Andrew Boal, PhD
MIOX

Presented at the 2015 Cooling Technology Institute Annual Conference New Orleans, Louisiana – February 9-12, 2015

ABSTRACT

Ammonia in the cooling loop poses an additional challenge for hypochlorite or oxidizing biocides in controlling the microbiological activity since chloramines are typically seen as less effective biocides as compared to free chlorine. Often, cooling tower biocidal treatment is accomplished with bromine based non-oxidizing biocides coupled with the occasional application of isothiazolin or gluteraldhyde. This paper demonstrated that Mixed Oxidant Solution (MOS), a biocide produced through the electrolysis of sodium chloride brines, is a highly effective biocide. Without overcoming ammonia, and in high pH environments, MOS was able to successfully control the microbial populations in the cooling tower waters of a major semiconductor facility in the US, where ammonia contaminated wastewater is used as part of the makeup water for cooling towers.

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The applications and scientific mechanisms of disinfectants generated on-site using salt, water and electricity

By Andrew Boal, Ph.D.

When you are researching a product, how frustrating is it to conduct your due diligence only to find answers segmented across dozens of sources? I’ve been there before.

That is why I wrote this digestible, technical overview of electrochemical generation, also known as on-site generation (OSG), to outline the applications and scientific mechanisms of this revolutionary technology in order to make your life easier and help you do your job better.

Many water treatment professionals are moving to OSG to produce disinfection chemistry on-demand, leaving traditional oxidizing and non-oxidizing biocides behind.

The benefits Continue reading →

Chlorate (ClO₃^–) was added to the Third Chemical Contaminant List (CCL3) in 2010, indicating that the Environmental Protection Agency (EPA) is reviewing chlorate as a potential candidate for regulation under the Safe Drinking Water Act. While there is no indication that chlorate is a potential carcinogen to humans, negative health impacts such as thyroid issues, reduced hemoglobin production, and reduced weight gain have been observed in laboratory animals subjected to prolonged exposure to chlorate.^{1, 2, 4}

Chlorate is a highly oxidized form of chlorine that can be introduced to a water source as an industrial or agricultural contaminant or into a finished water as a disinfection byproduct (DBP).  As a DBP, chlorate can result from water disinfection with bulk sodium hypochlorite, chlorine dioxide, or hypochlorite formed through electrolytic on-site generation (OSG) systems.

Regulatory Status

Currently, chlorate in drinking water is not regulated in the United States and there is no enforceable Maximum Contaminant Limit (MCL).  In Canada, chlorate is regulated at concentration of 1.0 mg/L (1000 µg/L).  The World Health Organization (WHO) recommends a chlorate limit of Continue reading →

On-site generators (OSGs) produce chlorine when a solution of sodium chloride is passed through an electrolytic cell and electricity is added. In essence, OSGs take a solution of sodium chloride (salt) and water and apply electricity, which produces chlorine and other oxidant species.

Water coming into the OSG goes through a softener, and then splits into two lines. One line is used to feed a salt filled tank, creating a saturated brine. The other line enters the OSG, acting as a dilution stream prior to the electrochemical process. Saturated brine is then precision mixed with the softened water stream prior to entering the electrolytic cell. Application of an electrical current to the cell results in the production of an oxidant solution from the diluted brine.

After leaving the electrolytic cell, the oxidant solution is temporarily stored in the oxidant tank. Then it is metered or injected into the water moving through the treatment process, typically with similar equipment as an existing chlorine system.  Injection options include a venturi or other eductor -, centrifugal feed pumps, or chemical metering pumps. Sites with multiple injection points may use a combination of these options.

Hydrogen gas is also produced inside the electrolytic cell and is removed from the cell and the oxidant storage tank through vents and/or dilution air blowers.

Process Flow Diagram

The OSG operates via a signal from the level switch/transmitter located in the downstream oxidant tank. When the tank is empty, the transmitter/switch sends a signal to the Programmable Logic Controller (PLC) to put the OSG online. As soon as the tank is full of oxidant, the transmitter/switch sends a signal to the PLC to put the OSG in standby mode. This means very minimal operator attention is required during normal operation.

Many communities are turning to OSGs for their water distribution systems because of the benefits, including better safety, high-quality disinfection, greener operations, and substantial economic savings. Because of the benefits that OSGs provide, many companies prefer OSG systems as opposed to more traditional chlorine delivery systems such as chlorine gas, concentrated sodium hypochlorite, and bulk calcium hypochlorite.

Click here for a tech brief on the science behind OSGs.