Liquid-liquid Membrane Contactors Research Articles

Liquid-liquid extraction of phenolic wastewater through a surface modified poly(vinylidene fluoride-co-hexafluoropropylene) hollow fiber membrane contactor and process optimization

BackgroundStrict environmental regulations have been recognized for phenolic wastewater treatment due to toxicity of the phenolic compounds. In this study, solvent extraction of a phenolic wastewater was investigated via a liquid-liquid membrane contactor system. MethodsPorous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were modified by coating an ultra-thin layer of hydrophobic surface modifying macromolecule (SMM). The membranes were characterized by various tests such as SEM-EDS, nitrogen permeation, overall porosity, contact angle and critical water entry pressure (CEPw). Significant findingsFrom SEM, an open structure with combination of finger-like and sponge-like structure was produced. The membrane exhibited high surface hydrophobicity (water contact angle of 109°) with good wetting resistance, overall porosity of 82% and mean pore size of 18 nm. From response surface methodology (RSM), the maximum phenol extraction flux of 2.02 × 10−3 kg/m2s was estimated by the model at the optimum process variables as phenol concentration of 448 mg/L, feed temperature of 42 °C, aqueous phase flowrate of 196 mL/min and organic phase flowrate of 117 mL/min. The coefficient of determination (R2) of 0.972 showed a close proximity between the model and the experimental data. The membrane showed a reasonable flux that can be a favorable alternative for industrial phenolic wastewater treatment.

Environmental and economic evaluation of implementing membrane technologies and struvite crystallisation to recover nutrients from anaerobic digestion supernatant

The present study investigates the environmental and economic feasibility of implementing membrane technologies and struvite crystallisation (SC) for nutrient recovery from the anaerobic digestion supernatant. To this end, one scenario combining partial-nitritation/Anammox and SC was compared with three scenarios combining membrane technologies and SC. The combination of ultrafiltration, SC and liquid–liquid membrane contactor (LLMC) was the less environmentally impactful scenario. SC and LLMC were the most important environmental and economic contributors in those scenarios using membrane technologies. The economic evaluation illustrated that combining ultrafiltration, SC and LLMC (with or without reverse osmosis pre-concentration) featured the lowest net cost. The sensitivity analysis highlighted that the consumption of chemicals for nutrient recovery and the ammonium sulphate recovered had a large impact on environmental and economic balances. Overall, these results demonstrate that implementing membrane technologies and SC for nutrient recovery can improve the economic and environmental implications of future municipal wastewater treatment plants.

Advanced Hybrid System for Ammonium Valorization as Liquid Fertilizer from Treated Urban Wastewaters: Validation of Natural Zeolites Pretreatment and Liquid-Liquid Membrane Contactors at Pilot Plant Scale.

This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH3) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before the HFMC. The system was tested with wastewater treatment plant (WWTP) effluent (mainstream, 50 mg N-NH4/L) and anaerobic digestion centrates (sidestream, 600-800 mg N-NH4/L) from another WWTP. Natural zeolite, primarily clinoptilolite, demonstrated effective desorption of retained ammonium using a 2% NaOH solution in a closed-loop configuration, resulting in an ammonia-rich brine that enabled over 95% NH3 recovery using polypropylene HFMCs. A 1 m3/h demonstration plant processed both urban wastewaters, which were pretreated by ultrafiltration, removing over 90% of suspended solids and 60-65% of COD. The 2% NaOH regeneration brines (2.4-5.6 g N-NH4/L) were treated in a closed-loop HFMC pilot system, producing 10-15% N streams with potential use as liquid fertilizers. The resulting ammonium nitrate was free of heavy metals and organic micropollutants, making it suitable for use as liquid fertilizer. This comprehensive N management solution for urban wastewater applications can contribute to local economies while achieving reduced N discharge and circularity goals.

