Treatment Systems for Single Houses

Date released: Aug 24 2005

The Environmental Protection Agency (EPA) has recently sponsored research into effective wastewater treatment systems for single houses.  The research involved a series of rigorous trials of various wastewater treatment systems to assess the performance of septic tanks and other small-scale secondary treatment applications.  Researchers from the Environmental Engineering Group from Trinity College undertook the project, on behalf of the EPA. 

In Ireland, wastewater from a significant proportion of the population is treated by small-scale on-site systems where connection to a sewer is unfeasible, usually in rural areas.

“The EPA has repeatedly stated that in many cases a lack of understanding of the treatment and disposal processes involved in small scale domestic wastewater treatment has led to poor design, siting and installation of on-site treatment systems. This has resulted in contamination of groundwater, rivers and streams”, said Gerard O’ Leary, EPA Programme Manager.

“Domestic wastewater contains many substances that are undesirable and potentially harmful to human health and the environment. Through our research the EPA aims to improve the functioning of wastewater treatment systems widely used across the country and so protect water quality”, he said.

A variety of on-site systems are available in Ireland, the most common system being the conventional septic tank system.  There are over 350,000 of these systems currently installed in Ireland.  They consist of a septic tank and below surface soil disposal field or percolation area.

Other system types, collectively called packaged secondary treatment systems, take the form of mechanical aeration systems, filter systems and constructed wetlands.

The main findings from four separate field trials covering a range of different soil types over a twelve month period are:

  • The systems studied were all capable of treating wastewater from a domestic house.
  • The conventional septic tank and percolation area provided a comparable performance to the packaged secondary wastewater treatment system and percolation area.

As well as sponsoring research into small wastewater treatment systems the EPA has published two guidance documents on the proper selection, design, operation and maintenance of these systems to enable sustainable development to take place in Ireland. 

“Local authorities, through the planning system, can ensure that housing developments in suitable areas have minimal impacts on water quality.  The EPA has advised local authorities in our most recent water quality report that the risk presented by a proliferation of on-site sewage treatment systems will need to be kept under surveillance if increased groundwater contamination is to be avoided” said Gerard O’ Leary.

The research report, entitled An Investigation into the Performance of Subsoils and Stratified Sand Filters for the Treatment of Wastewater from On-site Systems is available at