Anion and cation leaching or desorption from activated carbons from municipal sludge and poultry manure as affected by pH.

The conversion of municipal sludge and poultry manure to activated carbon results in a significant ash fraction that contains several different anions and cations. The objectives of this study were to determine whether the select ions are released or leached from virgin carbon into the sorption medium at different pH values. Activated carbon was placed in solutions of pH 1, 5, or 7, and the leaching of six cations (cadmium, chromium, copper, nickel, lead, and zinc) and two anions (arsenate and selenate) was recorded. Considerable quantities of zinc and copper were removed at pH 1 from all carbon sources. However, the amounts leached at pH 5 and 7 were small or undetectable. Our results indicate that leaching or desorption from carbons made from municipal sludge or poultry manure is pH-dependent and occurs readily under highly acidic conditions but minimally under pH conditions typically seen in contaminated water or wastewater.     

污泥果肥利用中重金属迁移特征研究

为了厦门城市污泥的安全利用,将石渭头污水处理厂污泥经过好氧堆肥后施用于柚子树,对重金属元素在土壤、树叶及果肉中的迁移特征进行了研究。结果表明：Cd在土壤中的富集能力强;重金属元素从土壤向树叶迁移累积能力比向果肉的大得多,污泥肥料不能用于叶类食用植物的施用;Cr向树叶、Ni向果肉的迁移累积能力强;泥肥的施用加重了土壤中Cd的污染,提高了Cr向树叶、Ni向果肉的迁移能力;污泥果肥利用需降低Ni的浓度,对污泥中含量较高的Cu、Zn、Ni、Cr和Cd需进行跟踪检测。     

Effect of reducing conditions on sludge melting process

The objective of this study was to compare the effects of CO/CO(2) reducing conditions with those of air oxidizing conditions on the pouring temperature of the sludge melting process and the heavy metal leachability of the resultant sludge slag. Synthetic sludge ash composed of SiO(2), CaO and Al(2)O(3), as well as sewage sludge ash generated from a laboratory incinerator was employed. The experimental results indicated that the pouring temperatures are significantly reduced under the reducing conditions of CO/CO(2), or 24 and 77 degrees C lower than under air conditions for synthetic and sludge ash, respectively. The heavy metal leaching tests further indicate lower heavy metal concentrations present in the leachate under the reducing conditions, notably an order of magnitude lower in Zn. However, X-ray diffractogram indicates similar peaks for these two slags produced under different conditions.     

电镀污泥的热处理特性以及对金属回收的影响

焙烧-酸浸法可有效回收电镀污泥中的有价金属,而污泥的热处理特性是决定能否采用焙烧预处理的重要因素。研究了氧化焙烧和还原焙烧对污泥成分和金属浸出性的影响,并对焙烧前后的污泥进行了金属形态分析和X射线衍射(XRD)分析。结果表明,焙烧预处理实现了污泥减量和金属富集;ES1经氧化焙烧后金属浸出率接近原泥,Cu的浸出率达99%;ES2的还原焙烧效果优于氧化焙烧,特别是Cu的浸出率超过97%,XRD分析发现,还原焙烧过程中金属Cu被还原为铁铜合金;2种焙烧均造成了ES3中目标金属Ni的浸出率的降低;金属浸出性的下降与残渣态的形成有关。     

Catalytic effects by metal oxides on the formation and degradation of chlorinated aromatic compounds in fly ash

Polychlorinated benzenes, dibenzo-p-dioxins (PCDD), and dibenzofurans (PCDF) may be formed below the combustion temperature in fly ash from municipal solid waste incinerators (MSWI). Copper catalyzes this formation, possibly by the Deacon reaction. Many other elements are also Deacon catalysts or promoters, and here we report results from a statistically designed experiment with 15 metal oxides added to fly ash and heated at 300 degrees C for 2h in an air atmosphere. A resolution IV fractional factorial design with four replicates was completed in 36 runs with the oxides of magnesium, yttrium, titanium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, and tin. All samples were analyzed for chlorinated benzenes and the results were evaluated by analysis of variance. The addition of copper significantly increased the amounts of the chlorinated benzenes, while cobalt, chromium and vanadium decreased the net formation. The oxides of zinc and iron seemed to have a slightly positive and negative effect respectively. The findings in this study seem to corroborate our previously reported results regarding the different catalytic effects of copper and chromium, and lack of a significant effect by nickel. Besides chromium, it also identifies cobalt and vanadium as potent catalysts for oxidative degradation of the chlorinated aromatic compounds found in MSWI fly ash.     

