The OH-induced degradation mechanism of 4-chloro-2-methylphenoxyacetic acid (MCPA) with two forms in the water: a DFT comparison

The initial degradation mechanisms of OH and 4-chloro-2-methylphenoxyacetic acid (MCPA) including molecular form and anionic form are studied at the MPWB1K/6-311+G(3df, 2p)//MPWB1K/6-31+G(d, p) level. Possible reaction pathways of H-atom abstraction and OH addition are considered in detail. By result comparison analysis, it is found that the reaction mechanisms for OH and two forms of MCPA are different, and most reactions for anionic MCPA are easier than those for molecular MCPA. For H-atom abstraction reactions, the calculated energies show that OH abstracting H-atom from -CH₃ group of molecular MCPA is the most kinetically favorable process; the potential energy surface for anionic MCPA indicates that H-atom in -CH₂ group is slightly easier to be abstracted than that in -CH₃ group. For OH addition reactions, the addition of OH to the C1 site is the initial step for molecular MCPA and the predominant product is 4-chloro-2-methylphenol (denoted P3), while the C4 site is the most reactive site for anionic MCPA and the primary product results from the hydroxylation of the aromatic ring, which is in good agreement with the experimental observation. In additional, results from PCM calculations show that most reactions in water phase are more kinetically favorable than those in gas phase, though the mechanisms discussed above will not be changed.     

Identification of cadmium-excluding welsh onion (Allium fistulosum L.) cultivars and their mechanisms of low cadmium accumulation

Purpose

Screening out cadmium (Cd) excluding cultivars of a crop in agricultural production is an effective way to prohibit Cd entering into food chain.

Methods

A judging criterion for Cd-excluding cultivars based on food safety was suggested and used in the identification of Cd-excluding welsh onion (Allium fistulosum L.) cultivars. A pot culture experiment was carried out to screen out Cd-excluding cultivars, of which the results were confirmed by plot experiments. The relevant factors of Cd accumulation in the pseudostem were analyzed and used in the correlation analysis aiming to study the low Cd accumulation mechanisms.

Results

The concentration of Cd in the pseudostem of welsh onions was 0.08?C0.20, 0.18?C0.41, and 0.26?C0.61?mg/kg fresh weight (FW) under three treatments (1.0, 2.5, and 5.0?mg/kg), respectively. The significant (p? ₃ ^? ?CN, and eight other elements in the tested welsh onion cultivars. Two cultivars were identified as Cd-excluding cultivars, mainly because the accumulation of Cd in their pseudostem was only 0.041?±?0.003 and 0.046?±?0.002?mg/kg FW, and 0.054?±?0.001 and 0.066?±?0.011?mg/kg FW, when growing in plots with Cd concentration of 0.49 and 0.99?mg/kg, respectively.

Conclusions

Ribentiegancongwang and Wuyeqi could be identified as Cd-excluding cultivars. Low bioaccumulation factor of the roots was the main mechanism of Cd-excluding welsh onion cultivars.     

Acute toxicity tests with Daphnia magna, Americamysis bahia, Chironomus riparius and Gammarus pulex and implications of new EU requirements for the aquatic effect assessment of insecticides

Threshold concentrations for treatment related effects of 31 insecticides, as derived from aquatic micro-/mesocosm tests, were used to calibrate the predictive value of the European Tier-1 acute effect assessment on basis of laboratory toxicity tests with Daphnia magna, Chironomus spp., Americamysis bahia and Gammarus pulex. The acute Tier-1 effect assessment on basis of Daphnia (EC(50)/100) overall was protective for organophosphates, carbamates and most pyrethroids but not for neonicotinoids and the majority of insect growth regulators (IGRs) in the database. By including the 28-day water-spiked Chironomus riparius test, the effect assessment improves but selecting the lowest value on basis of the 48-h Daphnia test (EC50/100) and the 28-day Chironomus test (NOEC/10) is not fully protective for 4 out of 23 insecticide cases. An assessment on basis of G. pulex (EC(50)/100) is sufficiently protective for 15 out of 19 insecticide cases. The Tier-1 procedure on basis of acute toxicity data (EC(50)/100) for the combination of Daphnia and A. bahia and/or Chironomus (new EU dossier requirements currently under discussion) overall is protective to pulsed insecticide exposures in micro-/mesocosms. For IGRs that affect moulting, the effect assessment on basis of the 48-h Chironomus test (EC(50)/100) may not always be protective enough to replace that of the water-spiked 28-day C. riparius test (NOEC/10) because of latency of effects.     

Enhanced degradation of azo dye alizarin yellow R in a combined process of iron–carbon microelectrolysis and aerobic bio-contact oxidation

Purpose

With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.

Materials and methods

The combined ABO (with effective volume of 2.4?l) and ICME (with effectively volume of 0.4?l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6?h.

Results

At the HRT of 6?h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4?h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.

Conclusion

The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.     

