Reduced Graphene Oxide Forward Osmosis Membranes for Lithium Brine Enrichment with Ultraviolet-Visible Spectroscopy for Monitoring.

Forward osmosis (FO) is an emerging membrane separation technology. It is different from the well-studied pressure-driven membrane separation processes. The FO process is based on water transport under an osmotic pressure difference across a semi-permeable membrane. The distinct operating conditions lead to unique technical challenges during the exploitation of FO technology. According to a comprehensive literature investigation, one of the stringent barriers is lacking of effective FO membranes. The objectives of this research were to develop high performance FO membranes, and furthermore, to systematically study the mass transport and the governing mechanisms in FO process. Thin film composite (TFC) FO membranes with a tailored support structure were developed in this study. The membranes consisted of a highly porous substrate with finger-like pore structure, which was prepared via phase inversion, and a polyamide rejection layer synthesized by interfacial polymerization. The TFC FO membranes had small structural parameters due to the thin cross-section, low tortuosity, and high porosity of the substrates. The membrane rejection layers exhibited superior separation properties (higher water permeability and excellent selectivity) relative to commercial FO membranes. Under FO testing conditions, these membranes achieved high water flux while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and reverse osmosis (RO) membranes revealed the critical importance of the substrate structure, with a straight finger-like pore structure preferred over a spongy pore structure to minimize internal concentration polarization (ICP), a unique and critical problem resulting in low water flux in the osmotically driven membrane processes. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux. The results proved that TFC membranes with a tailored porous substrate and rejection layer are promising for FO applications. In the study of polyamide rejection layer synthesis, the influence of monomer concentrations (i.e., m-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentrations) on the membrane separation properties as well as the FO performance was systematically investigated. A strong trade-off between the water permeability and salt rejection of the membranes was observed, where reducing the MPD concentration or increasing the TMC concentration may result in a higher membrane permeability but a lower salt rejection. In FO tests, membranes with poor salt rejection had severe solute reverse diffusion, which enhanced the severity of ICP. It was found that the FO water flux was governed by both the membrane water permeability and solute rejection. For a membrane with higher water permeability but lower solute rejection, the reduced membrane frictional resistance was compensated simultaneously by the more severe solute-reverse-diffusion-induced ICP. The net effect on the FO water flux depends on the competition of these two opposing mechanisms. Under conditions where solute reverse diffusion may cause severe ICP (e.g., high draw solution concentration and high water flux level), membranes need to be optimized to achieve a high salt rejection even if this is at the expense of lower water permeability. In view of the importance of the water permeability and salt permeability on FO performance, a systematic comparison study of prevailing semi-permeable FO membranes with nanofiltration (NF)-like and RO-like separation properties in terms of flux performance and fouling behavior was conducted. Due to the crucial influence of solute reverse diffusion on FO water flux, the high-rejection RO-like FO membranes generally performed better than the NF-like counterparts in sodium chloride based FO tests. On the other hand, the high permeability of NF-like FO membranes could achieve higher water flux, when proper draw solutes were used to minimize draw solute leakage. Fouling tests suggested that the NF-like TFC FO membranes tended to be more fouling resistant due to their relatively smooth membrane surface. This work further elucidated the major mechanisms that govern the FO performance. These mechanisms were summarized as a frictional resistance loss mechanism (MR), solute-reverse-diffusion-induced ICP (MICP-Js), concentration of feed solutes (concentrative ICP or MICP-feed in the active-layer-facing-draw-solution orientation) and dilution of draw solutes (dilutive ICP or MICP-draw in the active-layer-facing-feed-solution orientation). These mechanisms are related to the properties of membrane, draw and feed solutions. This work led to a set of systematic criteria for the selection of FO membranes, draw solution and optimization of other operating conditions, of which the practicability was demonstrated in potential FO applications.

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

In order to ensure long-term sustainability of the reservoir, the gas industry in Qatar is faced with the challenge of reducing the volume of produced and process water (PPW) sent to disposal wells by 50% [1-3]. Recently, Qatargas initiated a project to recycle process water and thus, reduce disposal volumes using commercial advanced water treatment technologies [4]. One emerging technology, “osmotic concentration” (OC) has been identified that offers a low-energy alternative to conventional thermal or membrane volume reduction methods. Osmotic concentration is a membrane filtration process that mimics first step in a forward osmosis (FO) system. It requires a high salinity draw solution (DS) which passes on one side of a semi-permeable FO membrane while the feed passes on the other side. Water from the feed is drawn through the membrane, via natural osmosis, reducing the feed volume and increasing the volume of the draw solution. This paper summarizes the results of bench-scale volume reduction tests wit...

