Accumulation and bioavailability of heavy metals in a soil-wheat/maize system with long-term sewage sludge amendments

A long-term field experiment was carried out with a wheat-maize rotation system to investigate the accumulation and bioavailability of heavy metals in a calcareous soil at different rates of sewage sludge amendment. There are significant linear correlations between the contents of Hg, Zn, Cu, Pb, and Cd in soil and sewage sludge amendment rates. By increasing 1 ton of applied sludge per hectare per year in soil, the contents of Hg, Zn, Cu, Pb, and Cd in soil increased by 6.20, 619, 92.9, 49.2, and 0.500 μg kg–1, respectively. For Hg, sewage sludge could be safely applied to the soil for 18 years at an application rate of 7.5 t ha–1 before content exceeded the soil environmental quality standards in China(1 mg kg–1). The safe application period for Zn is 51 years and is even longer for other heavy metals(112 years for Cu, 224 years for Cd, and 902 years for Pb) at an application rate of 7.5 t ha–1 sewage sludge. The contents of Zn and Ni in wheat grains and Zn, Cu, and Cr in maize grains increased linearly with increasing sewage sludge amendment rates. The contents of Zn, Cr, and Ni in wheat straws and Zn, Cu, and As in maize straws were positively correlated with sewage sludge amendment rates, while the content of Cu in wheat straws and Cr in maize straws showed the opposite trend. The bioconcentration factors of the heavy metals in wheat and maize grains were found to be in the order of Zn>Cu>Cd>Hg>Cr=Ni>Pb>As. Furthermore, the bioconcentration factors of heavy metals in wheat were greater than those in maize, indicating that wheat is more sensitive than maize as an indicator plant. These results will be helpful in developing the critical loads for sewage sludge amendment in calcareous soils.

Simulated Leaching Research on the Effects of Sewage Sludge on Nutrients and Heavy Metals in Aeolian Sandy Soil

[ Objective] The study aims at discussing the feasibility of urban sewage sludge applied to desertification forestland. [ Method] Through the simulated leaching test, the effects of sewage sludge application on the content of nutrients and heavy metals in aeolian sandy soil were ana- lyzed. [ Result] After the simulated leaching with sewage sludge, the contents of total nitrogen （TN）, total phosphorus （TP）, available nitrogen （AN） and available phosphorus （AP） in each layer of aeolian sandy soil increased significantly, and the increase in 0 -20 cm soil was more signifi- cant than that in 20 -40 and 40 -60 cm soil. Meanwhile, the content of each heavy metal in 0 -20 cm soil rose significantly, while the increase was small in 40 -60 cm soil. In addition, after the application of sewage sludge, the Nemrew Index of aeolian sandy soil was 0.67, lower than the na- tional soil quality standard of forestland （0.70）, and the short-time application of sewage sludge to sandy soil did not cause serious pollution. How- ever, if sewage sludge has been applied to aeolian sandy soil for a long term, the potential hazard of heavy metals （especially Cd） caused by loneterm accumulation should be paid more attention to.

Effect of substrate concentration on the bioleaching of heavy metals from sewage sludge

The effect of elemental sulfur concentration on bioleaching of Cu, Zn and Pb and loss of fertilizer value from sewage sludge was investigated in flasks by batch experiments. The results showed that the ultimate pH of sludges with 3—5 g/L of sulfur added was about 1.3 and the production of SO 2- 4 had good correlation with the elemental sulfur concentration. The sensitivity of removal efficiency of metals to sulfur concentration was: Pb>Cu>Zn. The sulfur concentration except for 3—5 g/L had significant effect on the solubilization of Cu, Pb and Zn. The highest solubilization efficiency for sludge with 3 g/L of sulfur was 87.86% for Cu, 32.72% for Pb and 92.14% for Zn, which could make the treated sludge easily meet the metal limitations for land application. The sulfur concentration of 3 g/L was enough for the solubilization of all three heavy metals. The influence of sulfur concentration on solubilization of total nitrogen and potassium from sludge was negligible, but that on solublization of total phosphorus was of great importance. The loss of nitrogen, phosphorus and potassium of sludge with 3 g/L of sulfur by bioleaching was 38.2%, 52.1% and 42.8% respectively, and the sludge still remained satisfactory fertilizer value after bioleaching.

