铬污染土壤的药剂修复及其长期稳定性研究

利用不同投加比例的硫化钠及连二亚硫酸钠,分别对不同类型的铬污染土壤进行修复处理,通过土壤总铬及六价铬浸出浓度的测定,研究了供试药剂对铬污染土壤的短期(3 d)和长期(1.5 a)稳定化效果。结果表明:两种药剂对铬污染土壤的稳定化均具有很好的效果,可以在短期内快速降低总铬和六价铬的浸出浓度,其效果随着投加量的增加而提高。在长期稳定过程中,不同药剂不同投加量的的稳定化效果进一步提高,且保持稳定。     

铬污染土壤的形态特征及药剂稳定化研究

基于典型污染场地中的铬污染土壤,以多种形态划分方法(Tessier法、BCR法、Maiz法)为体系,探讨了铬的污染特征以及多种形态划分方式的适用程度,并利用不同投加比例的FeSO_4、Na_2S、Na_2SO_3,以及复配药剂分别对铬污染土壤进行稳定化处理,通过土壤总铬及六价铬浸出浓度的测定,研究了药剂对铬污染土壤的短期(2 d,28 d)和长期(1 a)稳定化效果。结果表明,该土壤样品中,残渣态的铬含量最大,其次为铁锰氧化物结合态以及有机物和碳酸盐结合态,不同的提取方法虽然在划分形态方面的技术手段各不相同,但存在着一定的联系;3种药剂及复配剂型对污染土壤中的铬均有很好的稳定化效果,可以在短期内降低总铬和六价铬的浸出浓度,并在长期的稳定化过程中,进一步提高稳定效果并保持。     

硫化物对电镀厂铬污染土壤的稳定化效果及其机理研究

以某电镀厂旧址内的铬(Cr)污染土壤为研究对象,分别添加多硫化钙(CPS)、硫化钠(Na2S)以及焦亚硫酸钠(Na_2S_2O_5)3种硫化物稳定剂,探究3种稳定剂不同投加摩尔比对土壤中Cr的价态变化、浸出毒性和形态分布的影响.结果表明:CPS对Cr(Ⅵ)还原效果最佳,当CPS投加摩尔比为3时,土壤中Cr(Ⅵ)含量从1587.5 mg·kg-1减少至12.43 mg·kg~(-1),还原效率高达99.2%,然而相同条件下Na_2S和Na_2S_2O_5对Cr(Ⅵ)的还原效率仅分别为55.6%和74.5%.CPS对Cr(Ⅵ)和总Cr稳定效率最高,当CPS投加摩尔比为3时,浸出Cr(Ⅵ)和总Cr浓度分别为0.02mg·L~(-1)和0.32 mg·L~(-1),Cr(Ⅵ)和总Cr稳定效率分别为99.8%和99.1%,此时Cr(Ⅵ)浓度满足GB/T 14848-93《地下水水质标准》规定的限值.相同投加摩尔比下Na2S和Na_2S_2O_5对Cr(Ⅵ)稳定效率分别仅为63.0%和98.9%,对总Cr稳定效率分别为66.5%和77.2%;浸出Cr(Ⅵ)和总Cr浓度随着CPS和Na2S投加摩尔比的增加而降低,然而随着Na_2S_2O_5投加摩尔比的增加,浸出Cr(Ⅵ)浓度持续下降,但总Cr浓度不断升高.CPS和Na2S稳定化后土壤中Cr的有机物结合态变化不大(p0.05)、铁锰氧化物结合态显著增加(p0.05).硫化物稳定剂稳定化后土壤中Cr的可交换态含量的变化是影响浸出总Cr浓度变化的主要原因.基于3种硫化物稳定剂对土壤中Cr(Ⅵ)还原效率、Cr(Ⅵ)和总Cr稳定效率和Cr的可交换态含量的影响,CPS投加摩尔比为3时,对该电镀厂铬污染土壤的稳定化效果最佳.     

