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.     

Investigation of potentially toxic heavy metals in different organic wastes used to fertilize market garden crops

The benefits of using organic waste as fertilizer and soil amendment should be assessed together with the environmental impacts due to the possible presence of heavy metals (HMs). This study involved analysing major element and HM contents in raw and size-fractionated organic wastes (17 sewage sludges and composts) from developed and developing countries. The overall HM concentration pattern showed an asymmetric distribution due to the presence of some wastes with extremely high concentrations. HM concentrations were correlated with the size of cities or farms where the wastes had been produced, and HM were differentiated with respect to their origins (geogenic: Cr–Ni; anthropogenic agricultural and urban: Cu–Zn; anthropogenic urban: Cd–Pb). Size fractionation highlighted Cd, Cu, Zn and Pb accumulation in fine size fractions, while Cr and Ni were accumulated in the coarsest. HM associations with major elements revealed inorganic (Al, Fe, etc.) bearing phases for Cr and Ni, and sulfur or phosphorus species for Cd, Cu Pb and Zn.     

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.     

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.     

Determination of Cu and Ni incorporation ratios in Portland cement clinker

Cu and Ni are metals found in galvanic sludges; these sludges are considered hazardous due to their heavy metal content. The main objective of this work is to determine the incorporation amount of Cu and Ni in Portland clinker when a galvanic sludge containing these metals is added to the clinker raw-material. The influence of this addition on the clinkering reactions is evaluated as well as the possibility of co-incinerating galvanic sludges containing Cu and Ni in rotary cement kilns. This study also characterizes the galvanic sludge. Samples were prepared by additions from 0.25 to 5 wt.% of a galvanic sludge to an industrial clinker raw-material. The clinkering process was simulated in a laboratory device. The following techniques were applied to characterize the raw materials and the products of the tests: chemical analysis, differential thermal analysis (DTA) and thermogravimetric analysis (TG). Leaching tests were performed in the produced clinker samples in order to verify the incorporation of the studied metals in the clinker structure. The results led to the conclusion that additions of up to 2 wt.% of a galvanic sludge containing 2.4 wt.%Cu and 1.2 wt.% Ni to clinker raw-material do not affect the clinkering reactions and that these metals are totally incorporated into the clinker.     

An investigation on the potential of metal recovery from the municipal waste incinerator in Taiwan

This study aimed to identify distribution of metals and to estimate the amount of these metals that can be potentially recovered from incineration residues. First, the partitioning behavior of Cr, Cu, Fe, Cd, Al, Zn, and Pb in bottom ash and fly ash was investigated in one large municipal waste incinerator in Taiwan. In addition, the material flow analysis (MFA) method was used to estimate the material flux of metals within incinerator plant, and to calculate the amount of metal recovery. According to the findings of this study, six metals (Fe, Al, Cu, Zn, Cr, and Pb) concentrated in bottom ash mostly, while Cd existed primarily in fly ash. The weight percentages of Fe (4.49%), Al (5.24%), Cu (1.29%), Zn (2.21%), and Pb (0.58%) in incinerator ash are high, and even higher than the compositions of natural minerals. Finally, the amount of Cr, Cu, Fe, Cd, Al, Zn and Pb that can be potentially recovered from incineration residues will reach 2.69 x 10(2), 1.46 x 10(4), 4.91 x 10(4), 6.92 x 10(1), 5.10 x 10(4), 1.85 x 10(4) and 4.66 x 10(3) ton/yr, respectively.     

