Metal ions removal from wastewater or washing water from contaminated soil by ultrafiltration-complexation

In the present paper a process for removal of ions from wastewater or from washing water of contaminated soil by using the weakly basic water-soluble polymer polyethylenimine (PEI) as chelating agent and the Cu(2+) ion as model in combination with an ultrafiltration process was investigated. The complexing agent was preliminarily tested to establish the best operative conditions of the process. Next, ultrafiltration tests by using five different membranes were realised to check membrane performance like flux and rejection. Finally, the possibility for recovering and recycling the polymer was tested in order to obtain an economically sustainable process. Obtained results showed that complexation conditions depends on pH: indeed, at a pH>6 PEI-Cu(2+) complexes are formed, while at pH<3 the decomplexation reaction takes place. Saturation condition is 0.333 mg Cu(2+)/mg PEI, meaning a ratio PEI/Cu(2+)=3(w/w). UF tests showed good results using the PAN 40 kDa membrane reaching an average copper concentration in the permeate of 2 mg/l and a flux of 135.4 and 156.5l/h.m(2) at 2 and 4 bar, respectively. Metal rejection, permeate flow rate, and possibility to regenerating and recycling the polymer makes the polymer-assisted ultrafiltration process (PAUF) very interesting for metal ion removal from waters.     

Coupling enhanced water solubilization with cyclodextrin to indirect electrochemical treatment for pentachlorophenol contaminated soil remediation

This study undertakes to examine, at laboratory scale, the technical feasibility, mechanisms and performances provided by coupling the enhanced flushing abilities of cyclodextrin solutions for pentachlorophenol (PCP) removal from contaminated soil with indirect electrochemical treatment for the final disposal of soil extract solutions containing high PCP loads (0.77mmolL(-1)). The hydroxypropyl-beta-cyclodextrin (HPCD) solution increased the aqueous concentration of PCP in soil extract effluents to as much as 3.5 times the concentrations obtained during the water flush of the soil. PCP was treated with electrochemically generated Fenton's reagent in an aqueous medium. The increase in PCP water solubility in the presence of HPCD is balanced by the corresponding decrease in PCP degradation rate under indirect electrochemical treatment. This is due to the high carbon content (HPCD and dissolved natural organic matter) in the soil extract solutions, which compete for the non-selective hydroxyl radical reaction to PCP. However, our results indicate that HPCD has a beneficial effect on the degradation rates of PCP. This relative improvement in PCP degradation could be explained by the formation of the ternary complex (PCP-cyclodextrin-iron) which may direct hydroxyl reaction to PCP and which would, in any case, justify the use of a Fenton -like process for the final treatment of soil extract solutions. Total disappearance of PCP and 90% abatement of the chemical oxygen demand were achieved within an 11h electrolysis treatment time. Elucidation of the PCP degradation pathway indicates that after successive PCP hydroxylations, oxidative opening of the PCP aromatic ring quickly occurred, leading to small unstable non-chlorinated or partially chlorinated short chain carboxylic acids, such as monochloroacetic and dichloromaleic acid. Determination of the concentration of these acids shows that indirect electrochemical treatment leads to oxalic acid accumulation in aqueous solutions treated. A decrease in toxicity was observed at the end of the treatment time.     

Recovery of toxic metal ions from washing effluent containing excess aminopolycarboxylate chelant in solution

Aminopolycarboxylate chelants (APCs) are extremely useful for a variety of industrial applications, including the treatment of toxic metal-contaminated solid waste materials. Because non-toxic matrix elements compete with toxic metals for the binding sites of APCs, an excess of chelant is commonly added to ensure the adequate sequestration of toxic metal contaminants during waste treatment operations. The major environmental impacts of APCs are related to their ability to solubilize toxic heavy metals. If APCs are not sufficiently eliminated from the effluent, the aqueous transport of metals can occur through the introduction of APCs into the natural environment, increasing the magnitude of associated toxicity. Although several techniques that focus primarily on the degradation of APCs at the pre-release step have been proposed, methods that recycle not only the processed water, but also provide the option to recover and reuse the metals, might be economically feasible, considering the high costs involved due to the chelants used in metal ion sequestration. In this paper, we propose a separation process for the recovery of metals from effluents that contain an excess of APCs. Additionally, the option of recycling the processed water using a solid phase extraction (SPE) system with an ion-selective immobilized macrocyclic material, commonly known as a molecular recognition technology (MRT) gel, is presented. Simulated effluents containing As(V), Cd(II), Cr(III), Pb(II) or Se(IV) in the presence of APCs at molar ratios of 1:50 in H₂O were studied with a flow rate of 0.2 mL min⁻¹. The ‘captured’ ions in the SPE system were quantitatively eluted with HNO₃. The effects of solution pH, metal-chelant stability constants and matrix elements were assessed. Better separation performance for the metals was achieved with the MRT-SPE compared to other SPE materials. Our proposed technique offers the advantage of a non-destructive separation of both metal ions and chelants compared to conventional treatment options for such effluents.     

