Application of Osmotic Concentration for Volume Reduction of Produced/Process Water from Gas-Field Operations

Forward osmosis (FO) is a membrane process that occurs when solutions of different osmotic pressures are separated by a membrane which is selectively permeable to water. It is a process that drives water permeation across the membrane spontaneously even in the absence of hydraulic pressure difference across the membrane. FO has attracted lots of attention over the last decade and has been explored as a potential alternative to desalination, wastewater treatment and liquid food processing. Significant progress has been made in the development of high-performance FO membranes with high water flux and low reverse solute flux, particularly cellulosic membranes, thin-film composite (TFC) membranes and polyelectrolyte-based membranes. Yet, a few major challenges continue to hamper the widespread implementation of the process in the industry, mainly internal concentration polarization, reverse solute diffusion, membrane fouling, mechanical durability and draw solution regeneration. Most of these challenges are associated with membrane characteristics, which has significantly limited the efficiency of the FO process. To address these challenges, firstly, hollow fiber ultrafiltration membranes were fabricated from polyethersulfone (PES) via a non-solvent induced phase separation (NIPS) process and were used as substrates to prepare inner-selective TFC hollow fiber membranes via an interfacial polymerization (IP) process. The effect of the hollow fiber substrate fabrication conditions on the properties of the substrate and TFC membranes were briefly investigated. The FO performance of the TFC membranes were characterized by using 0.5 M NaCl and DI water as the draw and feed solutions. when the membrane was operated in the active layer-facing-feed solution (AL-FS) and active layer-facing-draw solution (AL-DS) configurations, water flux as high as 41.2 L/m2/h and 74.9 L/m2/h were achieved, while specific reverse solute flux were 0.11 g/L and 0.10 g/L, respectively. Subsequently, a novel double-skinned hollow fiber TFC FO membrane has been successfully fabricated. The FO membrane consisted of a one-step dual-layer substrate and a thin inner selective layer formed via the IP process. The substrate comprises a dense ultrafiltration (UF) outer layer and a relatively porous UF inner layer, both of which were constructed from PES by using a dual-layer co-extrusion technique. The fouling resistance of the double-skinned hollow fiber membrane was evaluated under various testing conditions to verify the viability of double-skinned hollow fiber membranes as a solution to membrane fouling in the FO process. Compared to the commercial and reported double-skinned FO membranes, the FO membrane developed in this thesis exhibited a higher permeate flux with humic acid solution as a feed solution. Furthermore, the double-skinned FO membrane was applied in concentrating activated sludge using 0.5 M NaCl as a draw solution. A permeate flux at 5.4 L/m2/h was achieved after 5-hour operation, which was higher than, or comparable to, those of the reported FO membranes. Membrane autopsies and foulant analysis suggested that the dense UF skin layer helped to reject larger-sized organic foulants (> 300 Da), which shed light on the importance of fabrication features and promising application of the double-skinned hollow fiber TFC FO membrane in sludge concentration. On the other hand, a series of characterization revealed that TFC hollow fiber membranes may experience significant compaction during the FO process despite the lack of applied pressure. Three TFC hollow fiber membranes were fabricated with varied water permeability to study the effect of the osmotic pressure on the TFC membranes. The TFC membranes were continuously tested in FO experiments for 24 h using DI water as feed and varied concentration of NaCl solutions as draw solutions, and their performances were evaluated again using fresh feed solutions. At the end of the FO experiments, all TFC membranes experienced water and salt flux decline to different extents. Visible changes in the cross-sectional morphology and surface topography of the TFC membranes were observed. These observations suggested that the occurrence of membrane compaction is strongly associated with the characteristics of the hollow fiber substrates that were used to prepare the TFC membranes and may be attributed to “negative pressure” build-up within the support layer of the TFC membranes.

