紫外线消毒中的光复活作用

近年来,紫外线消毒技术在水处理中得到了越来越广泛的应用,它主要是利用短波紫外对微生物的伤害作用,通过在DNA中形成环丁烷嘧啶二聚体,阻碍基因的正常复制,从而导致细菌失活.但是细菌体内的光裂解酶在远紫外光和可见光作用下能够使失活的细菌重新获得活性,这就是光复活作用.低压消毒设备处理后大肠杆菌表现出了一定的光复活能力,但中压消毒设备能够有效的抑制其光复活作用;而噬肺军团菌在低压和中压设备处理后都表现出了很强的光复活能力.在应用紫外线消毒技术时光复活作用的影响不容忽视.     

紫外线消毒后微生物的光复活特性及其评价方法

随着紫外线消毒技术应用的日益广泛,污水紫外线消毒后微生物的光复活特性值得关注。文章综述了光复活的机理、具有光复活能力的微生物种类、影响光复活的因素以及光复活的评价方式等,以期为系统研究光复活提供参考。具有复活能力的微生物种类较多,主要和体内所含光复活酶相关。影响光复活的因素涉及微生物、污水特性、紫外线系统及光复活条件四方面。评价光复活的方式至今没有统一标准。光复活及其对污水消毒的影响有待进一步深入研究。     

复活光照强度对再生水紫外线消毒后大肠杆菌和粪大肠杆菌光复活的影响

研究厂复活光照强度对污水三级处理出水紫外线消毒后大肠杆菌和粪大肠杆菌光复活的影响.复活光强对复活的影响依消毒时紫外线剂量及菌种的不同而不同.不同复活光强(0～43ìW/cm2)下.大肠杆菌在5 mJ/cm2的紫外线剂量消毒后,复活情况基本不受复活光强影响.紫外线剂量增高至20 mJ/cm2后复活光强存在阈值,在43 ìW/cm2复活光条件下检测到明显的光复活,低于此光强没有检测到明显的光复活.粪大肠杆菌的光复活基本不受复活光照强度的影响.复活光强对细菌光复活的不同影响在光复活控制措施提出过程中需要考虑.     

避光处理对污水紫外线消毒后大肠杆菌光复活的影响研究

以大肠杆菌为受试菌种,研究了避光处理对紫外线消毒后三级出水中细菌光复活的影响.将紫外线消毒后的水样避光放置一定时间后再置于光复活条件下,研究了大肠杆菌的复活特性.结果表明,避光放置6h以内,见光后大肠杆菌的光复活能力即刻恢复,并最终达到与非避光处理基本相同的最大复活值;5 mJ/cm2和20mJ/cm2紫外线剂量照射后,最大复活百分比分别为31.1%和0.45%,复活速率分别为1.67×104CFU·(mL·h)-1和125 CFU·(mL·h)-1.延长避光时间至24 h,5 mJ/cm2和20mJ/cm2紫外线剂量照射后的大肠杆菌见光后,最大复活百分比分别减小到10.0%和0.3%,复活速率分别减小到830CFU·(mL·h)-1和20CFU·(mL·h)-1.以上结果表明,延迟消毒后出水见光时间,只能在一定程度上推迟或削弱大肠杆菌的光复活,并不能有效保证复活受到抑制,即紫外线消毒后出水中的微生物仍然存在高的复活风险.     

紫外线消毒对大肠杆菌的损伤及复苏的研究

调查了紫外线消毒后大肠杆菌的光复活和暗修复能力,分析了紫外线消毒对细胞膜、三磷酸腺苷以及核酸(DNA、RNA)的损伤,结合rec A的SOS损伤修复机制,阐述大肠杆菌对紫外线的响应机制.结果表明:20m J/cm2紫外线剂量下,大肠杆菌去除率为5.63-log,且经光复活和暗修复24h后,光复活和暗修复百分比分别达到0.018%和0.00042%,光复活能力明显大于暗修复能力.紫外线消毒过程DNA的损伤取决于片段长度,长片段16s rRNA的基因损伤更明显,水处理常规的紫外线消毒剂量对总ATP含量和膜的完整性影响较小,为紫外线消毒过程的复苏提供了基本保障.然而紫外线消毒对大肠杆菌的RNA损伤较严重,紫外剂量达到50mJ/cm2时,大肠杆菌失去了SOS损伤修复的能力,因此培养法检测80mJ/cm2时大肠杆菌的复苏能力极弱,recA相关的RNA的消失可用于指示微生物发生了不可逆损伤.     

