Fertilizer drawn forward osmosis process for sustainable water reuse to grow hydroponic lettuce using commercial nutrient solution

On the evaluating membrane flux of forward osmosis systems: Data assessment and advanced intelligent modeling

As an emerging desalination technology, forward osmosis (FO) can potentially become a reliable method to help remedy the current water crisis. Introducing uncomplicated and precise models could help FO systems' optimization. This paper presents the prediction and evaluation of FO systems' membrane flux using various artificial intelligence-based models. Detailed data gathering and cleaning were emphasized because appropriate modeling requires precise inputs. Accumulating data from the original sources, followed by duplicate removal, outlier detection, and feature selection, paved the way to begin modeling. Six models were executed for the prediction task, among which two are tree-based models, two are deep learning models, and two are miscellaneous models. The calculated coefficient of determination (R2 ) of our best model (XGBoost) was 0.992. In conclusion, tree-based models (XGBoost and CatBoost) show more accurate performance than neural networks. Furthermore, in the sensitivity analysis, feed solution (FS) and draw solution (DS) concentrations showed a strong correlation with membrane flux. PRACTITIONER POINTS: The FO membrane flux was predicted using a variety of machine-learning models. Thorough data preprocessing was executed. The XGBoost model showed the best performance, with an R2 of 0.992. Tree-based models outperformed neural networks and other models.

Second-Generation Magnesium Phosphates as Water Extractant Agents in Forward Osmosis and Subsequent Use in Hydroponics

The recovery of nutrients from wastewater streams for their later use in agricultural fertilization is an interesting approach. Wastewater recovered magnesium phosphate (MgP) salts were used in a forward osmosis (FO) system as draw solution in order to extract water and to produce a nutrient solution to be used in a hydroponic system with lettuces (Lactuca sativa, L.). Owing to the low solubility of the MgP salts (i.e., struvite, hazenite and cattiite) in water, acid dissolution was successfully tested using citric and nitric acids to reach pH 3.0. The dilution by FO of the dissolved salts reached levels close to those needed by a hydroponic culture. Ion migration through the membrane was medium to high, and although it did not limit the dilution potential of the system, it might decrease the overall feasibility of the FO process. Functional growth of the lettuces in the hydroponic system was achieved with the three MgP salts using the recovered water as nutrient solution, once properly supplemented with nutrients with the desired concentrations. This is an innovative approach for promoting water reuse in hydroponics that benefits from the use of precipitated MgP salts as a nutrient source.

Treatment of textile industry wastewater by using high-performance forward osmosis membrane tailored with alpha-manganese dioxide nanoparticles for fertigation

Forward osmosis (FO) technology has been acknowledged as an energy-efficient cutting-edge water treatment innovation; however, the inefficient performance of polymer-based membranes remains a tailback in the practical utilization of FO. A significant issue in FO is membrane fouling, which negatively influences the flux efficiency, working expenses and membrane life expectancy. Membranes having high water flux and minimum reverse solute flux at low operating pressures are the ideal membranes for this process. This study reports a thin-film nanocomposite (TFNC) membrane for the treatment of textile industry wastewater utilizing fertilizer as draw solution fabricated via the phase inversion process. The chemical structure and morphology of the synthesized manganese oxide (MnO₂) incorporated membrane were studied by various characterization techniques like X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, contact angle and gravimetry. The outcomes demonstrated that the nanoparticles were bonded to cellulose acetate polymer via covalent bonds and showed very hydrophilic membrane surface, along with an increased osmotic water flux of 52.5 L.m².h^-1 and reverse salt flux of 10.9 g.m².h^-1, when deionized wastewater and potassium chloride were used as the feed solution and the draw solution, respectively. In this manner, incorporating manganese oxide into the FO membrane may introduce its extraordinary possible application for the production of diluted fertilizer solution with balanced nutrients.

