Assessment of chemical and biochemical stabilization of organic C in soils from the long-term experiments at Rothamsted (UK)

Biological and chemical stabilization of organic C was assessed in soils sampled from the long-term experiments at Rothamsted (UK), representing a wide range of carbon inputs and managements by extracting labile, non-humified organic matter (NH) and humic substances (HS). Four sequentially extracted humic substances fractions of soil organic matter (SOM) were extracted and characterized before and after a 215-day laboratory incubation at 25 degrees C from two arable soils, a woodland soil and an occasionally stubbed soil. The fractions corresponded to biochemically stabilised SOM extracted in 0.5M NaOH (free fulvic acids (FA) and humic acids (HA)) and chemically plus biochemically stabilised SOM extracted from the residue with 0.1M Na4P2O7 plus 0.1M NaOH (bound FA and HA). Our aim was to investigate the effects of chemical and biochemical stabilization on carbon sequestration. The non-humic to humic (NH/H) C ratio separated the soils into two distinct groups: arable soils (unless fertilised with farmyard manure) had an NH/H C ratio between 1.05 and 0.71, about twice that of the other soils (0.51-0.26). During incubation a slow, but detectable, decrease in the NH/H C ratio occurred in soils of C input equivalent or lower to 4Mgha(-1)y(-1), whereas the ratio remained practically constant in the other soils. Before incubation the free to bound humic C ratio increased linearly (R2=0.91) with C inputs in the soils from the Broadbalk experiment and decreased during incubation, showing that biochemical stabilization is less effective than chemical stabilization in preserving humic C. Changes in delta13C and delta15N after incubation were confined to the free FA fractions. The delta13C of free FA increased by 1.48 and 0.80 per thousand, respectively, in the stubbed and woodland soils, indicating a progressive biological transformation. On the contrary, a decrease was observed for the bound FA of both soils. Concomitantly, a Deltadelta15N of up to +3.52 per thousand was measured after incubation in the free FA fraction and a -2.58 Deltadelta15N in the bound FA. These changes, which occurred during soil incubation in the absence of C inputs, indicate that free FA fractions were utilised by soil microorganisms, and bound FA were decomposed and replaced, in part, by newly synthesized FA. The 13CPMAS-TOSS NMR spectra of free HA extracted before and after 215 days of incubation were mostly unchanged. In contrast, changes were evident in bound HA and showed an increase in aromatic C after incubation.     

Characterization of trace elements in chicken and duck litter ash

For safe and sustainable management of poultry litter, it is important to evaluate and understand the chemical forms and concentrations of their constituent trace elements during treatment for disposal. This experiment was carried out to compare changes in metal (Cu, Mn, Zn, Pb and Ni) fractions in chicken and duck litter after incineration at temperatures ranging from 200 to 900 degrees C. The metals were stepwise fractionated into exchangeable, adsorbed, organically bound, carbonate precipitated and residual forms by extracting with 0.5M KNO3, de-ionized water, 0.5M NaOH, 0.05M Na2 EDTA and 4M HNO3, respectively. The content of total metal and other elements (i.e., Ca, Mg and K) were was also determined. Results showed an increasing trend in the total concentrations of metals with increasing temperature with higher amounts in chicken litter ash (CLA) than duck litter ash (DLA). Higher temperatures significantly reduced the levels of H2O-soluble Mn, Zn and Ni and enhanced those of Cu and Pb. The metal fractions extracted by EDTA and HNO3 increased directly with increasing temperature while the fraction extracted with KNO3 and NaOH decreased with ashing. For Cu, Mn, Pb and Ni, the amount extracted varied in the order EDTA>HNO3>NaOH>KNO3>H2O, but the absolute amounts differed between CLA and DLA. Peak concentrations of the total metals were achieved at the highest burning temperature. The amount of H2O soluble Ca and Mg decreased and K increased in both CLA and DLA with temperature. Total and exchangeable forms of cations increased with increasing temperature. Total Ca was highest in DLA, whereas total Mg and K were higher in CLA. This study indicated that incinerating poultry litter before soil application may have mixed effects on the vulnerable metal fractions by increasing or decreasing some fractions, depending on poultry type.     

