Document Type

Thesis - University Access Only

Award Date

2006

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

Abstract

The ballasted-sand process, specifically the Actiflo® process, is a relatively new surface water pretreatment process which is gaining popularity among water treatment facilities. This pretreatment process is an attractive alternative to conventional pretreatment since it can effectively treat highly variable turbid waters with a small system footprint. However, the success of the Actiflo ® pretreatment process can be limited when treating highly turbid waters with a high TOC concentration. The Big Sioux River, which was used for the majority of analyses in this thesis, exhibits these characteristics. The purpose of this investigation was to examine methods to optimize coagulation and flocculation within the Actiflo® process. Bench-scale tests on the Big Sioux River were used to examine the Actiflo ® process and the use of streaming current as a process control. Final turbidities were used for assessment of treatment performance. The coagulant dose and the polymer selection and dose are the major process control parameters of the Actiflo® process. Optimizing these parameters is a significant part of successful operation. Bench-scale jar tests simulating the Actiflo® process were performed on the Big Sioux River to optimize the coagulant and polymer. The coagulant was ferric chloride (FeCh) at an optimum dose of 40 mg/L with anionic polymer and 20 mg/L with cationic polymer. Various polymers were tested and the optimum dose of each was found. The optimum dose while following National Sanitation Foundation (NSF) guidance was approximately 1.0 mg/L for the anionic polymers and 3 .0 mg/L for the cationic polymer. Jar test experiments were then conducted to investigate the impact of sand size and dosing and recycled sludge dosing on the system's performance. Results determined the impacts to be minor compared to the impacts of coagulant and polymer dosing. Charge density analysis of the bench-scale tested polymers was performed to identify the strength of each polymer and compare its strength to its success in the Actiflo® process. The results showed the higher the charge density of the polymer, the better its performance in the Actiflo ® process when using high doses of coagulant. This determined charge density analysis as a practical procedure for polymer characterization when the colloidal charge is sufficiently depressed, but indicated that molecular weight is more significant with lower coagulant dosages. In order to better understand the chemistry of the Actiflo ® process, zeta potential and streaming current examinations were used to describe the change in colloidal charge during the treatment process. After chemical additions, colloidal charge analyses were conducted and recorded. As expected, the colloidal charge was suppressed with the addition of coagulant, and further suppressed with the addition of cationic polymer. On the other hand, anionic polymer addition increased the negativity of the particle charge. The more the charge was depressed, the better the coagulation and flocculation. Streaming current was also analyzed for potential as a process control indicator for the Actiflo® process. The streaming current charge analyzer effectively responded to coagulant dosing and polymer dosing, although the polymer would stick to the piston of the analyzer and cause erroneous results when lengthy analyses were performed. Results of this examination showed good potential for using streaming current in process control with a predetermined optimal value. Finally, different source waters with variable TOC concentrations were analyzed with Actiflo® simulated jar tests and the impacts of TOC on process performance was evaluated. These tests showed TOC to definitely have an impact on the performance of the Actiflo ® process. Zeta potentials were used to identify some of these impacts. Although TOC impacted process performance, using a DADMAC as a secondary coagulant minimized these impacts. The use of potassium permanganate as a pretreatment oxidant also improved the Actiflo® process when treating high TOC waters. Overall, an extensive examination of the Actiflo® process was performed with bench-scale tests, and a better understanding of the system's chemistry and process parameters was obtained. This analysis will help to optimize coagulation and flocculation in operating Actiflo ® treatment processes.

Library of Congress Subject Headings

Water -- Purification -- Coagulation

Water -- Purification -- Flocculation

Water -- Purification -- Big Sioux River (S.D. and Iowa)

Format

application/pdf

Number of Pages

157

Publisher

South Dakota State University

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