Biosorption of lead by cotton shells powder: Characterization and equilibrium modeling study

Lead (Pb) is a toxic heavy metal causing serious health risks to humans and animals. In the present study, cotton (Gossypium hirsutum L.) shells powder was used as adsorbent for the treatment of synthetic Pb-contaminated water. The batch scale biosorption capacity of cotton shells powder was evaluated to study the effects of Pb concentrations, adsorbent doses and contact time at constant pH (6) and temperature (25?°C). Results revealed that sorption of Pb increased (q?=?0.09–9.60?mg/g) with increasing Pb concentration (1–15?mg/L) and contact time (15–90?min) while decreasing adsorbent dose (1–0.1?g/100?mL). The maximum Pb removal (90%) was achieved at Pb concentration (1?mg/L), contact time (90?min) and adsorbent dose (1?g/100?mL). Freundlich isotherm model proved best fit for Pb sorption (R²?=?0.99). The cotton shells powder has microporous structure confirmed by SEM, and has BET surface area (45 m²/g) and pore size (2.3 µm). These surface moieties along with various functional groups (C-H, C-O, C=O, O-H, S=O) confirmed by FTIR analysis might involve in Pb removal by complexation and ion exchange mechanisms. The cotton shells powder biomass could be considered as promising adsorbent for the removal of Pb from contaminated water.     

利用乙二胺四乙酸淋洗修复重金属污染的土壤及其动力学

通过室内模拟试验,采用振荡淋洗的方法研究了乙二胺四乙酸(EDTA)浓度、pH、淋洗时间对重金属去除效果的影响.利用一级反应动力学模型对试验数据进行拟合,并测定了EDTA处理前后土壤中重金属形态的变化.结果表明,EDTA溶液在浓度为0.1 mol·L^-1、pH 7、淋洗时间1 d的条件下能达到对污染土壤重金属的最大去除率,去除率分别为Cd 89.14%、Pb 34.78%、Cu 14.96%、Zn 45.14%.模型拟合结果表明,Cd的质量转移系数最大,其次是Zn、Pb和Cu.说明在土壤淋洗过程中,Cd和Zn最先达到质量转移的平衡状态,然后是Pb和Cu.形态分级结果表明,EDTA能有效地去除交换态、碳酸盐结合态和氧化物结合态重金属,而对有机态和残余态部分重金属作用效果不明显.     

Phytoremediation of landfill leachate waste contaminants through floating bed technique using water hyacinth and water lettuce

Abstract

In the present study, the effectiveness of water hyacinth and water lettuce was tested for the phytoremediation of landfill leachate for the period of 15?days. Fifteen plastic containers were used in experimental setup where aquatic plants were fitted as a floating bed with the help of thermo-pole sheet. It was observed that both plants significantly (p?<?0.05/p?<?0.01/p?<?0.001) reduce the physicochemical parameters pH, TDS, BOD, COD and heavy metals like Zn, Pb, Fe, Cu and Ni from landfill leachate. Maximum reduction in these parameters was obtained at 50% and 75% landfill leachate treatment and their removal rate gradually increased from day 3 to day 15 of the experiment. The maximum removal rate for heavy metals such as for Zn (80–90%), Fe (83–87%) and Pb (76–84%) was attained by Eichhornia crassipes and Pistia stratiotes. Value of bioconcentration and translocation factor was less than 1 which indicates the low transport of heavy metals from roots to the above-ground parts of the plants. Both these plants accumulate heavy metals inside their body without showing much reduction in growth and showing tolerance to all the present metals. Therefore, results obtained from the study suggest that these aquatic plants are suitable candidate for the removal of pollution load from landfill leachate.     