Implication of sewage sludge increased application rates on soil fertility and heavy metals contamination risk

This paper aims to assess soil fertility and risk contamination parameters in response to increased amendment rates of sewage sludge application,under semi-arid climatic conditions of Morocco,using two soil textures:soil A(clay-silty)and soil B(sandy-clay)over two years.To this end,sewage sludge and soils treatments physicochemical parameters,heavy metals content,degree of pollution and associated risks were evaluated and compared to controlled soils.The results showed that all studied parameters changed significantly(p<0.05)in a dose-dependent manner for both soils compared to the untreated control soils.Indeed,there were significant increase in organic matter(OM),total organic carbon(TOC)and nutrients content(N,P and K)of both sols as a response to increased sewage sludge amendment rates.Overall,sewage sludge application showed a positive agronomic potential for both soil and plant.However,there were concern about some heavy metals contamination risks,the results showed a gradual increase of heavy metals concentration in this order:Cu>Pb>Zn>Ni>Cd>Cr.Nevertheless,their concentrations were below the critical values established by the European Union for the agronomic use of soil.The obtained results of assessed parameters indicating SS degree of pollution and associated risks showed a low to a moderate contamination risks of heavy metals.Accordingly,environmental risks of sewage sludge application will be related to increase of heavy metals mainly in a long-term agricultural reuse.Thus,optimal management of sewage sludge application is recommended to ensure sustainability and benefits at the same time to master the contamination risks.

Comparison of Bioleaching of Heavy Metals from Sewage Sludge of Different Solid Concentrations Using Two Inocula

Two 10%(v/v) different inocula, iron-oxidizing bacteria and sulfur-oxidizing bacteria, were used to investigate the bioleaching of heavy metals from sewage sludge with 10-40 g/L sludge concentration in the batch experiment. The results demonstrated that most of bioleaching rates of Zn and Cu achieved above 80% and 60%, respectively, after 12 d in the sludge with different concentrations and inocula. The lower the solid concentration, the higher the removal rate of heavy metals and the quicker the removal speed in sludge. The system with iron-oxidizing bacteria had faster startup speed and was influenced by solid concentration lightly, while in the system with sulfur-oxidizing bacteria, the removal efficiency was affected by concentration seriously.

Effect of different surfactants on removal efficiency of heavy metals in sewage sludge treated by a novel method combining bio-acidification with Fenton oxidation

The aim of this work was to investigate the effect of different surfactants on the removal efficiency of heavy metals in sewage sludge treated by a method combining bio-acidification with Fenton oxidation. Four surfactants were adopted such as anionic surfactant(sodium dodecyl benzene sulfonate, SDBS), nonionic surfactants(tween-20 and tween-60) and cationic surfactant(hexadecyl trimethyl ammonium chloride, HTAC), respectively. The indigenous sulfur-oxidizing bacteria in bio-acidification phase were enriched and cultured from fresh activated sludge obtained from a wastewater treatment plant. It is shown that different surfactants exhibited distinct effect on the removal efficiency of heavy metals from sewage sludge. The nonionic surfactants,especially tween-60, promotes the solubilization of heavy metals, while the anionic and cationic surfactants hinder the removal of heavy metals. Copper is efficiently leached. The removal efficiency of cadium is relatively lower than that of Cu due to the demand for rigorous p H value. Lead is leached with a low efficiency as the formation of low soluble Pb SO4 precipitates.

Characteristics of heavy metal accumulation on fly ash-and sewage sludge-amended calcific soil

Land disposal of fly ash(FA)and sewage sludge(SS)is a major problem due largely to their potentially harmful constituents.In this paper,a potting experiment was performed to evaluate the effects on the plant growth and to discuss in particular the potential hazard to soils and plants according to the characteristics of heavy metal accumulation and migration when FA and SS are used as the amendments of calcific soil in a limestone mining area. The results showed that the application of FA-SS mixture is capable of accelerating the growth of plants and improving the biomass production at either 1:1 or 1:2 FA-SS mixture:soil(w/w).The highest yields were obtained at 1:1(w/w)mixing ratio.When compared with the Element Background Values of Soils in China,the analysis on heavy metals indicated that the contents of Pb,Cr,Hg,Cd,As,Ni,Cu and Zn in the amended soils came up to the second-class environmental quality standards,only Hg and Cd showed significant accumulation.At the same time, though the metal concentrations in roots were higher than those for the control,the concentrations except Cu,Zn in shoots were lower.And all the heavy metal contents in the plants were substantially lower than the toxicity limits. The results indicated that the combined use of FA and SS at a rational rate of application should pose no danger to both soil and food chain based on the characteristics of the FS and SS,heavy metals and calcific soil.

