40 mg/L,以氮计）长期驯化,考察了不同NO₃^-条件下An/A/O-SBR脱氮除磷及N₂O释放特性,基于不同微生物降解特性分析,确定了不同NO₃^-浓度下SBR系统内反硝化聚磷菌（denitrifying phosphorus accumulating organisms,DPAOs）和聚糖菌（glycogen-accumulating organisms, GAOs）竞争关系。结果表明：随NO₃^-浓度增加,总氮（TN）去除率由90%以上降至41.3%,TP去除率呈先增高后降低的趋势,N₂O产率（N₂O_emission/NO_x^-_removal）分别为1.68%、4.17%、8.92%和14.28%。An/A/O-SBR内微生物呈PAOs和GAOs共存的污染物降解特性,高浓度NO₃^-缺氧吸磷过程出现NO₂^-积累,抑制DPAOs活性,GAOs碳源竞争能力增强,NO₃^--N由10 mg/L增至40 mg/L,厌氧阶段PAOs的COD耗量比例由33.5%降至25.1%,相应GAOs的COD耗量由59.3%增至74.1%。DPAOs-GAOs共生体系内,反硝化过程NO₂^-/HNO₂积累耦合反硝化聚糖菌比例增加,加剧了高NO₃^-下An/A/O-SBR内N₂O释放。     

不同电子受体配比对反硝化除磷特性及内碳源转化利用的影响

以A²/O-生物接触氧化(biological contact oxidation,BCO)系统反硝化除磷活性污泥为研究对象,通过投加不同浓度的NO₂^--N和NO₃^--N(30 mg·L^-1),考察了反硝化聚磷菌(denitrifying polyphosphate accumulating organisms,DPAOs)在不同电子受体配比(NO₂^--N:NO₃^--N0, 0.2:0.8, 0.4:0.6, 0.5:0.5, 0.6:0.4)条件下的脱氮除磷特性。结果表明:乙酸钠为DPAOs用于反硝化除磷的理想碳源,且其浓度为200 mg·L^-1时最佳;仅以NO₃^--N为电子受体进行缺氧吸磷反应时,NO₃^--N的投加量为30 mg·L^-1时较为合适;以NO₂^--N作为电子受体,未经 驯化的DPAOs,短时间内很难利用NO₂^--N,但低浓度的 (6 mg·L^-1)不会影响DPAOs以 作电子受体进行反硝化除磷;同时,NO₂^--N对于DPAOs吸磷作用的抑制程度明显强于 反硝化作用,当NO₂^--N浓度达到18 mg·L^-1时,吸磷反应基本停止;此外,较高浓度的NO₂^--N不仅会抑制聚羟基脂肪酸酯(poly-β-hydroxyalkanoate,PHA)的分解利用,且会使PHA分解产生的能量较多地用于储存糖原(glycogen,Gly),而所分解利用的PHA中90%以上为聚-β-羟基丁酸酯(poly-β-hydroxybutyrate,PHB)。     

厌氧复合床处理模拟焦化废水的反硝化动力学

采用厌氧复合床(UBF)处理模拟焦化废水,进水中投加NaNO₃模拟硝化液回流,实现了同时反硝化/产甲烷,COD去除率达到94%,NO₃^--N去除率达到99%。取复合床下部污泥做反硝化动力学研究,在存在亚硝酸盐积累的情况下,以NO₃^--N+0.6NO₂^--N作为反硝化电子受体,采用双基质的Monod方程对实验数据进行拟合,拟合曲线与实验测定值相关性良好。其次,采用双基质的Monod微分方程组对NO₃^--N和NO₂^--N的浓度变化进行拟合,得到相关参数:硝态氮的最大比降解速率和半饱和常数分别为1.13 d^-1和2.0 mg·L^-1;亚硝态氮的最大比降解速率和半饱和常数分别为0.66 d^-1和2.5 mg·L^-1,基于硝态氮和亚硝态氮的有机物半饱和常数分别为90.8 mg·L^-1和96.8 mg·L^-1。     

