Research On Membrane Fouling During Micro-Flocculation-Ultrafiltration Process

In recent years, the pollution of drinking water sources gets more and more serious while the conventional treatment process couldn’t remove the organic matters completely. Applying for the increasing water quality standards and changing water quality, this research studies the performance of micro-flocculation, floc structure and membrane fouling by examining different basicity of PAC1, different turbidity’ water samples and different temperature’water samples. The main contents and results are as follows:1.Combined with directly ultrafiltration process, micro-flocculation-ultrafiltration process had better organic removal efficiency and membrane performance.2. Four different pH water samples (pH=5,6,7 and 10) were used in micro-flocculation-ultrafiltration process. Micro-flocculation performance showed that lower pH sample had better performance in removing organic matter and ultrafiltration process showed lower pH sample had lower membrane fouling.3. Effects of Al species on floc properties and membrane fouling in the micro-flocculation-ultrafiltration process were studied by comparing the humic acid (HA)-kaolin synthesized water treatment by polyaluminium chloride (PAC1) with three different basicity values (B=0.5,1.0 and 2.0) in this assay. The result indicated PAC1 (B=2), which has the highest Alb concentration, was able to form more compact flocs than PAC1(B=1) and PAC1(B=0) in the micro-flocculation process. The differences in floc structures contribute to the differences of membrane fouling in the subsequent ultrafiltration process. That’s why PAC1(B=2) had the worst membrane performance.4. The influence of turbidity on removal efficiency, floc growth and fractal dimension was examined. The results indicated that although the floc sizes were similar to different PAC1 in micro-flocculation process, PAC1 (NTU=5), which was beneficial to form more looser flocs than PAC1(NTU=10) and PAC1(NTU=20). And the difference of flocs structure makes the difference of membrane fouling in subsequent ultrafiltration process. The permeate fluxes of PAC1 with different turbidity values decreased in the following order:PAC1(NTU=20)<PAC1(NTU=10) <PAC1(NTU=5), which indicated PAC1 (NTU=5)had the best membrane performance.5. The removal of organic matter, the floc properties and the main mechanism of membrane fouling resulting from different temperatures were investigated using micro-flocculation-ultrafiltration process in this study. Results showed that flocs formed in the lower temperature water sample had better removal efficiencies of nature organic matter. Though the floc size of flocs formed in different temperature water samples had little difference, fractal dimension (dF) of the flocs formed in the low temperature water sample was lower than normal temperature water sample, indicating that flocs formed in the low temperatures water sample had a more loose interior floc structure. And the lower temperature water sample with higher permeate flux had better performance in membrane fouling and this was closely related to the floc properties of flocs formed in low temperature.6. Regardless of turbidity and temperature of water sample, the cake layer was the main reason of membrane fouling no matter what kind of PAC1 was used. Reducing the turbidity and temperature of water sample, or using PAC1 with higher Alb concentration can reduce membrane fouling effectively.