Metal fractionation in soil profiles at automobile mechanic waste dumps.

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

Variations of metal distribution in sewage sludge composting

In the study, the variations of heavy metal distributions (of Cu, Mn, Pb, and Zn) during the sewage sludge composting process were investigated by sequential extraction procedures. The total content of Cu and Zn in the composted mixture increased after the composting process. Mn and Zn were mainly found in mobile fractions (exchangeable fraction (F1), carbonate fraction (F2), and Fe/Mn oxide fraction (F3)). Cu and Pb were strongly associated with the stable fractions (organic matter/sulfides fraction (F4) and residual fraction (F5)). These five metal fractions were used to calculate the metal mobility (bioavailability) in the sewage sludge and composted mixture. The mobility (bioavailability) of Mn, Pb, and Zn (but not Cu) increased during the composting process. The metal mobility in the composted mixture ranked in the following order: Mn>Zn>Pb>Cu.     

Bioreactor treatment of municipal solid waste landfill leachates: characterization of organic fractions

Quantitative and qualitative changes in organic matter were studied at different stages of treatment in a bioreactor designed to process leachates from a municipal solid waste landfill. The particulate matter (PM) and macromolecular fractions of the dissolved organic matter with solubility properties comparable to humic (acid-insoluble) and fulvic (acid-soluble) acid fractions (AI, AS, respectively) from the incoming black liquid, the bioreactor content, and the final processed effluent were isolated, quantified, and characterized by visible and infrared (IR) spectroscopies. The macromolecular signature either aliphatic (glycopeptides, carbohydrates) or aromatic (coinciding with infrared patterns of lignin, tannins etc.) enabled us to characterize the different organic fractions during the course of microbial transformation. The results reveal significant changes in the nitrogen speciation patterns within the different organic fractions isolated from the wastewater. The final increase in the relative proportions of nitrogen in the least aromatic AS fraction during microbial transformation could be related to protein formation inside the bioreactor. After biological treatment and ultrafiltration, the amount of organic matter was reduced by approximately 70%, whereas aromaticity increased in all fractions, indicating preferential elimination of aliphatic wastewater compounds. Most of the remaining fractions at the end of the process consisted of a yellow residue rich in low molecular weight AS fractions.     

Kinetic Study Of The Composting Of Evergreen Oak Forestry Waste

The successive stages in the composting process of forestry waste from evergreen oak (Quercus ilx sbsp. ballota) were studied under controlled conditions (initial) carbon to nitrogen ratio = 30, T = 27°C). The original material was composted for 6 months and sampled every 15 days. The variables measured on the oak biomass in the course of the experiment showed different kinetics: the weight loss and germination index underwent a monotonic increase whereas the reducing sugars, phenols and E₄₆₅/E₆₆₅ extinction ratio of the water-soluble fraction stabilized at their lowest values after the first 2 weeks. Other variables, such as alkali solubility, water repellency, pH and particle size, showed maximum or minimum values at intermediate stages of the experiment. In contrast to the adverse agrobiological effects of the direct application to soil of the original waste, germination biotests and greenhouse experiments showed that plant response improved from the 2 first weeks of composting. The kinetics observed for the parameters studied suggested that the less favourable effect on plant yield may come from phytotoxic substances in compost but also from the microbial use of soil N required for the transformation of the most biodegradable compost fractions in special hemicelluloses.     

