Article

Electrolysis-assisted mitigation of reverse solute flux in a three-chamber forward osmosis system

Authors:
If you want to read the PDF, try requesting it from the authors.

Abstract and Figures

Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
Content may be subject to copyright.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... There have been various attempts to reduce RSF, such as membrane modification, using large-molecule DS and electrolysis-assisted methods. [16][17][18][19] Among them, bioelectricityinhibited RSF reduction is of particular interest to OsMFC operation. It was found that the movement of electrons (electrically driven) could affect ion transport across FO membrane. ...
... With electricity generation, the potential difference formed between the electrodes would generate a dragging effect for the anions at the anode and the cations at the cathode, which is highly effective in retaining opposite-charged ions, as opposite charges attract. 19 Correspondingly, the electrodes would generate a repelling effect for the same-charged ions (cations at the anode and anions at the cathode), as like charges repel. However, the movement of anions from the cathode to the anode was promoted by the repelling effect of the cathode electrode, and would be weakened by the FO membrane due to membrane rejection. ...
... Hence, the dragging effect of the cathode electrode for cations would be stronger than its repelling effect for anions of the DS. 19 In addition, the decreased cation transport from the cathode to the anode by EDM would generate a dragging force for anions of the DS to maintain the electroneutrality. ...
Article
BACKGROUND Osmotic microbial fuel cells (OsMFCs) integrate microbial fuel cell (MFC) and forward osmosis (FO) and can simultaneously achieve wastewater treatment, electricity generation, and water recovery. The selection of appropriate draw solutes (DS) and reduction of reverse solute flux (RSF) are the key challenges for OsMFC operation. This study has examined ten inorganic‐based DS and investigated the effect of electricity generation on the RSF. RESULTS The OsMFC exhibited the stable electricity generation with Na⁺‐series and K⁺‐series DS. For NH4⁺‐series DS, the ammonia‐nitrogen loss percentage that varied 12.5 ±0.4% ‐ 47.7 ±2.4% was significant due to the high pH and aeration in the cathode. Inorganic scaling/precipitation was observed with Mg²⁺‐series and Ca²⁺‐series DS with the DS loss percentage of 13.5 ± 2.8% to 28.0 ± 0.3%. Electricity generation could reduce the specific RSF by 70.3 ± 4.9% and 56.7 ± 13.4% for the Na⁺ and K⁺ DS, respectively. CONCLUSION The Na⁺‐series and K⁺‐series DS was identified as the ideal DS for the OsMFC because of stable electricity generation and water flux and significant RSF reduction. NH4⁺‐series, Mg²⁺‐series and Ca²⁺‐series DS were not appropriate due to significant loss. Bioelectricity generation could reduce both RSF and specific RSF. This article is protected by copyright. All rights reserved.
... It has been reported that effective RSF reduction (~57% decrease) could be obtained at an applied voltage ! 1.5 V (water splitting detected) (Zou and He, 2017a). To minimize the effect of pH on electrodes and FO membrane, a unique design of threechamber EAO with bilateral draw chambers (hydraulically connected) and middle feed chamber was proposed (Fig. 4A). ...
... Hence, a weak electrolysis (V ¼ 1.5e2.0 V) should be exploited in EAO to achieve stable water flux, reduced RSF, and less energy consumption (Zou and He, 2017a). EAO may offer an energy-efficient solution (0.022 kWh m À3 recovered water or 0.044 ± 0.002 kWh kg À1 reduced reversed solute) to secure an MR over 50%, and more research effort should be invested to better understand the underlying mechanism and optimizing system performance. ...
Article
Forward osmosis (FO) has emerged as a potentially energy-efficient membrane treatment technology to yield high-quality reusable water from various wastewater/saline water sources. A key challenge remained to be solved for FO is reverse solute flux (RSF), which can cause issues like reduced concentration gradient and loss of draw solutes. Yet no universal parameters have been developed to compare RSF control performance among various studies, making it difficult to position us in this “battle” against RSF. In this paper, we have conducted a concise review of existing RSF reduction approaches, including operational strategies (e.g., pressure-, electrolysis-, and ultrasound-assisted osmosis) and advanced membrane development (e.g., new membrane fabrication and existing membrane modification). We have also analyzed the literature data to reveal the current status of RSF reduction. A new parameter, mitigation ratio (MR), was proposed and used together with specific RSF (SRSF) to evaluate RSF reduction performance. Potential research directions have been discussed to help with future RSF control. This review intends to shed more light on how to effectively tackle solute leakage towards a more cost-effective and environmental-friendly FO treatment process.
... Novel DS, such as stimuli-responsive polymers, can theoretically produce low RSF, due to their large hydrodynamic diameter (> 100 nm), while achieving energy-efficient phase separation (Hartanto et al., 2015). Operational strategies have also been investigated, including pressure- (Blandin et al., 2013), electrolysis- (Zou and He, 2017b), and ultrasonic-assisted osmosis (Kowalski et al., 2015). However, additional energy is required to manipulate ion transport across the FO membrane, and inconsistent RSF reduction was reported due to potential membrane damage under a certain operating conditions (Lutchmiah et al., 2015). ...
Article
Full-text available
Forward osmosis (FO) has emerged as a promising membrane technology to yield high-quality reusable water from various water sources. A key challenge to be solved is the bidirectional solute flux (BSF), including reverse solute flux (RSF) and forward solute flux (FSF). Herein, zwitterion functionalized carbon nanotubes (Z-CNTs) have been coated onto a commercial thin film composite (TFC) membrane, resulting in BSF mitigation via both electrostatic repulsion forces induced by zwitterionic functional groups and steric interactions with CNTs. At a coating density of 0.97 g m −2 , a significantly reduced specific RSF was observed for multiple draw solutes, including NaCl (55.5% reduction), NH 4 H 2 PO 4 (83.8%), (NH 4) 2 HPO 4 (74.5%), NH 4 Cl (70.8%), and NH 4 HCO 3 (61.9%). When a synthetic wastewater was applied as the feed to investigate membrane rejection, FSF was notably reduced by using the coated membrane with fewer pollutants leaked to the draw solution, including NH 4 +-N (46.3% reduction), NO 2 −-N (37.0%), NO 3 −-N (30.3%), K + (56.1%), PO 4 3−-P (100%), and Mg 2+ (100%). When fed with real wastewater, a consistent water flux was achieved during semi-continuous operation with enhanced fouling resistance. This study is among the earliest efforts to address BSF control via membrane modification, and the results will encourage further exploration of effective strategies to reduce BSF.
... There have been various efforts to reduce RSF, e.g., via membrane modification, use of larger molecule chemicals as draw solute, and electrolysis-assisted reduction [18][19][20][21], or recovery of reverse-fluxed draw solute via electrodialysis [22]. In particular, bioelectricity generation in an OsMFC was able to inhibit solute movement and thus decrease RSF [23]. ...
