The MBR process, which uses membrane to separate solids instead of secondary clarifier, has the advantage of maintaining high MLSS (Mixed Liquor Suspended Solids) concentration in bioreactors. In this study, three MBR processes combined with chemical phosphorus removal facility were studied: the phase-isolated MBR process with one recirculation pump, the A2O MBR process with two recirculation pumps, and the MBR process without a oxygen depletion reactor with three recirculation pumps. 116 simulations by EQPS (Effluent Quality Prediction System) were performed, under same design influent characteristics and hydraulic retention time, to see the effects of recirculation ratio changes on effluent water quality. The final effluent limits for total nitrogen and phosphorus were set to as 10 ㎎/L or less and 0.2 ㎎/L or less, respectively. AlCl3 was fed at MBR effluent to make 0.2 ㎎/L of total phosphorus precisely by PI (Proportional-Integral) controller in EQPS. This study showed that the phase isolated MBR process (R1 600%) had the highest nitrogen removal efficiency, with a final effluent T-N concentration of 6.765 mg/L. However, the A2O MBR process (R1 400%, R2 100%) required the lowest AlCl3 flow of 0.742 m3/day, which is approximately 59.1% lower than the average AlCl3 flow of the phase-isolated MBR process. It also produced 4,835 kg/day of sludge, the lowest among the studying MBR processes. It seems that A2O MBR process is the most economic method to treat studying wastewater to meet final effluent nutrient limit targets. However, carbon neutrality must be considered to select the best process to treat studying wastewater and it will be presented later.

유기물과 질소를 동시에 제거하기 위하여 연속회분식으로 운전한 MBR (membrane bioreactor)시스템에서 미생물농도와 슬러지 부하량이 막오염과 미생물 활성에 미치는 영향을 살펴보았다. 막오염은 MLSS (mixed liquor suspended solid) 농도 증가에 따라 조금씩 증가하는 경향을 보였고, 그 효과는 비포기 조건보다 포기 조건에는 좀더 두드러지게 나타났다. MLSS 농도는 막오염에 직접적인 커다란 영향을 주지는 않으나, 지나치게 높은 MLSS에서 유도되는 낮은 슬러지 부하에서는 막오염이 크게 증가하는 현상이 발견되었고, 이러한 조건에서는 포기에 의한 막 세척 효과도 크게 줄어들었다. 미생물의 개별 활성도는 슬러지 부하가 감소할수록 지속적으로 감소하는 경향을 나타내었다 반응조 전체 활성도 또한 17,000 mg/L 이상의 높은 MLSS로부터 유도되는 낮은 슬러지 부하율에서는 높은 미생물 농도에도 불구하고 오히려 감소했는데 이는 기질 부족으로 인한 경쟁으로 활성도가 떨어지고, 용액의 점성 증가로 인해 산소 전달율이 저하되었기 때문이다.