Recovery of Clean Water and Ammonia from Domestic Wastewater: Impacts on Embodied Energy and Greenhouse Gas Emissions

Treatment of domestic wastewater can recover valuable resources, including clean water, energy, and ammonia. Important metrics for these systems are greenhouse gas (GHG) emissions and embodied energy, both of which are location- and technology-dependent. Here, we determine the embodied energy and GHG emissions resulting from a conventional process train, and we compare them to a nonconventional process train. The conventional train assumes freshwater conveyance from a pristine source that requires energy for pumping (US average of 0.29 kWh/m³), aerobic secondary treatment with N removal as N₂, and Haber-Bosch synthesis of ammonia. Overall, we find that this process train has an embodied energy of 1.02 kWh/m³ and a GHG emission of 0.77 kg-CO₂eq/m³. We compare these metrics to those of a nonconventional process train that features anaerobic secondary treatment technology followed by further purification of the effluent by reverse osmosis and air stripping for ammonia recovery. This "short-cut" process train reduces embodied energy to 0.88 kWh/m³ and GHG emissions to 0.42 kg-CO₂eq/m³, while offsetting demand for ammonia from the Haber-Bosch process and decreasing reliance upon water transported over long distances. Finally, to assess the potential impacts of nonconventional nitrogen removal technology, we compared the embodied energy and GHG emissions resulting from partial nitritation/anammox coupled to anaerobic secondary treatment. The resulting process train enabled a lower embodied energy but increased GHG emissions, largely due to emissions of N₂O, a potent greenhouse gas.

Investigating the performance of hydroponic nutrient solutions as potential draw solutions for fertilizer drawn forward osmosis

This research project aims at investigating the performance of hydroponic nutrient solutions as draw solutions for desalination using the fertilizer drawn forward osmosis (FDFO) process. Six different lettuce and leafy greens hydroponic nutrient stock solutions were prepared according to the literature and used in this study and tested on a bench-scale forward osmosis unit as draw solutions for the process. The feed solution for the process was deionized water mixed with NaCl in different concentrations, to represent different salinities of brackish groundwater. The draw efficiency of each solution was measured based on water flux, specific reverse solute flux, water recovery, and salt rejection. It was concluded that of the six tested nutrient solutions, the "Resh Florida, California" solution is the recommended solution to be used as draw solution for fertilizer drawn forward osmosis, due to its high performance in terms of water recovery (15.75%), flux (11 L/m²/h), salt rejection (92%), and SRSF (highest recorded SRSF for a specific ion (SO₄^2-) was 7.3 g/L), as well as its low cost, relative to the other highly performing draw solution "Chekli" ($1.07/L vs. $3.73/L).

Exploring the limitations of forward osmosis for direct hydroponic fertigation: Impact of ion transfer and fertilizer composition on effective dilution

There is a need for water reuse technologies and applications to minimize the imminent water crisis, caused by the world population growth, the reduction of freshwater resources and the increasing water pollution. Fertilizer-drawn forward osmosis (FDFO) is a promising process capable of simultaneously extracting fresh water from low-quality sources as feed water (e.g., wastewater or greywater), while diluting fertilizer solutions for direct fertigation, avoiding the demand for freshwater for irrigation. Achieving an adequate level of dilution for direct fertigation is a key element to be evaluated for the implementation of FDFO. This study assessed the performance of the forward osmosis process to dilute fertilizer solutions to be applied directly in hydroponic systems. Experiments were carried out under conditions close to osmotic equilibrium to evaluate the process performance up to the maximum dilution point. Tests were carried out with individual and blended fertilizers (i.e., (NH₄)₂HPO₄ or DAP, and KNO₃) used as draw solution (DS) and with deionized water or individual salts (NaCl, MgCl₂, Na₂SO₄, MgSO₄) in the feed solution (FS). Water fluxes and reverse salt fluxes indicated that both fertilizer DS composition and concentrations play a fundamental role in the process. Suitable nutrient concentrations to be directly applied without further dilution for N, P and K (119, 40, 264 mg.L^-1 respectively) were obtained with deionized water as FS and blended DAP (0.025 M) and KNO₃ (0.15 M) as DS. However, important fertilizer losses from DS to FS were observed, being the highest for NO₃^- (33-70% losses from DS to FS). The presence of salts in FS decreased the water fluxes and the DS dilution due to the osmotic equilibrium caused by a greater loss of nutrients from DS to FS (up to 100%), compared with tests using just deionized water as FS. This study points out the potential limitations of the FDFO process, due to the high solute fluxes and low water fluxes in conditions close to osmotic equilibrium.