污水厂二级出水中抗生素抗性细菌的紫外灭活与复活特性

抗生素抗性细菌(ARB)作为新兴污染物受到了广泛关注,但紫外线(UV)消毒对ARB去除效果的研究尚不够充分。以某城市污水处理厂过滤后的二级出水为研究对象,通过分析UV消毒前后水中四环素、氨苄西林、氯霉素及链霉素抗性细菌丰度的变化,探究了UV消毒对ARB的去除作用及ARB的光复活与暗修复潜能。结果表明:UV对过滤后二级出水中的4种ARB具有一定灭活能力,4种ARB对UV消毒的耐受能力由高到低分别为:氨苄西林抗性细菌>四环素抗性细菌>链霉素抗性细菌≈氯霉素抗性细菌。当UV消毒剂量为20 mJ/cm2时,氯霉素与链霉素抗性细菌可被完全灭活,消毒后24 h内,这2种ARB未出现光复活或暗修复现象,这一剂量的UV不能完全灭活氨苄西林与四环素抗性细菌,且被灭活后的ARB可实现部分光复活及暗修复。当UV消毒剂量达到80 mJ/cm2时,这4种ARB均被全部灭活,消毒后6 h内,氨苄西林抗性细菌出现了复活现象。不论是在光照还是避光的条件下,UV消毒24 h后水中的总异养菌群中有超过70.32%的细菌对氨苄西林具有抗性,因此,单独UV消毒并不能有效地控制ARB从污水处理厂向环境中的传播。     

污水中耐红霉素细菌的复活特性研究

耐红霉素(药物)细菌和基因在污水处理厂污水中普遍被检出。研究了耐红霉素细菌在不同消毒剂量、复活条件、复活强度条件下的复活程度,并对紫外线消毒处理后红霉素耐药性的后续生态风险进行了评价。结果表明:在紫外线消毒剂量为1mJ/cm~2时,耐红霉素细菌的复活程度比10mJ/cm~2时更为显著;对于耐红霉素细菌的复活,光复活处理比暗复活处理更为显著;对于耐红霉素细菌的暗复活,长时间的暗复活处理会增加耐红霉素细菌的复活程度,提升其生态风险。因此须重视耐药细菌复活在污水中的生态风险。     

连续流光催化消毒器灭活E.coli及病毒的性能

紫外消毒是污水处理常用技术.紫外线仅能破坏微生物的遗传物质,阻断其繁殖,并不能彻底杀死微生物,一旦停止紫外光照射,微生物可在修复酶的作用下恢复活性.光催化过程能产生强氧化性·OH,破坏细胞壁和细胞膜,彻底杀死微生物.为考察光催化技术消毒效率、抑制复活性能及应用潜力,在市售紫外消毒器中安装了光催化组件,搭建了连续流动式光催化消毒器.以大肠杆菌(E.coli)和噬菌体为目标物评价其消毒能力.紫外剂量50 m J·cm-2条件下,初始浓度3.40×106CFU·m L-1的E.coli原水流经紫外消毒器后被去除4.12 log10的E.coli,而流经光催化消毒器后去除4.79 log10.同时光催化处理后E.coli的光复活率仅为紫外消毒后的17%.连续运行40 h的灭菌能力稳定.光催化设备对噬菌体F2和噬菌体MS2的去除率分别为6.37 log10和6.00 log10,表明该设备也具有病毒去除能力.     

污水处理中紫外消毒效果的研究

紫外消毒技术相对于氯化法消毒,能够快速、有效地去除污水中粪大肠杆菌,操作简单方面,无副产物生成,对周围环境和人员安全可靠,在中国许多污水处理厂都已取代氯化法消毒并广泛应用。阐述了紫外消毒和微生物光复活现象的原理,并通过大量试验来研究紫外消毒技术去除粪大肠杆菌的效果,及经紫外消毒后出水中粪大肠杆菌光复活现象对紫外消毒效果的影响,提出可采用出水避光排放、增加紫外照射剂量、延长照射时间等方法来控制微生物光复活现象。     

紫外线消毒对再生水中微生物生长分泌特性的影响

膜污堵是阻碍污水再生处理反渗透（RO）系统稳定、高效运行的突出问题。前期研究表明,RO系统常用的氯消毒预处理会导致微生物群落结构及代谢产物分泌特性发生显著改变,从而引起严重的生物污堵。为优化污水再生处理RO系统的预处理工艺选择,该研究全面考察了紫外线消毒对再生水中细菌的生长、群落结构和分泌特性的影响。结果表明:紫外线剂量为20,40,80 mJ/cm2时,对膜生物反应器出水中细菌的灭活率分别可达1log、3log、4log。紫外消毒后,存活细菌再培养时其生长迟滞期变长,稳定期细菌数量在紫外线剂量为40,80 mJ/cm2时分别比对照组降低18.6%和19.2%。高紫外线剂量下（40,80 mJ/cm2）,变形菌门、β-变形菌纲、詹森菌属相对丰度有所增加。分泌特性方面,细菌胞外多聚物含量随紫外线剂量升高先减少后增多,且其中大分子物质增多,并表现出更强的RO膜污堵潜势。     

