Active Layer Facing Feed Solution Research Articles

Application of MnFe2O4 magnetic silica-covered ethylenediaminetetraacetic acid-functionalized nanomaterials to the draw solution in forward osmosis

Forward osmosis (FO) is an emerging and promising water treatment technology. However, selection of an optimal draw solution (DS) is essential for efficient FO process operations. In this study, the potential of ethylenediaminetetraacetic acid (EDTA) functionalized SiO2-covered magnetic nanoparticles (MNPs) as DS in FO process were investigated. The MNPs were synthesized and characterized for their morphology, size distribution, magnetic behavior, and dispersibility. Investigations were carried out to determine the effects of DS concentration and MNPs type, utilizing bare, SiO2 covered, and EDTA coated MNPs at concentrations of 20, 40, and 60 g/L. Furthermore, water flux generation capability and rejection efficiency of octanoic acid (OC) was evaluated with EDTA-MNPs as DS in FO mode (active layer facing feed solution) and PRO mode (active layer facing draw solution). Our results showed that a maximum water flux of 9.59 ± 2 LMH in FO mode, and 11.104 ± 2 LMH in PRO mode was achieved using 60 g/L of EDTA-MNPs. Additionally, we investigated the reusability of the EDTA-coated MNPs and found that their recovery was higher than (>90%) with no aggregation. The stability of EDTA-MNPs was due to strong covalent linkages between their four carboxylate groups and the hydrophilic SiO2 surface layer, which resulted in steric hindrance and prevented their aggregation. Finally, we assessed the rejection efficiency of OC at different pH values and found that it was low (30–39%) at pH values below pKa and high (90–97%) at pH values above pKa. Owing to internal concentration polarization, the rejection of OC in FO mode was (10–20%) higher than in PRO mode. The findings demonstrate EDTA-coated MNPs have significant potentials as an effective DS in FO process .

Evaluation of secondary effluent organic matter removal by an in-series forward osmosis-ultrafiltration hybrid process using parallel factor analysis with self-organizing maps

This study explores removal of effluent organic matter (EfOM) from secondary municipal wastewater effluent by a custom-devised in-series forward osmosis-ultrafiltration (FO-UF) hybrid system in which naturally-driven osmotic pressure, induced by the concentration difference between the feed solution and the draw solution, is a sole driving force for post UF filtration. Water flux and reverse salt flux are greatly affected by concentration and type of draw solution as well as different FO membrane configurations of the active layer facing feed solution (AL–FS) and the active layer facing draw solution (AL–DS). Maximum fluorescence intensity values obtained from parallel factor analysis (PARAFAC) revealed that the FO-UF hybrid process removes EfOM up to 97% of initial concentration over 2 h experimentation, owing to 6–8% of additional removal by post UF membrane. PARAFAC and self-organizing maps (SOM) modeling revealed that humic-like substances are removed preferentially over protein-like and smaller-sized organics in both AL–FS and AL–DS modes. However, in AL–DS mode, fouling, possibly due to humic-like substances, followed by deteriorating water quality, is observed earlier than in AL–FS mode. During the FO-UF processes, overall properties of EfOM in feed solution are shifted to hydrophilic and smaller-sized organic matter. This work provides a concept of pump-less FO-UF hybrid filtration and demonstrates the proposed system as a feasible option for EfOM removal in water reuse. As the first of its kind, the incorporation of PARAFAC with SOM modeling in FO process gives an insight into the fouling and transport of EfOM in the AL-FS and AL-DS modes.

