Domestic Wastewater Treatment

Molloy Precast

Over 400,000 households in Ireland have on-site wastewater treatment systems. Typical wastewater treatment systems have two components, namely, a septic tank and a percolation area. Both components are essential to ensure adequate wastewater treatment. Inadequately treated wastewater can impact on the quality of ground water, drinking water and surface water which in turn can affect human health as well as the surrounding environment.

Domestic wastewater is made up of solids, biological pollutants as well as fats, oils and greases (FOGs). Removal of these materials is by a combined effort between the septic tank and percolation system. The purpose of a septic tank is to remove FOGs and solids from the wastewater, while the purpose of the percolation area is to biologically treat the wastewater, removing biological pollutants and to distribute treated wastewater into the groundwater network. It is vital that both components are installed and maintained properly to ensure a trouble free on-site wastewater treatment system.

Other more advanced types of wastewater treatment systems include secondary treatment systems with polishing filters, septic tanks with bio-filters, septic tanks with reed beds and percolation systems and willow beds. These more advanced types of systems are required on poor sites. A site with good/reasonable soakage is suitable for a basic on-site wastewater treatment system. There are several site complications which might necessitate an advanced wastewater treatment system such as:

  • High water-table or high bedrock
  • Poor soakage
  • Small site
  • Sensitive area

Current legislation and guidelines

The current guidelines for the installation of on-site wastewater treatment systems in Ireland are contained within the EPA “Code of practice for wastewater treatment systems for single houses”, 2009. Septic tanks installed in Ireland should be certified to meet EN 12566-1 standards. Secondary treatment systems installed in Ireland should be certified to meet EN 12566-6 standards. Proposed new regulations dealing with domestic wastewater treatment systems were published earlier this year and some of the conditions include:

  • Homeowners should be aware of the location of their on-site wastewater treatment system and should carry out an annual visual inspection, to determine if it is causing pollution or is in need of maintenance
  • Only domestic wastewater should enter the treatment system, i.e. “black water (wastewater from toilets) and grey water” (Wastewater from showers, sink, kitchen etc.). - - Rainwater derived from roofs or surface water Should be excluded from the system. The homeowner must ensure that discharge from the treatment system only goes into the ground and does not seep, leak or otherwise escape from any part of the system where it is not intended to.
  • The homeowner must ensure that discharge is not to the surface of the ground and that wastewater does not rise to the surface causing “ponding”.
  • The homeowner must ensure that discharge is not directly into surface waters such as streams or rivers unless licenced to do so.
  • Sludge removal is dependent on occupancy and size of the septic tank. Larger tanks reduce de-sludging frequency. It is the homeowner’s responsibility to annually check the depth of sludge in their tank, if sludge depth is one third the height of the total liquid depth de-sludging is recommended. Only permitted wastewater collectors are allowed collect and transport sludge, this is to ensure it is disposed of in accordance with legislation.
  • The tank capacity and configuration should be large enough to create a big enough dwell time to allow a septic tank function properly - Roof water and surface water are not allowed to enter the wastewater treatment system
  • Inlet and outlet pipework must be free of blockages
  • Manhole covers, tanks, pipeworks, distribution boxes and t-pieces must be in good working order
  • Any distribution box must ensure even distribution between all trench
  • Any mechanical or electrical equipment must be fit for purpose and operational
  • Aeration vents should be dry and free from obstructions
  • Operational and maintenance regimes, as set out by the manufacturer, must be complied with.