Produced and process water (PPW) associated with gas production are often characterized by low total dissolved solids (TDS) and moderate organic content. The oil and gas (O&G) industry in Qatar currently practices disposal of PPW via deep well injection. To ensure long-term sustainability of the reservoir, Qatar operators aim to reduce the PPW disposal quantity by 50%. Recently, Qatargas had initiated a project to recycle process water and thus, reduce disposal volumes, by using commercial advanced water treatment technologies. For future projects/developments, the authors of this paper have proposed and evaluated, through funding by the Qatar National Research Fund (QNRF), an adaptation of forward osmosis (FO) membrane process for PPW concentration, which can be a cost-efficient alternative to achieve 50% volume reduction of PPW. In the first step of conventional FO, a draw solution (DS) of high osmotic pressure is used as driving force to "pull-in" fresh water from the feed through a membrane into the DS. In the second step, and requiring significant energy, water is recovered from the regenerated DS by various methods depending on the DS used. In this project, brine from thermal desalination plant was used as DS and PPW as feed. Due to the salinity difference between the DS and the PPW, natural osmosis resulted in water permeating from the PPW into the DS, reducing the volume of PPW. Instead of recovering permeated water from the DS, the diluted DS can be directly discharged into the Arabian Gulf bringing an additional benefit by discharging lower salinity brine to the aquatic environment. Commercial flat sheet membranes and hollow fiber (HF) membranes provided by Singapore Membrane Technology Centre have been tested through bench-scale experiments and the impact of various operating parameters such as DS concentration and temperature was investigated. Results indicated that FO can successfully treat the PPW to achieve the target volume reduction of 50%. The average flux for the HF membranes with pretreated feed was 17 L/m2-h (LMH) using 1M NaCl as DS. Organics passage from the feed to the DS was below detection limits which mitigates the potential concern of organics leaching into the Arabian Gulf. Appropriate pretreatment of the PPW is required to minimize membrane fouling. Results showed a flux decline of approximately 10% over 5 hours when the PPW was used without pretreatment. The fouling was attributed to the organics present in the PPW. Different pretreatment options were evaluated to reduce membrane fouling including: ceramic membranes, activated carbon; and an organosilica adsorbent. To validate the project concept, long-term experiments were conducted mimicking field conditions. Overall, the results indicated FO is cost-efficient in reducing PPW injection volume and pilot testing is recommended to further demonstrate treatment feasibility of the process.

Rejection of nutrients contained in an anaerobic digestion effluent using a forward osmosis membrane

Reverse solute flux(RSF) is a big challenge of forward osmosis(FO) technology. This experiment was based on the study of the performance of apple juice concentration by FO technology and the solute diffusion law of functional draw solution(sodium acetate, sodium bicarbonate and sodiumcitrate). Firstly, the basic properties of FO system were studied, including water flux, RSF and rejection rate, by varying the concentration of NaCl draw solution, influent flow rate and membrane operation mode. The concentration ability of deionized water and apple juice and solute diffusion law were analyzed. To achieve the purpose of converting the RSF into advantages, the effect of different functional draw solutions on apple juice concentration and RSF were compared. The results showed that the concentration efficiency and RSF were affected by the concentration of draw solution and membrane operation mode. The membrane mode of pressure retarded osmosis(PRO) led to the higher RSF and the concentration degree of apple juice than the FO mode. In the PRO mode, the RSF reach to 87.34±6.32 g·m−2·h−1 with the NaCl draw solution concentration of 5 mol·L−1. The ability of concentrating apple juice by different concentration of functional draw solution was various. The order of water extraction capacity from high to low was sodium bicarbonate, sodium chloride, sodium acetate, sodium citrate and the order of RSF from high to low was sodium citrate, sodium bicarbonate, sodium chloride, sodium citrate. The RSF was 29.61±2.19 g·m−2·h−1 with 2 mol·L−1 NaCl draw solution, which was only half of the same concentration of NaCl draw solution. Compared with traditional NaCl draw solution, sodium citrate draw solution could effectively control RSF.

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

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.

Assessing the major factors affecting the performances of forward osmosis and its implications on the desalination process

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.

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.

