The influence of soluble organic matter from municipal solid waste compost on trace metal leaching in calcareous soils

The use of municipal solid waste (MSW) compost as fertilizer may cause increased leaching due to its high content of trace metals and thus pose a threat to groundwater quality. The effect of MSW compost application on trace metal leaching in calcareous soils has been studied in soil column experiments under laboratory conditions using three soils from the study area in the Gaza Strip and Israel. Higher levels of organic matter in solution (TOMS), nitrate, and the trace metals Cu, Ni and Zn were found in the leachates of a sandy soil and, to a lesser extent, a loamy soil, to which MSW compost had been applied at a rate of 65 Mg ha(-1) (dry weight basis). Nevertheless, the majority of water-soluble trace metal species from compost accumulated in the topsoil rather than washing out, with the exception of aqueous Ni species. Ni concentrations exceeded the maximum allowable limits for drinking water (in Germany: 50 microg l(-1)) at peak times in the leachates from sandy soil, while all other trace metals remained far below the corresponding limits. The highest absolute concentrations of trace metals were found for the leaching of Cu from compost-amended sandy soil (100 microg l(-1)). For Cd, Pb and Hg no evidence of downward movement was found in any assay. Gel filtration studies of the collected soil leachates showed that all trace metals encountered in the leachates existed mostly as organic complexes. In sandy soil most of the water-soluble organic matter added with the compost had leached from the rootzone after a year's equivalent of rainfall, while TOMS mobility was greatly reduced in the loamy soil. The makeup of the TOMS in the sandy soil and its metal-binding capacity was strongly influenced by compost-derived dissolved organic matter (DOM) as observed by FTIR spectrometry. Hence the vertical displacement of trace metals (Cu, Ni, Zn) in these calcareous soils seemed to result primarily from the presence of mobile metal-organic complexes in the soil solution after compost addition. Further studies are required to validate these findings in the field, especially to assess the risk of Cu and Ni leaching in sandy soil.     

Removal and accumulation of Cu, Ni and Zn in horizontal subsurface flow constructed wetlands: Contribution of vegetation and filling medium

This study investigated the accumulation and removal of Cu, Ni and Zn in two horizontal subsurface flow constructed wetlands for domestic wastewater treatment, which differ by shape, presence of macrophytes and water depth. Between March and December 2007, the three metals were measured in the influent and effluents of the two systems. Average percentage removal rates were extremely low for Cu (3% and 9% in the two beds) and higher for Zn and Ni (between 25 and 35%). Under higher Zn influent concentrations, it was found to be between 78-87%, which is in agreement with other literature data.During the peak standing crop season (August), biomasses of the different parts of Phragmites australis (stems, leaves and flowers, roots and rhizomes) were analysed in terms of weight and heavy metal concentration in order to assess heavy metal distribution among the tissues. It was found that the plants contribute to total heavy metal removal to a lesser extent than the filling medium. Aboveground tissues remove 34% of Cu, 1.8% of Ni and 6.2% of Zn % and, once harvested, their disposal does not appear to pose a problem for the environment. If heavy metals are present at high concentrations in the horizontal subsurface flow bed influent, over time, their accumulation in the filling medium could necessitate special care in the bed's management to avoid release into the surrounding environment.     

腐殖土活性污泥中重金属的浸出行为研究

在不同pH值和腐殖土投加量条件下,对活性污泥中Zn、Ni、Cu和Pb四种重金属的浸出行为进行了研究。结果表明,污泥中Zn和Ni的浸出率随pH值的降低而呈明显升高的趋势,Cu和Pb的浸出率也随pH值的降低而升高,但变化幅度相对较小。在酸性条件下,随着腐殖土投量的增加,活性污泥中Zn、Ni、Cu和Pb的浸出率明显降低;而在中性偏碱性条件下,这种变化趋势不明显。投加腐殖土能明显改变活性污泥中重金属的形态分布,促进重金属的稳定化,进而显著改善重金属的浸出行为。     

