Enhanced chitosan beads-supported Fe-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers

The removal of heavy metals from electroplating wastewater is a matter of paramount importance due to their high toxicity causing major environmental pollution problems. Nanoscale zero-valent iron (NZVI) became more effective to remove heavy metals from electroplating wastewater when enhanced chitosan (CS) beads were introduced as a support material in permeable reactive barriers (PRBs). The removal rate of Cr (VI) decreased with an increase of pH and initial Cr (VI) concentration. However, the removal rates of Cu (II), Cd (II) and Pb (II) increased with an increase of pH while decreased with an increase of their initial concentrations. The initial concentrations of heavy metals showed an effect on their removal sequence. Scanning electron microscope images showed that CS-NZVI beads enhanced by ethylene glycol diglycidyl ether (EGDE) had a loose and porous surface with a nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 μm with an average aperture size of around 58.6 μm. The shell showed a tube structure and electroplating wastewaters may reach NZVI through these tubes. X-ray photoelectron spectroscope (XPS) demonstrated that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed via predominant reduction and auxiliary adsorption. However, main adsorption and auxiliary reduction worked for the removal of Cd (II). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) from actual electroplating wastewater was 89.4%, 98.9%, 94.9% and 99.4%, respectively. The findings revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and may become an effective and promising technology for in situ remediation of heavy metals.     

Phytoprotective influence of bacteria on growth and cadmium accumulation in the aquatic plant Lemna minor

Certain plants are known to accumulate heavy metals, and can be used in remediation of polluted soil or water. Plant-associated bacteria, especially those that are metal tolerant, may enhance the total amount of metal accumulated by the plant, but this process is still unclear. In this study, we investigated metal enhancement vs. exclusion by plants, and the phytoprotective role plant-associated bacteria might provide to plants exposed to heavy metal. We isolated cadmium-tolerant bacteria from the roots of the aquatic plant Lemna minor grown in heavy metal-polluted waters, and tested these isolates for tolerance to cadmium. The efficiency of plants to accumulate heavy metal from their surrounding environment was then tested by comparing L. minor plants grown with added metal tolerant bacteria to plants grown axenically to determine, whether bacteria associated with these plants increase metal accumulation in the plant.Unexpectedly, cadmium tolerance was not seen in all bacterial isolates that had been exposed to cadmium. Axenic plants accumulated slightly more cadmium than plants inoculated with bacterial isolates. Certain isolates promoted root growth, but overall, addition of bacterial strains did not enhance plant cadmium uptake, and in some cases, inhibited cadmium accumulation by plants. This suggests that bacteria serve a phytoprotective role in their relationship with Lemna minor, preventing toxic cadmium from entering plants.     

乐昌铅锌矿区水道底泥中的重金属潜在生态风险评价

调查了乐昌铅锌矿区霜降河与武江乐昌段水道底泥中的重金属污染现状,对其潜在的生态风险进行了评价。结果表明,采选矿废水排泄水道和霜降河底泥中的重金属含量远远超过当地的背景值和全国的背景值,武江与霜降河水汇合后底泥中的重金属含量超过当地背景值的程度较轻;采选矿废水排泄水道和霜降河底泥中重金属的潜在生态风险已达到非常高的程度,分析认为乐昌铅锌矿的采选废水是当地水道底泥中重金属的主要污染源。     

Precipitation of heavy metals from wastewater using simulated flue gas: Sequent additions of fly ash, lime and carbon dioxide

Lime is a preferred precipitant for the removal of heavy metals from industrial wastewater due to its relatively low cost. To reduce heavy metal concentration to an acceptable level for discharge, in this work, fly ash was added as a seed material to enhance lime precipitation and the suspension was exposed to CO₂ gas. The fly ash-lime-carbonation treatment increased the particle size of the precipitate and significantly improved sedimentation of sludge and the efficiency of heavy metal removal. The residual concentrations of chromium, copper, lead and zinc in effluents can be reduced to (mg L⁻¹) 0.08, 0.14, 0.03 and 0.45, respectively. Examination of the precipitates by XRD and thermal analysis techniques showed that calcium-heavy metal double hydroxides and carbonates were present. The precipitate agglomerated and hardened naturally, facilitating disposal without the need for additional solidification/stabilization measures prior to landfill. It is suggested that fly ash, lime and CO₂, captured directly from flue gas, may have potential as a method for wastewater treatment. This method could allow the ex-situ sequestration of CO₂, particularly where flue-gas derived CO₂ is available near wastewater treatment facilities.     

