Draw Solution Research Articles

Pre-ozonation coupled with forward osmosis with fertilizer as draw solution for simultaneous wastewater treatment and agricultural irrigation

Membrane-based processes have emerged as effective solutions for treating tannery wastewater. Persistent membrane fouling remains a significant obstacle to long-term operational sustainability, and residual pollutants often persist in the treated effluent. To address these challenges, we investigated an integrated ozone-forward osmosis (O3-FO) process, with a focus on evaluating the efficacy of pre-ozonation in alleviating membrane fouling, as well as exploring the possibilities of this integrated process for the reuse of tannery wastewater. Fertilizer, specifically 2 M Ca(NO3)2, served as the draw solution (DS) in this process. The findings reveal that the integrated system demonstrated remarkable pollutant retention capabilities. Notably, no metal was detected in the fertilizer. Therefore, the integrated process not only dilutes the fertilizer but also minimizes the risk of heavy metal contamination to both crops and soil. Furthermore, pre-ozonation effectively mitigated membrane fouling, resulting in an increase in membrane flux with a maximum increase of 20.98 % at 0.6 L/min. Orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed pre-ozonation has the most significant impact on four parameters: water flux (Jw), chemical oxygen demand (COD), fouling resistance (Rf) and oxidation reduction potential (ORP). Meanwhile, ammonium nitrogen (NH4-N) variation, dissolved organic carbon (DOC) variation and ORP played an important role in the four systems. Multi-criteria decision analysis (MCDA) showed that the 0.2 L/min O3-FO system achieved the highest score (0.66), followed by 0.6 L/min (0.53), 0.4 L/min (0.41) and 0 L/min (0.29). This research offers a theoretical framework for the synergistic integration of advanced oxidation and membrane technology in the treatment of industrial wastewater.

A two-step approach to recycling hydroponics waste nutrient solutions using fertiliser drawn forward osmosis and chemical precipitation

Hydroponic waste nutrient solutions (HWNS) present significant environmental and economic challenges due to their high phosphorus content and potential for eutrophication. Addressing these issues requires innovative approaches that mitigate environmental impacts and recover valuable resources. This study introduces a novel two-step approach that combines Fertiliser Drawn Forward Osmosis (FDFO) and chemical precipitation to recycle HWNS effectively.In the first phase, FDFO was employed to concentrate HWNS using a commercial hydroponic fertiliser as the draw solution. This process resulted in a diluted fertiliser solution (potentially suitable for reuse in hydroponics irrigation) and a concentrated HWNS rich in phosphorus. The concentrated HWNS was then subjected to chemical precipitation in the second phase, where phosphorus was recovered as calcium phosphate by adding sodium hydroxide at an optimised pH of 9.5.Bench-scale experiments demonstrated a 93% water recovery rate using FDFO and an impressive 99.5% phosphorus removal efficiency through chemical precipitation. These results indicate that the combined FDFO and chemical precipitation processes effectively recover water and phosphorus from HWNS and reduce reliance on synthetic fertilisers and freshwater in hydroponic systems.The findings of this study demonstrate that the two-step approach not only enhances water and phosphorus recovery but also improves the efficiency of the chemical precipitation process by achieving higher recovery rates resulting in more sustainable hydroponic systems.

Membrane fouling in integrated forward osmosis and membrane distillation systems – A review

With the increase in water consumption, especially by the industrial and agricultural sectors, more strategies capable of increasing the recovery and reuse of water resources have been sought. An example of technology that assists in this challenge is membrane separation processes. However, systems that use this type of separation may be limited by the phenomenon of fouling. Integrated systems such as forward osmosis (FO) with membrane distillation (MD) have several advantages, such as obtaining a high-quality permeate from raw wastewater, the constant regeneration of the draw solution, which assists in continuous operation, and the possibility of association with biological tanks that enable nutrients recovery. However, these systems face limitations related to low flux values caused by membrane fouling. Therefore, the present review seeks to study fouling in integrated FO-MD systems to understand the main challenges of applying this technology and achieving higher permeate flux values. From the most recent studies, many strategies are being evaluated, such as different membrane materials, deposition of antifouling materials on membrane surface, feed temperature, draw solution substances, concentration and temperature, use of spacers and new modules configurations. That way, the low flux from those systems may be bypassed, enabling FO-MD systems scale up.