Effect of dissolved organic carbon on the mobility of cadmium, nickel and zinc in leachate polluted groundwater

The ability of dissolved organic carbon (DOC) from landfill leachate polluted groundwater to form complexes with the heavy metals cadmium (Cd), nickel (Ni) and zinc (Zn) was investigated. The DOC samples originated from the leachate pollution plume at Vejen Landfill, Denmark and were studied in the original matrix with a minimum of manipulation. The experiments were performed as batch sorption experiments and the metal distribution between the aquifer material and the solution (K_d) was determined in the leachate polluted groundwater samples and in reference solutions of synthetic inorganic leachate. The difference in distribution coefficients was a direct indication of complex formation between DOC and heavy metals. The results showed, that DOC from landfill leachate polluted groundwater has the ability to form complexes with Cd, Ni and Zn, and the distribution coefficients were a factor of 2–6 lower in the presence of DOC. Based on the distribution coefficients, the relative migration velocities of the heavy metals were estimated. The migration velocity of the metals was increased by the presence of DOC but did not exceed 1.2% of the water migration velocity, indicating that the effect of DOC on the mobility of Cd, Ni and Zn may have only minor environmental importance. Conditional complex formation constants (log K_c) were estimated from the K_d-values. The constants for 1:1 complexes increased slightly in the following order Zn < Cd < Ni. However, increasing the metal concentration into the mg l⁻¹ level decreased the constants by about one order of magnitude, showing the importance of determining the constants at environmentally relevant metal concentrations.     

Arsenic pollution at the industrial site of Reppel-Bocholt (north Belgium)

An industrial site, polluted with As and heavy metals, was investigated by combining chemical (sequential extractions and pHstat leaching tests), physical and mineralogical characterization of soil samples and slag fragments, and by the analysis of soil porewater aimed at assessing the distribution, speciation and mobility of heavy metals and As. On the site itself, arsenic concentrations up to 3.6% in surficial soil samples and up to 22% in slag fragments were found, together with elevated concentrations (percentage level) of Cu, Co, Ni, Zn and Pb. High concentrations of arsenic (up to 38,000 microg/l) and heavy metals (up to 1700 microg/l Cu and 4700 microg/l Zn) were also found in the in situ sampled soil porewater, highlighting the considerable availability of As, Zn and Cu for uptake by plants and leaching to the ground water. Sequential extractions also indicated a high availability of arsenic and copper in most samples and slag fragments of the industrial site, although poorly reactive phases were encountered as well. pHstat leaching tests confirmed that the present leaching of contaminants is alarming. Moreover, soil acidification will enhance the leaching of contaminants, emphasizing that remediation of the industrial site is urgent. Small scale variability of total metal concentrations and metal speciation, both in the horizontal and vertical direction, and the occurrence of a camouflage layer underline the importance of elaborate sampling for pollution assessment on an industrial site.     

Heavy metals in the dump of an abandoned mine in Galicia (NW Spain) and in the spontaneously occurring vegetation

