Fractionation of heavy metals in sludge from anaerobic wastewater stabilization ponds in southern Spain

The analysis of heavy metals is a very important task to assess the potential environmental and health risk associated with the sludge coming from wastewater treatment plants (WWTPs). However, it is necessary to apply sequential extraction techniques to obtain suitable information about their bioavailability or toxicity. In this paper, a sequential extraction scheme according to the Standard, Measurements and Testing Programme of the European Commission was applied to sludge samples collected from ten anaerobic wastewater stabilization ponds (WSPs) located in southern Spain. Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Ti and Zn were determined in the sludge extracts by inductively coupled plasma atomic emission spectrometry. In relation to current international legislation for the use of sludge for agricultural purposes, none of the metal concentrations exceeded maximum permitted levels. Overall, heavy metals were mainly associated with the two less-available fractions (34% oxidizable metal and 55% residual metal). Only Mn and Zn showed the highest share of the available (exchangeable and reducible) fractions (25-48%).     

Heavy metal mobility and potential availability in animal manure: using a sequential extraction procedure

In this study, dairy cow manure, goat manure, and chicken manure were collected from three farms and analyzed to find out the concentration of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The concentration and potential of mobility and availability of heavy metals were studied in the animal manure samples. BCR Sequential extraction procedure was used to determine the binding forms of the metals. In this study, pseudo total concentrations of Mn and Zn were found out to be predominant in all the types of animal manure samples. According to the results, it was traced that Cr, Cu, and Ni were observed to be at the second highest level while Cd, Co, and Pb were seen at the lowest level in all the manure samples. When extractable amounts of heavy metals are taken into consideration, it is seen that the amount of the mobile fractions of heavy metals except for Cr and Ni are higher in comparison with that of immobile fraction in all the animal manure samples. It was also viewed that Mn, Cd, and Zn are more available in dairy cow manure and chicken manure whereas Cd, Co, and Mn are more available in goat manure.     

Characteristic of heavy metals in biochar derived from sewage sludge

This study investigates the characteristic of heavy metals (Pb, Zn, Cu, Cd, Cr, Ni and As) in biochar derived from sewage sludge at different pyrolysis temperatures (300, 400, 500, 600 and 700 °C). The heavy metal concentrations, chemical speciation distribution, leaching toxicity, and bio-available contents were investigated using ICP-OES after microwave digestion, a sequential extraction procedure recommended by the Community Bureau of Reference (BCR), an improved nitric acid–sulphuric acid method, and diethylenetriamine pentaacetic acid (DTPA) extraction method, respectively. The results showed that a great percentage of the heavy metals remained in biochar, the concentrations of heavy metals in biochar (except Cd in B7) were higher than that in sludge, and the enrichment of the heavy metals in biochar enhanced with the pyrolysis temperature. Although the effect of pyrolysis temperature on the chemical speciation distribution, the leaching toxicity and the bio-available contents of heavy metals in biochar was inconsistent, the potential risk of biochar on soil and groundwater contamination was lower than sewage sludge.     

