Effect of interactions between ammonium and organic fouling simulated by sodium alginate on performance of direct contact membrane distillation

Abstract

This study aims at observing the interactive effects between ammonium and sodium alginate (SA) on their rejection efficiency and organic fouling in direct contact membrane distillation (DCMD) process. Three feed solution pHs of 4, 6 and 8 as well as two feed temperatures of 35 and 50 °C were investigated without and with ammonium chloride in SA solution. The decrease in feed temperature and solution pH increased the fouling rate as the SA alone was filtered due to the protonation of the SA compound, leading to precipitate form. However, the fouling rate was reduced by increasing the feed temperature due to higher driving force through the membrane. This allowed the development of more porous cake structure than that formed at lower temperature. Rejection efficiency of total organic carbon was reduced by adding the ammonium chloride into SA solution probably due to the enhancement of membrane wetting. Nevertheless, the ammonium rejection was maintained 99 % since the fouling layer formed could act as secondary membrane. Predictions by using the classic blocking models showed that the fouling mechanisms associated with the SA were dominated by the cake formation without ammonium. Meanwhile, the internal fouling caused by the pore constriction was revealed more dominant as the ammonium was added into SA solution particularly at low solution pH.