Application of sub-critical water technology for recovery of heavy metal ions from the wastes of Japanese scallop Patinopecten yessoensis

Sub-critical water (sub-CW) technology was used as a new technology with environmental and financial benefits for the recovery of harmful heavy metal ions Cd (II), Zn (II), Cu (II), Fe (II), Mn (II) and Ni (II) in the waste of Japanese scallop Patinopecten yessoensis. The metals are responsible for environmental problems owing to the large amount of the waste. This study proposes a new method using sub-CW treatment to recover the metal ions from scallop waste and simultaneously produce harmless and valuable materials. Reactions were conducted in a temperature range of 473-653 K and for reaction times of 1-60 min. After the sub-CW reaction, four phases existed: an oil phase, metal-soap phase, aqueous phase and solid residual. Some oil was hydrolyzed by the sub-CW reaction and converted to free fatty acids and glycerin. Free fatty acids reacted with metal ions and became metal-soap phase. Both the metal-soap phase and oil phase caught almost all metal ions at low and medium reaction temperatures (473-573 K) from original wastes, although the concentrations of the metal ions in the metal-soap phase were much higher than those in the oil phase. With increasing temperature, these two phases decomposed and the metal ions concentrated in solid residual (un-reacted waste). The binding mechanisms in the oil and metal-soap phases are discussed including the key functional groups involved. The maximum concentrations of metal ions in metal-soap phase were 7225 ppm (Fe), 862 ppm (Zn), and 800 ppm (Cd) at 573 K. The aqueous phase showed the lowest concentration of metal ions especially at temperatures above 550 K (~1.5 ppm).     

Separation of monovalent and divalent ions from aqueous solution by electrodialysis and nanofiltration

The possibilities of separating monovalent and multivalent ions by electrodialysis (ED) and nanofiltration (NF) are explored. Five synthetic single salt solutions were applied to ED and NF: NaCl, Na(2)SO(4), MgCl(2), MgSO(4) and NaNO(3). Two combinations of anionic and cationic exchange membranes were evaluated for ED (AMV/CMV Selemion membranes and ACS/CMS Tokuyama membranes), and two membranes were evaluated for NF (NTR 7450 and UTC-60). The separation was evaluated using an alternative parameter, the separation efficiency, in order to compare ED and NF. The separation efficiency ranges from 0% (no separation) to 100% (perfect separation). Both NF membranes had a good separation efficiency for the separation of monovalent and divalent anions (ca. 60%); the ED membranes performed worse. For the separation of monovalent and divalent cations, the UTC-60 membrane was the best for the considered separation because of size exclusion effects for the larger divalent ion. The ACS/CMS membranes had a similar separation efficiency (ca. 60%); the NTR 7540 membrane and AMV/CMV ED membranes showed only a small separation.     

重金属污染土的工程性质及微观结构研究

利用纯净的粘土和重金属离子溶液,配制了不同含量的重金属污染土进行击实实验,获得了相对应的最优含水率,按照最优含水率重新配置土样,并通过直接剪切等其他工性试验,探讨了重金属的存在对土体工性的影响,在工性试验的同时,对不同的污染土进行SEM扫描,研究了其微观结构的变化规律,试验结果表明:土中重金属浓度的增加导致土中粘粒的含量逐渐减小,颗粒团聚,出现大孔隙,同时其工性变差,强度降低。     

Phosphorus recovery from sewage sludge with a hybrid process of low pressure wet oxidation and nanofiltration