Reclaiming of Amine CO2 Solvent Using Extraction of Heat Stable Salts in Liquid-Liquid Membrane Contactor

Amine CO2 solvents undergo oxidative degradation with the formation of heat stable salts (HSS). These HSS reduce the sorption capacity of amines and lead to intense corrosion of the equipment. In our work, we propose a membrane-supported liquid-liquid extraction of the HSS from alkanolamines. For this purpose, a hollow fiber membrane contactor was used for the first time. A lab-scale extraction system on the basis of a hollow-fiber liquid-liquid membrane contactor with hollow fiber ultrafiltration polyvinylidenefluoride and polysulfone membranes has been studied. The extraction of the HSS-ions from a 30 wt.% solution of monoethanolamine was carried out using a 0.25-1 M solution of OH-modified methyltrioctylammonium chloride in 1-octanol as an extractant. It has been shown that >90% of HSS ions can be extracted from the alkanolamine solvent within 8 h after extraction. The results obtained confirm the possibility of using membrane extraction with a liquid-liquid membrane contactor for the reclaiming of amine CO2 solvents to increase the general efficiency of carbon dioxide capture.

Ammonia Valorization by Liquid-Liquid Membrane Contactors for Liquid Fertilizers Production: Experimental Conditions Evaluation.

Liquid–liquid membrane contactors (LLMCs) were studied as a sustainable technology for ammonia recovery from wastewater. Ammonia can be valorized by LLMCs as a potential nutrient and produce liquid fertilizers. Thus, this work aims for the study of different experimental LLMC conditions to produce ammonium salts by an acid stripping stream. The experiments were conducted using two 3MTMLiqui-CellTM LLMC in a series, located in the vertical position and using HNO3 as the acid stripping solution. The flow rates for the feed and stripping sides were fixed during the tests, and two steps were conducted based on previous works. However, different experimental conditions were evaluated to determine its effect on the overall performance: (i) replacing the feed or stripping solution between the steps, (ii) the initial ammonia concentration of the feed solution, (iii) feed volume and (iv) feed temperature. The results demonstrated that better achievements were obtained replacing the acid stripping solution between steps, whereas the feed temperature did not substantially affect the overall performance. Additionally, a high initial ammonia concentration provided more ammonia recovery, although the concentration factor achieved was higher for the low initial ammonia concentration. Finally, a high feed volume afforded better results for the fertilizer side, whereas more NH3 recovery was achieved using less feed volume.

Ammonia recovery from anaerobic digester centrate using onsite pilot scale bipolar membrane electrodialysis coupled to membrane stripping

Ammonia recovery from centrate of an anaerobic digester was investigated using an onsite bipolar-electrodialysis (BP-ED) pilot scale plant coupled to two liquid/liquid membrane contactor (LLMC) modules. To investigate the process performance and robustness, the pilot plant was operated at varying current densities, load ratio (current to nitrogen loading), and in continuous and intermittent current (Donnan) mode. A higher load ratio led to higher total ammonium nitrogen (TAN, sum of ammonia and ammonium) removal efficiency, whereas the increase in the applied current did not have a significant impact the TAN removal efficiency. Continuous current application resulted in the higher TAN removal compared with the Donnan dialysis mode. The lowest specific energy consumption of 6.3 kWh kgN−1 was recorded in the Donnan mode, with the load ratio of 1.4, at 200 L h−1 flowrate and current density of 75 A m−2. Lower energy demand observed in the Donnan mode was likely due to the lower scaling and fouling of the ion exchange membranes. Nevertheless, scaling and fouling limited the operation of the BP-ED stack in all operational modes, which had to be interrupted by the daily cleaning procedures. The LLMC module enabled a highly selective recovery of ammonia as ammonium sulfate ((NH4)2SO4), with the concentration of ammonia ranging from 19 to 33 gN L−1. However, the analysis of per- and polyfluoroalkyl substances (PFASs) in the obtained (NH4)2SO4 product revealed the presence of 212–253 ng L−1 of 6:2 fluorotelomer sulfonate (FTS), a common substitute of legacy PFAS. Given the very low concentrations of 6:2 FTS (i.e., < 2 ng L−1) encountered in the concentrated stream, 6:2 FTS was likely released from the Teflon-based components in the sulfuric acid dosage line. Thus, careful selection of the pilot plant tubing, pumps and other components is required to avoid any risks associated with the PFAS presence and ensure safe use of the final product as fertilizer.

Interphase Surface Stability in Liquid-Liquid Membrane Contactors Based on Track-Etched Membranes.

