PHOTO 1
In August 2006, Malcolm Pirnie began a demonstration-scale study with the City of Glendale, California to determine the effectiveness of chlorite ion in controlling nitrification in Glendale's drinking water system. Photo 1 shows a satellite image of the demonstration study location of Glendale's distribution system, including three reservoirs serving the area.

PHOTO 2
This study was the first full-scale nitrification control study with direct feed of sodium chlorite coupled with intense monitoring and control procedures. Photo 6 depicts the sodium chlorite feed system, which included a carrier water dilution system to enable full mixing of sodium chlorite into the water flow to the 968 Reservoir.

PHOTO 3
During the demonstration study, the Glenoaks distribution system area was isolated from the rest of Glendale's system to enable each of the reservoirs to solely receive water containing chlorite ion. Photo 2 depicts Glendale operations staff preparing for the demonstration study by opening the valve to connect the 968 Reservoir to the Glenoaks distribution system.

---

PROJECT DESCRIPTION

Introduction

Nitrification is a problem for the approximately 30 percent of water utilities in the U.S. that use chloramines as a distribution system disinfectant. Capital and operations expenditures to implement chloramines and control nitrification in those systems is expected to cost hundreds of millions of dollars over the next 20 years. Since 1997, Malcolm Pirnie staff have conducted bench-, pilot-, demonstration- and full-scale studies to investigate the effectiveness of chlorite ion for nitrification control. These studies have shown that chlorite ion can control nitrification and prevent the subsequent loss of disinfectant residual.

Nitrification is the microbial process in which ammonia is oxidized to nitrite and potentially to nitrate. The adverse effects of nitrification on drinking water quality include a loss of total chlorine residual, release of free ammonia, increase in nitrite and nitrate concentrations, decrease in pH, increase in corrosion rates and increase in microbiological activity.

The City of Glendale, California faces significant water challenges caused by nitrification in their system. Between August 2006 and October 31, 2007, Glendale and Malcolm Pirnie conducted a demonstrationscale study to determine the effectiveness of chlorite ion for nitrification control by directly feeding sodium chlorite to a selected area of the Glendale distribution system. This project's successful results apply not only to Glendale but also to all utilities using chloramines.

Integrated Approach

Controlling nitrification eliminates need for massive flushing and water waste. At times, the only way for utilities to control nitrification is by flushing millions of gallons of nitrified water from the distribution system. In Southern California, this loss of water must be made up by pumping millions of gallons hundreds of miles from the Colorado River or Northern California. Preventing this waste of water and needless expenditure of electrical power will preserve land resources and reduce air emissions of particulates and greenhouse gases. Hundreds of utilities in Texas using chlorine dioxide as a primary disinfectant over the past 20 years have been unknowingly taking advantage of this benefit of chlorite and will continue to do so.

Nitrification control with chlorite will allow Glendale to maintain full reservoirs for fire suppression in the hilly areas of the City. Full reservoirs translate to high water age and nitrification problems. However, Glendale must maintain full reservoirs especially during the warmer months which are also the months of high fire danger. Effective fire suppression in Glendale hillsides protects the land by preventing soil erosion, loss of property due to fire and resulting mudslides and elimination of mass emissions of particulates into the atmosphere as well as control of carbon dioxide emissions resulting from massive brushfires.

Quality

Chlorite investigations of nitrification control have won national and regional awards. The first publication of this, until then, unknown phenomenon in 1999 won the Publication Award of the American Water Works Association recognizing the "...most notable contribution to the science of public water supply... ." A publication of the continuing research in 2006 won the Best Division Paper Award (for AWWA's Water Quality and Technology Division). This specific Glendale demonstration program won a 2008 Honor Award from the Consulting Engineers and Land Surveyors of California, which also nominated the project for the American Council of Engineering Companies national Engineering Excellence Awards.

Complexity

Chlorite provides a simple solution to a complex nitrification problem. Understanding and controlling the complex chemical, physical and microbiological aspects of nitrification is a challenge for most water utilities. If the problem were easy to solve, it would have been solved by now. The innovation of adding chlorite for nitrification control simplifies the complexity of traditional nitrification control approaches. A simple chemical feed system and appropriate monitoring replaces complex attempts to control nitrification by cycling reservoirs, adding hypochlorite to reservoirs, flushing programs and conversions to free chlorine for one month every year.

Originality and Innovation

The utility of nitrification control by chlorite ion was a unique discovery and the Glendale demonstration project has proven its real-world effectiveness. The use of chlorite ion for nitrification control is innovative. Besides being the first full-scale nitrification control study in California feeding sodium chlorite as the source of chlorite ion, it was also the first demonstration-scale project nitrification control study anywhere feeding sodium chlorite that has included detailed control and monitoring. The Glendale project employed a unique molecular DNA amplification analytical method for the first time to track changes in populations of ammonia oxidizing bacteria that promote nitrification. The project is also innovative for simplifying the chlorite standard method which made it more reliable for operators to use, and for recognizing that nitrite caused significant interference with the amperometric method.

Social and Economic Advancement.

Reliable control of nitrification using chlorite will have significant social and community benefits including lower exposures of customers to disinfection byproducts, fewer complaints by customers of a chlorinous taste to water, lower costs of control, more reliable distribution system operation and maintenance of substantial storage volumes for emergency conditions. Because operating a chlorite feed system is inherently much easier than traditional means of controlling nitrification, a cost analysis demonstrated that chlorite addition is more economical.

Nitrification control avoids violating other regulations or increasing public health risk. In the past, numerous utilities have violated the Total Coliform Rule (TCR) because nitrification went out of control. Using chlorite will improve microbiological quality and prevent violations of the TCR. Additionally, chlorite control of nitrification will eliminate the need to convert the entire system to free chlorine with resulting high DBP concentrations that likely would not comply with the Stage 2 DBP regulation.

Protecting public health is the first priority of controlling nitrification. The Committee on Public Water Supply Distribution Systems: Assessing and Reducing Risks, National Research Council in 2005 declared that "...the loss of chloramine residual driven by biological nitrification was deemed by the committee to be a significant health threat... ." Controlling nitrification with chlorite removes this significant health threat. Because chlorite levels are kept below the regulatory safe level of the maximum contaminant level goal for chlorite of 0.8mg/L, there is no risk/risk tradeoff.