H2O2 treatment boosts activity of NiFe layered double hydroxide for electro-catalytic oxidation of urea

Urea oxidation reaction (UOR) provides a method for hydrogen production besides wastewater treatment, but the current limited catalytic activity has prevented the application. Herein, we develop a novel H₂O₂ treatment strategy for tailoring the surface oxygen ligand of NiFe-layered double hydroxides (NiFe-LDH). The sample after H₂O₂ treatment (NiFeO-LDH) shows significant enhancement on UOR efficiency, with the potential of 1.37 V (RHE) to reach a current density of 10 mA/cm². The boost is attributed to the richness adsorption O ligand on NiFeO-LDH as revealed by XPS and Raman analysis. DFT calculation indicates formation of two possible types of oxygen ligands: adsorbed oxygen on the surface and exposed from hydroxyl group, lowered the desorption energy of CO₂ product, which lead to the lowered onset potential. This strategy is further extended to NiFe-LDH nano sheet on Ni foam to reach a higher current density of 440 mA/cm² of UOR at 1.8 V (RHE). The facile surface O ligand manipulation is also expected to give chance to many other electro-catalytic oxidations.     

Ammonium-dependent regulation of aerobic methane-consuming bacteria in landfill cover soil by leachate irrigation

The impacts of landfill leachate irrigation on methane oxidation activities and methane-consuming bacteria populations were studied by incubation of landfill cover soils with leachate and (NH₄)₂SO₄ solution at different ammonium concentrations. The community structures and abundances of methane-oxidizing bacteria (MOB) and ammonia-oxidizing bacteria (AOB) were examined by PCRDGGE and real-time PCR. Compared with the pure (NH₄)₂SO₄ solution, leachate addition was found to have a positive effect on methane oxidation activity. In terms of the irrigation amount, ammonium in leachate was responsible for the actual inhibition of leachate. The extent of inhibitory effect mainly depended on its ammonium concentration. The suppression of the predominant methaneconsuming bacteria, type I MOB, was responsible for the decreased methane oxidation activity by ammonium inhibition. Methaneconsuming bacteria responded diversely in abundance to ammonium. The abundance of type I MOB decreased by fivefold; type II MOB showed stimulation response of fivefold magnification upon the first addition but lessened to be lower than the original level after the second addition; the amount of AOB was stimulated to increase for 20-30 times gradually. Accumulated nitrate from nitrification strengthened the ammonium inhibition on type I and type II MOB, as a result, repetitive irrigation was unfavorable for methane oxidation.     

Degradation kinetics and mechanism of aniline by heat-assisted persulfate oxidation

Oxidation of aniline by persulfate in aqueous solutions was investigated and the reaction kinetic rates under different temperature, persulfate concentration and pH conditions were examined in batch experiments. The results showed that, the aniline degradation followed pseudo first-order reaction model. Aniline degradation rate increased with increasing temperature or persulfate concentration. In the pH range of 3 to 11, a low aniline degradation rate was obtained at strong acid system (pH 3), while a high degradation rate was achieved at strong alkalinity (pH 11). Maximum aniline degradation occurred at pH 7 when the solution was in a weak level of acid and alkalinity (pH 5, 7 and 9). Produced intermediates during the oxidation process were identified using liquid chromatography-mass spectrometry technology. And nitrobenzene, 4-4’-diaminodiphenyl and 1-hydroxy-1,2-diphenylhydrazine have been identified as the major intermediates of aniline oxidation by persulfate and the degradation mechanism of aniline was also tentatively proposed.     

Diversity of methanotrophs in a simulated modified biocover reactor

A simulated landfill biocover microcosm consisting of a modifying ceramsite material and compost were investigated. Results show that the mixture can improve the material porosity and achieve a stable and highly efficient (100%) methane oxidation over an extended operating period. The diversity of the methanotrophic community in the microcosm was assessed. Type I methanotrophs were enhanced in the microcosm due to the increased air diffusion and distribution, whereas the microbial diversity and population density of type II methanotrophs were not significantly affected. Moreover, the type I methanotrophic community structure significantly varied with the reactor height, whereas that of type II methanotrophic communities did not exhibit a spatial variation. Phylogenetic analysis showed that type I methanotroph-based nested polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) resulted in the detection of eight different populations, most of which are related to Methylobacter sp., whereas that of type II resulted in the detection of nine different populations, most of which are related to Methylocystaceae. Methanotrophic community analysis also indicated that a number of new methanotrophic genera not closely related to any known methanotrophic populations were present.     

pH值对纳米零价铁吸附降解2,4-二氯苯酚的影响

在不同pH条件下,对纳米铁(颗粒粒径为30～40 nm)及其降解2,4-二氯苯酚反应体系进行取样,并进行透射电子显微镜(TEM)、扫描电子显微镜-能谱联用(SEM-EDX)以及电感耦合等离子体发射光谱(ICP-OES)等形貌观测与分析表征,以考察pH值在纳米零价铁降解氯酚反应过程中的影响和作用.结果表明,在降解2,4-二氯苯酚的过程中纳米铁由分散的颗粒逐渐团聚,其表面逐渐氧化,并最终被呈针状结晶的碱式氧化亚铁(FeOOH)覆盖,从而阻碍了降解反应的进一步进行.在酸性体系中,纳米零价铁的氧化和团聚现象有所缓解,尽管会造成一部分铁量的损失,但反应产生大量的亚铁离子参与并促进了脱氯降解反应的进行,反应过程中溶液pH值有逐渐升高的趋势.不同pH条件下,纳米铁对氯酚的去除率随pH值的降低而升高,酸性条件有利于提高氯酚的还原降解速率,当pH=3时,24 h内氯酚的去除率可达到90%以上.     

