Engracia Madejón

In situ remediation of metal-contaminated soils with organic amendments: role of humic acids in copper bioavailability

The purposes of this study were to determine the Cu(II) binding behavior of humic acids (HAs) isolated from biosolid compost (BI), leonardite (LE), a metal-contaminated soil, and the soil remediated with either BI or LE in relation to their structural properties, and to explore the role exerted by the HA fractions in controlling soil Cu(II) bioavailability. Potentiometric titrations at pH 5 and ionic strength 0.1M and the Langmuir model were used to obtain the Cu(II) complexing capacity of the HAs examined and the conditional stability constant of the Cu(II)-HA complexes. The Cu(II) complexing capacity increased as the content of acidic ligands, especially COOH groups, aromaticity, and humification degree increased, following the order BI-HA<BI-amended soil HAs<unamended soil HA<LE-amended soil HAs<LE-HA. In contrast, the conditional stability constant of Cu(II)-HA complexes increased in the opposite order, probably due to an increased chelating effect. Compared to LE, amendment with BI was slightly more effective in decreasing soil CaCl(2)-extractable Cu content. The results obtained suggested that the pH of the soil-amendment system is the most important chemical property governing Cu(II) solubility and bioavailability in metal-contaminated soils remediated with BI and LE, although soil organic matter and the HA fraction may also be important factors. In particular, binding sites formed by N-, S-, and O-containing acidic functional moieties in HAs may play an important role in the Cu(II) behavior.

Agricultural use of three organic residues: effect on orange production and on properties of a soil of the ‘Comarca Costa de Huelva’ (SW Spain)

Disposal of urban, agricultural and industrial organic residues impliesan increasing problem because of all the economic and environmentalrepercussions involved. One of the most adequate ways of managing this problemis the agricultural use of these wastes as organic amendments. Three organicresidues (AC, olive mill waste water sludge compost; MWC, municipal solid wastecompost; and PS, paper mill sludge) were used in a 3-year field experimentinvolving orange production. The effect of their application on crop productionand on soil quality was investigated. Soil samples (0–20 cm depth)collected 11 months after the last soil amendment were analysed for: pH and EC,Kjeldahl-N, available-P, available-K, total organic carbon, humic substances,dehydrogenase, phosphatase, β-glucosidase, urease andbenzoyl-argininamidehydrolysing protease (BAA-protease) activities. Generally, the application of the MWC and PSincreased orange yield when compared to control. Moreover, total organic carbonand humic substances significantly increased in soils treated with all theorganic amendments. Organic fertilisation increased the Kjeldahl-N andavailable-P contents of the soil. The application of the organic residues also causedsignificant increases in dehydrogenase, β-glucosidase, urease andBAA-protease activities of the soil. Significant positive correlations (p <0.01) between these enzymatic activities and total organic carbon were foundforall treatments. Significant positive correlation between dehydrogenase, urease,β-glucosidase, and BAA-protease and orange yield was also found. However,a clear inhibition of phosphatase activity was observed in soils treated withPS. The results indicate that the repeated application to the soil of moderateamounts of organic amendments has positive effects on the chemical andbiochemical properties of the soil, as well as on the orange yield.

Evolution of humic acid molecular weight as an index of compost stability.

This paper proposes an index for the evaluation of compost maturity based on the evolution of molecular weights of humic acids (HA) during composting. The evolution of HA molecular weight was followed during the composting of both olive mill wastewater (OMW) and olive mill pomace (OMP). The wastes were composted in forced aeration static piles. Samples of the compost were collected at different times during composting. The elution profiles of HA obtained by gel filtration (Sephadex G-150) showed the disappearance of fractions with molecular weights ≤ 50 KDa and the contemporary increase of fraction with molecular weights ≥ 102 KDa. In this range, two fractions can be separated: the first one (A1) with molecular weights greater than 102 KDa and below 2 102 KDa, and the second one (A2) with molecular weight greater than 2 102 KDa. During composting, the ratio A2/A1 tends to reach a constant value which indicates the evolution toward the polymerization of HA. The ratio A2/A1 was named HAEI (Humic Acid Evolution Index). It varies with the material composted and the composting process and represents the maximum possible degree of HA polymerization. A comparison between HAEI and the usually used maturity indexes is also presented.