Enhancing nutrient water recovery: An integrated electrodialysis – Forward osmosis approach for reduced energy consumption and membrane fouling

The concept of combining electrodialysis (ED) and forward osmosis (FO) was previously introduced and proven effective in recovering nutrients and clean water from anaerobic effluents to produce safe liquid fertilizer. In this study, a novel and improved EDFO configuration (iEDFO) was proposed by merging the ED diluate with the FO feed solution and the ED concentrate with the FO draw solution, thus overcoming concentration limitations and fouling challenges inherent in traditional ED processes. Experimental results demonstrated significant improvements in performance, including up to 54 % and 43 % reductions in operation time and 21 % and 25 % energy savings for synthetic and real liquid digestate, respectively. These enhancements were attributed to altered ionic composition within the ED process, leading to higher, more stable current density and reduced ion back diffusion. Unlike conventional ED-only systems, the iEDFO configuration enabled continuous operation without requiring larger membrane areas or variable operational conditions. Additionally, the iEDFO configuration benefited from (1) reduced membrane fouling, and (2) decreased transport of organic contaminants across the anion exchange membranes (AEMs) into the ED concentrate product. Overall, the iEDFO system provides significant advantages in efficiency, energy savings, and operational stability, making it a highly effective and sustainable solution for resource recovery from liquid waste.

Reverse Solute Diffusion Enhances Sludge Dewatering in Dead-End Forward Osmosis.

Wastewater treatment plants produce high quantities of excess sludge. However, traditional sludge dewatering technology has high energy consumption and occupies a large area. Dead-end forward osmosis (DEFO) is an efficient and energy-saving deep dewatering technology for sludge. In this study, the reverse osmosis of salt ions in the draw solution was used to change the sludge cake structure and further reduce its moisture content in cake by releasing the bound water in cell. Three salts, NaCl, KCl, and CaCl2, were added to the excess sludge feed solution to explore the roles of the reverse osmosis of draw solutes in DEFO. When the added quantities of NaCl and CaCl2 were 15 and 10 mM, respectively, the moisture content of the sludge after dewatering decreased from 98.1% to 79.7% and 67.3%, respectively. However, KCl did not improve the sludge dewatering performance because of the "high K and low Na" phenomenon in biological cells. The water flux increased significantly for the binary draw solute involving NaCl and CaCl2 compared to the single draw solute. The extracellular polymer substances in the sludge changed the structure of the filter cake to improve the formation of water channels and decrease osmosis resistance, resulting in an increase in sludge dewatering efficiency. These findings provide support for improving the sludge dewatering performance of DEFO.

Mathematical modeling of osmotic membrane bioreactor process for oily wastewater treatment

ABSTRACT To evaluate the disposal effluent from the Aldura refinery in Iraq, which comprises oily wastewater, a mathematical model has been developed for both forward osmosis (FO) and osmotic membrane bioreactor (OsMBR). The procedure is explained mathematically, accounting for both the concentration and polarization aspects. As a result of mathematical modeling, the water flux was determined by the osmotic pressure, the concentration, and the polarization of the feed and draw solutions. Based on traditional methods of predicting water flux using external and internal concentration polarizations, it is determined that water flux will occur in the first model (Model-1). To increase the accuracy of Model-1, the resistivity (K) of the solute has been modified to be independent of the diffusivity of the solute. The old model (Model-1) and the updated model (Model-2) overestimated water flux by 17 and 25%, respectively. It was possible to make a valid comparison between the experiment and theory based on the results of both experiments.

