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Project Code [2000-MS-15-M1]

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Project title

Wastewater treatment Efficiency of Subsoils and Stratified Sand Filters

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 safe disposal of on-site wastewater is essential for the protection of groundwater in Ireland and has come more into focus recently due to the publication of the EPA guidance manual for Treatment Systems for Single Houses. This project reports the results from four separate field trials carried out on separate sites covering a range of different subsoil types whereby two sites were discharging septic tank effluent into conventional percolation areas and the other two sites were discharging secondary treated effluent from a peat filter into similar percolation areas. Stratified sand filters were also constructed; one receiving septic tank effluent the other receiving secondary treated effluent for comparison. The short duration of the research i- the maximum amount of time that each site was monitored was for 12 months - and the limited numbers of sites investigated mean that only tentative conclusions can be made about on-site wastewater treatment at this stage which will hopefully be corroborated by further research in the future. The project showed that the 1.2 m of unsaturated subsoil receiving septic tank effluent (or 0.6m for secondary treated effluent) as specified in the guidelines provided good removal of both chemical and microbiological pollutants. The majority of degradation of septic tank effluent occurred in the first 300mm below the percolation trenches and the quality of the percolating effluent after 1.0m depth was found to be acceptable for discharge to groundwater. There was a much better removal of nitrogen in the subsoil from the septic tank effluent than from the secondary treated effluent which remained largely untouched in its nitrified form of nitrate. Phosphate removal on the sites seemed to depend mainly on the mineralogy of the subsoil.

Grant Approved

�251,466.55

Research Hub

Natural Environment

Research Theme

Protecting our Water Resources

Start Date

01/11/2000

Initial Projected Completion Date

n/a