Heavy metal removal from contaminated sludge for land application: a review

In recent years, various methods for heavy metal removal from sewage sludge have been extensively studied in order to minimize the prospective health risks of sludge during land application. In this paper, a comparative review and critical analysis of the application of chemical extraction, bioleaching, electroreclamation, and supercritical fluid extraction (SFE), in removing heavy metals from contaminated sludges is presented. Moreover, speciation studies, which can indicate ease of leachability of the different forms of heavy metals in sludge, are also presented. Experimental studies revealed a broad range in metal extraction efficiencies of the different extraction technologies. Acid treatment seemed to effectively remove Cd, attaining as much as 100% removal for some studies, as compared to bioleaching. SFE also gave higher removal efficiency than bioleaching. Cr, Pb and Ni seemed to be also effectively removed by the acid treatment. For the removal of Cu, Mn and Zn, the bioleaching process seemed to be appropriate with maximum removal efficiencies of 91%, 93% and 96% for the three metals, respectively, and as high as 64% minimum removal efficiency for Zn. The SFE process also gave good results for Cu, Mn and Zn removal. Electroreclamation exhibited better removal efficiency for Mn, but is still inferior to acid treatment and bioleaching processes. For chemical extraction, because of the adverse impacts that can result from the use of inorganic acids and complexing agents, interest can be directed more toward utilizing organic acids as extracting agents because of their biodegradability and capability to remove metals at mildly acidic condition, hence requiring less acid. The bioleaching process, although it seems to give a higher yield of metal extraction with lower chemical cost than chemical extraction, may be limited by the inability of the system to cope with the natural environmental conditions, requires strict monitoring of aeration rate and temperature and has applicability to only low sludge solids concentration. A full-scale study would be useful to better assess the efficiency of the process. The electroreclamation technology is limited by its relatively higher energy consumption and limited applicability to sludge. The SFE method, on the other hand, is limited by the complexity of the process and the cost of ligands suitable for effective metal extraction. Both of these technologies are still in their early stage of application and hence there is a need for further basic and applied studies. Finally, the common advantage for almost all treatment technologies studied is that the extraction efficiencies for some metals are high enough to remove metals from sludge to levels suitable for land application.     

Variations of metal distribution in sewage sludge composting

In the study, the variations of heavy metal distributions (of Cu, Mn, Pb, and Zn) during the sewage sludge composting process were investigated by sequential extraction procedures. The total content of Cu and Zn in the composted mixture increased after the composting process. Mn and Zn were mainly found in mobile fractions (exchangeable fraction (F1), carbonate fraction (F2), and Fe/Mn oxide fraction (F3)). Cu and Pb were strongly associated with the stable fractions (organic matter/sulfides fraction (F4) and residual fraction (F5)). These five metal fractions were used to calculate the metal mobility (bioavailability) in the sewage sludge and composted mixture. The mobility (bioavailability) of Mn, Pb, and Zn (but not Cu) increased during the composting process. The metal mobility in the composted mixture ranked in the following order: Mn>Zn>Pb>Cu.     

Extractability and leachability of heavy metals in Technosols prepared from mixtures of unconsolidated wastes

Mixtures of wastes were prepared to improve on the characteristics of the individual ingredients as Technosols, with special attention given to heavy metal extractability. An anaerobic digested sewage sludge and a CaO-treated aerobic sludge were used. A mixture of the two sludges (50:50 DW basis) was also prepared to provide a third type of sludge. The residues were mixed with other types of waste, such as fly ash, Linz-Donowitz slag, foundry sand, shot blasting machine scrap, fettling and barley straw. Extractability of Cu, Cr, Ni, and Zn by 0.01 M CaCl(2) extraction (Me(CACI(2)) was carried out, and leachability of these elements was estimated by acidification of an aqueous suspension of the mixtures with 0.5 N acetic acid (Me(acetic)). The total concentrations of the metals were also determined (Me(T)). The Me(CACI(2)/Me(T) ratios for Cu and Ni (means: 4.0% and 3.1%) were higher than those for Cr and Zn (means: 0.07% each). The mean Me(acetic)/Me(T) ratios followed the order Ni, Zn, Cu, and Cr (19.5%, 4.1%, 3.7%, and 0.09%, respectively). The results highlight the existence of complex interactions among organic matter solubility, pH and heavy metal extractability.     