Phosphorus recovery from sewage sludge will become increasingly important within the next decades due to depletion of mineral phosphorus resources. In this work a new process concept was investigated, which aims at realising phosphorus recovery in a synergistic way with the overall sewage sludge treatment scheme. This process combines a low pressure wet oxidation for sewage sludge decomposition as well as phosphorus dissolution and a nanofiltration process to separate phosphorus from heavy metals and obtain a clean diluted phosphoric acid, from which phosphorus can be recovered as clean fertiliser.It was shown that this process concept is feasible for sewage sludge for wastewater treatment plants that apply enhanced biological removal or precipitation with alumina salts for phosphorus removal. The critical parameter for phosphorus dissolution in the low pressure wet oxidation process is the iron concentration, while in the nanofiltration multi-valent cations play a predominant role.In total, a phosphorus recovery of 54% was obtained for an exemplary wastewater treatment plant. Costs of the entire process are in the same range as conventional sewage sludge disposal, with the benefit being phosphorus recovery and reduced emission of greenhouse gases due to avoidance of sludge incineration.     

The potential of Lolium perenne for revegetation of contaminated soil from a metallurgical site

A greenhouse study was carried out to determine the possibility of using Lolium perenne for revegetation of soil from a former ferrous metallurgical plant (Naples, South Italy) contaminated by Cu, Pb and Zn at levels above current Italian regulatory limits. Surface soil samples (0-40 cm) from the facility area where raw minerals were disposed (RM1 and RM2), from a nearby unpolluted cultivated soil (C) as control and a 1:3 mixture of the control with the polluted ones (RM1+C and RM2+C) were utilized for the experiment. Revegetation trials were conducted in the greenhouse. At 90 days from seeding, shoot length, chlorophyll content, biomass yield, plant metal uptake and changes of organic carbon content and metal distribution among soil extractable phases defined by sequential extraction were determined. In the mixed substrates (RM1+C and RM2+C) concentrations of Cu, Pb and Zn were still two to three times higher than the Italian regulatory limits. Plants were healthy with 100% survival in all substrates, with no macroscopic symptoms of metal toxicity. The high pH of the soil could be one of the most important parameters responsible for the limited plant availability of the metals. On RM1, RM2 and mixed media, plants experienced retarded growth, reduced shoot length and biomass yield and higher total chlorophyll content compared to those cropped on the control soil, without any evident phytotoxic symptoms. In RM1 and RM2, the plant contents of Cu (19.3 and 12.6 mg kg(-1)), Pb (0.98 and 0.67 mg kg(-1)) and Zn (99 and 88 mg kg(-1)) were higher than that of plants grown on non-contaminated soil (Cu 10.1, Pb < 0.2, Zn 79 mg kg(-1)), but still in the range of physiologically acceptable levels. The distribution of metals in soil was slightly affected by Lolium growth with changes only regarding the organic-bound Cu and Zn pool, with reduction up to 24%. Results indicated that an acceptable healthy vegetative cover can be achieved on the contaminated soil by the proposed revegetation approach and that metals will remain stable over the study period with slight variation of the more available metal forms.     

Cadmium solubility in paddy soils: effects of soil oxidation, metal sulfides and competitive ions

Cadmium (Cd) is a non-essential element for human nutrition and is an agricultural soil contaminant. Cadmium solubility in paddy soils affects Cd accumulation in the grain of rice. This is a human health risk, exacerbated by the fact that rice grains are deficient in iron (Fe) and zinc (Zn) for human nutrition. To find ways of limiting this potential risk, we investigated factors influencing Cd solubility relative to Fe and Zn during pre-harvest drainage of paddy soils, in which soil oxidation is accompanied by the grain-filling stage of rice growth. This was simulated in temperature-controlled “reaction cell” experiments by first excluding oxygen to incubate soil suspensions anaerobically, then inducing aerobic conditions. In treatments without sulfur addition, the ratios of Cd:Fe and Cd:Zn in solution increased during the aerobic phase while Cd concentrations were unaffected and the Fe and Zn concentrations decreased. However, in treatments with added sulfur (as sulfate), up to 34 % of sulfur (S) was precipitated as sulfide minerals during the anaerobic phase and the Cd:Fe and Cd:Zn ratios in solution during the aerobic phase were lower than for treatments without S addition. When S was added, Cd solubility decreased whereas Fe and Zn were unaffected. When soil was spiked with Zn the Cd:Zn ratio was lower in solution during the aerobic phase, due to higher Zn concentrations. Decreased Cd:Fe and Cd:Zn ratios during the grain filling stage could potentially limit Cd enrichment in paddy rice grain due to competitive ion effects for root uptake.     

