Availability of Cd,Ni and Zn to Ryegrass in Sewage Sludge-Treated Soils at Different Temperatures

A pot experiment to compare the availability of Cd, Ni and Znto ryegrass (Lolium perenne L.) was conducted at 15 and 25 °C. For this purpose, three ratesof sewage sludge (0, 10 and 50 t ha^-1) were applied in aloamy sand (LS) and a clay loam (CL). Heavy metal availabilityassessed by soil extractions with 0.05 M CaCl₂ and the organic matter content were monitored during a period of twoyears, while uptake by ryegrass was monitored over one year after addition of the sludge. The concentrations of Cd and Ni in both the ryegrass and the soil extracts increased significantly, during the first year, especially at 50 t ha^-1. However, in the second year metal availability reached a plateau. During the first year, in the ryegrass Znconcentrations did not show an increase, but in the soil CaCl₂-extracted Zn increased. During the same period,the organic matter content decreased rapidly, especially at25 °C, in the first year and much more slowly in thesecond, giving a total decrease of 16%. Temperature had a marked effect on metal availability; both soil extracts andplant samples from the 25 °C treatment had greater concentrations of Cd, Ni and Zn than those at 15 °C. This may be attributed to the organic matter, which decomposedmore rapidly at 25 °C. Moreover, soil-plant transfercoefficients (Tc) of the metals were significantly higher at 25 °C than at 15 °C, with Cd showing the greatest difference, followed in decreasing order by Zn and Ni.     

Sorption of Cd and Pb by selected temperate and semi-arid soils: effects of sludge application and ageing of sludged soils

Five soils from semi-arid regions of India and 5 soils from England were compared with regard to their ability to sorb Cd and Pb when mixed with sewage sludge and as unsludged controls. The application of sewage sludge at 150t ha^?1 significantly increased the amount of Cd retained by the soils. The sorption data were statistically best-fit to the linearized Freundlich equation and the slopes of the isotherms were steeper with sludge application, indicating an increased affinity for Cd in the soil-sludge mixtures. A similar trend in Pb sorption was also observed for the English soils following the sludge treatment. In contrast, most of the Indian soils showed a decline in Pb sorption following the sludge application. Liming an acidic English soil to pH 7.0 was shown to increase its metal sorption capacity. The longer-term persistence of these observed effects of sewage sludge addition on metal sorption by soils was investigated in two sludge-soil mixtures maintained under experimental conditions for up to 450 days. Samples of these soils taken 1,60 and 450 days after the mixing with the sludge were batch equilibrated with Cd and Pb and it was found that the metal retention in both soils decreased significantly over this time period.     

Speciation of Metals in Sewage Sludge and Sludge-amended Soils

This study is aimed at ascertaining the chemical partitioning ofCu, Zn, Pb, Ni, Cr and Cd in sewage sludge and agricultural soils repeatedly amended with sludge. The operationally determined speciation was investigated by using selective five steps sequential extraction method for partitioning these metals into different chemicalforms, likely to be released in solution under various environmental conditions. It provides qualitative evidence regarding the form of the association of metals and indirectly of their bioavailability. It can help to explain the process by which metals are eliminated from sewagesludge and also indicate the impact of the use of sludge on agriculturalsoils, as amendments. Data obtained by extraction procedure showed different metal distribution trend among the fractions in sewage sludgeand sludge-amended soils. Comparison of distribution pattern of metals in sludge and sludge-applied soils shows that there is possible redistribution of metals among the different phases. The sum of the metal content in the fractions compared well with the total metal content in sewage sludge, the ratios averaging 1.02, 1.04, 1.07, 0.94, 1.06, and 1.12 for Cu, Zn, Pb, Ni, Cr, and Cd, respectively. The metal recovery efficiency in sludge-amended soils was found to be: 108±6%, 102±5%, 115±8%, 111±4%, 104±7%and 124±28% for Cu, Zn, Pb, Ni, Cr and Cd, respectively.     

