Increasing Feed Temperature Research Articles

Recovery of Whey Protein by Using Microfiltration: Artificial Neural Network–Based Modeling and Effects of Different Operating Parameters

ABSTRACTMicrofiltration is one of the most suitable processes for protein recovery from whey due to its low energy consumption and lack of use of heat and chemicals. However, membrane fouling is one of the limiting factors in the microfiltration process, preventing its commercial use. In this study, an artificial neural network (ANN) based model was employed to study the effects of different operating parameters on membrane fouling in whey concentration. Trans‐membrane pressure, Reynolds number, and feed temperature were selected as the input parameters. Experimental data from the available studies were used to train the ANN. The ANN with 23 neurons gave a minimum mean squared error (MSE) for trans‐membrane pressure and Reynolds number. The ANN with seven neurons gave the minimum MSE for feed temperature. The predicted values from both ANNs well fitted with the experimental results with R2 < 0.99. Simulations showed that membrane fouling increased as flux reduction increased from 36.3% to 76.39% when trans‐membrane pressure increased from 0.5 to 2 bar. In contrast, a 19.96% reduction in flux was observed by increasing the Reynolds number from 750 to 2500. An increment of 77.37% of flux reduction was observed with increasing feed temperature from 30°C to 40°C. Simulations confirmed that transmembrane pressure, Reynolds number, and feed temperature strongly influence membrane fouling. An ANN‐based approach was the most accurate method to model membrane fouling for whey protein separation.

Highly selective alginate/CuO mixed matrix membranes for efficient dehydration pervaporation of various organic solvents

Pervaporation is an energy-efficient technique for dehydrating organic solvents from aqueous mixtures. To develop a highly selective pervaporation membrane with broad usage, we incorporated three types of CuO particles (solid CuO-S, sea urchin-like CuO-U, and porous CuO-P) into sodium alginate (Alg) for fabricating the Alg/CuO mixed matrix membranes (MMMs). The CuO syntheses and membrane preparation are simple and eco-friendly. The synthesized particles and membranes were systematically characterized. The improved hydrophilic feature of Alg/CuO MMMs was validated from the reduced water contact angle and higher water swelling ratio with increasing CuO wt%. When the Alg/CuO MMMs were applied to the pervaporation of 30 wt% water/isopropanol (IPA) at 25 ℃, both the permeation flux and separation factor were enhanced significantly compared to the pure Alg membrane. The separation efficiency followed the order of Alg/CuO-S MMMs < Alg/CuO-U MMMs < Alg/CuO-P MMMs, in good agreement with their water swelling tendency. The incorporation of 3 wt% porous CuO-P particles in MMM achieved the optimal dehydration efficacy (normalized total flux of 3.5 kg m-2h−1, separation factor of ca. 5000, and water purity of 99.96 wt%, with a stable performance over 168 h). A further larger loading wt% led to a decreased separation selectivity due to more void formation from particle aggregation. With an increase in feed temperature, both the permeation flux and separation factor were improved; however, the increase in feed water concentration deteriorated the separation selectivity while enhancing the flux. Furthermore, the high selectivity and broad applicability of Alg/3% CuO-P MMM were fruitfully demonstrated by exhibiting superior separation efficiencies in dehydrating various polar aprotic solvents compared with several membranes discussed in the literature.

Sea and brackish water desalination through a novel PVDF-PTFE composite hydrophobic membrane by vacuum membrane distillation