The concentrations of different forms of heavy metals (Fe, Mn, Zn, Cu, Cr, Ni, Cd and Pb) were determined in a mine dump material rich in chalcopyrite. The concentrations were compared with those of the natural vegetation colonising the dump. Samples taken from the dump are acid (pH(H(2)O) between 3.0 and 5.0), have carbon contents lower than 0.5%, N lower than 0.2%, effective cation exchange capacity between 0.74 and 4.96 cmol(+)kg(-1) and percent Al saturation in the exchange complex higher than 20% in 85% of the samples. Iron was the most abundant heavy metal, in both total and bioavailable forms, and the relative abundance of metals was: Fe>Cu>Mn>Zn>Cr. The total Fe concentrations ranged between 4315 and 31578 mg x kg(-1), the total Cu between 273 and 5241 mg x kg(-1), the total Mn between 294 and 2105 mg x kg(-1), the total Zn between 73 and 894 mg x kg(-1) and total Cr between 0.01 and 30 mg x kg(-1). Ni, Cd and Pb were below the analytical detection limits. The concentration of bioavailable Fe ranged between 40 and 1550 mg x kg(-1); Zn was the least abundant metal in this fraction (between 2 and 100 mg x kg(-1)). Copper was the most abundant heavy metal in the exchange complex and in the aqueous extracts, followed by Zn, Mn and Fe. Exchangeable Cu ranged between 17.7 and 1866 mg x kg(-1), whereas the maximum concentrations of exchangeable Zn, Mn and Fe did not exceed 140 mg x kg(-1). The Cu concentration in the aqueous extracts varied between 0.1 and 8.3 mg x l(-1) and the concentration of Fe was always less than 0.52 mg x l(-1). The heavy metal contents in the spontaneously occurring vegetation in the dump ranged between: 150 and 900 mg Fe x kg(-1), 84 and 2069 mg Mn x kg(-1), 20.5 and 106 mg Cu x kg(-1) and between 35 and 717 mg Zn x kg(-1), when considering all the plant samples analysed. Festuca sp. accumulated Fe, Salix atrocinerea accumulated Zn and Mn, and Frangula alnus and Quercus robur accumulated Mn. These native plant species may contribute to decrease the heavy metal contents in the dump material.     

Correlations, partitioning and bioaccumulation of heavy metals between different compartments of Lake Balaton

Correlations between trace metals in dissolved and particulate phases, zooplankton, mussels and sediments in Lake Balaton were investigated. The degree of correlation between the various metals was different in each of the investigated compartments. Particulate metal concentrations (microg g(-1)) were anti-correlated with suspended particulate matter (SPM) (mg l(-1)), indicating a dilution effect, while total metal concentrations in the water column (microg l(-1)) were highly correlated with SPM, implying a major influence of the turbidity on the total metal concentrations. Between compartments, not many significant correlations were recognized. Only Ba, Ca, Sr and Mg are correlated in the sediments and in the particulate phase, suggesting common sources for both compartments. Partitioning coefficients (Kd) of trace metals between dissolved and particulate phases are generally low, typical for natural water and fairly stable over the lake. Most of the trace metals (Zn, Co, Cd and Pb) exist in the particulate phase (for about 70% of the total metal load). Cu and Ni are exceptions, showing a more equal distribution. Bioconcentration factors (BCF) of zooplankton and mussels were comparable to those of other natural waters. A negative biomagnification from suspended particulate matter to zooplankton and from sediment to mussel was recognized for all trace metals, except a small enrichment of Zn in zooplankton and Cd in mussel. Four factors were recognized in SPM and in sediments but they did not contain the same group of metals. Cluster analysis showed that metal accumulations in the sediments were different between northern and southern shores and in SPM between western and eastern areas.     

电渗析法去除未脱水污泥中重金属的试验研究

为了降低城镇生活污泥中重金属含量,采用三槽型电解槽研究了反应时间和NaClO预处理对未脱水污泥中重金属Zn、Cu、Cr和Ni去除率的影响。试验结果表明,延长反应时间可以提高未脱水污泥中重金属去除率。电渗析反应时间为14 h时,污泥中Zn、Cu、Cr和Ni的去除效果较好,去除率分别为52. 08%、27. 24%、31. 66%和46. 42%。污泥中重金属的初始非稳定态比例越大,电渗析反应后的去除率越高。NaClO/HNO_3组合预处理的污泥中重金属去除率最高,对Zn、Cu、Cr和Ni的去除率分别达到70. 32%、35. 39%、36. 80%和56. 78%。     

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.     

