| With increasing drinking water pollution and the continuous improvement of drinking water quality standards, conventional treatment process can not meet the requirements of the people in water quality and safety. Ultrafiltration has been widely applied in the field of water treatment because of its unique advantages. However, membrane fouling is always a key issue to restrict the ultrafiltration processes. Coagulation pretreatment is considered as the most successful technology to control membrane fouling in water treatment so far. Although previous investigations have adopted the coagulation pretreatment to control membrane fouling, few researches deeply studied the influence of flocs characteristics on membrane fouling.This article studied the effect of organic matter on the membrane fouling firstly. The results showed that humic acid(HA) and bovine serum albumin(BSA) could cause significant membrane fouling especially irreversible fouling when they existed in water solution alone. The membrane fouling caused by BSA was more serious than that of HA An interesting founding that the decline trend of specific flux when HA and BSA coexisted was similar with that of HA.Then the enhanced coagulation treatment was used to remove organic matter for sake of mitigation membrane fouling. The dosage of PACl, p H value of raw water, ionic strength, and hardness were chosen to investigate the effect of removal organic matter. The results indicated that optimal dosage of PACl was 20 mg/L and the optimum p H was 7. The removal efficiency of hydrophobic HA was significantly higher than that of hydrophilic BSA. When PACl dosage was 5 mg/L, the increase concentration of Na+ and Ca2+ could effectively improve the removal efficiency of organic matter. Whereas, the removal efficiency of organic matter was less affected by Na+ and Ca2+ dosing at the PACl of 20mg/L.Researchers were more concerned about the inputs and outputs of coagulation, while few researches has focused on the temporal evolution of flocs characteristics in the coagulation process. In our study, a non-intrusive optical sampling technique was applied to capture digital images of particles from the moment of coagulant addition, which were then analyzed to form particle size distributions, geometrical properties, and calculations of the fractal dimension. Then a link between the floc morphology and membrane fouling was established. We could control membrane fouling by changing the floc structure and properties during the coagulation process. The results showed that large size of flocs with low fractal dimension were formed on the conditions of neutral and alkaline water solution and existence of Na+ and Ca2+ dosing at the lower dosage of PACl. These optimization measures could effectively reduce membrane fouling. Besides, the flux of ultrafiltration membrane was positively correlated with the average particle size of flocs and negatively correlated with the fractal dimension of flocs. Additionally, the correlationship between flocs fractal dimension of ultrafiltration membrane flux was significantly stronger than that of flocs average size. The cake-layer formed on the surface was more loose and porosity with the large particle size and low fractal dimension of flocs, thereby membrane fouling was reduced.Finally, for further remitting the membrane fouling additional coagulant dosing after flocs breakage process was put forward. The results indicated that average particle size of flocs was larger, the proportion of small floc was less and the fractal dimension of flocs was significantly reduced by additional coagulant dosing after flocs breakage process. Flocs formed with additional PAM were able to more remarkably alleviate membrane fouling than that of additional PACl. |
PDF Full Text Request