The influence of process parameters on the removal of heavy metals in activated sludge

The behavior of six heavy metals in an activated sludge pilot plant under conditions of normal and elevated influent metal concentrations has been studied. Percentage heavy metal removals at sludge ages of 4, 9, and 12 d were more consistent when metals were added to the system, possibly as a result of lesser variations in heavy metal speciation in the settled sewage, and the greatest degree of accumulation of heavy metals by the biomass occurred at the 12 d sludge age. When shock loads of heavy metals were introduced into the system, their concentrations in the effluent did not immediately rise in proportion; however, heavy metal removal efficiencies were similar under steady state conditions of normal and elevated influent metal concentrations. Cadmium, Cu, and Ni were largely soluble in the effluent samples, but Cr, Pb, and Zn were predominantly insoluble, indicating that particulate forms of these metals may escape removal in secondary sedimentation. The high degree of Ni solubility in the settled sewage and final effluent reflected its consistently poor removal in the process. The two most soluble metals, Cu and Ni, appeared to be associated to a large degree with high molecular weight substances in the settled sewage and final effluent, possibly influencing their availability for uptake by the biomass.     

Effect of pruning-derived biochar on heavy metals removal and water dynamics

Biomass-derived biochar is considered as a promising heavy metal adsorbent, due to abundance of polar functional groups, such as carboxylic, hydroxyl, and amino groups, which are available for heavy metal removal. The aims of this study were to evaluate the effectiveness of an orchard pruning-derived biochar in removing some heavy metals (through the evaluation of isotherms) and to study water dynamics at the solid-liquid interface as affected by heavy metal adsorption (through an innovative nuclear magnetic resonance (NMR) relaxometry approach). Both isotherms and NMR spectra revealed that Pb and Cr showed a good affinity for the biochar surface (Pb > Cr), while Cu was less affine. Accordingly, higher amounts of Pb and Cr were adsorbed by biochar as compared to those of Cu in the single systems. In binary systems (i.e., when two metals were applied simultaneously), Pb showed the highest inhibition of the adsorption of the other two metals, whereas the opposite was evidenced when Cu was used; the competitive adsorption was also strongly influenced by the metal residence time on biochar surface. In ternary systems (i.e., when all metals were applied simultaneously), even in the presence of high amounts of Pb and Cr, considerable adsorption of Cu occurred, indicating that some biochar adsorption sites were highly specific for a single metal.     

Selective removal of heavy metals from contaminated kaolin by chelators

The competitive desorption/dissolution of kaolin-adsorbed heavy metal mixtures and mixtures of adsorbed Cd with Mg and/or Ca by four chelators (NTA, EDTA, EGTA, and DCyTA) was investigated. Metals were adsorbed on kaolin at pH 7 and the effects of chelator type and concentration on the extent of metal dissolution was studied at a solution pH of 10. EGTA addition. EGTA was the most effective chelator in selectively removing Cd from kaolin in the presence of adsorbed alkaline-earth metals. Approximately 90% of the adsorbed Ca and Mg were retained on the kaolin until almost all (> 80%) of the cadmium was dissolved by EGTA chelator. NTA was the least effective chelator in selectively dissolving Cd from kaolin contaminated with both Cd and Ca (≈ 45% of the adsorbed Cd could not be removed). All four chelators exhibited some desorption/dissolution selectivity for Cd, Cu, and Pb adsorbed on kaolin. When the concentration of chelator in solution was insufficient to dissolve all adsorbed metals, the observed metal ordering for chelation and dissolution was Cd > Cu > Pb (for EGTA), Cd > Pb > Cu (for EDTA and DCyTA), and Cu > Cd > Pb (for NTA).     

Elimination of heavy metals from process waters of the bioleaching process by electrolysis

2 Conclusions  The investigations into the membrane electrolysis cell show that electrochemical metal separation from bioleaching process waters can represent a practical alternative for metal separation by alcalization, Coal and platinized titanium material exhibit good anodic resistance at the current densities tested. By contrast, high-grade steel and to some extent lead anodes were dissolved and are hence unsuitable for this purpose. However, for practical application, suitable ways are required to discharge the precipitates containing heavy metals deposited on the electrodes from the electrolysis cell and to prevent membrane clogging. Regarding the main components zinc, manganese, and nickel, the combination electrodes proved to be suitable for eliminating the heavy metals from the aqueous phase. Another way of treating diluted process waters containing sulphuric acidic and heavy metals is to concentrate the sulphuric acid in the anode region and to precipitate the heavy metals in the cathode region. The sulphuric acid recovered could then be returned to the leaching process, hence avoiding wastewater.     