Possibilities of using sewage sludge as nitrogen fertilizer for maize

Abstract

The objective of this study was to determine the effects of nitrogen fertilizer sources of ammonium sulphate and municipal sewage sludge on yield, N content and uptake of the maize (Zea mays L.). Nutrient and heavy metals were determined in soil and plant. The experiment with three sludge rates (256, 513 and 1026 kg total N ha^?1 or 9.5, 18.0 and 38.1 t ha^?1 sludge), two nitrogen rates (80 and 160 kg N ha^?1) and zero-N control were conducted on a clay loam soils under irrigated conditions in Eastern Anatolia region in Turkey. Treatments were arranged in a randomized complete block design with four replications. Yield, N content and total N uptake of maize increased significantly with sludge application. 9.5 t and 19.0 t ha^?1 sewage sludge applications did not significantly affect heavy metal content of leaf and grain. However, 38.1 t ha^?1 sludge applications increased leaf Pb and Zn. DTPA-extractable Cd, Cu, Fe, Pb and Zn concentrations of the soil increased at applications of 38.1 t ha^?1 sewage sludge, whereas applications of 9.5 t and 19.0 t ha^?1 sludge only resulted in elevated levels of Cu and Zn, We conclude that if sewage sludge is to be used in production of maize, applications rate up to 19 t ha^?1 could be accepted. However, this means also that the N requirement of maize crop is not covered by the sludge; therefore, the rest of nitrogen could be supplied as inorganic N.     

Determination of the Residual Metal Binding Characteristics of Soils Polluted by Cd and Pb

Four soils contaminated by Pb-Zn mining, Pb-Zn smelting, sewage sludge application, and clay pigeon shooting, respectively, were evaluated for their ability to attenuate relatively high concentrations of supplied Cd and Pb. The retention characteristics of the polluted soils and ‘background’-unpolluted soils for Cd and Pb, were assessed by batch adsorption experiments and equilibrium dialysis titration of the soil organic component. From the sorption data it was observed that the mining polluted and sewage sludge treated soils showed no significant change in Cd affinity when compared to the unpolluted soils. However, for Pb, the reduction in the slopes in the isotherms of the sludge treated and shot over soils were significant when compared to the background soils – indicating a reduced affinity for Pb. The Cd and Pb complexation capacities of the organic component were reduced in the mining, smelter and shot over soil compared to their respective background soils. However, the complexation capacity for Cd of the sludged soil increased from 1.01 µmol Cd g^-1 of organic matter to 4.38 µmol Cd g^-1 of organic compared to the background soil, but, the stability constant of the organo-metal complex formed was lower (6.05 cf. 6.85).     

污泥与施污土壤重金属生物活性及生态风险评价

将城市污泥以不同质量比施于土壤中构成污泥混合土壤,研究各污泥配比土壤中重金属的生物活性,并采用三种重金属评价方法(地累积指数法、潜在生态风险指数法、综合毒性指数模型)和黑麦草对重金属的吸收富集效果来对施污土壤中重金属具有的生态风险性进行评价。结果表明:污泥的添加使土壤中生物活性态Cd、Cu和Zn含量显著增加,对三种重金属具有活化作用,但对Pb却起到钝化作用。生态风险评价结果表明:污泥的添加使土壤中Pb呈现无污染和低生态风险;Cu和Zn呈现中度污染和低生态风险;Cd达到强度污染和重度生态风险,重金属潜在生态风险(RI)总体处于强度生态风险水平。当污泥添加比例大于6:10(污泥S3处理)时,施污土壤中重金属的综合毒性指数高于土壤对照。黑麦草对Cd、Pb、Cu和Zn的富集浓度与施污土壤中对应重金属的生物活性态含量存在显著正幂指数关系,同时黑麦草对施污土壤中Cd、Cu和Pb的富集能力大小与地累积指数法和潜在生态风险指数法对三种重金属具有的生态风险性的评价结果具有一致性。     

Comparative availability to wheat of metals from sewage sludge and inorganic salts

