The Sioux Falls, South Dakota Water Department provides water treatment and distribution to the City of
Sioux Falls and surrounding areas. Strong population growth, increasing water demands, and the
introduction of surface water into a treatment plant originally designed for groundwater required
evaluations and upgrades to the water system. The City completed a Water Purification Plant
(WPP) Master Plan in 1993. Several projects were completed based on the recommendations of
the Master Plan: filter modifications, a new chemical feed facility, and the addition of filter to
waste.
After the completion of these projects, some operational issues still remained at the plant. In July
of 2001, HDR updated the City's Master Plan. In the Master Plan Update several improvement
projects were identified to improve reliability, enhance treatment, increase capacity, comply with
regulations, or to improve safety, operation and maintenance conditions. In a workshop, HDR's
Master Plan team and technical experts met with key City staff to evaluate these proposed
improvements and prioritize project implementation. During that evaluation, it became apparent
that the addition of clarification basins preceding the existing water purification processes was
critical and would have a significant immediate benefit.
The major issue related to the performance of the purification plant is the large variation in the
raw water quality of the Big Sioux River. Significant, rapid changes in turbidity as well as
periodic high algae concentration in the impoundment at the intake caused problems with the
consistency of the solids contact basin effluent, which in turn impacted the turbidity and loading
rate of the filters. Also, the backwash water was directed off site to the sanitary sewer, because
the solids loading would upset the softening basins when recycled. Recovery of the backwash
water would maximize use of the limited water resources.
The City elected to go forward with HDR's recommendation and proceeded with the
clarification basins addition project.
The addition of clarification basins enhanced the treatment process and reduced the chemical
usage by removing the majority of the particulates from the surface water source, prior to
treatment in the lime softening and filtration processes. The purpose of the clarification basins is
to provide consistent influent water to the softening basins that exhibit the following
characteristics:
turbidity less than 5 NTU;
Total Organic Carbon (TOC) reduced by 25 percent or more; and,
maximized algae reduction.
Providing consistent water quality to the softening basins allows for a more stable operation.
Benefits include a more stable solids blanket, which in turn allows for more consistent residuals
withdrawal, and reduced powdered activated carbon (PAC) dosages for taste and odor control.
More stable operation of the softening basins maximizes the hydraulic loading rate to the filters. Includes 7 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.4 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 17 |
| Published : | 06/17/2005 |