The applicability of anaerobically treated domestic wastewater as a nutrient medium in hydroponic lettuce cultivation: Nitrogen toxicity and health risk assessment

The applicability of anaerobic effluent (AE) from an anaerobic membrane bioreactor (AnMBR) treating domestic wastewater as a nutrient medium was evaluated through hydroponic cultivation of lettuce. The growth of lettuce plants on AE media was significantly inhibited to 31-40% in height and 36-48% in number of leaves compared to that on half-strength Hoagland solution (HHS) as a control. The primary cause of inhibition was nitrite toxicity as induced by partial nitrification. Therefore, the nitrification of AE as a pre-treatment step was adopted to prevent the toxicity of nitrite. The heights of lettuce grown on nitrified anaerobic effluent (NAE) and nitrified anaerobic effluent with 96 mg/L sulfate (NAES) were in the range of 11.4-11.5 cm and was comparable to that on control solution (11.4 cm). The potential health risk for heavy metals was insignificant based on health risk index (HRI < 1) and targeted hazardous quotient (THQ < 1). These results show that efficient crop production can be achieved with AE, but suitable pre-treatment steps should be followed.

Evaluating Fertilizer-Drawn Forward Osmosis Performance in Treating Anaerobic Palm Oil Mill Effluent

Fertilizer-drawn forward osmosis (FDFO) is a potential alternative to recover and reuse water and nutrients from agricultural wastewater, such as palm oil mill effluent that consists of 95% water and is rich in nutrients. This study investigated the potential of commercial fertilizers as draw solution (DS) in FDFO to treat anaerobic palm oil mill effluent (An-POME). The process parameters affecting FO were studied and optimized, which were then applied to fertilizer selection based on FO performance and fouling propensity. Six commonly used fertilizers were screened and assessed in terms of pure water flux (J_w) and reverse salt flux (J_S). Ammonium sulfate ((NH₄)₂SO₄), mono-ammonium phosphate (MAP), and potassium chloride (KCl) were further evaluated with An-POME. MAP showed the best performance against An-POME, with a high average water flux, low flux decline, the highest performance ratio (PR), and highest water recovery of 5.9% for a 4-h operation. In a 24-h fouling run, the average flux decline and water recovered were 84% and 15%, respectively. Both hydraulic flushing and osmotic backwashing cleaning were able to effectively restore the water flux. The results demonstrated that FDFO using commercial fertilizers has the potential for the treatment of An-POME for water recovery. Nevertheless, further investigation is needed to address challenges such as J_S and the dilution factor of DS for direct use of fertigation.

The Effects of Fertilizer Type and Application Time on Soil Properties, Plant Traits, Yield and Quality of Tomato

Compost is considered to be superior fertilizer for soil quality and productivity, and is commonly used with chemical fertilizer. The optimal mixed ratio of compost with chemical fertilizer and the best application time is necessary to know for sustainable agriculture practices and management. Compared to the control treatment, this study comprehensively evaluated the effects of four mixed ratios of compost with chemical fertilizer, two nitrogen application times of chemical fertilizer, and their interaction on the soil properties, plant traits, yield, and quality of tomato plants. The soil properties, plant traits, and yield of tomato with all compost-mixed fertilizers performed better than the treatment without fertilizer. Furthermore, the amounts of available nitrogen, phosphorus, organic matter, plant weight, and yield in a 30% chemical fertilizer + 70% compost treatments (CF30) were even better than those with pure chemical fertilizer (CF100). No significant effect of nitrogen application time and its interaction with the mixed ratio treatment was detected, and the quality of fruit remained consistent among treatments. This study demonstrated a suitable practical application method for cow manure compost as a nutrient source in tomato crop production under silty loam soil.