Sequential extraction of metals from mixed and digested sludge from aerobic WWTPs sited in the south of Spain

The content of heavy metals is the major limitation to the application of sewage sludge in soil. However, assessment of the pollution by total metal determination does not reveal the true environmental impact. It is necessary to apply sequential extraction techniques to obtain suitable information about their bioavailability or toxicity. In this paper, sequential extraction of metals from sludge before and after aerobic digestion was applied to sludge from five WWTPs in southern Spain to obtain information about the influence of the digestion treatment in the concentration of the metals. The percentage of each metal as residual, oxidizable, reducible and exchangeable form was calculated. For this purpose, sludge samples were collected from two different points of the plants, namely, sludge from the mixture (primary and secondary sludge) tank (mixed sludge, MS) and the digested-dewatered sludge (final sludge, FS). Heavy metals, Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Ti and Zn, were extracted following the sequential extraction scheme proposed by the Standards, Measurements and Testing Programme of the European Commission and determined by inductively-coupled plasma atomic emission spectrometry. The total concentration of heavy metals in the measured sludge samples did not exceed the limits set out by European legislation and were mainly associated with the two less-available fractions (27-28% as oxidizable metal and 44-50% as residual metal). However, metals as Co (64% in MS and 52% in FS samples), Mn (82% in MS and 79% in FS), Ni (32% in MS and 26% in FS) and Zn (79% in MS and 62% in FS) were present at important percentages as available forms. In addition, results showed a clear increase of the concentration of metals after sludge treatment in the proportion of two less-available fractions (oxidizable and residual metal).     

Recovery of metals from waste printed circuit boards by supercritical water pre-treatment combined with acid leaching process

Waste printed circuit boards (PCBs) contain a large number of metals such as Cu, Sn, Pb, Cd, Cr, Zn, and Mn. In this work, an efficient and environmentally friendly process for metals recovery from waste PCBs by supercritical water (SCW) pre-treatment combined with acid leaching was developed. In the proposed process, waste PCBs were pre-treated by SCW, then the separated solid phase product with concentrated metals was subjected to an acid leaching process for metals recovery. The effect of SCW pre-treatment on the recovery of different metals from waste PCBs was investigated. Two methods of SCW pre-treatment were studied: supercritical water oxidation (SCWO) and supercritical water depolymerization (SCWD). Experimental results indicated that SCWO and SCWD pre-treatment had significant effect on the recovery of different metals. SCWO pre-treatment was highly efficient for enhancing the recovery of Cu and Pb, and the recovery efficiency increased significantly with increasing pre-treatment temperature. The recovery efficiency of Cu and Pb for SCWO pre-treatment at 420 °C was 99.8% and 80%, respectively, whereas most of the Sn and Cr were immobilized in the residue. The recovery of all studied metals was enhanced by SCWD pre-treatment and increased along with pre-treatment temperature. Up to 90% of Sn, Zn, Cr, Cd, and Mn could be recovered for SCWD pre-treatment at 440 °C.     

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。     

Use of dewatered municipal sludge on Canna growth in pot experiments with a barren clay soil

The present study evaluated the possibility of using the dewatered municipal sludge for non-agricultural purposes. The sludge was amended with soil and was applied at 0, 165, 330, 495 and 660 t/ha to promote the growth of Canna. The results showed that the Canna growth pattern exhibited a pronounced positive growth response in the range of 165–495 t/ha, and the Canna could not survive at an amendment rate of 660 t/ha. The analysis of chlorophyll fluorescence parameters showed that sludge did no harm to Canna, while under the conditions of barren soil alone, the plants were put into nutrients stress conditions. Due to the application of sludge, the concentration of heavy metals (Cu, Zn, Cr, Cd, Pb and Ni) in soil increased. However, by planting of Canna, contents of Cd, Ni and Zn showed trends of decline; Cd and Ni have shown a significant decline in concentration, while Zn had only limit response. As a result, dewatered sludge might be used to amend the barren soil and Canna could be used for phytoremediation of sludge.     

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%).     

Metal fractionation in soil profiles at automobile mechanic waste dumps.