Arsenic Removal from Contaminated Groundwater by Zero Valent Iron: a Mechanistic and Long-Term Performance Study

The present study investigated the application of zero valent iron to remediate the arsenic in naturally contaminated groundwater. A performance evaluation was conducted in the laboratory on groundwater contaminated with artificial arsenic using sodium arsenate (Na₂HAsO₄.7H₂O) to simulate the arsenic concentration in the groundwater. Batch and column experiments were performed to evaluate the arsenic removal capacity by zero valent iron and the removal mechanism. The flow rate (up-flow mode) was maintained for 180 days in each column. The results from both the batch and the column experiments showed that more than 99% of the arsenic was removed successfully. In the column experiments, the arsenic was efficiently removed and the arsenic concentration in the treated water decreased to below the limit of 10 μg /L (WHO's standard) even when the columns were packed with only 25% ZVI by volume. We used SEM and XRD to characterize the surface morphology and the corrosion layer which formed on pristine ZVI and arsenic-treated ZVI to elucidate the arsenic removal mechanism. XRD and SEM results revealed that ZVI gradually converted to a magnetite/maghemite corrosion product mixed with lepidocrocite. Adsorption followed by co-precipitation was an important pathway to removing the arsenic by ZVI. Our results suggest that ZVI, combined with sand, is a suitable candidate for the ex-situ treatment of groundwater in the neutral pH range and in the presence of dissolved oxygen.     

Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification

The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates.     

Bioleaching of heavy metals from sludge after biological treatment of municipal effluent

The article has compared the efficiency of removing heavy metals from the sludge after biological treatment of municipal wastewaters in the course of biological leaching involving heterotrophic and chemotrophic microorganisms and chemical leaching. The article also showed advantages of the bioleaching of metals under conditions of acidogenic heterotrophic metabolism. The efficiency of the leaching of heavy metals from the sludge varies 80% (Zn) to 15% (Cr) and corresponds to the following series: Zn > Mn > Cu > Ni > Cd > Pb > Cr.     

A comparison of the properties of polyurethane immobilised Sphagnum moss, seaweed, sunflower waste and maize for the biosorption of Cu, Pb, Zn and Ni in continuous flow packed columns

The biosorption of Cu, Pb, Zn and Ni from a mixed solution of the metals was investigated in continuous flow packed columns containing polyurethane immobilised biomass. The characteristics and biosorption properties of Sphagnum moss, the brown seaweed Ascophyllum nodosum, waste biomass from the preparation of sunflower oil, and whole plant maize were compared. All the biomass types showed a preference for the sequestration of Pb followed by Cu, with Ni and Zn having roughly equal affinity. With continuous metal loading to the column there was an initial binding of all metals and then a displacement of the lower affinity metals by those with a high affinity. This led to a chromatographic effect in the column with breakthrough concentrations for low-affinity metals higher than the concentration in the feed. A similar phenomenon was found on desorption using acidic solutions where low-affinity metals were desorbed preferentially. The results also indicated that despite competitive displacement of one metal species by another the biomass appeared to succeed in retaining some low-affinity metal species indicating that there may be selective sites present with different affinity characteristics. When using a multi-metal solution with Cu, Pb, Zn and Ni at equal 10 mgl(-1) concentrations as column influent, the total quantities of metal sequestered were: seaweed, 117.3 mg g(-1); sunflower waste, 33.2 mg g(-1); Sphagnum moss, 32.5 mg g(-1); and maize, 2.3 mg g(-1). The use of an acid base potentiometric titration showed a relationship between the number of acid functional groups and biosorption capacity, although this was not proportional for the biomass types studied. It can, however, be used in conjunction with a simple classification of metals into high and low-affinity bands to make a preliminary assessment of a biosorption system.     

