The authors have developed what we call the submerged iron contactor process as a simple and inexpensive phosphorus removal method for small-scale plants disposing of domestic wastewater and household wastewater treatment tanks. In this method iron contactors are submerged in biological treatment tanks, where phosphate anions in wastewater are combined with iron cations produced through corrosion of the contactors, and the compound thus produced is precipitated and removed together with biological sludge.

In these studies, laboratory experiments were made on the contact aeration process combined with the above-mentioned method, and the following findings were obtained. (1) It is desirable to treat wastewater by making use of corrosion by sulfate-reducing bacteria instead of corrosion by oxygen dissolved in wastewater, to conduct a stable phosphorus removal by this combined method. (2) The corrosion rate of iron contactors is affected by the volumetric loading of BOD in the tanks where they are submerged. (3) Assuming that an iron contactor continues to suffer corrosion evenly all over the surface when our combined method is applied, it is estimated that the corrosion rate is about 1mm or less in 30 years.

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