纳米零价铁去除水中硝酸盐氮研究进展

水中硝酸盐氮(NO₃^--N)的危害对人类健康和生态环境构成了严重威胁,纳米零价铁(nZVI)可以通过化学反应反硝化技术快速去除水中NO₃^--N,但nZVI自身易团聚,表面活性颗粒不稳定,所以在NO₃^--N还原过程中存在着氮气(N₂)的选择性较低、NO₃^--N去除率不理想的问题。通过对nZVI去除NO₃^--N技术的归纳总结,探讨了nZVI在还原NO₃^--N的基本原理,影响因素和提高去除效率和N₂选择性的改性方法。通过负载纳米材料,表面活性剂及添加还原剂等,NO₃^--N去除率和N₂选择性都会得到不同程度上的提高。不同的改性方法对nZVI的改性效果不同,也决定了nZVI复合材料对NO₃^-     

驯化后的聚糖菌对NO2——N和NO3——N内源反硝化速率的影响

在序批式（sequencing batch reactor,SBR）反应器中,通过分段厌氧-好氧（厌氧后排水）运行方式,在以葡萄糖为碳源、P/C比小于2/100的条件下,成功实现了聚糖菌（glycogen accumulating organisms,GAOs）的驯化富集,厌氧段磷酸盐的释放量（phosphorus release amounts,PRA）稳定在1.0 mg·L^-1以内,胞内糖原（glycogen,gly）含量是初始阶段的1.2倍。驯化后的GAOs分别以NO₂^--N、NO₃^--N为电子受体经厌氧-缺氧运行方式,可进行内源反硝化反应过程。GAOs在内源反硝化过程中依次利用胞内的聚β-羟基戊酸酯（poly-β-hydroxyvalerate,PHV）、聚β-羟基丁酸酯（poly-β-hydroxyvalerate,PHB）和gly作为内碳源。在22℃时,反硝化聚糖菌（denitrifying glycogen accumulating organisms,DGAOs）以NO₂^--N、NO₃^--N为电子受体平均比内源反硝化速率分别为0.067 g N·（g VSS）^-1·d^-1、0.023 g N·（g VSS）^-1·d^-1,常温短程内源反硝化速率约是全程内源反硝化速率的3倍。     

氮浓度对新型生物电化学-颗粒污泥反应器运行的影响

探讨了新型生物电化学-颗粒污泥反应器在不同进水氮浓度下的脱氮效能与产电性能,并从颗粒污泥的关键酶活性、胞外聚合物组分以及微生物群落分布等角度系统研究了其影响机制。结果表明,COD、NO₃^--N、NO₂^--N和溶解性甲烷在第Ⅰ、Ⅱ、Ⅲ、Ⅳ阶段（进水NO₃^--N和NO₂^--N浓度分别为60 mg·L^-1和20 mg·L^-1、100 mg·L^-1和40 mg·L^-1、140 mg·L^-1和60 mg·L^-1、180 mg·L^-1和80 mg·L^-1）均得以有效去除,其中COD去除率在第Ⅳ阶段效果最佳,去除率达96%以上,NO₃^--N出水浓度在第Ⅱ阶段更为稳定,其去除率达99%以上,NO₂^--N去除率在各阶段均达99%以上;该反应器最大的功率密度与输出电压值为第Ⅳ阶段的4号格室,分别为471.2 mV·m^-3和608.1 mV。污泥疏松型胞外聚合物（LB-EPS）中多糖与蛋白含量最高为第Ⅱ阶段的5号格室,分别为13.7 mg·g^-1和14.7 mg·g^-1;1号格室污泥中辅酶F₄₂₀活性最低,进水氮浓度的增大提高了污泥中蛋白酶活性。由第Ⅰ阶段至第Ⅳ阶段,该反应器中变形菌门（Protebaoteria）相对丰度减少,而绿弯菌门（Chloroflexi）、厚壁菌门（Firmicutes）和浮霉菌门（Planctomycetes）相对丰度增加;具有脱氮作用的陶厄氏菌属（Thauera）在1号格室减少了8.64%,但该反应器脱氮效果未受到影响;甲烷丝状菌属（Methanothrix）在4号格室相对丰度增至12.3%,表明产甲烷菌可在该反应器中与其他菌群联营共存。     