A promising solution for the implementation of extraction processes is liquid–liquid membrane contactors. The transfer of the target component from one immiscible liquid to another is carried out inside membrane pores. For the first time, highly asymmetric track-etched membranes made of polyethylene terephthalate (PET) of the same thickness but with different pore diameters (12.5–19 nm on one side and hundreds of nanometers on the other side) were studied in the liquid–liquid membrane contactor. For analysis of the liquid–liquid interface stability, two systems widely diverging in the interfacial tension value were used: water–pentanol and water–hexadecane. The interface stability was investigated depending on the following process parameters: the porous structure, the location of the asymmetric membrane in the contactor, the velocities of liquids, and the pressure drop between them. It was shown that the stability of the interface increases with decreasing pore size. Furthermore, it is preferable to supply the aqueous phase from the side of the asymmetric membrane with the larger pore size. The asymmetry of the porous structure of the membrane makes it possible to increase the range of pressure drop values between the phases by at least two times (from 5 to 10 kPa), which does not lead to mutual dispersion of the liquids. The liquid–liquid contactor based on the asymmetric track-etched membranes allows for the extraction of impurities from the organic phase into the aqueous phase by using a 1% solution of acetone in hexadecane as an example.

Study of the operational parameters in the hollow fibre liquid-liquid membrane contactors process for ammonia valorisation as liquid fertiliser

The transformation of wastewater treatment plants (WWTPs) to resources recovery plants (nutrients and energy) is forcing the development of specific technologies for selective recovery. Ion-exchange and hollow fibre liquid-liquid membrane contactors (HF-LLMCs) appeared as promising technologies to reduce operation costs, at ambient temperature, on the N-recovery from main-streams of urban WWTPs. A concentrated ammonia stream (4.5 g/L), recovered from treated wastewater using zeolites and NaOH, was used to test different operational parameters on the performance of the HF-LLMC process for ammonia recovery. These tested parameters were HF-LLMC position (horizontal and vertical), HF-LLMC feed and acid streams inputs (shell and lumen), type of acid stripping solution (0.4 M H3PO4 and 0.4 M HNO3), membrane drying, flow rate for each stream (263–770 mL/min), number of steps (1 and 2) and number of membrane contactors (1 and 2 in series). The maximum ammonia recovery (>95%) was achieved by a one-step configuration using two vertical membrane contactors in series; using the shell side for feed stream and the lumen side for the acid stripping solution (HNO3); at 450 mL/min and 770 mL/min flow rates for feed and acid stripping solutions, respectively. The liquid fertiliser composition obtained was around 4.6% N (from NH4+). Additionally, the ammonia treated stream, rich in NaOH, had residual levels of NH3 (about 200 mg/L) that could be reused for the regeneration of the zeolites. This optimized HF-LLMC process allowed to recover ammonia from a tertiary treatment solution of an urban WWTP and at the same time to produce ammonium salts that could be used as liquid fertilisers in irrigation applications. Therefore, this technology promotes the circular economy concept for nutrient recovery in urban WWTPs.

Integrating crystallisation into transmembrane chemical absorption: Process intensification for ammonia separation from anaerobic digestate

In this study, reactive crystallisation is introduced into a liquid-liquid membrane contactor for the selective separation, purification and recovery of ammonia from concentrated waste. Whilst liquid-liquid membrane contactor technology has been previously demonstrated for ammonia absorption, further process intensification can be achieved by incorporating crystallisation into transmembrane chemisorption to recover the ammonia as crystalline ammonium sulphate. Reactive crystallisation occurred in the draw solution (sulphuric acid) which was supplied to the lumen-side of the polypropylene hollow-fibre. The ammonium sulphate concentration in the draw solution increased through ammonia mass transfer to supersaturation, at which time induction (the onset of nucleation) commenced. Ammonia mass transfer at draw concentrations above the solubility limit was not limited provided sufficient ‘free’ sulphate was available. This resulted in nucleation which occurred at a low level of supersaturation (C/C*, 1.03) to produce small crystals of around 2.5 μm, which indicated that nucleation was favoured. The nucleation rate was found to be proportional to the ammonia flux in the draw solution. As the solution became more saturated, crystal number increased but crystal growth was comparatively small; this is symptomatic of reactive crystallisation, where the rate of reaction exceeds the rate of mass transfer. Due to the large difference in the ratio between the lumen internal diameter and the mean crystal diameter (dfibre/dmean,CSD, ~180), no fibre clogging was observed despite facilitating crystallisation on the lumen-side of the membrane. Transmembrane chemisorption crystallisation presents a feasible process intensification for the selective separation of ammonia from environmental applications. For its integration into environmental applications, solutions to wetting and fouling remain due to associative interactions with the complex organic matrix that are practically achievable through engineering intervention. Subsequent transformation of ammonia into a crystalline phase of ammonium sulphate presents a new product which is of commercial interest.

