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Application of drinking water treatment sludges to land: opportunities and implications

Applying drinking water treatment residuals to land: opportunities and implications.

Scottish Water has identified the need to transition the outlet for water treatment residuals (WTR) from land restoration to agricultural land due to the increase in WTR, landfill charges, reduced lifespan of sites and sustainability. 

This study supports transition by addressing knowledge gaps e.g.,

  • what are the benefits and disbenefits of applying drinking WTR to land?
  • How does this align with the circular economy?  
  • What is best practice for application to land? 

The key findings, published here, are that application of WTR has resulted in benefits to soil properties i.e., water retention, porosity, hydraulic conductivity and P storage capacity without negative impacts on groundwater. No change in plant yield was reported. Application of WTR to lands with pH<5.5 should be avoided. The parameters to be assessed for application are described. Sole application of WTR is suitable for land restoration. However, if separate applications of fertilisers are made, WTR application could enhance soil and plant properties in agricultural land and forestry. The circular economy may benefit through the recovery of chemical resources, although investment and appropriate legislation are missing. A decision support tool for the application of WTR to land in Scotland was developed (available on the here).

Project Objectives

Contact Nikki Dodd
24th March 2022

Moving to more sustainable methods of slurry application: implications for water quality of waterbodies and water protected areas


This report is a quick scoping review (QSR) of peer reviewed and grey literature to provide an evidence-based comparison of different low emission slurry spreading (LESS) approaches in terms of farming practice, ammonia and nitrous oxide emissions and risk of water pollution from slurry spreading to inform farmer-focused guidance on LESS. The work is focused on slurry-borne contaminants that are relevant to the water quality objectives under the river basin management plans (RBMP) set by the Scottish Environment Protection Agency (SEPA), such as nitrate, phosphorus and faecal indicator organisms (FIO).

The key question addressed by the project is ‘What are the effects of low emission slurry spreading (LESS) approaches on water quality?

This QSR showed that the key factors influencing the impact of LESS approaches on losses of slurry-borne pollutants to water are precipitation, soil moisture, soil permeability and drainage, and presence of vegetation, be it crop, grass or vegetated buffer strips. The role of these factors has already been captured in the current regulatory framework, stipulating specific obligations for farmers under GBR18 and The Action Programme for Nitrate Vulnerable Zones (Scotland) Regulations 2008. The already existing guidance is still valid to protect water quality.  However, the choice of LESS approach should be determined by environmental designations and account for the most vulnerable environmental component (soil/atmosphere/ waterbodies) of the agro-ecosystem. Guidance to farmers should also consider a compromise between feasibility, cost, and environmental and agronomic objectives.

Winners announced at World Water Day!

In March 2020 when the pandemic succeeded to 'lock Scotland down', CREW, in partnership with SEFARI Gateway, SAGES and HEIs, opened a video competition to virtually engage Scotland’s water community and share contemporary views of the importance of water in research, management, innovation and recreation.

Videos were submitted to one of seven thematic areas and were captured online for future use as a teaching resource and to promote wider engagement of our water community.

At World Water Day (22nd March 2022), a film of the winning entries was shown and prizes awarded for each category (see below).

The acceptance speech of the Sefari Gateway theme winner, Kate MacLeod can be viewed here.

Thanks to everyone for supporting this project by sharing excellent videos, the universities etc for helping to promote the project and SEFARI Gateway and SAGES for their financial support.

Theme Title Winner
Droughts and Floods Allt Lorgy, 'Stage Zero' Approach to River Restoration Duncan Ferguson (Spey Fishery Board and Partners)
Freshwater Restoration The River Leven Restoration Project Sarah Macdonald (Fife Coast and Countryside Trust)
Innovation in the Water sector Innovator in water treatment technology Victoria Porley (Uni of Edinburgh)
Living with Climate Change Wetland farming for climate adaptation Yanik Nyberg (Seawater Solutions)
Nature Based Solutions

Overview of work undertaken to understand the ecosystem

service provision potential of floating treatment wetlands

Jonathan Fletcher (University of Stirling/HNIC)
Water Quality "We all have a role to play in reducing water contamination" Lucille Groult (Uni of Dundee)
Water and Wellbeing Rocket Man!! Citizen science project : OurVoice Susan Grant (Glasgow Caledonian Uni, Cadder Primary School)
SEFARI Gateway

The Hebridean Mermaid shares her love of the ocean and

the therapeutic benefits of the underwater world.