Article
Osmotic microbial fuel cells (OsMFCs) combine the merits of microbial fuel cell (MFC) and forward osmosis (FO) for simultaneous contaminant removal, electricity generation, and high-quality water extraction. As an FO based technology, reverse solute flux (RSF) is one of the key challenges for its operation. Herein, RSF was converted into a positive effect on the system performance by using NaHCO3 solution as a draw solution (DS)/catholyte. It was found that reverse-fluxed NaHCO3 helped buffer the anolyte pH and thus enhance electricity generation, compared to the OsMFC using the NaCl DS/catholyte. At the same concentration, the NaHCO3 DS/catholyte achieved a higher Coulomb production of 1349.2 ± 80.3 C and higher anolyte pH of 6.48 ± 0.19 than those of the NaCl DS/catholyte. At the same conductivity, the NaHCO3 DS/catholyte exhibited better electricity generation performance with a comparable recovered water volume of 417.7 ± 13.7 mL to that of the NaCl DS/catholyte. As the NaHCO3 concentration increased from 0.1 M to 0.75 M, the OsMFC electricity generation was enhanced due to the increased RSF from 19.2 ± 2.3 to 210.8 ± 17.5 mmol m⁻²h⁻¹. In the anode, 92.0 ± 0.8% to 97.1 ± 0.9% of reverse-fluxed NaHCO3 was used to neutralize protons. These results have demonstrated a new strategy that uses the bicarbonate migration driven by both a concentration gradient and electricity generation to successfully raise the alkalinity of the anolyte towards enhancing electricity generation.
... The power needed for recirculation, feeding and extracting pumps (P, expressed in kW) was computed using the formula reported in Zou and He (2017): ...
Article
Nitrate contamination of groundwater is a mounting concern for drinking water production due to its healthy and ecological effects. Bioelectrochemical systems (BES) are a promising method for energy efficient nitrate removal , but its energy consumption has not been well understood. Herein, we conducted a preliminary analysis of energy consumption based on both literature information and multiple assumptions. Four scenarios were created for the purpose of analysis based on two treatment approaches, microbial fuel cells (MFCs) and controlled biocathodic denitrification (CBD), under either in situ or ex situ deployment. The results show a specific energy consumption based on the mass of NO 3 −-N removed (SEC N) of 0.341 and 1.602 kWh kg NO 3 −-N −1 obtained from in situ and ex situ treatments with MFCs, respectively; the main contributor was the extraction of the anolyte (100%) in the former and pumping the groundwater (74.8%) for the latter. In the case of CBD treatment, the energy consumption by power supply outcompeted all the other energy items (over 85% in all cases), and a total SEC N of 19.028 and 10.003 kWh kg NO 3 −-N −1 were obtained for in situ and ex situ treatments, respectively. The increase in the water table depth (from 10 to 30 m) and the decrease of the nitrate concentration (from 25 to 15 mg NO 3 −-N) would lead to a rise in energy consumption in the ex situ treatment. Although some data might be premature due to the lack of sufficient information in available literature, the results could provide an initial picture of energy consumption by BES-based groundwater treatment and encourage further thinking and analysis of energy consumption (and production).
... gMH at all the tested concentrations (Fig. 2B). The ratio of salt leakage (J S ) to water flux (J W ), i.e. specific reverse solute flux (J S /J W ) [36], was used to estimate the amount of DS loss in the FO process. The trend of J S /J W was similar to that of RSF, but the 5000 PAA-Na had higher J S /J W than the 2000 PAA-Na (Fig. 2C). ...
Article
Forward osmosis (FO) technology has long been constrained by the slow development of appropriate draw solutes (DS) and the relatively high cost associated with DS recovery. In this study, a series of polyelectrolytes, polyacrylic acid sodium salts (PAA-Na) with different molecular weights, were explored as DS for FO applications with a focus on the recovery using combined pH and microfiltration (MF). The FO system achieved a high water flux of 18.02 ± 0.51 LMH, low reverse salt flux (RSF) of 0.110 ± 0.004 gMH, and the JS/JW of 6.1 ± 0.3 mg L− 1 with 25 wt% PAA-Na (2000 Da) as the DS and DI water as the feed. The DS recovery efficiency by the combined pH + MF approach was 99.68% at pH of 4.35, and the operation cost was estimated at 0.037 $ m− 3. Dynamic light scattering revealed that the hydrodynamic diameter of PAA increased with decreasing pH, resulting in PAA polymers precipitated as aggregates at the pH response point. The 25 wt% 2000 PAA-Na achieved the water flux of 11.56 ± 0.32 LMH from synthetic seawater and 17.19 ± 0.52 LMH from the treated wastewater. These results have demonstrated efficient and cost-effective recovery of PAA DS for FO-based applications.
... However, to truly reduce RSF and strengthen long-term performance, membrane advancements, for example emerging fabrication materials with specialized salt rejection, and operation strategies (e.g. electrolysis-assisted solute capture) ( Zou and He, 2017) should be encouraged. Second, the MEC and FO exhibit different treatment capacity and should be well-coordinated for maximized resource recovery output ( Lu et al., 2014). ...
Article
Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
Article
Forward osmosis (FO) is an emerging permeation-driven membrane technology that manifests advantages of low energy consumption, low operating pressure, and uncomplicated engineering compared to conventional membrane processes. The key issues that need to be addressed in FO are membrane fouling, concentration polarization (CP) and reverse solute diffusion (RSD). They can lead to problems about loss of draw solutes and reduced membrane lifetime, which not only affect the water treatment effectiveness of FO membranes, but also increase the economic cost. Current research has focused on FO membrane preparation and modification strategies, as well as on the selection of draw solutions. Unfortunately, these intrinsic solutions had limited success in unraveling these phenomena. In this paper, we provide a brief review of the current state of research on existing external field-assisted FO systems (including electric-, pressure-, magnetic-, ultrasonic-, light- and flow-assisted FO system), analyze their mitigation mechanisms for the above key problems, and explore potential research directions to aid in the further development of FO systems. This review aims to reveal the feasibility of the development of external field-assisted FO technology to achieve a more economical and efficient FO treatment process.
Article
Agricultural wastewater contains high concentrations of nitrogen and phosphorus. There is a growing interest in recovering these nutrients. In this study, an electrically charged forward osmosis (eFO) system was developed to recover struvite and water from synthetic livestock wastewater. By applying a voltage near the surface of the FO membrane, magnesium migrated reversely into the feed chamber and reacted with the ammonium and phosphate in the feed solution to form struvite. As a result of electrical charging, the recovery of struvite and water was enhanced by 77% and 39%, respectively. The enhancement might be because dilutive and concentrative polarization was alleviated on the draw and feed side of the FO membrane during ion migration. High external voltage, high draw concentration, and alkaline/neutral draw pH favored water recovery and struvite precipitation. This study provides insights into harnessing reverse salt flux to improve the recovery of nutrients and water in FO systems.
Article
Reverse solute flux (RSF) is a key issue for operating forward osmosis (FO) systems and can cause the loss of draw solute (DS) and salt accumulation in the feed. Herein, an electrolysis-assisted FO (e-FO) system was developed for simultaneous RSF reduction and recovery of the reverse-fluxed DS. Applying a voltage of 1.5 V led to RSF of 3.34 ± 0.01 mmol m⁻² h⁻¹ (0.47 g m⁻² h⁻¹) in the e-FO system, 67.5 ± 0.5% lower than that of the control system; in addition, the e-FO system recovered ~0.32 g L⁻¹ of the reverse-fluxed DS and this could not be realized in the control. When the e-FO system was examined with three types of the mimicked fertilizer, RSF reduction and DS recovery were largely affected by the individual components of a fertilizer DS. The energy consumption of the e-FO system was reduced by ~90%, from 0.38 ± 0.01 to 0.04 ± 0.01 kWh m⁻³ when the recirculation rate decreased from 60 to 15 mL min⁻¹. Those results have demonstrated the technical feasibility of an e-FO system that is capable of reducing RSF and recovering the lost DS and will encourage further investigation by addressing several identified challenges.