Changes in Extractability of Cr and Pb in a Polycontaminated Soil After Bioaugmentation With Microbial Producers of Biosurfactants, Organic Acids and Siderophores

Partly because of the low bioavailability of metals, the soil cleaning-up using phytoremediation is usually time-consuming. In order to enhance the amount of metals at the plant's disposal, the soil bioaugmentation coupled together with phytoextraction is an emerging technology. In this preliminary work, two agricultural soils which mainly differed in their Cr, Hg and Pb contents (LC, low-contaminated soil; HC, high-contaminated soil) were bioaugmented in laboratory conditions by either bacterial (Bacillus subtilis, Pseudomonas aeruginosa, Pseudomonas fluorescens or Ralstonia metallidurans) or fungal inocula (Aspergillus niger or Penicillium simplicissimum) and incubated during three weeks. The LC soil pots bioaugmented with A. niger and P. aeruginosa contained higher concentrations of Cr (0.08 and 0.25 mg.kg⁻¹ dw soil) and Pb (0.25 and 0.3 mg.kg⁻¹ dw soil) in the exchangeable fraction F1 (extraction with MgCl₂) by comparison with the non-bioaugmented soil where neither Cr nor Pb was detected. Conversely, immobilization of Cr and Pb in the soil were observed with the other microorganisms. The soil bioaugmentation not only modified the metal speciation for the most easily extractable fractions but also modified the distribution of metals in the other fractions, to a lesser extent nevertheless. The difference in microbial concentrations between the bioaugmented or not HC soils reached up to 1.8 log units. Thus the microorganisms that we chose for the soil bioaugmentation were competitive towards the indigenous microflora. The PCA analysis showed close positive relationships between the microorganisms which potentially produced siderophores in the soil and the amount of Cr and Pb in the fraction F1.     

Dynamics of Cd, Cu and Pb added to soil through different kinds of sewage sludge

A greenhouse experiment was set up to study the distribution of Cd, Cu and Pb in three typical soils of the Pampas Region amended with sewage sludge. A sequential extraction procedure was used to obtain four operationally defined geochemical species: exchangeable, bound to organic matter, bound to carbonates, and residual. Two kinds of sewage sludge were used: pure sewage sludge and sewage sludge containing 30% DM of its own incinerated ash, at rates equivalent to a field application of 150 t DM ha(-1). Pots were maintained at 80% of field capacity through daily irrigation with distilled water. Soil samples were obtained on days 1, 60, 270 and 360, and then air-dried and passed through a 2 mm sieve for analysis. Results showed that sludge application increased the less available forms of Cd, Cu and Pb. The inorganic forms became the most prevalent forms for Cu and Pb, whereas Cd was only found in the residual fraction. The concentrations of OM-Cu and INOR-Cu in the amended soil samples were closely correlated with soil pH, whereas the chemical behavior of Cd and Pb did not depend on soil physico-chemical characteristics.     

The storage of sewage sludge: influence of liming on the evolution of copper chemical fractions

Sewage sludge re-used in agriculture has to be stabilized and is often stored for several months before land spreading. Stabilization treatment may affect the behaviour of heavy metals such as Cu, which is an element potentially toxic to the environment. In the present study, the chemical forms of copper have been investigated in heaps of limed and unlimed sludge coming from the wastewater treatment plant of Roselies (Belgium). These limed and unlimed aerobically digested sludges were stored during 4 mo in controlled conditions close to field ones. The sequential extraction procedure developed by Tessier was used to determine the copper chemical forms of representative samples taken in the outer shell and in the depth of the heaps. The physico-chemical properties (pH, organic matter, dry matter and temperature) of these samples were also monitored. This study shows that liming transforms part of organically-bound copper into both exchangeable and residual copper. These changes mainly occur during the first 2 wk of storage. After several months of storage, copper passes from the residual fraction to the exchangeable and oxide fractions. During the whole experiment, changes occur faster in the outer shell than in the depth of the heaps. Thus, we demonstrate that the distribution of the copper forms depends on the storage time and it is different in the outer shell from that in the depth of the heaps.     

