역삼투법(RO) 해수담수화 전처리 공정으로 모래여과와 UF 막 공정의 비교

Abstract

Recently, RO desalination for seawater application is rapidly becoming the technology of choice in a world plagued with increasingly limited water resources. RO membranes are susceptible to a wide variety of organic and inorganic foulants. To mitigate membrane fouling, RO systems require sufficient, and reliable pretreatment to produce superior quality RO feedwater that will ensure stable, and long-term performance of RO membrane elements; regardless of the turbidity variations of the raw water. Ineffective or unreliable pretreatment can lead to problems with the RO system including high rates of membrane fouling, high frequency of membrane cleanings, lower recovery rates, high operating pressure, poor product quality, and reduced membrane life; all having a direct impact on plant productivity and operational costs. Accordingly, pretreatment optimization is the key factor for a successful RO desalination system. Therefore, this research is focused on comparison of sand filtration and UF process as a pretreatment of seawater desalination by reverse osmosis. The experiment is conducted by different coagulant dose, flocculation mixing intensity, and flocculation mixing time, and then, the turbidity, flux, UV254, SDI, and particle counts are evaluated. The result of sand-filtration experiment shows similar efficiencies in turbidity and particle removal regardless of coagulant dose, mixing intensity, and mixing time. Also it shows the increase of UV254 removal as the coagulant dose is increased. With the SDI15 average of 6.00, however, it can be concluded that the sand-filtration is not appropriate for obtaining proper pre-treatment water quality in RO process. In the UF membrane experiment, the permeate flux is decreased as the coagulant dose is increased and, although the amount is not significant, the flux tends to decrease when mixing intensity is increased. But, since there is not much difference in flux change as the mixing time is changed, and also, the SDI15 average becomes 1.99, the UF membrane is a proper method in obtaining pre-treatment water quality of RO process. Finally, the experiment of combining the sand-filtration and UF membrane processes is conducted and it shows the decrease of permeate flux.