Backwash Basin and Filter Expansion for Water Purification Plant
The City of Sioux Falls, SD needed to upgrade a filter and backwash basin to expand the capacity of the existing plant to meet the future water demands.
The City constructed five new gravity filters for an expansion that increased the total filtration capacity. A new building addition was constructed to match the architecture of the existing filter building, and the new filters are located directly west of the existing filters.
The filter upgrade and backwash basin project included: filter media and underdrains; filter gallery piping and control valves; backwash storage and pumping system; electrical, instrumentation and controls; chlorine solution feed system; filter building; related site work and appurtenances. The project engaged a variety of technical disciplines, all provided in-house by HR Green. In addition to design services, HR Green provided full-time on-site construction observation.
A unique component of the backwash basin project demonstrating the innovative design approach was the implementation of vane-type pneumatic actuators for the filter control valves instead of the commonly used cylinder-type actuators. Plant staff had noticed delayed control valve response during winter/spring operation due to jerky or sticky movement of their existing cylinder-type actuators. This issue was researched and coordinated with leading manufacturers of vane-type actuators to arrange a side-by-side demonstration period on the control valves of the existing filters. This real demonstration verified the improved operation of the vane actuators over the existing cylinder actuators during the design phase providing the City with confidence in the change before they purchased the product.
Another key element to the capacity expansion was improvements to the backwash basin and pumping system. The existing backwash storage basins limited the number of filter backwashes that could be performed in one day and did not allow for consecutive filter backwashes. This limitation restricted operational flexibility, especially during high demand periods. The new backwash basin has solids separation and removal capabilities to improve the quality of water recycled to the head of the treatment plant.
A strict construction sequence was developed to keep the plant in operation during construction, requiring a significant amount of work to take place during the non-peak season between October and May.