Field Study on Dephosphorization for Rural Sewage Treatment

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In order to develop the new treatment method of phosphorous using submerged iron filter, adaptable to the small-scale sewage treatment plants such as those of rural community, field expeiments were carried out in three practical treatment plants of different systems.1.Application to contact aeration method at Hirayama districtIn the first experiments, 1160 pieces of iron filter were submerged in the contact aeration tank. Iron ion was desolved from the iron filter with bacteria corrosion according to the growth of biological menbrane, and then the stable dephosphorization was achieved.In the second, in which 2400 pieces of iron filter were submerged in anaerobic tank, phosphorous removal rate was gradually decreased by the blockage of biological menbrane.2. Application to rotary disc method at Hanami districtIn this plant, 60 sheets of plastic discs were replaced by the iron discs. Although the phosphorous concentration of treated water in plastic discs was 4.1 mg/1 in average, that of iron discs was 2.2 mg/1 in average, and the average removal rate was 53% during 1.5 years after replacing iron discs.3. Application to intermittent aeration method at jyouanji districtThe phosphorous concentration of treated water from the tank without iron filter was remarkably fluctuated month by month. But those from the tank with submerged iron filter were almost always less than 1 mg/1. The average removal rate was between 60 and 80% in the period of experiment. Submerged iron filter did not show any detrimental influences on high rate removal of BOD, COD and that of nitrogen.