The present study aims to evaluate the performance of porous hydrophobic Polyvinylidene fluoride − Polytetrafluoroethylene (PVDF-PTFE) composite membranes for desalination by vacuum membrane distillation (VMD) technique. The effect of operating parameters such as feed NaCl concentration (10,000 to 40,000 mg/L), feed temperature (50 °C to 80 °C), and downstream pressure (80 to 120 mmHg) on water permeation rate was studied. The increase in feed temperature enhanced the water permeation rate due to a rise in driving force across the membrane. For a constant downstream pressure of 80 mmHg, feed temperature of 80 °C and feed flow rate of 80 L/h, the membrane exhibited a maximum water flux of 3 kg/m2h with 99.86% salt rejection when aqueous NaCl concentration of 10,000 mg/L was charged as feed. Membrane characterization was performed using various analytical tools to determine physico-chemical properties such as pore size, structural elucidation, thermal stability, crystallinity, and hydrophobicity of the membrane material. Further, a temperature and concentration polarization coefficient-based analysis was performed by solving the mass and heat transport model equations using MATLAB software. The proposed research study promotes the application of VMD for recovering potable water from highly saline sea/brackish water and alleviates brine disposal issues.

The effect of pretreatment and the operating temperature on reverse osmosis in make-up water preparation

Raw water cannot be used directly to compensate for water losses in power plants. Thus, a series of technological steps are required to produce ultra-pure water from fresh- or seawater. This study recommends using a proper pretreatment consisting of two-steps of microfiltration, ultrafiltration and nanofiltration. Desalination was carried out using two stages of reverse osmosis. The effect of increasing feed temperature from 25 °C to 48 °C on the second stage of reverse osmosis was studied and showed an exponential increase in flux and permeability, and reduced operation time. For freshwater, no temperature effect was observed on rejection in this temperature range; however, the highest rejection values calculated based on conductivity were observed at a 40 % recovery at all temperatures in seawater (96.6 % and 97.6 % at 48 and 25 °C, respectively). As a result of the multiparameter evaluation using the ranking method for the second reverse osmosis stage, 36 °C is found to be the optimum temperature.

Performance of membrane distillation assisted crystallization and crystal characteristics for resource recovery from desalination brine

Membrane distillation crystallization (MDC) has been widely studied in recent year for its potential for resource recovery from desalination brine with high concentrations. In this study, crystal samples produced from a bench-scale MDC system have been analysed for crystal morphology, crystal purity and crystal size distribution (CSD). In addition, orthogonal fractional factorial (OFF) experimental design has been introduced to evaluate the influence of various operating conditions on the crystal size and CSD. Feed temperature (40 to 60 °C), crystallization time (60 to 180 min) and the feed composition have been used as the control factors. The results show that the MD in the MDC system maintains a consistent flux of 1.32 to 4.2 kg/m2·h across various feed compositions; higher feed temperatures led to the formation of larger crystal clusters, while longer crystallization time yielded more cubic-shaped crystals; an overall NaCl purity exceeding 99.08 % has been achieved throughout all the experiments; and the increased feed temperature and prolonged crystallization time results in a narrower CSD. The result of OFF experimental design identifies feed temperature as the dominant factor affecting crystal size and CSD. However, the presence of impurities in the feed water could pose challenge to the thermal stability and longevity of the membrane.

Valorization of acid mine drainage into potable water and valuable minerals through membrane distillation crystallization

Owing to the rise in population growth and demands for the current living standards, mineral and water resources are depleting at the alarming rate. Also, the mineral–water-energy nexus raises a concern of high-quality water and mineral production at low costs. Membrane distillation crystallization (MDC) has emerged as a promising technology capable of simultaneous water and mineral recovery from wastewater or industrially discharged brines. Herein, the MDC was evaluated for recovery of water and precious minerals from acid mine drainage discharged from the mine tailings. High quality fresh water with 99.9 % salt rejection and permeate flux of 2.32 kg·m−2·h−1 was recovered at 52 °C feed inlet temperature. Also, feed temperatures were varied to determine their impact on mineral crystal morphology, size distribution and growth rate. Predominantly recovered minerals were gypsum, manganese fluoride, potassium iron oxide, nickel oxide hydroxide, sodium sulphate and dihydrogen sulphate. Orthorhombic crystal structure of mineral salts was attained at low feed inlet temperature (34 °C). Higher feed inlet temperatures (i.e. 41° C and 52° C) promoted co-crystallization giving rise to orthorhombic polymorph structures. Narrow crystal size distribution was reported at low water recovery factor (initial growth) for all temperatures. However, the particle size distribution broadened as the recovery factor increased. The crystal sizes ranged from 3.91 ± 0.97 µm to 14.04 ± 3.31. Remarkably, crystal growth rate increased with an increase in feed inlet temperature. These findings open a research direction towards economic recovery of mineral and water to supplement the existing shortages. With a myriad of crystals obtained from the MDC process, an additional operational unit is required to selectively recover high economic minerals.