Soil profiles at five automobile mechanic waste dumps in Port-Harcourt, Nigeria were investigated to assess the spatial distribution, chemical speciation, and likely mobility of Cd, Cu, Pb, Zn, Cr and Ni in the soil as a function of the soil properties. A sequential fractionation protocol was used that generated six different fractions into which soil metal could partition. Cadmium was associated with non-residual fractions at surface horizons, but at lower depths it was in the residual fractions. Copper and Cr partitioned into organic and residual fractions, while Pb was associated with an Fe-Mn oxide fraction and the residual fractions. Zinc in surface horizons partitioned into an Fe-Mn oxide fraction and a fraction that captured carbonate-bound species, but in subsurface horizons, it was mainly in the residual fractions. Ni was predominantly found in the residual fractions. Mobility factors were calculated, and their values tended to decrease with increasing profile depth, indicating that these metals are relatively mobile in the surface horizons compared the subsurface except for chromium in the 15-30 cm depths. The mobility factors for the heavy metals follow the order: Cd > Zn > Pb > Cu > Cr > Ni. The results suggest that there is serious contamination hazard with Cd, Pb, and Zn in the soil profiles.     

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.     

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.     

添加CaO对燃煤重金属元素富集效果的影响

选取CaO作为吸附剂,探究了不同燃烧温度下添加CaO对重金属元素在燃煤灰渣中富集效果的影响规律。实验结果表明:添加CaO对重金属元素Cr未起到富集作用,而对Mn,Ni,Cu,Zn,As,Cd,Pb 7种重金属元素的富集效果显著;随燃烧温度的升高,CaO对各赋存形态的Mn,Ni,Cu,Zn,As的富集效果先变好而后变差,对各赋存形态的Cd和Pb的富集效果越来越好;CaO添加比(预处理后的CaO颗粒与预处理后的原煤的质量比)越大,CaO对Mn,Ni,Cu,Zn,As,Cd,Pb的富集效果越好,燃烧温度为850℃时的最佳CaO添加比为4%。     

Sludge earthworm composting technology by Eisenia fetida

Prior to vermicompost application to the soils, there is a need to determine the heavy metal concentrations in the final vermicomposts. Acute toxicity on Eisenia fetida for copper (Cu) and cadmium (Cd) were conducted by artificial soils tests. The dosage of interest is typically the median lethal concentration (LC₅₀) that will kill 50 % of the population of organisms within the test period. The dry artificial soil is pre-moistened 1 or 2 days before the test by adding deionized water to obtain approximately half of the required final water content of 40–60 % of the maximum water holding capacity. The 14-day LC₅₀ values (95 % confidence interval) for Cu and Cd were 530 (450–624) and 1118 (988–1265) mg kg^?1, respectively. The vermicomposting was designed to evaluate the effects of earthworm activity on heavy metals in sewage sludge. Compared with the sludge before vermicomposting by Eisenia fetida, the results are as follows: (1) water content, the pH value and organic matter content decreased, (2) total nitrogen content increased, total phosphorus content and total potassium content decreased, (3) available nitrogen concentration, available phosphorus content increased, and (4) the total content of five metals (Cu, Ni, Cd, Pb and Zn) decreased, and the bioaccumulation factor shows that vermicomposting can efficiently remove heavy metals. Therefore, it can be concluded that the soil use of sludge of the Wastewater Treatment Plant in Huaibei is feasible.     

Urban Metal Flows – A Case Study of Stockholm. Review and Conclusions

Metals have rapidly accumulated in the anthroposphere, especiallyin urban areas, indicating possible environmental and resource problems. Here, Stockholm City was chosen for a case study of urban metal flows, i.e. metal inflow to, metals in the stock of,and metal outflow from the anthroposphere to the biosphere. Themetal stock of Stockholm is large and still growing. The large amounts of metals in the solid waste fraction totally dominatethe outflow from the city. For major parts of the stock, the emissions from goods in use are negligible. There are, however,goods applications corresponding to significant emissions: e.g. the traffic sector (Cu, Zn, Cr, Ni, Pb), the tapwater system (Cu), roofs/fronts or other metal surfaces (Cu, Zn). Today's known metal flows from the anthroposphere of Stockholm to the biosphere and sewage sludge are quantitatively dominated by Zn(34 ton y^-1) and Cu (14 ton y^-1). Historical and present emissions have resulted in high metal concentrations insediments (especially Cd, Hg and Pb, but also Cu and Zn), groundwater (Cu, Hg) and in soils (Hg, Cu, Pb). At present theannual median concentrations are below the Swedish limits for metals in sewage sludge, even if the safety margins aresmall for Cd, Hg and to some extent Cu. The flows of Cu and Zn to Stockholm soils are high with a significant accumulationindicating an environmental impact in a longer time perspective.High levels of metals in surface sediments in the waterenvironments reflects an ongoing input where these metals aretransported from known (Cu, Zn) and or partly unknown (Cd, Hg, Pb) sources. In future urban areas, monitoring of metal flows must be performed both in the anthroposphere and the biospherein order to have a pro active approach to urban environmentalproblems and to get prompt answers to measures taken.     