A greenhouse experiment was conducted to evaluate the availability of metals from sewage sludge and inorganic salts, and the effect of pH and soil type on yield and metal (Zn, Cu, Cd and Ni) uptake by wheat (Triticum aestivum L. var. ‘holly’). Soils used in this study were Hartsells sandy loam (fine-loamy, siliceous Thermic Typic Hapludult) and Decatur silty clay loam (Clayey, kaolinitic, Thermic Rhodic Paleudult). Two treatments of sewage sludge containing metals were applied at the rate of 20 and 100 mt ha^?1. Inorganic Salts of Zn, Cu, Cd, and Ni were applied (as sulfate salts) at concentrations equivalent to those found in the 20 and 100 mt ha^?1 sludge. One treatment consisted of inorganic metals plus sewage at the 20 Mg ha^?1 rate. Two soil pH levels, one at field pH (below 6.0) and another pH adjusted between 6.5 and 7.0 were used. Wheat plants were harvested four weeks after germination. Two more subsequent harvests were made at four week intervals. For each harvest, dry matter yield increased as the rate of sludge application increased for both soil types. The soil pH also influenced the dry matter yield. High yield was observed when the pH was adjusted between 6.5 to 7.0 for both soils. An increase in yield was also observed at each subsequent harvest for most of the treatments. Inorganic salt treatments produced lower dry matter yields when compared with the sludge. Both sludge application and metal salts increased plant tissue concentration of Zn, Cu, Cd, and Ni at field pH for both soils. However, increasing the pH of the soil for both sludge and inorganic salt treatments generally decreased the tissue concentration of the above metals.     

Sustainability of in situ remediation of Cu- and Cd-contaminated soils with one-time application of amendments in Guixi,China

Purpose

In situ immobilization of heavy metal-contaminated soils with the repeated incorporation of amendments can effectively reduce the bioavailability of soil heavy metals. However, the long-term application of amendments would lead to the destruction of soil structure and accumulation of soil toxic elements, ultimately affecting food security and quality. Thus, the sustainability of the amendments in a heavy metal-contaminated soil was evaluated from 2010 to 2012.

Materials and methods

Batch field experiments were conducted in the soils, which were amended with apatite (22.3 t ha^?1), lime (4.45 t ha^?1), and charcoal (66.8 t ha^?1), respectively. The amendments were applied only one time in 2009, and ryegrass was sown each year. Ryegrass and setaria glauca (a kind of weed) were harvested each year. Concentrations of copper (Cu) and cadmium (Cd) were determined by batch experiments. Five fractions of Cu and Cd were evaluated by a sequential extraction procedure.

Results and discussion

Ryegrass grew well in the amended soils in the first year, but it failed to grow in all the soils in the third year. However, setaria glauca could grow with higher biomass in all the amended soils. The treatment of apatite combined with plants was more effective than lime and charcoal treatments in removing Cu and Cd from the contaminated soils by taking biomass into account. Apatite had the best sustainable effect on alleviating soil acidification. The Cu and Cd concentrations of CaCl₂-extractable and exchangeable fractions decreased with the application of amendments. Moreover, apatite and lime could effectively maintain the bioavailability of Cu and Cd low.

Conclusions

Apatite had a better sustainable effect on the remediation of heavy metal-contaminated soils than lime and charcoal. Although all the amendment treated soils did not reduce soil total concentrations of Cu and Cd, they could effectively reduce the environmental risk of the contaminated soils. The findings could be effectively used for in situ remediation of heavy metal-contaminated soils.

     

Effect of sewage sludge and its biochar on chemical properties of two calcareous soils and maize shoot yield

Little information is available regarding the effect of sewage sludge biochar on soil properties and crop yield. Thus, our objective was to evaluate the effect of sewage sludge (S) and its biochar (B) on maize shoot yield, nutrients and heavy metals uptake in two calcareous soils. The amendments were applied at the rates of 0, 10, 20 and 40 Mg ha^?1. Moreover, NK treatment was included to compare the effects of S and B with conventional fertilization. At harvest time, plant shoots and soil samples were collected for yield, nutrients uptake and chemical analyses. The highest shoot dry matter was obtained in the S treatment. The B application in the clay loam and loam soils resulted in 5.2% increment and 17.7% decrement of shoot dry matter relative to the control, respectively. Shoot dry matter in the NK treatment was significantly higher than in the control. B application decreased Fe, Zn, Mn, Cu and Pb uptake by maize shoot. DTPA-extractable Pb in B-amended soils was lower than in control, while an inverse trend was obtained for available Fe, Zn, Mn and Cu. Biochar application at the rate of 7.3 Mg ha^?1 might be suggested for maize cultivation in clay loam soils.     