超强静磁场对染料脱色菌Escheriehia coli的acpD基因的影响

将大肠杆菌E.coli ATCC8739置于12.0 T超强静磁场(ultra-strong static magnetic field,SMF)中进行处理,获得了磁场处理0.5、1、2、4和8 h的菌株E.coli-SMFn(n=0.5、1、2、4、8)。在37℃、pH 7、静置的条件下,菌株对偶氮染料AR14(I.C.Acid Red 14)的脱色结果指出,当反应进行到4、6和8 h时,E.coli-SMF8的脱色效率分别为18%、55%和96%,远高于E.coli ATCC8739的3%、19%和50%,表明SMF作用显著地增强了菌株的脱色效率。基因组DNA提取、PCR扩增、分子克隆以及基因测序的实验结果进一步表明,全部6例E.coli ATCC8739菌株的偶氮还原酶基因(acpD)序列均与GenBank中报道的完全一致;而E.coli-SMF8菌株的acpD-SMF8核酸序列中缺失了第99位的胞嘧啶。该缺失突变不仅使acpD-SMF8的核酸序列与acpD的存在显著不同,同时得到了具新活性中心的偶氮还原酶AzoR-SMF8。这个新的活性中心具有更强的黄素(FMN)结合能力,因此使该酶与偶氮染料的亲和力大大增加,促进了脱色效率的提高。     

MBR在橡胶废水处理中的应用

橡胶废水具有含盐量高、色度高、有机污染成分含量高且难于生化降解等特点。膜生物反应器(MBR)技术的核心是生化处理加微滤膜过滤,通过将MBR技术应用于橡胶废水处理的实践表明,该技术对COD、氨氮、磷酸盐的平均去除率都达到了85%以上,再辅之以药剂处理后,降低了色度和难降解有机物含量,出水水质完全符合排放标准的要求,是一种解决橡胶污水处理难题的有效途径。     

Fe2O3-Cr2O3/TiO2系列催化剂的结构和脱硝性能

研究以纳米TiO2为载体,浸渍负载过渡金属氧化物,以CO为还原剂的脱硝催化剂的脱硝性能。实验中以计算量的Ni(NO3)2和Fe(NO3)3混合溶液浸渍纳米TiO2粉末,室温下搅拌30 min至混合均匀,放入旋转蒸发器中,70℃下至水分蒸干为止;所得粉末在550℃下、空气气氛中焙烧4 h即得所需催化剂。用以上方法分别制备2%Fe2O3-10%Cr2O3/TiO2、4%Fe2O3-8%Cr2O3/TiO2、6%Fe2O3-6%Cr2O3/TiO2、8%Fe2O3-4%Cr2O3/TiO2与10%Fe2O3-2%Cr2O3/TiO2等5种催化剂样品。实验结果表明,制备的催化剂具有较好的结构,分散较为均匀。对于CO+NO反应,Fe2O3-Cr2O3/TiO2系列催化剂具有较好的催化活性,NO的转化率都达到了100%。其中,10%Fe2O3-2%Cr2O3/TiO2样品具有最好的低温活性,H2-TPR结果表明,这是由于10%Fe2O3-2%Cr2O3/TiO2催化剂更易于被CO预还原。     

垃圾渗滤液处理工艺运行参数优化与技术比较

垃圾渗滤液是公认的一种成分复杂且难以处理的高浓度有机废水,笔者在北京市海淀区六里屯垃圾填埋场通过2007—2010年垃圾渗滤液处理的工程实践,以COD和氨氮的去除率为指标,研究了不同的垃圾渗滤液处理工艺组合,以及不同运行参数条件下对垃圾渗滤液的处理效果。结果表明,在中温UASB和A/O的平均水力停留时间(HRT)缩短1/3的情况下,通过改进A/O段曝气方式,优化系统的pH、DO等运行参数,用MBR替代絮凝工艺,使整个组合工艺对COD的年平均去除率达到了94.3%,氨氮的去除率维持在99.5%以上,出水氨氮稳定在10 mg/L以内,而改造前的COD与氨氮的年平均去除率仅为82.2%与55.3%。与改造前的UASB+A/O+絮凝工艺组合相比,改造后的UASB+A/O+MBR工艺组合具有更高的污染物去除能力、更好的抗缓冲性和稳定性。     

地下水PRB原位生物修复中一种释氧材料的改进技术及效果分析

释氧材料经济有效的释氧是地下水原位生物修复的关键因素。实验通过在释氧材料中加入膨润土、磷酸二氢钾和硫酸铵等,改进释氧材料的性能。柱实验结果显示,该释氧材料释氧速率缓慢,释氧时间长,可以使溶液中DO长期保持在5 mg/L以上;另外,释氧材料中添加的缓冲剂及天然含水层介质对pH值有较好的缓冲作用,可以使pH值达到后续生物修复的要求。     

南京大气细粒子中重金属污染特征及来源解析

利用2011年1月、4月、7月和10月在南京市区和北郊采集的气溶胶样品,研究了南京大气细粒子中zn、Ph、Hg、As和cd5种重金属的污染水平,通过元素相关性分析和因子分析方法,对细粒子中这些重金属的污染来源进行了初步解析。结果表明,南京大气细粒子及其重金属污染严重,北郊普遍比市区严重;As严重超标,cd在南京北郊超标约5倍,zn在市区与北郊的质量浓度均高于其他重金属元素。每种重金属的浓度均随季节而变化。市区细粒子中,As和zn可能主要与燃煤、轮胎灰尘和建筑扬尘等有关,Pb、Hg和cd主要来自交通尘、城市垃圾焚烧等。北郊细粒子中,As、Hg和zn主要来源于燃煤、钢铁冶炼等工业,Pb和cd主要与农作物秸秆燃烧、汽车尾气、道路扬尘等影响有关。