碳酸钙对土壤镉吸附及解吸的影响

采用等温吸附法,并以1mol/L KNO3进行解吸试验,研究CaCO3对3种土壤镉吸附和解吸的影响。结果表明,3种土壤的原状土样对镉吸附总趋势为：栗钙土＞棕壤＞淋溶褐土,均符合Langmuir方程、Frenudlich方程和Temink方程,其中以Freumdlich方程最佳。镉的专性吸附量表现为栗钙土＞淋溶褐土＞棕壤。添加CaCO3使3种土壤中镉的吸附量增加,增加幅度棕壤为4％－11％,淋溶褐土2％－11％,栗钙土2％－8％。外界加入的镉浓度越高,增加幅度越大。Freundlich方程（lgX=lgK lgC/n）拟合的参数结果表明：加入CaCO3后,K和n值均下降;Langmuir方程中镉最大吸附值增加,吸附平均常数减小。可以推测,CaCO3的存在之所以能够使土壤体系吸附镉能力增加,除CaCO3本身的吸附作用增加,吸附平衡常数减小。可以推测,CaCO3的存在之所以能够使土壤体系吸附镉能力增加,除CaCO3本身的吸附作用外,还可能影响反应体系的平衡系数。加入CaCO3,土壤对镉的专性吸附明显增加,尤其以棕壤专性吸附的镉最多,淋溶褐土其次,而栗钙土增加较少,栗钙土去除CaCO3后,镉的吸附减少了2.0%-26.0%,土壤专性吸附的镉减少4.0%-38.2%。3种土壤镉的解吸能力表现为：棕壤＞淋溶褐土＞栗钙土。添加CaCO3,土壤镉的解吸量下降。去除CaCO3后,栗钙土匐解吸量明显增加。     

Removal of Pb2+ from aqueous system by live Oscillatoria laete-virens (Crouan and Crouan) Gomont isolated from industrial effluents

Cyanobacteria have been found to be potential biosorbents of metal ions from waste water. The Pb(2+) removal capacity of growing cells of indigenous cyanobacterium Oscillatoria laete-virens (Crouan and Crouan) Gomont was studied under batch experiments and it was found capable of removing Pb(2+) of lower concentrations (below 100?mg L(-1)). The effects of different concentrations of Pb(2+), on the growth rate of alga were also evaluated. The research parameters include the pH of the solution, contact time, initial concentration of Pb(2+), and culture density. Of the parameters studied, the pH of the solution was found to be the most crucial. The removal of Pb(2+) peaked at an initial pH of 5. The data obtained from the equilibrium experiments were found well fitting with the Langmuir isotherm with a maximum sorptive capacity (q (max)) of 20.36?mg?g(-1), indicating a good biosorbtive potential of growing cells. This was confirmed using scanning electron microscope and energy dispersive X-ray analysis, which showed the adsorption of lead on the surface of the cell. The species could tolerate a concentration as high as 60?mg L(-1) of Pb(2+). It was observed that the removal obeyed the pseudo-second-order kinetics. The percentage removal was found to decrease with increasing metal concentration, from 10 to 100?mg L(-1). FTIR analysis indicates the involvement of amino, carboxylic and amide groups in the sorption process. Among the desorbing agents evaluated, an efficient recovery of 90.2?% was achieved by HCl, in 24?h. Thus Oscillatoria laete-virens (Crouan and Crouan) Gomont seems to be a promising metal biosorbent for the treatment of Pb(2+), in waste waters.     

Studies on the preparation and properties of ribonucleoprotein particles from rat liver nuclei

Ribonucleoprotein particles of 38 S were extracted from rat liver nuclei with isotonic salt buffer under concomitant sonication. The fate of the endogeneous nuclear RNAases assayed with poly(A), high molecular weight yeast RNA and rapidly labeled hnRNA was followed during the preparation of 38-S nuclear ribonucleoprotein (nRNP) particles. Essentially all the RNAase activity could be removed from the particle preparation. The effect of synthetic RNAase inhibitors on the nRNP particles was studied. Upon extraction of nuclei with 0.14 M NaCl, approximately 38% of the total nuclear radioactivity was found in the 38-S nRNP particles. By two successive extractions of the remaining chromatin with either isotonic or 0.22 and 0.3 M NaCl, an additional 25 and 9% of rapidly labeled hnRNA of 38 S particle were dissociated from chromatin, respectively. The chromatin components, DNA, nonhistone proteins, histones and RNA were determined after successive salt extractions. Particularly alterations in the nonhistone proteins and RNA were found. The protein patterns upon SDS-acrylamide gel electrophoresis of the salt-extracted chromatin preparations were compared with those of the 38-S nRNP particles. Particularly proteins in the molecular weight range of 32 000-43 000 were dissociated from chromatin after treatment with 0.22 or 0.3 M NaCl.     