NOx——N对初沉污泥厌氧发酵及反硝化性能的影响

为了解决低C/N比污水的脱氮问题,本研究将NO_x^--N引入到初沉污泥厌氧发酵系统,利用初沉污泥厌氧发酵过程释放的有机碳源完成反硝化,以达到利用初沉污泥作为碳源强化污水脱氮的目的。通过对系统中VFAs积累、NO_x^--N去除及VSS变化情况的考察,对比研究了4种不同电子受体类型初沉污泥厌氧系统发酵性能、反硝化能力。得出:在34 d的发酵期里,NO₃^--N型系统以及NO₂^--N、NO₃^--N混合型系统中没有出现明显VFAs积累,而在NO₂^--N型系统和纯厌氧系统中出现了不同程度的VFAs积累,说明在试验条件下,NO₃^--N型和混合型系统发酵过程所释放的碳源能得到较好的利用;各系统中NO_x^--N还原总量分别为1692 mg·L^-1(NO₃^--N型)、1330 mg·L^-1(混合型)、1223 mg·L^-1(NO₂^--N型),表明NO₃^--N型系统反硝化能力最强;此外,虽然各NO_x^--N系统中的VSS减量程度相对于厌氧系统稍有降低,但各系统均达到了60%以上的高VSS减量水平,其中NO₃^--N型系统VSS减量67.9%,在各NO_x^--N系统中最高。综上,NO₃^--N型初沉污泥厌氧发酵系统能同时取得相对最好的反硝化脱氮及污泥减量性能。     

高效反硝化分段组合式反应器运行性能

氮素污染是水体富营养化的主要诱因之一,反硝化技术是氮素污染控制的有效手段。采用模拟废水,研究了反硝化分段组合式反应器(CAR)的脱氮除碳性能。实验结果表明,CAR具有很高的容积效能,在进水NO₃^--N浓度为964.7 mg·L^-1、水力停留时间为0.86 h条件下,硝氮去除速率(NRR)为26.8 kg·(m³·d)^-1,COD去除速率(CRR)为93.76 kg·(m³·d)^-1,NRR高于文献报道的最高值,CRR也达到文献报道的领先水平。CAR具有良好的运行稳定性,在反应器的效能上升阶段和效能稳定阶段,出水基质浓度的变异系数比和极差分别小于9.85和9.07,出水pH的相对标准差小于1。CAR运行性能出众的原因是它能持留浓度高(MLVSS高于17 g·L^-1)、活性强(最大比活性为1.573 g NO₃^--N·(g VSS)^-1·d^-1)的颗粒污泥。     