Fertilizer-driven FO and MD integrated process for shale gas produced water treatment: Draw solution evaluation and PAC enhancement

It is a great challenge for effective treatment of shale gas produced water (SGPW), a typical industrial wastewater with complex composition. Single forward osmosis (FO) or membrane distillation (MD) process has been widely used for desalination of SGPW, with membrane fouling not well addressed. Fertilizer draw solution (DS) with high osmotic pressure is less likely to cause FO fouling and can be used for irrigation. An integrated process using fertilizer-driven FO (FDFO) and MD process was proposed for the first time for SGPW treatment, and characteristics of fertilizer DS and powdered activated carbon (PAC) enhancement were assessed. The DS using KCl and (NH4)2SO4 had high MD fluxes (36.8–38.8 L/(m2·h)) and low permeate conductivity (below 50 μS/cm), increasing the contact angle of the MD membrane by 113 % than that without FO, while the DS using MgCl2 and NH4H2PO4 produced a lower reverse salt flux (0.9–3.2 g/(m2·h)). When diluted DS was treated using PAC, the MD permeate conductivity was further reduced to 35 μS/cm without ammonia, and the membrane hydrophobicity was maintained to 71–83 % of the original. The mechanism of the FDFO-MD integrated process for mitigating MD fouling and improving permeate quality was analyzed, providing guidance for efficient SGPW treatment.

Critical flux-based fouling control method for forward osmosis during simultaneous thickening and digestion of waste activated sludge

The use of forward osmosis (FO) membranes for simultaneous thickening and digestion of waste activated sludge (WAS) (FO-MSTD) has recently garnered significant interest. However, a major challenge hindering the widespread adoption of the FO-MSTD process is severe membrane fouling, which results from increasing sludge concentrations and deteriorating sludge properties. In response, this study proposes a novel FO membrane fouling control strategy based on the critical flux concept, involving a variable draw solution (DS) operating mode. Two operating modes were examined based on the critical flux behavior of the FO membrane: a constant DS concentration mode (with a fixed DS concentration of 1.5 M, referred to as Constant DS1.5) and a variable DS concentration mode (with varying DS concentrations at different operational stages, referred to as Variable DS1.5-1.0 and Variable DS1.5-0.75). Over 21 days of operation, the MLSS concentrations of WAS in the Constant DS1.5, Variable DS1.5-1.0, and Variable DS1.5-0.75 reactors increased from initial values of 3.46, 3.88, and 4.20 g/L to 35.2, 31.5, and 29.2 g/L, respectively. Concurrently, the cumulative digestion rates of MLVSS in the three FO-MSTD processes reached 29.3 %, 29.0 %, and 36.3 %, respectively. After adjusting the DS concentration, the FO membrane flux decay rates for Constant DS1.5, Variable DS1.5-1.0, and Variable DS1.5-0.75 were 57.7 %, 49.4 %, and 13.8 %, respectively. In addition to experiencing a lower flux decline, the Variable DS1.5–0.75 mode achieved a significantly higher flux recovery rate of 98.5 % compared to the other two modes. Moreover, the biovolume of proteins and microorganisms in the membrane fouling layer decreased by 85.2 % and 72.7 %, respectively, in the Variable DS1.5–0.75 mode compared to the Constant DS1.5 mode. These findings indicate that operating with a DS below the critical concentration can significantly improve the reversibility of membrane fouling and reduce the presence of organic and biological foulants in the fouling layer, thereby mitigating membrane fouling in the FO-MSTD reactor.

