Arsenic Basic Process Assessment Guide

The concentraion of Iron in source water can be one of the main drivers in technology selection, therefore the presnece of iron will play a prominent role in technology selection and the treatability of a given water source.  The most effective arsenic removal processes available are iron-based treatment technologies such as chemical coagulation/filtration with iron salts and adsorptive media with iron-based products.  These methods are particularly effective in removing arsenic because iron has a strong affinity to adsorb arsenic.  Because of the unique role iron plays in facilitating arsenic removal, the level of iron in the source water is a primary consideration in the selection of an optimal treatment approach.

Arsenic to Iron ratio chart

The above chart shows a detailed description of the range of iron concentrations relative to arsenic concentrations and how the Fe:As ration could influence the treatment technology chosen.

  • HIGH iron levels (>0.3 mg/L).  HIGH Fe:As ratio (>20:1)
    Iron removal processes can be used to promote arsenic removal from drinking water via adsorption and co-precipitation.  Source waters with this ratio are potential candidates for arsenic removal by iron removal.  (A)
  • MODERATE iron levels (>0.3 mg/L). LOW Fe:As ratio (<20:1)
    If the iron to arsenic ratio in the source water is less than 20:1, then a modified treatment process such as coagulation/filtration with the addition of iron salts should be considered. (B)
  • LOW iron levels (<0.3 mg/L).
    Technologies such as adsorptive media, coagulation/filtration, and ion exchange are best suited for sites with relatively low iron levels in their source waters at less than 300 ug/L, the secondary MCL for iron. (C)

This process selection is very basic and the removal capacities depicted are meant to be a general rule of thumb.  It is important to run a General Mineral Analysis on your water to determine the best treatment approach.