On-Site Treatment of Shale Gas Flowback and Produced Water in Sichuan Basin by Fertilizer Drawn Forward Osmosis for Irrigation

Fertilizer drawn forward osmosis (FDFO) was proposed to extract fresh water from flowback and produced water (FPW) from shale gas extraction for irrigation, with fertilizer types and membrane orientations assessed. The draw solution (DS) with NH₄H₂PO₄ displayed the best performance, while the DS with (NH₄)₂HPO₄ resulted in the most severe membrane fouling. The DS with KCl and KNO₃ led to substantial reverse solute fluxes. The FDFO operation where the active layer of the membrane was facing the feed solution outperformed that when the active layer was facing the DS. The diluted DS and diluted FPW samples were used for irrigation of Cherry radish and Chinese cabbage. Compared to deionized water, irrigation with the diluted DS (total dissolved solid (TDS) = 350 mg·L^-1) promoted plant growth. In contrast, inhibited plant growth was observed when FPW with high salinity (TDS = 5000 mg·L^-1) and low salinity (TDS = 1000 mg·L^-1) was used for irrigation of long-term (8-week) plant cultures. Finally, upregulated genes were identified to illustrate the difference in plant growth. The results of this study provide a guide for efficient and safe use of FPW after FDFO treatment for agricultural application.

Exploring the Operation Factors that Influence Performance of a Spiral-Wound Forward Osmosis Membrane Process for Scale-up Design

Forward osmosis (FO) technology has increasingly attracted attention owing to its low operational energy and low fouling propensity. Despite extensive investigations on FO, very few module-scale FO studies on the operation and design of the FO process have been conducted. In this paper, a simple and practical FO process design parameter called normalized membrane area is suggested based on a performance analysis of spiral-wound FO elements. The influence of operation factors on operating pressures and water recovery was investigated using 8-inch spiral wound elements in the continuous operation mode. The membrane area was adjusted by series connection of FO elements to a maximum value of 46 m² (three elements). The feed and draw flow rates were varied between 5 and 15 LPM under various feed (10, 20, and 30 g/L) and draw (58.4 and 233.8 g/L) concentration combinations. The analysis of flow rates (feed, draw, and permeate flow rates) indicated not only high flow channel resistance on the draw side but also high permeate flow rates can induce higher operating pressures owing to strong mutual interaction of the feed and the draw streams. Feed water recovery was focused on as a key performance index, and the experimental recovery (R_Exp) and theoretical maximum recovery (R_Th) values were compared. The results revealed the significance of the feed flow rate and the membrane area in terms of enhancing the water recovery performance. In addition, a clear relationship was observed between the membrane area normalized by the initial feed flow rates and the water recovery ratio (R_Exp/R_Th), even though the applied operation conditions were different. Finally, an empirical equation to estimate the required membrane area of spiral-wound FO was proposed for the FO process design. The equation can be used to predict water recovery of FO systems as well, for example, if an FO system is operated at 0.08 m²L⁻¹h of the normalized membrane area, the system is expected to offer 78% of the R_Th value.

Unlocking the application potential of forward osmosis through integrated/hybrid process

Study of forward osmosis (FO) has been increasing steadily over recent years with applications mainly focusing on desalination and wastewater treatment processes. The working mechanism of FO lies in the natural movement of water between two streams with different osmotic pressure, which makes it useful in concentrating or diluting solutions. FO has rarely been operated as a stand-alone process. Instead, FO processes often appear in a hybrid or integrated form where FO is combined with other treatment technologies to achieve better overall process performance and cost savings. This article aims to provide a comprehensive review on the need for hybridization/integration for FO membrane processes, with emphasis given to process enhancement, draw solution regeneration, and pretreatment for FO fouling mitigation. In general, integrated/hybrid FO processes can reduce the membrane fouling propensity; prepare the solution suitable for subsequent value-added uses and production of renewable energy; lower the costs associated with energy consumption; enhance the quality of treated water; and enable the continuous operation of FO through the regeneration of draw solution. The future potential of FO lies in the success of how it can be hybridized or integrated with other technologies to minimize its own shortcomings, while enhancing the overall performance.