Chapter
The aquaculture industry have shown drastic growth over the years due to increased aquatic product consumption. With tremendous growth, the amount of generated aquaculture effluent has surged. The global shift toward sustainable goals has caused degradative treatment methods to be obsolete and induced the birth of new resource recovery treatment methods. However, the fluctuating and dilute nature of aquaculture effluent renders nutrient recovery methods inefficient. Hybrid membrane technologies provides promising potential in handling the complex effluent and effectively concentrating the nutrients for recovery. This chapter compiles the existing research on various hybrid membrane systems alongside depleting and recovering conventional treatment methods. The nature of aquaculture effluent is also briefly introduced to apprehend the complexity of the effluent. Hybrid membrane systems present in this chapter are an integration of conventional treatment methods (chemical or biological methods) and membrane technologies. The purpose of this chapter is to evaluate the performance and efficiency of existing hybrid membrane systems on water and nutrient recovery. Conventional treatment methods and membrane technologies on aquaculture effluent treatment are included for comparison and act as reference for possible combinations of hybrid membrane systems in the future. Existing hybrid membrane technologies displayed satisfactory rejection of nutrients and high-quality water effluent but are lacking in the recovery of nutrients. Thus further research and innovations are required for better performance of hybrid membrane systems in treating and recovering the resources from aquaculture effluent.
Article
The impact of ion migration induced by an electrical field on water flux in a forward osmosis (FO) process was examined using thin-film composite (TFC) reverse osmosis membranes (TFC-SW for seawater applications, and TFC-BW for brackish water), held between two cation exchange membranes. An applied fixed current of 100 mA (~1.7 mA cm−2) was sustained by the proton flux through the TFC-BW membrane using a feed of 34 mM NaCl, and a 257 mM NaCl draw solution. Protons generated at the anode were transported through the cation exchange membrane and into the draw solution, lowering the pH of the draw solution. Additional proton transport through the TFC-BW membrane also lowered the pH of the feed solution. Concentration polarization (CP) of the protons on the draw side of the TFC-BW membrane resulted in high CP modulus of 1.41 ×105, which enhanced the water flux into the draw solution by 5 times to 5.56 LMH, compared to the control (1.10 LMH, no current). Water flux was also enhanced using the TFC-SW, although to a lesser extent (from 0.32 to 0.70 LMH), due to the smaller pore sizes of this membrane that limited the applied current to 25 mA and did not produce a high CP modulus. These results using this electro-forward osmosis (EFO) process demonstrated enhancement of water flux into the draw solution could be achieved using ion accumulation induced by an electrical field. This EFO system could be used for FO applications where a higher osmotic pressure is required with limited use of draw solute.
Thesis
Nitrate occurrence in groundwater is a worldwide issue, due to the high exploitation of the resource for water supply, and the worldwide diffusion of the contamination. The consumption of nitrate-contaminated drinking water may lead to severe health issues. Several technologies have been applied; in the last 15 years, bioelectrochemical systems (BES) have emerged as an alternative to conventional technologies for water and wastewater treatment. BESs can be defined as electrochemical systems in which microorganisms act as catalysts in the anode and/or cathode reactions. In the thesis, the design, and application of BESs for groundwater denitrification was described, analyzed, and discussed. Firstly, the development of a denitrifying biocathode was described and analyzed: the biocathode was obtained by the reversal of the anode of a Microbial Fuel Cell (MFC), following a procedure described in literature on smaller scale reactors. Then, the obtained CBD (Controlled Biocathodic Denitrification system) was operated under different operational conditions (i.e. hydraulic retention times, nitrate loading rate, nitrate concentration in the influent). The performances of the CBD in terms of denitrification and energy consumption were analyzed and discussed, and the limitations of the systems were identified. To overcome the emerged limitations, a sequential system composed by 2 CBDs connected in series was developed, and operated at decreasing hydraulic retention times. The combined system showed to obtain high nitrate and total nitrogen removal rates, and to decrease its specific energy consumption (in terms of mass of nitrate removed, and volume treated) at the decrease of the hydraulic retention times. Then, the operation of a buried biocathode for in situ groundwater denitrification was described and analyzed. The biocathode was immersed in sand or gravel, to simulate its displacement in a saturated aquifer. The lack or recirculation in the reactor due to the presence of the sand/gravel led to a substantial decrease in the total nitrogen removal rate, with consequent accumulation of intermediate N-forms, and to an increase in the specific energy consumption. The operation of the buried biocathode suggested the necessity of the development of specially-designed BES for in situ applications. The analysis of the energy consumption of CBD and MFC for groundwater denitrification in ex situ, and in situ configurations was calculated using data from literature and assumptions, and highlighted the fact that, even though the operation of the CBD was more energy expensive compared to the MFC due to the necessary use of a power supply or a potentiostat, the CBD was the only option to achieve satisfactory performance in terms of nitrate and total nitrogen removal rates. In the last chapter of the thesis, the application of BES for the removal of other contaminants (arsenic, cadmium, chromium, perchlorate, and vanadium) from groundwater is reviewed.
Article
Bioelectrochemical systems (BES) can accomplish simultaneous wastewater treatment and resource recovery via interactions between microbes and electrodes. Often deemed as “energy efficient” technologies, BES have not been well evaluated for their energy performance, such as energy production and consumption. In this work, we have conducted a concise review and analysis of energy balance in BES with parameters like normalized energy recovery, specific energy consumption, and net energy production. Several BES representatives based on their functions were selected for analysis, including direct electricity generation in microbial fuel cells, hydrogen production in microbial electrolysis cells, nitrogen recovery in BES, chemical production in microbial electrosynthesis cells, and desalination in microbial desalination cells. Energy performance was normalized to water volume (kWh m−3), organic removal (kWh kg COD−1), nitrogen recovery (kWh kg N−1), chemical production (kWh kg−1), or removed salt during desalination (kWh kg−1). The key operating factors such as pumping system (recirculation/feeding pumps) and external power supply were discussed for their effects on energy performance. This is an in-depth analysis of energy performance of various BES and expected to encourage more thinking, analysis, and presentation of energy data towards appropriate research and development of BES technology for resource recovery from wastewater.
Article
Osmotic microbial fuel cells (OsMFCs) take advantages of synergy between forward osmosis (FO) and microbial fuel cells (MFCs) for simultaneous wastewater treatment, bioenergy production, and water recovery. A unique feature for healthy operation of OsMFCs is an appropriate draw solute (DS) that can also act as a catholyte. Herein, polyelectrolytes (polyacrylic acid sodium salts, PAA-Na) was investigated as a DS/catholyte and reproduced with the aid of the high catholyte pH. Such a reproduction method is innovative, because it turns a drawback (high catholyte pH) into a useful resource, thereby reducing the demand for external input and leading to a clean production process. The results have showed that the OsMFC achieved a current density of 159 ± 6 A m⁻³, water flux of 12.7 ± 0.2 LMH, and low reverse salt flux of 0.05 ± 0.00 gMH with 32 wt% PAA-Na (2000 Da) as the DS. The DS recovery efficiency could be as high as 99.86 ± 0.04%, and the reproduced DS was successfully applied in the subsequent operation. With this reproduction method, the highest total operation cost was estimated at 0.104 $ m⁻³. Those results have demonstrated a new approach based on pH-dependent PAA DS reproduction towards further development of OsMFC technology for sustainable water/wastewater treatment and resource recovery.