Effect of Alkali Treatment on Heavy Metals Adsorption Capacity of Sewage Sludge

Sewage sludge is the promising raw material for biosorbent preparation. In this work, we evaluated the heavy metals adsorption characteristics of alkali treated sewage sludge (ATSS) by equilibrium studies. The adsorption isotherms were fitted with Langmuir and Freundlich models. Comparing with untreated sewage sludge, the total adsorption capacity (qm) of ATSS (prepared with 0.125 mol/L NaOH) for Cd, Pb, Ni, increased by 0.51, 0.70 and 0.32 mmol/g, respectively. When the NaOH concentration for ATSS preparation increased from 0.125 mol/L to 0.25 mol/L, the qm of ATSS for Pb decreased from 1.05 mmol/g to 0.84 mmol/g. However, when the NaOH concentration increased from 0.25 mol/L to 7.5 mol/L, it showed increasing trend. According to the IR spectra data, the adsorption effect of biosorbent for heavy metals was mainly due to the complexation of -N-H groups and -COOH groups.

Sewage sludge ditch for recovering heavy metals can improve crop yield and soil environmental quality

The treatment and disposal of municipal sewage sludge(MSS)is an urgent problem to be resolved in many countries.Safely using the nutrients within MSS to increase crop yield and enhance the fertility of poor soil could contribute to achieving sustainable development.An indirect use of MSS in ditches alongside Pennisetum hybridum plants was studied in field plots for 30 months and the contents of heavy metals and macronutrients were monitored in soil,sludge and plant samples.We found that the yield of P.hybridum was significantly increased by 2.39 to 2.80 times and the treated plants had higher N content compared with no sludge.In addition,the organic matter(OM)and N contents in the planted soil increased significantly compared with the initial soil.The OM content in the planted soil of the MSS treatment was 2.9 to 5.2 times higher than that with no sludge,and N increased by 2.0 to 3.8 times.However,MSS had no significant effect on the N,P and K contents in the soil at the bottom of the MSS ditch,and the content of heavy metals(Cd,Pb,Cu and Zn)were also within the safe range.Moreover,the moisture content and phytotoxicity of MSS after this indirect use were reduced and the heavy metal contents changed little,which is favorable to the further disposal of recovered MSS.Therefore,this indirect use of MSS is beneficial to agricultural production,soil quality and environmental sustainability.

Effects of Municipal Sewage Sludge on Fixation of Cr,Ni,Cu,and Zn during Co-processing of Heavy Metal-containing Waste in Cement Kilns

Cement raw meal with MSS and different heavy metals was blended to examine the fixation ratios, chemical species, and cement crystalline phases in clinkers. The results showed that blending MSS could decrease the fixation ratio of Cr, Ni, Cu, and Zn in the produced clinker by 5% to 25%. And Cr, Cu, and Zn were mainly incorporated into clinkers as metal silicates, Ni was mainly solubilized in Mg O to form magnesium nickel oxides, and the transition phases were mainly metal aluminum oxides as indicated by X-ray diffraction. The reduction of fixation ratios was likely attributed to the presence of impure elements, such as sodium and phosphorus in MSS. In addition, high concentrations（eg, 1.7 wt%） of chlorine in MSS led to metal chloride formation that could vaporize Cu, Cr, Ni, and Zn. To summarize, introducing MSS would decrease the fixation ratios of heavy metals due to the presence of impure elements, such as sodium and phosphorus and chlorine.

Mobilities and leachabilities of heavy metals in sludge with humus soil

Chemical forms of Zn, Ni, Cu, and Pb in municipal sewage sludge were investigated by adding humus soil to sludge and by performing sequential extraction procedures. In the final sludge mixtures, Zn and Ni were mainly found in Fe/Mn oxide-bound （F3） and organic matter/sulfide-bound （F4） forms. For Zn, exchangeable （F1）, carbonate-bound （F2）, and F3 forms were transformed to F4 and residual forms （F5）. For Ni, F1 and F2 forms were transformed to F1, F2, and F3 forms. Both Cu and Pb were strongly associated with the stable forms F4 and F5. For Cu, F2 and F3 forms were major contributors, while for Pb, F3 and F4 forms were major contributors to F5. Humus soil dosage and pH conditions in the sludge were strongly correlated with the forms of heavy metals. Five forms were used to evaluate metal mobilities in the initial and final sludge mixtures. The mobilities of the four heavy metals studied decreased after 28 days. The metal mobilities in the final sludge mixtures were ranked in the following order： Ni 〉 Zn 〉 Cu = Pb. Leaching tests showed that the mobilities of Zn and Ni in lower pH conditions （pH 4） were higher than those in higher pH conditions （pH 8）.

