Ozone: Treatment Applications for POU/POE and Small Water Systems
By Thomas P. Palkon, CWS-VI
Summary: As the POU/POE industry strives to serve the public with the most effective treatment, ozone is becoming more accessible as a treatment alternative. The issue then shifts on what methodologies and protocols to use. The following describes what steps the WQA will take, as we approach the group’s annual convention.
While the scare of the atmosphere’s depleting ozone layer has risen and fallen in the public consciousness as of late, the interest in ozone for use in the water treatment industry is exploding. Municipalities, public swimming pools, bottled water plants and residential treatment of ground and surface waters are employing ozone more and more because of its strong oxidizing abilities and reduced production of disinfection by-products (DBPs), such as trihalomethanes and haloacetic acids. Even the issue of bromate production as a DBP in ozonated waters where natural bromine is present—ozone’s primary shortcoming—has been played down recently in regulatory matters.
The Water Quality Association’s Ozone Task Force is addressing chief concerns of the point-of-use/point-of-entry (POU/POE) and small water system industries by providing technical education and white papers on ozone applications. In addition, the task force has produced a testing guideline for generators to determine ozone production and concentration, and is in the process of turning the guideline into a protocol for third party performance verification testing.
Ozone production and uses
Ozone gas is a strong, naturally occurring oxidizing and disinfecting agent. During electrical storms, lightning forms ozone gas naturally. Ozone has a distinct, sharp and pungent odor beginning at concentrations as low as 0.02 parts per million (ppm).1 Ozone’s clear fresh scent is most commonly noticed as the clean smelling air after a thunderstorm. Electrical equipment, photocopying machines and photochemical smog reactions can also create ozone. The water treatment industry generates ozone by exposing oxygen molecules to ultraviolet (UV) radiation or a high-energy electrical charge—corona discharge—in manufactured ozone generators.
Because of ozone’s oxidizing and disinfecting strength, the water treatment industry utilizes it to solve a variety of drinking water problems. The POU/POE and small system markets currently use ozone for oxidation of heavy metals, breakdown of organic compounds and disinfection. Ozone’s strong oxidizing capabilities are used for the treatment of inorganics such as iron, manganese, organically bound heavy metals, cyanides, sulfides, nitrites and arsenic. Through oxidation, ozone can also treat organics such as color, taste and odor, detergents, pesticides, algae, turbidity and phenols. Ozone’s strong disinfecting abilities allow for the treatment of bacteria, viral and cyst inactivation, as well as biofouling prevention. Bacterial cells and viruses are lysed—or inactivated—through oxidation of their DNA and RNA chains by ozone in water and wastewater treatment applications.
Common treatment techniques used by POU/POE water treatment professionals (i.e., filtration, ion exchange, activated carbon adsorption, reverse osmosis, etc.) can be coupled beneficially with ozone to solve water treatment problems. Some examples follow. Oxidation of iron and manganese causes these contaminants to precipitate. Once the elements precipitate out of the water, simple mechanical filtration can be used for removal. Arsenic naturally occurs in two forms: trivalent arsenite (As-III) and pentavalent arsenate (As-V). Trivalent arsenite isn’t readily removed by reverse osmosis (RO) or ion exchange; however, if the arsenite is oxidized to arsenate by a strong oxidant such as ozone, RO and ion exchange can more effectively remove it.
Task force issues
One issue facing the industry lies in informing water treatment professionals about the proper use of ozone to treat common water problems. The Ozone Task Force is addressing this issue by producing general education materials such as the WQA Ozone reference manual and application specific white papers. The first paper to be developed will be ozone treatment of iron, manganese and sulfides. The paper will serve as a template for future papers.
Each white paper will consist of four sub-sections. The first section will be a brief introduction including the primary purpose of the white paper and explaining the current role of ozone in drinking water treatment.
The second section will describe the fundamental aspects of ozone. It will contain a brief explanation of ozone chemistry, ozone reactivity, reactions with inorganics and decomposition of ozone. This section will also describe the basic principals of ozone generation, either by corona discharge or other generation methods such as UV light. In addition, ozone gas transfer, the solubility of ozone in water, contacting ozone with water and measuring ozone in water will be discussed.
The practical applications of ozone will be covered in the third section. This section will vary for each particular white paper. Again, the first paper will address oxidation of iron, manganese and sulfides. It will contain principals of removal, design considerations and, most importantly, case studies. These case studies will cite particular success stories of iron, manganese or sulfide removal using ozone.
The final section will cover a variety of engineering aspects. There will be general considerations, pilot testing and interpretation of results. It will also address gas preparation, feed gas selection and quality. Other aspects covered in this section will be ozone generation, commercial ozone generator designs and variables that affect performance. Subsections will also consider ozonated water detention and filtration. They will focus, for example, on the effects of detention time on oxidation and flocculation, filtration system design and variables that affect performance. Other subsections will address ozone destruction, instrumentation and controls, and piping systems.
Details of white papers and specific case studies will provide an excellent resource for the industry.
Methods and protocols
The second issue facing the industry is the lack of an ozone generator performance measurement standard. For water treatment dealers to successfully solve the myriad of water problems consistently at various flow rates, performance data on the treatment equipment being utilized must be known. The WQA adopted the “Testing Methodology Guideline for Performance Measurement of Ozone Generators used in Point-of-Use and Point-of-Entry Water Treatment Applications,” printed in WQA’s Ozone reference manual textbook in March 1996. The objective of this protocol is to provide a method to determine ozone production performance characteristics of ozone generators. It identifies accepted technology for gas phase ozone measurement, protocols and conditions for testing, and a format in which test results are to be presented so as to enable meaningful comparisons among ozone generation equipment products.
The Ozone Task Force is reviewing the methodology and changing the format to harmonize the other drinking water treatment testing protocols. Once the protocol is revised, the task force feels that manufacturers will seek to have their generators tested accordingly. The WQA hopes the methodology will one day be used as a basis for an ANSI/NSF standard, but the task force’s main concern remains to have a methodology that third party labs can utilize to test generators and verify their performance. The Ozone Task Force test protocol guidelines and attendant third party verifications will provide dealers with the necessary information about ozone generators in order to solve specific water problems.
NSF International has recently informed the WQA Ozone Task Force that it will help to create the ozone generator performance standard. NSF has appointed a project manager in the standards department to work with the task force. The project manager will be introduced at the task force meeting at the WQA 2001 annual convention in Orland, Fla. The task force also looks forward to presenting the first white paper and the first draft of the revised testing guidelines at the show.
- Kinman, R.N., “Ozone in Water Disinfection,” Ozone in Water and Waste Water Treatment, Ann Arbor Science, Ann Arbor, Mich., 1972.
About the author
Thomas P. Palkon is the laboratory supervisor at the Water Quality Association in Lisle, Ill. He holds a bachelor’s degree in biology from the University of Illinois in Champaign/Urbana. Palkon has been managing the WQA’s analytical and product performance testing laboratories for three years. He holds the WQA’s highest Certified Water Specialist designation, Level 6. He can be contacted at (630) 505-0160, (630) 505-9637 (fax) or http://firstname.lastname@example.org.