The development of environmental rehabilitation techniques of lakes and rivers by purification system based on substances circulation

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In the former of the study period using the purification water equipment by the natural circulation system which is composed by only natural materials, the development of high performance filtration material was tried to attain the discharge concentration of less than 0.5mg/l for nitrogen and less than 0.01mg/l for phosphorus. For the nitrogen, the ceramic filtration material obtained by heat-treated mixtures of charcoal granular and zeolite powder succeeded to reduce the nitrogen discharge concentration to less than 0.5mg/l in regular working time. However, for the phosphorus, the filtration materials mainly composed of calcium silicate could not attain the limitation. On the other hand, at the pond where is suffered from the heavy pollution with foul water it was cleared that the pollution originates from the nutrients decomposed gradually from a large quantity of the mud sediments (sludge). For the effective collection of the pond sludge, calcium silicate materials was newly developed as a cohesive and safety ones instead of usual poly aluminum chloride (PAC), and we demonstrated that this method is effective for the collection of pond sludge as a dehydrated cake. In the later of the study period, studies were conducted to heavily polluted rivers at urban area. In these studies, a filtration material was developed to eliminate only BOD and SS in the short time treatment for a large amount of foul water. As results, we succeeded to produce a ceramic small ball having charcoal granular treated with chitosan built-in and demonstrated that this ceramic material coated with clay can display in short time and for a large amount of foul water the discharge water with very high transparency.