Abstract
Forward osmosis (FO) is an emerging membrane technology that uses naturally occurring osmotic pressure as the main driving force. As an emerging membrane technology, FO has attracted much interest in the scientific community in the last decade. Due to its unique characteristics—use of draw solutes, no hydraulic pressure, loose fouling, etc— FO can serve as an alternative to other pressure-driven membrane processes such as ultrafiltration (UF), nanofiltration (NF) or reverse osmosis (RO); or coupled with the pressure-driven membrane processes as the pre-treatment. Although FO has different mode of operation, it still is a membrane process, and membranes play a significant role in the FO process; hence, membrane design must be carefully considered in order to enhance the overall FO performance. Further, membrane fouling, and its control method should also be carefully determined. Lastly, it is of utmost importance that hybrid process—which can allow FO to be operated as a stand-alone process—is designed and optimized.The overall volume of wastewater and membrane life are important factors that influence the overall operating cost in wastewater treatment process. In order to minimize the operating cost, there have been many attempts to dewater the wastewater. However, due to the high concentration of the wastewater—especially after dewatering—the membrane life was expected to be shorter, which makes the dewatering process not as effective due to added cost for the membrane. Thin film nanocomposite (TFN) outer selective hollow fiber polyamide forward osmosis (OSHF FO-PA) membranes incorporated with negatively charged silver nanoparticles (NPs) were fabricated for wastewater dewatering. The performances of five silver loading concentrations, namely 0% (pristine), 0.0002%, 0.0005%, 0.0010%, and 0.0015%, were compared. Among the four non-zero loading concentrations, 0.0010% showed the best performance in terms of flux and RSF. The flux of 0.0015% was the highest, but the RSF was significantly high, making the membrane with silver loading of 0.0010% a better membrane. The pristine membrane had a better flux performance than the silver-loaded membranes; however, the silver-loaded membranes lasted longer (over 30 days) and had a higher flux recovery after salt cleaning. The pristine membrane also concentrated the feed solution 4 h faster than the silver-loaded membranes (68 h); however, the performance was not stable, and the water flux continuously decreased. In contrast, the performance of the silver-load membranes was more stable and plateaued between 2 L·m-2·h-1 and 3 L·m-2·h-1. Due to the negatively charged silver NPs, the TFN OSHF FO membranes showed a stronger fouling resistance and stable performance, and thus a longer life expectancy. Therefore, the use of TFN OSHF FO membranes with embedded silver NPs can be an alternative strategy for wastewater treatment and dewatering.
The discharge of untreated effluent from aquaculture farms containing excessive pharmaceutical chemicals has caused several negative effects on aquatic ecosystems. Therefore, we used a hybrid system based on two emerging technologies, namely FO and nanobubbles (NBs), as an energy-efficient, sustainable, and effective alternative to conventional processes for the treatment and reuse of aquaculture wastewater. The combination of NB technology with FO served as a single-step treatment process for the removal of aquaculture pharmaceutical contaminants, and thus has the potential to prevent serious environmental degradation. In the hybrid system, the polyamide FO membrane retained organic matter, dissolved solids, and pharmaceutical chemical residues from aquaculture effluents with high efficiency (99%), whereas NBs functioned as a physical membrane-cleaning agent that enhanced the performance and longevity of the FO membrane. In addition to membrane cleaning, ozone NBs could break down up to 30% of the oxytetracycline antibiotic in the water owing to their unique physicochemical properties, such as strong negative surface charge and generation of free radicals. We believe that this study will offer an innovative solution for aquaculture wastewater treatment and will play a vital role in the sustainable development of the fisheries industry.
Forward osmosis is an energy efficient process that is capable of recovering high-quality water from secondary wastewater treatment. However, regeneration of the draw solution (DS) is a problem that needs to be addressed. Herein, we developed and optimized a pressure assisted-volume retarded osmosis (PA-VRO) process, which utilizes the naturally occurring pressure with the aid of a small inlet pressure (< 1 bar). PA-VRO process was optimized through single FO and ultrafiltration (UF) process with Poly (sodium-4-styrenesulfonate, PSS) with concentrations of 10, 20, 30, 40 and 50 g/L as the DS and the feed solution (FS), respectively. PA-VRO process uses naturally occurring pressure with the aid of small inlet pressure (less than 1 bar) from the FS, thereby minimizing the energy consumption and maximizing the permeate production while being able to remove micropollutants. It was found that the rejection in single UF (86.4%) was lower than the lowest rejection in PA-VRO process (94.8%). Nonetheless, this was due to difference in sampling time, and rejection values both from UF and PA-VRO were in well agreement with the logarithmic relationship that was determined through the 6-day pretreatment of PSS using PA-VRO. After the 6-day pretreatment, real wastewater from Ngong Ping Sewage Treatment Works was used as the FS for 2 days to determine the applicability of PA-VRO for removing perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). During the 2-day operation, the rejection for PSS, PFOA and PFOS were all over 90%, with PSS rejection greater than 99% for both days. In addition, there were no traceable amount of PFOA and PFOS in the DS, hence the detected concentration of PFOA and PFOS may be the result of residuals from the equipment. Therefore, well-optimized PA-VRO process can be applied for potable water production.
| Date of Award | 2 Sept 2021 |
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| Original language | English |
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| Supervisor | Kyoung Jin Alicia AN (Supervisor) |