Saturday, 15 July 2006

A Column Study Using Mixtures of Anthropogeomorphic Materials.

Ander Santesteban1, Rocio Melendez1, Fernando Blanco1, Miriam Pinto1, Maria Luisa Ibargoitia1, Felipe Macias2, and Marta Camps Arbestain1. (1) NEIKER, Berreaga 1, Derio, Spain, (2) Univ. Santiago de Compostela, Dpto. Edafologia; Fac. Biologia, Santiago de Compostela, 15782, Spain

The elaboration of soils from anthropogeomorphic materials can be a feasible method of re-using waste products and restored degraded areas, while at the same time recycling essential nutrients and stabilising the organic matter present in these materials, if they are of adequate quality and applied according to good practices. The best mixture of the different ingredients is the blend that generates a soil that would restore the affected area without any risk to the environment, but would provide a supporting media for plant growth and site reclamation. The objective of this study was to carry out a soil column experiment in which mixtures of different organic and inorganic waste products were tested to achieve a correct balance of essential nutrient concentrations, immobilization of heavy metals, organic C stabilization, and good drainage. Waste materials were mixed in a proportion of 56:44 organic waste:inorganic waste (dry weight basis). The mixtures used were: sewage sludge + foundry sand, sewage sludge + L-D slag, sewage sludge + mixture of foundry sand and L-D slag (50:50; dry weight basis). Two different types of sewage sludge were tested, anaerobic (AN) and aerobic (AE), which were previously air-dried and sieved through a 4 mm sieve. The columns were made of polypropylene, and had 250 mL volume and 4.5 cm diameter. Three replicates per treatment were used. The columns were filled with the different mixtures, which were previously wetted to field capacity. A drip irrigation system was used to add 100 mL of distilled deionized water to the soil columns twice a week, and leachates were collected thereafter. The experiment is being carried out at present (week 3) and will last 8 weeks. The results of X-ray diffraction analysis indicates the presence of wustite (FeO), portlandite (Ca(OH)2), calcite (CaCO3), larnite (Ca2SiO4), carbon (C), and aragonite (CaCO3) in the L-D slag, and that of quartz (SiO2) and microcline (KAlSi3O8) in the foundry sand. Soil particle size analysis, obtained using a laser diffraction particle size analyser, indicates the following compositions according to the USDA system: foundry sand (1.0% coarse sand, 46.3% fine sand, 8.5% silt, and 20.4% clay) and L-D slag (44.8% coarse sand, 35.9% fine sand, 16.5% silt, and 2.9% clay). The pH values of the foundry sands and LD slag were 9.6 and 12.1 respectively, and those of the AN and AE sewage sludge were 7.9 and 6.7, respectively. The leachates are being analysed for pH, EC, major anions and cations, and heavy metals. Ecotoxicological analysis will also be carried out. The soil columns will be dismantled at the end of the experiment and analysed for total C, N, major nutrient elements and heavy metal contents. Organic matter will be characterized by different methodologies: extractability with sodium pyrophosphate, oxidability with 33 mM KMnO4, FTIR, and thermal analysis. Results of the experiment will provide data for predicting nutrient availability, heavy metal mobility, and C stability in order to carry out environmental risk assessment of the use of waste mixtures in soil environments.

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