Abstract
Various types of cellulose acetate (CA), cellulose acetate propionate (CAP) and polyethersulfone (PES) hollow fiber membranes were prepared to evaluate energy consumption in submerged filtrations. It is possible to obtain CAP and PES microfiltration membranes with maximum pore size ranging from 0.3 to 2.0 μm by addition of hydrophilic non-solvent to polymer solution. Using CA membrane with pure water permeate velocity of 8.6×10−5m3·m−2·s−1 at 0.1 MPa and molecular weight cut-off (MWCO) of 150 kDa, submerged filtration of waste carwash water after flocculation was performed at the treatment rate of 0.8 m3·h−1 for 1 month. Average electric power consumption was 0.81 kWh·m−3 when backwashing and bubbling were conducted for 1 min after every 15 min of filtration. For comparison, cross-flow filtration using a conventional cross-flow CA membrane with MWCO of 150 kDa was performed under the same experimental conditions as in the case of the submerged filtration. When the cross-flow rate to permeate rate was 1, average electric power consumption was 1.2 kWh·m−3. This result indicates that energy consumption in submerged filtration is lower than that in cross-flow filtration. Using CAP and PES microfiltration membranes, energy consumption in submerged filtration was also measured under the same experimental conditions as in submerged filtration using CA membrane. The average electric power consumption was 0.78 kWh·m−3 for the CAP membrane with pure water permeate velocity at 0.1 MPa of 1.0×10−4, and 0.69 kWh·m−3 for the PES membrane with pure water permeate velocity at 0.1 MPa of 2.8×10−4m3·m−2·s−1. It was found that energy consumption decreased more when the membrane with higher pure water permeate velocity was used.
