Treatment and Distribution System Effects on Chloramine Decay, pH, Nitrification, and Disinfection By-Products: Case Study1
Publication: Journal of Water Resources Planning and Management
Volume 131, Issue 3
Abstract
The Massachusetts Water Resources Authority (MWRA) supplies wholesale unfiltered surface water to 2.2 million people in 43 communities, including Boston. Current MWRA treatment consists of adding hypochlorite for primary disinfection, soda ash and carbon dioxide for corrosion control, hydrofluosilicic (hexafluosilicic) acid for fluoride treatment, and hypochlorite and ammonia for maintaining distribution system residuals. The new Walnut Hill water treatment plant, scheduled to come on line in early 2005, will consolidate current treatment facilities under one roof and use ozone instead of hypochlorite as the primary disinfectant. It was observed from distribution system monitoring and bench-test results that the decay of chloramines was affected by prechlorination. The decay of chloramines released ammonia for subsequent nitrification. Complete nitrification and subsequent denitrification at current target alkalinity and combined chlorine levels affected pH. Increased microbiological activity associated with nitrification also decreased haloacetic acid concentrations. Bench and pilot tests indicate that the use of ozone will increase the rate of chloramine decay and will affect pH stability. Ozonation of natural organic matter produces organic acids, which typically decreases the pH in bottle tests. Results from a pilot plant, set up to simulate the new treatment plant with old cast-iron pipes simulating the distribution system, indicate that corrosion and biological activity inside the pipe have major impacts on water quality and that pipe surface reactions often cause pH to increase.
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Acknowledgments
Robert Moses faithfully collected the weekly samples and performed the field measurements. Peter Green performed bacterial testing and recorded much of the water quality data. The Division of Laboratory Services of MWRA performed all the chemical analyses. This article represents the opinions of the authors and not those of the Massachusetts Water Resources Authority.
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Information & Authors
Information
Published In
Journal of Water Resources Planning and Management
Volume 131 • Issue 3 • May 2005
Pages: 201 - 207
Copyright
© 2005 ASCE.
History
Received: Aug 31, 2004
Accepted: Dec 23, 2004
Published online: May 1, 2005
Published in print: May 2005
Notes
Portions of the manuscript were presented at the 2004 World Water and Environmental Resources Congress in Salt Lake City, Utah.
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