Fabrication of novel thin-film composite membrane based on ultrathin metal-organic framework interlayer for enhancing forward osmosis performance

To improve operation efficiency, an interlayered thin-film composite forward osmosis (iTFC-FO) membrane was designed by introducing an ultrathin and porous interlayer based on aluminum tetra-(4-carboxyphenyl)porphyrin (a stable metal−organic framework nanosheet, Al-MOF). Surface characterization results revealed that Al-MOF spread evenly in the macro-porous substrate, and provided a flat and smooth reaction interface with moderate hydrophilicity and uniform small aperture. The resultant polyamide (PA) layer had a thin base (without intrusion into substrate) and crumpled surface (with abundant leaves). The leaves size and cross-linking degree of PA layer firstly increased and then decreased with the Al-MOF loading. Compared to the original membrane, the iTFC-FO showed an enhanced water permeability and a reduced reverse sodium flux in both modes of active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS). To be specific, the specific reverse sodium flux (reverse sodium flux/pure water flux) decreased from 0.27 g/L to 0.04 g/L in the AL-FS mode, while from 1.36 g/L to 0.23 g/L in the AL-DS mode with 2 mol/L NaCl as DS. Moreover, the iTFC-FO maintained high stability and high permeability under high-salinity and contaminated environment. This study offers a new possibility for the rational fabrication of high-performance TFC-FO membranes.

Dual-responsive imidazolium-based ionic liquid with different alkyl chains as draw solutes for forward osmosis

Imidazolium-based magnetic ionic liquids (MILs) with dual responsiveness, a series of 1-alkyl-3-methylimidazolium tetrachloroferrates (Cn-FeCl4, n = 4, 8, and 12, where n denotes the number of carbon atoms in the alkyl group of 1-alkyl-3-methylimidazolium), were synthesized to assess their ability as smart draw solutes for forward osmosis (FO). The recovery properties and FO performance of Cn-FeCl4 were investigated extensively. This series of Cn-FeCl4 exhibits lower critical solution temperature (LCST) characteristics and paramagnetic behavior in the magnetization curve as a function of the magnetic field, which minimizes the energy consumption for recovering draw solutes from spent draw solutions. The LCSTs of the C4-FeCl4, C8-FeCl4, and C12-FeCl4 draw solutions at a concentration of 20 wt % were approximately 76, 43, and 55 °C, respectively. The respective calculated magnetic susceptibilities of MILs were 5.92 × 10−5, 4.53 × 10−5, and 4.12 × 10−5 emu cm−3 at 300 K. Moreover, when the concentration of the draw solution was 20 wt %, the water flux of C8-FeCl4 was approximately 17.30 LMH and 10.04 LMH in active layer facing draw solution and active layer facing feed solution modes, respectively. Subsequently, in desalination applications, C8-FeCl4 exhibited feasibility in saline water with 2000 and 30,000 ppm NaCl. Therefore, for the first time, we studied the effect of the structural transformation of MILs on draw solute properties and examined the applicability of magnetic and thermal dual-responsive MILs as draw solutes for FO processes.

Resources Recycle of Printing and Dyeing Wastewater: UF/FO Hybrid System Optimization and TPA Recovery

Printing and dyeing wastewater has characteristics of high pH, poor biodegradability, complex composition, and a large amount of water, which means it remains a daunting environmental issue. The development of efficient and economic printing and dyeing wastewater treatment technology has gained considerable interest in the field of environmental protection. The performance of ultrafiltration/forward osmosis (UF/FO) hybrid system focused on recycling valuable materials in actual printing and dyeing wastewater was investigated. The effects of pressure, temperature, membrane orientation, and feed pH on membrane performance were also studied. The results showed that the optimal pressure and temperature (T) are 0.15 MPa and 25 °C, respectively; active-layer facing feed solution (AL-FS) mode at pH 7 was used for a UF/FO hybrid system. The recovery of terephthalic acid (TPA) was 99.78% under pH 4. This paper provided a resourceful proposal for the treatment of printing and dyeing wastewater.