Treatment of greywater by forward osmosis technology: role of the operating temperature

Effects of operating conditions were investigated in terms of water flux, reverse salt flux (RSF) and pollutant rejection in a forward osmosis (FO) membrane system treating synthetic greywater. Changing cross-flow velocity had a slight impact on the performance of the FO membrane. Elevating operating temperature was more effective than increasing draw solution concentration to enhance the water flux. Further observation on the effect of heating mode showed that when the temperature was increased from 20 to 30°C, heating the feed solution (FS) side was better than heating the draw solution (DS) side or heating both sides; further increasing the temperature to 40 and 50°C, heating both the FS and DS achieved much higher water flux compared with only increasing the FS or DS temperature. Under isothermal conditions, a higher water flux and a lower RSF were achieved at 40°C than at other temperatures. Changing either FS or DS temperature had similar influences on water flux and RSF. The FO process revealed high rejection of nitrate (95.7%-100%), ammonia nitrogen (98.8%-100%), total nitrogen (97.4%-99.9%), linear alkylbenzene sulfonate (100%) and Mg (97.5%-100%). A mathematical model that could well simulate the water flux evolution in the present FO system was recommended.

Human urine as a forward osmosis draw solution for the application of microalgae dewatering

Human urine is a unique solution that has the right composition to constitute both a severe environmental threat and a rich source of nitrogen and phosphorous. In fact, between 4-9% of urine mass consists of ions, such as K⁺, Cl^-, Na⁺ or NH₄⁺. Because of its high ionic strength, urine osmotic pressure can reach values of up to 2000 kPa. With this in mind, this work aimed to study the effectiveness of real urine as a novel draw solution for forward osmosis. Water flux, reverse nitrogen flux and membrane fouling were investigated using fresh or hydrolysed urine. Water flux as high as 16.7 ± 1.1 L m^-2 h^-1 was recorded using real hydrolysed urine. Additionally, no support layer membrane fouling was noticed in over 20 h of experimentation. Urine was also employed to dewater a Chlorella vulgaris culture. A fourfold increase in algal concentration was achieved while having an average flux of 14.1 L m^-2 h^-1. During the algae dewatering, a flux decrease of about 19% was noticed; this was mainly due to a thin layer of algal deposition on the active side of the membrane. Overall, human urine was found to be an effective draw solution for forward osmosis.

Understanding the organic micropollutants transport mechanisms in the fertilizer-drawn forward osmosis process

We systematically investigated the transport mechanisms of organic micropollutants (OMPs) in a fertilizer-drawn forward osmosis (FDFO) membrane process. Four representative OMPs, i.e., atenolol, atrazine, primidone, and caffeine, were chosen for their different molecular weights and structural characteristics. All the FDFO experiments were conducted with the membrane active layer on the feed solution (FS) side using three different fertilizer draw solutions (DS): potassium chloride (KCl), monoammonium phosphate (MAP), and diammonium phosphate (DAP) due to their different properties (i.e., osmotic pressure, diffusivity, viscosity and solution pH). Using KCl as the DS resulted in both the highest water flux and the highest reverse solute flux (RSF), while MAP and DAP resulted in similar water fluxes with varying RSF. The pH of the FS increased with DAP as the DS due to the reverse diffusion of NH₄⁺ ions from the DS toward the FS, while for MAP and DAP DS, the pH of the FS was not impacted. The OMPs transport behavior (OMPs flux) was evaluated and compared with a simulated OMPs flux obtained via the pore-hindrance transport model to identify the effects of the OMPs structural properties. When MAP was used as DS, the OMPs flux was dominantly influenced by the physicochemical properties (i.e., hydrophobicity and surface charge). Those OMPs with positive charge and more hydrophobic, exhibited higher forward OMP fluxes. With DAP as the DS, the more hydrated FO membrane (caused by increased pH) as well as the enhanced RSF hindered OMPs transport through the FO membrane. With KCl as DS, the structural properties of the OMPs were dominant factors in the OMPs flux, however the higher RSF of the KCl draw solute may likely hamper the OMPs transport through the membrane especially those with higher MW (e.g., atenolol). The pore-hindrance model can be instrumental in understanding the effects of the hydrodynamic properties and the surface properties on the OMPs transport behaviors.