Novel draw solution system based on trisodium dicarboxymethyl alaninate for water desalination applications

Novel draw solution system based on trisodium dicarboxymethyl alaninate for water desalination applications

Fouling-resistant Na-ZSM-5 zeolite membrane for fruit juice concentration in forward osmosis process

To evaluate the potential of Na-ZSM-5 membrane for liquid food concentration, the concentration of fruit juice by a tubular Na-ZSM-5 membrane was demonstrated in forward osmosis operation. Apple, orange, and pineapple juices were successfully concentrated, maintaining their quality without contamination by a draw solution based on a molecular sieving effect of the zeolite membrane. For example, the sugar content of apple juice increased from 10.7 to 17.1 oBrix after 24 h of dehydration. The fouling resistance of Na-ZSM-5 membrane was evaluated using a 10 g L-1 pectin solution and cellulose suspension. Na-ZSM-5 membrane showed stable dehydration performance for fruit juice concentration over 120 h without fouling due to pectin or cellulose. In addition, the membrane exhibited high heat resistance, with no deterioration up to 353 K. We showed that Na-ZSM-5 membrane is a potential material for fruit juice concentration because of its superior heat, acidity, and fouling resistances.

Energy comparison and cost estimation of pressure-retarded osmosis using spiral wound membrane

Advancements in Pressure Retarded Osmosis (PRO) technology are enhancing the feasibility of evaluating its economic viability against other renewable energy production methods. This is done using the Levelized Cost of Energy (LCOE) as a metric. The study focuses on three PRO scenarios designed to minimize environmental impact and promote sustainable energy. These scenarios utilize a spiral-wound membrane module combined with hyper-saline solutions from Reverse Osmosis (RO) and wastewater from demineralization processes. Experimental results using a commercial spiral-wound membrane in the PRO system yielded LCOE values of USD 0.0702/kWh for a draw solution (DS) concentration of 36.2 g/l, USD 0.0563/kWh for 44.2 g/l, and USD 0.0721/kWh for 51.8 g/l. The study also evaluated environmental viability by considering the cost of CO2 emissions. This comprehensive comparison highlighted PRO's competitiveness with fossil fuels, showing it to be a reasonable alternative to coal and oil but less practical than natural gas. Specifically, the environmental analysis revealed that PRO is approximately 25.2 % more competitive than coal and 9.76 % more competitive than oil but 27.16 % less competitive compared to natural gas in terms of CO2 emission costs. This underscores the importance of considering carbon emission mitigation in energy generation.

Incorporation of zeolitic imidazolate framework-8 (ZIF-8) in the polyamide and polysulfone layers of forward osmosis membranes for enhancing aquaculture wastewater recovery and PPCPs removal

Wastewater recovery is essential to alleviate water resource shortages, and this can be achieved through a high-energy-efficient forward osmosis (FO) process combined with an emerging material, zeolitic imidazolate framework-8 (ZIF-8). Here, we create thin-film composite FO membranes (TF-CFOMs) by incorporating ZIF-8 into the active polyamide (PA) and/or support polysulfone (PSf) layers to address the challenges of low water flux and loss of draw solutes during operation. Experimental factors included the dosage of ZIF-8 nanoparticles in PA preparation solutions and the dosages of 2-methylimidazole (2-Hmim) and zinc nitrate hexahydrate (ZNH) in n-methyl-2-pyrrolidone (NMP) to fabricate the PSf casting solutions with in-situ formed ZIF-8 nanoparticles. Successful ZIF-8 incorporation on the TF-CFOM surface was confirmed, and the ZIF-8 TF-CFOMs exhibited increased surface hydrophilicity and separation performance. Only modifying the PA layer by adding 0.025 wt% ZIF-8 nanoparticles in trimesoyl chloride (TMC) resulted in the membrane (PA0.025T-PSf0) with water flux 2.3 times higher than the pristine TF-CFOM (4.9 LMH). The pristine and modified TF-CFOMs were further applied for aquaculture wastewater (AWW) recovery and removal of pharmaceuticals and personal care products (PPCPs). Results of water recovery demonstrated that the recovery rate reached 89.1% in 3.5 days when using the dual-layer modified TF-CFOM. Results of PPCP removal indicated that both pristine and modified TF-CFOMs can achieve high PPCP rejection efficiency (>90%), with the modified TF-CFOM (PA0.025T-PSf2.0) performing the best. Overall, the PA0.025T-PSf2.0 TF-CFOM achieved high and stable separation efficiency in long-duration AWW recovery, making it well-suited for practical field applications.