A study of heavy metals and their fate in the composting of tannery sludge

Tannery waste is categorized as toxic and hazardous in Malaysia due to its high content of Cr (in excess of 500 mg/kg) and other heavy metals. Heavy metals, when in high enough concentrations, have the potential to be both phytotoxic and zootoxic. Heavy metals are found as contaminants in tannery sludge. This investigation aimed to identify the fate of chromium, cadmium, copper, lead, and zinc concentrations in tannery sludge throughout a 50-day composting cycle. The results of this study showed a general increase in the removal of Cr, Cd, Pb, and to a much smaller extent Zn and Cu, manifested by a decrease in their overall concentrations within the solid fraction of the final product (the decreases were likely the result of leaching). Furthermore, in using a sequential extraction method for sludge composting at different phases of treatment, a large proportion of the heavy metals were found to be associated to the residual fraction (70-80%) and fractions more resistant to extraction, X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of the metals were bound to bioavailable fractions X-(KNO3+H2O).     

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH-HCl); (4) oxidizable fraction (H2O2 + CH3COONH4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg(-1) (dry weight) in bottom ash and of 68.5 g kg(-1) (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg(-1) (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (approximately 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.     

Speciation of Cu and Zn during composting of pig manure amended with rock phosphate

Pig manure usually contains a large amount of metals, especially Cu and Zn, which may limit its land application. Rock phosphate has been shown to be effective for immobilizing toxic metals in toxic metals contaminated soils. The aim of this study work was to investigate the effect of rock phosphate on the speciation of Cu and Zn during co-composting of pig manure with rice straw. The results showed that composting process and rock phosphate addition significantly affected the changes of metal species. During co-composting, the exchangeable and reducible fractions of Cu were transformed to organic and residue fractions, thus the bioavailable Cu fractions were decreased. The rock phosphate addition enhanced the metal transformation depending on the level of rock phosphate amendment. Zinc was found in the exchangeable and reducible fractions in the compost. The bioavailable Zn fraction changed a little during the composting process. The composting process converted the exchangeable Zn fraction into reducible fraction. Addition of an appropriate amount (5.0%) of rock phosphate could advance the conversion. Rock phosphate could reduce metal availability through adsorption and complexation of the metal ions on inorganic components. The increase in pH and organic matter degradation could be responsible for the reduction in exchangeable and bioavailable Cu fractions and exchangeable Zn fraction in rock phosphate amended compost.     

Exploring the Biodegradation Potential of Polyethylene Through a Simple Chemical Test Method

Oxidatively degradable polyethylene is finding widespread use, particularly in applications such as single use packaging and agriculture. However, the key question which still remains unanswered is the ultimate fate and biodegradability of these polymers. During a short-time frame only the oxidized low molecular weight fraction will be amenable to significant biodegradation. The short-time frame biodegradation potential of different LDPE-transition metal formulations was, thus, explored through a simple chemical extraction of oxidized fraction. In addition the effectiveness of different transitions metals was evaluated by comparing the extractable fractions. Blown LDPE films modified with different transition metal based pro-oxidants were thermo-oxidized at 60 °C over extended periods. The structural changes occurring in the polymer were monitored and the oxidized degradation products formed as a result of the aging process were estimated by extractions with water and acetone. The extractable fraction first increased to approximately 22 % as a result of thermo-oxidative aging and then leveled off. The extractable fraction was approximately two times higher after acetone extraction compared to extraction with water and as expected, it was higher for the samples containing pro-oxidants. Based on our results in combination with existing literature we propose that acetone extractable fraction gives an estimation of the maximum short-term biodegradation potential of the material, while water extractable fraction indicates the part that is easily accessible to microorganisms and rapidly assimilated. The final level of biodegradation under real environmental conditions will of course be highly dependent on the specific environment, material history and degradation time.     