苯酚对污水生物脱氮系统亚硝积累及污泥性能的影响

采用SBR缺氧/好氧反应工艺,研究了不同苯酚浓度对脱氮过程中亚硝积累与污泥性能的影响。结果表明,苯酚浓度在0~90 mg·L^-1变化时系统出现2次明显亚硝酸盐积累,最终稳定维持在70%±5%,低浓度(0~30 mg·L^-1)系统亚硝酸盐积累恢复是微生物改变自身结构及分泌胞外聚合物导致;高浓度(60~90 mg·L^-1)苯酚条件下亚硝积累是由于苯酚对AOB(ammonia-oxidizing bacteria,氨氮氧化细菌)和NOB(nitrite-oxidizing bacteria,亚硝酸氧化细菌)抑制作用引起的微生物种群改变形成。氨氮氧化速率和氮氧化物生成速率由10.85 mg N·(g MLSS)^-1·h^-1和10.12 mg N·(g MLSS)^-1·h^-1降低至2.79 mg N·(g MLSS)^-1·h^-1和2.32 mg N·(g MLSS)^-1·h^-1,亚硝酸盐积累率和氮氧化物生成速率呈现负相关性,与苯酚浓度呈正相关;荧光原位杂交表明苯酚的抑制使得硝化菌群结构发生了变化,AOB 相对数量由2.80%增加为9.30%。苯酚的可降解性使得系统污泥浓度由2500 mg·L^-1左右上升至5870 mg·L^-1。当EPS(extracellular polymeric substances,胞外聚合物)总量由67.20 mg·(g VSS)^-1减少至32.10 mg·(g VSS)^-1时,SVI从165 ml·g^-1降到50 ml·g^-1。亚硝酸盐积累、丝状菌和胞外聚合物是引起活性污泥系统SVI变化的原因,其中NAR影响最大,丝状菌次之。     

基于FNA处理污泥实现城市污水部分短程硝化

为实现城市污水短程硝化厌氧氨氧化生物脱氮,以去除有机物的实际污水为研究对象,考察了游离亚硝酸盐(FNA)处理污泥实现城市污水部分短程硝化的可行性。 结果表明,FNA处理活性污泥后,亚硝酸盐氧化菌(NOB)的亚硝酸盐氧化速率下降程度大于氨氧化菌(AOB)的氨氧化速率,且在0～0.75 mg HNO₂-N·L^-1范围内随着FNA浓度的增加抑制作用增强。接种实际污水厂活性污泥后,系统亚硝酸盐(NO₂^--N)积累率仅为1%,即为全程硝化。在控制污泥龄约为15 d的条件下,采用FNA处理污泥可使系统亚硝酸盐积累率增加至90%以上。水力停留时间调至2.5 h时,实现了部分短程硝化,且出水NO₂^--N/NH₄⁺-N平均值为1.24,可满足厌氧氨氧化脱氮反应的要求。因此采用FNA处理污泥,结合水力停留时间和污泥龄控制可实现城市污水部分短程硝化。     

缺氧环境对颗粒污泥强化除磷系统释磷的影响

以除磷颗粒污泥为研究对象,采用批次试验,以混合丙酸和乙酸（2∶1）为外加碳源,在厌氧起始阶段投加不同浓度的NO^-₃-N（0, 20, 30, 50和75 mg·L^-1, pH=8.0）和NO^-₂-N（10,20,40和60 mg·L^-1, pH=7.0, 7.5和8.0）,研究缺氧环境对颗粒污泥强化除磷系统释磷的影响。结果表明,硝态氮的投加对聚磷菌释磷无明显抑制,系统中VFA的吸收、磷的释放和硝态氮的反硝化同时发生,挥发性脂肪酸（相似文献   

Cu2O/rGO复合材料修饰阴极强化MFC产电脱氮性能及其机理

微生物燃料电池(MFC)在处理含硝酸盐(NO_3^--N)废水时具有同时产电和脱氮的潜力,寻找成本低且改善其产电脱氮性能的阴极修饰材料是MFC在含氮废水处理领域应用的关键。氧化亚铜/还原氧化石墨烯(Cu₂O/rGO)复合材料具有良好的电化学性能,在替代铂基材料提高MFC性能方面具有一定的应用前景。本研究通过还原法制备了Cu₂O/rGO复合材料,并对材料的结构和氧还原性能进行表征；同时,将其负载于阴极碳布后分析其电化学性能,并通过MFC的输出电压、功率密度和NO_3^--N的去除率探究Cu₂O/rGO阴极对MFC产电和脱氮性能的强化作用；通过对反硝化相关酶活性和胞外聚合物的测定,探究Cu₂O/rGO阴极强化MFC性能的机理。结果表明：Cu₂O/rGO复合材料具有大量的介孔结构,能够为电子传递提供更多的通道,并且Cu₂O/rGO复合材料具有良好的氧化还原可逆性；与Pt/C阴极相比,Cu₂O/rGO阴极的交换电流密度升高33.53%,电子转移阻力降低65.53%；Cu₂O/rGO-MFC在处理NO_3^-N废水时获得的最大平均输出电压(662.54 mV)、最大功率密度(26.27 mW/cm^₂)、平均库伦效率(32.02%)和NO_3^--N去除速率(83.33 mg NO_3^--N L/h)均高于Pt/C-MFC(485.33 mV,16.98 mW/cm^₂,7.38%,41.67 mg NO_3^--N L/h)；Cu₂O/rGO复合材料通过提高MFC阴极反硝化关键酶活性和类蛋白组分含量,改善了MFC的产电和脱氮性能。     

