To Örebro University

Soil contamination is an urgent issue world wide. More than 83,000 contaminated sites have been identified in Sweden alone, of which approximately some 4,000 require treatment in the near future. Most of the sites carry a mixture of contaminants, metals as well as persistent organics. Most soil remediation efforts are made ex situ, which means that the soil or sludge is dug up and transported to a facility for treatment, or simply for deposition. The aim of the present project is to design a strategy for ex situ treatment of soils with mixed contaminants. A variety of soils and sludges from different sites (around 10), essentially all with organic as well as inorganic (metallic) contaminants, have been selected for experimental studies in laboratory and pilot scale: Military sites (metals, explosives), wood preservation sites (PAHs, As, metals), industrial sites (metals, hydrocarbons, mercury, dioxins and others). Of particular importance in the present study are:

Metals – Pb, Cu, Zn, Cr, Hg, as well as As Organics – PAHs, nitro aromatics, dioxins

A number of processes are selected and applied: •Biodegradation - use of commercially available cultures, as well as bacteria cultivated from the contaminated site itself •Mobilisation of organics - use of surface active agents •Mobilisation of metals - use of (1) complexing microbial metabolites produced in the soil (by fungii in paricular), (2) complexing agents generated by degradation of natural organic products (polyhydroxy carboxylic acids), and (3) artificial complexing agents (polyamino carboxylic acids).

Biodegradation is performed in batches (anaerobic in most cases), while release and mobilisation of contaminants from soil aggregates are achieved during soil-wash performed in a dynamic system where wash solution is forced through the soil under high pressure (the WTC-process). The efficiency of biodegradation and subsequent soil-wash under various conditions is evaluated from chemical analysis, but also by several ecotoxicological tests. Some results are given that illustrates suitable strategies for treatment of mixed contaminated soil from real sites (soil) as well as for treatment of residues from industrial production (sludges etc).