Effect of aging process on the fractionation of heavy metals in some calcareous soils of Iran

This study was conducted to investigate the effect of time on lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu) availability in some calcareous soils of Iran. Heavy metals were added to soils at the rate of 500 mg kg^? 1 of Pb, Zn, and Cu and 8 mg kg^? 1 of Cd as chloride. The samples were incubated for 3 h, 1, 3, 7, 14, 21, and 28 days at 25 °C and constant moisture. After incubation, metals in amended and control soils were fractionated by the sequential extraction procedure. There were changes in the proportional distribution of heavy metals in all five studied soils during 28 days of incubation with spiked heavy metals. In general the proportions of heavy metals associated with the most weakly bound fraction (EXCH) tended to decrease, with corresponding increases in the other five more strongly binding fractions during the incubation. The distribution of added heavy metals into different solid phase fractions appears to be consisted of two phases involving the initial rapid retention followed by a slow continuous retention. Three kinetic equations were used to fit the experimental data. The parabolic equation fits well the data used in this work. The transformation rate of EXCH fraction for soils was estimated by parabolic equation for above incubation periods. There were differences in the rates at which redistribution took place between soils and heavy metals. The constant b in parabolic equation was defined as the transformation rate, which were in the order Cu > Zn ≥ Pb ? Cd. The higher proportions of EXCH fraction of spiked Cd in these calcareous soils indicates its higher potential of downward leaching and runoff transport especially at the early stage of pollution.     

Feasibility of a counter-current extraction procedure for the removal of heavy metals from contaminated soils

Effective remediation and sanitation technologies for soils contaminated with heavy metals are limited. We investigated the feasibility of a counter-current metal extraction procedure for the removal of selected heavy metals (Cd, Cu, Ph, and Zn) from two contaminated soils. The process involved a decarbonation (removal of carbonates), acid solubilisation, washing, and liming step. Results from batch equilibration experiments simulating the counter-current process showed more than 85% of the Cd present to be removed. Removal efficiencies for Cu and Pb were limited to approximately 15%, this mainly due to resorption of these elements during the decarbonation step. As most Zn was found to be present in a more difficult acid-extractable solid phase, its extractability accounted for only 25%. While reaction (pH) conditions of both decarbonation and solubilisation determined removal efficiencies, washing the extracted soil with deionized water only slightly increased the amount of metals removed. Metal distribution among solid phases — exchangeable, carbonate, reducible, organically bound, and residual — was affected by the different treatments. The amount of metals contained in the exchangeable and residual fractions determined their extractability. Except for Cu, the reducible and organically bound fractions were less important. After solubilisation 13 to 70% of the metals were present in an exchangeable solid phase. This implicates that washing the solubilized soil with a salt may increase the extractability of metals, especially for Zn and Pb. Based on our results the process is critically evaluated and possibilities for optimization formulated.     

Review of impact of heavy metals on stream invertebrates with special emphasis on acid conditions

Studies of the accumulation and toxicity of Cd, Zn, Fe, Pb and Cu under acid conditions to stream invertebrates are reviewed. The influence of pH on metal speciation decreases in the following order: Cu > Pb > Cd > Zn. The free metal ion is one of the most toxic species and is generally taken up directly from the water by organisms. The role of food in the uptake of metals depends mainly on feeding habits of the species, body size, life span and duration of the exposure. Surface adsorption can be regarded as a form of metal ‘uptake’ which increases at high pH. Biomagnification of metals along aquatic trophic food chains has not been proved for many metals. Toxicity of Cd, Fe, Zn and Pb increases at low pH, however not for all invertebrates. More knowledge is needed concerning sublethal effects of metals on invertebrates at different pH values and uptake, bioconcentration and biomagnification of metals at different pH values. Future studies should include experiments in artificial streams or in the field instead of short term tests and simple recording of field data.     

