Cleaning efficiency of the gas-forward osmotic backwashing in the reverse-osmosis processes for high-salinity wastewater reuse

摘要

This study aimed to explore the possibility of a new cleaning technique for which air flushing and forward osmotic backwashing (FOB), from among the maintenance-cleaning techniques and the reverse-osmosis (RO) processes, were combined for high-salinity wastewater reuse. Therefore, this study analyzed the cleaning efficiency in the effluent organic matter (EfOM), which is the major source of fouling for the RO membranes in terms of wastewater reuse. When non-dissolved gas and FOB are simultaneously injected into the RO membrane at a 10 % flux decline rate (FDR), the injected gas reduced the cleaning efficiency by interrupting the FOB. Although the nitrogen gas (N-2) and air did not generate bubbles via the low solubility in the FOB for which a gas-dissolved NaCl solution was used, the carbon dioxide (CO2) generated bubbles by high-solubility showed a high cleaning efficiency. Although the pH was lowered when the CO2 was dissolved, only a slight effect occurred in the organic-fouling cleaning; in this case, the physical effects increased the cleaning efficiency. The experiment also comprises the cleaning efficiency according to the dissolved pressure of the CO2, and as a result, the bubble volumes was increased grew by the dissolved pressure, but the cleaning efficiency was reduced through the FOB interruption. In particular, the highest cleaning efficiency was observed at the dissolved pressure of 200 kPa because the gas/liquid ratio became 1:1.