Agarose-coated Fe3O4 magnetic nanoparticles (ACMNPs) as draw solute for enhance forward osmosis (FO) desalination

Drawing on the collective insights and findings of prior researchers in the field of draw solution (DS) exploration, we have synthesized agarose-coated Fe3O4 magnetic nanoparticles (ACMNPs) with precise control at each stage to achieve superparamagnetic properties. This allows them to be separated from the DS at the end of the forward osmosis (FO) desalination process using a magnet, thereby producing fresh water. Furthermore, coating the magnetic nanoparticles (MNPs) with agarose, a superhydrophilic polymer, increases their solubility in an agarose-shell/Fe3O4-core structure. This approach represents the culmination of our efforts and ensures alignment with our desired objectives. In the experimental phase, Fe3O4 MNPs and ACMNPs were compared at different concentrations as draw solutes in the FO desalination process. The results demonstrated the effect of the agarose coating on the hydrophilicity of the ACMNPs. Ultimately, the findings indicate that MNPs, when appropriately coated with agarose, can be used as effective draw solutes in FO systems.

Forward osmosis for concentrating lithium-enriched brine: From membrane performance to system design

Using concentrated salt-lake brine as the draw solution (DS), forward osmosis (FO) has been proposed as the low carbon footprint concentration technology for extracting water from lithium-enriched brine. From membrane modules to a process, there exist tremendous risks when considering total cost in time and investment for a trial. To address this issue, a bridge between the FO membrane/ module characteristics and a FO system design is highly desirable. This study for the first time developed a system design model using hollow fiber (HF) FO membrane modules for FO concentration of lithium-enriched brine. The concentration polarization along the module, the membrane structural parameters (S), crossflow velocity, and DS concentration were the main factors considered in the model. The effect of all factors on module water flux and total membrane area was systematically investigated for a typical industrial output of 10 k ton of Li2CO3. A master curve of the water flux verse feed concentration for the tailor-made HF modules was utilized as the basis. On a module scale, the structural parameter S is of first importance and indicates requirement of FO membranes with low S. The crossflow velocity has relatively small impact to the membrane area, but not negligible. On a system scale, the empirical equation of the structural parameters and crossflow velocity on the theoretical minimum system membrane area was summarized. The results show that increasing the stages can reduce the number of modules and required DS flow. Increasing DS dilution rate in system design efficiently utilizes the osmotic pressure of DS. The present model serves as a practical solution for process optimization and FO membrane selection. The methodology is valuable for other FO applications using HF FO membranes.

Investigating Water and Ion Transport in a Novel Cell Design for Seawater Electrolysis

With increasing concerns about the climate change associated with the carbon dioxide emission from utilizing traditional fuels, hydrogen has become a preferred low-carbon energy carrier. For hydrogen to truly be a clean source of energy, it must be produced from a renewable source of energy through water electrolysis. Theoretically, for each kilogram of hydrogen to be produced 9 kg of high-purity water need to be consumed, thus the enormous use of clean water for H2 production may worsen the shortage of fresh water in many parts of the world.Owing to its abundance, seawater has received great attention in the field of hydrogen production; however, there are many challenges associated with the direct use of seawater for electrolysis. In traditional systems, the seawater is first deionized by reverse osmosis (RO) before being fed to the electrolyzer. The RO system adds complexity to the system and requires energy to be expended for the deionization. Therefore, modern systems have aimed to directly electrolyze seawater, but this comes with it own issues including electrode corrosion, scaling from the ions present in saline water, environmental concerns associated with competitive chlorine evolution reaction, and increased membrane resistance limiting the overall performance of saline water electrolysis. Several strategies have been proposed to overcome these challenges including developing selective electrocatalysts, blocking strategy, pH buffer strategy, etc.This project sought to overcome the issues with direct seawater utilization by designing a cell that is driven by osmotic separation, but does not require an external power source. In this device, high concentration acid/base concentrations are maintained in contact with another compartment containing seawater. The acid/base reservoirs act as draw solutions, taking water passively from seawater due to their differences in osmotic pressure. This talk will focus on the cell design and operation, and include both experimental and modeling results. The rate of water transport with various cell operating configurations was quantified alongside the rate of chloride ion crossover through the anion exchange membrane. New methods for chloride mitigation were explored – including cell operating conditions, membrane design and absorption. Multiple cell configurations will be shown and strategies for reducing the cell operating voltage will be discussed.