铬污染土壤还原—固化稳定化过程研究

以我国某铬渣堆场六价铬污染土壤为研究对象,探讨硫酸亚铁、氧化钙、水泥等作为还原—固化稳定化药剂对六价铬污染土壤还原—固化稳定化效率的影响。试验结果表明:土壤六价铬浓度与七水合硫酸亚铁投加倍数呈指数关系,当七水合硫酸亚铁投加剂量为理论值的6.5倍,土壤中六价铬浓度未检出(<0.002mg/kg)。氧化钙的加入抑制了土壤中水溶性六价铬的浸出,正交试验的所有样品中水溶性六价铬浓度在4~56.6 mg/L。水泥加入后,初始浓度为3880 mg/kg的土壤水溶性六价铬浓度浓度降低至19.9mg/L。造成反应后水溶性六价铬浓仍较高的可能原因是含水量较低,土壤颗粒内部六价铬未全部溶出。因此在实际工程中,可考虑增大体系含水率、加酸调节pH值或提高添加氧化钙、水泥比例等方法提高土壤还原—固化稳定化效率。     

铬渣污染土壤稳定化技术研究

选用3种不同类型的铬渣污染土壤(A土、B土和C土)作为研究对象,探讨了6种稳定化药剂对污染土壤中Cr(Ⅵ)的还原效果,并研究了不同药剂对各形态Cr稳定化效果。结果表明:FeSO4和Na2S对Cr(Ⅵ)都有很好的还原效果,葡萄糖次之,Na2SO3效果一般,柠檬酸和腐植酸效果不好;FeSO4和Na2S对B土、C土中Cr(Ⅵ)的还原率达到90%以上,对A土中Cr(Ⅵ)的还原率则低于85%;稳定化药剂主要是将酸可提取态Cr转化为其他形态,FeSO4效果最明显,可将80%以上的酸可提取态Cr转化为其他形态,主要为可还原态Cr;葡萄糖主要将之转化为可氧化态Cr;鉴于FeSO4的良好的还原效果,选择FeSO4作为稳定化药剂,且FeSO4添加量为理论投加量的20时较合适,浸出液可以满足地下水三级标准的50μg/L;经济性分析,处理1t清洗后土壤的药品费用为8.91元。     

FeS纳米颗粒修复镉铅铬污染土壤的试验研究

文章利用FeS纳米颗粒对人工配制的高、中、低3种水平的镉铅铬复合污染土壤进行修复,并对氧气和FeS纳米颗粒投加量等关键因素对土壤修复过程的影响进行了探究.结果 表明:氧气对稳定化过程影响不大;对于低浓度污染土壤,土壤中Cr(Ⅵ)含量和浸出液中Cd、Pb、Cr(Ⅵ)、总Cr浓度一般可达标,可不进行处理;对于中浓度污染土壤,当FeS与(Cd+Pb+Cr(Ⅵ))的摩尔比为2:1时,可将土壤中Cr(Ⅵ)含量可降低至标准值以下,但浸出液中的Pb无法得到较好的稳定化,按PO43-与Pb的摩尔比为8∶1复合投加磷酸盐后,浸出液中Cd、Pb、Cr(Ⅵ)、总Cr浓度均可降至标准值以下;对于高浓度污染土壤,当FeS与(Cd+Pb+Cr(Ⅵ))的摩尔比在2∶1及以下时,FeS对土壤中的Cr(Ⅵ)的还原效果存在波动,达标存在难度,与磷酸盐复合投加可有效稳定高浓度污染土壤浸出液中的Cd、Pb、Cr(Ⅵ)和总Cr.经FeS NPs和磷酸盐稳定化处理后,土壤中生成了Pb3(PO4)2、CdS、PbS、Cr(OH)3、[Cr,Fe](OH)3和Fe3(PO4)2等沉淀物,3种重金属形态由可交换态等形态向稳定性较高的残渣态转化,释放迁移到环境的可能性减小,对环境的风险降低.修复后的土壤pH呈弱碱性,利于土壤中Cr(Ⅲ)、Cd和Pb的长期稳定;有机质含量和阳离子交换容量升高;氧化还原电位降低,体系保持还原环境,可有效防止Cr(Ⅵ)的再次氧化.     