Toxic effects of acetochlor, methamidophos and their combination on nifH gene in soil

Toxic effects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel electrophoresis （DGGE） and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene diversity （both in gene richness and diversity index values） and caused changes in the nifH gene composition. The effects of acetochlor on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed that nifH gene composition which had been affected by low concentration of acetochlor （50 mg/kg） recovered firstly. Methamidophos reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos （150 mg/kg） caused the most apparent changes in nifH gene diversity at the first week while the high concentration of methamidophos （250 mg/kg） produced prominent effects on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found at 1 week and maximal changes at 4 weeks. Toxic effects of acetochlor and methamidophos combination on nifH gene were also apparent. Different nifH genes （bands） responded differently to the impact of agrochemicals： four individual bands were eliminated by the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 different nifH sequences, which were used for phylogenetic reconstructions. All sequences were affiliated with the alpha- and beta-proteobacteria, showing higher similarity to eight different diazotrophic genera.     

Arsenic uptake by arbuscular mycorrhizal maize （Zea mays L.） grown in an arsenic-contaminated soil with added phosphorus

The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment.Non-mycorrhizal and zero-P addition controls were included.Plant biomass and concentrations and uptake of As,P,and other nutrients,AM colonization,root lengths,and hyphal length densities were determined.The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium.Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments,but shoot and root biomass of AM plants was depressed by P application.AM fungal inoculation decreased shoot As concentrations when no P was added,and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition,respectively.Shoot and root uptake of P,Mn,Cu,and Zn increased,but shoot Fe uptake decreased by 44.6%,with inoculation, when P was added.P addition reduced shoot P,Fe,Mn,Cu,and Zn uptake of AM plants,but increased root Fe and Mn uptake of the nonmycorrhizal ones.AM colonization therefore appeared to enhance plant tolerance to As in low P soil,and have some potential for the phytostabilization of As-contaminated soil,however,P application may introduce additional environmental risk by increasing soil As mobility.     

Impact of atrazine and nitrogen fertilizers on the sorption of chlorotoluron in soil and model sorbents

Sorption of chlorotoluron in ammonium sulfate, urea and atrazine multi-solutes system was investigated by batch experiments. The results showed application of nitrogen fertilizers to the soil could affect the behavior of chlorotoluron. At the same concentration of N, sorption of chlorotoluron decreased as the concentration of atrazine increased on the day 0 and 6 in soil, respectively. The sorption of chlorotoluron increased from 0 to 6 d when soils were preincubated with deionized water, ammonium sulfate and urea solution for 6 d. That indicated incubation time was one of the most important factors for the sorption of chlorotoluron in nitrogen fertilizers treatments. The individual sorption isotherms of chlorotoluron in rubbery polymer and silica were strictly linear in single solute system, but there were competition sorption between pesticides or between pesticides and nitrogen fertilizers. That indicated the sorption taken place by concurrent solid-phase dissolution mechanism and sorption on the interface of water-organic matter or water-mineral matter.     

Degradation of metabolites accumulated of benzo[a]pyrene by coupling Penicillium Chrysogenum with KMnO4

Several main metabolites of benzo[a]pyrene （BaP） formed by Penicillium chrysogenum, Benzo[a]pyrene-1,6-quinone （BP 1,6- quinone）, trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene （BP 7,8-diol）, 3-hydroxybenzo[a]pyrene （3-OHBP）, were identified by high-performance liquid chromatography （HPLC）. The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that （1） the method of coupling Penicillium chrysogenum with KMnO4 was better and was the first method to be used in the degradation of BaP and its metabolites; （2） the metabolite, BP 1,6-quinone was the most liable to be accumulated in pure cultures; （3） the effect of degradation was the best when the concentration of KMnO4 in the cultures was 0.01% （w/v）, concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.     

