Modelling the effect of pipe material, water quality and time on chlorine dissipation

Keywords

Chlorine; Water -- Purification; Water quality

Abstract

This study was conducted to identify the parameters that influence the rate of chlorine residual dissipation in distribution systems and develop empirical models to predict chlorine residual with time based on those parameters. Groundwater and surface waters were treated utilizing seven different treatment systems (aeration (G 1), softening (G2 and G3), nanofiltration of GW (G4), CSF-03-GAC filtration (S1), integrated membrane system (CSP-NF or S2), and high pressure RO) to obtain waters with a wide range ofwater quality characteristics. The finished waters were blended and distributed to eighteen (18) pilot distribution systems (PDS) using PVC, unlined cast iron, lined ductile iron and galvanized steel pipes that were extracted from existing distribution systems. The hydraulic retention time (HR T) was five days. Free chlorine and chloramines were used as disinfectants. The PDSs were monitored for time, temperature, pH, free and total chlorine, and organic carbon. The data obtained was grouped by pipe material and separate models were developed for free and combined chlorine. The models followed first-order kinetics with respect to initial chlorine concentration and were dependent on pipe material, UV-254 and temperature. Residual was independent of pH for the range of pH data (7.9 to 8.3). The model for free chlorine residual included an overall decay constant whereas the chloramines residual model was 111 further developed to separate the effect of bulk reactions from the pipe wall reactions. The results for the models showed that chlorine dissipation is highly affected by the pipe material. The rate of chlorine decay for PVC and lined iron pipes is similar and significantly slower than for unlined cast iron and galvanized steel. PVC and lined iron could be considered inert materials with a very small chlorine demand. In general PVC pipes have the capacity to maintain chlorine residual longer than the other materials. The iron-based pipes showed a rapid residual decline due to the reaction of chlorine with the corrosion products of iron. The models showed that the rate of chlorine dissipation increased with an increase of either temperature or organic content of the water. A fifty percent reduction in TOC will increase the time the water maintains the residual by 100% for free chlorine and 50% for chloramines. Processes that reduce TOC in the water will increase the life ofthe residual in the PDSs. Chlorine decay was also found to be dependent on the water temperature. The rate of chlorine dissipation increased with an increase in temperature and can be described following the Arrhenius relationship. Residuals were difficult to maintain in metallic pipes for temperatures at or above 25°C. The models for free and combined chlorine were verified to the 95% confidence interval utilizing independent data that was not used in the model development.

Notes

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Graduation Date

2003

Advisor

Taylor, James S.

Degree

Master of Science (M.S.)

College

College of Engineering

Department

Civil and Environmental Engineering

Degree Program

Environmental Engineering

Format

PDF

Pages

82 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0029086

Subjects

Dissertations, Academic -- Engineering; Engineering -- Dissertations, Academic

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