Phytoremediation of Metal-Contaminated Soil in Temperate Humid Regions of British Columbia,Canada

The suitability of five plant species was studied for phytoextraction and phytostabilisation in a region with temperate maritime climate of coastal British Columbia, Canada. Pot experiments were conducted using Lolium perenne L (perennial rye grass), Festuca rubra L (creeping red fescue), Helianthus annuus L (sunflower), Poa pratensis L (Kentucky bluegrass) and Brassica napus L (rape) in soils treated with three different metal (Cu, Pb, Mn, and Zn) concentrations. The bio-metric characters of plants in soils with multiple-metal contaminations, their metal accumulation characteristics, translocation properties and metal removal were assessed at different stages of plant growth, 90 and 120 DAS (days after sowing). Lolium was found to be suitable for the phytostabilisation of Cu and Pb, Festuca for Mn and Poa for Zn. Metal removal was higher at 120 than at 90 days after sowing, and metals concentrated more in the underground tissues with less translocation to the aboveground parts. Bioconcentration factors indicate that Festuca had the highest accumulation for Cu, Helianthus for Pb and Zn and Poa for Mn.     

Characterization of plant growth-promoting Bacillus edaphicus NBT and its effect on lead uptake by Indian mustard in a lead-amended soil

The plant growth promotion characteristics of a heavy-metal-resistant strain of Bacillus edaphicus NBT was characterized. The strain was also evaluated for promoting plant growth and lead (Pb) uptake of Brassica juncea L. Czern (Indian mustard) in soil artificially contaminated with 0, 400, and 800 mg Pb.kg-1 soil. Atomic absorption spectrometer analysis demonstrated that strain NBT could release water-soluble Pb from lead carbonate in the solution. Strain NBT had the capacity to produce indole acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylate deaminase. Low and high Pb treatments significantly decreased the growth of Indian mustard. Inoculation with strain NBT was found to increase root dry mass (ranging from 16% to 22%) and above-ground tissue dry mass (ranging from 24% to 30%) of Indian mustard in the Pb-amended soil. Strain NBT was able to mobilize Pb efficiently in plants in Pb-amended soil. In the soil treated with 400 and 800 mg Pb.kg-1 soil, the increase in Pb uptake varied from 18% to 46% in live bacterium-inoculated Indian mustard plants compared with dead bacterium-inoculated control. The strain was also able to colonize and develop in the rhizosphere soil of Indian mustard after root inoculation.     

The effect of calcium on the treatment of fresh leachate in an expanded granular sludge bed bioreactor

This research investigated the calcium effect on the anaerobic treatment of fresh leachate in an expanded granular sludge bed (EGSB) bioreactor under mesophilic conditions. The observations show that the bioreactor, inoculated with anaerobic granular sludge, can be started up only in about 40 days for the treatment of calcium-containing fresh leachate with chemical oxygen demand (COD) removal efficiency above 90% and organic loading rate up to 72.84 kg COD/m³ day. The calcium accumulation onto the granules was monotonically related to the calcium concentration, accounting for 17-18 wt.% of Ca in the suspended solid in the form of calcium carbonate, phosphates/phosphonates and carboxylates. The mineral formation significantly increased the granule settling velocity (by ∼50%) and the suspended solid concentration (by ∼100%). However, the effect of calcium precipitation on the specific methanogenic activity and the CH₄ production rate was complex, first positive during the start-up but later on negative.     

