Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

Abstract

Microfiltration (MF) and Ultrafiltration (UF) membrane installations have exponentially increased in recent years in order to treat more complex source waters and to comply with more stringent drinking water regulations. Submerged membrane technology is a relatively new technology compared to low pressure membranes but is becoming more attractive as treatment plants require a retrofit for additional capacity or to meet the more stringent standards. Mid-Dakota Rural Water System (RWS) has reached the design capacity of their existing treatment plant due to sustained expansion of their distribution system. Submerged membranes were the preferred filtration alternative for the expansion since they could be installed in the existing filter basins thereby eliminating the need for additional floor space. Two submerged membrane pilot plants were installed at the Mid-Dakota water treatment plant (WTP) to demonstrate to the South Dakota Department of Environment and Natural Resources (SD DENR) that this type of filter is able to produce treated water that complies with all current drinking water regulations. The pilot plants were also used to obtain data for full-scale design. The objective of this research project was to evaluate the effect of coagulant addition on organics removal and the performance of submerged membranes pilot plants treating Missouri River water. Bench-scale and pilot-scale tests on Missouri River water were used to evaluate the effectiveness of submerged membranes. Final total organic carbon (TOC) concentrations, disinfection byproducts (DBPs) concentrations, and normalized permeability were used to assess impacts of coagulant addition on treatment performance. Bench-scale tests were performed to determine the dosages of aluminum sulfate (alum), aluminum chlorohydrate (ACH), and ferric chloride (ferric) to use in the pilot- scale tests. At the dosages used during the bench-scale tests, ACH exhibited superior dissolved organic carbon (DOC) removals compared to the other coagulants. The maximum DOC removal achieved with ACH was 33.1 percent at a dosage of 30 mg/Las ACH. Membrane filtration of coagulated raw water and coagulated flocculated raw water was investigated with all three coagulants at three different dosages. Alum was investigated at dosages of 10, 20, and 30 mg/Las alum; ACH was tested at dosages of 5, 10, and 15 mg/L as ACH; and ferric chloride was evaluated at dosages of 10, 20, and 30 mg/Las ferric. Direct filtration of coagulated raw water generally achieved better TOC removal then filtration of coagulated flocculated raw water. It was theorized that direct filtration of coagulated raw water resulted in greater TOC removals due to the cake layer formation on the surface of the membranes. During the coagulant addition phases of the pilot study the Zenon pilot plant achieved TOC removals ranging from O to 28.5 percent with the greatest removal occurring at a ferric chloride dosage of 30 mg/L as ferric. The US Filter pilot plant achieved TOC removals ranging from Oto 27.4 percent with the greatest removal also occurring at a ferric chloride dosage of 30 mg/L as ferric. The pilot-scale TOC removals did not significantly impact DBP formation since the incubation results for one hour, nine days, and fifteen days were relatively the same. Chlorine was being fed near the intake during the coagulant addition phase of the pilot study which resulted in a high disinfectant contact time prior to TOC removal. The samples were then combined with ammonia to form chloramines which quenched the remaining DBP formation potential. It is theorized that the majority of the DBP concentrations were formed prior to TOC removal by the pilot plant. Filtration of coagulated flocculated raw water appeared to result in more stable membrane performance at lower dosages compared to direct filtration of coagulated raw water which may have been the result of the flocculation step creating a more permeable cake layer on the membrane surface. Direct filtration of coagulated raw water resulted in more organics removal but also resulted in a greater degree of membrane fouling. Overall, a thorough assessment of the submerged membrane process was performed with bench-scale and pilot-scale tests, and data for full scale design were obtained. This research project demonstrated to the SD DENR that submerged membranes are capable of producing acceptable treated water that meets current and proposed drinking water regulations.

Library of Congress Subject Headings

Water -- Purification -- Coagulation

Water -- Purification -- Organic compounds removal

Water -- Purification -- Membrane filtration

Water -- Purification -- Missouri River

Format

application/pdf

Number of Pages

186

Publisher

South Dakota State University

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