The toxicological effects of arsenic are related to its chemical form and oxidation state: As(III) is about 100 times more toxic and mobile than arsenate As(V). Methyl Arsenic may present comparable toxicity or higher than inorganic species, As(III) or As(V). Hence, it is necessary to remove all arsenic species from waters. In recent years, a range of inexpensive, iron-based, water clean-up technologies have been developed to address the major problem of As-rich drinking water. The possible use of AsIII oxidising bacteria has been investigated as effective oxidation step overcoming drawbacks of chemical oxidation in biofilter studies coupled with As removal treatment based on Fe adsorbents.