Article
Abstract Landfill leachate contains substances that can be potentially recovered as valuable resources. In this study, magnesium in a landfill leachate was recovered as struvite with calcium pretreatment; meanwhile, the leachate volume was reduced by using a submerged forward osmosis (FO) process, thereby enabling significant reduction of further treatment footprint and cost. Without pretreatment, calcium exhibited strong competition for phosphate with magnesium. The pretreatment with a Ca2 +: CO32– molar ratio of 1:1.4 achieved a relatively low loss rate of Mg2 + (24.1 ± 2.0%) and high Ca2 + removal efficiency (89.5 ± 1.7%). During struvite recovery, 98.6 ± 0.1% of magnesium could be recovered with a significantly lower residual PO43 −-P concentration (< 25 mg L− 1) under the condition of (Mg + Caresidual): P molar ratio of 1:1.5 and pH 9.5. The obtained struvite had a similar crystal structure and composition (19.3% Mg and 29.8% P) to that of standard struvite. The FO process successfully recovered water from the leachate and reduced its volume by 37%. The configuration of calcium pretreatment - FO - struvite recovery was found to be the optimal arrangement in terms of FO performance. These results have demonstrated the feasibility of magnesium recovery from landfill leachate and the importance of the calcium pretreatment, and will encourage further efforts to assess the value and purity of struvite for commercial use and to develop new methods for resource recovery from leachate.
Article
Full-text available
Forward osmosis (FO) is one of the evolving membrane technologies in desalination with recent expanded new interest as a low energy process. The most significant parts of FO process are the membrane and draw solution since both play a substantial role in its performance. Hence, the selection of an appropriate membrane and draw solution is crucial for the process efficiency. Improvements in the development of membranes and draw solutes have been recorded recently. However, limitations such as fouling of FO membranes, reverse solute flux, concentration polarization, and low permeate flux in standalone FO systems. This work targets the review of recent progress in FO, aiming on the prospects and challenges. It starts with addressing the advantages of the FO process. The crucial part of this review is a thorough discussion of hybrid FO systems, different FO membranes, and draw solutes available coupled with their effects on FO performance. Finally, the future of FO for sustainable desalination is also discussed.
Article
Full-text available
The applications of forward osmosis (FO) have been hindered because of the lack of an optimal draw solution. The reverse salt flux from the draw solution not only reduces the water flux but also increases the cost of draw solute replenishment. Therefore, in this study, Tergitol NP7 and NP9 with a long straight carbon chain and low critical micelle concentration (CMC) were coupled with highly charged ethylenediaminetetraacetic acid (EDTA) as an innovative draw solution to minimize reverse salt diffusion in FO for the first time. The results showed that the lowest reverse salt flux of 0.067 GMH was observed when 0.1M EDTA-2Na coupled with 15mM NP7 was used as a draw solution and deionized water was used as a feed solution in FO mode (active layer facing with the feed solution). This is due to the hydrophobic interaction between the tails of NP7 and the FO membrane, thus creating layers on the membrane surface and constricting the FO membrane pores. Moreover, 1M EDTA-2Na coupled with 15mM NP7 is promising as an optimal draw solution for brackish water and sea water desalination. Average water fluxes of 7.68, 6.78, and 5.95 LMH were achieved when brackish water was used as a feed solution (5, 10, and 20g/L NaCl), and an average water flux of 3.81 LMH was achieved when sea water was used as a feed solution (35g/L NaCl). The diluted draw solution was recovered using a nanofiltration (NF-TS80) membrane with a high efficiency of 95% because of the high charge and large size of the draw solution. Copyright © 2015 Elsevier B.V. All rights reserved.
Article
Full-text available
The osmotic membrane bioreactor (OMBR) is a hybrid biological-physical treatment process that has been gaining interest for wastewater treatment and water reuse. The OMBR couples semi-permeable forward osmosis (FO) membranes for physiochemical separation with biological activated sludge process for organic matter and nutrient removal. The driving force for water production in OMBR is the osmotic pressure difference across the FO membrane between the activated sludge and a concentrated draw solution, which is made with inorganic or organic salts that have a high osmotic pressure at relatively low concentrations. The draw solution becomes diluted during OMBR treatment and may be reconcentrated using reverse osmosis, membrane distillation, or thermal distillation processes. The combination of processes in the OMBR presents unique opportunities but also challenges that must be addressed in order to achieve successful commercialization. These challenges include membrane fouling, elevated bioreactor salinity that hinders process performance, degradation of the draw solution by chemicals that diffuse through the FO membrane, and the potential for simultaneous water, mineral, and nutrient recovery. In this article, results from past and most recent OMBR studies are summarized and critically reviewed. Information about similar and more established technologies (e.g., traditional porous membrane bioreactors and FO) is included to help compare and contrast state-of-the-art technologies and the novel OMBR approach, and to elucidate practical configurations that should be considered in future OMBR research and development.
Article
Full-text available
This study investigates the performance of an integrated osmotic and microfiltration membrane bioreactor (O/MF-MBR) system for wastewater treatment and reclamation. The O/MF-MBR system simultaneously used microfiltration (MF) and forward osmosis (FO) membranes to extract water from the mixed liquor of an aerobic bioreactor. The MF membrane facilitated the bleeding of dissolved inorganic salts and thus prevented the build-up of salinity in the bioreactor. As a result, sludge production and microbial activity were relatively stable over 60days of operation. Compared to MF, the FO process produced a better permeate quality in terms of nutrients, total organic carbon, as well as hydrophilic and biologically persistent trace organic chemicals (TrOCs). The high rejection by the FO membrane also led to accumulation of hydrophilic and biologically persistent TrOCs in the bioreactor, consequently increasing their concentration in the MF permeate. On the other hand, hydrophobic and readily biodegradable TrOCs were minimally detected in both MF and FO permeates, with no clear difference in the removal efficiencies between two processes. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.
Article
Full-text available
The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in voltage application and membranes when treating brackish water reverse osmosis concentrate waste. Synthetic BWRO concentrates from Arizona and Texas of 7890-14,800 mg/L total dissolved solids were prepared with poly-phosphonate antiscalants. Experimentation was performed using a laboratory-scale electrodialyzer with two sets of membranes (AMV-CMV and PCSA-PCSK) with a nominal transfer area of 64 cm(2) per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic samples were analyzed for specific anion and cation concentrations. The BWRO concentrates were successfully treated with stack voltage applications of 0.5-1.5 V/cell-pair for salinity removal ratios up to 99% with current density less than 500 A/m(2). This paper highlights that (1) the specific energy consumption was proportional to the applied voltage and equivalent concentration separated (i.e., approximately 0.03 kW h/m(3) per Volt/cell-pair applied per meq/L separated); (2) lower voltage applications decreased the relative separation rate of sulfate compared to chloride; and (3) water transport by electro-osmosis was independent of voltage application or resulting current densities, while it is affected by the ion exchange membranes.
Article
Full-text available
Recently, forward osmosis (FO) has attracted growing attention in many potential applications such as power generation, desalination, wastewater treatment and food processing. However, there are still several critical challenges, including concentration polarization, membrane fouling, reverse solute diffusion and the need for new membrane development and draw solute design in FO. These challenges are also the current research focus on FO. This paper aims to review the recent developments in FO, focusing on the opportunities and challenges. It begins with discussing the advantages of the FO process over pressure-driven membrane processes. These potential advantages lie in FO's low energy consumption, low fouling propensity, reduced or easy cleaning, low costs, high salt rejection and high water flux. Next, the recent applications of FO, as the outcomes of the above advantages, are described. The key part of this review is a detailed discussion of five critical challenges faced by FO and their relationships. Finally, the future of FO is viewed. This review provides a clear outline for FO-concerned researchers on the recent developments in FO.