Influence of draw solution type and properties on the performance of forward osmosis process: Energy consumption and sustainable water reuse

Single and multi-component fertilizers were used as a draw solution (DS) in forward osmosis (FO) to produce high-quality water from synthetic and seawater solution, eliminating the need for DS regeneration and reducing the operational energy. The effect of DS type, concentration, circulation flow rates on the FO water flux (WF), specific water flux (SWF), percentage water recovery (%W_recovery), reverse salt flux (RSF) and percentage salt rejection (%R) were studied. The results showed that single fertilizer draw solution (SFDSs) produced higher WF (4.43 L/m².h), %W_recovery (30%) and RSF (60%) in comparison with multi-component draw solution (MCDS) with WF, %W_recovery and RSF of 2.57 L/m².h, 17% and 46%, respectively. DS with higher concentration produced the highest SWF and %W_recovery and consumed less energy. MCDS with concentration of 200 g/L showed SWF in the range of 14.0 to 10.4 L/m²h and energy consumption of 0.312 kW/h m³ in comparison with 10 to 7.8 L/m²h and 0.23 kW/h m³ for MCDS with concentration of 100  g/L. Increasing the recirculation flow rate showed minimum effect on WF and up to 35% energy saving. Pure water extracted using liquid fertilizers utilizing the unique FO mass transport properties balanced nutrient requirement and the water quality parameters, thereby sustaining the aquaponics industry.

Application of volume retarded osmosis - Low pressure membrane hybrid process for recovery of heavy metals in acid mine drainage

Recovery of heavy metals in acid mine drainage (AMD) such as Mn, Fe, Cu, Zn, As, Cd and Pb was evaluated using volume retarded osmosis and low-pressure membrane (VRO-LPM) process. In VRO-LPM process, the draw solution (DS) is regenerated by the naturally generated pressure, giving its economic value. Ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) and Poly (sodium-4-styrenesulfonate, PSS-Na) were used and compared to determine more suitable DS in heavy metal recovery from the AMD. Forward osmosis (FO) and nanofiltration (NF) membrane were employed in VRO-LPM process, due to the low EDTA-4Na rejection (about 50%) in ultrafiltration (UF) process. For the FO part in the VRO-LPM process, PSS-Na had flux values of 0.12, 0.11 and 0.05 L m^-2 h^-1 and at osmotic pressure of 8.9, 12 and 13 bar, respectively. Unlike the flux values, the RSF of PSS remained at 0.01 mmol h^-1 at all osmotic pressures. For EDTA-4Na, the flux values were 0.10, 0.06 and 0.04 L m^-2 h^-1, which are relatively higher than those of PSS-Na; and the RSF values were 0.1, 1.2, 2.2 mmol h^-1, which are higher compared to those of PSS-Na. Unlike PSS-Na, RSF for EDTA-4Na increased as the concentration increases. In the NF part of the VRO-LPM process, PSS-Na had higher water flux and rejection than EDTA-4Na, and the flux and rejection both decreased with concentration for both PSS-Na and EDTA-4Na. The overall rejection in VRO-LPM process was over 95% for all heavy metal ions. Therefore, VRO-LPM process has proven its ability to be used in AMD treatment for heavy metal removal.

