Environmental evaluation of sewage sludge application to reclaim limestone quarries wastes as soil amendments

Restoration of degraded soils with organic wastes could be a feasible practice to minimize erosion in the Mediterranean area, but with the risk of soil and groundwater pollution. Currently the use of sewage sludge to improve the nutrient contents of a soil is a common practice. The soil to which a great amount of fertilizers is usually applied, may favour the solubilization of inorganic compounds. In order to study the mobility of some of these elements through the soil, we designed an experiment aimed to reproduce the behaviour of different compounds and heavy metals in the soil as a part of the non-saturated zone. A controlled experiment in a greenhouse using soil columns was used. A mineral residue from a limestone quarry in Alicante (south-east of Spain) was amended with 30 and 90 t of sludge ha⁻¹. Nitrate, ammonium, cadmium, and nickel were analysed in leachates collected at the bottom of the columns. We found high concentrations of nitrates and ammonium in leachates, which imply an important environmental risk. No important displacements of Cd and Ni were found.