Developing and validating a decision support tool for media selection to mitigate drainage waters

Authors: EZZATI, GONAZ - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); HEALY, MARK - National University Of Ireland; CHRISTIANSON, LAURA - University Of Illinois; Feyereisen, Gary; THORTON, STEVEN - University Of Sheffield; DALY, KAREN - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY); FENTON, OWEN - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY)

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2019
Publication Date: 8/1/2019
Citation: Ezzati, G., Healy, M.G., Christianson, L.E., Feyereisen, G.W., Thorton, S.F., Daly, K., Fenton, O. 2019. Developing and validating a decision support tool for media selection to mitigate drainage waters. Ecological Engineering. 2:100010. https://doi.org/10.1016/j.ecoena.2019.100010.
DOI: https://doi.org/10.1016/j.ecoena.2019.100010

Interpretive Summary: Losses of nitrate-nitrogen (-N), ammonium-N, and dissolved reactive phosphorus (DRP) through subsurface drainage systems to natural waterways is an international concern. Treatment options include filtration or bioremediation with media that tend to be more effective for one nutrient than the others. This paper introduces a new decision support tool, FarMit, that guides selection of a filter medium appropriate for a given site given the water chemistry, filter medium physical properties (e.g., hydraulic conductivity, breadth of removal capacity, potential for unintended consequences), local availability, and cost. Through literature review, 75 media were catalogued and used as possible candidates within FarMit. FarMit is built in spreadsheet format and is relatively simple to operate. Case studies are presented from Ireland, Belgium, and the USA, each having different drainage water quality issues. The DST is designed to facilitate discussion and decision making among conservation professionals and producers. The findings of this research are also pertinent to researchers, policy makers, and industry personnel.

Technical Abstract: The nitrogen (nitrate (NO3-N) and ammonium (NH4-N)) and/or dissolved reactive phosphorus (DRP) load discharging from a drainage system can be minimised by a reactive or biological media filter. Knowledge of the nutrient content of the drainage water may be elucidated directly from water testing which immediately focuses the filter media selection. However, selection of a filter media must not only consider its nutrient removal capacity but also must consider criteria such as lifetime of media, hydraulic conductivity, the potential of “pollution swapping”, capacity of removing other contaminants than the target contaminant (e.g. pesticides, organic carbon, etc.) and dynamic criteria such as local availability and media price and delivery to site. At present there is no decision support tool (DST) that houses and connects all this information. Therefore the objective of the present study was to develop such a DST that could facilitate all of these criteria and give the “DST user” a quick list of media options to solve their site specific drainage water quality issue. A literature review enabled farm nutrient losses along the drainage pathway to be divided into five scenario types (A1, A2, B1, B2 and C), which on any site could be matched with water test results. Furthermore the literature review enabled a static scoring system to be developed across seven criteria and a dynamic scoring system to be developed across two criteria for 75 media types. The DST was validated using case studies from Ireland, Belgium and the USA which had different drainage water quality issues. For the Irish case study, water test results indicated elevated NH4-N and DRP (Scenario B2) in drainage water. The static scoring system placed zeolite and vertiver grass as top media options for NH4-N and DRP, respectively. This changed to zeolite and sand after the dynamic criteria were considered. For the Belgium case study, NO3-N and DRP (Scenario A2) needed mitigation with woodchip and vertiver grass selected based on static criteria but changing to woodchip and crushed concrete after consideration of dynamic criteria. The USA case study presented NO3-N only (Scenario A1) issues and therefore woodchip was selected after both static and dynamic criteria. In practice the DST takes a very short period of time to get a list of potential media for particular drainage water issues and can act as a discussion piece with a client to make informed choices based on local availability and economics. The DST framework can facilitate data on an infinite number of media and should be developed further to include other pollutants that discharge with drainage waters.