부산대학교 도서관

There is growing concern over the stable availability of water resources due to global climate change, population growth, and industrialization, thus reuse of highly saline wastewater is gaining acceptance as a mean of securing water resources. Membrane based processes such as reverse osmosis (RO) and forward osmosis (FO), have been widely used to produce fresh water from wastewater. However, both RO and FO processes still suffer from theoretical performance limiting factors: limitation of water recovery for RO and energetic limitation for FO. Recently, combining the advantages of RO and FO, a novel design of osmotically-enhanced dewatering (OED) that can achieve both high energy efficiency and water recovery has been proposed. In this work, the superiority of the OED performance was demonstrated by the simulation and experimental results. OED process using a moderate draw solution which has lower osmotic pressure than the feed can theoretically achieve higher water recovery than RO at the same hydraulic pressure applied. In addition, it was observed that OED exhibited more water flux than FO because the adverse effect of internal concentration polarization (ICP) was significantly reduced. Moreover, the effects of membrane characteristics (A, B, and S) were evaluated by modeling. In treating high salinity feed water, the structure parameter (S) of the membrane has a greater effect on the water flux performance of OED than the water permeability coefficient (A).The OED performance is affected by both hydraulic and osmotic driving forces. Existing membrane characterization methods cannot effectively reflect the combined driving force. Therefore, we evaluated the effect of operating hydraulic pressure on the determination of membrane characteristics through the modified method. The modified method uses the non-linear least-square method to find membrane parameters (A, B, and S) under different hydraulic pressures. It was clearly demonstrated that the solute permeability of the membrane varies depending on operating pressures. Our experimental observations suggested that membrane parameters should be determined by the characterization method simulating actual operating conditions, particularly under the hydraulic pressure applied.To develop the OED technology into an actual implementation, it is necessary to understand the OED performance at a system-level. We systematically investigated the influences of operating conditions (i.e., flow rate fraction, driving force fraction, and normalized membrane area) on overall OED performance through module scale numerical simulation. The results showed that OED yield more water recovery as the feed flow fraction decreases, the normalized membrane area increases, and hydraulic driving force fraction increases. Moreover, it was shown that OED-RO hybrid process can produce more water with energy efficiency similar to that of one-stage RO under actual operating conditions considering the inefficiency of pump and energy recovery device (ERD).Finally, ethanol as a draw solution was investigated for the desalination of the ultra-saline wastewater. Compared with existing draw solutes, ethanol provides unique advantages including: 1) high osmotic pressure due to its low molecular weight and high solubility, and 2) easy-separation by vacuum distillation due to its high vapor pressure. The FO experimental results showed that an ethanol draw solution can exhibit water flux comparable to NH4HCO3 at equivalent osmotic pressure, but the reverse solute flux was relatively high due to its high volatility. Easy-separation of the ethanol draw solution was also verified by vacuum distillation experiments at room temperature and exergy analysis of the integrated system. Our analytical study provides useful insight for improving the feasibility of OED process. This research concludes that further research is needed to prove the potential of OED process for ultra-saline wastewater treatment through the development of membranes tailored for OED and plant verifications.