缺氧FNA对氨氧化菌和亚硝酸盐氧化菌的选择性抑菌效应

为了研究缺氧条件下游离亚硝酸（FNA）对氨氧化菌（AOB）和亚硝酸盐氧化菌（NOB）的选择性抑菌效应,通过批次试验考察活性污泥经缺氧FNA（0.27 mg HNO₂^--N·L^-1）处理6 h后,其氨氧化速率与亚硝酸盐氧化速率的变化及AOB和NOB活性恢复情况。结果表明：经缺氧FNA处理的活性污泥,NOB活性下降83.57%,而AOB的活性仅下降22.34%。此污泥在正常条件下运行34个周期后,NOB的活性仍未得到恢复,且硝化过程中亚硝酸盐积累率逐渐增加,最后稳定在90%以上。典型周期内氮化合物浓度变化研究表明,即使在过曝气2 h的条件下,亚硝酸盐积累并未遭到破坏。上述试验结果表明基于缺氧FNA选择性抑菌效应有望稳定实现城市污水短程硝化,为城市污水短程硝化厌氧氨氧化提供基础。     

不同盐度生活污水硝化及N_2O释放特性

以14 L序批式活性污泥反应器(SBR)处理含盐生活污水,控制曝气体积流量60 L/h、时间300 min,考察不同盐度(NaCl)SBR内微生物活性变化,并确定反应器脱氮及N_2O释放特性。结果表明,盐度对各菌群抑制程度亚硝态氮氧化菌(NOB)氨氧化菌(AOB)碳氧化菌。盐度10 g/L,AOB和NOB受抑制程度较低,而N_2O还原受明显抑制,N_2O产率由盐度0时的5.14%增至10 g/L时的7.96%。盐度增至20 g/L,AOB和NOB均受到明显抑制,系统内亚硝化率达90%以上。系统淘洗出NOB,由全程硝化转变为短程硝化过程。NO_2~--N大量积累和AOB相对含量增加,为低含氧条件下AOB的好氧反硝化提供了条件,高盐度对氧化亚氮还原酶活性抑制也导致了系统N_2O释放量增加。     

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。     

短程生物脱氮过程菌群调控影响因素研究进展

短程生物脱氮技术可有效降低污水处理成本。本文介绍了温度、pH、溶解氧(DO)、游离氨(FA)、游离亚硝酸(FNA)等环境因素对氨氧化菌(AOB)和亚硝酸盐氧化菌(NOB)的不同影响;特异性硝化抑制剂:丙烯基硫脲(ATU)、氯酸盐、叠氮化钠(NaN3)等对短程硝化的抑制效应。这些研究有助于更好地调控硝化菌群的类型,实现更稳定的短程生物脱氮。     

部分硝化-短程反硝化-厌氧氨氧化系统脱氮效能及N2O排放特性的研究

为建立城市污水主流厌氧氨氧化脱氮系统并研究其温室气体N₂O排放特征,采用低氧SBBR处理模拟生活污水并获得了94.1%的TN去除率。连续试验及批量试验结果表明,高效脱氮是部分硝化-短程反硝化耦合厌氧氨氧化共同耦合作用结果。典型周期内N₂O排放呈快速上升、波动式快速下降、缓慢消失的规律,其中第75 min N₂O排放速率最高,达6.7μg/(L·min),推测是由于低氧硝化过程中羟胺氧化作用所致。高通量测序揭示了体系内同时存在着厌氧氨氧化、好氧异养、反硝化、硝化等功能菌属,与系统脱氮和N₂O产生密切相关。     

长波紫外辐照实现城市污水短程硝化研究

利用紫外线A(UVA,波长315～400 nm,最高365 nm)辅助照射活性污泥,研究了紫外辅助实现城市污水短程硝化工艺的可行性,考察了UVA对活性污泥中氨氧化菌(AOB)和亚硝酸氧化菌(NOB)活性影响。结果表明,不同辐射强度UVA照射下AOB活性略有提高而NOB活性显著下降,辐射强度1.67×10^-6 Einstein/(L·s)下对NOB活性的抑制率达40%。通过序批式反应器(SBR),以模拟城市污水为处理对象,在UVA紫外辐射强度0.867×10^-6 Einstein/(L·s)下,在常温(25～27℃)、COD为100～150 mg/L、进水NH₄⁺-N的质量浓度为50 mg/L的条件下,运行30 d后出水NH₄⁺-N去除率达到90%以上、NO₂^--N积累率稳定在80%左右,成功实现了城市污水短程硝化。     