Hybrid flotation--membrane filtration process for the removal of heavy metal ions from wastewater

A promising process for the removal of heavy metal ions from aqueous solutions involves bonding the metals firstly to a special bonding agent and then separating the loaded bonding agents from the wastewater stream by separation processes. For the separation stage, a new hybrid process of flotation and membrane separation has been developed in this work by integrating specially designed submerged microfiltration modules directly into a flotation reactor. This made it possible to combine the advantages of both flotation and membrane separation while overcoming the limitations. The feasibility of this hybrid process was proven using powdered synthetic zeolites as bonding agents. Stable fluxes of up to 80l m(-2)h(-1) were achieved with the ceramic flat-sheet multi-channel membranes applied at low transmembrane pressure (<100 mbar). The process was applied in lab-scale to treat wastewater from the electronics industry. All toxic metals in question, namely copper, nickel and zinc, were reduced from initial concentrations of 474, 3.3 and 167mg x l(-1), respectively, to below 0.05 mg x l(-1), consistently meeting the discharge limits.     

Film-pore diffusion modeling for the sorption of metal ions from aqueous effluents onto peat

The sorption of three metal ions, namely, copper, nickel and lead onto sphagnum peat moss has been studied using an agitated batch sorber system. The equilibrium isotherms were determined and kinetic runs were performed over a range of concentrations for each metal ion. A film-pore diffusion mass transfer model has been developed based on a single effective diffusion coefficient for each system. Error analysis of the experimental and theoretical data indicated relatively large errors at low initial metal ion concentrations. Therefore the model was modified to introduce a surface coverage concentration dependent effective diffusivity to account for a contribution from surface diffusion.     

Membrane treatment by nanofiltration of exhausted vegetable tannin liquors from the leather industry

A rational use of water in the leather industry is described by applying the criteria of "clean technologies" by means of membrane processes. A nanofiltration (NF) process was used for recovering tannins and water from exhausted baths and reusing them as tanning agents and washings. Results of experiments performed on laboratory and semi-industrial pilot scale plants, operating and fluid-dynamic conditions and mass balance of the NF process are reported and discussed. Chemical and physical analytical values measured on skins treated with the recovered solutions were very similar to those measured on control skins tanned with standard solutions. According to the obtained results, a process scheme is suggested. It permits both to recover water and to increase the tannin/non tannin (T/NT) ratio in the retentate solution, starting from exhausted tanning baths and by using a NF membrane purification/concentration. The final volume reduction factor of tested exhausted baths was 5.25, the increase of T/NT ratio was from 1.1 to 2.3 and the average permeate flux was 12.5l/m(2)h. Advantages are in terms of: reduction of environmental impact (up to 75% of COD reduction of the global effluent), simplification of cleaning-up processes of wastewaters, decrease of disposal costs, saving of chemicals and water.     

Heavy metal contamination in sediments from vehicle washing: a case study of Olarong Chhu Stream and Paa Chhu River,Bhutan

Heavy metal contamination owing to anthropogenic activities affects human health and is of worldwide concern. The aim of the study was to investigate the possible linkage between vehicle washing and heavy metal contamination. Heavy metal concentration in sediment samples from vehicle wash wastewater settlement tanks (WSTs) and water bodies (Olarong Chhu and Paa Chhu) used for discharging untreated wastewater was determined with an atomic absorption spectrophotometer. High concentrations of Cd, Cr, Cu, Fe, Pb, Ni and Zn were found in WSTs. Assessment of sediment pollution in water bodies was determined using contamination factor (CF), pollution load index (PLI), geo-accumulation index (Igeo) and enrichment factor (EF); these indices denoted anthropogenic inputs of heavy metals. Significant Pearson correlations between heavy metals in sediments from Olarong Chhu, Paa Chhu and WSTs indicated their common origin. Thus, this study confirms the linkage between vehicle washing and heavy metal contamination. Bhutan’s policy on installation of wastewater treatment plants should be implemented effectively. Bhutan should consider feasible methods for the safe disposal of sludge from WSTs.

