Salt rejection and water flux through a tubular pervaporative polymer membrane designed for irrigation applications

The performance of a hydrophilic polyester tubular pervaporative membrane in treating high-salinity water for irrigation was investigated. The membrane was filled with contaminated water and placed in air, soil or sand media. When this occurs water diffuses through the tube, trapping salts within the tube. Sorption and permeation tests and scanning electron microscopy (SEM) were used to assess salt rejection and permeate flux through the tubular membrane when surrounded by deionized water, air, top soil or silver sand. Mean water uptake by the membrane was 0.5Lm(-2) at room temperature and the water diffusion coefficient was 3.8x10(-4)cm(2)s(-1). The permeate flux across the membrane was 7.9x10(-3)L(m(-2)h(-1)) in sand and 5.6x10(-2) in air. The rejection of sodium chloride by the tubular membrane in sand was 99.8% or above under all tested conditions. However, when the tube was filled with sodium chloride solution and placed in deionized water, salt was observed to permeate the membrane. SEM images confirmed that variable amounts of sodium chloride crystals were retained inside the membrane walls. These results support the potential application of such a tubular pervaporative membrane for irrigation applications using saline waters; however there may be reduced salt rejection under waterlogged soil conditions.