Biodesulphurization of coal: effect of pulse feeding and leachate recycle

Biodesulphurization of coal was carried out under four modes of operation namely: conventional batch, constant volume pulse feeding (CVPF), increasing volume pulse feeding (IVPF) and leachate recycle. The effects of different pulse feeding strategies and leachate (product) recycle on biological performance were studied and compared with a conventional batch process. The sulphur removal rates for each of the four processes were 0.04 g/day (batch), 0.09 g/day (CVPF), 0.19 g/day (IVPF) and 0.05 g/day (leachate recycle). The values of iron solubilization rate (batch-83 μg/ml/day; CVPF-136 μg/ml/day; IVPF-198 μg/ml/day; leachate recycle-133 μg/ml/day) also followed the same trend. The percentage sulphur removal on the 30th day using batch, CVPF, IVPF and leachate recycle processes was 72%, 93%, 97% and 90%, respectively. IVPF was found to be the best operational strategy for biodesulphurization process at enhanced rates for longer duration.     

Removal of Heavy Metals from Contaminated Soil and Sediments Using the Biosurfactant Surfactin

The feasibility of using a biodegradable surfactant, surfactin from Bacillus subtilis, for the removal of heavy metals from a contaminated soil (890?mg/kg zinc, 420?mg/kg copper, 12.6% oil and grease) and sediments (110?mg/kg copper, 3300?mg/kg zinc) was evaluated. Results showed that after one and five batch washings of the soil, 25 and 70% of the copper, 6 and 25% of the zinc, and 5 and 15% of the cadmium could be removed by 0.1% surfactin with 1% NaOH, respectively. From the sediment, 15% of the copper and 6% of the zinc could be removed after a single washing with 0.25% surfactin/1% NaOH. The geochemical speciation of the heavy metals among the exchangeable, oxide, carbonate, organic, and residual fractions was determined by selective sequential extraction procedure. For both matrices, the exchangeable fractions were minimal, while the carbonate and the oxide fractions accounted for over 90% of the zinc present and the organic fraction constituted over 70% of the copper. Results after washing indicated that surfactin with NaOH could remove copper from the organic fraction, zinc from the oxide, and cadmium from the carbonate fractions. The residual fraction remained untouched. These experiments indicate that the sequential extraction studies could be useful in designing soil-washing procedures.     

Effects of potassium carbonate as an alternative road de-icer to sodium chloride on soil chemical properties

The effect of potassium carbonate on soil chemical characteristics was compared with that of the most common de‐icer, sodium chloride, in a 4‐yr outdoor pot experiment with poplar and lime trees. Soil pH was raised more by K₂CO₃ than by NaCl. Potassium carbonate increased the electrical conductivity mainly in the upper soil layers. When K₂CO₃ was applied at an average annual dose of 154 g m^?2, only the water‐soluble fractions of calcium and magnesium were affected. At an average annual dose of 617 g m^?2, total potassium increased by 33% and calcium was displaced from the exchange sites. Calcium saturation was reduced from 85% of the cation exchange capacity in the untreated control to 69% in the higher dose K₂CO₃ treatment and to 75% in the NaCl treatment. The results show that the negative impact of K₂CO₃ on soil chemical and osmotic properties is as high as that of NaCl. For plants, however, potassium carbonate in contrast to chloride is not toxic and, applied in moderate doses, may even remedy potassium deficiencies in roadside trees.     