Kate MacLeod



18th March 2022

Effectiveness of construction mitigation measures to avoid or minimise impact to groundwater dependent wetlands and to peat hydrology


The overall aim of the project was to review the effectiveness of standard mitigation measures to maintain the hydrological conditions within peat soils and wetland habitats. The findings of this work will assist the Scottish Environment Protection Agency (SEPA) to provide knowledge and guidance to developers in relation to appropriate construction techniques and enhance practice around avoidance, impact minimisation, habitat creation and restoration.

This research identified the most common impacts from construction activities as well as the efficacy of different mitigation methods in minimising those construction impacts on peatlands and wetlands. The work involved a literature review of evidence of the impacts of construction on habitats and groundwater in groundwater dependent wetlands and peat. Developers and contractors were consulted regarding the effectiveness of different approaches; on remedial actions taken during monitoring or observation and on identifying ongoing issues. The research was also used to develop policy and regulatory relevant recommendations.

15th March 2022

Applying drinking water treatment residuals to land: opportunities and implications

Applying drinking water treatment residuals to land: opportunities and implications.

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.  

15th March 2022

Pharmaceuticals in the water environment: baseline assessment and recommendations

Front page image

This study carried out by researchers at Glasgow Caledonian University (GCU), with the James Hutton Institute and the Environmental Research Institute (University of the Highlands and Islands) delivered the first national assessment of the emerging area of concern around pharmaceutical pollution of Scotland’s water environment, with an innovative Scottish partnership (One Health Breakthrough Partnership) using results to promote practical actions to reduce this globally recognised public health and environmental issue.

Pharmaceuticals (medicines) enter the water environment when people taking medicines go to the toilet (between 30-100% of a dose is excreted) and when partially used or expired medicines are inappropriately flushed down the toilet instead of being returned to a pharmacy for proper disposal.

Key messages from the study include:

  • Data on 60 medicines in the water environment, known to occur through consumption and inappropriate disposal into wastewater systems, were obtained from a range of sources
  • Nine medicines were recommended for further action to reduce the potential environmental risk
  • The need to promote positive action on medicine use and disposal, to reduce pharmaceutical pollution
14th March 2022

Sediment continuity through run-of-river hydropower schemes


The Scottish Government’s ambition to decarbonise its electricity generation means that run-of-river hydroelectric power schemes are now a feature of many Scottish catchments. The essential requirements of these schemes (adequate hydraulic head and flow) mean that their locations often coincide with important freshwater habitat. A scheme can have various effects on the quality and extent of this habitat, in and downstream of the depleted reach (between the intake and tailrace), and upstream of the impoundment. The interruption of natural sediment movement is one such effect and, if measures to ensure that conveyance is maintained are not included in the design of a scheme, it can have significant and far reaching consequences for habitats, species, channel evolution, and adjacent land. It can also, significantly for the operator, affect the efficiency and profitability of a scheme. The realisation that the need to maintain sediment continuity has not been adequately taken into account for many schemes was the impetus for this project. The research published in this report has led to recommendations for dealing with accumulations of sediment at operational schemes, and for the incorporation of sediment management measures in proposed schemes. The effects of climate change and the biodiversity crisis have increased the imperative for remedial action and to ensure that measures for maintaining sediment movement and other natural processes are incorporated in the design of existing and new schemes.

9th March 2022

First Annual CREW Lecture (22nd March 2022) - view online

On World Water Day 2022, CREW hosted the first annual CREW Lecture at Our Dynamic Earth (Edinburgh) & on live-stream. Professor Alan Jenkins (Deputy Director and Science Director, UKCEH), available online.

1st Annual CREW Lecture: Water science supporting policy- reflections and future challenges 

Find out more about - World Water Day 2022

Profile: Professor Alan Jenkins

Professor Alan Jenkins is Chief Scientist at UK Centre for Ecology & Hydrology (UKCEH). He is Hydrological Adviser to the Permanent Representative of the UK with World Meteorological Organisation, acts as UK Head of Delegation with the UNESCO IHP and chairs the UK Committee for International Hydrology. He holds an Honorary Professorship at Lancaster University and is a Visiting Professor at University College London. 