Article
Full-text available
Air Gap Membrane Distillation (AGMD) has been implemented to treat produced water. The permeate fluxes, rejection factor and energy consumption for three different membranes, TF200, TF450 and TF1000, with pore sizes of 0.2, 0.45 and 1 μm, respectively, are measured at different operating parameters. The influence of membrane pore size is investigated for the produced water. Also, the effect of feed flow rate, coolant temperature and feed temperature on permeate flux is studied. The flux increases as the feed temperature and flow rate increase, and declines as the coolant temperatures increase. Moreover, the energy consumption was measured at different pore size and was found to be independent of membrane pore size.
Article
Full-text available
Forward osmosis (FO) represents a tremendous and untapped opportunity with the potential to solve the global water crisis. The biggest challenge facing the application of FO technology is the economical separation of drinkingwater from its draw solution. Using advances in nanotechnology, we herein describe a novel draw solute separation system which mimics a natural “destabilization” phenomenon with the help of superparamagnetic nanoparticles, thus separating drinkingwater from draw solution without any intensive energy, such as, hydraulic pressure or heat. Also, this process is not afflicted by the commonly observed problem of reverse salt diffusion. All these characteristics of this novel draw solution separation system make FO to be an eco-sustainable process for the production of drinkingwater from wastewater without any waste.
Article
Full-text available
Forward osmosis (FO) is a novel and emerging low energy technology for desalination. It will be particularly more attractive, if the draw solution separation and recovery are not necessary after FO process. The application of this new concept is briefly described here in this paper for the desalination of saline water for irrigation, using fertilizer as a draw agent. Instead of separating the draw solution from desalinated water, the diluted fertilizer draw solution can be directly applied for fertigation. We report the results on the commonly used chemical fertilizers as FO draw solution. Based on the currently available FO technology, about nine different commonly used fertilizers were finally screened from a comprehensive list of fertilizers and, their performances were assessed in terms of pure water flux and reverse draw solute flux. These results indicate that, most soluble fertilizers can generate osmotic potential much higher than the sea water. The draw solutions of KCl, NaNO3 and KNO3 performed best in terms of water flux while NH4H2PO4, (NH4)2HPO4, Ca(NO3)2 and (NH4)2SO4 had the lowest reverse solute flux. Initial estimation indicates that, 1kg of fertilizer can extract water ranging from 11 to 29L from sea water.
Article
Full-text available
Dark fermentation effluents of wheat powder (WP) solution containing different concentrations of volatile fatty acids (VFAs) were subjected to low voltage (1–3V) DC current to produce hydrogen gas. Graphite and copper electrodes were tested and the copper electrode was found to be more effective due to higher electrical conductivity. The effects of solution pH (2–7), applied voltage (1–3V) and the total VFA (TVFA) concentration (1–5gL−1) on hydrogen gas production were investigated. Hydrogen production increased with decreasing pH and became maximum at pH=2. Increases in applied voltage and the TVFA concentration also increased the cumulative hydrogen formation. The most suitable conditions for the highest cumulative hydrogen production was pH=2, with 3V applied voltage and 5g TVFA L−1. Up to 110ml hydrogen gas was obtained with 5gL−1 TVFA at pH=5.8 and 2V applied voltage within 37.5h. The highest energy efficiency (56%) was obtained with the 2V applied voltage and 10.85gL−1 TVFA. Hydrogen production by electrolysis of water in control experiments was negligible for pH>4. Hydrogen production by electrohydrolysis of VFA containing anaerobic treatment effluents was found to be an effective method with high energy efficiency.
Article
Full-text available
One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water.
Article
Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
Article
Using liquid fertilizer as a draw solute in forward osmosis (FO) to extract high-quality water from wastewater is of strong interest because it eliminates the need for regenerating draw solute, thereby requiring less energy input to system operation. However, energy consumption of such an approach has not been evaluated before. Herein, a submerged FO system with all-purpose liquid fertilizer as a draw solute was studied for energy consumption of water recovery from either deionized (DI) water or domestic wastewater. The results showed that a higher draw concentration led to higher water flux and lower energy consumption, for example 0.25 ± 0.08 kWh m⁻³ with 100% draw concentration, but reverse salt flux (RSF) was also more serious. Decreasing the recirculation flow rate from 100 to 25 mL min⁻¹ had a minor effect on water flux, but significantly reduced energy consumption from 1.30 ± 0.28 to 0.09 ± 0.02 kWh m⁻³. When extracting water from the secondary effluent, the FO system exhibited comparable performance of water flux and energy consumption to that of the DI water. However, the primary effluent resulted in obvious fouling of the FO membrane and higher energy consumption than that of the secondary effluent/DI water. This study has provided important implications to proper evaluation of energy consumption by the FO system using liquid fertilizer or other non-regenerating draw solutes.
Article
Forward osmosis (FO) is one of the emerging membrane technologies which has gained interest in the last decade for being a low energy desalination process. The most important factors controlling FO processes are performance, recyclability and cost of the draw solution (DS) used together with the FO membrane itself because they play a crucial role on the feasibility of this technology. Consequently, the selection of an appropriate DS is vital for the process efficiency, besides the required selectivity and permeance of the membrane and the efficient DS regeneration process. A wide variety of DS have been tested so far and this paper aims to review recent advances in the synthesis and selection of an appropriate DS. It provides valuable information on a new type of draw solutes based on hybrid organic-inorganic nanosystems which, at a certain extent, show synergistic properties that face some of the technology shortcomings. Magnetic nanoparticles (MNPs) are the most promising nanosystems intended for desalination because they can be readily recovered applying a magnetic field or by conventional membrane processes. This review also deals with the most important characteristics of DS based on nanoparticles (NPs) and how they affect the performance of the overall processes. Finally, this review also highlights future research directions, where nanosystems will mitigate inverse diffusion and concentration polarization phenomena widely reported as limiting factors in FO processes.
Article
Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min−1 did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m−3. These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.
Article
Fresh water scarcity has led to increased use of reclaimed wastewater as an alternative and reliable source for crop irrigation. Beyond microbiological safety, concerns have been raised regarding contamination of reclaimed wastewater by xenobiotics including pharmaceuticals. This study focuses on carbamazepine, an anticonvulsant drug which is ubiquitously detected in reclaimed wastewater, highly persistent in soil, and taken up by crops. In a randomized controlled trial we demonstrate that healthy individuals consuming reclaimed wastewater-irrigated produce excreted carbamazepine and its metabolites in their urine, while subjects consuming fresh water-irrigated produce excreted undetectable or significantly lower levels of carbamazepine. We also report that the carbamazepine metabolite pattern at this low exposure level differed from that observed at therapeutic doses. This "proof of concept" study demonstrates that human exposure to xenobiotics occurs through ingestion of reclaimed wastewater-irrigated produce, providing real world data which could guide risk assessments and policy design to ensure the safe use of wastewater for crop irrigation.
Article
Electro-osmosis has the potential to reduce concentration polarisation (CP) because it induces the movement of fluid in the vicinity of membrane, thus improving mixing within the boundary layer and enhancing mass transfer. Computational Fluid Dynamics (CFD) is used to simulate steady and unsteady electro-osmotic flow (EOF) in 2D spacer-filled channels, using the Helmholtz-Schmoluchowski slip velocity approximation. The results show that mass transfer enhancement due to EOF is larger in spacer-filled channel than in empty channels. For the steady EOF, the simulation results show that uniform slip velocity reduces the development of stagnant and high concentration regions near spacer filaments when the slip velocity direction is away from the spacer. For unsteady EOF in spacer-filled channels, the simulation results show that an oscillating slip velocity has the potential to induce vortex shedding. This occurs when a resonant slip velocity frequency is used for Reynolds numbers near the transition from steady to unsteady flow. EOF induced vortex shedding due to the resonant slip velocity results in significant increase in maximum wall shear stress along the membrane, therefore potentially delaying the onset of fouling. The data also shows that at the same permeate flux, EOF at the resonant slip velocity frequency results in a significantly lower Power number (a proxy for pumping energy) than the case without EOF.