Hydroponic Solutions for Soilless Production Systems: Issues and Opportunities in a Smart Agriculture Perspective

Soilless cultivation represent a valid opportunity for the agricultural production sector, especially in areas characterized by severe soil degradation and limited water availability. Furthermore, this agronomic practice embodies a favorable response toward an environment-friendly agriculture and a promising tool in the vision of a general challenge in terms of food security. This review aims therefore at unraveling limitations and opportunities of hydroponic solutions used in soilless cropping systems focusing on the plant mineral nutrition process. In particular, this review provides information (1) on the processes and mechanisms occurring in the hydroponic solutions that ensure an adequate nutrient concentration and thus an optimal nutrient acquisition without leading to nutritional disorders influencing ultimately also crop quality (e.g., solubilization/precipitation of nutrients/elements in the hydroponic solution, substrate specificity in the nutrient uptake process, nutrient competition/antagonism and interactions among nutrients); (2) on new emerging technologies that might improve the management of soilless cropping systems such as the use of nanoparticles and beneficial microorganism like plant growth-promoting rhizobacteria (PGPRs); (3) on tools (multi-element sensors and interpretation algorithms based on machine learning logics to analyze such data) that might be exploited in a smart agriculture approach to monitor the availability of nutrients/elements in the hydroponic solution and to modify its composition in realtime. These aspects are discussed considering what has been recently demonstrated at the scientific level and applied in the industrial context.

Techno-economic feasibility of recovering phosphorus, nitrogen and water from dilute human urine via forward osmosis

Due to high phosphorus (P) and nitrogen (N) content, human urine has often proven to suitable raw material for fertiliser production. However, most of the urine diverting toilets or male urinals dilute the urine 2 to 10 times. This decreases the efficiency in the precipitation of P and stripping of N. In this work, a commercial fertiliser blend was used as forward osmosis (FO) draw solution (DS) to concentrate real diluted urine. During the concentration, the urea in the urine is recovered as it diffuses to the fertiliser. Additionally, the combination of concentrate PO₄^3-, reverse Mg²⁺ flux from the DS and the Mg²⁺ presents in the flushing water, was able to recover the PO₄^3- as struvite. With 50% concentrated urine, 93% P recovery was achieved without the addition of an external Mg²⁺. Concurrently, 50% of the N was recovered in the diluted fertiliser DS. An economic analysis was performed to understand the feasibility of this process. It was found that the revenue from the produced fertilisers could potentially offset the operational and capital costs of the system. Additionally, if the reduction in the downstream nutrients load is accounted for, the total revenue of the process would be over 5.3 times of the associated costs.

Application of a volume retarded osmosis-low pressure membrane hybrid process for treatment of acid whey

This study evaluated the treatment of acid whey through a volume-retarded osmosis-low-pressure membrane (VRO-LPM) hybrid process. The VRO-LPM process uses pressure naturally generated inside the closed draw solution (DS) tank to regenerate the DS, making it an economic process. Poly (sodium-4-styrenesulfonate) (PSS) and carboxymethyl cellulose (CMC) were compared to determine which was a more suitable DS for acid whey treatment. Forward osmosis (FO) and ultrafiltration (UF) membranes were used in the VRO-LPM hybrid process because a single UF process showed high water flux and rejection efficiencies above 85% for both PSS and CMC. In both the FO and UF parts of the VRO-LPM process, PSS had a higher water flux than CMC. However, the increasing rate of the feed solution (FS) for CMC was greater than that of PSS, however the overall rejection efficiencies were similar for both DS. Therefore, the VRO-LPM process can be applied to acid whey treatment, and CMC seems to be a better choice of DS than PSS because of its higher concentrating ratio of FS and high overall rejection.

Combining high performance fertiliser with surfactants to reduce the reverse solute flux in the fertiliser drawn forward osmosis process

Solutions to mitigate the reverse diffusion of solutes are critical to the successful commercialisation of the fertiliser drawn forward osmosis process. In this study, we proposed to combine a high performance fertiliser (i.e., ammonium sulfate or SOA) with surfactants as additives as an approach to reduce the reverse diffusion of ammonium ions. Results showed that combining SOA with both anionic and non-ionic surfactants can help in reducing the reverse salt diffusion by up to 67%. We hypothesised that, hydrophobic interactions between the surfactant tails and the membrane surface likely constricted membrane pores resulting in increased rejection of ions with large hydrated radii such as SO₄^2-. By electroneutrality, the rejection of the counter ions (i.e., NH₄⁺) also therefore subsequently improved. Anionic surfactant was found to further decrease the reverse salt diffusion due to electrostatic repulsions between the surfactant negatively-charged heads and SO₄^2-. However, when the feed solution contains cations with small hydrated radii (e.g., Na⁺); it was found that NH₄⁺ ions can be substituted in the DS to maintain its electroneutrality and thus the diffusion of NH₄⁺ to the feed solution was increased.

