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Project title

Willow evapotranspiration systems as nature-based solutions for on-site wastewater treatment in low permeability areas

Primary Funding Agency

Environmental Protection Agency

Co-Funding Organisation(s)

n/a

Lead Organisation

University of Dublin, Trinity College (TCD)

Lead Applicant

Laurence Gill

Project Abstract

The research project, EVAPOTREAT, will evaluate the applicability of nature-based, on-site wastewater treatment systems in areas with low soil permeability where solutions specified in the current legislation (i.e. the 2021 Code of Practice for Domestic Waste Water Treatment Systems (PE ≤ 10)) involving soil percolation will not work. The main focus will be on carrying out full-scale field trials using willow evapotranspiration (ET) systems in an Irish climate in areas with representative low permeability soils in order to provide data from which robust design guidelines can be developed for zero discharge wastewater treatment systems. The project will be completed over a 36-month time-frame. Existing full-scale willow ET systems constructed in Ireland over the past few years have demonstrated that that they can act as effective nature-based, passive treatment systems that operate effectively, thereby significantly lowering risks of pollution to either groundwater or surface waters. They also produce a renewable source of energy, the wood biomass which needs to be harvested every three years to ensure vigorous growth of the willows. However, the trials have shown that such open systems backfilled with the native soil in an Irish climate will inevitably produce some runoff overflow over the winter period following periods of heavy rain. One aim of the project is to assess and quantify the water pollution impact of these existing fully open willow ET systems (designed according to the current EPA guidelines) with respect to local receiving water quality in low permeability areas, especially after periods of heavy rainfall in the wintertime. This project will use all of the data collected from these existing willow ET treatment systems, as well as the continued monitoring of some of them, in order to characterise the realistic evapotranspiration performance by the willows on Irish wastewater. This knowledge will then be used to modify the process design to incorporate a surface mound which is partially covered with an impermeable liner (in order to limit the rainfall ingress) to see if they can operate as zero -discharge systems. Three of these new partially covered systems will be constructed in collaboration with Leitrim County Council and monitored over the period of the project, to assess whether they can indeed act as zero-discharge systems. The data from the fieldwork studies, as well as simulations from numerical models that will be developed, will then be used to produce robust design guidelines for zero discharge solutions (if feasible) for different geographic locations across the country, based on the concept of a mounded impermeable cover diverting a fraction of the rainfall off to the sides. The project will also synthesis the current state of knowledge with respect to alternative low / zero effluent wastewater treatment, ecosanitation and nature-based technologies via a combination of literature review and international contacts. Finally, the research project will provide a quantitative comparison of the long-term environmental sustainability of these nature-based systems (compared to other more conventional on-site wastewater treatment systems) using Life Cycle Assessment methodologies.

Grant Approved

�349,314.60

Research Hub

Healthy Environment

Research Theme

n/a

Start Date

31/03/2022

Initial Projected Completion Date

30/03/2025