Article
The two ambient forward osmosis membrane bioreactors (M-FOMBR and A-FOMBR) with same operating condition were utilized to treat the effluent of mesophilic and ambient anaerobic bioreactors, respectively. It could be observed that the FOMBR could significantly remove the NH4+-N, PO43--P and total organic carbon (TOC) in the influent, and the removals of NH4+-N, PO43--P and TOC were related to the microorganism community. With operation time, the flux decline of M-FOMBR was gradually higher than that of A-FOMBR. The higher content of SMP may be one of the reasons for severe membrane fouling in the M-FOMBR, and the different soluble microbial products (SMP) content between the M-FOMBR and A-FOMBR might be associated with the variation of microbial community structures. The microbial community analysis showed that the abundance of Bacteroidetes in the M-FOMBR cake sludge was much higher than that in the A-FOMBR cake sludge. For the Bacteroidetes phylum, the most abundant bacterial genus was Chryseolinea. Therefore, the decrease of Chryseolinea in cake sludge might be responsible for membrane fouling mitigation.
Article
Reverse flux of ammonium draw solute is a serious problem for applying forward osmosis (FO) in water/wastewater treatment. In this study, anaerobic ammonium oxidization (anammox) was synergistically linked to FO for removal of reverse-fluxed ammonium, thereby creating an osmotic anammox system. The feasibility of this system was demonstrated through both batch and continuous operation, and the anammox process was developed in two stages: sole anammox and nitritation-anammox. With addition of nitrite, the sole anammox process achieved an effluent ammonium concentration of 9.9±9.5mgNL-1. The nitritation-anammox maintained an ammonium concentration of 3.1±4.2mgNL-1, and increased the water flux to 2.46±0.24LMH (Lm-2h-1) compared with the sole anammox (1.90±0.14LMH). The nitritation-anammox process exhibited advantages over anammox process in assisting the FO with respect to water flux improvement and chemical savings. The osmotic anammox system can be linked to previously developed microbial electrolysis cells that recover ammonium from high-strength wastes as a draw solute for FO operation. The results encourage further investigation of this system for effects of organic residues, decreasing nitrate accumulation, understanding biofilm on the FO membrane, and long-term performance with actual waste.
Article
Osmotic membrane bioreactor (OMBR) is an emerging technology using water osmosis to accomplish separation of biomass from the treated effluent; however, accumulation of salts in the wastewater due to water flux and loss of draw solute due to reverse salt flux seriously hinders OMBR development. In this study, a hybrid OMBR-Electrodialysis (ED) system was proposed and investigated to alleviate the salinity buildup. The use of an ED (3 V applied) could maintain a relatively low conductivity of 8 mS cm-1 in the feed solution, which allowed the OMBR to operate for 24 days, about 6 times longer than a conventional OMBR without a functional ED. It was found that the higher voltage applied to the ED, the smaller area of ion exchange membrane was needed for salt separation. The recovered salts by the ED were successfully reused as a draw solute in the OMBR. At energy consumption of 1.88-4.01 kWh m-3, the hybrid OMBR-ED system could achieve a stable water flux of about 6.23 LMH and an efficient waste salt recovery of 1.26 kg m-3. The hybrid OMBR-ED system could be potentially more advantageous in terms of less waste saline water discharge and salt recovery, compared with an OMBR+RO system. It also offers potential advantages over the conventional OMBR+post ED treatment in higher water flux and less wastewater discharge.
Article
Desalination of brackish water can provide freshwater for potable use or non potable applications such as agricultural irrigation. Brackish water desalination is especially attractive to microbial desalination cells (MDCs) because of its low salinity, but this has not been well studied before. Herein, three brackish waters prepared according to the compositions of actual brackish water in three locations in Israel were examined with domestic wastewater as an electron source in a bench-scale MDC. All three brackish waters could be effectively desalinated with simultaneous wastewater treatment. The MDC achieved the highest salt removal rate of 1.2 g L(-1) d(-1) with an initial salinity of 5.9 g L(-1) and a hydraulic retention time (HRT) of 0.8 d. The desalinated brackish water could meet the irrigation standard of both salinity (450 mg L(-1) TDS) and the concentrations of major ionic species, given a sufficient HRT. The MDC also accomplished nearly 70% removal of organic compounds in wastewater with Coulombic efficiency varied between 5 and 10%. A previously developed MDC model was improved for brackish water desalination, and could well predict salinity variation and the concentrations of individual ions. The model also simulated a staged operation mode with improved desalination performance. This integrated experiment and mathematical modeling approach provides an effective method to understand the key factors in brackish water desalination by MDCs towards further system development. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
Recently, many materials have been evaluated as draw agents for forward osmosis (FO) processes. In the present work, it is the first attempt to regard electric-responsive polymer hydrogels as draw agents in an FO process. Electric-responsive hyaluronic acid/polyvinyl alcohol (HA/PVA) polymer hydrogels have been prepared by repeated freezing–thawing. Polymer hydrogels with different freezing–thawing cycles were designated as HA–PVA-3, HA–PVA-5, HA–PVA-7, and HA–PVA-9, respectively. The effects of freezing–thawing cycle, voltage, and concentrations of the feed solution on the FO process were examined, while the as-prepared polymer hydrogels were used as draw agents. By using HA–PVA-5, HA–PVA-7, and HA–PVA-9 polymer hydrogels as draw agents and deionised water as the feed solution in FO process, the initial water fluxes reached 1.2, 0.91, and 0.9 L m−2 h−1, respectively. When the voltage of the electric field was 0, 3, 6, and 9 V, the total water fluxes produced by HA–PVA-5 polymer hydrogels in 24 h reached 17.27, 20.95, 25.49, and 26.47 L m−2, respectively. When the different concentrations of sodium chloride was used as feed solutions, the total water fluxes produced by HA–PVA-5 polymer hydrogels at a voltage of 6 V in 24 h were recorded at 22.66, 15.77, and 12.41 L m−2 for 2000, 5000 and 8000 ppm, respectively. Compared with the other published studies which also adopted polymer hydrogels as draw agents in FO process, the fluxes in our article are desirable. In addition, salt reverse diffusion of the draw agent can be avoided and the complexity of the operation can be minimized when the electric-responsive hydrogels are employed as draw agents in FO process.
Article
This study has presented a proof-of-concept system for the self-sustained supply of ammonium-based draw solute for wastewater treatment through coupling a microbial electrolysis cell (MEC) and forward osmosis (FO). The MEC produced an ammonium bicarbonate draw solute via recovering ammonia from a synthetic organic solution, which was then applied in the FO for extracting water from the MEC anode effluent. The recovered ammonium could reach a concentration of 0.86 mol L–1, and with this draw solution, the FO extracted 50.1 ± 1.7% of the MEC anode effluent. The lost ammonium during heat regeneration could be supplemented with additional recovered ammonium in the MEC. The MEC achieved continuing treatment of both organic and ammonium in the returned feed solution mixed with fresh anolyte, although at lower efficiency compared to that with completely fresh anolyte. These results encourage further investigation to optimize the coordination between MEC and FO with improved performance.