MUCT工艺处理生活污水短程脱氮的实现及硝化菌群动态变化

采用连续流MUCT工艺处理实际生活污水,研究短程生物脱氮的实现,并采用实时荧光定量PCR方法(quantitative real time PCR,QPCR)分析全程脱氮向短程脱氮转变过程中氨氧化细菌(ammonia-oxidizing bacteria,AOB)和亚硝酸盐氧化菌(nitrite-oxidizing bacteria,NOB)的动态变化。通过降低溶解氧浓度为0.5mg·L^-1和缩短水力停留时间为6h,实现短程硝化,亚硝酸盐积累率达到90%。在短程硝化稳定运行阶段总氮去除率高达90%以上,远远大于全程阶段的74%。QPCR结果表明全程脱氮阶段水力停留时间的缩短使AOB细胞数呈现下降的趋势,NOB细胞总数稳定维持在10⁸cells·(g dried sludge)^-1。短程脱氮阶段,AOB细胞数小幅度上升,由3.17×10⁶cells·(g dried sludge)^-1增长到1.32×10⁷cells·(g dried sludge)^-1,同时AOB占全菌的比例也小幅度增长。NOB的细胞数在5.9×10⁷~1.78×10⁸cells·(g dried sludge)^-1之间波动。NOB占全菌的比例由1.44%下降到0.47%。因此,MUCT工艺处理实际生活污水的系统中NOB丰度降低及活性抑制是实现并维持短程生物脱氮的重要原因。短程脱氮运行期间由于控制低溶解氧浓度和短的水力停留时间,AOB丰度及相对含量没有显著增加,甚至下降,但不会影响氨氮和总氮的去除。     

短程硝化过程中硝化速率与N2O产生速率的关系

N₂O是3种主要的温室气体之一,污水的生物脱氮过程是N₂O产生的一个主要人为来源。通过对不同条件下生活污水短程硝化过程中N₂O的产生情况进行研究,考察了短程硝化过程中硝化速率(AOR)与N₂O产生速率(N₂OR)之间的关系。结果表明:随着DO水平的提高,AOR逐渐上升,N₂OR则呈现先增加后减少的趋势;最大N₂OR出现在DO为0.6 mg·L^-1时,为1.29 mg N₂O-N·(g MLVSS)^-1·h^-1。低DO水平下AOR的提高会引起N₂OR的增加;但高DO水平下较高的AOR不一定产生较多的N₂O。不同条件下,N₂O的产生途径不同,引起N₂OR的变化。在DO较低时,N₂O的产生以NH₂OH/NOH途径为主,AOR的提高会促进N₂O产生;随着DO的增加,N₂O的产生途径主要为AOB的有氧反硝化作用,此时较高的DO水平会对这一反应造成抑制,虽然反应过程中AOR较高,但N₂OR处于较低水平。     

协同调控C/N负荷提升好氧颗粒污泥亚硝化性能

以异养颗粒污泥为接种污泥启动SBR反应器,通过协同调控进水碳、氮负荷比值,成功获得了具备短程亚硝化功能的自养型颗粒污泥。基于对粒径分布、胞外聚合物（EPS）和功能菌动力学活性的分析,系统阐述了影响污泥性状与功能演化的关键因素。结果表明,随着氨氧化菌（AOB）活性（μ_NO3-N）的持续增强和对亚硝酸盐氧化菌（NOB）活性（μ_NO3-N）的有效抑制,反应器对亚硝态氮（NO₂^--N）的累积速率可达1.34 kg·（m³·d）^-1。污泥平均粒径由1.4 mm增至2.2 mm,颜色变为红棕色,沉降性能明显改善。得益于EPS的不断累积,颗粒污泥在高选择压条件下（沉淀时间3 min）,仍能有效截留、固定AOB。曝气反应期间,游离氨（FA）和游离亚硝酸（FNA）对NOB的选择性抑制也是实现稳定亚硝化反应的重要原因。     

