By Michael Abraham
Thanks to agricultural runoff that included significant amounts of the herbicide atrazine, viruses, turbidity, and total organic carbon (TOC), the City of Wichita, KS, together with engineering consulting firm CDM, is now at work on the installation of a 30 mgd stormwater treatment system for an aquifer storage and recovery system.
Known as the Aquifer Storage Recovery (ASR) project, the plant is anticipating a full-scale startup in the spring of 2011, and will meet Primary Drinking Water Standards' maximum contaminant levels (MCLs) as required by the Kansas Department of Health and Environment (KDHE).
In making the decision to build the facility, the City of Wichita selected an ozone-based advanced oxidation process (AOP) known as HiPOx® to destroy atrazine, as well as provide disinfection and virus destruction. Although ozone treatment is extremely effective, the HiPOx system also controls the formation of bromate by-products. When it is up-and-running, the Wichita ASR project will be the world's largest system to be based on an advanced oxidation process.
HiPOx is a process created by APTwater, a California-based company developing advanced water treatment process technologies that enable water reuse.
"Not only has the City of Wichita chosen a system that meets current requirements for reduction of atrazine and viruses, they have ensured that anticipated requirements for micro-contaminants will already be covered," said Michael Rudy at Environmental Process Equipment Company in Wichita. "What's more, HiPOx will significantly reduce natural colors in the water, enabling the city to add ultraviolet disinfection capabilities in the future."
The City of Wichita did not make the decisions lightly. Following discovery of the high levels of herbicides and other contaminants in its storm runoff, the city embarked on a complex series of bench-scale tests. These were followed by an extensive on-site pilot scale evaluation of the advanced oxidation process.
|Local streams were being polluted by agricultural runoff.|
The HiPOX bench tests were performed in late 2008 through early 2009 under circumstances designed to emulate a "worst-case" scenario. Filtered water from the Little Arkansas was spiked with varying concentrations of TOC, bromide, and atrazine. The process, which uses a combination of ozone and hydrogen peroxide, proved to be extremely efficient, particularly for obliterating atrazine, but also for controlling the formation of bromate.
The system allows the ASR project to simultaneously achieve the disinfection credits necessary for eradicating viruses, without the need for another process step. All of the treatment goals adhered closely to the very stringent regulatory requirements for drinking water established by the KDHE.
The system's success in handling worst-case scenarios prompted the City of Wichita to submit the AOP to real-life scenarios. Pilot testing designed to simulate the full-scale treatment system began in May 2009. Water from the Little Arkansas was collected during one of the storms that frequently visit the area, and was then run through an Ultrafiltration (UF) Membrane before being going through a HiPOx system operating at a flow rate of 20 gpm.
The UF effluent was collected in storage tanks to enable spiking of the water quality parameters to meet maximum design conditions. The pilot-scale testing included an evaluation of virus destruction using MS2 bacteriophage spiking, a safer surrogate than dealing with real, live pathogens. HiPOx technology has been accepted by the State of California for 5-log reduction of poliovirus in Title 22 water reuse applications, making it acceptable to the KDHE.
|A typical pilot unit testing the ozone-based advanced oxidation system.|
In the end, the pilot tests involved more than 70 test runs and some 500 analyses. The exhaustive process proved conclusively that APTwater's HiPOx AOP simultaneously reduced atrazine to minute levels, controlled bromate development, and successfully met virus and pathogen destruction goals. As a result, CDM, the City of Wichita, and the KDHE decided to use the technology in the ASR project. The project is currently in the construction phase and being conducted by APTwater's technology licensee Air Products and Chemicals, Inc.
Headquartered in Long Beach, Calif., APTwater develops and commercializes advanced water treatment process technologies that enable water reuse. Its technologies are based on renewable resources and minimize or eliminate production residuals or waste byproducts. For additional information, visit www.aptwater.com.
APT Water is an exhibitor at the WEFTEC.10 event and can be found at Booth No. 5351