The Differences between On-Site Generated Mixed-Oxidant Solution and Sodium Hypochlorite (aka the Master Features Summary) Wesley L. Bradford, Ph.D., formerly Los Alamos Technical Associates, Inc. (LATA), Los Alamos, NM, and Chief Scientist, Product Development, MIOX Corporation, Albuquerque, NM Currently Chief Scientist, MIOX Corporation, Albuquerque, NM Last updated 8 February 2011 Table of Contents Background .................................................................................................................................................. 2 Chemistry ..................................................................................................................................................... 3 Differences between MIOX Mixed-Oxidant Solution and Sodium Hypochlorite ................................ 3 Chemical Analyses .......................................................................................................................... 3 Other Laboratory Evidence for the Presence of Oxidants Other than Chlorine ............................ 5 Chemistry-Related Differences in Behavior of Mixed-Oxidant Solution Compared to Chlorine ........ 8 Superior Microorganism Inactivation in Potable Water and Processes ........................................ 8 Superior Effectiveness of Mixed-Oxidant Solution for Cryptosporidium Inactivation ................... 9 Early Work Suggests Effectiveness at Practical FAC Concentrations ..................................... 9 Difficulties in Repeating the Early Observations ................................................................... 10 Recent Studies Suggest Mixed-Oxidant Solution is Superior but Not Effective at Practical FAC Concentrations ............................................................................................................... 11 Oxidation of Manganese (Mn(II)) and Removal in Classical Treatment ..................................... 11 Evidence for the Microflocculation Effect Similar to that of Ozone ............................................. 11 Biofilm Removals in Distribution Systems .................................................................................... 13 Early Observations Suggest Unusual Behavior against Biofilms .......................................... 13 Experiments with Laboratory Biofilm Models ....................................................................... 15 Recent Indirect Evidence of Biofilm Removal from Distribution Systems ........................... 16 Ammonia Oxidation at Sub-Breakpoint Chlorine Doses as Mixed-Oxidant Solution and Apparent Superior Fragmentation of Organic Nitrogen Compounds Typically Found in Human Body Fluids ............................................................................................................................................ 17 Reduced Concentrations of Total Trihalomethanes but Increased Production of Brominated Forms ............................................................................................................................................ 19 Stoichiometric Oxidation of Sulfides to Elemental Sulfur in Waters at Normal pH and Rapid Oxidation to Sulfate ...................................................................................................................... 20 Water Treatment Summary ........................................................................................................................ 21 Conclusions ................................................................................................................................................ 22 A BRIEF HISTORY OF THIS DOCUMENT .......................................................................................... 22 Citations ..................................................................................................................................................... 23 MIOX Master Features Summary Page 2 Background The electrolysis of salt water to generate chlorine has been practiced commercially for more than 100 years. Electrolysis is the basic process used to manufacture nearly all chlorine-based oxidizing compounds including gas, liquid, and solid forms of chlorine. These forms of chlorine have been traditionally produced at large chlor-alkali plants, packaged in various forms and sold. Chlorine gas safety concerns and regulation have caused many water utilities to convert from gas to safer forms such as sodium hypochlorite (liquid or bleach) or calcium hypochlorite (solid); even these forms carry their own risks from spillage and contact with strong reducing agents or oils. Within the past 40 years, several manufacturers began to produce and sell equipment that generated sodium hypochlorite on-site by the same processes used in larger chemical plants. The first on-site generators were installed at large coastal industrial plants, and used seawater as the salt brine source. Subsequently, manufacturers made the equipment smaller and water utilities began to use them as alternatives to chlorine gas. In 1978, a number of companies in the US and Europe began to experiment with electrolytic devices that generated a gas thought to be comprised of multiple oxidants. As a class of equipment, these became known as mixed-oxidant gas generation on-site devices (MOGGODs)1. Use of the MOGGODs involved extraction of the oxidants generated as gases and injection of the gases into the water being treated. The Pan American Health Organization (PAHO) experimented with several MOGGOD brands in various Latin American countries as a method for rural water disinfection. In 1985, the first MIOX generator was demonstrated to the US Navy and US Army. This patented device was considered an improvement over the MOGGOD generators because it was much more robust, having fewer critical parts and not requiring salt of high purity to function effectively, and generated mixed oxidants in solution which could then be injected directly into the water. The mixed-oxidant solution injection method simplified the handling and dosing of the oxidants. PAHO began testing MIOX generators in 1987 and many subsequent improvements made them even more robust. In 1991, LATA (the parent company of MIOX) modified the generators for automated operation and in 1992, the first MIOX generator was installed in the US. Another year of field testing and equipment modification followed and in 1994, MIOX Corporation began manufacturing and selling its products to the public. Since that date MIOX has continually improved the performance of its Anode: Cathode: generation process and expanded its product line to include - - - - 2 Cl Cl2 + 2e 2 H2O+ 2e H2 + 2 HO systems producing from a few pounds per day to several hundred pounds per day of measured Free Available Chlorine (FAC) as the mixed-oxidant solution. The schematic shows a Cl- Na+ HO- H2 general description of chlorine generation in a typical OSG Cl- HO- electrolysis cell. Chloride ions are oxidized at the anode to Na+ form aqueous chlorine which manifests as hypochlorite or hypochlorous acid depending upon solution pH. At the cathode water is reduced in an overall reaction that produced Cl2 hydrogen and hydroxide ions. H2O H2O H O HOCl + HCl 2 MIOX generators have sometimes been considered and discussed together with on-site hypochlorite generators as just another hypochlorite generator. One reason for this Overall reaction: NaCl + H2O NaOCl + H2 perception is that solution concentration and monitoring is performed by measuring FAC. However, evidence both in laboratory and in field applications suggests that this is not the case. There are important differences in the MIOX process chemistry, the disinfection effectiveness of the mixed-oxidant solution, and other features which provide benefits in water treatment. MIOX engineering is also different. While all On-Site Generators (OSGs) and MIOX generators use salt, water and electricity to generate an oxidant solution on-site, the overall engineering and controls schemes are very different. MIOX Master Features Summary Page 3 Chemistry Differences between MIOX Mixed-Oxidant Solution and Sodium Hypochlorite It should be noted initially that among the OSGs, only the manufacturers of the MOGGOD-like devices claim to produce mixed oxidants. All others claim only to produce chlorine and small amounts of oxygen (O2) as an unavoidable product of the electrolysis of water at the anode. Early tests on prototypes of the MIOX electrolytic cell suggested the presence in the electrolyzed brine of other oxidants in quantitatively small but chemically significant concentrations in addition to the major product – chlorine – and oxygen in small concentrations but possibly exceeding brine saturation by a substantial amount. The evidence for the presence of other oxidants in the tests on prototypes led to the name “MIOX” (from MIxed OXidants), and to the characterization of the electrolyzed brine from MIOX cells as a “mixed-oxidant solution”. Attempts to both chemically characterize and quantify the other oxidants in the mixed-oxidant solution continue at MIOX and in academia. Chemical Analyses ξ - The MIOX mixed-oxidant solution contains chlorine (as Cl2, HOCl, or OCl in relative fractions depending on pH) as the primary analyzable oxidant constituent. The Free Available Chlorine (FAC) and Total Chlorine (TC) are measured routinely in testing and field application using the Hach Company (Hach) adaptation of the DPD method (Standard Methods2 (SM) 4500-Cl G. DPD Colorimetric Method). Early attempts to measure