Reversibility of PVDF membrane performance and structure caused by cold water temperature and elevated conditioning water temperature

Abstract

Thousands of dollars are wasted each year due to the impact that cold temperature has on membrane filters. There are many areas around the world that are subjected to cold climate, and the study of how cold temperature has an impact on membrane filters and whether or not that impact could be reversed is of great interest. The impact that cold temperature, warm water treatment, and treatment time would have on the performance and structure of a polyvinylidene fluoride flat sheet membrane was studied. Three modules were used and the flux was maintained 30LMH while the TMP was monitored for three month duration in the cold temperature. One module stayed in the cold temperature constantly, while every two weeks, the other two modules were treated with 23⁰C or 35⁰C water for six hours. In addition, pieces of the polyvinylidene fluoride membrane were placed in the cold temperature for the three months and treated every two weeks in the same manner for six and 24 hours, and the structural changes (pore size) that occurred were tested. The use of periodical warm water (35°C) membrane treatment could completely or almost completely recover the membrane performance and pore size structure loss caused by cold water temperature, while the use of room temperature (23±1°C) treatment recovered majority of the membrane permeability and structure loss caused by cold water temperature. Membranes periodically treated in warmer water temperature showed a better membrane performance (higher permeability) than that periodically treated at room temperature from a long-term operation of three months. The results suggest the change in polyvinylidene fluoride membrane structure caused by cold water temperature is almost completely reversible after periodical warm water treatment, and thus the use of warm water treatment and/or chemical cleanings will benefit the recovery of membrane performance and structure change caused by cold water temperature in cold regions.