活性焦负载MnO2对气态Hg0的吸附脱除研究

研究了活性焦(AC)及负载MnO2的活性焦(MnO2/AC)对气态Hg0的吸附脱除,发现负载MnO2到AC明显提高了其对Hg0的吸附脱除能力.考察了MnO2负载量、温度、Hg0浓度和烟气成分等对MnO2/AC吸附脱除Hg0的影响.结果表明,MnO2/AC对Hg0的吸附脱除能力随MnO2负载量的增加而增强;在120～200℃的温度范围内,随着温度升高,MnO2/AC对Hg0的吸附脱除能力增强;O2和HCl对MnO2/AC吸附脱除Hg0具有促进作用,而SO2和H2O具有抑制作用.SEM-EDX和逐级化学提取结果证实,MnO2将Hg0催化氧化为HgO并吸附在AC上,这是MnO2/AC具有较高的吸附脱除Hg0能力的原因.     

水体中二甲胺的吸附与氧化降解

模拟二甲胺的水体污染,采用静态实验装置,从吸附的热力学和动力学方向,讨论活性炭对水体中二甲胺的降解情况;同时讨论了Fenton氧化-活性炭联合法降解二甲胺的效果。结果表明,活性炭吸附二甲胺是一个放热自发的过程,在常温下吸附符合Langmuir的吸附等温模型,吸附速率较慢,在90 min左右才能够达到吸附平衡,同时,溶液的pH值越大,活性炭对二甲胺的吸附作用越明显;而Fenton氧化-活性炭联合法对高浓度的二甲胺溶液降解效果明显,当按H2O2 2.4 mL/L,FeSO.47H2O 12 mg/L,活性炭0.2 g/L的比例投加药剂时,二甲胺的去除率在99%以上,溶液COD的去除率达到81.6%。     

厌氧氨氧化电子受体的研究

在无机条件下,以该课题组已经培养出来的厌氧氨氧化污泥作为接种污泥,分别以硫酸盐、硝酸盐和亚硝酸盐为电子受体来研究氨的氧化反应。从去除速率的角度来看,以NO2--N、NO3--N和SO42--S为电子受体的反应器,分别在运行的第24.5天、40天和31天时达到0.030 0 kg/(m.3d)NH4+-N去除速率,则氧化氨的能力由大到小依次是:亚硝酸盐>硫酸盐>硝酸盐;从标准吉布斯自由能变化来看,3种反应都是可以发生的;以亚硝酸盐为电子受体的反应过程是一个消耗酸度的生物过程,而以硫酸盐为电子受体的反应过程是一个消耗碱度的生物过程。     

水解酸化-接触氧化法处理生活污水的工艺设计

厂区生活污水有机物及悬浮颗粒含量高,可生化性好。采用水解酸化-接触氧化法(厌氧/好氧)处理生活污水,目前系统运行稳定,出水各项指标达到国家GB 8978—1996《污水综合排放标准》中二级排放标准。设计处理能力为1 500 m3/d,处理后出水进入厂区回用水池。     

Photodegradation of amoxicillin by catalyzed Fe3+/H2O2 process

Three oxidation processes of UV-Fe³⁺(EDTA)/H₂O₂ (UV: ultraviolet light; EDTA: ethylenediaminetetraacetic acid), UV-Fe³⁺/H₂O₂ and Fe³⁺/H₂O₂ were simultaneously investigated for the degradation of amoxicillin at pH 7.0. The results indicated that, 100% amoxicillin degradation and 81.9% chemical oxygen demand (COD_Cr) removal could be achieved in the UV-Fe³⁺ (EDTA)/H₂O₂ process. The treatment efficiency of amoxicillin and COD_Cr removal were found to decrease to 59.0% and 43.0% in the UV-Fe³⁺/H₂O₂ process; 39.6% and 31.3% in the Fe³⁺/H₂O₂ process. Moreover, the results of biodegradability (biological oxygen demand (BOD₅)/COD_Cr ratio) revealed that the UV-Fe³⁺ (EDTA)/H₂O₂ process was a promising strategy to degrade amoxicillin as the biodegradability of the effluent was improved to 0.45, compared with the cases of UV-Fe³⁺/H₂O₂ (0.25) and Fe³⁺/H₂O₂ (0.10) processes. Therefore, it could be deduced that EDTA and UV light performed synergetic catalytic effect on the Fe³⁺/H₂O₂ process, enhancing the treatment efficiency. The degradation mechanisms were also investigated via UV-Vis spectra, and high performance liquid chromatography-mass spectra. The degradation pathway of amoxicillin was further proposed.