Case Study: Arsenic Oxidation

Problem:

Arsenic is a naturally occurring element found in rocks and soil and is used for a variety of purposes in industries such as agriculture, mining, smelting, and industrial products manufacturing thus contributing to major contamination in media such as groundwater and landfill leachate. Arsenic can enter the water supply in high concentrations from industrial use if not managed properly. A lower standard of 10 ppb of arsenic in drinking water was recommended by the World Health Organization; however, it is estimated that over 140 million people in 50 different countries have been exposed to arsenic levels above the provisional guideline. The highly toxic organic form of arsenic is linked to many cardiovascular diseases, diabetes, and cancers.

Once released, arsenic stays in the environment taking years to naturally degrade. There are several different methods used in arsenic removal such as ion exchange, membrane technology, and adsorption which are costly and require frequent replacement, management, and disposal.

Solution:

Electrochemical treatment of arsenic consists of a two-step approach where arsenite is oxidized to arsenate followed by coagulation for solid arsenate removal. Aclarity’s electrochemical reactor offers the benefit of producing mixed oxidants in situ to immediately precipitate dissolved arsenic without the usage of additional chemicals.

In one project, Aclarity’s reactor was operated in a single pass open-loop system passing water with 42 µg/L arsenic. Samples were collected after 10 and 30 minutes of treatment. A passing current is used to oxidize natural occurring compounds found in the water to form species such as hypochlorite and ozone. These species oxidize arsenite to arsenate, which is then removed with a ferrous chloride or alum coagulant. With a low power usage of 23W, Aclarity was able to remove arsenic from a starting concentration of 42 down to 4 μg/L, well below the EPA limit.

Aclarity’s electrochemical technology offers many advantages such as low operating costs and no transport or storage of chemicals. Electrochemical oxidation is a highly effective method in treating arsenic and only requires a small oxidant to arsenic ratio. Aclarity’s reactor can produce up to 78 mg/L of oxidizing species in an open loop setting with 70W, which can easily oxidize typical arsenic levels.