Simultaneous bioaccumulation of multiple metals from electroplating effluent using Aspergillus lentulus

Toxic impacts of heavy metals in the environment have lead to intensive research on various methods of heavy metal remediation. However, in spite of abundant work on heavy metals removal from simple synthetic solutions, a very few studies demonstrate the potential of microbial strains for the treatment of industrial effluents containing mixtures of metals. In the present study, the efficiency of an environmental isolate (Aspergillus lentulusFJ172995), for simultaneous removal of chromium, copper and lead from a small-scale electroplating industry effluent was investigated. Initial studies with synthetic solutions infer that A. lentulus has a remarkable tolerance against Cr, Cu, Pb and Ni. During its growth, a significant bioaccumulation of individual metal was recorded. After 5 d of growth, the removal of metals from synthetic solutions followed the trend Pb²⁺ (100%) > Cr³⁺ (79%) > Cu²⁺ (78%), > Ni²⁺ (42%). When this strain was applied to the treatment of multiple metal containing electroplating effluent (after pH adjustment), the metal concentrations decreased by 71%, 56% and 100% for Cr, Cu and Pb, respectively within 11 d. Based on our results, we propose that the simultaneous removal of hazardous metals from industrial effluents can be accomplished using A. lentulus.     

A N-Nitrosodimethylamine (NDMA) precursor analysis for chlorination of water and wastewater

N-nitrosodimethylamine (NDMA) is a potent carcinogen formed during chloramination of water and wastewater treatment plant effluents. A procedure is described for quantifying the concentration of the organic precursors of NDMA that could be formed during chlorination of wastewaters and natural waters. The method involves applying a high dose of monochloramine to a pH-buffered sample followed by a 10-day contact period, during which the monochloramine decays at a rate unrelated to the composition of the sample. Analyses of samples of municipal wastewater effluents and surface waters indicate that the method provides a robust and reproducible measurement of NDMA precursors over a wide range of conditions. A sensitive GC/CI/MS/MS analytical procedure for dimethylamine also is described and used to demonstrate that NDMA formation during chlorination of wastewater and natural waters cannot be explained by dimethylamine concentrations alone.     

Differential persistence of F-specific RNA phage subgroups hinders their use as single tracers for faecal source tracking in surface water

The four subgroups of F-specific RNA bacteriophages (I-IV) have been proposed as potential tracers for faecal source tracking. Groups II and III predominate in human sources while groups I and IV are most abundant in animal sources. The four subgroups of naturally occurring F-specific RNA bacteriophages were identified in different samples by plaque hybridization with genotype-specific probes and the persistence of each subgroup was evaluated. The proportions of the F-specific RNA bacteriophage subgroups were measured in wastewaters, after inactivation in surface waters or after wastewater treatment and in mixtures of wastewater of human and animal origin. Our results indicate that phage groups differ in their persistence in the environment and to different disinfecting treatments. The greater survival of subgroups I and II in treated samples hinders the interpretation of results obtained with F-specific RNA bacteriophages. The phages of subgroups III and IV were the least resistant to all treatments. These results should be considered when using genotypes of F-specific RNA as sole tracers for faecal source tracking.     