Supercritical water oxidation of tannery sludge: Stabilization of chromium and destruction of organics

The supercritical water oxidation (SCWO) of industrial tannery sludge was investigated to understand the simultaneous destruction of organic pollutants and recovery of high content chromium. Experiments were performed in a batch reactor at temperatures of 350–500 °C, reaction time of 150–300 s and different oxygen ratios, to exhibit the effect of operation conditions. Results showed that removal efficiency of chemical oxygen demand (COD) increased with higher temperature, larger oxidant amount and reaction time; a maximum value of 96% was obtained. Meanwhile, destruction yield was much higher under supercritical conditions than that in subcritical water. In addition, removal efficiency of Cr from sludge reached more than 98% under all conditions; higher temperature played a positive role. Further, leaching toxicity tests of heavy metals in solid products were conducted based on toxicity characteristic leaching procedure. All heavy metals except nickel showed a greatly reduced leaching toxicity through their stabilization. The chromium oxide recovered in ash was amorphous below 550 °C, so that the structure of Cr could not be identified by X-ray diffraction pattern. Special attention should be paid on nickel as its leaching toxicity increased due to the corrosion of reactor surface under severe reaction conditions.     

利用高炉瓦斯泥中的锌制备活性氧化锌的研究

利用高炉炼铁瓦斯泥中的锌,采用火法富集和湿法浸取制取活性氧化锌。考察了温度、时间对火法富集产品中氧化锌含量和原料瓦斯泥中锌挥发率的影响,确定了富集工艺的最佳条件为:在氮气氛围下,温度从常温以10℃/min升温至1 000℃并且在1 000℃下保持1 h,得到的富集产品中氧化锌含量82.24%;瓦斯泥中锌挥发率97%。同时考察了温度、氨水用量、碳酸氢铵用量和液固比等因素对氧化锌浸取率的影响。确定的最佳工艺条件为:浸取温度40℃,氨水用量为理论量的2倍,碳酸氢铵用量为理论量的2倍,液固比4∶1,浸取时间2 h,氧化锌浸取率达99.9%。湿法制得的活性前驱体碱式碳酸锌,经煅烧得到纯度为98.4%的活性氧化锌产品,氧化锌的总回收率达95.3%。     

Heavy metal speciation and mobility assessment of arid soils in the vicinity of Al Ain landfill, United Arab Emirates

Sixty-four surface soil samples taken in the vicinity of Al Ain landfill were analysed for cadmium, chromium, copper, nickel, lead and zinc by inductively coupled plasma spectroscopy. Extraction techniques were used to establish the association of the total concentrations of the six metals in the soil samples with their contents in the exchangeable, carbonate, iron/manganese oxides, and residual fractions. In the investigated soils, the recorded concentrations were as follows: 0.043 mg kg^-1 for cadmium, 19.1 mg kg^-1 for chromium, 53.3 mg kg^-1 for copper, 60 mg kg^-1 for nickel, 13.7 mg kg^-1 for lead, and 117 mg kg^-1 for zinc. Cadmium, chromium, nickel, lead and zinc concentrations in the investigated soil samples reflect the natural background values in shale, whereas copper is slightly enriched. I-geo (geoaccumulation index) values of the metals in the soils under study indicate that they are uncontaminated with cadmium, chromium, nickel, lead and zinc, but contaminated to moderately contaminated with copper. Heavy metal contents in the sediments were found to be significantly influenced by different physico-chemical parameters. The effect of these parameters can be arranged in the following order: clay fraction > carbonate fraction > silt fraction > organic matter fractions. A sequential extraction procedure showed that the total concentrations of the heavy metals are largely bound to the residual phase (retained 71.4% of cadmium, 77.8% of chromium, 75% of copper, 47% of nickel, 62.8% of lead, and 75.8% of zinc). A likely sequence of mobility in the investigated soils is as follows: chromium > lead > nickel > cadmium > zinc > copper.     

Change of PCBs and forms of heavy metals in sewage sludge during thermophilic anaerobic digestion

Determination of seven congeners of PCBs was carried out for sewage sludge before, during and after thermophilic digestion. The overall content of heavy metals (Zn, Cu, Ni, Cd, Pb, Cr) in sludge before and after digestion was determined. Moreover the concentration of heavy metals in particular chemical fractions of the sludge was analyzed. After the thermophilic digestion total concentration of seven PCBs was reduced by 47%, which suggests that thermophilic digestion affects PCB reduction positively. On the 10th d of the process, concentration of lower chlorinated PCBs increased, whereas those of higher chlorinated PCBs decreased. The thermophilic digestion process showed no accumulation of the studied heavy metals in the mobile fractions (exchangeable and carbonate) of the stabilized sewage sludge, except for nickel. The highest increase in zinc, copper, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase in lead was found in the residual fraction of the sludge. In case of nickel both fractions of organic-sulfide and exchangeable-carbonate fractions were enriched.     