Performance evaluation of a modified anaerobic/anoxic/oxic (A/O) process treating low strength wastewater

A full scale modified A²/O process which combined pre-anoxic selector and the staging strategy treating low strength wastewater was investigated. In South China, domestic wastewater is always low in strength due to the high level of groundwater and setting of septic tank at the beginning of wastewater collection system. The results suggested that inadequate denitrification could result in deterioration of phosphorus removal. In addition, influent phosphorus concentration had effect on phosphorus removal. The pre-anoxic selector in modified A²/O process changed the distribution of nitrogen denitrified in different tanks. Characteristics of 3-stage aeration tanks were also studied. The simplified design of rectangular aeration tank could also perform as plug flow as conventional channel aeration tank. In 3-stage aeration tanks, mixed liquid suspended solid (MLSS) increased from one tank to another, while specific oxygen uptake rate (SOUR) of sludge, chemical oxygen demand (COD) and total phosphorus (TP) removal rate decreased, however ammonia nitrogen (NH₃-N) and nitrate nitrogen (NO₃-N) reaction rate remained constant. Furthermore, high MLSS concentration was not suitable for treating low strength wastewater. Waste sludge discharge could improve removal efficiency of COD, NH₃-N, and TP. Without waste sludge discharge, nitrite accumulated in settler.     

NO reduction by CH4over La2O3: temperature‐programmed reaction and in situ DRIFTS studies

The chemistry between NO _x species adsorbed on La₂O₃ and CH₄ was probed by temperature‐programmed reaction (TPR) as well as in situ DRIFTS. During NO reduction by CH₄ in the presence of O₂, NO ₃ ^- does not appear to activate CH₄, thus either an adsorbed O species or an NO ₂ ^- species is more likely to activate CH₄. In the absence of O₂, a different reaction pathway occurs and NO^- or (N₂O₂)^2- species adsorbed on oxygen vacancy sites seem to be active intermediates, and during NO reduction with CH₄ unidentate NO ₃ ^- , which desorbs at high temperature, behaves as a spectator species and is not directly involved in the catalytic sequence. Because reaction products such as CO₂ or H₂O as well as adsorbed oxygen cannot be effectively removed from the surface at lower temperatures, steady‐state catalytic reactions can only be achieved at temperatures above 800 K, even though formation of N₂ and N₂O from NO was observed at much lower temperature during the TPR experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low Activation Energy Pathway for the Catalyzed Reduction of Nitrogen Oxides to N<Subscript>2</Subscript> by Ammonia

A low activation energy pathway for the catalytic reduction of nitrogen oxides to N₂, with reductants other than ammonia, consists of two sets of reaction steps. In the first set, part of the NO _x is reduced to NH₃; in the second set ammonium nitrite, NH₄NO₂ is formed from this NH₃ and NO + NO₂. The NH₄NO₂ thus formed decomposes at ~100 °C to N₂ + H₂O, even on an inert support, whereas ammonium nitrate, NH₄NO₃, which is also formed from NH₃ and NO₂ + O₂, (or HNO₃), decomposes only at 312 °C yielding mainly N₂O. Upon applying Redhead's equations for a first order desorption to the decomposition of ammonium nitrite, an activation energiy of 22.4 is calculated which is consistent with literature data. For the reaction path via ammonium nitrite a consumption ratio of 1/1 for NO and NO₂ is predicted and confirmed experimentally by injecting NO into a mixture of NH₃ + NO₂ flowing over a BaNa/Y catalyst. This leads to a yield increase of one N₂ molecule per added molecule of NO. Little N₂ is produced from NH₃ + NO in the absence of NO₂.     

