Treatment of domestic wastewater using microfiltration for reuse of wastewater

This study was conducted to evaluate the applicability of microfiltration in treating domestic wastewater for reuse. A hollow fiber microfiltration membrane was used in the pilot test. The pore size of the membrane was 0.1 m and effective surface area was 20 m2. The maximum capacity of the pilot plant was 10 m3/d. The microfiltration system could be operated for 120 days without any cleaning procedure. It was found that agitation in the membrane tank had an effect on fouling prevention. In particular, the bi-directional agitation significantly reduced fouling. Chemical cleaning was effective in recovering of permeate flux and resistance, but in spite of chemical cleaning, fouling slowly progressed. According to the particle size distribution, in the membrane tank particles were transformed into smaller size by agitatorinduced shear force. Based on mass balance analysis, about 60% of dissolved TOC mass removal in the system was attributed to biodegradation, indicating its important role. But suspended solids and colloidal matter were removed by the sieve mechanism of the membrane. Effluent quality was found to be lower than 30 mg/L of COD, 10 mg/L of BOD, 10 mg/L of TOC, 1 NTU of turbidity and 2 mg/L of SS, respectively. It satisfies the standard for wastewater reuse.

Fig. 6. Changes of COD in (a) influent, (b) equalization tank, (c) membrane tank and (d) effluent. In the reclamation of domestic wastewater, microfiltration was able to be operated for 120 days without any cleaning procedure. It indicated that the agitation in the membrane tank was effective for preventing fouling. In particular, the bi-directional rotation of the agitator significantly reduced the progress of membrane fouling. Chemical cleaning was effective on the recovery of filtration performance such as flux and filtration resistance, but the fouling which could not be recovered, even by chemical cleaning, slowly progressed. Ultimately, the replacement of the membrane is necessary for long-term operation. About 60% of dissolved TOC mass removal in the system was attributed to biodegradation. It concluded that biodegradation had an important role in the removal of dissolved organic matter, while suspended solids and colloids are removed by the sieve mechanism of the membrane. According to changes of particle size distribution in the membrane tank, particles were transformed into a smaller size by agitatorinduced shear force. Regardless of the variations of influent qualities, effluent qualities were found to be lower than 30 mg/L of COD, 10 mg/L of BOD, 10 mg/L of TOC, 1 NTU of turbidity and 2 mg/L of SS, respectively. It satisfies the standard for wastewater reuse.