Optimization of osmotic backwashing cleaning protocol for produced water fouled forward osmosis membranes

Produced water (PW) is a contaminated effluent from oil and gas operations that can be treated using forward osmosis (FO) before discharge. However, the FO membrane suffers fouling issues during PW treatment, which can be addressed using the osmotic backwashing (OB) technique. In this study, desalter effluent (DE) was used as feed solution (FS) and water-oil separator outlet (WO) as a draw solution (DS). Long-term experiments of 5 cycles of 20 h each were performed with OB executed between the cycles. With 60 min OB, the active layer facing feed solution configuration outperformed the active layer facing draw solution configuration with a stable 35% higher flux and lesser specific reverse solute flux (SRSF). Further optimization was done between 60, 30, and 2 × 30 min OB protocols. Effective flux recovery (water recovered minus water used for OB) and system availability (total time minus OB time) measured the system efficiency. The 30 min OB exhibited the highest system efficiency, with 3% higher flux recovery and 52% lesser SRSF achieved with real streams. The major foulants on the active layer were CaSiO3 and NaCl, while CaSiO3, CaSO4, and NaCl were identified on the support layer. Membrane characteristics remained the same after OB; hence, 30 min OB is feasible for cleaning the PW fouled FO membranes.

Performance of novel sericin doped reduced graphene oxide membrane for FO based membrane crystallization application

Forward osmosis (FO) could be an energy-efficient process for industrial effluent treatment given the easy availability of energy-efficient FO membranes and economical draw solutes. Due to its atomically thin two-dimensional (2D) structure, hydrophilicity, and anti-fouling characteristics, GO/r-GO layers showed excellent potential of application as dense layer of FO membrane. This study reports application of a hydrophilic natural protein named sericin as the doping material to r-GO-based dense layer to solve the trade-off between permeability and selectivity of FO membranes, and also to improve the membrane stability for higher operational hours during the antibiotics recovery process. Our membranes achieved an outstanding water fluxes of 54 LMH (r-GO-S) and 36.8 LMH (S-r-GO) for the initial 2 h of operation, and a lower specific revere salt fluxes (SRSF) of 0.12 g/L (r-GO-S) and 0.18 g/L (S-r-GO) as compared to that of commercial FO membranes (0.4–0.5 g/L). The optimized r-GO-S membrane showed higher stabilized water flux (38 LMH) as compared to r-GO membrane (12.2 LMH) for 30 h of continuous operation. Furthermore, due to cross-linking capability of sericin with r-GO, r-GO-S membrane exhibited better regeneration efficiency with FRR% of around ∼ 84% in active layer facing feed solution (ALFS) mode while recovering rifaximin crystals and yielded good durability and better long-term stability performance. Overall, this study demonstrates that sericin doped r-GO membrane can be used for fouling intensive FO based membrane crystallization process for the recovery of valuables from pharma effluents.

Black odorous water concentrating by forward osmosis: rejection performance of characteristic pollutants based on cation exchange

ABSTRACT This study aimed to investigate pollutant concentration and nitrogen interception characteristics of a forward osmosis (FO) process for concentrating black odorous water. The membrane cell was operated in active layer facing feed solution (AL-FS) mode with aquaporin (AQP) as the membrane material and NaCl solution as the draw solution (DS). The organic pollutants (COD), TP, NH+4–N, NO−3–N, TN, Fe and Mn in black odorous water were concentrated non-intermittently for 24 h, and their interception characteristics were investigated. The results showed that the average interception rates of COD, TP, NO- 3-N, TN, Fe and Mn were 97.2%, 98.0%, 58.7%, 54.3%, 61.8% and 60.0%, respectively, while the average interception rate of NH+ 4–N was only 1.27%–3.47%. To explore the characteristics of nitrogen interception, a comparison was conducted between AQP membrane and thin film composite (TFC) membrane. Because the surface electronegativity of AQP membrane was stronger than that of TFC, the effect of cation exchange on ammonia nitrogen interception was more serious with AQP membrane. With NaCl solution as DS, the reverse osmosis flux of Na+ was (0.53 ± 0.02 mol·m−2·h−1), which was significantly higher than that of Cl− (0.29 ± 0.03 mol·m−2·h−1) (P < 0.05). The interception effect of AQP membrane on TN was related to the proportion of NH+ 4–N in TN. The pretreatment of black odorous water by aeration could transform part of NH+ 4–N into NO−3-N, and reduce the negative effect of cation exchange effect on nitrogen interception. The TN interception rate increased from 54.3% to 66.1%.

