The contamination problem is getting worse now a day because of the industrial activities. Recently it has been announced that there's environmental hormone in river and lake which produces clean water, also there's too many of algae reproduces under the water and some virus in the drinking water. The quality of water is very important. pure and clean water is not only a precondition for human being to live but a basic factor to improve the quality of life. so a water purification system must be developed. This study is about the surface washing treatment technique. We tried to use a rotary nozzle to get a tush degree of efficiency, for it was not enough with present way of washing. The nozzle is run by water pressure. The results of the experiment are as follows. We got a clean and equal surface after washing. After washing, the water's maximum consistency was 330NTU and it shows that this way is better than before one with 215NTU. Clean level of the filter was 6˚and it's 2.8 times higher than 17˚with the old way. We can see the results that the new way of washing is more effective than old way based on this study.

본 실험에서는 수리구조물의 보호되는 토립자의 필터내 이동과 이로인한 필터의 기능 저하를 실험을 통하여 비교분석한 결과 다음과 같은 결론을 얻었다. 1. 수두가 높고 공극이 클수록 필터내 세사의 이동은 심했으며 조기에 흐름의 안정화에 도달하게 되었지만 필터외부로의 입자유출도 많았으며, 공극이 작고 유속이 빠르면 필터와 모래의 접촉면에 인접한 곳에서 Blocking현상이 크게 일어남을 알 수 있었다. 2. 필터기능에 영향을 주는 세사의 이동은 공극의 크기와 수두에 큰 영향을 받음을 알 수 있었고, USCE 필터와 USSPL 필터는 공극이 크기 때문에 같은 조건하에서 흐름의 안정이 다른 필터들 보다 조기에 이루어 졌다. 3. 세사의 이동잔류량은 USSPL, USCE, USBR, Newton & Hurley, Bertram 필터순으로 많이 나타났다. 4. 흐름의 안전에 소요된 시간은 Bertram, Newton & Hurley, USBR, USSPL, USCE 필터순으로 적었고, 투수계수는 USBR, Bertram, Newton & Hurley, USSPL, USCE 필터순으로 크게 나타났다. 5. 여러 가지 종류의 필터기준중 USCE와 USSPL기준의 필터가 투수계수의 안정에 소요된 시간이 가장 짧고, 세사의 이동량이 적으므로 가장 적합한 것으로 인정된다.

The H water treatment plant has been operating since 1982 and has had no renovation. It is assumed that the filters have been operated for more than 30 years and therefore are deteriorated. Many of the filters show an unequal state of air scouring during backwashing. For this study one filter, which was presumed most deteriorated among eighteen filters, was selected as a model filter for renovation. Some of the effects seen after renovation of the underdrain system were a lower average filtrated turbidity by approximately 0.02 NTU and an equal backwash state throughout the filter bed. Sand wash efficiencies by backwash before renovation of the underdrain system were 28%, 8%, and 5% at the surface, 50 cm depth, and 100 cm depth, respectively, and after renovation of the underdrain system were 94%, 26%, and 15% , respectively. The standard deviation of the effective sand size was 0.025-0.033 mm before renovation of the underdrain system and 0.002-0.011 mm after renovation of the underdrain system, meanings there was equal backwash pressure throughout the filter. Filtration time after renovation was approximately 2 times longer than before renovation.

After identifying species by collecting the suspended and attached algae mat inhabiting in the slow sand-filter, Spirogyra sp., Mougeotia sp. and Closterium sp. were main green algae and Synedra sp. was diatom algae. Among them green algae Spirogyra sp. was dominant species. A result of observing the life mode of apple snail for a month after introducing into the slow sand-filter, apple snail eggs were discovered on the filter walls 2 weeks after introducing, 4 weeks later lots of eggs were observed all of the slow sand-filter walls, it means there is no problem for apple snail to live in the slow sand-filter. The observation result for algae removal potential by introduced apple snail after 2 months later, slow sand-filter where apple snail were introduced, a few algal mat were observed. On the other hand, no introduced apple snail into the slow sand-filter, lots of suspended algal mats were formed in the water and attached algal mats on the sand surface as well, these algal mat induced much of operating problems.

The purpose of this research was to investigate the efficiency of coagulants dose after backwashing. The turbidity of initial effluent was high after backwashing in the rapid sand filtration and the high turbidity was almost removed by coagulants dose into filter-sand after backwashing. It was found that the turbidity of initial effluent was well removed by all kinds of the coagulants used in this study. When filtration was performed input water with differentiated pH's, the turbidity of effluent was low at the range of pH 5 - pH 7. But the removal was not good about over pH 9. This result was considered into the existence forms of aluminium, Al(OH)2+ and Al(OH)2+ at pH 5. Cryptosporidiums of effluent were 4/ml for ten minutes immediately after back washing and 3/ml until sixty minutes. However, the case of coagulant dose after backwashing, Cryptosporidiums of effluent were 0.5/ml for ten minutes with no detection after twenty minutes.