Influence of the process parameters on hollow fiber-forward osmosis membrane performances

Forward osmosis (FO) relying on the osmotic pressure difference across semi-permeable membrane draws permeate by the effect of saline draw solution (DS) turning diluted and leaving the feed solution (FS) concentrated. However, the energy intensive step of DS recovery makes FO a challenging process. The energy benefit of FO emerges when recovery step is obviated and FO is applied as an osmotic concentration (OC) process. OC implementations for volume reduction are still at bench-scale and the investigation at larger scale is among the breakthroughs. In this paper, the performance of hollow fiber (HF) membrane in pilot-scale OC process for reducing volume of feed was investigated. The impact of operating conditions such as flowrates and temperature was evaluated. FS and DS flowrates of 1.35 and 0.35 L.min-1 respectively are optimum conditions with 75% feed recovery and 1.90 LMH water flux. Reverse solute flux increased at higher flowrates. Results indicated the role of high DS flowrate and temperature in improving the performance. DS flowrate of 0.35 L.min-1 at constant FS flow of 1.10 L.min-1 and 27 °C was most suitable for achieving 84.5% feed recovery and 1.82 LMH water flux. Above all, the long-term performance of OC pilot-plant was demonstrated through 48 h of continuous operation where stable flux trend at an average water flux of 1.66 LMH was successfully achieved. Lastly, the permeability coefficients of HF membrane were enhanced at higher temperature.

Concentration polarization results in significant reduction in the difference in osmotic pressure between the draw solution and the feed solution in forward osmosis (FO) and is regarded as a major challenge in the FO process. Hence, mitigating concentration polarization is essential for increasing the efficiency of the FO process. In the current study, vibration of hollow fiber (HF) membranes was systematically studied as a method for the mitigation of concentration polarization in submerged FO process. A membrane module consisting of polyether sulfone (PES) HF membranes with inner selective layer was designed and fabricated. Using a water flux model that takes into account the internal concentration polarization (ICP) and external concentration polarization (ECP) on both the lumen and shell sides of the HF membranes, the vibrating frequency and amplitude were evaluated with regards to the change of mass transfer coefficient. Results showed that when low vibration frequency and amplitude of (3 Hz and 1.2 cm) were applied, the mass transfer coefficient increases from 0.7×10-5 m/s (at no vibration) to 1.8×10-5 m/s, which approaches the optimal value as determined from the FO modelling results. The effects of the vibration of membranes were then evaluated in the active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS) orientations. Results showed that in the AL-FS orientation, vibration could enhance mass transfer coefficient significantly at low water flux. However, in the AL-DS orientation, the enhancement of mass transfer coefficient was minimal at low water flux level due to minimal concentrative ECP present. Interestingly, there was significant improvement of mass transfer coefficient at high DS concentration/high water flux level attributed to the significant concentration polarization under high water flux condition. In addition, the vibration-assisted FO process was carried out using polyelectrolyte poly (sodium-4-styrenesulfonate) (PSS) as a draw solute. The change of draw solute to PSS has limited effects on the vibration, as the low diffusion coefficient and high viscosity of PSS offsets the benefits of vibration of membranes. In summary, this study demonstrated a facile method for mitigating concentration polarization in submerged FO process, whereby vibration of HF membranes at low frequency and amplitude could enhance FO water flux by improving hydrodynamic mixing and induce boundary layer disturbances at the shell side of submerged HF membranes. The method could possibly be adopted for improving FO efficiency in submerged osmotic processes.

Composite forward osmosis hollow fiber membranes: Integration of RO- and NF-like selective layers to enhance membrane properties of anti-scaling and anti-internal concentration polarization

Fabrication of novel poly(amide–imide) forward osmosis hollow fiber membranes with a positively charged nanofiltration-like selective layer

Produced and process water (PPW) from oil and gas operations, specifically in Qatar, are disposed of by deep well injection in onshore facilities. Disposing large volumes of PPW may affect deep well formation sustainability highlighting the need for effective PPW management. Forward osmosis (FO) was applied as an "osmotic concentration" process to reduce PPW injection volumes by 50% using brines and seawater as draw solutions (DS). The energy intensive step of restoring the salinity of the DS was eliminated; the diluted DS would be simply discharged to the ocean. Both hollow fiber and flat sheet FO membranes were tested and the former exhibited better flux and rejection; they are the focus of this study. Optimization experiments, conducted using Box-Behnken statistical design, confirmed that temperature and DS concentration had a substantial effect on performance. To validate the concept, a long-term experiment, under optimized conditions, was conducted with PPW as feed and brine from thermal desalination plant as DS which yielded an average flux of 24 L/m(2)h. The results confirmed that low-energy osmotic concentration FO has the potential for full-scale implementation to reduce PPW injection volumes. Pilot testing opportunities are being evaluated to demonstrate the effectiveness of this technology under field conditions.