Fixation and partitioning of heavy metals in slag after incineration of sewage sludge

Fixation of heavy metals in the slag produced during incineration of sewage sludge will reduce emission of the metals to the atmosphere and make the incineration process more environmentally friendly. The effects of incineration conditions (incineration temperature 500-1100°C, furnace residence time 0-60min, mass fraction of water in the sludge 0-75%) on the fixation rates and species partitioning of Cd, Pb, Cr, Cu, Zn, Mn and Ni in slag were investigated. When the incineration temperature was increased from 500 to 1100°C, the fixation rate of Cd decreased from 87% to 49%, while the fixation rates of Cu and Mn were stable. The maximum fixation rates for Pb and Zn and for Ni and Cr were reached at 900 and 1100°C, respectively. The fixation rates of Cu, Ni, Cd, Cr and Zn decreased as the residence time increased. With a 20min residence time, the fixation rates of Pb and Mn were low. The maximum fixation rates of Ni, Mn, Zn, Cu and Cr were achieved when the mass fraction of water in the sludge was 55%. The fixation rate of Cd decreased as the water mass fraction increased, while the fixation rate of Pb increased. Partitioning analysis of the metals contained in the slag showed that increasing the incineration temperature and residence time promoted complete oxidation of the metals. This reduced the non-residual fractions of the metals, which would lower the bioavailability of the metals. The mass fraction of water in the sludge had little effect on the partitioning of the metals. Correlation analysis indicated that the fixation rates of heavy metals in the sludge and the forms of heavy metals in the incinerator slag could be controlled by optimization of the incineration conditions. These results show how the bioavailability of the metals can be reduced for environmentally friendly disposal of the incinerator slag.     

Chemical properties of heavy metals in typical hospital waste incinerator ashes in China

Incineration has become the main mechanism for hospital waste (HW) disposal in China after the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003. However, little information is available on the chemical properties of the resulting ashes. In the present study, 22HW ash samples, including 14 samples of bottom ash and eight samples of fly ash, were collected from four typical HW incineration plants located across China. Chemical analysis indicated that the HW ashes contained large amounts of metal salts of Al, Ca, Fe, K, Mg, Na with a concentration range of 1.8-315gkg(-1). Furthermore, the ashes contained high concentrations of heavy metals such as Ag, As, Ba, Bi, Cd, Cr, Cu, Mn, Ni, Pb, Ti, Sb, Sn, Sr, Zn with a vast range of 1.1-121,411mgkg(-1), with higher concentrations found in the fly ash samples. Sequential extraction results showed that Ba, Cr, Ni and Sn are present in the residual fraction, while Cd existed in the exchangeable and carbonate fractions. As, Mn, Zn existed in the Fe-Mn oxide fraction, Pb was present in the Fe-Mn oxide and residual fractions, and Cu was present in the organic matter fraction. Furthermore, toxicity characteristic leaching procedure (TCLP) results indicated that leached amounts of Cd, Cu and Pb from almost all fly ash samples exceeded the USEPA regulated levels. A comparison between the HW ashes and municipal solid waste (MSW) ash showed that both HW bottom ash and fly ash contained higher concentrations of Ag, As, Bi, Cd, Cr, Cu, Pb, Ti, and Zn. This research provides critical information for appropriate HW incineration ash management plans.     

Metal separation from mixed types of batteries using selective precipitation and liquid-liquid extraction techniques

The purpose of this paper is to study metal separation from a sample composed of a mixture of the main types of spent household batteries, using a hydrometallurgical route, comparing selective precipitation and liquid-liquid extraction separation techniques. The preparation of the solution consisted of: grinding the waste of mixed batteries, reduction and volatile metals elimination using electric furnace and acid leaching. From this solution two different routes were studied: selective precipitation with sodium hydroxide and liquid-liquid extraction using Cyanex 272 [bis(2,4,4-trimethylpentyl) phosphoric acid] as extracting agent. The best results were obtained from liquid-liquid extraction in which Zn had a 99% extraction rate at pH 2.5. More than 95% Fe was extracted at pH 7.0, the same pH at which more than 90% Ce was extracted. About 88% Mn, Cr and Co was extracted at this pH. At pH 3.0, more than 85% Ni was extracted, and at pH 3.5 more than 80% of Cd and La was extracted.     