Poorly humified peat as an adsorbent for metals in wastewater

Metal adsorption and surface charge determinations were performed previously on well-characterised Sphagnum and Carex peat samples. The aim of this investigation was to determine metal adsorption from complex wastewaters onto these peat samples and compare it to the adsorption onto peat granules, clinoptilolite, glauconite and a flue dust from steel production. A sulphide mine leachate, a landfill leachate and a laundry wastewater were chosen, giving a variation in pH, ionic strength, total organic carbon and concentrations of metals. Metal adsorption was determined in batch and column experiments. The wastewater composition was of great importance for metal removal efficiency, mainly due to the difference in dominating metal species. In the sulphide mine leachate, containing free metal ions, a high metal adsorption was observed onto both peat and inorganic adsorbents. In the landfill leachate the metals formed carbonate and organic complexes and a low metal removal was achieved. Contrary to the leachates, the laundry wastewater contained suspended particles. The high amount of metals removed, 80% of the Cu and 30-60% of the Zn concentration, was probably withdrawn bound to the particle fraction. The highest removal of metal ions was obtained in the sulphide mine leachate with Carex peat, removing 97-99% of the Zn and 85-100% of the Cu content. The Sphagnum peat sample removed 37-77% of the Zn and 80-100% of the Cu content. The differences found between Sphagnum and Carex peat were attributed to the original chemistry of the plant material and the habitat conditions at the time of peat formation. Generally, the combination of glauconite or clinoptilolite with the peat samples in column experiments gave a minor improvement in metal removal.     

Environmental aspects of the use of NTA as a detergent builder

The behaviour, fate and significance of the detergent builder nitrilotriacetic acid (NTA) has been reviewed with particular reference to the removal of NTA during wastewater treatment and the effects of NTA on heavy metal solubility both during treatment and in the receiving environment. It is concluded that NTA removal during secondary biological treatment is subject to considerable variation, both temporal and between works as a result of changes in NTA load, temperature, water hardness and treatment process parameters. As a result of such variability, effluent NTA concentrations may be sufficient to mobilise heavy metals resulting in metal contamination of receiving waters and potable waters, particularly in areas of low effluent dilution and high water re-use. Removal of NTA during primary sedimentation and septic tank treatment is concluded to be predominantly due to adsorption to the sludge solids while removal in anaerobic sludge digestion is subject to operational characteristics of the treatment works. Disposal of NTA contaminated sludge to land may contaminate groundwaters and affect heavy metal speciation, while the disposal of contaminated sludge or sewage to sea may result in toxic algal blooms, in addition to effects on metal speciation.     

Pharmaceutical compounds in the wastewater process stream in Northwest Ohio

In order to add to the current state of knowledge regarding occurrence and fate of Pharmaceutical and Personal Care Products (PPCP's) in the environment, influent, effluent and biosolids from three wastewater treatment facilities in Northwest Ohio, USA, and a stream containing effluent discharge from a rural treatment facility were analyzed. The three WWTP facilities vary in size and in community served, but are all Class B facilities. One facility was sampled multiple times in order to assess temporal variability. Twenty compounds including several classes of antibiotics, acidic pharmaceuticals, and prescribed medications were analyzed using ultrasonication extraction, SPE cleanup and liquid chromatography-electrospray ionization tandem mass spectrometry. The highest number of compounds and the greatest concentrations were found in the influent from the largest and most industrial WWTP facility. Short-term temporal variability was minimal at this facility. Many compounds, such as clarithromycin, salicylic acid and gemfibrizol were found at concentrations more than one order of magnitude higher than found in the effluent samples. Effluent waters contained elevated levels of carbamazepine, clindamycin and sulfamethoxazole. Differences in composition and concentration of effluent waters between facilities existed. Biosolid samples from two different facilities were very similar in PPCP composition, although concentrations varied. Ciprofloxacin was found in biosolids at concentrations (up to 46 mug/kg dry mass) lower than values reported elsewhere. Diclofenac survived the WWTP process and was found to persist in stream water incorporating effluent discharge. The low variability within one plant, as compared to the variability found among different wastewater treatment plants locally and in the literature is likely due to differences in population, PPCP usage, plant operations and/or local environment. These data are presented here for comparison with this emerging set of environmental compounds of concern.     