Heavy metal content in soil reclaimed from a municipal solid waste landfill

Residues reclaimed from a municipal solid waste (MSW) landfill were characterized for the concentrations of a number of heavy metals. The residue fractions analyzed included a fine fraction (<0.425 mm), an intermediate fraction (>0.425 and <6.3 mm) and a fraction consisting of paper products that could ultimately degrade to a smaller size. The intermediate fraction appeared to be organic in nature, while the fine fraction was more soil-like. In general, the metal concentrations were greatest in the intermediate fraction and lowest in the fine fraction. The effect of sample age on the elemental content was also investigated. The concentrations of several elements were greater in older samples (sample approximately 8 years in age) when compared to newer samples (sample approximately 3 years in age). Limitations associated with the land application of residual soil (composed of the fine and intermediate fractions) were assessed by comparing measured concentrations to regulatory threshold values. In general, most metal concentrations were below regulatory thresholds for use in unrestricted settings. At the concentrations measured, however, several elements might limit reuse options, depending on which regulatory threshold serves as a benchmark. Elevated concentrations of arsenic presented the greatest limitation with respect to common US thresholds while elevated cadmium concentrations presented the greatest limitation when compared to UK thresholds. The source of the arsenic was determined to be the waste, not the cover soil.     

Concentrations of heavy metals in fly ash from a coal-fired power plant with respect to the new Finnish limit values

In Finland, the new limit values for heavy metals in fertilizers used in agriculture and in forestry came into force in March 2007, and for materials used as earth construction agents, in June 2006. From the utilization point of view, it was notable that the total heavy metal concentrations (Cd, Cu, Pb, Cr, Mo, Zn, As, Ni, Ba, and Hg) in fly ash from a coal-fired power plant were lower than those limit values. The concentrations of the easily soluble elements Ca, Mg, Na, P, and Zn in the fly ash were between 3.5 and 35 times higher than those found in the coarse mineral soils of Finland. Fly ash is a potential agent for soil remediation and for improving soil fertility. If inorganic materials and by-products are utilized in earthworks, the content of harmful compounds must be low and the harmful components must be tightly bound to the matrix. Therefore, a five-stage sequential extraction procedure was used to evaluate the extractability of different elements in fly ash into the following fractions: (1) the water-soluble fraction, (2) the exchangeable fraction (CH₃COOH), (3) the easily reduced fraction (NH₂OH-HCl), (4) the oxidizable fraction (H₂O₂ + CH₃COONH₄), and (5) the residual fraction (HF + HNO₃ + HCl).     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

Evolution of organic matter fractions after application of co-compost of sewage sludge with pruning waste to four Mediterranean agricultural soils. A soil microcosm experiment

The effect of co-compost application from sewage sludge and pruning waste, on quality and quantity of soil organic carbon (SOC) in four Mediterranean agricultural soils (South Spain), was studied in soil microcosm conditions. Control soil samples (no co-compost addition) and soils treated with co-composts to a rate equivalent of 140 Mg ha^?1 were incubated for 90 days at two temperatures: 5 and 35 °C. The significances of incubation temperature and the addition of co-compost, on the evolution of the different fractions of SOC, were studied using a 2³ factorial design. The co-compost amendment increased the amounts of humic fractions: humic acids (HA) (1.9 times), fulvic acids (FA) (3.3 times), humin (1.5 times), as well as the free organic matter (1.4 times) and free lipids (21.8 times). Incubation of the soils enhanced its biological activity mainly in the amended soils and at 35 °C, leading to progressive SOC mineralization and humification, concomitant to the preferential accumulation of HA. The incubation results show large differences depending on temperature and soil types. This fact allows us to select suitable organic amendment for the soil when a rapid increase in nutrients through mineralization is preferred, or in cases intending the stabilization and preservation of the SOC through a process of humification. In soils with HA of more than 5 E₄/E₆ ratio, the incubation temperature increased rates of mineralization and humification, whereas lower temperatures limited the extent of both processes. In these soils the addition of co-compost in spring or summer is the most recommendable. In soils with HA of lower E₄/E₆ ratio (<5), the higher temperature favoured mineralization but not humification, whereas the low temperature maintained the SOC levels and even increased the HA/FA ratio. In these soils the moment of addition of organic amendment should be decided depending on the effect intended. On the other hand, the lower the SOC content in the original soil, the greater are the changes observed in the SOC after amendment with co-compost. The results suggest that proper recommendations for optimum organic matter evolution after soil amendment is possible after considering a small set of characteristics of soil and the corresponding soil organic matter fractions, in particular HA.     

