Arsenic, a naturally occurring chemical found in the earth’s crust, can be dangerous to humans when erosion releases the chemical into drinking water supplies. Studies have linked long-term exposure to arsenic contamination with cancer and cardiovascular, pulmonary, immunological, neurological and endocrine problems. In June 2003, the City of Brown City, Mich., located about 60 miles north of Detroit, was awarded the first of the US Environmental Protection Agency’s (EPA) treatment systems as part of the EPA Arsenic Removal Demonstration Program.
Similarly to a number of other demonstration sites throughout the country, the EPA and its team of consultants on the Demonstration Program panel selected Severn Trent Services’ SORB 33 arsenic adsorption system for the site.
Brown City’s water system serves a population of 1,300 with water coming from two wells known as Number 3 and 4. Wells Number 1 and 2 were capped when 3 and 4 were introduced in the late 1960s. Prior to the demonstration study, both wells provided water on an alternating basis. However, during the demonstration, well Number 3 was reserved for emergency backup and well Number 4 became the sole source of water. Number 4 has a capacity of 640 gpm, and the water is delivered to a storage tank at a pressure of 60 psig. The well water has an arsenic (As) level of 19-25 micrograms per liter (µg/L), most in the form of reduced As(III), and also contains a modest level of iron (Fe), typical of Michigan well waters. The pump building, which also houses a motor control center and chlorination unit, required a significant increase in floor space to accommodate the arsenic removal system.
Severn Trent Services installed two of its automated SORB 33 APU 300 package units, each with a capacity to treat 320 gpm, or half of the well pump’s total flow. The 16’L x 6’W x 9’H skid-mounted units each consist of two 5 1/4-O FRP adsorbers and 152 ft? of Bayoxide E33 iron oxide media, which were installed as modules after the building was completed. Each unit includes 10 automatic valves, five for each adsorber, which are controlled by individual PLCs. The four adsorbers operate in parallel flow configuration. Piping for the system is schedule 80 PVC with PVC butterfly valves.
After the pump building was expanded to house the additional equipment, the two APU systems were installed and began operation in April 2004. Since installation, the system’s performance has by monitored by EPA’s contractor.
The SORB 33 system was designed to treat Brown City’s unchlorinated water directly from the well pump, however, an injection point was installed upstream of the adsorbers during construction. Spent backwash water is discharged through a swale to a nearby county storm water drain. Backwash is initiated by the operator, although the system does have features for automatic backwash on a timed schedule or on high differential pressure across the adsorber vessel. Since the well operates only four to six hours per day, backwash is initiated manually, and the operator ensures the backwash procedure is completed before the pump shuts down.
The system performed well, successfully removing the arsenic and iron in the drinking water supply. However, after several months of operation, reduced arsenic, As(III), began to break through because the adsorbed reduced iron, Fe (II), lowered the media’s ability to oxidize and adsorb As(III). To fix the situation, the chlorination injection point was moved upstream of the SORB 33 system. As a result, the effectiveness of the Bayoxide E33 media improved, reducing arsenic to <2 µg/L in the treated water, and performance has been consistent since prechlorination was implemented. Manganese (Mn) is also being removed in the process. Backwashing has since been increased to once every two weeks.
With the successful removal of arsenic at Well Number 4, Brown City has decided to build a second arsenic removal facility that will also use the SORB 33 system. Construction of the new facility is scheduled to begin in June 2007 and will be operational by the end of the year.
Beth Kennedy is the Marketing Communications Manager at Severn Trent Services. She can be reached at 866-646-9201 or by email at firstname.lastname@example.org
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