Behaviour of Cd,Cr, Mn,Ni, Pb,and Zn in sewage sludge incineration by fluidised bed furnace

Cd, Cr, Mn, Ni, Pb, and Zn behaviour during sewage sludge incineration was investigated in seven pilot tests using a circulating fluidised bed furnace. Dewatered sludge at a solids concentration of 15-18% was fed to the furnace either alone (two tests) or spiked with chlorinated organic compounds (five tests). The behaviour of metals in the fluidised bed furnace was studied by comparing metal concentrations in the two main ash streams: ash separated from the cyclone immediately following the fluidised bed furnace, and fly ash recovered in the final bag filter. A metal enrichment factor was defined as the ratio of metal concentration between filter ash and cyclone ash. Only Cd and Pb showed any significant enrichment. Their enrichment factors were mainly affected by chlorine concentration in the feed sludge. To check whether simple equilibrium models may explain and predict metal behaviour, experimental data were compared with percentage of the metal vaporisation in the combustion chamber predicted using a thermodynamic model. Discrepancies between model predictions and experimental results are accounted for by considering that kinetics may be a limiting factor in the formation of metal chloride gaseous species. Due to the very short sludge residence time in the fluidised bed furnace, the gaseous compounds have little chance to evolve completely.     

Characterization of a thermal power plant air heater washing waste: a case study from Iran.

In Iran most of the electricity is generated by thermal power plants. As a result of fuel oil burning in winter time, the air heaters of the boilers have to be washed and cleaned frequently. The wastewater originating from air heater washing is then treated in an effluent treatment plant by chemical precipitation followed by dewatering of the sludge produced. The resulting waste is classified as specific industrial waste that should be characterized in detail under the Waste Management Act of Iran. The quantity of this waste produced in the studied power plant is about 20 tonnes year(-1). In the present investigation, the first to be carried out in Iran, seven composite samples of dewatered sludge from air heater washing wastewater treatment were subjected to investigation of the physical properties, chemical composition and leaching properties. The most likely pollutants that were of concern in this study were heavy and other hazardous metals (Cd, Co, Cr, Mn, Ni, Pb, Zn and V). The results revealed that mean pH, wet and dry density and moisture content of the waste were 6.31, 1532 kg m(-30, 1879 kg m(-3) and 15.35%, respectively. Magnetite, SiO2, P2O5, CaO, Al2O3 and MgO were the main constituents of the waste with a weight percentage order of 68.88, 5.91, 3.39, 2.64, 2.59 and 1.76%, respectively. The toxicity characteristic leaching procedure test results for some heavy and other hazardous metals showed that mean elemental concentrations of Cd, Co, Cr, Mn, Ni, Pb, V and Zn in leachate were 0.06, 1.55, 5.49, 36.32, 209.10, 0.58, 314.06 and 24.84 mg L(-1), respectively. According to the Waste Management Act of Iran this waste should be classified as hazardous and should be disposed of in accordance with hazardous waste disposal regulations.     

气化炉渣的重金属浸出特性及化学形态分析

分别采用硫酸硝酸法、水平振荡法和醋酸缓冲溶液法制取气化炉渣的浸出液,考察了不同提取方式对浸出液中重金属质量浓度的影响。采用改进BCR连续提取法对气化炉渣中的重金属Cr,Zn,Cu,Pb,Ni,As,Cd的化学形态进行了分析。实验结果表明：煤气化工艺中的气化炉渣属第Ⅰ类一般工业固体废物;在3种提取方式中,醋酸缓冲溶液法的重金属浸出种类最多,且浸出量最大;Cd和Cr对环境具有较高的潜在危害性,Cu次之,Zn,Pb,Ni,As主要以残渣态形式存在,对环境的直接危害性较低。     

