Sedimentation and Filtration Improvements
The City of Oswego retained Wendel to complete an upgrade of the existing sedimentation and filtration systems. The existing sand filtration system was originally installed in 1974 and consists of clay tile dual manifold underdrain block with water and surface wash backwashing facilities. The City had been experiencing reduced filter run times, deteriorating filter effluent quality and reduced filtration capacity due to the deterioration of the filter system. The degradation of performance of the existing filtration system, which will not allow the City to meet future projected water demands of 17.0 MGD, along with the fact it is at the end of its useful life, has led the upgrade the filtration system with an air-water backwash system.
The existing tube settlers were installed in 1974. The existing system consists of 60° tube settlers that cover approximately 1,040 square feet per each of the four basins. The tube settlers are past their useful life and are cracked and breaking.
The filter underdrain was replaced with a Dual/Parallel Lateral type underdrain. The new underdrain is corrosion resistant, high density polyethylene. Also part of the proposed underdrain system is a media retainer that replaces the support gravel and allows additional freeboard to be provided between the media and the wash water troughs to reduce media washout. The air/water backwash system includes new air piping to supply the air water backwash system, as well as two 40 hp air supply blowers. The filter media was fully removed and replaced with new media.
The new filter system is designed to maintain the current approved filtration rate of 5 gpm/sf and will allow the plant to operate at its rated capacity of 20.1 MGD. It will also allow more water to be available to city customers by increasing the filter capacity, but also by reducing the amount of water being used during backwash.