Heavy metal uptake by blue grama growing in a degraded semiarid soil amended with sewage sludge

Sewage sludge application to semiarid grassland may represent a beneficial means of utilizing this waste product for restoration of degraded sites. Consequently, dried municipal sewage sludge was applied at three rates (22.5, 45, and 90 Mg ha^–1) to a degraded semiarid grassland soil in order to determine the effects of sludge amendments on forage productivity, soil heavy metal content, and metal uptake by blue grama (Bouteloua gracilis).Soil and plant properties in control and amended plots were measured after 1, 2, and 5 growing seasons.Soil nutrients increased linearly with increased sludge application in the first two growing seasons. Consequently, forage quality and total production of blue grama improved significantly over the unamended control as the tissue levels of N, P, K, and crude protein increased. Cadmium and Pb in the sludge-treated plots did not increase significantly over the control after 1 and 2 growing seasons. Levels of DTPA-extractable soil micronutrients (Cu, Fe, Mn, Zn) increased linearly with increased sludge application rate to soil concentrations recommended for adequate plant growth. Soil N, P, and K concentrations remained higher in the sludge-amended soils after 5 growing seasons, while Cu and Cd increased to slightly above desireable limits as the soil pH decreased to 7.4 and 7.0 in the 45 and 90 Mg ha^–1 treatments, respectively. However, with the exception of Mn which remained within desirable limits, metal concentrations (including Cu and Cd) in blue grama tissue were not significantly different from the control treatment after five growing seasons. Based on soil and plant tissue metal concentrations, it appears that sludge applied at rates between 22.5 and 45 Mg ha^–1 will maintain the most favorable nutrient levels coupled with significant improvements in forage production in this semiarid grassland environment.     

Yield response of crops amended with sewage sludge in the field is more affected by sludge properties than by final soil metal concentration

Adverse effects on crop yield or quality have been reported in sewage‐sludge treated soils at soil total metal concentrations below those of the current EU directives. A field trial was set up in Belgium (2002–2004) to assess crop response to the application of sewage sludge below these soil thresholds but with sludge metal concentrations either above (high‐metal) or below (low‐metal) sludge metal limits. Two lime‐stabilized and two raw, dewatered sludges were applied annually at rates of 10, 25 and 50 t dry matter (dm) ha^?1 for 3 years with four rates of N‐fertilizer as a reference. Final soil metal concentrations increased to maximums of 1.6 mg Cd kg^?1 and 225 mg Zn kg^?1 through sludge applications. Maize yield was marginally affected by treatments in year 1, whereas wheat and barley grain yields in subsequent years increased up to threefold with increasing sludge or fertilizer rates and were mainly explained by grain‐N. However, the grain yield of winter wheat in year 2 was reduced by about 14% in lime‐stabilized high‐metal sludge treatments compared with wheat receiving N‐fertilizer at equivalent grain‐N. Wheat grain and straw analysis showed no nutrient deficiencies but Zn concentrations in grain and straw were greater than in N‐fertilizer and lime‐stabilized, low‐metal sludge treatments, suggesting Zn toxicity. Sludge properties other than Cd concentration (e.g. electrical conductivity) affected crop Cd in the first year (maize), whereas significant correlations between Cd application and wheat grain Cd were found in the second year. Wheat grain Cd concentrations reached the international trade guideline of 0.1 mg Cd kg^?1 fresh weight in the plots amended with lime‐treated, high‐metal sludge even though soil Cd remained below EU limits. In the third year, barley grain Cd remained largely below EU limits. We discuss the possibility that sludge properties rather than soil total metal concentrations are related to effects on crops in the initial years after sludge applications. In none of the 3 years were any adverse effects on crops found for sludge meeting current EU regulations.     

Sewage sludge treated with bentonite,vermiculite or biochar can improve soil properties and enhance growth of grasses

Sewage sludge treated with 15% bentonite, vermiculite or biochar was evaluated as a soil amendment in comparison to limed and untreated sludge. Seven treatments were established to two soils, an acid and an alkaline, in three replications, i.e. 2% addition of sludge treated with bentonite, vermiculite, biochar and lime and application of 2% untreated sludge, inorganic fertilization and no sludge or inorganic fertilizers (control). Then, the soil treatments were used in a pot experiment with perennial ryegrass (Lolium perenne L.) as a test plant. Sludge treated with the clay minerals or biochar improved pH of the acid soil and significantly increased organic matter and available nutrients of both soils compared to control. Although no salinity or sodicity hazard was evidenced, the initial salinity of acid and alkaline soil increased by four-eight and two-three times, respectively, upon addition of all sludge treatments, especially that of untreated sludge. Moreover, soil available zinc (Zn) increased by four-eight times. Soil application of sludge treated with the clay minerals or biochar increased the total aboveground biomass yield of ryegrass in the acid and alkaline soil by 133%–171% and 72%–88%, respectively, compared to control and enhanced nutrient uptake by plants. Furthermore the microbial metabolic quotient indicated lack of low pH and heavy metal stress with addition of sludge to the acid soil. After three harvests of ryegrass, the residual effect of sludge on pH of acid soil and salinity, available phosphorus (P), Zn and boron (B) of both soils still persisted. Thus sewage sludge treated with 15% bentonite, vermiculite or biochar could be applied to soils at a rate of 2% (≈80 Mg ha⁻¹) to serve as soil amendment and fertilizer for grasses and pasture species; however, caution is needed regarding possible P build-up, Zn phytotoxicity and salinization risks.     

