Study On Osmotic Cleaning Process Of Reverse Osmosis Membrane In Municipal Wastewater Reclamation

Reverse osmosis（RO）technology is widely used due to its superior capabilities in desalination and decontamination,and plays an important role in seawater desalination and reclamation of municipal wastewater.However,the contamination of the RO membrane is a key factor in limiting the efficiency of RO treatment and the life-time of RO facilities.The commonly used physical and chemical cleaning methods have some limitations,such as low efficiency in contamination removal,irreversible damage to membrane materials and secondary contamination.The paper investigates the performance of a new cleaning technology,i.e.osmotic cleaning,in reducing the contamination on RO membrane applied in municipal wastewater reclamation.This work focuses on the effects of key parameters,such as cleaning fluid concentration,cleaning fluid flow rate and cleaning time on the performance of osmotic cleaning approach.The main findings of this paper are as follows.（1）Pressure and temperature have a significant effects on the reverse osmosis membrane flux during filtration.In addition,the results of the tandem resistance model calculations show that the inherent resistance of the membrane accounts for approximately 80%of resistance in the filtration process.The concentration polarization resistance is the main reason resulting in the decline of membrane flux.With the gradual formation of the filter cake layer on the membrane surface membrane contamination resistance accounted for an additional increase.（2）The results of the optimization of the osmotic cleaning process show that the use of the draw solution of 16%Na₂SO₄for 10 min with a membrane surface flow rate of 0.010 m/s could restore more than 95%of the initial flux for contaminated RO membranes with 80%flux reduction.（3）The microscopic morphological characteristics of the reverse osmosis membrane show that calcium scaling was the main fouling on membrane surface.Osmotic cleaning can effectively remove calcium scaling and recover the surface roughness of the membrane.（4）The research on the osmotic cleaning process found that the osmotic flux remained at a high level and decreased rapidly in the early stage of cleaning,indicating that osmotic cleaning was efficient and fast in removing the concentration polarization resistance.In addition,the osmotic cleaning efficiency showed an accelerated upward trend with the increase of the total amount of osmotic water.