Effect of SiO2 on immobilization of metals and encapsulation of a glass network in slag

The final disposal of ash from an incinerator is of special concern because of the possibility of its releasing toxic substances. Melting/vitrification has been regarded as a prospective technology of ash treatment. The object of this investigation was to evaluate the effect of silica (SiO2) addition on the immobilization of hazardous metals and the encapsulation of a glass network during the vitrification process. Four specimens with SiO2/fly ash mixing ratios of 0, 0.1, 0.2, and 0.3, respectively, were tested. The mobility of metals in slag was then estimated by a sequential extraction procedure. X-ray diffraction analysis indicates that SiO2 leads to the polymerization of silicates. The encapsulation of aluminum, calcium, and magnesium would not be observed unless adequate amount of SiO2 was added. It was also found that SiO2 addition enhances the formation of a compact and interconnected glass network structure and, thus, contributes to the chemical stability of metals in slag. After vitrification, the mobility of cadmium, copper, iron, chromium, nickel, lead, and zinc was significantly reduced. However, there is no significant correlation between the immobilization of these metals and the addition of SiO2.     

Fractionation and leachability of Fe,Zn, Cu and Ni in the sludge from a sulphate-reducing bioreactor treating metal-bearing wastewater

This work presents and discusses experimental results on the characterisation and metal leaching potential of a biogenic, metal-rich sulphidic sludge, generated in a sulphate-reducing bioreactor, operated to treat acidic synthetic solutions bearing Fe, Zn, Ni and Cu. The sustainability of the metal removal bioprocess strongly depends on the fate of the sludge. To propose appropriate management practices, a detailed characterisation of the sludge is necessary. The granulometry, chemical composition and mineralogy of the sludge were initially determined. The mobility of the metals was assessed via a modified Tessier experimental procedure. The leachability of the sludge metal content was determined via a standard compliance method (EN 12457-2) and experiments designed to evaluate the effect of pH and time on metal leaching from the sludge. The sludge metal content sums up to 69.5% dw, namely iron (14.8%), zinc (18.7%), nickel (17.7%) and copper (18.2%) and, based on the criteria set by European Union, the sludge is characterised as hazardous and inappropriate for landfilling without any pretreatment. The sludge consists mainly of very fine poorly crystalline aggregates of Fe, Zn, Cu and Ni sulphides. The fine grain size, the poorly crystalline structure and the oxidation of sulphide upon exposure to water/air render the high metal content of the sludge recoverable.     

Occurrences and inventories of heavy metals and brominated flame retardants in wastes from printed circuit board production

Pollutants including heavy metals and brominated flame retardant were detected in 10 types of production wastes from a typical printed circuit board manufacturing plant, and their inventories were estimated. Rinsing water from etching process had the highest concentrations of copper (665.51 mg/L), lead (1.02 mg/L), nickel (3.60 mg/L), chromium (0.97 mg/L), and tin (1.79 mg/L). Powdered solid waste (SW) from the cut lamination process contained the highest tetrabromobisphenol-A (TBBPA) levels (49.86 mg/kg). Polybrominated diphenyl ethers (PBDEs) were absent in this plant, in agreement with the international regulations of PBDE phase out. The pollutant inventories in the wastes exhibited in the order of copper >?>?zinc?>?tin?≈?nickel?>?lead?>?chromium >?>?TBBPA. The potential environmental impact of pollutants in SW during production and disposal were further investigated. A high partitioning of pollutant concentration between the total suspended particle and SW (?0.10?K _TS?相似文献   