Trace elements, pH and organic matter evolution in contaminated soils under assisted natural remediation: A 4-year field study

A 4-year study was undertaken on the effect of three amendments (biosolid compost (BC), sugar beet lime (SL), and combination of leonardite plus sugar beet lime (LESL)) on reclamation of a moderately trace element-contaminated soil under field conditions. Results showed that organic C increased in BC and LESL treatments. BC and SL treatments increased soil pH and reduced CaCl(2)-extractable metal concentrations more efficiently. At the end of the experiment, CaCl(2)-extractable metal concentrations decreased and were similar in all treatments pointing out the importance of the natural remediation processes in contaminated soils. Addition of amendments showed no clear reduction in EDTA-extractable trace element concentrations, even, BC and LESL subplots showed some little increase of these elements with time. Amendments did not cause any change in total trace element concentration in soil. Addition of amendments could be a successful and reliable long term technique for stabilization of trace elements in contaminated soils at a field scale with minimum maintenance.

Nitrogen mineralization and nitrate leaching of a sandy soil amended with different organic wastes

Organic wastes can be recycled as a source of plant nutrients, enhancing crop production by improving soil quality. However, the study of the dynamic of soil nutrient, especially the N dynamic, after soil application of any organic material is vital for assessing a correct and effective use of the material, minimizing the losses of nitrate in leachates and avoiding the negative environmental effects that it may cause in groundwater. To estimate the effect of three organic materials, a municipal solid waste compost (MWC), a non-composted paper mill sludge (PS), and an agroforest compost (AC) on the N dynamic of a sandy soil two experiments were carried out: an incubation experiment and a column experiment. The incubation experiment was conducted to estimate the N mineralization rate of the different soil-amendment mixtures. The soil was mixed with the organic amendments at a rate equivalent to 50 000 kg ha-1 and incubated during 40 weeks at constant moisture content (70% of its water-holding capacity) and temperature (28°C) under aerobic conditions. Organic amendment-soil samples showed an immobilization of N during the first weeks, which was more noticeable and longer in the case of PS-treated soil compared to the other two amendments due to its high C/N ratio. After this immobilization stage, a positive mineralization was observed for all treatment, especially in MWC treated soil. Contemporaneously a 1-year column (19 cm diameter and 60 cm height) experiment was carried out to estimate the nitrate losses from the soil amended with the same organic materials. Amendments were mixed with the top soil (0-15 cm) at a rate equivalent to 50 000 kg ha-1. The columns were periodically irrigated simulating rainfall in the area of study, receiving in total 415 mm of water, and the water draining was collected during the experimental period and analysed for NO3-N. At the end of the experimental period NO3-N content in soil columns at three depths (0-20, 20-35 and 35-50 cm) was determined. The nitrate concentration in drainage water confirmed the results obtained in the incubation experiment: nitrate leaching was higher in soil treated with MWC due to its higher N-mineralization rate. Nevertheless, the nitrate losses represented a low amount compared with the total nitrogen added to soil. No clear signs of water-draining contamination were observed during the first year after the application of AC and PS; however, the nitrate leaching in soil treated with MWC slightly exceeded the limit allowed for the Drinking Water Directive 98/83/CE.

Co-composting of sugarbeet vinasse: influence of the organic matter nature of the bulking agents used

Two composts were obtained by co-composting of a concentrated depotassified beet vinasse and two agricultural solid residues with different organic matter nature: grape marc (GM; lignin waste) and cotton gin trash (C; cellulosic waste). Composting was carried out in aerated piles with mechanical turning, in controlled conditions during 4 months. After 71 days of composting, a new addition of vinasse similar to the initial addition was made. Changes in temperature, pH and inorganic nitrogen followed a similar path for both mixtures. However, organic matter fractions showed different behaviour depending on the material co-composted with vinasse. Lower organic matter degradation was observed when GM was used as bulking agent due to its high lignin content. No phytotoxicity was detected in the end products. The chemical and physical properties of both vinasse composts suggest their possible use as fertiliser.

