Power

Use Of Monochloramine Feed To Reduce Ro Biofouling

By Robert Mitzel

BIOFOULING CHLORINE ION EXCHANGE MEMBRANES MONOCHLORAMINE ORGANICS OXIDIZING BIOCIDES POWER REVERSE OSMOSIS TOC

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Abstract

Reverse osmosis (RO) membranes used in the Newton Power Station (near Newton, IL) water treatment process were showing short service life. The use of typical biocides was not providing the expected increases in service, even with periodic cleaning. The decision was made to use monochloramine (MCA) as an alternate biocide to extend the useful service of RO membranes. For this project, plant personnel selected a treatment technology that will produce a pure form of MCA.

Treatment Process Description

The water source for the water treatment process is a surface lake, which has a conductivity of approximately 450 microsiemens per centimeter (µS/cm). The lake is near farm fields and runoff from heavy rain can quickly increase the lake turbidity from the typical 20 Nephelometric turbidity units (NTU) to more than 200 NTU. The raw water has typical biological activity.

The water treatment process is shown in Figure 1, which was before changes related to the MCA feed were made. Chemical feeds of bleach, cationic polymer, and aluminum chlorhydrate are added to a coagulation tank. This water is fed to ceramic microfilters with a pore size of approximately 1 micron (µm). This water goes to the filtered water storage tank, after which it passes through a forced-draft decarbonator. After this step, pre-RO chemical feeds of biocide, antiscalant, and caustic for pH adjustment are added.

Water goes through RO prefilters (RO prefilters since changed to 1-µm pore size), and chlorine is removed with sodium bisulfite. Water then passes through the RO and onto a packed-bed demineralizer, mixed-bed demineralizer, and storage tanks.

This article reviews use of this alternative treatment and reports on the results.

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