Enhanced forward osmosis desalination of brackish water using phase-separating ternary organic draw solutions of hydroxypropyl cellulose and propylene glycol propyl ether.

This study introduces draw solutions for application in forward osmosis (FO) processes, combining mono propylene glycol propyl ether (PGPE) with the cellulose derivative hydroxypropyl cellulose (HPC). A total of 16 unique single-solute and ternary organic draw solutions were prepared and evaluated, leading to the selection of three promising solutions for further investigation. Notably, eight of the initial organic draw solutions demonstrated osmotic pressures exceeding 2.4MPa. The dynamic viscosities of all draw solutions exhibited a significant reduction with increasing temperature. Among the investigated solutions, the 0.25HPC-3.75PGPE demonstrated the most favorable FO performance, achieving average experimental water fluxes of 11.062 and 9.852 Lm-2h-1 (LMH) against a 1g/L NaCl brackish feed solution across two FO runs. PRACTITIONER POINTS: Hydroxypropyl cellulose (HPC, MW ~100,000) was mixed with propylene glycol propyl ether (PGPE) as draw solutes for FO processes. Seven combinations of HPC and PGPE produced osmolalities greater than 1000 mOsm/kg. 0.5HPC-7.5PGPE ternary draw solution achieved experimental water fluxes of 11.062 and 9.852 LMH against 1g/L NaCl brackish feed solution. Leveraging the LCSTs of these ternary organic solutions holds promise for improved separation and regeneration processes.

Polyvinyl alcohol-modified β-cyclodextrin incorporated forward osmosis membranes with good chlorine resistance

The applications of β-cyclodextrin (β-CD) in chlorine-resistant membranes have always faced the challenge of agglomeration at high concentrations. In this study, polyvinyl alcohol (PVA) modified β-CD was used as a monomer to prepare forward osmosis (FO) membranes with high chlorine resistance. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), automated contact angle meter (CAM), electrodynamic analyzer (EA), X-ray photoelectron spectroscopy (XPS), and true color confocal microscopy (CSM) have been used to characterize the physicochemical properties of the FO membrane. The agglomerated β-CD affected the formation of the selective layer, resulting in reduced water fluxes ranging from 12.4 L m−2 h−1 to 1.75 L m−2 h−1. The modified TFC-PVA-β-CD FO membrane had a complete, defect-free selective layer, and water flux of 16.75 L m−2 h−1 at 1 M NaCl as a draw solution. FTIR spectra showed that the absorption peak intensity of the carbonyl (CO) group generated from β-CD and 1,3,5-Benzene tricarbonyl trichloride (TMC) increased after PVA modification. After 6 hours of chlorination, the reverse salt flux of the thin film composite (TFC) FO membranes abided by the following order: TFC (80.35 g m−2 h−1) > TFC-β-CD (60.95 g m−2 h−1) > TFC-PVA-β-CD (12.45 g m−2 h−1). The results indicated that the PVA effectively promotes uniform dispersion of β-CD. More chlorine-resistant ester bonds (-COO-) were formed in the TFC-PVA-β-CD FO membrane, so it possessed good chlorine resistance. This study provides a green, simple, and environmentally economical method for the preparation of chlorine-resistant FO membranes.