Phytostabilization of semiarid soils residually contaminated with trace elements using by-products: Sustainability and risks

We investigated the efficiency of various by-products (sugarbeet lime, biosolid compost and leonardite), based on single or repeated applications to field plots, on the establishment of a vegetation cover compatible with a stabilization strategy on a multi-element (As, Cd, Cu, Pb and Zn) contaminated soil 4-6 years after initial amendment applications. Results indicate that the need for re-treatment is amendment- and element-dependent; in some cases, a single application may reduce trace element concentrations in above-ground biomass and enhance the establishment of a healthy vegetation cover. Amendment performance as evaluated by % cover, biomass and number of colonizing taxa differs; however, changes in plant community composition are not necessarily amendment-specific. Although the translocation of trace elements to the plant biotic compartment is greater in re-vegetated areas, overall loss of trace elements due to soil erosion and plant uptake is usually smaller compared to that in bare soil.

Modelling vinasse/cotton waste ratio incubation for optimum composting

Abstract A central composite experimental design was used to investigate the influence of incubation conditions (vinasse added and operation time) for vinasse/cotton waste mixtures on the properties of products obtained (pH, electrical conductivity, organic matter, Kjeldahl-N, C/N ratio, biodegradability, Kjeldahl-N losses and germination index) in order to determine the best in-vessel composting conditions. The range of the independent variable measured was 0–80% for vinasse added and 1–50 days for operation time. A second-order polynomial model consisting of two independent process variables was found to accurately describe the vinasse/cotton waste incubation. The differences between the experimental values and those estimated by using the equations never exceeded 10% of the former. Obtaining products with acceptable chemical properties, high biodegradability and minimum N losses entails operating at medium operation time (20–35 days) and 20–30% of vinasse added.

Growth of Populus alba and its influence on soil trace element availability

The use of fast growing trees is a common practice for phytoremediation of contaminated soils. Plant roots can change trace element bioavailability in soils. We studied the effect of Populus alba on trace element bioavailability on two contaminated soils (one with neutral pH and other with acid pH) comparing two methods (0.01 M CaCl2-extractable in soil and concentration in soil pore water SPW), trace element accumulation in leaves and plant development over 36 months. Results were compared to those obtained with a non-contaminated soil. The experiment was carried out in containers (95 L of volume and 1m height). Half of the containers for each soil were planted with P. alba saplings and the others remained without plant. In neutral soils plant growth did not influence soil pH; the greatest effect due to plant growth was found in acid soil. Values of pH obtained by SPW showed a similar trend compared to those obtained after soil KCl extraction. Bioavailability of trace elements determined by both methods followed the same behavior in the three studied soils. Both methods for determining trace element bioavailability in soil were accurate to predict plant uptake. In non-contaminated soil, plants tended to increase micronutrients (Cu, Mn and Zn) availability. However, in case of contaminated soil, the growth of P. alba did not increase trace element availability. Moreover, results on height and diameter of the trunk of the trees, during 36 months, demonstrated that the presence of total trace elements in soil did not affect plant development.

Phytostabilization of Amended Soils Polluted with Trace Elements Using the Mediterranean Shrub: Rosmarinus Officinalis

We evaluate the mid-term effects of two amendments and the establishment of R. officinalis on chemical and biochemical properties in a trace element contaminated soil by a mine spill and the possible use of this plant for stabilization purposes. The experiment was carried out using containers filled with trace element polluted soil, where four treatments were established: organic treatment (biosolid compost, OAR), inorganic treatment (sugar beet lime, IAR), control with plant (NAR) and control without plant (NA). Amendment addition and plant establishment contributed to restore soil chemical (pH, total organic carbon, and water soluble carbon) and biochemical properties (microbial biomass carbon and the enzymatic activities: aryl-sulphatase and protease). The presence of rosemary did not affect soluble (0.01 M CaCl2) Cd and Zn and decreased trace element EDTA extractability in amended soils. There were no negative effects found on plant growth and nutrient content on polluted soils (NAR, OAR, and IAR). Trace element contents were within normal levels in plants. Therefore, rosemary might be a reliable option for successful phytostablization of moderate trace element contaminated soils.