Forward Osmosis Application in Manufacturing Industries: A Short Review

Forward osmosis (FO) is a membrane technology that uses the osmotic pressure difference to treat two fluids at a time giving the opportunity for an energy-efficient water and wastewater treatment. Various applications are possible; one of them is the application in industrial water management. In this review paper, the basic principle of FO is explained and the state-of-the-art regarding FO application in manufacturing industries is described. Examples of FO application were found for food and beverage industry, chemical industry, pharmaceutical industry, coal processing, micro algae cultivation, textile industry, pulp and paper industry, electronic industry, and car manufacturing. FO publications were also found about heavy metal elimination and cooling water treatment. However, so far FO was applied in lab-scale experiments only. The up-scaling on pilot- or full-scale will be the essential next step. Long-term fouling behavior, membrane cleaning methods, and operation procedures are essential points that need to be further investigated. Moreover, energetic and economic evaluations need to be performed before full-scale FO can be implemented in industries.

Simultaneous phosphorous and nitrogen recovery from source-separated urine: A novel application for fertiliser drawn forward osmosis

Re-thinking our approach to dealing with waste is one of the major challenges in achieving a more sustainable society. However, it could also generate numerous opportunities. Specifically, in the context of wastewater, nutrients, energy and water could be mined from it. Because of its exceptionally high nitrogen (N) and phosphorous (P) concentration, human urine is particularly suitable to be processed for fertiliser production. In the present study, forward osmosis (FO) was employed to mine the P and N from human urine. Two Mg²⁺-fertilisers, i.e. MgSO₄ and Mg(NO₃)₂ were selected as draw solution (DS) to dewater synthetic non-hydrolysed urine. In this process, the Mg²⁺ reverse salt flux (RSF) were used to recover P as struvite. Simultaneously, the urea was recovered in the DS as it is poorly rejected by the FO membrane. The results showed that, after concentrating the urine by 60%, about 40% of the P and 50% of the N were recovered. XRD and SEM - EDX analysis confirmed that P was precipitated as mineral struvite. If successfully tested on real urine, this process could be applied to treat the urine collected in urban areas e.g., high-rise building. After the filtration, the solid struvite could be sold for inland applications whereas the diluted fertiliser used for direct fertigation of green walls, parks or for urban farming. Finally, reduction in the load of N, P to the downstream wastewater treatment plant would also ensure a more sustainable urban water cycle.

Application of volume-retarded osmosis and low-pressure membrane hybrid process for water reclamation

A new concept of volume-retarded osmosis and low-pressure membrane (VRO-LPM) hybrid process was developed and evaluated for the first time in this study. Commercially available forward osmosis (FO) and ultrafiltration (UF) membranes were employed in a VRO-LPM hybrid process to overcome energy limitations of draw solution (DS) regeneration and production of permeate in the FO process. To evaluate its feasibility as a water reclamation process, and to optimize the operational conditions, cross-flow FO and dead-end mode UF processes were individually evaluated. For the FO process, a DS concentration of 0.15 g mL^-1 of polysulfonate styrene (PSS) was determined to be optimal, having a high flux with a low reverse salt flux. The UF membrane with a molecular weight cut-off of 1 kDa was chosen for its high PSS rejection in the LPM process. As a single process, UF (LPM) exhibited a higher flux than FO, but this could be controlled by adjusting the effective membrane area of the FO and UF membranes in the VRO-LPM system. The VRO-LPM hybrid process only required a circulation pump for the FO process. This led to a decrease in the specific energy consumption of the VRO-LPM process for potable water production, that was similar to the single FO process. Therefore, the newly developed VRO-LPM hybrid process, with an appropriate DS selection, can be used as an energy efficient water production method, and can outperform conventional water reclamation processes.