Sewage Sludge Usage in Cotton Crop: I. Influence on SoilProperties

INTRODUCTIONTheneedoftreatingsewageeffiuentstomaintainhighqualitydischargesintoreceivingwatersleadstotheproductionofappreciableamountsofsewagesludgewhichmustbedisposedinaneconomicandsafeway.Sewagesludgecontainshighamountsofelementslikenitrogen(N),pho...

Extractable Fractions of Metals in Sewage Sludges from Five Typical Urban Wastewater Treatment Plants of China

Metal content and bioavailability are often the limiting factors for application of sewage sludge in agricultural fields. Sewage sludge samples were collected from five typical urban wastewater treatment plants in China to investigate their contents and distribution of various chemical fractions of Cu, Zn, Ni, Cr, Pb and Mo by using the BCR (Community Bureau of Reference) sequential extraction procedure. The sludges contained considerable amounts of organic matter (31.8%-48.0%), total N (16.3-26.4 g kg-1) and total P (15.1-23.9 g kg-1), indicating high potential agricultural benefits of their practical applications. However, total Zn and Ni contents in the sludge exceeded the values permitted in China's control standards for pollutants in sludges from agricultural use (GB 4284-1984). The residual fraction was the predominant fraction for Mo, Ni and Cr, the oxidizable fraction was the primary fraction for Cu and Pb, and the exchangeable and reducible fractions were principal for Zn. The distribution of different chemical fractions among the sludge samples reflected differences in their physicochemical properties, especially pH. The sludge pH was negatively correlated with the percentages of reducible fraction of Cu and exchangeable fraction of Zn. The sludges from these plants might not be suitable for agricultural applications due to their high contents of Zn, Ni and Cr, as well as high potential of mobility and bioavailability of Zn.

Evolution of Heavy Metal Speciation During a Large-scale Sewage Sludge Composting

The evolution of metal species during sludge composting in aerobic reactor has been widely investigated,but little is known in large scale.In this study,the transformations of heavy metals speciation(Zn,Cu,Pb and Cd)in the process of sludge composting were studied in a bunker.Physico-chemical parameters,such as pH,moisture content(MC),organic matter(OM),humic acids(HA)and fulvic acids(FA)contents,were determined to evaluate their impacts on the redistribution of Zn,Cu,Pb and Cd in sludge compost.During the composting process,the contents of Cu,Pb,Zn and Cd in oxidizable and residual forms increased,whereas the contents of the exchangeable Cu,Pb,Zn and Cd decreased,with a slight increase in the total heavy metal contents.The contents of Cu,Zn and Cd in carbonate form and the reducible Cu,Zn and Pb falled;however,the content of Pb in carbonate formed and the reducible Cd increased.The results indicated that heavy metals(Zn,Cu,Pb and Cd)in sewage sludge could be passivated during composting process.The heavy metals speciation in the compost correlated with the physico-chemical parameters.In addition,linear regression analysis indicated that the content of mobile Pb could predict the total content of Pb.The contents of the residue fraction for Pb,Zn and Cd were decreased,but those for Ni and Cr were increased;the Cu residue fraction was almost constant.The contents of the total mobile fractions(including fractions 1-4)for Zn and Pb were significantly increased,but the increase of those for Cu and Ni were not so remarkable.There were significant degrees of correlation between heavy metal fractions and changes of some selected parameters(for example,pH,composting temperature and OM content).Only the content of the total mobile fractions for Cu could be predictable from its total content.For the prediction of the total mobile fractions of Zn,Ni,Cd and Cr,the R2 value was significantly increased by the inclusion of other variables such as pH,temperature and OM content.