Integration of liquid-liquid membrane contactors and electrodialysis for ammonium recovery and concentration as a liquid fertilizer.

The accumulation of ammonia in water bodies can cause eutrophication and reduce water quality. Furthermore, 80% of the ammonia in the world is consumed as fertilizer, which makes it a resource that can be recovered under the circular economy concept. Then, ammonia from wastewater can be valorised for agricultural applications. Liquid-liquid membrane contactors (LLMCs) have been postulated as a novel and eco-friendly technology for ammonia recovery, because they can convert dissolved ammonia into ammonium salts by an acid stripping solution. The concentration of the ammonium salt produced is limited by the co-transport of water in LLMC. Further concentration by electrodialysis (ED) is presented as a solution to overcome this problem. In this work, ammonia streams with different initial ammonia concentrations (1.7-4.0g/L) were treated by LLMCs to produce liquid ammonium salt fertilizers (as NH4NO3 and NH4H2PO4). Then, these ammonium solutions were concentrated by ED in order to achieve the nitrogen content required for direct application in agriculture for fertigation. After the LLMC process, the fertilizer obtained was composed of approximately 5.1% or 10.1% (w/w) nitrogen, depending on the initial ammonia concentration. After that, it was possible to concentrate these ammonium salts by a factor of 1.6±0.3 using ED with an optimal energy consumption of 0.21±0.08kWh/kg ammonium salt and 93.1±4.2% of faradaic yield. This gave a liquid fertilizer composed of 15.6% (w/w) nitrogen as NH4NO3. Overall, it was possible to integrate two innovative membrane technologies for the valorisation and concentration of nutrients from ammonia wastewater streams.

Liquid fertilizer production by ammonia recovery from treated ammonia-rich regenerated streams using liquid-liquid membrane contactors

The nitrogen load on urban wastewater should be considered as a secondary resource for nitrogen-based fertilizers. From this point of view, ammonia-rich streams obtained from a regeneration step with zeolites using 70–80 g NaOH/L could contain up to 3.5–4.5 g NH3/L as well as other ionic species (Na+, K+, Ca2+, Mg2+) and dissolved organic matter (DOM). Thus, they could be treated to obtain a valuable product composed by ammonia for fertilizing applications. A sorption pre-treatment process was carried out to remove the residual amount of DOM and to reduce membrane fouling before processing with hollow fibres liquid-liquid membrane contactors (HF-LLMC). Polypropylene HF-LLMC was used to selectively extract ammonia in single or two-step configurations using different acid stripping solutions (H3PO4, HNO3 or a mixture of HNO3/H3PO4). For ammonia recovery, the ammonia mass transfer coefficient (Km(NH3)) and water transport by HF-LLMC were determined. H3PO4 was found to be the best acid stripping solution by one-step HF-LLMC; the ammonia removal was 76% with a Km(NH3) of 8.8 × 10−7 m/s. Additionally, the ammonia was concentrated 26 times, and it was recovered as multi-nutrient liquid fertilizer (NP) composed of 7.8% N and 21.6% P2O5. Furthermore, ammonia recovery was increased, reaching values up to 94%, through two-step HF-LLMC, and again H3PO4 was used as stripping solution. Finally, water transport from the feed to the stripping phase was estimated to be 0.022 L/m2·h for one-step HF-LLMC with H3PO4. Finally, the use of UV–Vis and 2D-Fluorescence was shown to be a successful approach for monitoring pore wetting events.

Membrane contactor aided catalyst recycle and organic acid recovery from aqueous solutions using porous hydrophobic polyvinylidene fluoride barriers

