Ottumwa Lime Residual Improvements

Challenge: Ottumwa Water & Hydro was looking to improve the capacity and redundancy of the existing lime residual handling system and improve system reliability to continue to deliver a reliable water supply.

Solution: Options were evaluated for expanding and providing redundancy to the existing lime solids handling facilities, which consisted of a single thickener, and single plate-and-frame press with single feed pumps. Options included pre-expansion of the existing facilities with redundant equipment or providing a lagoon storage system remote to the existing water treatment plant.

Following the initial evaluation and analysis, design, bidding, and construction phase services were provided for the addition of a 2nd lime sludge thickener, lime sludge holding tanks, a backwash waste attenuation tank, associated pumps, and a new 2nd lime sludge plate-and-frame press. These improvements increased the capacity and redundancy of the existing residuals handling system, improved system reliability, and comply with the Iowa Department of Natural Resources (IDNR) design standards.

The building is primarily reinforced concrete with precast panels used for the upper floors and roof. The structure consists of stacked lime residual and attenuation holding tanks to fit within a small footprint. The base structure is a filter backwash attenuation basin with a deep concrete foundation down to bedrock, and two thickened lime sludge holding basins on top of the larger basin. The two-story-high tanks are adjacent to a pump room and an electrical room and a storage room. A new two-story lime sludge thickening bay with a new plate-and-frame press separates the existing lime sludge thickening bay from the deeper structure with a new pump room and tanks.

Benefit: The Ottumwa Lime Residual Improvements project significantly enhanced the community by improving water treatment efficiency and providing a stable, reliable water supply. Compliance with environmental standards, increased system capacity, and long-term cost savings were achieved, promoting community health and safety.