Abbreviations: Atomic Absorption Spectrophotometry - (AAS)     

Characterisation and application of a novel positively charged nanofiltration membrane for the treatment of textile industry wastewaters

The present study demonstrates the high potential for the application of a novel self assembled positively charged nanofiltration membrane, PA6DT-C, in processes such as the recovery of valuable cationic macromolecules in the bioprocess and pharmaceutical industries or removal of multi-valent cations such as dyes and heavy metals in the paper and pulp, textiles, nuclear, and automotive industries. The nanofiltration membrane, prepared in this laboratory, is further characterised and then tested for the removal and recovery of Methylene Blue from a synthetic dye house wastewater. The characterisation process involved the construction of a rejection profile for NaCl over a wide range of pH and concentration, which illustrates that the optimal process conditions for the removal of small cations using this membrane is in the region pH <8.0 and concentration less than 15 mol m⁻³. The salt rejection data was used to calculate the magnitude of the effective membrane charge density and this was found to be significantly higher for the PA6DT-C membrane than two commercially available membranes (Desal-DK and Nanomax-50). The membrane flux for this new membrane is also superior to the commercial membranes with an approximate increase of 3-4 fold. The PA6DT-C membrane was successful in removal of Methylene Blue dye from synthetic dye house wastewaters achieving 98% rejection and a membrane flux of ∼17 LMH bar⁻¹. Thus, this new membrane both adds to and complements the existing short supply of positively charged NF membranes.     

The mechanism of the surfactant-aided soil washing system for hydrophobic and partial hydrophobic organics

A surfactant-aided soil washing mechanism is proposed in this study by examining nine common organic contaminants, which were divided into two groups, hydrophobic compounds and partial hydrophobic compounds, depending on the respective soil partitioning of contaminants, K(oc). The presence of a free non-aqueous phase liquid in the soil washing system is critical to determine the soil washing performance curves. A mathematical model is proposed to describe soil-washing performance at various surfactant concentrations. The resulting slopes and intercepts from the model for the performance prediction are linearly related to K(oc). In addition, a transition zone between the hydrophobic and partial hydrophobic compounds was observed, and has been used in verifying the proposed mechanism successfully by overdosing and underdosing the contaminants in the system.     

Chemical stabilization of scrap metal yard contaminated soil using ordinary portland cement: Strength and leachability aspects

In this study, the strength development and lechability aspects of metal-contaminated soil treated with ordinary portland cement (OPC) were investigated. The soil was collected from a scrap metal yard within the outskirts of Kuala Lumpur, Malaysia. Metal composition analysis indicated that the predominant metals present in the soil were iron (42,194 mg/kg), aluminium (8874 mg/kg), zinc (690 mg/kg), lead (428 mg/kg), copper (107 mg/kg) and chromium (52 mg/kg). The contaminated soil was treated with OPC using cement-to-dry soil (C/S_d) ratios of 0.5, 1 and 2. The effectiveness of the treatment was evaluated by performing unconfined compressive strength (UCS) as well as crushed and whole block leaching (WBL) tests on the treated soil. The treatment results were compared to the solidified waste acceptance criteria which were compiled based on the regulatory waste disposal limit at a disposal site in the United Kingdom and the maximum concentration of contaminants for toxicity characteristic of solid wastes from United States Environmental Protection Agency. Results indicated that chemical stabilization of metal-contaminated soils using OPC was effective for prevention of metal leaching from both disintegrated samples subsequent to years of weathering (crushed block) and intact samples (whole block) into the environment.     

