AWWA ACE61835

The Sioux Falls, South Dakota Water Department provides water treatment and distribution to the City ofSioux Falls and surrounding areas. Strong population growth, increasing water demands, and theintroduction of surface water into a treatment plant originally designed for groundwater requiredevaluations 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 ofthe Master Plan: filter modifications, a new chemical feed facility, and the addition of filter towaste.After the completion of these projects, some operational issues still remained at the plant. In Julyof 2001, HDR updated the City's Master Plan. In the Master Plan Update several improvementprojects were identified to improve reliability, enhance treatment, increase capacity, comply withregulations, or to improve safety, operation and maintenance conditions. In a workshop, HDR'sMaster Plan team and technical experts met with key City staff to evaluate these proposedimprovements and prioritize project implementation. During that evaluation, it became apparentthat the addition of clarification basins preceding the existing water purification processes wascritical and would have a significant immediate benefit.The major issue related to the performance of the purification plant is the large variation in theraw water quality of the Big Sioux River. Significant, rapid changes in turbidity as well asperiodic high algae concentration in the impoundment at the intake caused problems with theconsistency of the solids contact basin effluent, which in turn impacted the turbidity and loadingrate of the filters. Also, the backwash water was directed off site to the sanitary sewer, becausethe solids loading would upset the softening basins when recycled. Recovery of the backwashwater would maximize use of the limited water resources.The City elected to go forward with HDR's recommendation and proceeded with theclarification basins addition project.The addition of clarification basins enhanced the treatment process and reduced the chemicalusage by removing the majority of the particulates from the surface water source, prior totreatment in the lime softening and filtration processes. The purpose of the clarification basins isto provide consistent influent water to the softening basins that exhibit the followingcharacteristics: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 residualswithdrawal, 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.

Product Details

Edition:

Vol. - No.

Published:

06/17/2005

Number of Pages:

17

File Size:

1 file , 1.4 MB