본 연구에서는 막결합생물반응조(MBR)공법을 비롯한 하수고도처리공법에서 유입하수량의 변화에 따른 슬러지 특성 변화를 파악하고자 하였다. 일 1.5톤을 처리하는 모형실험시설에서 설계유량 대비 유입하수량을 100, 70, 40, 10%로 변 화시켜가며 이에 따른 비탈질속도(specific denitrification rate)와 비질산화속도(specific ammonia oxidation rate)의 변화를 측 정하였다. 각 공법의 폭기조에서 채취한 슬러지의 비질산화속도는 유입하수량 100% 조건에서 세 가지 공법 모두 유사한 값 (0.10 gNH4/gMLVSS/day)으로 측정되었다. 유입하수량이 70%에서 40%로 감소함에 따라 비질산화속도가 크게 감소하는 경향을 나타냈다. 비탈질속도 역시 유입하수량이 감소함에 따라 최대 50%가량 감소하였다. 유입하수량이 감소할수록 비탈질속 도와 비질산화속도가 감소하는 경향을 나타냈으나 원수의 총질소 농도와 반응조 내 미생물 농도를 고려하면 질소제거율에 영향을 미칠 정도는 아니었다. 따라서 유입하수량이 감소하는 경우에도 반응조 내 미생물 농도를 높게 유지할 수 있다면 안정적인 질소 제거가 가능할 것으로 판단된다.

In this research, characteristics of nitrification and denitrification using the microorganism attached on sponge and plates were examined. The denitrification and nitrification performance were investigated under the anaerobic and aerobic condition for about 2 months. Because the basins of denitrification and nitrification were connected in series, wastewater was flowed from denitrification basin to nitrification one. The 90% of influent flowrate was returned from nitrification basin to denitrification one. Most of organic material was removed in nitrification basin, wherease the only exact amount of organics required in denitrification process was removed in denitrification one. This experiment resulted in that heterotrophic bacteria existing in aerobic basin governed the removal efficiency of organic compounds. In case the influent BOD concentration into nitrification basin was 80mg/l, it did not affect to accumulation of nitrifying bacteria, the balance of heterotrophic bacteria was proved to be an important factor in nitrification/denitrification method such as anaerobic and aerobic cycling type.

In order to investigate the possibility as a simple technique of wastewater treatment for recirculating aquaculture system, the experiment by a biofilter unit was carried out. The high and stable removal efficiency of nitrogen could be obtained by selecting the optimum recycle ratio and DO concentration. It was found that the proper combination of nitrification and denitrification step in the reactor would be required for increasing the removal efficiency. The extent of nitrogen removal gradually decreased with the rise of recycle ratio since the depression of denitrification by the lack of hydrogen donor. The depression of nitrogen removal was overcome by increasing the C/N ratio in the wastewater. The extent of phosphorus removal was increased slightly with the increase of DO concentration and recycle ratio, but high removal efficiency was not observed. However, the extent of COD removal was not affected by recycle ratio and DO concentration and showed the stable removal of above 90%.