Article
Global water shortage is placing an unprecedented pressure on water supplies. Treated wastewater is a valuable water resource, but its reuse for agricultural irrigation faces a roadblock: the public concern over the potential accumulation of contaminants of emerging concern (CECs) into human diet. In the present study, we measured the levels of 19 commonly-occurring pharmaceutical and personal care products (PPCPs) in 8 vegetables irrigated with treated wastewater under field conditions. Tertiary treated wastewater without or with a fortification of each PPCP at 250 ng/L, was used to irrigate crops till harvest. Plant samples at premature and mature stages were collected. Analysis of edible tissues showed a detection frequency of 64% and 91% in all vegetables from the treated wastewater and fortified water treatments, respectively. The edible samples from the two treatments contained the same PPCPs, including caffeine, meprobamate, primidone, DEET, carbamazepine, dilantin, naproxen, and triclosan. The total concentrations of PPCPs detected in edible tissues from the treated wastewater and fortified irrigation treatments were in the range of 0.01 3.87 and 0.15 7.3 ng/g (dry weight), respectively. Annual exposure of PPCPs from the consumption of mature vegetables irrigated with the fortified water was estimated to be only 3.69 μg per capita. Results from the present study showed that the accumulation of PPCPs in vegetables irrigated with treated wastewater was likely limited under field conditions.
Article
Water electrolysis derived by renewable energy such as solar energy and wind energy is a sustainable method for hydrogen production due to high purity, simple and green process. One of the challenges is to reduce energy consumption of water electrolysis for large-scale application in future. Cell voltage, an important criterion of energy consumption, consists of theoretical decomposition voltage (U-theta), ohmic voltage drop (i*Sigma R) and reaction overpotential (eta). The kinetic and thermodynamic roots of high cell voltage are analyzed systemically in this review. During water electrolysis, bubble coverage on electrode surface and bubble dispersion in electrolyte, namely bubble effect, result in high ohmic voltage drop and large reaction overpotential. Bubble effect is one of the most key factors for high energy consumption. Based on the theoretical analysis, we summarize and divide recent intensification technologies of water electrolysis into three categories: external field, new electrolyte composition and new thermodynamic reaction system. The fundamentals and development of these intensification technologies are discussed and reviewed. Reaction overpotential and ohmic voltage drop are improved kinetically by external field or new electrolyte composition. The thermodynamic decomposition voltage of water is also reduced by new reaction systems such as solid oxide electrolysis cell (SOEC) and carbon assisted water electrolysis (CAWE).
Article
To meet mounting water demands, treated wastewater has become an important source of irrigation. Thus, contamination of treated wastewater by pharmaceutical compounds (PCs) and the fate of these compounds in the agricultural environment are of increasing concern. This field study aimed to quantify PC uptake by treated wastewater-irrigated root crops (carrots and sweet potatoes) grown in lysimeters and to evaluate potential risks. In both crops, the nonionic PCs (carbamazepine, caffeine, and lamotrigine) were detected at significantly higher concentrations than ionic PCs (metoprolol, bezafibrate, clofibric acid, diclofenac, gemfibrozil, ibuprofen, ketoprofen, naproxen, sulfamethoxazole and sildenafil). PCs in leaves were found at higher concentrations than in the roots. Carbamazepine metabolites were found mainly in the leaves, where the concentration of the metabolite 10,11-epoxycarbamazepine was significantly higher than the parent compound. The health risk associated with consumption of wastewater-irrigated root vegetables was estimated using the threshold of toxicological concern (TTC) approach. Our data show that the TTC value of lamotrigine can be reached for a child at a daily consumption of half a carrot (~60 g). This study highlights that certain PCs accumulated in edible organs at concentrations above the TTC value should be categorized as contaminants of emerging concern.
Article
In this paper, a novel phase-shedding control scheme for multiphase interleaved dc-dc converters is proposed to improve the light load efficiency. The proposed phase-shedding scheme is based upon power efficiency estimation with a numerically constructed lookup table and a phase configuration selector to automatically determine the load current point of phase shedding for the minimization of the power loss during the light load condition. The proposed scheme is verified on a three-phase-interleaved dc-dc synchronous buck converter with a 12 V input and 1.2 V, 60 A output. Experimental results are presented to demonstrate the effectiveness of the proposed scheme.
Article
Seawater desalination for agricultural irrigation will be an important contributor to satisfying growing water demands in water scarce regions. Irrigated agriculture for food production drives global water demands, which are expected to increase while available supplies are further diminished. Implementation of reverse osmosis, the current leading technology for seawater desalination, has been limited in part because of high costs and energy consumption. Because of stringent boron and chloride standards for agricultural irrigation water, desalination for agriculture is more energy intensive than desalination for potable use, and additional post-treatment, such as a second pass reverse osmosis process, is required. In this perspective, we introduce the concept of an integrated forward osmosis and reverse osmosis process for seawater desalination. Process modeling results indicate that the integrated process can achieve boron and chloride water quality requirements for agricultural irrigation while consuming less energy than a conventional two-pass reverse osmosis process. The challenges to further development of an integrated forward and reverse osmosis desalination process and its potential benefits beyond energy savings are discussed.
Article
The industrial thermal processing of foods may have a severe impact on the sensorial and nutritional properties of the final product. Membrane technologies have been extensively studied as alternative processes. Forward osmosis (FO) is a promising membrane technology to be used in food industries. The only driving force of the process is the osmotic pressure difference between the two solutions that flow in counter-current mode on opposite sides of a permeable membrane. Thus, the main advantages of FO, compared to both thermal and conventional membrane processing, include low hydraulic pressure, low treatment temperature, low fouling tendency, high solids content processing capability and easy scale-up. A detailed, up-to-date summary of potential FO applications for concentrating liquid foods is presented in this review article. The effect of the main process parameters on the filtration performance and their impact on the sensorial and nutritional factors of the final product are described and discussed for a broad spectrum of foods.
Article
In emergencies, access to water plays a critical role in limiting loss of life. Point of use water treatment (PoUWT) is increasingly being used to fill this need. One emerging PoUWT technology is Hydration Technology Innovations'™ (HTI's) osmotic water purification system, which produces a clean sugar–electrolyte drink from almost any water source. This drink not only hydrates users, but also relieves malnutrition and diarrheal illness, two of the most prolific killers in refugee camps and disaster relief scenarios. In this study, HTI's HydroWell™ system is independently evaluated for on contaminant removal, cost, and material availability. Bench-top testing showed that HTI's systems have superior contaminant removal, rejecting > 88.3% of copper, lead, arsenic, and chromium at concentrations of 10 mg/L. The cost of the drink could be minimized to 0.23 USD/L by adjusting process variables. A sensitivity analysis showed significant room for cost reductions, especially if draw solutes could be locally sourced or if the system lifetime could be extended through the use of cleaning reagents or pretreatment. Further research on long-term operations and maintenance and community–technology interaction could yield more information about the efficacy of forward osmosis for this application.