Effect of sewage sludge on some chemical properties of calcareous sandy soils

Abstract

City sewage sludge was applied to the surface layer (0–10 cm) of two sandy soils, slightly calcareous with 8.9% CaCO₃ and moderately calcareous with 26.7% CaCO₃, at the rates of 0, 25, 50, 75, and 100 Mg ha^‐1. The effects of sewage sludge and its rates on total soluble salts, pH of soils and concentration and movement of some heavy metals within soils were investigated. Soil samples were packed at bulk density of 1.5 g cm^‐3 in PVC columns and incubated for 19 weeks. The results indicated that total soluble salts (EC) of the treated layer increased with increasing sewage sludge rates. Soluble salts also increased with an increase in soil depth for both soils. The pH values of treated layers in two soils decreased with increasing sewage sludge rates. With increasing sewage sludge rates, concentrations of heavy metals [cobalt (Co), nickel (Ni), cadmium (Cd), and leaf (Pb)] increased in the treated layers compared to the untreated layers and their mobility was restricted mostly to the upper 30‐cm depth. Movement of Co and Pb in both the soils was predominately limited up to a depth of 40 cm for Co and 5 cm for Pb below the treated soil layer. Nickel and Cd movement was mostly limited to a depth of 10 cm in slightly calcareous soil and 5 cm in moderately calcareous soil. Metal movement in the respective soils is ranked as Co>Ni=Cd>Pb and Co>Ni=Cd>Pb. The low concentrations of heavy metals and the restricted mobility with soil depth, suggest that this material may be used for agricultural crop production without any toxic effect on plants.     

Sequential fractionation and plant availability of heavy metals as affected by sewage sludge applications to soil

Abstract

The effect of sewage sludge applications on extractability and uptake by chard and lettuce of soil cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), leaf (Pb), and zinc (Zn) was investigated. Ten different treatments (0, 150, 300, and 500 kg N ha^‐1) as mineral fertilizer, and 400, 800, and 1,200 kg N ha^‐1 of aerobically and anaerobically‐digested sewage sludges were applied annually to a sandy‐loam soil since 1984. Seven years after the start of the treatments, higher levels of heavy metals were detected in the soil, depending on the type of metal, depth of sampling, type of sludge used, and, especially, rate of application. Following a sequential extraction procedure incorporating 0.1M CaCl₂, 0.5M NaOH, and 0.05M Na₂EDTA, most of the heavy metals in soil were detected in the Na₂EDTA solution and the residual fractions. Large amounts of Cd appeared to be extracted by CaCl₂, whereas substantial amounts of Cu and Ni were isolated by NaOH. The effect of treatments on the percentages of the metals found in each fraction depended on the type of metal, sampling depth, sludge used, and application rate. No significant increases were found in the heavy metal contents of chard and lettuce leaves, but some of the treatments resulted in a significant decrease of Cd and Cr levels in lettuce leaves.     

Mudflat soil amendment by sewage sludge: Soil physicochemical properties,perennial ryegrass growth,and metal uptake