Acidic bioleaching of heavy metals from sewage sludge

The overall objective of this study was to evaluate the use of controlled bio-acidification prior to land application as a decontamination process to remove heavy metals from sludge. The sulfur-oxidizing bacteria were naturally available in the sludge samples and were activated by providing sulfur and aeration at 28°C–30°C. Activation resulted in bio-acidification to pH 2 within 5–11 days. Successive inoculation of fresh sludges with 5% acidified samples reduced the acidification time to 2–3 days in most samples. Bio-acidification resulted in dissolving significant quantities of heavy metals from all sludge types tested. The maximum solubilization results were: 86%–97% for Ni; 48%–98% for Pb; 26%–71% for Cr; 18%–91% for Zn; 16%–90% for Cu; 7%–60% for Cd. Limited metal solubilization results were observed in the various control samples that accompanied the bio-acidified samples. The leaching results in the control samples were limited to 2%–19% for Ni, 0%–7% for Pb, 0%–5% for Cr, 0.3%–4% for Zn, 0.2%–4% for Cu and 0%–3% for Cd. The results confirmed that Ni and Pb were the easiest metals to dissolve from the various sludge types. On the other hand, the lowest solubilization results were observed for Cu and Cd, and moderate solubilization results were achieved for Cr. The bio-acidification process resulted in moderate gains in terms of improving the suitability of tested sludges for land application. Received: April 19, 1999 / Accepted: November 4, 1999     

Waste paper and clinoptilolite as a bulking material with dewatered anaerobically stabilized primary sewage sludge (DASPSS) for compost production

Environmental problems associated with sewage sludge disposal have prompted strict legislative actions over the past few years. At the same time, the upgrading and expansion of wastewater treatment plants have greatly increased the volume of sludge generated. The major limitation of land application of sewage sludge compost is the potential for high heavy metal content in relation to the metal content of the original sludge. Composting of sewage sludge with natural zeolite (clinoptilolite) can enhance its quality and suitability for agricultural use. However, the dewatered anaerobically stabilized primary sewage sludge (DASPSS) contained a low concentration of humic substances (almost 2%), and the addition of the waste paper was necessary in order to produce a good soil conditioner with high concentrations of humics. The final results showed that the compost produced from DASPSS and 40-50% w/w of waste paper was a good soil fertilizer. Finally, in order to estimate the metal leachability of the final compost product, the generalized acid neutralization Capacity (GANC) procedure was used, and it was found that by increasing the leachate pH, the heavy metal concentration decreased. The application of the sequential chemical extraction indicated that metals were bound to the residual fraction characterized as a stabilize fractions.     

酸浸出法回收冶金污泥中的有价金属

采用二次酸浸出的方法回收镍钴湿法冶金工业污泥中的有价金属。先采用水和硫酸作为浸出剂浸出Mg和Na,最佳工艺条件为浸出液的pH 7.5、浸出时间5 min、浸出剂体积与干污泥质量的比(ω)为10 mL/g。再采用硫酸作为浸出剂、焦亚硫酸钠作为还原剂进行二次酸浸,在硫酸与污泥质量比为1.3、焦亚硫酸钠与污泥质量比为0.3、ω为5 mL/g、浸出温度85℃、浸出时间20 min的最佳工艺条件下,Co、Ni、Cu、Mn和Zn的浸出率分别达92.45%、93.48%、89.52%、97.78%和94.79%。经XRD表征,浸出后污泥中未见原污泥中的矿物相,说明原污泥中的矿物几乎全部被溶解。     

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH-HCl); (4) oxidizable fraction (H2O2 + CH3COONH4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg(-1) (dry weight) in bottom ash and of 68.5 g kg(-1) (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg(-1) (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (approximately 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.     