The research aims to use a new technology for industrial water concentrating that contains poisonous metals and recovery quantities from pure water. Therefore, the technology investigated is the forward osmosis process (FO). It is a new process that use membranes available commercial and this process distinguishes by its low cost compared to other process. Sodium chloride (NaCl) was used as draw solution to extract water from poisonous metals solution. The driving force in the FO process is provided by a different in osmotic pressure (concentration) across the membrane between the draw and poisonous metals solution sides. Experimental work was divided into three parts. The first part includes operating the forward osmosis process using TFC membrane as flat sheet for NaCl. The operating parameters studied were: draw solutions concentration (10 – 95 g/l), draw solution flow rate (12-36 I/h), temperature of draw solution (30 and 40°C), feed solution concentration (10 -210 mg/l), feed solution flow rate (10 -50 l/h), temperature of feed solution (30 and 40°C) and Pressure (0.4 bar). The second part includes operating the forward osmosis process using CTA membrane as flat sheet for NaCl. The operating parameters studied were: draw solution concentration (15 – 95 g/l), feed solution concentration (10-210 mg/l). Constant temperature was maintained at 30°C. The last part includes operating the reverse osmosis process using TFC membrane as spiral wound module in order to separate NaCl salt from draw solution and obtain on pure water so as to usefully in different uses and also obtain on solution of NaCl concentrate which was recirculated to forward osmosis process. It is then used as draw solution. The operating parameter studied was: feed solution flow rate (15-55 l/h). The experimental results show that the water flux increases with increasing draw solution concentration, feed solution flow rate, temperature of draw solution and decreases with increasing feed solution concentration, draw solution flow rate and temperature of feed solution. The experiments also show that CTA membrane gives higher water flux than TFC membrane for forward osmosis operation.

Evaluation of forward osmosis as a pretreatment process for multi stage flash seawater desalination

Pressure retarded osmosis for power generation and seawater desalination: Performance analysis

11 - Reverse osmosis and forward osmosis in integrated systems

Water is crucial for enhancing the yield of agricultural land to meet the growing demand. Forward osmosis (FO) is a developing technology that utilizes the natural osmotic gradient of solutions. In this study, fertilizer drawn FO setup was considered by using potassium chloride (KCl) as the draw solution (DS) for treating textile wastewater as the feed solution (FS). This study investigated the effects of FS temperature, pH, and FS and DS concentrations. The performance investigation involved the study in terms of water flux, reverse salt flux, and specific reverse salt flux. DS and FS properties, osmotic potential, and temperature played a vital role in the performance. At 30°C FS temperature, the highest water flux (5.5 LMH) was observed. Reverse salt flux increased due to the increase in solute diffusivity. The highest value of water flux was obtained at a DS of 1.150 M and FS of 1000 mg/L. The permeation of water improved due to the difference in DS and FS concentrations at pH values above 7. The results of this study suggest that KCl as DS has a higher potential for the treatment of textile wastewater at a temperature of 30°C. Additionally, the functional groups attached to the FO membrane were identified through Fourier-transform infrared (FTIR) spectroscopic study. PRACTITIONER POINTS: Treatment of textile wastewater with the use of fertilizer draw solution (KCl) by forward osmosis process as carried out. The performance was assessed in terms of water flux, reverse salt flux, and specific reverse salt flux. The effects of feed and fertilizer draw solution concentrations; pH and temperature were evaluated on the performance of FO process.

Nowadays, inadequate access to clean water has become one of the most pervasive problems due to the rapidly expanding global population and thus the exponentially growing demand in water and food supply, industry and social life (Shannon et al. 2008). Problems with water have called out for a large number of researchers to pay more attention to water sustainability and put forth effort to explore more robust technologies for wastewater treatment and desalination in addition to improving the efficiency of the current water production and distribution systems (Sikdar 2011). Among many potential solutions, membrane processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) have found their overwhelming applications in water industry. However, these technologies are either chemically or energetically intensive, thus are castigated for high cost due to substantial chemical and energy consumptions as well as high fouling propensity which requires frequent backwash or cleaning. Forward osmosis (FO), utilizing the natural phenomenon of osmosis, is an emerging membrane process driven by the osmotic pressure gradient created across a semipermeable membrane by two flowing streams of varying concentration (i.e., the draw solution and the feed). Hence, the energy required to transport water across the membrane is almost negligible. Far from being so, FO creates much less problem of fouling and cleaning (Mi and Elimelech 2010). By virtue of these unique features, FO distinguishes itself from other membrane processes for sustainable supply of clean water. An example of the FO unit for wastewater treatment is shown in Fig. 1. In the FO process as illustrated, the draw solution (an aqueous solution of magnetic nanoparticles covered with thermosensitive polymer) (Ling et al. 2011) and the feed (wastewater) partitioned by the membrane flow co-currently through corresponding channels. The draw solution, having a higher osmotic pressure than the feed, draws water from the feed and flows back to the reservoir. As it continuously takes clean water from the feed, the draw solution in the reservoir becomes diluted. A regeneration process is connected to the reservoir to re-concentrate the draw solution as well as to produce clean water. A portion of the diluted draw solution is pre-heated with the aid of solar panel or waste heat and traverses a magnetic field. Upon heating, the magnetic nanoparticles covered with thermosensitive polymers change their surface property from hydrophilic to hydrophobic and are easily seized by the magnetic field or other filtration processes. As a result, clean water freely passes through and is collected as the product. The trapped magnetic nanoparticles are then sent back to the reservoir to replenish the draw solution. The 1st key component of the FO unit is the membrane material which should be semipermeable, i.e., allowing water to permeate through while blocking all the solutes in the draw and feed solutions. A tremendous amount of research has been conducted on the molecular design of new membrane materials with superior FO performance and great progress has been achieved in the past 5 years. To date, several types of FO membranes have been reported such as (1) flat sheet membranes made of cellulose esters (Wang et al. 2010a; Zhang et al. 2010); (2) J. Su M. M. Ling T.-S. Chung (&) Department of Chemical & Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore e-mail: chencts@nus.edu.sg