Recent Sediment of Lake Bled (NW Slovenia): Sedimentological and Geochemical Properties

Sediment cores collected in eutrophic subalpine Lake Bled (NW Slovenia) were analyzed sedimentologically in terms of grain size, mineralogy and sedimentation rates, and geochemically in terms of metals and nutrients. Surficial sediment is composed of dark gyttya type clayey silt with 5%–10% of organic matter. The sediment below is fine laminated and composed of homogenous silt and clayey silt: Mineralogically, low-Mg calcite prevails, followed by dolomite, quartz, partially of diatomaceous origin, and feldspar. Clay minerals are composed of muscovite/illite and chlorite. Authigenic minerals are pyrite and ‘lake chalk’ (low-Mg calcite). Lake sediment is especially polluted by Pb, Zn and P. Higher contents were found in the northwestern and eastern parts due to the particle input by local inflows. Increasing eutrophication and pollution, indicated by Cd, Cu, V, Cr, Co and total N and P enrichment in the top layers of the cores, started almost 100 years B.P., and especially 50 years ago.     

Century Perspective of Heavy Metal Use in Urban Areas. A Case Study in Stockholm

The inflow and stock (amount in use) of heavy metals (cadmium(Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni) and zinc (Zn)) in goods in 1995 have been quantifiedin the anthroposphere of Stockholm, Sweden. Statistics on national, regional and local level were used. Contacts were established with representatives from production and constructionin the industrial sector and with authorities. The results show that the stock of Cd is 0,2 kg per capita. For the other heavymetals the corresponding result per capita is: Cr 8, Cu 170, Hg 0,01, Ni 4, Pb 73 and Zn 40 kg. The inflow varies between2–8%of the stock indicating the importance of the stock. The lowestlevels are for Cu and Pb. Heavy metal levels in solid waste are high, between 15–45% of the amount in the inflow (Hg excluded), the lowest values were for Cu and Pb. Thus, recyclingis incomplete. Long life expectancy goods form the majority of the stock but there is a tendency that short life expectancy goods increase their importance in the inflow. Concealedgoods are also more frequent in inflow than in the stock.     

Health risk assessment of heavy metals (Cr, Ni, Cu, Zn, Cd, Pb) in circumjacent soil of a factory for recycling waste electrical and electronic equipment

The aim of the study was to determine the potential environmental contamination in a typical factory for recycling waste electrical and electronic equipment in Shanghai. Heavy metals (Cr, Ni, Cu, Zn, Cd, Pb) in the soil around the factory have been evaluated in this paper. Compared with the background value, the concentrations of six metals detected in all the samples were higher, which showed that toxic metals were released into soil around the factory. Compared with the Environmental Quality Standards for Soils, China grade III, all the six metals are under soil guidelines. The non-cancer risk in different directions from the factory was in the order of: the north > the west > the south > the east. For inhalation and ingestion, the non-cancer risk in the soil west of the factory was biggest. Nevertheless, the non-cancer risk in the soil north of the factory was the biggest for dermal contact. The trend of cancer risk was the west > the south > the north > the east. The non-cancer risk and the carcinogenic risk for Cr, Ni, and Cd were all below the limiting value. This study might provide a reference for the risk assessment involved in electronic waste management and recycling activities.