Certain antioxidant enzymes of Allium cepa as biomarkers for the detection of toxic heavy metals in wastewater

The utility of antioxidant enzymes, viz glutathione-S-transferase (GST), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), as biomarkers of heavy metal pollution in water was investigated using the Allium cepa (onion) system. These antioxidant enzymes were assayed in onion bulbs exposed to certain heavy metals taken separately, the test metals taken in combination as well as the industrial wastewater especially found to contain these metals. GST exhibited significantly enhanced activity upon treatment with individual heavy metals. However, GR, SOD and CAT did not show such a pronounced increase in activities. At higher heavy metal concentrations, GR, SOD and CAT showed a steep decline while GST activity still showed a rise. Moreover, APX, GPX and MDHAR also exhibited remarkable induction with increase in the concentration of individual heavy metals. However, there was no significant change in DHAR activity with respect to the controls. Metabolites like ascorbate (ASC) and glutathione (GSH) exhibited significant decline with increase in the concentration of individual heavy metals while the level of H(2)O(2) continued to display the rise up to a heavy metal concentration of 100 microM, after which it showed a gradual decline. A. cepa bulbs treated with wastewater sample showed enzyme activity profiles similar to that shown with heavy metals, thereby suggesting the presence of heavy metals in the test wastewater. Atomic absorption spectrophotometry also detected large amounts of Cd, Cr, Cu, Hg, Pb and Zn in the test water sample. The metal mixture, containing the amounts of heavy metals equivalent to those found in the wastewater, resulted in steep declines in GR, SOD and CAT activities in A. cepa while GST showed a rise. However, when this metal mixture was diluted to 2000-fold, GR, SOD and CAT also showed enhanced activities compared with the controls. Contrary to the above finding, APX, GPX and MDHAR exhibited the rise in activities in A. cepa exposed to the metal mixture at all dilutions. In the presence of cycloheximide, all the enzymes returned to the levels of untreated controls while chloramphenicol did not have any effect on the test enzymes, thereby suggesting de novo protein synthesis of the test antioxidant enzymes in the cytosolic compartment of the cell as a result of exposure to the heavy metals.     

Mercury mass balance at a wastewater treatment plant employing sludge incineration with offgas mercury control

Efforts to reduce the deliberate use of mercury (Hg) in modern industrialized societies have been largely successful, but the minimization and control of Hg in waste streams are of continuing importance. Municipal wastewater treatment plants are collection points for domestic, commercial, and industrial wastewaters, and Hg removal during wastewater treatment is essential for protecting receiving waters. Subsequent control of the Hg removed is also necessary to preclude environmental impacts. We present here a mass balance for Hg at a large metropolitan wastewater treatment plant that has recently been upgraded to provide for greater control of the Hg entering the plant. The upgrade included a new fluidized bed sludge incineration facility equipped with activated carbon addition and baghouse carbon capture for the removal of Hg from the incinerator offgas. Our results show that Hg discharges to air and water from the plant represented less than 5% of the mass of Hg entering the plant, while the remaining Hg was captured in the ash/carbon residual stream exiting the new incineration process. Sub-optimum baghouse operation resulted in some of the Hg escaping collection there and accumulating with the ash/carbon particulate matter in the secondary treatment tanks. Overall, the treatment process is effective in removing Hg from wastewater and sequestering it in a controllable stream for secure disposal.     

水洗磷酸盐预处理后飞灰中重金属的热稳定性

探讨了磷酸盐对城市生活垃圾焚烧(MSMI)飞灰中重金属在常温下的稳定作用以及高温挥发抑制作用.结果表明,经水洗磷酸盐预处理后,常温下,飞灰中重金属Pb,Cd,Zn,Cr在毒性浸出程序(TCLP)中的浸出浓度低于美国EPA标准限值;高温下,飞灰中重金属Cd,Pb,Zn的挥发率分别由未处理参比样的97.2%,94.3%和79.3%降低至10.2%,23.5%,13.5%,均小于25%.     

高压脉冲电絮凝与硅藻精土组合工艺处理电镀废水

电镀废水成分复杂,其中含有多种重金属离子,不适于生物降解,而化学处理工艺复杂、运行费用高。在生产性试验的基础上,对电镀综合废水采用高压脉冲电絮凝与硅藻精土组合技术处理,对Cr^6＋、Ni^2＋、Cu^2＋、COD的去除率分别达到99．77％、99．90％、100％和90％,出水各项指标均达到了排放标准。该工艺与传统化学处理法相比,具有处理效率高、速度快、占地省、操作方便、运行可靠、投资省、处理成本低的特点。     

Determination of the heavy metal binding capacity of aquatic samples using MetPLATE: a preliminary study.

