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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Civil Engineering

First Advisor

Lyle Johnson


The studies described in this thesis were conducted at the Sioux Falls, South. Dakota Water Reclamation Facility. This facility uses the activated sludge process to oxidize ammonia nitrogen to nitrates. The treated water is then discharged to the Big Sioux River. National Pollutant Discharge Elimination Standards (NPDFS) requires the PI at the effluent from the Sioux Falls Wastewater Treatment Facility to be maintained between 6.3 and 9.0. Wastewater entering the plant first passes through the aerated grit removal unit before entering the primary clarifiers. The primary clarifiers remove many of the solids reducing the strength of the wastewater. The wastewater then proceeds through the trickling filters where organisms consume much of the carbonaceous waste in the water. The activated sludge process follows the trickling filters and is the process for renewal of ammonia. After this stage the remaining solids in the wastewater are removed in the final clarifiers and sand filters. The wastewater is then chlorinated and discharged to the Big Sioux River. Between influent and the second stage trickling filter clarifiers, the alkalinity slowly drops. The alkalinity concentration then falls very rapidly as the water passes through the activated sludge process. Because of the aggressive nature of the low alkalinity water, the Water Reclamation Department has been experiencing corrosion problems in the units following the aeration basins, especially in the final clarifiers. To combat this alkalinity problem and to maintain adequate effluent pH levels, slaked lime is currently being added directly to the aeration basins. The lime is used at an average rate of approximately 6 tons per week and with the cost of lime at about $68 per ton makes this a costly procedure. The intent of this study is to determine if lime sludge, a waste by-product of water softening at the Sioux Falls Water Treatment Facility, when added to the wastewater, can solve the corrosion problem. This study will also determine if lime sludge can be used as a substitute for slaked lime to increase the pH and alkalinity to satisfactory operating conditions in the activated sludge system.

Library of Congress Subject Headings

Sewage -- Purification --Activated sludge process

Water softening sludge -- Recycling

Sewage -- Purification -- Oxidization




Number of Pages



South Dakota State University