Abstract

The fast pace of cropland loss in China is causing alarm over food security and China’s ability to remain self-reliant in crop production. Mudflats after organic amendment can be an important alternative cropland in China. Land application of sewage sludge has become a popular organic amendment to croplands in many countries. Nevertheless, the land application of sludge to mudflats has received little attention. Therefore, the objective of the present work was to investigate the impact of sewage sludge amendment (SSA) at 0, 30, 75, 150 and 300 t ha^?1 rates on soil physicochemical properties, perennial ryegrass (Lolium perenne L.) growth and heavy metal accumulation in mudflat soil. The results showed that the application of sewage sludge increased organic matter (OM) content by 3.5-fold while reducing salinity by 76.3% at the 300 t ha^?1 rate as compared to unamended soil. The SSA reduced pH, electric conductivity (EC) and bulk density in mudflat soil, increased porosity, cation exchange capacity (CEC) and contents of nitrogen (N), phosphorus (P), exchangeable potassium ions (K⁺), sodium ions (Na⁺), calcium ions (Ca²⁺) and magnesium ions (Mg²⁺) in comparison to unamended soil. There were 98.0, 146.6, 291.4 and 429.2% increases in fresh weight and 92.5, 132.4, 258.6 and 418.9% increases in dry weight of perennial ryegrass at 30, 75, 150, and 300 t ha^?1, respectively, relative to unamended soil. The SSA increased metal concentrations of aboveground and root parts of perennial ryegrass (p < 0.05). The metal concentrations in perennial ryegrass were Zn > Cr > Mn > Cu > Cd > Ni, and the metal concentrations in roots were significantly higher than aboveground parts. The metal accumulation in perennial ryegrass correlated positively with sludge application rates and available metal concentrations in mudflat soil. Land application of sewage sludge was proved to be an effective soil amendment that improved soil fertility and promoted perennial ryegrass growth in mudflat soil. However, heavy metal accumulation in plants may cause food safety concern.     

Metal accumulation by bermudagrass grown on four diverse soils amended with secondarily treated sewage effluent

Land treatment is increasingly being utilized as a method of waste disposal for both sewage effluent and sludges. While there has been considerable attention directed toward the fate of metallic constituents of sewage sludges, there have been fewer studies of the fate and mobility of metals appled to soils in sewage effluent. This study was undertaken utilizing secondarily treated sewage effluent amended to contain less than 1 mg l^?1 each of Cd, Cu, Ni, Pb, and Zn. The effluent was applied weekly for a period of 1 yr on large undisturbed monoliths of four diverse soils enclosed in lysimeters and sprigged to common bermudagrass (Cynodon dactylon L.). Soil samples were collected periodically and extracted with DTPA to measure plant available metals. Vegetation was harvested, weighed, subsampled and analyzed for total metal content. Total plant uptake of Cd, Cu, Pb, and Ni during the year was less than 1% of that applied. Vegetative uptake of Zn was as high as 2%. Metal uptake was greatest in the soil with the lowest initial pH. Heavy metal concentrations in plant tissue exhibited a cyclic trend. A similar increasing cyclic trend was evident in the DTPA extractable metals in the surface 0 to 12.5 cm of the treated soils. Decreases in plant and DTPA extractable metals occurred when the soils dried, allowing O₂ to enter. Vegetative concentrations of Cd, Cu, and Ni exceeded normal ranges of 0.2 to 0.8, 4 to 15, and 1.0 mg kg^?1, respectively, for vegetation while Pb and Zn were near normal. Only Cd concentration of vegetation posed a threat to grazing animals.     

Growth of apple seedlings on sludge‐amended soils in the greenhouse

Abstract

Open pollinated ‘York Imperial’ apple (Malus domestica Borkh.) seeds were germinated and grown for a period of 7 months in: (1) sand with complete nutrient solutions added; (2) limed and unlimed soil, (3) limed and unlimed soil amended with two different sewage sludges at rates of 25, 50 or 100 dry kg ha^‐1. A third composted, lime stabilized sludge was added either sieved or non‐sieved (to remove wood chips) at the same rates. The sludge materials used were: (1) a high metal, composted sludge from Baltimore, MD (BALT); (2) a high Cd sewage sludge (CITY) and (3) a low metal, composted sewage sludge from Washington, D.C. (DC).

Germination was unaffected by treatments. After 7 months, the best growth was obtained from the sand plus nutrient solution media. Two of the three sludge materials increased seedling growth over that of the soil, either limed or unlimed. The BALT compost treated soils produced the lowest growth, particularly when unlimed. Elevated tissue metal levels indicated that Mn, Zn, Cu and Ni were the probable causes of reduced growth noted from the BALT compost treatment. The use of soil with or without low metal sludges as media for early apple seedling growth when compared to standard sand culture is not recommended.     