A Novel Hybrid Reactor of Pressure-Retarded Osmosis Coupling with Activated Sludge Process for Simultaneously Treating Concentrated Seawater Brine and Wastewater and Recovering Energy.

As an attractive way to deal with fresh water shortage, membrane-based desalination technologies are receiving increased interest. However, concentrated seawater brine, in needing further treatment, remains a main obstacle for desalination via membrane technology. Here, a hybrid technology integrating pressure-retarded osmosis with activated sludge process (PRO-MBR) was applied for simultaneously treating concentrated seawater brine and municipal wastewater. Performance of the PRO-MBR, including water flux, power density, contaminants removal, and membrane fouling was evaluated and compared at two different membrane orientations (i.e., active layer facing feed solution (AL-FS) mode and active layer facing draw solution (AL-DS) mode). During the PRO-MBR process, the municipal wastewater was completely treated regardless of the membrane orientation, which means that there was no concentrated sewage needing further treatment, owing to the biodegradation of microorganisms in the bioreactor. In the meantime, the concentrated brine of seawater desalination was diluted into the salinity level of seawater, which met the standard of seawater discharge. Owing to the high rejection of forward osmosis (FO) membrane, the removal efficiency of total organic carbon (TOC), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) was higher than 90% at both modes in the PRO-MBR. In addition, the PRO-MBR can simultaneously recover the existing osmotic energy between the municipal wastewater and the seawater brine at both modes. Compared with the AL-DS mode, the AL-FS mode took a shorter time and achieved a bigger power density to reach the same terminal point of the PRO-MBR owing to a better water flux performance. Furthermore, the membrane fouling was much more severe in the AL-DS mode. In conclusion, the current study demonstrated that the PRO-MBR at the AL-FS mode can be a promising and sustainable brine concentrate and municipal wastewater treatment technology for its simultaneous energy and water recovery.

A unified thermodynamic fouling mechanism based on forward osmosis membrane unique properties: An asymmetric structure and reverse solute diffusion

Fouling mechanism of the forward osmosis membrane, which was peculiarly featured by the asymmetric membrane structure and reverse solute diffusion, was investigated at the molecular level and from the energy perspective. Two noteworthy fouling behaviors were observed in batch fouling tests conducted in AL-FS mode (active layer facing feed solution) and AL-DS mode (active layer facing draw solution) after filtering foulants with identical volume: 1) after filtering 100 mL of foulants, the flux decline rate in AL-DS mode was 1.78 times faster than that in AL-FS mode, but the flux decline behaviors of the two modes were similar in the subsequent filtration stages; 2) although the foulant layer weight of the same mode increased linearly in middle and late stages, the flux loss rate was distinctly different. Thermodynamic analysis indicated that the attractive interaction energy between the foulants and the support layer was about 5 times higher than that between the foulants and the active layer, well interpreting the higher flux decline rate of AL-DS mode in initial stage. Meanwhile, a non-invasive microscope observed that the structure of the fouling layer remarkably changed from loose to dense in the middle stage, and stabilized in the late stage. Furthermore, quantum chemistry calculation proved that the reverse diffusion of NaCl brought alginate molecular chains closer, whereas the distance between them tended to be constant as the continuous increase of NaCl. Based on these findings, the thermodynamic fouling mechanism proposed by combining the structure change process of the fouling layer with Flory-Huggins lattice theory satisfactorily interpreted the noteworthy fouling behaviors caused by reverse NaCl diffusion in middle and late stages. The revealed fouling mechanism unifies the adhesion and filtration behaviors related to the unique properties of FO membrane, deepening understanding of membrane fouling in the dynamic and complex ternary system of the FO process.