Potato absorption and phytoavailability of Cd, Ni, Cu, Zn and Pb in sierozem soils amended with municipal sludge compost

Effects of sludge utilization on the mobility and phytoavailability of heavy metals in soil-plant systems have attracted broad attention in recent years. In this study, we analyzed the effects of municipal sludge compost （MSC） on the solubility and pIant uptake of Cd, Ni, Cu, Zn and Pb in a soil-potato system to explore the mobility, potato plant uptake and enrichment of these five heavy metals in sierozem soils amended with MSC through a potato cultivation trial in Lanzhou University of China in 2014. Ridge regression analysis was conducted to investigate the phytoavailability of heavy metals in amended soils. Furthermore, CaC12, CH3COONH4, CH3COOH, diethylene triamine pentacetic acid （DTPA） and ethylene diamJne tetraacetic acid （EDTA） were used to extract the labile fraction of heavy metals from the amended soils. The results show that the MSC could not only improve the fertility but also increase the dissolved organic carbon （DOC） content of sierozem soils. The total concentrations and labile fraction proportions of heavy metals increase with increasing MSC percentage in sierozem soils. In amended soils, Cd has the highest solubility and mobility while Ni has the lowest solubility and mobility among the five heavy metals. The MSC increases the concentrations of heavy metals in the root, stem, peel and tuber of the potato plant, with the concentrations being much higher in the stem and root than in the peel and tuber. Among the five heavy metals, the bioconcentration factor value of Cd is the highest, while that of Ni is the lowest. The complexing agent （DTPA and EDTA） extractable fractions of heavy metals are the highest in terms of phytoavailability. Soil properties （including organic matter, pH and DOC） have important impacts on the phytoavailability of heavy metals. Our results suggest that in soil-potato systems, although the MSC may improve soil fertility, it can also increase the risk of soils exposed to heavy metals.

Selecting and optimizing of the heavy metal inactivator in sewage sludge composting

In sewage sludge composting, adding ash from stove （FA20） inactivated active Cu effectively and the results were significantly better than control. For Zn, Mn, Pb and Cd, satisfying results was,achieved by adding ash from stove and phosphorite powder （FA20, PR10）, phosphorite powder and lime （PR15, CL10）, ash from stove and phosphorite powder （FA10, PR10）, and ash from stove and peat （FA20, PT 10）. Based on their effects of inactivating available forms of heavy metals, ash from stove, phosphorite powder and peat were supposed to be effective inactivators with optimum percentages of 20%, 15% and 10% （FA20, PR15, PT10）.

Environmental Contamination by Industrial Effluents and Sludge Relative to Heavy Metals

Oman is located in the tropic of Cancer with extremely hot temperatures ranging between 15&deg;C-25&deg;C in winter and 30 - 48 in the summer with low rainfall. Most of the water source is desalinated seawater. Recycling of sewage effluent is a common practice used for farming, public parks and industry. The dried sludge product is used as fertilizer. The highly concentrated sludge with heavy metals is either incinerated or buried in landfills. Heavy metals were analyzed and compared in treated sewage effluent (TSE), slurry sludge, dried sludge, landfill and underground water. Heavy metal concentrations were analyzed using the inductive coupled plasma optical emission spectrometer (ICP-EOS). All samples contained the same heavy metals with different concentrations. The heaviest concentrations were Zn, Cu, Cr and Ni with traces of V, Cd, Pb and Ba. TSE and sludge were the main sources of landfill and underground water contamination. Due to water evaporation, heavy metals concentrations in sludge were higher compared to TSE and underground water. Dried sludge and landfill contained higher concentrations than the others. Based on this investigation, it appears that the source of heavy metals is from TSE originated mainly in industries. If the infiltration of heavy metals to soil and underground water continues, it will be a serious environmental and health problem in the future.

Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash(ISSA)and dredged contaminated marine sediments(CMSs)is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity.The present study investigates the use of high content(20%of sediment by mass)of ISSA in combination with cement/lime for solidification/stabilization(S/S)treatment of CMSs to provide a way to reuse the wastes as construction materials.The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content(w80%).The S/S treatment improved the engineering properties of the sediment,but reduced the workability,especially for the lime-treated samples.Lime can be used to replace ordinary Portland cement(OPC)for better heavy metal immobilization and carbon emission reduction.The hardened sediment samples prepared with 10%of lime and 20%of ISSA could attain a strength of 1.6 MPa after 28 d of curing.In addition,leaching tests confirmed that there was no environmental risk induced by these stabilized materials.The formation of hydrated cementitious compounds including calcium silicate hydrate(CeSeH)/calcium aluminate silicate hydrate(C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.