Article
Osmotically driven membrane processes (ODMPs) such as forward osmosis (FO) and pressure retarded osmosis (PRO) are extensively investigated for utilization in a broad range of applications. In ODMPs, the operating conditions and membrane properties play more critical roles in mass transport and process performance than in pressure-driven membrane processes. Search of the literature reveals that ODMP membranes, especially newly developed ones, are tested under different temperatures, draw solution compositions and concentrations, flow rates, and pressures. In order to compare different membranes, it is important to develop standard protocols for testing of membranes for ODMPs. In this article we present a standard methodology for testing of ODMP membranes based on experience gained and operating conditions used in FO and PRO studies in recent years. A round-robin testing of two commercial membranes in seven independent laboratories revealed that water flux and membrane permeability coefficients were similar when participants performed the experiments and calculations using the same protocols. The thin film composite polyamide membrane exhibited higher water and salt permeability than the asymmetric cellulose-based membrane, but results with the high permeability thin-film composite membrane were more scattered. While salt rejection results in RO mode were relatively similar, salt permeability coefficients for both membranes in FO mode were more varied. Results suggest that high permeability ODMP membranes should be tested at lower hydraulic pressure in RO mode and that RO testing be conducted with the same membrane sample used for testing in FO mode.
Article
Forward osmosis (FO) membranes were successfully fabricated using layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene-sulfonate) (PSS) on a porous polyacrylonitrile (PAN) substrate. In addition, chemical crosslinking of LbL polyelectrolyte layers was performed with glutaraldehyde (GA). The resultant crosslinked (the xLbL series) and non-crosslinked (the LbL series) membranes were characterized in terms of the substrate morphology and structure, the separation layer water permeability and salt rejection, and the FO water flux and solute flux performance. Both LbL and xLbL membranes had relatively high water permeability (∼ or >7.0L/m2hbar). On the other hand, the crosslinked xLbL membranes showed better and more stable MgCl2 rejection, leading to a relatively low FO solute reverse transport (the solute flux over water flux ratio
Article
We have proposed a novel dual-stage FO system and conceptually demonstrated its applications, for the first time, to enrich proteins without causing protein structural changes. Highly hydrophilic nanoparticles were utilized as the draw solute to dehydrate protein solutions in the up-stage FO, while model RO retentate as the draw solute to regenerate the nanoparticle solution in the down-stage FO. As a result, the protein enrichment process can be sustainable as the draw solute is re-concentrated continuously by the RO retentate. Proteins enriched in the dual-stage FO are kept intact as examined by both gel track and CD spectra analyses. To explore the universal applicability of the dual-stage FO system for protein enrichment, various types of proteins of different sizes and charge characteristics were studied under different membrane orientations and testing modes. Excellent enrichment performance can be achieved by increasing membrane surface area and osmotic pressure of nanoparticles under the pressure retarded mode in both up-stage and down-stage FO systems. It is believed that the dual-stage FO system has great potential in future applications of protein and pharmaceutical enrichments because of its simplicity, practicality, and economy.
Article
The use of energy still remains the main component of the costs of desalting water. Forward osmosis (FO) can help to reduce the costs of desalination, and extracting water from impaired sources can be beneficial in this regard. Experiments with FO membranes using a secondary wastewater effluent as a feed water and Red Sea water as a draw solution demonstrated that the technology is promising. FO coupled with low pressure reverse osmosis (LPRO) was implemented for indirect desalination. The system consumes only 50% (~1.5kWh/m³) of the energy used for high pressure seawater RO (SWRO) desalination (2.5–4kWh/m³), and produces a good quality water extracted from the impaired feed water. Fouling of the FO membranes was not a major issue during long-term experiments over 14days. After 10days of continuous FO operation, the initial flux declined by 28%. Cleaning the FO membranes with air scouring and clean water recovered the initial flux by 98.8%. A cost analysis revealed FO per se as viable technology. However, a minimum average FO flux of 10.5L/m²-h is needed to compete with water reuse using UF–LPRO, and 5.5L/m²-h is needed to recover and desalinate water at less cost than SWRO.
Article
For the first time, a potentially sustainable integrated FO–UF (forward osmosis–ultrafiltration) system for water reuse and desalination with the aid of super hydrophilic nanoparticles as draw solutes has been proposed. The system uses an FO membrane as the semi-permeable membrane to reject salts, super hydrophilic nanoparticles as draw solutes to induce water across the FO membrane, and UF membranes to regenerate the draw solutes. For comparison, a magnetic separator was also used to recycle super hydrophilic magnetic nanoparticles but agglomeration was observed. Ultrasonication proved to effectively reduce the size of agglomerated magnetic nanoparticle and the FO performance was partially restored. However, the resultant magnetic properties were weakened under ultrasonic processes and thus jeopardized regeneration efficiency in magnetic fields. The novel FO–UF process was tested for 5 continuous runs for the purpose of desalination without increasing nanoparticle draw solute size or reducing osmotic functionality. UF membranes of small pore diameter and narrow pore size distribution can enhance the recovery efficiency of nanoparticle draw solution. The proposed FO–UF integrated system using super hydrophilic nanoparticles as draw solutes is believed to be a promising technology to desalinate both seawater and brackish water and to reclaim water from wastewater.
Article
It isn't just membrane fouling that is seen as an important issue in Membrane Bioreactor (MBR) operation. Research undertaken in Australia and US highlights other areas of concern for users and operators…
Article
In this investigation, a protocol for the selection of optimal draw solutions for forward osmosis (FO) applications was developed and the protocol was used to determine the most appropriate draw solutions for specific FO applications using a currently available FO membrane. The protocol includes a desktop screening process and laboratory and modeling analyses. The desktop screening process resulted in 14 draw solutions suitable for FO applications. The 14 draw solutions were then tested in the laboratory to evaluate water flux and reverse salt diffusion through the FO membrane. Internal concentration polarization was found to lower both water flux and reverse salt diffusion by reducing the draw solution concentration at the interface between the support and dense layers of the membrane. Draw solution reconcentration was evaluated using reverse osmosis (RO) system design software. Analysis of experimental data and model results, combined with consideration of the costs associated with the FO and RO processes showed that a small group of seven draw solutions appeared to be the most suitable. The different characteristics of these draw solutions highlighted the importance of considering the specific FO application and membrane types being used prior to selecting the most appropriate draw solution.
Article
The empirical correction to Stokes' law proposed by Robinson and Stokes has been extended for small ions to provide a concordant set of radii for the hydrated ions. Ions with a crystal ionic radius of about 2 Å. exhibit a minimum hydrated radius of 3.3 Å. corresponding to the maximum in the equivalent conductance. The internal consistency of the set of radii is demonstrated by correlation with the temperature coefficient of equivalent conductance, the viscosity B-coefficient and the partial molar ionic entropy. Except for the small monatomic ions with the minimum hydrated radius, the hydrated ionic radius at 25° is demonstrated to be a linear function of the viscosity B-coefficient. The significance of this relation is discussed in terms of the structural modification rendered by the ions to water.
Article
Highly hydrophilic magnetic nanoparticles have been molecularly designed. For the first time, the application of highly water-soluble magnetic nanoparticles as novel draw solutes in forward osmosis (FO) was systematically investigated. Magnetic nanoparticles functionalized by various groups were synthesized to explore the correlation between the surface chemistry of magnetic nanoparticles and the achieved osmolality. We verified that magnetic nanoparticles capped with polyacrylic acid can yield the highest driving force and subsequently highest water flux among others. The used magnetic nanoparticles can be captured by the magnetic field and recycled back into the stream as draw solutes in the FO process. In addition, magnetic nanoparticles of different diameters were also synthesized to study the effect of particles size on FO performance. We demonstrate that the engineering of surface hydrophilicity and magnetic nanoparticle size is crucial in the application of nanoparticles as draw solutes in FO. It is believed that magnetic nanoparticles will soon be extensively used in this area.
Article
The purpose of this short communication is to share our perspectives on future R & D for FO processes in order to develop effective and sustainable technologies for water, energy and pharmaceutical production.Research Highlights► A review of current and future FO technologies for water, energy and pharmaceuticals.