Assessing the potential of integrally skinned asymmetric hollow fiber membranes for addressing membrane fouling in pressure retarded osmosis process

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules.

Electricity generation and pollutants removal of landfill leachate by osmotic microbial fuel cells with different forward osmosis membranes

In this study, thin-film composite with embedded polyester screen, cellulose triacetate with a cast nonwoven and cellulose triacetate with embedded polyester screen (CTA-ES) was examined as the intermediate membranes in osmotic microbial fuel cells (OsMFCs). The reactors were fed with actual landfill leachate and the performance was studied in two operation modes: active layer facing draw solution and active layer facing feed solution (AL-FS). The OsMFC with CTA-ES exhibited the best energy generation (maximum power density: 0.44 W m− 2) and pollutant removal efficiency (ammonia nitrogen: 70%, total nitrogen: 74%) in the AL-FS mode, which could be ascribed to the lowest internal resistance (237 Ω) and highest microbial richness. Pseudomonas was the highest proportion of microbial in OsMFCs. The result of this study has demonstrated the potential of OsMFCs for landfill leachate treatment.

Feasibility of H2O2 cleaning for forward osmosis membrane treating landfill leachate

This study reports landfill leachate treatment by the forward osmosis (FO) process using hydrogen peroxide (H2O2) for membrane cleaning. Although chemical cleaning is an effective method for fouling control, it could compromise membrane integrity. Thus, understanding the impact of chemical cleaning on the forward osmosis membrane is essential to improving the membrane performance and lifespan. Preliminary results revealed a flux recovery of 98% in the AL-FS mode (active layer facing feed solution) and 90% in the AL-DS (draw solution faces active layer) using 30% H2O2 solution diluted to 3% by pure water. The experimental work investigated the effects of chemical cleaning on the polyamide active and polysulfone support layers since the FO membrane could operate in both orientations. Results revealed that polysulfone support layer was more sensitive to H2O2 damage than the polyamide active at a neutral pH. The extended exposure of thin-film composite (TFC) FO membrane to H2O2 was investigated, and the active layer tolerated H2O2 for 72 h, and the support layer for only 40 h. Extended operation of the TFC FO membrane in the AL-FS based on a combination of physical (hydraulic flushing with DI water) and H2O2 was reported, and chemical cleaning with H2O2 could still recover 92% of the flux.

Performance Evaluation and Fouling Propensity of Forward Osmosis (FO) Membrane for Reuse of Spent Dialysate.

The number of chronic renal disease patients has shown a significant increase in recent decades over the globe. Hemodialysis is the most commonly used treatment for renal replacement therapy (RRT) and dominates the global dialysis market. As one of the most water-consuming treatments in medical procedures, hemodialysis has room for improvement in reducing wastewater effluent. In this study, we investigated the technological feasibility of introducing the forward osmosis (FO) process for spent dialysate reuse. A 30 LMH of average water flux has been achieved using a commercial TFC membrane with high water permeability and salt removal. The water flux increased up to 23% with increasing flowrate from 100 mL/min to 500 mL/min. During 1 h spent dialysate treatment, the active layer facing feed solution (AL-FS) mode showed relatively higher flux stability with a 4–6 LMH of water flux reduction while the water flux decreased significantly at the active layer facing draw solution (AL-DS) mode with a 10–12 LMH reduction. In the pressure-assisted forward osmosis (PAFO) condition, high reverse salt flux was observed due to membrane deformation. During the membrane filtration process, scaling occurred due to the influence of polyvalent ions remaining on the membrane surface. Membrane fouling exacerbated the flux and was mainly caused by organic substances such as urea and creatinine. The results of this experiment provide an important basis for future research as a preliminary experiment for the introduction of the FO technique to hemodialysis.