Investigation of Cr(VI) reduction in continuous-flow activated sludge systems

The aim of this research was to investigate hexavalent chromium, Cr(VI), reduction by activated sludge and to evaluate the use of continuous-flow activated sludge systems for the treatment of Cr(VI)-containing wastewater. Three series of experiments were conducted using two parallel lab-scale activated sludge systems. During the first experiment, one system was used as a control, while the other received Cr(VI) concentrations equal to 0.5, 1, 3 and 5mg l(-1). For all concentrations added, approximately 40% of the added Cr(VI) was removed during the activated sludge process. Determination of chromium species in the dissolved and particulate phase revealed that the removed Cr(VI) was sorbed by the activated sludge flocs mainly as trivalent chromium, Cr(III), while the residual chromium in the dissolved phase was mainly detected as Cr(VI). Activated sludge ability to reduce Cr(VI) was independent of the acclimatization of biomass to Cr(VI) and it was not affected by the toxic effect of Cr(VI) on autotrophic and heterotrophic microorganisms. During the second experiment, both systems were operated under two different hydraulic residence time (theta equal to 20 and 28h) and three different initial organic substrate concentration (COD equal to 300, 150 and 0mg l(-1)). Cr(VI) reduction was favored by an increase of theta, while it was limited by influent COD concentration. Finally, at the last experiment the effect of anoxic and anaerobic reactors on Cr(VI) reduction was investigated. It was observed that the use of an anoxic zone or an anaerobic-anoxic zone ahead of the aerobic reactor favored Cr(VI) reduction, increasing mean percentage Cr(VI) reduction to almost 80%.     

Bacterial leaching of heavy metals from sewage sludge-bioreactors comparison

More than 50% of municipal sewage sludges cannot be used on agricultural land because of their heavy metals content. Therefore, microbial leaching of heavy metal from municipal sludge was studied in a continuously stirred tank reactor without recycling (CSTR) or with sludge recycling (CSTRWR) at residence times of 1, 2, 3 and 4 days. The reactor CSTRWR is supposed to be more efficient for bacterial process due to the recycling of active bacteria from the settling tank to the reactor. The CSTRWR and the CSTR with 1 g litre(-1) FeSO(4).7H(2)O addition were equally efficient because of copper reprecipitation or recomplexation in the settling tank of the CSTRWR. In the CSTR, about 62% of copper and about 77% of zinc were dissolved in 3 days residence time compared to 50% of copper and 64% of zinc in the CSTRWR, if 3 g litre(-1) FeSO(4).7H(2)O was added. Thus with larger amount of substrate, the CSTR was more efficient than the CSTRWR. Residence time and pH were the main factors for zinc solubilization while for copper, the redox potential was also a major factor. The effect of FeSO(4).7H(2)O concentration on bacterial activity to solubilize heavy metals was also studied, increased concentration of FeSO(4).7H(2)O yielded better copper solubilization while it had no effect or a negative effect on zinc. This supports the hypothesis of a direct mechanism for zinc solubilization and of an indirect mechanism for copper solubilization.     

提高生物法分离制革污泥中铬分离效率的研究

在已确定污泥驯化最佳条件的基础上,通过改变滤材、液固分离条件,添加营养物质继续降低pH等方法,进行提高生物沥滤法分离制革污泥中铬的分离效率的研究。同时考察化学沥滤法（1∶1硫酸）在相同条件下的分离效率。试验结果表明：用相应pH值酸液（1∶1硫酸配制）淋洗,淋洗+闷洗和抽真空＋酸液淋洗等过滤方式可提高铬的分离效率。生物沥滤中当pH值下降至1.8时,分离效率即可达到94.65%,与直接用蒸馏水淋洗相比要高得多。化学沥滤中当pH值下降到1时,分离效果可达96.7%,沥滤污泥中剩余铬含量可达到制革污泥农用标准。     

含重金属水处理污泥的固化和浸出毒性研究

工业危险固体废物在进行安全填埋前需要进行固化稳定处理。针对电镀厂和皮革厂含重金属的水处理污泥 ,用不同比例的水泥、粉煤灰进行固化稳定处理。考虑酸雨环境 ,浸出实验采用TCLP标准。电镀厂污泥单独固化时 ,其浸出液中铜离子浓度由 78 0mg/L下降到 1 5mg/L ;镍离子浓度由 2 2 4 5mg/L下降到 2 2 2mg/L ,高于危险废物允许进入填埋区 15mg/L的控制限值。电镀厂污泥与皮革厂污泥混合后固化 ,浸出液毒性明显降低。铜离子的浸出浓度降低到1 98mg/L ,镍离子降低到 4 10mg/L ,总铬降低到 0 4 0mg/L ,各项指标均低于国家危险废物允许进入填埋区的控制限值 ,可安全填埋。     

Municipal landfill leachate treatment for metal removal using water hyacinth in a floating aquatic system.

Experiments were carried out to investigate the ability of water hyacinth (Eichhornia crassipes) to remove five heavy metals (cadmium, chromium, copper, nickel, and lead) commonly found in leachate. All experiments were conducted in batch reactors in a greenhouse. It was found that living biomass of water hyacinth was a good accumulator for copper, chromium, and cadmium. The plants accumulated copper, chromium, and cadmium up to 0.96, 0.83, and 0.50%, respectively, of their dry root mass. However, lead and nickel were poorly accumulated in water hyacinth. Also, nonliving biomass of water hyacinth dry roots showed ability to accumulate all metals, except Cr(VI), which was added in anionic form. The highest total metal sorption by nonliving dry water hyacinth roots was found to take place at pH 6.4. The current research demonstrates the potential of using water hyacinth for the treatment of landfill leachate containing heavy metals.     