A kinetic study of NOx reduction over Pt/SiO2 model catalysts with hydrogen as the reducing agent

Flow reactor experiments and kinetic modeling have been performed in order to study the mechanism and kinetics of NO_x reduction over Pt/SiO₂ catalysts with hydrogen as the reducing agent. The experimental results from NO oxidation and reduction cycles showed that N₂O and NH₃ are formed when NO_x is reduced with H₂. The NH₃ formation depends on the H₂ concentration and the selectivity to NH₃ and N₂O is temperature dependent. A previous model has been used to simulate NO oxidation and a mechanism for NO_x reduction is proposed, which describes the formation/consumption of N₂, H₂O, NO, NO₂, N₂O, NH₃, O₂ and H₂. A good agreement was found between the performed experiments and the model.     

Fluxes of NO and N2O from temperate forest soils: impact of forest type, N deposition and of liming on the NO and N2O emissions

Annual cycles of NO, NO₂ and N₂O emission rates from soil were determined with high temporal resolution at a spruce (control and limed plot) and beech forest site (Höglwald) in Southern Germany (Bavaria) by use of fully automated measuring systems. The fully automated measuring system used for the determination of NO and NO₂ flux rates is described in detail. In addition, NO, NO₂ and N₂O emission rates from soils of different pine forest ecosystems of Northeastern Germany (Brandenburg) were determined during 2 measuring campaigns in 1995. Mean monthly NO and N₂O emission rates (July 1994–June 1995) of the untreated spruce plot at the Höglwald site were in the range of 20–130 µg NO-N m^-2 h^-1 and 3.5–16.4 µg N₂O-N m^-2 h^-1, respectively. Generally, NO emission exceeded N₂O emission. Liming of a spruce plot resulted in a reduction of NO emission rates (monthly means: 15–140 µg NO-N m^-2 h^-1) by 25-30% as compared to the control spruce plot. On the other hand, liming of a spruce plot significantly enhanced over the entire observation period N₂O emission rates (monthly means: 6.2–22.1 µg N₂O-N m^-2 h^-1). Contrary to the spruce stand, mean monthly N₂O emission rates from soil of the beech plot (range: 7.9–102 µg N₂O-N m^-2 h^-1) were generally significantly higher than NO emission rates (range: 6.1–47.0 µg NO-N m^-2 h^-1). Results obtained from measuring campaigns in three different pine forest ecosystems revealed mean N₂O emission rates between 6.0 and 53.0 µg N₂O-N m^-2 h^-1 and mean NO emission rates between 2.6 and 31.1 µg NO-N m^-2 h^-1. The NO and N₂O flux rates reported here for the different measuring sites are high compared to other reported fluxes from temperate forests. Ratios of NO/N₂O emission rates were >> 1 for the spruce control and limed plot of the Höglwald site and << 1 for the beech plot. The pine forest ecosystems showed ratios of NO/N₂O emission rates of 0.9 ± 0.4. These results indicate a strong differentiating impact of tree species on the ratio of NO to N₂O emitted from soil.     

An acid catalyzed step in the catalytic reduction of NO x to N2

Contact of adsorbed ammonium nitrite, NH₄NO₂, with HCl vapor or a solid acid such as the zeolite HY, significantly lowers the temperature of its decomposition to N₂ + H₂O. Protonated NH₄NO₂ decomposes at room temperature. The decomposition of ammonium nitrite is one of the steps in the catalytic reduction of NO _x with ammonia or other reductants.