Concentration of lithium by forward osmosis

As an applying potential for a part of production of lithium (Li) from salt lake brine, forward osmosis was investigated by using semi-permeable membranes, sodium chloride (NaCl) and magnesium chloride (MgCl2) as draw solutions under several operational conditions. Cellulose triacetate and thin-film composite membranes and their orientations were compared. The results indicated that concentration of Li was higher using the thin-film composite membrane with MgCl2 as the draw solution. The effect of pH was insignificant. The results also showed that water flux decreased with increasing Li concentration on the feed side. Internal concentration polarization played an important role when rejection of Li was higher in the active layer facing feed solution system.

ZIF-8 membrane supported on alumina hollow fiber with enhanced salt removal by forward osmosis

This work describes the development of ZIF-8 membranes supported on alumina hollow fiber via electroless deposition (ELD) of ZnO followed by solvothermal synthesis for water desalination. The relatively low operating temperature of ELD of ZnO provided an alternative method to fabricate pure-phase ZIF-8 membrane. As-prepared ZnO and ZIF-8 samples were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), water contact angle, and Fourier transform infrared spectroscopy (FTIR). The performance of ZIF-8 membrane was evaluated using forward osmosis (FO) using active layer facing feed solution. The well-intergrown membrane provided high water flux up to 12.25 L/m2h with reverse solute flux as low as 0.029 kg/m2h when using 100,000 ppm NaCl solution and water as the draw and feed solutions, respectively. Furthermore, the membrane showed high KCl (87.8%) and NaCl (88%) rejection and excellent CaCl2 (95%) and MgCl2 (98%) salt rejection in FO using 1.0 M dextrose solution as the draw solution. Interestingly, the rejection of AlCl3 salt was only as high as 46% due to the instability of ZIF-8 in the AlCl3 solution causing the loss of its crystallinity. The ZIF-8 material showed no degradation in various saline solutions (e.g., KCl, NaCl, CaCl2, and MgCl2) except for AlCl3 solution even at a high concentration of 40,000 ppm for 720 h. The findings suggest that the prepared ZIF-8 membrane is a potential membrane for desalination application due to its excellent separation performance toward certain salts.

Dissolved methane rejection by forward osmosis membrane to achieve in-situ energy recovery from anaerobic effluent

Dissolved CH4 (D-CH4) rejection by forward osmosis (FO) membranes requires systematically investigate to mitigate anaerobic effluents pollution and energy loss. In this study, effects of membrane materials, orientations and alginate fouling on dissolved CH4, H2 and CO2 rejections were evaluated. FO was further connected with UASB effluent (FO-UASB) to recover D-CH4 for the first time. Results showed that D-CH4 rejections by CTA-ES and CTA-NW membranes were above 99.99% in the active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS) orientations. Dissolved H2 rejections (87.5–92.3%) achieved higher than dissolved CO2 rejections (52.5–73.8%) in AL-FS orientation which was attributed to dissolved gas permeability through FO. Alginate fouling layer improved dissolved H2 rejection while concentrative internal concentration polarization aggravated dissolved CO2 rejection by fouled CTA-ES membrane in AL-DS orientation. D-CH4 was successfully collected by FO-UASB in the synergy effect of FO rejection and liquid-to-gas mass transfer. The maximum total CH4 collection rate was 599.0 mg COD/(L d) and 603.4 mg COD/(L d) at 35 °C and 25 °C in the FO-UASB.

Treatment of biologically treated landfill leachate with forward osmosis: Investigating membrane performance and cleaning protocols