The present study investigates the performance of indigenous hydrophobic polyvinylidene fluoride (PVDF) based porous membranes for separation of valuable organics such as acetamide catalyst and tartaric acid from aqueous media. Dehydration of acetamide was carried using ultraporous hydrophobic PVDF membrane by vacuum membrane distillation (VMD) technique. Effect of feed concentration on membrane performance was studied. Membrane exhibited a high total flux of 0.32 kg/m2h with <1.2% acetamide losses in permeate during concentration of acetamide catalyst from 30% to 70% (w/v). The separation of tartaric acid from synthetic mixture was carried out using indigenous ultraporous PVDF/Polyurethane (PU) blend membrane by liquid-liquid membrane contactor (LLMC) system. Influence of various additives such as LiCl2, ZnCl2, glycerol and polyvinylpyrrolidone (PVP) on membrane performance was studied. PVDF/PU/glycerol membrane exhibited extraction efficiency of nearly 12% for initial acid and extractant concentration of 100 mol/m3 and 30%, respectively, within a processing time of 2 h. All the indigenously synthesized membranes were characterized using analytical tools to study the physico-chemical properties of polymer films. A mathematical model for VMD system has also been developed to validate the experimental results. The study inferred that the processes employed could be considered as alternative techniques over conventional methods for recovery of both solid catalyst and organic acids which are widely used in industry.

Experimental And Mathematical Modeling Studies Of Liquid-Liquid Membrane Contactor

Experimental and modeling studies of the effect of tempetarature on liquid-liquid membrane contactor (LLMC) have been done. The experiments were conducted by varying temperature of 25 up to 80 0C, cross flow velocity from 0.02 to 0.05 m/s and feed concentration of 0, 5000 and 30,000 mg/l. In these experiments microporous hydrophobic hollow fiber polypropylene membrane with 0.2 μm was used as a contacting device. The modeling has been done by compiling mathematic equation of mass and heat transfers in liquid-liquid membrane contactor. Both the experimental and modeling result show, the increase in feed temperature increase the flux of pure water exponentially, whereas the flux decrease with increasing the permeate temperature. The feed temperature increase at higher temperature result in hogher flux increase. The concentration of pure water result in the range of 1.8 to 5.6 mg/l depending on feed concentration.Keywords : membrane contactor, modeling

Recovery of ammonia from domestic wastewater effluents as liquid fertilizers by integration of natural zeolites and hollow fibre membrane contactors.

The integration of up-concentration processes to increase the efficiency of primary sedimentation, as a solution to achieve energy neutral wastewater treatment plants, requires further post-treatment due to the missing ammonium removal stage. This study evaluated the use of zeolites as a post-treatment step, an alternative to the biological removal process. A natural granular clinoptilolite zeolite was evaluated as a sorbent media to remove low levels (up to 100mg-N/L) of ammonium from treated wastewater using batch and fixed bed columns. After being activated to the Na-form (Z-Na), the granular zeolite shown an ammonium exchange capacity of 29±0.8mgN-NH4+/g in single ammonium solutions and 23±0.8mgN-NH4+/g in treated wastewater simulating up-concentration effluent at pH=8. The equilibrium removal data were well described by the Langmuir isotherm. The ammonium adsorption into zeolites is a very fast process when compared with polymeric materials (zeolite particle diffusion coefficient around 3×10-12m2/s). Column experiments with solutions containing 100mgN-NH4+/L provide effective sorption and elution rates with concentration factors between 20 and 30 in consecutive operation cycles. The loaded zeolite was regenerated using 2g NaOH/L solution and the rich ammonium/ammonia concentrates 2-3g/L in NaOH were used in a liquid-liquid membrane contactor system in a closed-loop configuration with nitric and phosphoric acid as stripping solutions. The ammonia recovery ratio exceeded 98%. Ammonia nitrate and di-ammonium phosphate concentrated solutions reached up to 2-5% wt. of N.

Ammonium removal by liquid–liquid membrane contactors in water purification process for hydrogen production

In this work, a liquid–liquid membrane contactor (LLMC) was evaluated to remove ammonia traces from water used for hydrogen production by electrolysis. Three operational parameters were evaluated: the feed flow rate, the initial ammonia concentration in the water stream, and the pH of solution. Synthetic aqueous solutions with ammonium concentration of 5–25 mg L−1 and a sulfuric acid solution (pH 2) were supplied to the LLMC in countercurrent and open-loop configuration with flow rates between 2.72 × 10−6 and 22.6 × 10−6 m3 s−1 and the pH values of the solution with ammonium between 8 and 11. A 2D numerical model was developed considering advection–diffusion equation inside a single fiber of the lumen with fully developed laminar flow and liquid–gas equilibrium in the membrane–solution interface. Predictions of the model were then validated against experimental data, which were found to be in good agreement. According to both, experimental data and numerical predictions, the hollow-fiber membrane contactor technology is a suitable alternative to remove ammonium from water and to feed the membrane distillation unit in order to fulfill water quality requirements for electrolysis-based hydrogen production.