Keele Research Repository

Land application of water treatment residuals (WTRs), a by-product of drinking water treatment, is increasingly common due to tightening landfilling regulations and attempts to embrace greener practices. In this thesis a thorough literature review into WTRs was firstly conducted, with a focus on their end of life uses and any effects they might have on earthworms, soil microbial populations and element bioavailability. The review identified clear knowledge gaps in relation to any such effects, hence these were investigated through a series of interrelated field, semi-field and laboratory studies encompassing WTR-treated and control sites in Wales; indoor and outdoor mesocosms, column leaching and batch extraction experiments, and analysis of WTR and WTR treated soils’ bacterial communities using 16S rRNA sequencing. Key receptors were observed and analysed throughout including earthworms, soil porewater chemistry, bacterial populations, and soil respiration. It can be concluded that the spreading of WTRs to land produced no meaningful, measured negative impacts on terrestrial ecology or soil chemistry when following common practise and respecting current regulatory limits. Key findings include confirming that Al leaching from WTRs is unlikely to occur under common natural conditions, identifying that WTRs can immobilise organic carbon in the soil column, finding that WTRs are unlikely to adversely affect microbial populations, and concluding that earthworm populations were not negatively affected by field or laboratory application of WTRs to soil. Most of the experiments within this thesis were short-term (<1 month), leaving room for longer-term experiments to confirm the permanence of this lack of negative effects. Further avenues for research include exploring the carbon capture potential of WTRs in soils, investigating the effects of WTRs on other terrestrial invertebrates, and exploring the effect of storage time and seasonality on WTRs properties.