Model experimental study on the migration behavior of heavy metals in electrokinetic remediation process for contaminated soil

Recently in Japan, like in other industrialized countries, treatment of contaminated soil or ground has become an important issue in redeveloping such areas as old factories, mining sites, and other polluted sites. In these cases, measures such as a construction of cut-off walls and disposal to controlled waste disposal sites have been so far taken. But, the treatment of contaminated soils has become more difficult nowadays. Therefore, remediation of contaminated soil by removal or extraction of contaminants is necessary and various methods have been developed and applied in many countries. Authors have tried to develop an electrokinetic remediation method for soil contaminated with heavy metals and some basic and pilot scale experiments have been carried out. In this paper, the results of a model experiment using an artificial soil contaminated with Cu or Ph or Cr are presented as follows. i) In the electrokinetic process, migration of water to the cathode by electroosmosis, migration of ions to the cathode or anode by electrophoresis and electrolysis of water occur spontaneously. ii) Upon DC loading, Cu and Pb migrate to the cathode and accumulate as oxides or hydroxides near the cathode but are not removed from contaminated soil. However, in the case of Cr contaminated soil, Cr in the form of Cr(VI) migrates to the anode and is removed from soil through the drainage water. iii) After DC loading for 2 weeks, the concentration of exchangeable cations and composition of soil changed drastically while the CEC and clay mineralogy did not change appreciably.     

不同pH值混合螯合剂对土壤重金属淋洗及植物提取的影响

为了得出混合螯合剂（MC）淋洗去除重金属的最佳pH值以及对后续植物提取重金属的影响,用Ca(OH)2将pH值为2.75的MC提高至pH值5、7和9,对重金属污染土壤进行了盆栽淋洗试验,而后种植东南景天（Sedum Alfredii）,测定淋出液及植物重金属含量。另外,通过浸提试验研究了含有不同阳离子的MC对重金属淋洗效果的影响。结果表明,pH值为5和7的MC显著提高了Cd、Pb和Cu的淋出率。与Na+、K+离子相比,Ca2+的存在能够提高MC对重金属的淋洗去除。pH值7和9的MC淋洗土壤后提高了东南景天的生物量,但是降低东南景天中Cd和Zn的浓度,导致其植物提取率低于无淋洗剂对照。在化学淋洗+植物提取联合技术中,Cd和Zn主要靠植物提取去除,植物提取率分别可达土壤Cd的30%～40%和土壤Zn的6.5%～6.9%;而Pb和Cu主要靠混合螯合剂淋洗去除,去除率分别为2.3%～2.6%和1.6%～2.0%。综合来说,如果需要同时去除Cd、Zn、Pb和Cu,降低土壤重金属有效态含量,用pH值9的MC淋洗土壤联合植物提取较为合适。     

Study of nickel sorption onto biological sludges. possibilities for heavy metals removal treatments

Nickel adsorption onto a sludge wasting from a biological aeration tank is described in this work. This procedure is planned as an alternative method for metal removal from industrial effluents containing heavy metals in low concentrations. Experimental results of equilibrium adsorption and laboratory equipment operation are reported. Equilibrium data of nickel adsorption were fitted to the Freundlich equation. On the basis of this equation, the effect of several parameters such us metal concentration, sludge concentration and metal dosing rate were tested. Nickel removal efficiency is about 80% in the most favourable cases. Aeration during metal-sludge contact was also tested but little enhancing in metal uptake was observed. This analysis can be used to define the best operation conditions in practical cases either for metal or organic matter removal.     

生物淋滤去除农用污泥中重金属的效果及工艺

污水处理厂污泥中的重金属含量高是污泥农用的主要障碍。该文针对天津污水处理厂污泥含铜量高的特性,分别以硫酸亚铁和硫粉作为培养基进行生物淋滤对比试验,前者对铜的去除率远远高于后者。以硫酸亚铁作为培养基,研究了投配比、接种污泥量、pH值和温度对污泥中重金属去除效果的影响。结果表明,在硫酸亚铁投配比为10 g/L、污泥接种量为20%、温度为28℃、淋滤时间为4 d时,污泥中重金属Cu、Pb、Cr、Ni、Zn和Cd的去除率分别为89%、38%、61%、76%、72%和57%,其相应残余量分别为116、62.5、98、22、174、1.1 mg/kg。在7～28℃范围内,温度越高,氧化亚铁硫杆菌活性越高,生物淋滤时间越短;28℃和35℃下氧化亚铁硫杆菌活性基本相同。以硫酸亚铁为培养基淋滤处理后污泥中重金属的含量可满足《农用污泥中污染物控制标准》(GB4284-1984)。     

