Mareeba Shire Council engaged Amiad Water Systems to design, construct and commission a 6-10 L/s Arsenic Filtration Plant for the township of Chillagoe in far North Queensland. The town sources its water from a local bore field which suffers from Arsenic levels in the range of 0.010 – 0.020 mg/L; exceeding the Australian Drinking Water Guidelines. The contract specified that the plant must achieve a target level of Arsenic of less than 0.005 mg/L in the product water.
To achieve the target Amiad proposed a system of Chlorination, Ferric Chloride Dosing, DMI65 Catalytic Media Filtration and Cartridge Filter Polishing. The supplied plant is fully automatic and controlled by an Allen Bradley PLC with a Schneider PC / Touch Screen loaded with Citect Software, for local and remote operation, to remove arsenic from the water.
TREATMENT PROCESS
Chlorination:
In ground water, Arsenic occurs predominantly as arsenite As (III), and requires conversion to arsenate As (V) by chlorination to enhance the effectiveness of the filtration process. Chlorine also acts as catalyst for the DMI-65 media, and is required for its regeneration to re-establish the oxidizing environment on the surface of the media.
Ferric Chloride Dosing:
Arsenic can bond with iron salts in the water and with metal based coagulants such as Ferric Chloride. Ferric Chloride is dosed such that there is a sufficient reservoir of iron for arsenic to form complexes and precipitants with the iron salts via the chemical processes of precipitation, co-precipitation and adsorption, which can then be filtered.
DMI65 Catalytic Media Filtration:
DMI-65 is a manganese dioxide (MnO2) infused media whose surface acts as a good oxidant and is effective in removing both arsenite and arsenate, as well as iron/arsenic complexes and precipitants. The DMI-65 Media Filters are periodically backwashed and rinsed based on either pressure differential across the media filters or on time, whichever occurs first.
Cartridge Filters: 1 micron cartridge filters were installed to polish the product water and provide a final barrier to the precipitated arsenic.
CONCLUSION
The Arsenic Filtration Plant, designed and constructed by Amiad utilizing DMI65 Media, was commissioned in March, 2015, and has been successfully reducing the Arsenic to 0.001 mg/L, making it suitable for consumption by the community of Chillagoe, Queensland.