Please contact event co-ordinator for any enquries:


2nd March 2022

Moderating extremes in water availability: a review of the role of functioning wetlands

Wetlands can be defined as areas of marsh, fen, or peatland with permanent or temporary water (brackish or freshwater). They cover an estimated 2 million hectares of Scotland’s land area from uplands to the coastline and are important for sequestering carbon, providing habitat, storing water, and maintaining biodiversity. When in good health, these wetlands can have capacity to buffer both high and low flows for moderating extremes in water availability (i.e., flood and drought risks respectively, both individually and in combination) which are predicted to become more frequent due to climate change. Yet the health of wetlands is under extensive pressure from land use conversion, management, and climate change. Furthermore, what has been missing up to now is an assessment of a broad range of wetlands with respect to their buffering capacities for both high and low flows. To improve wetland resilience, we also need to better understand the various impacts on such capacities, as well on their biodiversity.

The aim of this project was to review the role of functioning wetlands in moderating extremes in water availability in a Scottish context. A comprehensive assessment of the current and future buffering capacity to high and low water flows of the eighteen wetland types that occur in Scotland was undertaken. This used an interdisciplinary approach and synthesised information from the available literature, expert opinion, indicator data analysis, mapping visualisation methods, climate change scenario modelling and workshop participation for responding to the overall objective and four research questions asked. Assessments on the health, biodiversity, and ability to mitigate droughts and flooding was made across this broad range of wetlands. Wetland area extent was also mapped, and the impacts of climate change were assessed using models. This enabled an assessment of how the water holding and biodiversity characteristics of wetlands may be impacted by climate change. Together, these strands of work informed recommendations for creating, maintaining and restoring wetlands.  The evidence on the ability of wetlands to buffer extremes of water quantity was often limited with the effects depending on the timing, location, and health of a particular wetland. Thus, a cautious assessment was made. It was found that most wetland types have a limited ability to moderate extremes in water availability, with particular wetland types like floodplain fens, swamps, wet woodland and reedbeds having the best potential. These should be prioritised for restoration especially in catchments that are at high risk of drought and flooding. However, given the poor health or loss of wetlands, it is expected that restoring all wetland types where opportunities arise will also improve mitigation. Climate change is expected to lead to wetter conditions in wetlands in the north-west with wetlands in the east becoming drier; the health of 10 out 18 wetland types and the ability to moderate water extremes, is at risk.  More frequent drought is also expected to threaten rare plant species and 98 out of 700 species in the Scottish Biodiversity List are vulnerable to change which could in turn have impacts on the water holding capacity of wetlands. Some existing policies, such as the Flood Risk Management Act and Scottish Climate Change Action Programme, already provide support for maintaining and restoring wetlands. This project also made key recommendations, such as maintaining reliable funding, improving the planning framework, and redesigning agri-environmental schemes, for enhancing wetland buffering capacity in Scotland.

2nd March 2022

Taking a collaborative approach in the water sector: A review of the Metropolitan Glasgow Strategic Drainage Partnership

Front page to the MGSDP report

The Metropolitan Glasgow Strategic Drainage Partnership (MGSDP) is a non-statutory partnership between public bodies involved in managing surface water, water quality, flood risk, investment planning and economic delivery, with a vision to ‘Sustainably Drain Glasgow’. The MGSDP began following severe flooding in July 2002 in the East End of Glasgow. It was recognised that an integrated strategy to master planning was required to meet the needs of all stakeholders as responsibilities for stormwater management in Scotland are divided between several parties, with conflicting statutory duties and unaligned funding streams making collaboration difficult.

The Partnership vision is to “transform how the city region thinks about, and manages rainfall, to end uncontrolled flooding and improve water quality”. The vision provides a strategic focus and is supported by five objectives and eight guiding principles.

As the MGSDP enters its next phase, now is an ideal time to take stock of the gains made, study its impact, and fully understand how the knowledge gained can be used to address challenges other cities in Scotland face. In the coming decade the scientific, political and public aspirations to mitigate climate change impacts will result in increased demand for investment in adaptive approaches and collaborative working. To support the MGSDP and inform policy developments, the research team reviewed how it has operated to identify the lessons learnt. To deliver this, a literature review was undertaken, consultation data gathered, case studies developed, and recommendations made.

Lessons learnt are considered in the context of both the MGSDP’s future and the development of new partnerships.

Lessons learnt from the MGSDP: (1) A coordinator is required to drive the partnership working process and sustain strong collaborative groups; (2) Knowledge building is crucial to avoid narrow-focussed partnerships and deliver broad agendas; (3) Being open, honest and sharing information builds trust and helps overcome barriers such as lack of equity and misaligned policy/funding cycles.

Lessons learnt for Policy Makers: (1) robust coordination maintains focus on a co-developed vision; (2) Overlapping responsibilities and misaligned funding cycles are challenges to efficient progress; (3) Establishing trust, leads to enhanced problem solving and a willingness to take risks.


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