This study presents systematic investigations to evaluate the performance, rejection rate, fouling, cleaning protocols and impact of physical and chemical cleaning strategies on the performance of commercial cellulose triacetate (CTA) membrane. The treatment of landfill leachate (LFL) solution was performed in the active layer facing feed solution and support layer facing the draw solution (AL-FS mode), and active layer facing the draw solution and support layer facing the feed solution (AL-DS mode). Compared to the AL-FS mode, a higher flux for AL-DS mode was achieved, but membrane fouling was more severe in the latter. In both membrane orientations, the rejection rate of the FO membrane to heavy ions and contaminants in the wastewater was between 93 and 99%. Physical and chemical cleaning strategies were investigated to recover the performance of the FO membrane and to study the impact of cleaning methods on the membrane rejection rate. Physical cleaning with hot water at 35 °C and osmotic backwashing with 1.5 M NaCl demonstrated excellent water flux recovery compared to chemical cleaning. In the chemical cleaning, an optimal concentration of 3% hydrogen peroxide was determined for 100% flux recovery of the fouled membrane. However, slight membrane damage was achieved at this concentration on the active layer side. Alkaline cleaning at pH 11 was more effective than acid cleaning at pH 4, although both protocols compromised the membrane rejection rate for some toxic ions. A comparison of the membrane long-term performance found that cleaning with osmotic backwashing and hot water were effective methods to restore water flux without comprising the membrane rejection rate. Overall, it was found that physical cleaning protocols are superior to chemical cleaning protocols for forward osmosis membrane fouled by landfill leachate wastewater.

Black odorous water concentrating by forward osmosis (FO) with aquaporin biomimetic membranes: Pollutants concentrating and membrane fouling characteristics

This study aimed to investigate pollutant concentration and membrane fouling characteristics of a forward osmosis (FO) process using aquaporin biomimetic membrane (ABM) for concentrating black odorous water. The membrane cells were operated in active layer facing feed solution (ALFS) mode with 2 M NaCl solution as the draw solution. The system was continuously performed for 64 batch cycles, and each cycle duration was 24 h. At the end of each cycle, physical cleaning with deionized water was employed as the membrane recovery strategy. The results showed that the rejection ratios of chemical oxygen demand (COD), total phosphorus (TP) and nitrate (NO3−-N) could reached 97.2%, 98.0%, and 85.0%, respectively, while most NH4+-N penetrated into the draw solution due to cation exchange. The total nitrogen (TN) rejection ratio was largely dependent upon the NH4+-N/TN ratio. At high NH4+-N/TN ratio, the successions of ammonia oxidizing bacteria (AOB) communities enriched in the biofouling layer in different experimental stages would affect the transformation degree of NH4+-N, and thus lead to much fluctuations of TN rejection. The average initial water flux reached 9.84 L/(m2·h), and the average water flux of each cycle kept stable especially in the later stage of the experiment. In the biofouling layer, polysaccharides enhanced while proteins decreased in the later period. P, Mn, Fe and Na also accumulated on the surface. Norank_f__Reyranellaceae, Erythrobacter, SM1A02, Pirellula, and Hydrogenophaga were the predominant genera enriched in the fouling layer, which would lead to complex pollutants transformations, especially nitrogen transformation, during the FO process.

Volume reduction and water reclamation of reverse osmosis concentrate from coal chemical industry by forward osmosis with an osmotic backwash strategy.

Coal chemical industry (CCI) generally utilizes reverse osmosis (RO) for water reclamation, which generates a highly concentrated stream containing refractory organic substances and high-concentration total dissolved solids (TDS). To address this issue, the present work focuses on volume reduction of RO concentrate (ROC) produced from CCI by forward osmosis (FO). We investigated the effects of membrane orientation and draw solution (DS) concentration on FO performance. Foulant removal was tested by using chemical cleaning, physical cleaning and osmotic backwash (OB). AL-FS (active layer facing feed solution) mode outcompeted AL-DS (active layer facing draw solution) mode, achieving a flux of 26.4 LMH, 92.5% water reclamation and energy consumption of 0.050 kWh·m-3 with 4 M NaCl as DS. The FO process was able to reject >98% SO4 2-, Mg2+and Ca2+, 92-98% Si and 33-55% total organic carbon (TOC). Ten-cycle (10 × 20 h) accelerated fouling test demonstrated approximately 30% flux decline in association with Si-containing foulants, which could be removed almost completely through OB with 97.1% flux recovery. This study provides a proof-of-concept demonstration of FO for volume reduction and water reclamation of ROC produced from CCI, making the treatment of ROC more efficient and more energy effective.