酸溶液淋溶作用下重金属污染土固化体浸出特性及机理

采用KH_2PO_4—水泥复合材料对铅污染土进行固化/稳定化处理,为了研究酸雨淋溶对铅污染土固化体浸出特性的影响规律及其机理,开展了不同KH_2PO_4添加量、浸出时间和淋溶液pH对Pb浸出行为的影响规律试验研究。探讨了铅污染土固化体浸出机理。结果表明,KH_2PO_4对铅污染土有良好的稳定作用。酸溶液淋溶作用下固化体中Pb的释放行为与pH直接相关,强酸作用下Pb的溶出量大。固化体中Pb的浸出也与浸出液pH相关,强碱性有利于Pb的迁移。浸出液pH与固化体中的碱性水化产物释放量有关。对于pH=2和5溶液,Pb的累积浸出率随时间呈线性变化,而对于pH=3溶液,Pb的累积浸出率随时间呈两阶段线性变化。固化体在pH=2溶液浸泡下,Pb的释放机理为溶解控制;对于pH=3溶液浸泡,机理则为先溶解控制再表面冲刷;而对于pH=5溶液浸泡,Pb的释放机理为扩散控制。     

Aspects of the aquatic chemistry of cadmium and zinc in a heavy metal contaminated lake

Concentrations of the heavy metals cadmium (Cd) and zinc (Zn) were determined at several sites in Palestine Lake, Indiana, and in the stream (Williamson Ditch) which transports metal-bearing wastes to the lake. Average dissolved Cd and Zn concentrations in the lake were as high as 17.3 μg 1^-1 and 293 μg 1^-1, respectively, while corresponding suspended levels were 30.3 μg Cd 1^-1 and 270 μg Zn 1^-1. Average levels of both Cd and Zn in the dissolved fraction exceeded those in the suspended fraction, except at one site in the lake where suspended Cd was higher. During anaerobic conditions occurring in lake's hypolimnion, a marked decrease in the dissolved fraction and concomitant increase in the suspended fraction of both Cd and Zn were noted. A cadmium-specific ion electrode was used to determine the chemical forms of dissolved Cd present in the lake. Free Cd²⁺ was the dominant form; however, Cd-organic complexes sometimes comprised a significant portion of the total dissolved Cd.     

石油污染土中微生物的分离鉴定及降解特性

为了为汽油污染土的微生物修复提供优良菌种,以LB培养基为基质,从石油污染土中对汽油降解菌进行了分离鉴定,以降油培养基为基质对分离得到的菌株进行汽油降解率的测定,以培养温度、培养基pH值及培养时间为参数对5种具有优良汽油降解性能的菌株进行单因素试验,基于单因素试验结果进行三因素三水平的正交试验后,以汽油降解率为响应值对试验结果进行响应面分析,筛选出具有优良降解性能的菌株,并确定了菌株降解汽油的最佳条件。结果表明:从石油污染土中分离出了9种具有汽油降解性能的菌株,其中,铜绿假单胞菌、假单胞菌属、苍白杆菌属、博得特氏菌属以及戈登氏菌属具有优良降解性能,这5种菌降解汽油的最优条件为:铜绿假单胞菌、假单胞菌属、苍白杆菌属、博得特氏菌以及戈登氏菌的最佳培养温度均为32℃,培养基pH值均为7.0,培养时间均为20h,降油培养基中的汽油降解率分别为70.12%、76.42%、75.66%、77.50%和73.22%。     

Effectiveness of an anaerobic granular activated carbon fluidized-bed bioreactor to treat soil wash fluids: a proposed strategy for remediating PCP/PAH contaminated soils

An integrated system has been developed to remediate soils contaminated with pentachlorophenol (PCP) and polycyclic aromatic hydrocarbons (PAHs). This system involves the coupling of two treatment technologies, soil-solvent washing and anaerobic biotreatment of the extract. Specifically, this study evaluated the effectiveness of a granular activated carbon (GAC) fluidized-bed reactor to treat a synthetic-waste stream of PCP and four PAHs (naphthalene, acenaphthene, pyrene, and benzo(b)fluoranthene) under anaerobic conditions. This waste stream was intended to simulate the wash fluids from a soil washing process treating soils from a wood-preserving site. The reactor achieved a removal efficiency of greater than 99.8% for PCP with conversion to its dechlorination intermediates averaging 46.5%. Effluent, carbon extraction, and isotherm data also indicate that naphthalene and acenaphthene were removed from the liquid phase with efficiencies of 86 and 93%, respectively. Effluent levels of pyrene and benzo(b)fluoranthene were extremely low due to the high-adsorptive capacity of GAC for these compounds. Experimental evidence does not suggest that the latter two compounds were biochemically transformed within the reactor.