Solubility and Potential Mobility of Heavy Metals in Two Contaminated Urban Soils from Stockholm,Sweden

The solubility and potential mobility of heavy metals (Cd, Cu,Hg, Pb and Zn) in two urban soils were studied by sequential andleaching extractions (rainwater). Compared to rural (arable) soils on similar parent material, the urban soils were highlycontaminated with Hg and Pb and to a lesser extent also with Cd,Cu and Zn. Metal concentrations in rainwater leachates were related to sequential extractions and metal levels reported fromStockholm groundwater. Cadmium and Zn in the soils were mainly recovered in easily extractable fractions, whereas Cu and Pb were complex bound. Concentrations of Pb in the residual fractionwere between two- and eightfold those in arable soils, indicatingthat the sequential extraction scheme did not reflect the solidphases affected by anthropogenic inputs. Cadmium and Zn conc. inthe rainwater leachates were within the range detected in Stockholm groundwater, while Cu and Pb conc. were higher, whichsuggests that Cu and Pb released from the surface soil were immobilised in deeper soil layers. In a soil highly contaminatedwith Hg, the Hg conc. in the leachate was above the median concentration, but still 50 times lower than the max concentration found in groundwater, indicating the possibilityof other sources. In conclusion, it proved difficult to quantitatively predict the mobility of metals in soils by sequential extractions.     

Concentrations of heavy metals in fly ash from a coal-fired power plant with respect to the new Finnish limit values

In Finland, the new limit values for heavy metals in fertilizers used in agriculture and in forestry came into force in March 2007, and for materials used as earth construction agents, in June 2006. From the utilization point of view, it was notable that the total heavy metal concentrations (Cd, Cu, Pb, Cr, Mo, Zn, As, Ni, Ba, and Hg) in fly ash from a coal-fired power plant were lower than those limit values. The concentrations of the easily soluble elements Ca, Mg, Na, P, and Zn in the fly ash were between 3.5 and 35 times higher than those found in the coarse mineral soils of Finland. Fly ash is a potential agent for soil remediation and for improving soil fertility. If inorganic materials and by-products are utilized in earthworks, the content of harmful compounds must be low and the harmful components must be tightly bound to the matrix. Therefore, a five-stage sequential extraction procedure was used to evaluate the extractability of different elements in fly ash into the following fractions: (1) the water-soluble fraction, (2) the exchangeable fraction (CH₃COOH), (3) the easily reduced fraction (NH₂OH-HCl), (4) the oxidizable fraction (H₂O₂ + CH₃COONH₄), and (5) the residual fraction (HF + HNO₃ + HCl).     

苯甲酸生产残液中锰、钴和镍的提取及分离

探讨了苯甲酸生产残液中锰、钴和镍的提取及分离方法。首先采用酸溶液提取残液中的金属元素;然后通过氨水沉淀法分离锰;最后使用p507萃取剂分离钴和镍。实验结果表明:当苯甲酸生产残液中锰、钴和镍的质量分数分别为0.085 0%,0.307 1%,0.015 5%时,在硫酸浓度为2.0 mol/L、过氧化氢溶液质量分数为25%的条件下,锰、钴和镍的提取率分别为88.59%,87.77%,86.50%;当氨水浓度为2 mol/L时,锰的沉淀率达94.24%;在平衡水相p H为4、p507萃取剂皂化率为60%、油相中p507萃取剂的体积分数为15%的条件下,钴萃取率达87.53%,镍萃取率仅为8.46%,钴镍分离系数为68.70。     

A study of heavy metals and their fate in the composting of tannery sludge

Tannery waste is categorized as toxic and hazardous in Malaysia due to its high content of Cr (in excess of 500 mg/kg) and other heavy metals. Heavy metals, when in high enough concentrations, have the potential to be both phytotoxic and zootoxic. Heavy metals are found as contaminants in tannery sludge. This investigation aimed to identify the fate of chromium, cadmium, copper, lead, and zinc concentrations in tannery sludge throughout a 50-day composting cycle. The results of this study showed a general increase in the removal of Cr, Cd, Pb, and to a much smaller extent Zn and Cu, manifested by a decrease in their overall concentrations within the solid fraction of the final product (the decreases were likely the result of leaching). Furthermore, in using a sequential extraction method for sludge composting at different phases of treatment, a large proportion of the heavy metals were found to be associated to the residual fraction (70-80%) and fractions more resistant to extraction, X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of the metals were bound to bioavailable fractions X-(KNO3+H2O).