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UBC Theses and Dissertations

Chemically enhanced backwash as the only ultrafiltration fouling control approach in seawater applications Beswick, Michael


The use of ultrafiltration (UF) membranes as a pre-treatment technology for seawater applications, such as desalination and water production for deep sea oil extraction, has expanded in recent years. Controlling fouling during filtration remains a crucial operational challenge, particularly in applications with equipment footprint constraints. The present study sought to investigate a simplified fouling control approach where chemically enhanced backwash (CEB) was the only technique utilized. Short-term benchmarking trials were performed to evaluate a wide range of operating conditions. These included: CEB duration, CEB frequency, CEB make up solution, and sodium hypochlorite (NaClO) concentration. Long-term trials were then completed to determine the viability of this approach, and provide operational insight for future applications. NaClO concentrations as low as 8 ppm were effective in achieving sustainable fouling rates in low temperature UF operation with CEB as the only fouling control approach. Extended CEBs using 150 ppm NaClO solutions were effective at restoring lost permeability, though may not be required for periods of 6 months or more. Both outside-in, and inside-out membrane configurations were evaluated, with outside-in observed to have a lower fouling rate. No difference was observed when comparing UF permeate and nanofiltration concentrate as CEB make up solutions. A new measure, termed ‘cleaning effort’ (i.e. the product of CEB duration and NaClO concentration divided by CEB frequency), was proposed to compare fouling control efficiency for different CEB operating conditions. Fouling rate followed an exponential decay relationship with respect to cleaning effort. Accumulation of active biomass on membrane fibers was not observed after long-term trials. Residual chlorine in the CEB reject stream was observed to be above regulatory limits, and decayed slowly.

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