Urban Wastewater Management

Water Waste Treatment Process

Typical Treatment Process
© Department of Environment, Community and Local Government

Water Waste Treatment Process:

Step 1: Sanitary Sewer                                    Step 4: Aeration Tanks

Step 2: Grit Chamber                                      Step 5: Secondary Treatment Tank

Step 3: Primary Treatment                          

The image above shows the layout of a typical treatment works. Ideally, wastewater treatment in a municipal treatment works involves four stages: preliminary, primary, secondary and tertiary treatment. There are two end products from the treatment process; sludge solids and liquid effluent. The treatment process reduces the effluent so that it will not adversely affect the quality of the receiving waters.

Preliminary treatment takes large solids and floating debris from the raw wastewater.

Primary treatment separates the smaller solids.

Secondary treatment uses micro-organisms to remove the biodegradable or organic waste.

Tertiary treatment includes nutrient removal and filtration. 


Urban Waste Water Treatment Directive

Urban wastewater can be described as a mixture of domestic and industrial wastewater and run-off rain water. The level of treatment wastewaters receive depends on the size of population served. In urban areas wastewater from homes and industry is carried off by a network of pipes and pump stations to a municipal treatment plant. This treatment of the sewage (the contaminated wastewater) involves primary, secondary and tertiary treatment:

  1. solids are separated from the wastewater
  2. dissolved biological matter is converted to solid mass using micro-organisms
  3. solids are then neutralised and reused or discarded
  4. treated wastewater is discharged to receiving waters

The proportion of waste water subject to secondary treatment has increased significantly from 26%  between 1998-1999 to 69% in 2016 (EPA, 2017). This is mainly due to the new waste water treatment plants at Ringsend (Dublin), Cork City, Limerick City, Galway City and Dundalk. Furthermore, because of major investment in recent years, construction of secondary treatment facilities at many locations around the country is at an advanced stage. This is expected to deliver significant improvements in the quality of urban waste water discharges.

Less than half (44%) of improvement works due between 2009 and 2016 were reported as complete at the end of 2016. There were 50 large areas where waste water was not treated to European Union standards. 44 areas were discharging untreated waste water into bathing and other waters. It is clear that significant improvement is required in the treatement of waste water. 

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