Ultrafiltration fouling control Demineralized water backwashing Sheng Li Sanitary Engineering, Delft University of Technology The Netherlands 2017年4月12日星期三

Content Introduction Hypotheses Results Conclusion 2017年4月12日星期三

Demi water is better than UF permeate for backwashing Why is demineralized water better? No pre-treatment! No in-line coagulation! 2017年4月12日星期三

Difference between UF permeate and demineralized water for backwashing Divalent ions Monovalent ions Organic matter 2017年4月12日星期三

Hypotheses of NOM fouling Ca-bridging effect and/or Ca complexation Charge screening effect (DLVO theory) NOM molecule adsorption 2017年4月12日星期三

Ca-bridging effect (filtration) 2017年4月12日星期三

Ca-bridging effect (Backwash with permeate) 2017年4月12日星期三

Ca-bridging effect (Backwash with demi water) 2017年4月12日星期三

Charge screening effect (filtration) 2017年4月12日星期三

Charge screening effect (Backwash with permeate) 2017年4月12日星期三

Charge screening effect (Backwash with demi water) 2017年4月12日星期三

Results (Impact of calcium, flux: 85 lmh) No pre-treatment! No in-line coagulation! 2017年4月12日星期三

Results (Impact of sodium, flux: 85 lmh) No pre-treatment! No in-line coagulation! 2017年4月12日星期三

Experiment set-up and Material UF set-up: “MFI-UF” (Kiwa Water Research, NL) Membrane: Capillary membrane, 0.8 UFC M5 (X-Flow), with a surface area of 0.07 m2 2017年4月12日星期三

Backwash solutions Demineralized water UF permeate UF permeate after dialysis (organic matter is isolated)

Permeate after dialysis MWCO of Dialysis bags:3.5K Da

Feed water: Schie canal water (Delft, NL) Water quality parameter Feed Ca2+ (mg/l) 101 Na+ (mg/l) 58.57 Conductivity (µs/cm) 836 Turbidity (NTU) 4.5 DOC (mg/l) 20 2017年4月12日星期三

Composition of backwash solutions Ca2+ (mg/l) Na+ DOC UF permeate 100 58.56 18.65 UF permeate after dialysis 20 8.7 17 Demineralized water <1 0.5

Impact of organic matter (flux:120 lmh) No pre-treatment! No in-line coagulation! 2017年4月12日星期三

Effect of backwash solution on membrane surface charge Two types of backwash solution were used in this study Milli Q water UF permeate 2017年4月12日星期三

Measurement set-up Wilbert van der Ven et al. 2008 Along fiber Through pore Wilbert van der Ven et al. 2008 2017年4月12日星期三

Measurement method 1 mM KCl solution was used in this study as background electrolyte solution 2017年4月12日星期三

Streaming potential of membrane Backwash with permeate Streaming potential were measured before and after 14 filtration cycles. One cycle consists of 15-minute filtration at a flux of 120 lmh and 1-minute backwash at a flux of 240 lmh 2017年4月12日星期三

Streaming potential of membrane Backwash with Milli Q water 2017年4月12日星期三

Conclusions Backwashing with demineralized water is more efficient than UF permeate on fouling control Both Ca and Na in backwash water contribute to the fouling of UF, probably by maintaining the bridge effect or decreasing the zeta potential of the membrane and the foulant Organic matter in backwash water does not influence the fouling control of the UF membranes Backwashing with pure water can maintain the negative charge of membrane 2017年4月12日星期三