生活污水对成熟厌氧氨氧化颗粒污泥的影响

部分短程硝化和厌氧氨氧化技术的研究主要集中在高氨氮废水方面，对低氨氮浓度生活污水的研究相对较少。使经过除碳和部分短程硝化后的实际生活污水进入厌氧氨氧化UASB反应器，探究生活污水对成熟厌氧氨氧化颗粒污泥的影响。结果表明，当厌氧氨氧化UASB反应器的进水由配水变为生活污水后，反应器出水中氨氮浓度可降到5 mg·L^-1以下，亚硝态氮浓度可降到1 mg·L^-1以下，但是硝态氮的生成量高于理论值，可能是溶解氧被带入UASB反应器使硝化作用增强。UASB反应器内厌氧氨氧化污泥颜色由红色变为红黑色，T-EPS含量减少，PN/PS由1.13增大到3.66，沉降性变好，反应器内污泥中厌氧氨氧化菌Candidatus Brocadia所占比例由17.7%减少为14.4%，系统内AOB和NOB菌的含量增加，如果能够降低进入UASB反应器的溶解氧，有可能会减少出水硝氮，达到较好总氮去除效果。     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

SO2 and NO removal from flue gas over V2O5/AC at lower temperatures — role of V2O5 on SO2 removal

Supporting V₂O₅ onto an activated coke (AC) has been reported to significantly increase the AC's activity in simultaneous SO₂ and NO removal from flue gas. To understand the role of V₂O₅ on SO₂ removal, V₂O₅/AC is studied through SO₂ removal reaction, surface analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) techniques. It is found that the main role of V₂O₅ in SO₂ removal over V₂O₅/AC is to catalyze SO₂ oxidation through a VOSO₄-like intermediate species, which reacts with O₂ to form SO₃ and V₂O₅. The SO₃ formed transfers from the V sites to AC sites and then reacts with H₂O to form H₂SO₄. At low V₂O₅ loadings, a V atom is able to catalyze as many as 8 SO₂ molecules to SO₃. At high V₂O₅ loadings, however, the number of SO₂ molecules catalyzed by a V atom is much less, due possibly to excessive amounts of V₂O₅ sites in comparison to the pores available for SO₃ and H₂SO₄ storage.     

Study of the Supported K2MoO4 Catalyst for Methanethiol Synthesis by One Step from High H2S-Containing Syngas

ESR and XPS are used to study the Mo-based catalysts MoO₃/K₂CO₃/SiO₂ and K₂MoO₄/SiO₂ prepared with two kinds of precursors, (NH₄)₆Mo₇O₂₄4H₂O and K₂MoO₄. The catalytic properties of the catalysts for methanethiol synthesis from high H₂S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of oxo-Mo(V) (g=1.93), thio-Mo(V) (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO₃/SiO₂ modified with K₂CO₃, as increasing amounts of K₂CO₃ are added, the content of oxo-Mo(V) increases, but thio-Mo(V) decreases. The XPS characterization indicates that Mo has mixed valence states of Mo⁴⁺, Mo⁵⁺ and Mo⁶⁺, and that S includes three kinds of species: S^2– (161.5 eV), [S–S]^2– (162.5 eV) and S⁶⁺ (168.5 eV). Adding K₂CO₃ promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo₂S and oxo-M(V), and the derivation of [S–S]^2– and S^2– species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo⁶⁺ + Mo⁵⁺)/Mo⁴⁺ 0.8 and S^2–/[S–S]^2– is kept at a value of about 1.     

Preparation and characterization of multicomponent porous materials prepared by the sol-gel process

An experimental strategy was developed to obtain transparent Si-Al-Ti-Ni-Mo and Si-Zr-Ti-Ni-Mo sols via the sol-gel process. The sol was prepared from Si(OEt)₄ (TEOS), Al(OBu^s)₃ (OBu^s: C₂H₅CH(CH₃)O), Ti(OEt)₄ (OEt: OCH₂CH₃), Zr(OPrⁿ)₄ (OPrⁿ: OCH₂CH₂CH₃). In both cases nickel nitrate hexahydrate (Ni(NO₃)₂ · 6H₂O) and ammonium heptamolybdate tetrahydrate ((NH₄)₆Mo₇O₂₄ · 4H₂O) were the Ni and Mo sources, respectively. The sols were characterized by Fourier Transform Infrared Spectroscopy (FTIR). Assignments of the simultaneous formation of the Si-O-Al, Si-O-Ti, Si-O-Ni, and Si-O-Zr bonds were done. The sols were polymerized at room temperature (293 K) to obtain gels, and these were dried at 423 K and calcined at 573, 853 and 893 K in air. The characterization techniques used were small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR). The density of the solids was measured following ASTM method D-4892 and the porosity and surface area were determined by N₂ adsorption/desorption isotherms. The corresponding average pore diameters were evaluated using the BJH, HK, and DA methods.     