MetPLATE, a microbial toxicity test which is specific for heavy metal toxicity, was used to rapidly determine the heavy metal binding capacity (HMBC) of a wide range of surface waters from Florida and Georgia. HMBC determines the impact of physicochemical factors on metal bioavailability and toxicity. The new developed protocol, using MetPLATE as the toxicity assay, showed that HMBC varied from 1.7 to 39.2 for Cd whereas the ranges for Cu and Ag were < 1-11.9 and < 1-2.1, respectively. The effect of seasons on HMBC was determined using samples from the Hogtown Creek, Gainesville, FL, and from the St John's river in Jacksonville, FL. Both surface waters displayed the highest HMBC during the Fall season. Preliminary examination of the limited data set confirms that HMBC may be influenced by the concentration of dissolved organic carbon (DOC). These preliminary data show that the impact of physical and chemical parameters on the toxicity of metals in aquatic environments can be rapidly assessed using rapid and low-cost microbiotests.     

Simultaneous removal of As, Cd, Cr, Cu, Ni and Zn from stormwater: experimental comparison of 11 different sorbents

The potential of using alumina, activated bauxsol-coated sand (ABCS), bark, bauxsol-coated sand (BCS), fly ash (FA), granulated activated carbon (GAC), granulated ferric hydroxide (GFH), iron oxide-coated sand (IOCS), natural zeolite (NZ), sand, and spinel (MgAl(2)O(4)) as sorbents for removing heavy metals from stormwater are investigated in the present study. The ability of the sorbents to remove a mixture of As, Cd, Cr, Cu, Ni and Zn from synthetic stormwater samples were evaluated in batch tests at a starting pH of 6.5. The metal speciation and saturation data is obtained using the PHREEQ-C geochemical model and used to elucidate the sorption data. It is found that BCS, FA, and spinel have significantly higher affinity towards heavy metals mainly present as cationic or non-charged species (i.e. Cd, Cu, Ni and Zn) compared to those present as anionic species (i.e. As and Cr). However, IOCS, NZ and sand have higher affinity towards As and Cr, while alumina has equally high affinity to all tested heavy metals. The Freundlich isotherm model is found to fit the data in many cases, but ill fitted results are also observed, especially for FA, BCS and GAC, possibly due to leaching of some metals from the sorbents (i.e. for FA) and oversaturated conditions making precipitation the dominant removal mechanism over sorption in batches with high heavy metal concentrations and pH. Calculated sorption constants (i.e. K(d)) are used to compare the overall heavy metal removal efficiency of the sorbents, which in a decreasing order are found to be: alumina, BCS, GFH, FA, GAC, spinel, ABCS, IOCS, NZ, bark, and sand. These findings are significant for future development of secondary filters for removal of dissolved heavy metals from stormwater runoff under realistic competitive conditions in terms of initial heavy metal concentrations, pH and ionic strength.     

Elemental analyses of pine bark and wood in an environmental study

Bark and wood samples were taken from the same individuals of Scots pine (Pinus sylvestris L.) from a polluted area close to a Cu-Ni smelter in Harjavalta and from some relatively unpolluted areas in western Finland. The samples were analysed by thick-target particle induced X-ray emission (PIXE) after preconcentration by dry ashing at 550 degrees C. The elemental contents of pine bark and wood were compared to study the impact of heavy metal pollution on pine trees. By comparison of the elemental contents in ashes of bark and wood, a normalisation was obtained. For the relatively clean areas, the ratios of the concentration in bark ash to the concentration in wood ash for different elements were close to 1. This means that the ashes of Scots Pine wood and bark have quite similar elemental composition. For the samples from the polluted area the mean concentration ratios for some heavy metals were elevated (13-28), reflecting the effect of direct atmospheric contamination. The metal contents in the ashes of pine bark and wood were also compared to recommendations for ashes to be recycled back to the forest environment. Bark from areas close to emission sources of heavy metal pollution should be considered with caution if aiming at recycling the ash. Burning of bark fuel of pine grown within 6 km of the Cu-Ni smelter is shown to generate ashes with high levels of Cu, Ni as well as Cd, As and Pb.     