Heavy metals in drilling‐waste leachates from East Java,Indonesia

This study examined the leaching toxicity characteristics of heavy metals in drilling‐waste mud by the toxicity characteristic leaching procedure (TCLP). Ten heavy metal elements As, Ba, Cd, Cr, Cu, Pb, Se, Ag, Zn and Hg were investigated. Test drilling‐waste mud samples were collected from eight active exploration wells. The TCLP results showed that the concentrations of the metals were below the Indonesian Regulatory Standards Nos. 18 and 85 (1999) regarding hazardous waste management. Barium was detected in all the leachates, and ranged from 0.40 to 6.59 mg/l. Mercury was below detectable levels at only two stations. Values of the other metals varied significantly from one station to another.     

Removal of heavy metals from aqueous solution by nonliving Ulva seaweed as biosorbent

The growth of dense green seaweed mats of Ulva spp. is an increasing problem in estuaries and coasts worldwide. The enormous amount of Ulva biomass thus becomes a troublesome waste disposal problem. On the other hand, it has been revealed that nonliving seaweed biomass, particularly brown seaweeds, has a high capacity for assimilating heavy metals. In this study, the possibility of using Ulva seaweed biomass as a biosorbent for the removal of heavy metals was examined. After processing, the biomass material was very easy to separate from the aqueous solution using a mesh. The sorption capacity of Cd on Ulva biomass increased upon pretreatment with alkali solution. The outstanding function of the biosorbent was demonstrated at around pH 8. On the basis of the Langmuir isotherms of Cd, Zn and Cu using the alkali-pretreated biomass, the parameters q(m) and b were determined to be within the narrow range of 60-90 mg/g and 0.03-0.04 L/mg, respectively, for each metal. Given the q(m) and b values, Ulva seaweed is a good biosorbent material for removing heavy metals. In an experiment using artificial wastewater containing Cd, Zn, Cu, Cr and Ni, it was possible to remove each metal simultaneously using Ulva biomass. Adsorption by Ulva biomass is effective for the removal of heavy metals from wastewater.     

Removal of dissolved metals by zero-valent iron (ZVI): kinetics, equilibria, processes and implications for stormwater runoff treatment

Infiltration of stormwater runoff contaminated with metals is often questionable in several cases due to its long-term potential to cause deterioration of groundwater quality. To ensure the quality of filtrate, a pre-treatment of contaminated runoff is required. This study investigates the processes of copper and zinc ion removal from stormwater runoff using zero-valent iron (ZVI, Fe0). Kinetic and equilibrium tests were performed with laboratory-prepared and in situ stormwater runoff samples collected from roof, street and highway catchments. Based on the results, a substantial portion of Cu2+ is reduced and transformed to insoluble forms of Cu0 and Cu2O. Unlike copper, the adsorption and co-precipitation associated with freshly precipitated iron oxides play important roles for the removal of Zn2+. Investigations under various water quality conditions demonstrated a relatively minor impact on Cu2+ uptake rates. However, the different conditions apparently altered the removal stoichiometry and phases of the copper deposits. The removal rates of Zn2+ increase with higher dissolved oxygen (DO), ionic strength (IS), temperature (T) and pH. Dissolved organic carbon (DOC) in runoff samples forms complexes with metals and Fe2+, thereby kinetically decreasing the metal uptake rates. Furthermore, depending on its composition, a larger molecular weight organic fraction was found to preferentially compete for the adsorption sites. The study demonstrates that ZVI is a promising medium for achieving comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). Long-term performance of ZVI, however, may be limited and governed by the formation of non-conductive layers of iron and cuprous oxides.     

Hexavalent chromium removal from near natural water by copper-iron bimetallic particles

The reduction of hexavalent chromium (Cr(VI)) by zero-valent iron (ZVI) is self-inhibiting in near natural groundwater because insulating Fe(III)-Cr(III) (oxy)hydroxide film forms on the ZVI surface during the reaction. This study tries to overcome this deficiency by coating the surface of ZVI with copper to form copper-iron bimetallic particles. The Cr(VI) removal rate by ZVI rose significantly after the copper coating was applied. The copper loading needed for enhancing Cr(VI) removal was much higher than that needed for enhancing removal of chlorinated organic compounds or other oxidative contaminants, because of the higher oxidation potential of Cr(VI). The results of X-ray photoelectron spectroscopy (XPS) indicate that coating copper onto the surface of ZVI can not only increase the deepness of the oxidation film but also increase the oxidation state of iron in the film. This phenomenon means higher Cr(VI) removal capacity per unit weight of ZVI.     

