Seawater ultrafiltration fouling control: Backwashing with demineralized water/SWRO permeate

• Published in: Separation and purification technology 2012-09, Vol.98, p.327-336
• Main Authors: Li, Sheng, Heijman, S.G.J., Verberk, J.Q.J.C., Amy, Gary L., van Dijk, J.C.
• Format: Article
• Language: English
• Subjects: Applied sciences; Backwash; Backwashing; calcium; Cations; Chemical engineering; Continental surface waters; Demineralized water; Demineralizing; Desalination; Drinking water and swimming-pool water. Desalination; Exact sciences and technology; Fouling; long term experiments; Membrane separation (reverse osmosis, dialysis...); Membranes; Natural water pollution; Pollution; salinity; screening; Sea water; seawater; Seawaters, estuaries; sodium chloride; surface water; Ultrafiltration; Water treatment and pollution
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2012.07.002

► Demineralized water backwashing substantially improve seawater UF fouling control. ► Monovalent cations in backwash water reduce fouling control efficiency of backwash. ► In spring, the membrane showed more fouling probably due to the algae bloom. In this study, the effect of demineralized water backwashing on fouling control of seawater ultrafiltration was investigated. Seawater from Scheveningen beach in The Hague and a desalination plant of Evides Company at Zeeland in the Netherlands was used as feed water, while demineralized water and UF permeate were used as backwash water for a fouling control efficiency comparison under different fluxes and backwash durations. Furthermore, demineralized waters with 5 or 50mmol/l NaCl were applied for backwashing as well, to check the influence of monovalent cations on UF fouling control. Additionally, SWRO permeate was used for backwashes in long-term experiments to check the possibility of it replacing demineralized water. Results show that seawater UF fouling control is substantially improved by demineralized water backwashing. However, due to the high salinity of seawater, more water was required to dilute the cation concentration and limit the dispersion effect near the membrane surface than was needed for surface water. A 2-min demineralized water backwash showed better fouling control efficiency than a 1-min backwash. Furthermore, the presence of monovalent cations in the backwash water deteriorated the fouling control efficiency of the backwash, indicating the existence of a charge screening effect. The demineralized water with 5 and 50mmol/l NaCl both showed a similar fouling control efficiency which is better than the UF permeate backwash. The calcium ions in UF permeate probably deteriorates the fouling control efficiency by maintaining a Ca-bridging effect between the membranes and NOM. SWRO permeate backwashing successfully controls membrane fouling as well.