The research aims to apply the novel forward osmosis (FO) process to recover pure waterfrom contaminated water. Phenol was used as organic substance in the feed solution, while sodiumchloride salt was used as draw solution. Membranes used in the FO process is the cellulosetriacetate (CTA) and polyamide (thin film composite (TFC)) membrane. Reverse osmosis processwas used to treatment the draw solution, the exterior from the forward osmosis process. In the FOprocess the active layer of the membrane faces the feed solution and the porous support layer facesthe draw solution and this will show the effect of dilutive internal concentration polarization andconcentrative external concentration polarization.In the FO process was a run-time for five hours, and the concentration of phenol 100 and1000 mg/l, and for the NaCl the concentration was 10000 and 30000 mg/l. It was found thatrecovery percent increases with increasing time, while water flux through membrane decreases withincreasing time. Also, it was found that recovery and water flux increases with increasing drawsolution concentration, on the contrary, water flux and the percentage of recovery decreases withincreasing the concentration of phenol (feed solution). Increase in draw solute (NaCl) concentrationhas more effect on the water flux in FO process compared with increase in the concentration ofphenol. Outlet phenol concentration increases with time, while the outlet salt concentrationdecreases with increasing the time. The results showed that the cellulose triacetate membrane gavethe highest recovery ratio from the thin film composite membrane. The highest recovery wasreached in five hours is 51.33%, while using CTA membrane recovery rate increase, by 23%compared with TFC membrane. The value of the resistance to solute diffusion within the membraneporous support layer is 36.83 h/m. Reverse osmosis is perfect method for removal of dissolved saltsfrom water, thus its suitable process for reducing the content of NaCl in draw solution; therefore thesodium chloride rejection percentage was 91.6 – 96 % for polyamide membrane (TFC). Within twohours of work of the reverse osmosis system the recovery percentage of pure water is 58%.

Predicting power density of pressure retarded osmosis (PRO) membranes using a new characterization method based on a single PRO test

Effects of feed and draw solution temperature on the performance of Aquaporin HFFO.6 membrane in forward osmosis

This study aimed to concentrate and recover resources from municipal wastewater with a novel forward osmosis (FO) system. The FO system used synthetic seawater as the draw solution (DS) to extract water from the feed solution (FS) (synthetic raw municipal wastewater). Because ammonium passed through the FO membrane from the FS to the DS, we cultivated an algal strain (Chlorella vulgaris) in the DS to remove and recover ammonium. For three consecutive FO cycles, the algal FO system removed 35.4% of the ammonium from the DS, increased the concentrations of COD and in the FS by 43.0%, and achieved a water flux of 11.59±0.49Lm-2 hr-1 . Throughout the FO cycles, the algal biomass concentration of the DS stayed at 606±29mgCOD/L due to simultaneous algal growth and DS dilution. This FO process may be feasible to implement for full-scale applications to concentrate wastewater and recover resources. PRACTITIONER POINTS: A novel forward osmosis (FO) system with an algal draw solution (DS) concentrated municipal wastewater and recovered resources (ammonium). Ammonium but not organic matter or phosphate diffused across the FO membrane from the feed solution (FS) to the DS. The algal FO system increased COD/phosphate concentration in the FS by 43.0% and removed 35.4% of ammonium from the DS. The water fluxes in the algal FO system and the control were 11.59 and 12.02Lm-2 hr-1 , respectively. The novel algal FO process has the potential to improve full-scale efficiency by concentrating municipal wastewater and recovering nutrients.

A novel analysis of reverse draw and feed solute fluxes in forward osmosis membrane process

A dendrimer-based forward osmosis (FO) draw solute, poly(amidoamine) terminated with sodium carboxylate groups (PAMAM-COONa), was investigated for seawater desalination. Compared with existing FO draw solutes, PAMAM-COONa offers unique advantages: (1) Its aqueous solution can generate high osmotic pressure because of the large number of −COONa groups. (2) The low viscosity of PAMAM-COONa solution can reduce internal concentration polarization (ICP), which adversely affects FO water flux. (3) PAMAM-COONa has a relatively large molecular size, favoring reduced reverse solute flux. In our FO tests using 2.5-generation (2.5G) PAMAM-COONa draw solution (33.3 wt %) and seawater (Singapore coast) feed solution, a relatively high water flux of 9 L m–2 h–1 was achieved with commercial HTI FO membrane. In addition, a considerably reduced reverse solute flux of PAMAM-COONa compared to that of NaCl was attained. After FO testing, the diluted PAMAM-COONa solution was reconcentrated to its original osmotic pressure wit...