Influence of homogeneous decane oxidation on the catalytic performance of lean NO x catalysts

Extensive homogeneous gasphase reactions were observed when decane was used as the hydrocarbon reductant for the selective reduction of NO _x . The catalytic performance of a SnO₂/CoO _x /Al₂O₃ catalyst was found to be strongly dependent on the extent of the homogeneous reaction in the precatalytic volume. The effect of the homogeneous reaction on the catalytic performance also depended on whether SO₂ was present in the feed. By filling the precatalytic volume with 25–35 mesh irregularly shaped quartz chips, gasphase reaction was suppressed significantly. This methodology was used to evaluate the inherent catalytic performance of SnO₂/CoO _x /Al₂O₃ and SnO₂/Al₂O₃ catalysts with decane as a reductant. It was found that in the absence of SO₂, SnO₂/Al₂O₃ was a better catalyst than SnO₂/CoO _x /Al₂O₃, but in the presence of 30 ppm of SO₂ the latter was a far better catalyst.     

Development of new alumina-modified sorbents for CO2 sorption and regeneration at temperatures below 200 °C

A new regenerable alumina-modified sorbent was developed for CO₂ capture at temperatures below 200 °C. The CO₂ capture capacity of a potassium-based sorbent containing Al₂O₃ (KAlI) decreased during multiple CO₂ sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO₃)(OH)₂ phase, which could be converted into the original K₂CO₃ phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO₂ capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO₂ capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al₂O₃ with 60 wt.% K₂CO₃ was about 128 mg CO₂/g sorbent. This excellent CO₂ capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO₃ phase during CO₂ sorption, unlike the KAlI30 sorbent which formed the KHCO₃ and KAl(CO₃)(OH)₂ phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO₃)(OH)₂ phase which was prepared by impregnation of Al₂O₃ with K₂CO₃ in the presence of CO₂.     

Combustion characteristics of lignite-fired oxy-fuel flames

This experimental work describes the combustion characteristics of lignite-fired oxy-fuel flames, in terms of temperature distribution, gas composition (O₂, CO₂, CO, total hydrocarbon concentration and NO) and ignition behaviour. The aim is to evaluate the flame structure of three oxy-fuel cases (obtained by changing the flue gas recycle rate) including a comparison with an air-fired reference case. Measurements were performed in Chalmers 100 kW test unit, which facilitates oxy-fuel combustion under flue gas recycling conditions. Temperature, O₂ and CO concentration profiles and images of the flames indicate that earlier ignition and more intense combustion with higher peak temperatures follow from reduction of the recycle rate during oxy-fuel operation. This is mostly due to higher O₂ concentration in the feed gas, reduced cooling from the recycled flue gas, and change in flow patterns between the cases. The air case and the oxy-fuel case with the highest recycle rate were most sensitive to changes in overall stoichiometry. Despite significant differences in local CO concentration between the cases, the stack concentrations of CO are comparable. Hence, limiting CO emissions from oxy-fuel combustion is not more challenging than during air-firing. The NO emission, as shown previously, was significantly reduced by flue gas recycling.     

Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/γ-Al2O3 under mild and solvent free conditions

An efficient process to remove organic sulfur compounds from model fuel has been explored. Dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) can be completely oxidized into their corresponding sulfones by H₂O₂ over 14 wt.% MoO₃/γ-Al₂O₃ catalyst under mild conditions in 15 min. The effects of solvent, initial sulfide concentration, loading of MoO₃ and amount of catalyst on oxidative removal of DBT were studied. The employments of solvents have decreased the reaction rate of DBT, which can be attributed to the competitive adsorption between the sulfide and solvent. The oxidative reactivity increases in the order of thiophene (Th) < benzothiophene (BT) < DBT < 4, 6-DMDBT. The catalyst can be regenerated by methanol washing at 333 K.     

Dehydrogenation of ethylbenzene over TiO2-Fe2O3 and ZrO2-Fe2O3 mixed oxide catalysts

The mixed metal oxides TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO₂-Fe₂O₃ catalysts. However, for TiO₂-Fe₂O₃ catalysts, the surface area, the amount of acidic and basic sites and TiFe₂O₅ crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ catalyst system and also for the TiO₂-Fe₂O₃-ZrO₂ system, i.e. the activities of these catalysts can be ranked in the following order: TiO₂-Fe₂O₃-ZrO₂>TiO₂-Fe₂O₃ >ZrO₂>Fe₂O₃>TiO₂. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.