Control of protein (BSA) fouling by ultrasonic irradiation during membrane distillation process

Ultrasonic irradiation was introduced into membrane distillation process and the influence of ultrasonic irradiation on protein (bovine serum albumin, BSA) fouling control was investigated. Although the initial BSA concentration did not affect permeate flux in experimental ranges, the feed concentration increasing caused permeate BSA raise due to partial wetting of the hydrophobic membrane. The ultrasonic irradiation could enhance permeate flux about 20% without modification of the hydrophobicity/hydrophilicity of BSA in feed. The higher the concentration factor was, the larger the ultrasonic enhancement of permeate flux could be. Severe permeate flux decline can be found when the salt CaCl2 was added into the BSA solution. The presence of Ca2+ would aggravate membrane fouling because the BSA molecules interacted with each other via salt bridging and formed BSA-Ca complex. The BSA aggregates scattered on membrane surface and resulted in a dense fouling layer. With ultrasonic irradiation, ultrasonic wave refreshed liquid-membrane interface continuously and alleviated the deposition of BSA aggregates. Therefore, although there were still some small foulant aggregates scattered on membrane surface, most of the membrane pores kept open and clean, the relative permeate flux can maintain about 98% and was hardly affected by concentration factor increasing.