Isolation and characterization of Bacillus cereus IST105 from electroplating effluent for detoxification of hexavalent chromium

Purpose

Electroplating industries are the main sources of heavy metals, chromium, nickel, lead, zinc, cadmium and copper. The highest concentrations of chromium (VI) in the effluent cause a direct hazards to human and animals. Therefore, there is a need of an effective and affordable biotechnological solution for removal of chromium from electroplating effluent.

Methods

Bacterial strains were isolated from electroplating effluent to find out higher tolerant isolate against chromate. The isolate was identified by 16S rDNA sequence analysis. Absorbed chromium level of bacterium was determined by inductively coupled plasma-atomic emission spectrometer (ICP-AES), atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive X-ray analysis (EDX). Removal of metals by bacterium from the electroplating effluent eventually led to the detoxification of effluent confirmed by MTT assay. Conformational changes of functional groups of bacterial cell surface were studied through Fourier transform infrared spectroscopy.

Results

The chromate tolerant isolate was identified as Bacillus cereus. Bacterium has potency to remove more than 75% of chromium as measured by ICP-AES and AAS. The study indicated the accumulation of chromium (VI) on bacterial cell surface which was confirmed by the SEM-EDX and TEM analysis. The biosorption of metals from the electroplating effluent eventually led to the detoxification of effluent. The increased survivability of Huh7 cells cultured with treated effluent also confirmed the detoxification as examined by MTT assay.

Conclusion

Isolated strain B. cereus was able to remove and detoxify chromium (VI). It would be an efficient tool of the biotechnological approach in mitigating the heavy metal pollutants.     

Evaluation of the critical factors controlling stability of chromium, copper, arsenic and zinc in iron-treated soil

Various environmental factors are expected to affect the mobility of elements in chemically stabilized soils. The aim of this study was to evaluate the effects of pH, oxidizing-reducing potential (Eh), liquid-to-solid ratio (L/S), presence of organic matter (OM) and microbial activity (MA) on the mobility of chromium, copper, arsenic and zinc in zerovalent iron (Fe(0))-stabilized soil. A 2(5) full factorial design was applied to assess the leaching of the elements from the treated soil. The factor having the most impact on the mobility of Cr, Cu and Zn was pH; low pH (3) led to the release of these elements. Arsenic remobilization was controlled by L/S and MA, whilst Eh, though also significant, had less influence. In the identified worst-case scenarios, more than half of the total Zn and Cu and 14% of As can be expected to remobilize from the treated soil. The leaching procedure concerning sample agitation and type of filtration showed to substantially affect the results of As leaching, especially in OM rich soil.     

Metals removal from aqueous solution by iron-based bonding agents

GOAL AND SCOPE AND BACKGROUND: The application of a promising method, termed sorptive flotation, for the removal of chromium(VI) and zinc ions was the aim of the present paper. A special case of sorptive flotation is adsorbing colloid flotation. Suitable sorbent preparation techniques have been developed in the laboratory. METHODS: Sorptive flotation, consisting of the sorption and flotation processes combined in series, has proved to give fast and satisfactory treatment of the industrial streams and effluents bearing dilute aqueous solutions of zinc and chromium(VI). RESULTS AND DISCUSSION: Goethite has proved to be effective for the removal of chromium(VI) and zinc ions. Also, adsorbing colloid flotation with ferric hydroxide (as the co-precipitant) could be an alternative method to the above-mentioned separation of metal ions. In both cases, chromium(VI) (pH=4) and zinc (pH=7) removal was about 100%. CONCLUSION: The reasons for selecting the iron-based bonding materials, like goethite and/or in-situ produced ferric hydroxide, are that they are cheap, easily synthesized, suitable both for cation and anion sorption, and, furthermore, that they present low risks for adding a further pollutant to the system. Promising results were obtained. RECOMMENDATION AND OUTLOOK: The application of goethite and in-situ produced ferric hydroxide has demonstrated their effectiveness in the removal of heavy metal ions, such as chromium anions and zinc cations. A proposed continuation of current work is the utilization of similar iron oxides, for instance synthesized akaganeite. The comparison between the results reported in this paper with the results reported in the literature, also deserves attention.