Chemical Changes in Soil and Plants After Successive Amendments of Tunisian MSW Compost

A field study was carried out to evaluate long-term heavy metal (HM) accumulation in the top 20 cm of a Tunisian clayey loam soil amended for (four years) with municipal solid waste compost (MSWC) at three levels (0, 40 and 80 t ha^?1 year^?1). HM uptake and translocation within wheat plants grown on these soils were also investigated. Compared to untreated soils, MSWC-amended soils showed significant increases in the content of all measured HM (Cd, Cr, Cu, Ni, Pb and Zn) in the last three years, especially for the 80 t ha^?1 year^?1 MSWC-amended plots. Wheat plants grown on MSWC-amended soils showed a general increase in metal uptake and translocation, especially for Cr and Ni. This HM uptake was about three fold greater for treatment 80 t h^?1 as compared to plots amended at a rate of 40 t h^?1. At times, the diluting effect resulting from enhanced growth rates of the plants with compost application resulted in lower concentrations in the plants grown (grain part) on treated plots. On the other hand, Cr and Ni were less mobile in the aerial part of wheat plants and were accumulated essentially in root tissues. Plant/soil transfer coefficients for MSWC-amended treatments were higher than threshold range reported in the literature, indicating that there was an important load/transfer of HM ions from soils to wheat plants.     

Soil phosphorus dynamics and phytoavailability from sewage sludge at different stages in a treatment stream

The effect of different stages of sewage sludge treatment on phosphorus (P) dynamics in amended soils was determined using samples of undigested liquid (UL), anaerobically digested liquid (AD) and dewatered anaerobically digested (DC) sludge. Sludges were taken from three points in the same treatment stream and applied to a sandy loam soil in field-based mesocosms at 4, 8 and 16 t ha⁻¹ dry solids. Mesocosms were sown with perennial ryegrass (Lolium perenne cv. Melle), and the sward was harvested after 35 and 70 days to determine yield and foliar P concentration. Soils were also sampled during this period to measure P transformations and the activities of acid phosphomonoesterase and phosphodiesterase. Data show that the AD amended soils had the greatest plant-available and foliar P content up to the second harvest, but the UL amended soils had the greatest enzyme activity. Characterisation of control and 16 t ha⁻¹ soils and sludge using solution ³¹P nuclear magnetic resonance (NMR) spectroscopy after NaOH–EDTA extraction revealed that P was predominantly in the inorganic pool in all three sludge samples, with the highest proportion (of the total extracted P) as inorganic P in the anaerobically digested liquid sludge. After sludge incorporation, P was immobilised to organic species. The majority of organic P was in monoester-P forms, while the remainder of organic P (diester P and phosphonate P) was more susceptible to transformations through time and showed variation with sludge type. These results show that application of sewage sludge at rates as low as 4 t ha⁻¹ can have a significant nutritional benefit to ryegrass over an initial 35-day growth and subsequent 35-day re-growth periods. Differences in P transformation, and hence nutritional benefit, between sludge types were evident throughout the experiment. Thus, differences in sludge treatment process alter the edaphic mineralisation characteristics of biosolids derived from the same source material.     

Biological and physical resilience of soil amended with heavy metal-contaminated sewage sludge

Stability and resilience of a variety of soil properties and processes are emerging as key components of soil quality. We applied recently developed measures of biological and physical resilience to soils from an experimental site treated with metal‐contaminated sewage sludge. Soils treated with cadmium‐, copper‐ or zinc‐contaminated, digested or undigested sewage sludge were studied. Biological stability and resilience indices were: (i) the time‐dependent effects of either a transient stress (heating to 40°C for 18 hours) or a persistent stress (amendment with CuSO₄) on decomposition, and (ii) the mineralization of dissolved organic carbon (DOC) released by drying–rewetting cycles. Physical stability and resilience measures were: (i) compression and expansion indices of the soils, and (ii) resistance to prolonged wetting and structural regeneration through drying–rewetting cycles. Soil total carbon and DOC levels were greater in the sludge‐amended soils, but there were no differential effects due to metal contamination of the sewage sludge. Effects of metals on physical resilience were greater than effects on soil C, there being marked reductions in the expansion indices with Cd‐ and Cu‐contaminated sludge, and pointed to changes in soil aggregation. The rate of mineralization of DOC released by drying and wetting was reduced by Zn contamination, while biological resilience was increased in the Zn‐contaminated soil and reduced by Cd contamination. We argue that physical and biological resilience are potentially coupled through the microbial community. This needs to be tested in a wider range of soils, but demonstrates the benefits from a combined approach to the biological and physical resilience of soils.