Low Level Ozonation to Control Discharges of Organic Chlorine Compounds from Municipal Wastewater Treatment Plants

Massachusetts Division of Water Pollution Control, 9/1/86-8/31/89

PI: Reckhow
Students: Eric Lehan, R.V. Rajan, Chris Hull & Diana King

The purpose of this study was to evaluate the extent to which ozone treatment prior to final disinfection with chlorine can limit the formation of hazardous TOX, and under what conditions it is most effective

Proposal, Plans and Reports

Project Data


Jounal Publications based on this work

Conference presentations based on this work

Theses/Dissertations based on this work


Additional Background: Chlorine reacts very rapidly with ammonia and some of the highly nucleophilic organics present in treated municipal wastewaters to give chloramines and stable organohalides (TOX). Chlorinated organic by-products of this sort have been associated with toxicity to aquatic organisms, mutagenicity, and carcinogenicity in laboratory tests. To date much research has focused on the control of these TOX compounds in chlorinated drinking waters and power plant cooling waters, but the domain of municipal wastewater has barely been touched. One promising pretreatment for the purposes of reducing TOX formation in municipal wastewater is pre-ozonation. Ozone has the capability. of reacting specifically with the same nucleophilic organics that react with chlorine (but it does not react with ammonia). The ozone pretreatment would then preclude their subsequent reaction with chlorine during disinfection.

The problem was investigated in the laboratory using samples of non-nitrified or partially nitrified secondary wastewater effluent. A brief preliminary survey of TOX concentrations in the chlorinated effluents of several local wastewater treatment plants was conducted in order to identify a suitable treatment plant for this study. Samples of the designated wastewater was then be collected just upstream from terminal chlorination and brought to the laboratory when needed for the chlorination and ozonation experiments. First, the wastewater was chlorinated (constant pH) at a variety of chlorine doses on both sides of the breakpoint. These were compared with similar studies where pure solutions of monochloramine are added directly, thus avoiding the effects of a momentary free chlorine residual. Then the wastewater was given small doses of ozone at various pH's and free radical scavenger concentrations and retested for the formation of organohalides.



See other MDWPC R&D Projects


Return to Dave Reckhow's home page.