Initial Changes in Refilled Lysimeters Built with Metal Polluted Topsoil and Acidic or Calcareous Subsoils as Indicated by Changes in Drainage Water Composition

Soil translocation for recultivation of soil removed from construction sites and for the preparation of refilled lysimeters inevitably involves disturbance of soil structure, and, if intermediate storage is included, also drying and rewetting of the soil. We report on an experiment with model forest ecosystems, where uncontaminated forest subsoils were covered with non-contaminated or freshly heavy metal (mainly Zn and Cu) contaminated topsoil in large lysimeters. Monitoring of the chemical composition of the drainage water revealed two distinct soil conditioning phases. During an initial phase of about a year strongly elevated nitrate and sulfate concentrations occurred that were attributed to a mineralisation flush caused by the increased accessability of mineralisable nitrogen and sulfur in destroyed aggregates. These effects were significantly larger in lysimeters with calcareous subsoil than in those with acidic subsoil. The second phase was characterised by a gradual decrease in dissolved organic carbon and sulfate concentrations, in particular in the acidic subsoil. This decrease may be attributed to the depletion of pools made accessible during aggregate destruction or the formation of new aggregates. These chemical changes had only little effects on the concentrations of copper and zinc in the drainage water. Based on our results, it can be concluded that large refilled lysimeters can be used for many purposes without risk of compromised results, if a conditioning phase of about 1 year with sufficiently moist soil conditions is respected. Nevertheless, gradual changes in soil chemical characteristics still occur after this initial phase. Implications for the recultivation of sites using relocated soils are discussed.     

Maturity assessment of compost from municipal solid waste through the study of enzyme activities and water-soluble fractions

In this work the dynamics of biochemical (enzymatic activities) and chemical (water-soluble fraction) parameters during 100 days of municipal solid wastes composting were studied to evaluate their suitability as tools for compost characterization. The hydrolase (protease, urease, cellulase, beta-glucosidase) and dehydrogenase activities were characterized by significant changes during the first 2 weeks of composting, because of the increase of easily decomposable organic compounds. After the 4th week a "maturation phase" was identified in which the enzymatic activities tended to gently decrease, suggesting the stabilisation of organic matter. Also the water-soluble fractions (water-soluble carbon, nitrogen, carbohydrates and phenols), which are involved in many degradation processes, showed major fluctuations during the first month of composting. The results obtained showed that the hydrolytic activities and the water-soluble fractions did not vary statistically during the last month of composting. Significant correlations between the enzymatic activities, as well as between enzyme activities and water-soluble fractions, were also highlighted. These results highlight the suitability of both enzymatic activities and water soluble fractions as suitable indicators of the state and evolution of the organic matter during composting. However, since in the literature the amount of each activity or fraction at the end of composting depends on the raw material used for composting, single point determinations appear inadequate for compost characterization. This emphasizes the importance of the characterization of the dynamics of enzymatic activities and water-soluble fractions during the process.     

Effect of sewage sludge or compost on the sorption and distribution of copper and cadmium in soil

The application of biosolids such as sewage sludge is a concern, because of the potential release of toxic metals after decomposition of the organic matter. The effect of application of sewage sludge (Sw) and compost (C) to the soil (S) on the Cu and Cd sorption, distribution and the quality of the dissolved organic matter (DOM) in the soil, was investigated under controlled conditions. Visible spectrophotometry, infrared spectroscopy, sorption isotherms (simple and competitive sorption systems), and sequential extraction methods were used. The E4/E6 (lambda at 465 and 665 nm) ratio and the infrared spectra (IR) of DOM showed an aromatic behaviour in compost-soil (C-S); in contrast sewage sludge-soil (Sw-S) showed an aliphatic behaviour. Application of either Sw or C increased the Cu sorption capacity of soil. The Cd sorption decreased only in soil with a competitive metal system. The availability of Cu was low due to its occurrence in the acid soluble fraction (F3). The Cu concentration varied in accordance with the amounts of Cu added. The highest Cd concentration was found in the exchangeable fraction (F2). The Sw and C applications did not increase the Cd availability in the soil.