Publication

In 2018/19, Scottish Water’s treatment processes generated c.29,000 tDS²) of Water Treatment Residuals (WTR). WTR, also termed drinking water treatment sludges or bioresource, are produced due to the addition of chemical coagulants to water. The Scottish Water Bioresource Strategy has identified the need to transition the outlet for WTR from purely land restoration to agricultural land due to the likely significant increase in tonnage of WTR over the next 25 years, increasing landfill charges, reduced lifespan of restoration sites and environmental sustainability. 

This study is designed to support this transition to agricultural land by understanding the implications of applying WTR to land by addressing key knowledge gaps including: what are the benefits and disbenefits of applying drinking water treatment sludges to land? How does this fit in the context of the circular economy in Scotland?  What is best practice in terms of assessment of the suitability for application to land? Which measures could help to mitigate the disbenefits? 

Key findings of the study are that the application of WTR to land has predominately resulted in the improvement in soil physical properties such as water retention, porosity, hydraulic conductivity and P storage capacity without negative impacts on groundwater. However, no significant change in plant yield was reported. Application of WTR to lands with pH<5.5 should be avoided, given the potential for the Al in the WTR to become soluble. Sole application of WTR is deemed to be suitable for land restoration. However, if separate applications of fertilisers such as compost, manure or Wastewater Treatment Residuals (WWTR) are made, WTR application could enhance soil and plant properties in agricultural land and forestry. A user-friendly, decision support tool for guiding the application of WTR to land in Scotland has been developed for end users.