Potential of plant polyphenol oxidases in the decolorization and removal of textile and non-textile dyes

In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

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Isolation and preliminary characterization of a 3-chlorobenzoate degrading bacteria

A study was conducted to compare the diversity of 2-, 3-, and 4-chlorobenzoate degraders in two pristine soils and one contaminated sewage sludge. These samples contained strikingly different populations of mono-chlorobenzoate degraders. Although fewer cultures were isolated in the uncontaminated soils than contaminated one, the ability of microbial populations to mineralize chlorobenzoate was widespread. The 3- and 4-chlorobenzoate degraders were more diverse than the 2-chlorobenzoate degraders. One of the strains isolated from the sewage sludge was obtained. Based on its phenotype, chemotaxonomic properties and 16S rRNA gene, the organism S-7 was classified as Rhodococcus erythropolis. The strain can grow at temperature from 4 to 37℃. It can utilize several （halo）aromatic compounds. Moreover, strain S-7 can grow and use 3-chlorobenzoate as sole carbon source in a temperatures range of 10-30℃ with stoichiometric release of chloride ions. The psychrotolerant ability was significant for bioremediation in low temperature regions. Catechol and chlorocatechol 1,2-dioxygenase activities were present in cell free extracts of the strain, but no （chloro）catechol 2,3- dioxygenase activities was detected. Spectral conversion assays with extracts from R. erythropolis S-7 showed accumulation of a compound with a similar UV spectrum as chloro-cis,cis-muconate from 3-chlorobenzoate. On the basis of these results, we proposed that S-7 degraded 3-chlorobenzoate through the modified ortho-cleave pathway.     

Single and joint effects of pesticides and mercury on soil urease

The influence of two pesticides including chlorimuron-ethyl and furadan and mercury （Hg） on urease activity in 4 soils （meadow burozem and phaeozem） was investigated. The soils were exposed to various concentrations of the two pesticides and Hg individually and simultaneously. Results showed that there was a close relationship between urease activity and organic matter content in soil. Chlorimuron-ethyl and furadan could both activate urease in the 4 soils. The maximum increment of urease activity by chlorimuronethyl was up to 14%-18%. There was almost an equal increase （up to 13%-21%） in the urease activity by furadan. On the contrary, Hg markedly inhibited soil urease activity. A logarithmic equation was used to describe the relationship （P〈0.05） between the concentration of Hg and the activity of soil urease in the 4 tested soils. Semi-effect dose （ED50） values by the stress of Hg based on the inhibition of soil urease in the 4 soils were 88, 5.5, 24 and 20 mg/kg, respectively, according to the calculation of the corresponding equations. The interactive effect of chlorimuron-ethyl or furadan with metal Hg on soil urease was mainly synergic at the highest tested concentrations.     

Organochlorine pesticides in soils under different land usage in the Taihu Lake region, China

A field study was conducted in the Taihu Lake region, China in 2004 to reveal the organochlorine pesticide concentrations in soils after the ban of these substances in the year 1983. Thirteen organochlorine pesticides (OCPs) were analyzed in soils from paddy field, tree land and fallow land. Total organochlorine pesticide residues were higher in agricultural soils than in uncultivated fallow land soils. Among all the pesticides, ΣDDX (DDD, DDE and DDT) had the highest concentration for all the soil samples, ranging from 3.10 ng/g to 166.55 ng/g with a mean value of 57.04 ng/g and followed by ΣHCH, ranging from 0.73 ng/g to 60.97 ng/g with a mean value of 24.06 ng/g. Dieldrin, endrin, HCB and α-endosulfan were also found in soils with less than 15 ng/g. Ratios of p,p'-(DDD DDE)/DDT in soils under three land usages were: paddy field ＞ tree land ＞ fallow land, indicating that land usage inlfuenced the degradation of DDT in soils. Ratios of p,p'-(DDD DDE)/DDT ＞1, showing aged residues of DDTs in soils of the Taihu Lake region. The results were discussed with data from a former study that showed very low actual concentrations of HCH and DDT in soils in the Taihu Lake region, but according to the chemical half-lives and their concentrations in soils in 1980s, the concentration of DDT in soils seemed to be underestimated. In any case our data show that the ban on the use of HCH and DDT resulted in a tremendous reduction of these pesticide residues in soils, but there are still high amounts of pesticide residues in soils, which need more remediation processes.     

Alterations of organ histopathology and metallolhionein mRNA expression in silver barb, Puntius gonionotus during subchronic cadmium exposure

Common silver barb,Puntius gonionotus,exposed to the nominal concentration of 0.06 mg/L Cd for 60 d,were assessed for histopathological alterations(gills,liver and kidney),metal accumulation,and metallothionein(MT)mRNA expression.Fish exhibited pathological symptoms such as hypertrophy and hyperplasia of primary and secondary gill lamellae,vacuolization in hepatocytes,and prominent tubular and glomerular damage in the kidney.In addition,kidney accumulated the highest content of cadmium,more than gills and liver.Expression of MT mRNA was increased in both liver and kidney of treated fish.Hepatic MT levels remained high after fish were removed to Cd-free water.In contrast,MT expression in kidney was peaked after 28 d of treatment and drastically dropped when fish were removed to Cd-free water.The high concentrations of Cd in hepatic tissues indicated an accumulation site or permanent damage on this tissue.