Adsorption of heavy metals on Na-montmorillonite. Effect of pH and organic substances

Clays (especially montmorillonite and bentonite) are widely used as barriers in landfills to prevent contamination of subsoil and groundwater by leachates containing heavy metals. For this reason it is important to study the adsorption of metals by these clays. The sorption of seven metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) on Na-montmorillonite was studied as a function of pH and in the presence of ligands, forming complexes of different stabilities with the metals of interest. The continuous column method was used as it better simulates natural conditions. The total capacity of Na-montmorillonite towards these metals was determined. The pH variations influence to a higher extent the concentrations of Cu, Pb and Cd in the effluent. Moreover the results suggest that complex formation hinders the sorption of the metals on the clay, with an increasing influence in the order: Mn < or = Pb < or = Cd < or = Zn < Ni < Cu < Cr. The evaluation of the total capacity of Na-montmorillonite shows that this clay is a good sorbent towards all examined metals.     

Comparisons of low-cost adsorbents for treating wastewaters laden with heavy metals

In this article, the removal performance and cost-effectiveness of various low-cost adsorbents derived from agricultural waste, industrial by-product or natural material are evaluated and compared to those of activated carbon for the removal of heavy metals (Cd(II), Cr(III), Cr(VI), Cu(II), Ni(II) and Zn(II)) from metals-contaminated wastewater. To highlight their technical applicability, selected information on pH, dose required, initial metal concentration, adsorption capacity and the price of the adsorbents is presented. It is evident from the survey of 102 published studies (1984-2005) that low cost adsorbents derived from agricultural waste have demonstrated outstanding capabilities for the removal of heavy metal (Cr(VI): 170 mg/g of hazelnut shell activated carbon, Ni(II): 158 mg/g of orange peel, Cu(II): 154.9 mg/g of soybean hull treated with NaOH and citric acid, Cd(II): 52.08 mg/g of jackfruit), compared to activated carbon (Cd(II): 146 mg/g, Cr(VI): 145 mg/g, Cr(III): 30 mg/g, Zn(II): 20 mg/g). Therefore, low-cost adsorbents can be viable alternatives to activated carbon for the treatment of metals-contaminated wastewater. It is important to note that the adsorption capacities presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of surface modification and the initial concentration of the adsorbate. In general, technical applicability and cost-effectiveness are the key factors that play major roles in the selection of the most suitable adsorbent to treat inorganic effluent.     

Semi-empirical approach to modeling of soil flushing: model development, application to soil polluted by zinc and copper

This paper describes a semi-empirical approach to modeling the soil flushing technology. A new mathematical model aimed at predicting the course of the continuous soil flushing process by use of the input data obtained from simple batch laboratory experiments is described in the theoretical part. An objective of the study is to apply this new model to soil polluted by zinc and copper (11949 mg kg(-1) and 1895 mg kg(-1), respectively) by flushing the soil with an ammonia nitrogen solution. A set of batch experiments provided both equilibrium and kinetic data characterizing the leaching ability of both metals. By use of the model, the optimal ammonia concentration in the flushing solution was estimated (0.6 mol L(-1)). For this concentration, validity of the model results was verified by a column experiment. The removal efficiency obtained was 44% (zinc) and 54% (copper). The model correctly predicted the period of time needed for the removal of weakly bound metal fractions as well as the estimate of the overall removal efficiency of metals from the soil during the flushing process. It has also proven that it is possible to use the column experiment for model calibration through the modification of the input data. Agreement of the model and experimental results can be further improved this way.