ABPBI-based hollow fiber membranes for forward osmosis (FO) possessing low reverse salt flux

The poly(2,5-Benzimidazole), known for its excellent thermochemical stability, was evaluated as a membrane material for forward osmosis. The dope in methane sulfonic acid was used to make hollow fiber membranes. The availability of bound MSA in HFMs was compared with its neutral form. Aqueous solutions of two common salts reported for FO (NaCl and MgCl2) were used as a draw solution at varying concentrations. The performance was determined in terms of water flux and reverse salt flux. The long-term performance of the membrane was assessed. The heat pretreatment of membranes was beneficial in offering low reverse salt flux, a crucial parameter in FO. The heat treatment at 350 °C exhibited excellent performance of low-RSF, irrespective of the draw solute used. The presence of MSA in the membrane matrix was found to be beneficial. Present HFMs exhibited reverse salt flux as low as 0.003 mol m−2 h−1 using 2 mol L−1 MgCl2 as a draw solution. The water flux of present membranes was lower than that of reported FO-membranes, which is attributable to the larger thickness of the present membranes. The findings will be used to make ABPBI-based membranes in thin form to elevate the fluxes and their practical applicability.

Thermal Desalination Through Forward Osmosis Coupled With CO2-Mixture Power Cycles for CSP Applications

This work, performed in the framework of the H2020 EU project “DESOLINATION”, analyses the coupling between CSP plants using transcritical power cycles with CO2-mixtures and an innovative thermal desalination technique based on Forward Osmosis. Calculations are presented for a large scale CSP plant with central tower receiver and direct storage with solar salts in Dubai, adopting the mixtures CO2+SO2 and CO2+C6F6 in the power cycles. The heat rejected from the cycle condenser is recovered directly by the FO plant, where the draw solute is heated up from 40 °C to 76 °C, to allow for the regeneration of the draw solution used in the forward osmosis membrane. The thermo-responsive polymer adopted is PAGB2000, already considered in literature as a promising option. Results show a very effective synergy between the electricity and the freshwater production: high yearly solar to electric efficiencies are possible (around 19%), with a low freshwater specific thermal consumption (around 100 kWhth/m3). The proposed desalination method is more effective than a conventional MED system (with + 50% of yearly freshwater produced), while a larger solar field (+ 28% in surface area) is necessary for a PV+RO plant to produce annually both the energy and freshwater produced by the CSP+FO plants.

Enrichment of nutrients from anaerobically digested centrate minimizing microplastics content using a combination of membrane processes

Centrifuge effluent, or centrate, is a liquid stream generated in the sludge line of wastewater treatment plants in the sludge dewatering process. Nutrients are solubilized in the anaerobic digestion of the sludge, mainly in the form of ammonium-nitrogen and phosphates. Thus, when the dewatering of the digested sludge is performed (usually by centrifugation), a sludge liquor stream enriched in nutrients is generated. However, it also contains microparticles, including microplastics, since most of the microparticles from the wastewater are transferred to the sludge treatment line in wastewater treatment plants. In this work, microplastics in centrate have been analyzed (counted and identified), and membrane technologies (ultrafiltration and forward osmosis) have been applied to concentrate nutrients and to obtain a microplastic-free stream for further nutrient recovery. Two alternative configurations have been compared, changing the application order of these processes. The results showed that obtaining a stream with a concentration higher than 6000 mg/L of ammonium has been possible by using ammonium sulfate (150 g/L) as a draw solution in the forward osmosis process. On the other hand, as a consequence of the ultrafiltration application, microparticles were concentrated in the reject stream up to 800 microparticles/L. At the same time, the permeate presents a lower concentration of microplastics without reducing the concentration of the nutrients. In this way, this pioneering study enables the production of a nutrient-enriched stream with reduced microplastic concentrations, that could be applied to the agricultural soil as biofertilizer.