A membrane bioreactor (MBR) was designed using polyvinylidene fluoride(PVDF)-type hollow fiber membrane modules with a treatment capacity of 10 ton/day. A pilot plant was installed in a sewage treatment plant and was operated with an intermittent aeration method which avoids any concentration gradient of suspended solids (SS) in the MBR. For continuous operation, the pilot plant was first tested with influent (mixed liquor suspended solid:MLSS of 1000-2000 mg/L) of aeration tanks in the sewage treatment plant. The MBR was pre-treated with washing water, 10% ethanol solution, 5% NaOCl solution and finally washing water, one after another. To demonstrate the effect of the MBR on sewage treatment, compared with conventional activated sludge processes, we investigated the relationships among permeate amount (LMH), change in operation conditions, influent MLSS level and sludge production. It was found that the optimum aeration rate and suction pressure were 0.3 m 3 /min and 30~31 cmHg, respectively. Under stable conditions in aeration, suction pressure, influent flow rate and drainage, the SS removal efficiency was more than 99.99% even when the MLSS loading rate changes. Compared with conventional activated sludge processes, the MBR was more effective in cost reduction by 27% based on permeate amount and by 51.5% on sludge production.

Abstract
 1. Introduction
 2. Materials and methods
  2.1. Membrane arrangement
  2.2. Membrane module configuration
  2.3. Module manufacture
  2.4. Operating conditions
  2.5. Optimum MLSS level for continuous operationof the MBR
  2.6. Identification of microorganisms in the MBR
  2.7. Estimation of operating cost
 3. Results and discussion
  3.1. Microbial growth in the MBR
  3.2 Optimum MLSS level in the MBR
  3.3. Sludge production with influent volumetric loadingrates
  3.4. Effect of aeration rates on effluent MLSS levelThe effect of aeration rates on the effluent (permeate)
  3.5. Suction pressure with aeration rates
  3.6. SS removal efficiency
  3.7. COD removal efficiency
  3.8. Comparison of operating costs
 4. Conclusions
 References

• Choon-Hwan Shin(Department of Energy & Environmental Engineering, Dongseo University) Corresponding Author