Technoeconomic Indicators Pertinent to Environmental Management in Metal Forging Industry

Effluents from metal forging industry are characterized by significant concentrations of heavy metals and cyanides which normally exceed allowable discharge limits. Pickling and electroplating processes are considered the principal generators of hazardous waste in this industry. This paper addresses development of upgraded environmental management practices in a metal forging plant located south of Cairo with the aim to establish an adequate pollution control system. Current pollution loads have been assessed with respect to quantity and characteristics. Optional environmental management systems have been proposed and compared, based on treatability studies and relevant technoeconomic grounds. The selected scheme encompassed chemical precipitation using lime for the treatment of pickling effluents. Zinc electroplating effluents are proposed to be treated through alkaline chlorination. Drying ponds are the proposed solution for the drying of sludges. The estimated average treatment cost for the combined flows is about L.E. 0.72/m 3 .     

The mechanism of metals precipitation by biologically generated alkalinity in biofilm reactors

Microbial strains, characterized by increased tolerance and ability to grow in metal bearing wastewaters as well as by effective metal sequestering capability by both active (bioaccumulative) and passive (biosorptive) processes, were tested as inoculum for metal laden wastewater treatment systems. Their capacity to grow in metal bearing wastewater, using an easily available and inexpensive carbon source such as acetate, was studied in batch experiments. Two principal conclusions were drawn: (1). Growth was observed for all the strains examined suggesting that the strains can be acclimated to metals bearing wastewaters. (2). Solution pH increased from neutral to alkaline values during growth (pH(initial)=7, pH(final)=10). The later was observed systematically for all strains. Metal precipitation, due to the metabolically generated alkalinity is expected as a result.Supporting evidence for this hypothesis was provided during the operation of two pilot moving bed sand filters treating two different metal bearing wastewaters. Acetate was used as carbon source to support the growth and maintenance of microbial biomass on the sand grains of the filters. The characteristics of the sludge produced from the operation of the pilot plants were subsequently studied in the laboratory. Both sludges were significantly loaded with large amounts of metals.A mechanism of metal precipitation induced by the metabolically generated alkalinity, when acetate is used as carbon source, could be proposed as the main process responsible for the metals sequestering inside the moving bed sandfilter reactor.     

The use of town refuse ash in urban agriculture around Jos, Nigeria: health and environmental risks

This paper reports on a study that examines the health and environmental risks of using town refuse ash in urban vegetable production in Jos, Nigeria, in terms of heavy metal accumulation in the food chain. Soil and crop samples, collected from five study farms, and samples of the river water used for irrigation, were analysed for seven heavy metals Fe, Mn, Zn, Cu, Ni, Cd and Pb. On the basis of the field data the paper discusses: (1) the potential soil deficiencies and toxicities; (2) the probable links between soil heavy metal levels and fertilisation practices; (3) the heavy metal concentrations in crop tissue in relation to crop growth and human health. The findings suggest that soil concentrations of the seven metals fall within 'typical' soil levels, and that there should not be any problems of either toxicities or deficiencies for crop growth. There was evidence of slight accumulation of Zn, Cu and Cd on some of the farms with a history of town refuse ash use. However, in all farms lettuce crops contained very large concentrations of Fe, and Pb concentrations that were 20 to 40 times higher than the WHO/FAO maximum recommended level in leafy vegetables for human consumption. The Cd content of carrot tissue was 10 times higher than the WHO/FAO recommended limit. The relatively small number of soil and crop samples precluded any formal attempt at correlating the concentrations of heavy metals found in the vegetable crops with the farm levels. Nevertheless, the data suggested that these were not linked. The paper goes on to consider various potential sources of the metals found in the crops, including irrigation water, town refuse ash and air-borne dust, and discusses additional health and environmental risks pertaining to the use of town refuse ash. Undoubtedly, the heavy Pb and Cd contamination of certain crops indicates the urgent need for future studies to ascertain the precise source of these metals, and although the practice of using town refuse ash does not appear to have resulted in large-scale contamination of soil in the farming area, there are a number of unsafe practices associated with it that call for the identification of strategies for the safe utilisation of urban waste in Jos.