Arsenic Reduction in Alaska
In late 2009, VEI Consultants contacted AdEdge Technologies to design, implement and start up an arsenic, iron and manganese treatment system for the Talkeetna Water System in Talkeetna, Alaska. The existing water supply consisted of a well rated for 250 gal per minute (gpm) with an arsenic level of 20 parts per billion (ppb). Iron and manganese levels were 0.04 mg/L and 0.1 mg/L, respectively. The water supply serves a population of approximately 430 and uses 63,000 gal of water per day.
The AdEdge treatment system features a skid-mounted GS+ coagulation and filtration package unit sized for a maximum design flow of 250 gpm. The model AD26-5460CS-3-AVH utilizes AdEdge GS+ media in a three-vessel carbon steel configuration in parallel. The system is equipped with automated control valves and harness, central control panel with programmable logic controller and a color user interface screen. System features also include differential pressure switches, control panel and local gauges, flow sensors and totalizers, and a central hydraulic panel with sample ports for a complete functioning packaged unit.
A continuous feed of both sodium hypochlorite and ferric chloride is fed prior to the treatment system to optimize the removal of arsenic. Each 54-in. diameter treatment vessel contains 38 cu ft of AdEdge GS+ coagulation/filtration media. AdEdge GS+ is a black filter media used for the removal of arsenic, iron and manganese. The manganese dioxide-coated surface of GS+ acts as a catalyst in the oxidation-reduction reaction of iron and manganese. Backwashing of the treatment system occurs every two or three days depending on the incoming levels of iron and manganese to remove any suspended solids that may accumulate in the bed.
The system was started up and commenced operation in January 2011. Since the system began operation, arsenic levels have lowered from 20 ppb to 1.5 ppb and iron and manganese levels are at non-detectable levels.