In 1969 the number of primary sedimentation tanks were increased from three to seven. In 1975 a fourth secondary tank was added, the trickling filters upgraded and a third digester built. In 1980 the power station was commissioned and in 1983 the gas vehicle fuelling began. In 1986 covers were constructed over the trickling filters to capture odorous air and an odour treatment system installed. Primary treatment At the Treatment Plant the sewage passes through screens that remove debris from the flow.
Rakes automatically clean the debris off the screens and pass it to containers for later burial.
Downstream of the screens the flow is measured in special flumes. In the Pre-aeration and Grit Removal Tanks air is injected along one side of the tank above the hoppers that the settled grit is pumped from. The injected air provides oxygen to the flow and assists in removing fat and grease and induces a spiral flow pattern that allows the grit and sand-size particles to settle out and be removed while maintaining organic matter in suspension. The grit removed from the flow is pumped to grit washers that separate the grit in preparation for burial. The sewage then enters the primary sedimentation tanks and travels very slowly along these tanks.