Trialling water treatment residuals in the remediation of former mine site soils: investigating improvements achieved for plants, earthworms and soil solution.

During clarification processes of raw water a vast amount of by-product known as drinking water treatment residuals (WTRs) are produced, being principally composed of hydroxides of the Al or Fe salts added during water treatment plus the impurities they remove. Aluminium-based (Al-WTR) and iron-based (Fe-WTR) materials were applied at 10% w/w to degraded, bare (un-vegetated) soils from a restored coal mining site in central England (pH <3.9) to study their potential amelioration effects on earthworm mortality, biomass yield of seedling plants and element concentrations in plant tissues, earthworm tissues and in soil solutions. A separate treatment with agricultural lime was also conducted for comparison to evaluate whether any observed improvements were attributable to the liming capacity of the WTRs. After completion of the trials all samples were subjected to a wet-dry cycle and the experiments were repeated (i.e. simulating longer-term effects in the field). Both types of WTRs significantly increased biomass of plants and, in some treatments, survival of earthworms was also enhanced compared to non-amended soils. Excess plant tissue element concentrations and element concentrations in soil solutions were reduced in amended soils. The implications are that adding WTRs to mining impacted soils is a potentially viable, sustainable and low cost remediation method that could be used globally to improve the soil condition. This article is protected by copyright. All rights reserved.