Adsorption behavior of heavy metals on biomaterials

We have investigated adsorption of Cd(II) and Pb(II) at pH 2-6.7 onto the biomaterials chitosan, coffee, green tea, tea, yuzu, aloe, and Japanese coarse tea, and onto the inorganic adsorbents, activated carbon and zeolite. High adsorptive capabilities were observed for all of the biomaterials at pH 4 and 6.7. In the adsorption of Cd(II), blend coffee, tea, green tea, and coarse tea have comparable loading capacities to activated carbon and zeolite. Although activated carbon, zeolite, and chitosan are utilized in a variety of fields such as wastewater treatment, chemical and metallurgical engineering, and analytical chemistry, these adsorbents are costly. On the other hand, processing of the test biomaterials was inexpensive, and all the biomaterials except for chitosan were able to adsorb large amounts of Pb(II) and Cd(II) ions after a convenient pretreatment of washing with water followed by drying. The high adsorption capability of the biomaterials prepared from plant materials is promising in the development of a novel, low-cost adsorbent. From these results, it is concluded that heavy metal removal using biomaterials would be an effective method for the economic treatment of wastewater. The proposed adsorption method was applied to the determination of amounts of Cd(II) and Pb(II) in water samples.     

Influence of carbonate on the reaction of heavy metals in soils

The reaction of Cu, Zn and Cd with soils with carbonate contents ranging from 0 to 75 mg g⁻¹ was studied before and after removal of soil carbonates with acetate buffer at pH 5. Treatment with acetate buffer caused a strong decrease in metal retention by those soils containing carbonates, although if no carbonate was originally present, the treatment caused little effect or even an increase in the amounts sorbed. Before the treatment, adsorption of increasing amounts of Cu and Zn was accompanied by a continuous increase in Ca + Mg released, and those soils containing carbonate released Ca + Mg in excess of their exchangeable amounts, due to dissolution of carbonates and/or penetration of the heavy metal into the carbonate structure. It is suggested that Cu was preferentially retained by the treated soils through precipitation of Cu oxide, and by adsorption on the soil carbonates in the case of the original samples. Zn was removed from the solution by the original carbonate soils through formation of ZnCO₃. Treated soils were likely to retain Zn by cation exchange and/or adsorption. Adsorption was probably the main process involved in retention of Cd. In all cases pH was the master variable in controlling the extent and probably the nature of the reaction.     

Immobilization of heavy metals in soils by the application of bauxite residues: pot experiments under field conditions

In previous greenhouse experiments red mud, a residue of the alumina industry, was identified as effective amendment for in situ fixation of heavy metals. In the present study, we further evaluated the efficiency and potential drawbacks of red mud in an outdoor pot experiment. Application of 5 % (w/w) red mud (RM) should reveal possible drawbacks of red mud due to indigenous pollutants such as As, Cr, and V. Three soils from arable land in Lower Austria named Untertiefenbach (U) (Eutric Cambisol), Weyersdorf (W) (Dystric Cambisol), and Reisenberg (R) (Calcic Chernozem) were spiked with Cd, Zn, Cu, Ni, and V at two concentration levels in 1987, two soils originate from long‐term industrially polluted sites, located in Carinthia (Arnoldstein – Rendzic Leptosol; Zn, Cd, and Pb) and Tyrol (Brixlegg – Dystric Fluvisol; Cu, Zn). Zea mays was cultivated in pots for three months in outdoor conditions. Extraction with 1 M NH₄NO₃ was used to assess the influence of RM on the labile metals. Lability of Cd, Zn, Ni, and Pb was reduced upon RM treatment on a sandy soil up to 91 %, 94 %, 71 %, and 83 % of the control, respectively. Metal accumulation in shoots was reduced for Cd and Zn up to 54 % and for Ni up to 75 % (soil W), but not for Pb (soil A). Addition of RM (5 % w/w) increased the total As, Cr, and V concentrations in soils by 5, 20, and 50 mg kg^–1, respectively. Whereas the lability of Cr was not affected, 1 M NH₄NO₃‐extractable As and V exceeded the trigger value for water quality according to Prüeß (1994). Lability of Cu increased upon RM application, especially on the Cu polluted industrial soil (B), while Cu toxicity appeared to be reduced as indicated by the higher corn biomass production. Red mud holds promise as soil amendment in terms of reduction Cd, Zn, and Ni bioavailability. However, at additions as high as 5 % (w/w) large As, Cr, and V concentrations of this material may limit its application.     

