|【Water treatment techniques-What is the Iron bacteria treatment technique？】|
Groundwater quality is influenced by the geological environment and condition of recharge. However, groundwater has higher water quality than surface water of barrages, rivers, and pond water.
When general groundwater from diluvium deposits of plains and hills is used, iron, manganese, and ammoniac nitrogen are the compounds which need to be removed. A typical groundwater treatment technique that can easily remove these compounds is the “iron bacteria treatment technique”. The iron bacteria treatment technique is a method which filtrates oxygenized and suspended iron and manganese by adsorbing bacteria living in groundwater on media and then cultivating the bacteria, which can oxygenize iron.
The iron bacteria treatment technique was first used in 1952. In water purification plants conducting slow filtration of raw water groundwater, when a filter is clogged, work to remove sand is needed. When the filtration load was raised and continued being filtrated, it was found that water quality was higher than with the conventional method. .
In 1976, the “Manganese Removal Treatment” description published by the Japan Water Works Association described that iron can be removed by iron bacteria when water is naturally filtrated. Moreover, manganese, which is found in lower quantities than iron, is also partially removed by biological contact oxidation at a filtration flow rate of approximately 40m/d. .
In 1986, Joyo City in Kyoto started an experiment with the iron bacteria treatment technique. In 1993 the water purification plants conducting iron bacteria treatment improved their filtration flow rate to approximately 70m/d..
In 2001, the Department of Water Works of Koriyama City in Nara prefecture achieved simultaneously more than 90% removal rate of three compounds: iron 4.52mg/L, manganese 0.58mg/L, and ammoniac nitrogen 0.33mg/ L..
Even if iron, manganese, and ammoniac nitrogen are highly concentrated, they can be removed at a filtration flow rate of 300m/d. It has been proved that the mechanism of biological contact oxidation from the iron bacteria treatment technique can be catalyzed by polysaccharide, enzymes, and metabolism products which microorganisms produce on the body surface of microorganisms..
In July of 2006, it was found that in arsenic removal technology using the iron bacteria treatment technique, not only chemisorption is conducted by iron but also there is an oxidation reaction involved in microorganisms. For example, it was reported that 90% of arsenic in raw water with arsenic concentrations of mean 0.3mg/L was removed at a filtration flow rate of 600m/d in Kawanishi City, Hyogo Prefecture. .
Currently, there are 22 water purification plants using the iron bacteria treatment technique in Japan. Furthermore, three more water purification plants have been experimented. Future technological development and worldwide use are anticipated.