渗滤液溶解性有机物对土壤Cd、Pb有效性的影响

在Cd、Pb污染土壤中,通过生物盆栽试验,研究了2种不同填埋年龄的垃圾渗滤液溶解性有机物(DOM)对黑麦草生长的影响及其对重金属Cd、Pb吸收的影响.鲜样、水阁样分别为填埋年龄0和12年的垃圾渗滤液.结果表明,垃圾渗滤液DOM施入土壤,残留在土壤中的DOM平均浓度为对照的1.39倍(鲜样)和1.47倍(水阁样).2种垃圾渗滤液DOM处理的土壤水溶态Cd、Pb和交换态Cd、Pb均在前期呈波动变化,到后期则上升.在Cd污染土壤中,鲜样和水阁样垃圾渗滤液DOM处理土壤水溶态Cd、交换态Cd分别高出对照37.44%、4.81%,48.97%、14.94%;在Pb污染土壤中,鲜样和水阁样垃圾渗滤液DOM处理土壤水溶态Pb、交换态Pb分别高出对照8.56%、7.22%,18.99%、11.47%.鲜样和水阁样垃圾渗滤液DOM处理黑麦草总Cd浓度分别高于对照19.59%和104.4%,总Pb浓度分别高36.03%和44.66%;但两处理的黑麦草总生物量下降14.03%～52.24%.因此,垃圾渗滤液DOM进入污染土壤后,有利于土壤重金属生物有效性的提高和植物体内重金属的累积,却抑制植物的生长, 尤以填埋年龄长的垃圾渗滤液DOM影响更大.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.     

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.     

Leaching Behavior of Heavy Metals and Transformation of Their Speciation in Polluted Soil Receiving Simulated Acid Rain

Heavy metals that leach from contaminated soils under acid rain are of increasing concern. In this study, simulated acid rain (SAR) was pumped through columns of artificially contaminated purple soil. Column leaching tests and sequential extraction were conducted for the heavy metals Cu, Pb, Cd, and Zn to determine the extent of their leaching as well as to examine the transformation of their speciation in the artificially contaminated soil columns. Results showed that the maximum leachate concentrations of Cu, Pb, Cd, and Zn were less than those specified in the Chinese Quality Standards for Groundwater (Grade IV), thereby suggesting that the heavy metals that leached from the polluted purple soil receiving acid rain may not pose as risks to water quality. Most of the Pb and Cd leachate concentrations were below their detection limits. By contrast, higher Cu and Zn leachate concentrations were found because they were released by the soil in larger amounts as compared with those of Pb and Cd. The differences in the Cu and Zn leachate concentrations between the controls (SAR at pH 5.6) and the treatments (SAR at pH 3.0 and 4.5) were significant. Similar trends were observed in the total leached amounts of Cu and Zn. The proportions of Cu, Pb, Cd, and Zn in the EXC and OX fractions were generally increased after the leaching experiment at three pH levels, whereas those of the RES, OM, and CAR fractions were slightly decreased. Acid rain favors the leaching of heavy metals from the contaminated purple soil and makes the heavy metal fractions become more labile. Moreover, a pH decrease from 5.6 to 3.0 significantly enhanced such effects.     

Effects of a Combined Amendment on Pb,Cd, and As Availability and Accumulation in Rice Planted in Contaminated Paddy Soil

The objectives of the present study were to investigate the mitigation of lead (Pb), cadmium (Cd), and arsenic (As) in a multi-metal contaminated soil and their accumulation in rice plants (Oryza sativa L., cv II You 93) using a combined amendment (CMF, calcium carbonate + metakaolin + fused calcium–magnesium phosphate fertilizer). The results showed that application of CMF was effective in reducing the acid-extractable concentrations of soil Pb and Cd. The exchangeable concentrations of soil As showed an initial decrease followed by a gradual increase. The application of 0.2% CMF notably reduced the concentrations of Pb, Cd, and As in brown rice by 46.5%, 43.6%, and 32.0%, respectively. The concentration of As in brown rice was 0.179 mg kg^?1 at 0.2% CMF, which met the maximum levels of contaminants in foods of China (MLs) (the ML of Pb, Cd, and As is 0.2 mg kg^?1 according to the China national standard GB 2762-2012). At 1.6% CMF, the concentrations of Pb and Cd in brown rice were 0.002 and 0.185 mg kg^?1, respectively, i.e., reductions of 99.6% and 74.1%, and these values also fell within the MLs.     

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb_total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56?mg Pb?ha^?1 for TML and 222?kg Pb?ha^?1 for Pb_total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb_total (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall?+?litterfall fluxes, amounted to 3.7?mg Pb?ha^?1 year^?1 for TML and 52?g Pb?ha^?1 year^?1 for Pb_total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb_total in wet precipitation were: fog?>?throughfall?>?bulk precipitation. The annual fluxes with runoff from the catchment was 0.5?mg Pb?ha^?1 year^?1 for TML and 2.8?g Pb?ha^?1 year^?1 for Pb_total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t) of 33.5 days. The degradation of TML in Fen (t?=?421 days) and in the mineral soil (Bw-C horizon, t?=?612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen?>?Oa?>?A?≥?Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb_total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pb_total. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.     