煤矸石山重金属元素研究进展

对煤矸石及其周围土壤、水体、大气,以及煤矸石山上植物体中重金属元素的有关研究分析表明1)我国大多数矿区煤矸石属于普通固体废弃物,重金属元素超标倍数不大;2)煤矸石山对周围土壤、水体、大气影响较小,但其本身不宜生产具有食用价值的植物产品;3)煤矸石植被恢复后,大多数植物体内重金属元素含量超过蔬菜限量物质指标.     

扬州市土壤重金属含量的调查

对全市385个土样分析结果表明,扬州市耕地土壤总体是清洁的,全市89 35%的土壤属于清洁地范围(综合污染指数≤0 7),7 53%的土壤属尚清洁范围(综合污染指数0 7～1 0之间),3 12%的土壤属轻度污染(综合污染指数1 0～2 0之间)。全市土壤重金属污染的顺序是Hg>Cr>As>Cu>Pb>Cd,各地区中,以邗江区土壤重金属含量相对较高。     

The influence of technogenic and natural factors on the content of heavy metals in soils of the Middle CisUrals region: The town of Chusovoi and its suburbs

The content of heavy metals in the soils of the Middle CisUrals (the town of Chusovoi and its vicinities) is controlled by both natural and technogenic factors. The enrichment of the parent rocks in Cr, Pb, Zn, and Cu, which influences the chemical composition of the soils, is the most important among the natural factors. Among the other natural factors, the gleying and washing of the alluvial soils with flood water are significant. The technogenic contamination of the urban soils reaches its maximum in the technozems, where the content of Cu, Zn, Pb, and Cr exceeds their clarkes by 4–8 times. The index of technogeneity (the share of technogenic metals referring to their total content) is high for the bulk of metals in technozems, in particular, ranging within 36–97%. The technogeneity sequence is the following for the urban soils: Cr > Zn = Mn > Pb > Cu > Fe. The soil contamination with metals is confined to the depression where the metallurgical plant is operating, and it significantly falls already at a distance of 2–3 km in the settlements located at higher topographic positions.     

Assessment of the migration of heavy metals in soils

Qualitative and quantitative studies of the kinetics and dynamics of technogenic migration of heavy metals (HMs) have been performed in laboratory experiments. It is shown that the redistribution of HMs applied into soils in neutral form has an impulsive pattern. Soil texture does not have a decisive influence on the migration capacity of metals. An important feature of the technogenic migration of HMs is the effect of the polymetallic contamination, upon which the migration capacity of a set of heavy metals is higher than that of separate metal compounds. An index characterizing the ratio of absolute values of migration rates of ionic forms of metals estimated from electrical conductivity values to the rate of infiltration of the soil solution (v_m/v_f) is suggested to estimate the kinetics of HM migration in soils.     

The effect of heavy metals and other pollutants on the sediments of Onondaga Lake

Physical and chemical characterization of the recent sediments of Onondaga Lake indicate significant pollution based alterations to the system.²¹⁰Pb data depict an extremely high sedimentation rate within the consolidated layers (5 to 9 cm yr^?1), that has resulted largely from the loading of the Lake with industrially derived Ca. A further alteration of the sedimentary system is the very extensive flocculent layer (up to 2.5 m deep) between the overlaying water and the consolidated sediments. The chemistry of the sediments, though not unusual in dominant component makeup for a hardwater lake, is characterized by very severe heavy metal and Fe contamination that has resulted from culturally derived loadings. Heavy metals and P are concentrated within the upper flocculent strata. Indirect evidence is presented for the upward vertical migration of heavy metals within the sedimentary system.