As concerns over the health effects of arsenic increase, so do the regulations to minimize the levels of arsenic in drinking water.
To help communities accommodate new regulations—especially the U.S. EPA’s new arsenic rule effective in January 2006—U.S. water treatment companies are finding and implementing commercially available technologies suitable for treating and removing arsenic contamination in drinking water to levels below the required 10 µg/L arsenic MCL.
Current arsenic removal treatment options include ion exchange, activated alumina, reverse osmosis, adsorption and coagulation/filtration (see Figure 1 for a comparison of arsenic removal technologies).
Before evaluating an arsenic removal technology, a utility should characterize its system by obtaining a detailed water quality analysis of a wide range of parameters for each location with arsenic contamination. Because, for example, well water in similar regions can differ significantly. The water analysis should consist of both basic values and special analysis for species that have the potential to interfere with the performance of a treatment technology. A utility can then perform a pilot test or undertake rapid small-scale column testing to predict full-scale performance of certain arsenic removal treatment technologies.
In addition to capital and operating costs, an arsenic removal technology should be evaluated on a variety of performance criteria as well as the technology supplier’s experience in the arsenic removal market. Performance criteria should address technical requirements and history, along with commercial needs—examples of which can be found in Figure 2.
Empty bed contact time, which dictates the amount of water resident within the bed required to effect complete arsenic adsorption, is another key process parameter. Adsorption is a continuous process conducted at a specific flow rate or velocity, normally about 7 gpm/sq ft, downward through a fixed bed adsorber. An attractive characteristic of adsorption technology is its simplicity and relatively low cost.
Coagulation/filtration has higher initial capital costs and is labor intensive, with labor costs often not adequately accounted for in operating cost estimates. In addition, this technology is more complex than adsorption, a key concern for utilities without centralized treatment plants. The technology requires frequent
backwashing (water losses) and constant calibration of significant automation required for chemical dosing, backwashing and sludge management. However, coagulation/filtration can prove to be an effective solution when treating for high levels of multiple contaminants.
Although adsorption and coagulation/filtration are just two arsenic removal options, as arsenic removal technologies evolve and the water treatment market offers more effective treatment at lower costs, the long-term success of any commercially available arsenic removal process will result from continued research and development to ensure that the technology remains simple, effective and proven.
RSS: WWD Articles