Bio-Acidification and Leaching of Metals,Nitrogen, and Phosphorus from Soil and Sludge Mixtures

Soil and wastewater treatment sludge are commonly brought together in mixtures for a variety of beneficial purposes. The mixtures contain bioacidifying (i.e., sulfur-oxidizing) microorganisms that can easily be activated through providing the appropriate substrate and environmental conditions. In this study, contaminated soil and sludge mixtures were subjected to controlled bio-acidification and the impacts of the process on the partitioning of heavy metals, nitrogen, and phosphorus were examined. Three successive bio-acidification cycles resulted in significant leaching of metals from sludge. The leaching results, expressed as fraction of total mass of metals in the sludge, averaged 67% for Cr, 96% for Ni, 24% for Zn; 16% for Cu; 23% for Cd; and 96% for Pb. Bio-acidification of the sludge also converted 28 to 45% of the organic nitrogen into ammonia and increased the soluble orthophosphates fraction of total phosphorus by approximately 18 to 20%. Bio-acidification also resulted in significant metals leaching from the contaminated soils in the soil/sludge mixtures. Soil/sludge mixtures were prepared using six soil particle sizes (less than 0.075?mm to 2.38?mm) contaminated with 22,500?mg/kg Zn, 14,000?mg/kg Pb, 1500?mg/kg Cr, 9500?mg/kg Cu, 1000?mg/kg Ni, and 1000?mg/kg Cd. The addition of metals to the soil inhibited the sulfur-oxidizing microorganisms, preventing bio-acidification in the mixtures containing 4 to 50?g soil in 130?ml sludge, and considerably slowing bio-acidification in the mixtures containing 1 to 3?g soil. Using a mixture that contained 2-g soil samples, three successive bio-acidification cycles resulted in significant cumulative metals leaching results. The leaching results, expressed as percentage of the mass of metals added to the soil, were in the range of 56 to 98% for Cr, 77 to 95% for Zn, 33 to 66% for Ni, 64 to 82% for Cu, and 10 to 33% for Pb, with the higher results in each range belonging to the larger size soil particles. On the other hand, only Cr was leached in neutralized soil samples. The results confirmed the potential for inhibition of the sulfur-oxidizing microorganisms and bio-acidification in contaminated soil/sludge mixtures, and the significant impacts of bio-acidification on the mobility of metals, nitrogen, and phosphorus. In addition, the results confirmed the potential for using controlled bioacidification for removing heavy metals from contaminated soil using the indigenous sulfur oxidizing microorganisms in sludge.     

Modeling of heavy metals removal from municipal landfill leachate using living biomass of water hyacinth

Water Hyacinth, Eichhornia crassipes, a fast-growing floating aquatic macrophyte; was used for the removal of heavy metals from a municipal landfill leachate. The leachate was spiked with different mixtures of five heavy metals (Cd, Cr, Cu, Pb and Ni), at a range of concentrations to cover the ranges reported in literature. The initial concentrations of the total heavy metals in leachate ranged from 0.06 to 5.5 mequiv L(-1). All experiments were carried out in batch reactors in a greenhouse environment. The water hyacinth plants showed a very promising ability to remove and accumulate these metals from the leachate (24% to 80% removal of total heavy metals). Generally, the reduction in concentration of total heavy metals followed two distinct patterns, a rapid initial decrease followed by a slower decrease. An exponential mathematical model was established to estimate the remaining concentration of total heavy metals in the leachate over time for the rapid initial decrease. Also, a linear relationship was established to estimate the concentration of total heavy metals over time for the slower decrease. In addition, Langmuir and Freundlich isotherms were applied to the observed data and the constants of each isotherm were obtained.