复合材料对砷污染土壤稳定化处理及机理研究

通过投加FeS、电石渣、菌渣及其复配组合对砷污染土壤进行稳定化处理,根据稳定效率对稳定材料进行筛选,并分析处理前后土壤中砷的生物有效性、赋存形态及土壤物相成分,探索稳定机理.结果表明:单因素实验中,FeS对砷的稳定效率最高,当FeS投加量为n(Fe)/n(As)=20时,砷的稳定效率达84.69%;复配实验中,FeS投加量为n(Fe)/n(As)=15,电石渣投加量为0.5%(质量分数),菌渣投加量为6%(质量分数)时,砷的稳定效率高达90.53%.机理研究表明:稳定处理后,土壤中有效态砷和有机体内砷的可给量分别降低80.14%和92.86%;土壤中易溶态砷占总砷的比例降低了18.61%,铁型砷和钙型砷占总砷的比例分别提高了10.36%和5.81%,易溶态砷主要转化为铁型砷和钙型砷;稳定处理后土壤中矿物成分新增了Ca Al_2Si_2O_8·4H_2O(斜方钙沸石)、Ca_3Fe_4(AsO_4)_4(OH)_6·3H_2O(菱砷铁矿)、Fe_2(AsO_4)(SO_4)OH·5H_2O(砷铁矾矿)、(Al,Fe~(3+))_3AsO_4(OH)_6·5H_2O(砷铁铝矿)4种矿物,稳定处理使土壤中的砷生成了难溶性铁-砷、钙-砷矿物质.     

铁氧化物法对铬污染黄棕壤钝化效果的研究

该文以模拟的六价铬污染的黄棕壤为研究对象,探讨了铁氧化物法钝化铬污染土壤的稳定化效率。实验结果表明:硫酸铁和硫酸亚铁混合液(0.35 mmol硫酸铁和3.2 mmol硫酸亚铁)的投加会在铬污染土壤中形成铁氧化物晶体钝化修复土壤中的铬;当n(Fe2+)/n(Fe3+)=5,n(Fe)/n(Cr)=40,p H=9.0时,稳定化效果最佳;经过铁氧化物法钝化修复的土壤,通过BCR连续提取发现松散结合的酸可提取态的铬由原来的78.83%降至0.36%,可还原态由原来的9.89%增至14.98%,可氧化态由9.33%增至17.88%,残渣态由1.95%增至66.78%,铬稳定性明显增强;此外,铁氧化物法钝化效果在25~100℃不同特定温度条件下无明显性差异。通过硫酸硝酸法浸出实验,pH在3.2时,修复后铬浸出率由56.47%降至0.16%。     

铬污染场地修复技术研究及应用

综述了国内外铬污染场地修复技术的研究动态,探讨了铬污染修复技术研发的需求,重点讨论了铬污染土壤的主要修复技术如:土壤清洗技术、化学解毒技术、电动修复技术和稳定化技术等。并针对这些技术存在的不足,开发了化学解毒与稳定化联合技术,对山西某铬渣堆存场地中受污染土壤进行修复。结果表明:运用化学解毒与稳定化联合技术可以降低污染土壤中总铬和六价铬的浸出浓度,稳定效果好且能在工程实际中高效应用。     

液态铁基稳定剂对钒矿污染土壤的稳定化效果

选用Fe Cl_2、Fe Cl_3、Fe SO_4、Fe_2(SO_4)_3共4种液态铁基稳定剂,对钒矿污染的土壤中的V等重金属进行了固化稳定化.结果表明,铁基液态稳定剂对V的稳定化效果良好,稳定化7d后最佳稳定效率均可达到100.0%,稳定剂的最佳用量为0.5wt%,最佳稳定剂为Fe SO_4,120d内效果良好.亚铁盐可对Cr实现稳定化,120d内稳定化效果稳定,Fe Cl_2的稳定效率稳定在98.0%左右.由于对p H的影响,过量铁基液态稳定剂会在15d内促进Cd、Zn、Cu的浸出,之后浸出浓度逐渐降低,120d后,与未稳定化土样浸出浓度类似.     

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.