| Due to low energy consumption, easy operation, high removal efficiency of bacteria and micro-organisms, ultra filtration(UF) has been widely used in drinking water purification. However, like other membrane processes, membrane fouling was one of the main technical challenges impeding the industrialization of UF process caused by concentration polarization and particle deposition. How to extend the application of membrane technology in the water treatment industry and mitigate the membrane fouling was a technical difficulty in membrane. In this work, PVC ultra filtration membrane was selected to treat municipal sewage and two methods were considered to reduce membrane fouling. CFD was applied to analysis the effects of pulse feed on membrane flux. 1、Treating municipal sewage with PAC/UFIn order to investigate the application of activated carbon combined with PVC membrane for treating municipal sewage, effects of PAC/UF and PVC ultra filtration were compared. Results showed that with PAC/UF, the turbidity of permeate was 0.1NTU and the removal efficiencies was 99%, it was improved by 4% compared with only ultra filtration; the CODcr of effluent was 68.4mg/L, the removal efficiencies was 45.4%, and it was improved by 27%; the DOC of effluent was 8.1 mg/L, the removal efficiencies was 56%, and it was improved by 35%. 2、Multistage treating of municipal sewage with PVC membrane and membrane controlling with pulse feedIn order to investigate the application of PVC hollow fiber membrane for sewage treatment, PVC membrane was directly applied to treat municipal sewage with cross-flow filtration. Results showed that when municipal sewage was treated three times continuously by PVC membrane, related indexes were up to the national standard of A for Class One, the turbidity is below 0.1NTU, CODcr decreased from 120.97mg/l to 47.34mg/l, the removal efficiencies was 60.9%, DOC changes from 8.95mg/l to 4.08mg/l, the removal efficiencies was 54.4%. And, rejection rate of bacteria was 99.6%. After the secondary treatment for COD and DOC, the removal efficiencies got the highest value of 35.2% and 37.2%. Pulse feed was used to control membrane fouling. The effects of low – frequency and high – frequency pulse feed were considered. The resulted showed that the higher pulse frequency, the greater of membrane flux and the lower membrane fouling. 3、CFD modeling and experimental study of pulse flow in PVC membrane for wastewater treatmentIn this paper, two kinds of pulse feed including sinusoidal pulse flow(SPF) and intermittent pulse flow(IPF) were applied at the entrance of the ultrafiltration(UF) module with hollow fiber membrane, which were more effective for flux enhancement. As compared to continuous flow at the same average velocity(0.2 m/s), the improvement of permeation flux could reach up to 45% for SPF and 35% for IPF, respectively. Take example for SPF, The effects of the pulse intensity and pulse duration on membrane flux were discussed. It was found that short pulse duration and high pulse amplitude could effectively promote membrane flux, however, the pulse duration played a critical role. When the pulse amplitude was 0.2 m/s and pulse duration was 30 s, the flux showed the highest value. Comprehensive analysis of the shear stress distribution along the membrane surface has been performed by a three-dimensional computational fluid dynamics(3D CFD) model. Additionally, comparison of pressure drop between pulse feed and steady flow was done to evaluate energy consumption. The simulation results showed: under the same operation conditions, compared the steady flow, the shear force would be higher with pulse feed and decreased more slowly along the direction of fluid flow. When pulse amplitude was controlled as 0.1 – 0.2 m/s and pulse duration was 30 s, the pressure drop was closed to the condition of steady flow. Results indicated pulse flow would be effective method for controlling membrane fouling. |
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