Introuction Mutton Island Wastewater Treatment Plant(WWTP) is located on Mutton Island in the middle of Galway Bay. The plant officiallyopened in 2003, and first took flow in September of the same year. This cameafter some 15 years of objections. Locals were opposed to the sewage treatmentplant as they believed it would damage the scenery of the bay, as the island isalso home to the Mutton Island lighthouse and a keeper’s cottage, which werebuilt in 1815. Others objected to the plant over fears for the various birdsand wildlife that inhabited the island, which is located in the Galway BaySpecial Area of Conservation. The primary concern relating to the plant was itsenvironmental impact.
In October 1995, approval for EU funding for the plant waswithdrawn due to the same fears of a significantly negative impact on thesurrounding environment. However, Irish government officials decided to proceedwith the plans, instead using State funding. Construction began, and a 1.2kmlong causeway was built to connect the island to the mainland. The first plansdesigned the plant for a population equivalent (PE) of 12,000. However, due tothe several years of delays, when construction finally began on the plant, it hadto be increased to facilitate a PE of 91,000. In 2016, to cope with furtherexpansion of Galway city’s population, the capacity of the plant was upgradedto 170,000 PE. The upgrade was funded by a €5 million investment, and the plantcurrently averages out at around 150,000 PE.
Mutton Island WWTP is responsiblefor the treatment of wastewater from the towns of Barna to Oranmore. Figure 1. Map showing location of MuttonIsland WWTP and the area it serves Treatment Processes The wastewater treated by Mutton IslandWWTP comes from five pumping stations located throughout the designated catchmentarea. The raw sewage is pumped collectively into South Park, an area approximately900m north of Mutton Island.
From South Park, the sewage flows by gravity tothe plant through a steel mains sewer. It is then pumped into the site where itundergoes a number of treatment processes. Preliminary Treatment The first stage of treatment is thepreliminary stage. The raw effluent is preliminarily treated, meaning it isscreened to remove any inorganic materials, such as rags and plastics.
MuttonIsland WWTP uses bar or rack screens, inclined at 45 degrees, to screen forparticles that are larger than 6mm, such as pebbles, stones, golf balls, etc. Thisstep is vital in preventing damage to any equipment and machinery further downthe process due to clogging. Bar screens are composed of a number of parallel bars,usually between Screens with openings of 6mm or greater are defined as coarsescreens, whereas fine screens have openings of between 1.
5 and 6mm. Bar screenscan be cleaned manually or mechanically to remove trapped particles. The plantuses mechanical screens, which use a raking action to remove the solids fromthe screens