Thermodynamic analysis of a hybrid novel solar powered humidification-dehumidification coupled with direct contact membrane distillation system

Water scarcity is a well-known global issue, and obtaining potable water in many regions is challenging. Some technologies exist but require high-grade energy for freshwater production, which is not universally accessible. This work emphasizes desalinating saline water using low-grade energy, such as solar energy. The study introduced a novel design of hybrid solar-powered humidification-dehumidification coupled with direct contact membrane distillation (HDH-DCMD), including modeling heat transfer, mass transfer, and fluid flow. The obtained results are further validated against previously published findings. Additionally, a thermodynamic analysis of the hybrid system was conducted to examine the effects of several parameters, including variation in membrane area, top brine temperature (TBT), feed temperature, mass flow rate ratio (MR), and dimensions of the membrane module. The objective was to assess the influence of these factors on the overall distillate production, gain output ratio (GOR), and recovery ratio (RR). The hybrid system offers a significantly improved solution, yielding nearly double the distillate production and GOR compared to standalone HDH and DCMD systems. The performance of HDH and DCMD is interconnected, meaning that if one outperforms the other, the overall output remains constant. The overall distillate production remains unaffected by MR, while GOR is influenced by it, resulting in varying optimal points depending on the specific operating parameters. It has been observed that increasing the TBT results in an increase in distillate production, RR, and GOR. However, when the feed temperature increases, the distillate production and RR remain almost constant while the GOR continues to increase.

Experimental investigation on the hybrid system of mechanical vapor recompression and hollow fiber vacuum membrane distillation applied for wastewater treatment

In order to achieve zero discharge and resource utilization of industrial high salt wastewater, a hybrid system of mechanical vapor recompression (MVR) and hollow fiber vacuum membrane distillation (HFVMD) was constructed, and several experiments of air tightness, single working condition and multiple working conditions were carried out with ammonium chloride solution as feed, then thermal economic performance were evaluated via a single factor analysis method. The obtained results showed that the system had excellent airtightness to ensure normal evaporation experiment, and high separation efficiency of 99.9% and lower evaporation energy consumption to achieve high efficient separation by combining the advantages of the hydrophobic membrane evaporation and latent heat recovery in view of MVR and HFVMD technologies. Furthermore, increasing feed temperature and feed flow rate increased evaporation rate and decreased evaporation energy consumption, while increasing feed concentration decreased evaporation rate and increased evaporation energy consumption. Finally, the single factor analysis indicated that total investment cost, annual operation cost and annual evaporation capacity were the main factors while environmental cost and equipment service life were the secondary factors which affected the specific evaporation cost. The above research provides theoretical and experimental bases for the development of the proposed system in the future.

A novel intensified approach for treating produced water from oil extraction using a multi-tube type falling-film distillation column equipped with a biphasic thermosiphon: a promising feasibility study.

This study has the novel aim of experimentally examining the efficiency of a pilot-scale treatment plant, composed of a multi-tube type falling-film distillation column equipped with a biphasic thermosiphon, for treating a real sample of high-salinity produced water (electrical conductivity of 20,700 μS cm-1). It investigates the influence of operational parameters, including feed temperature and steam chamber temperature of the biphasic thermosiphon, on distillate flow rate and reduction of conductivity. All experimental conditions tested achieved a reduction greater than 98% in terms of electrical conductivity. The production of treated water increased with increasing feed temperature; the flow rate increased from 20.8 L h-1 to 28.2 L h-1 as the feed temperature was increased from 80 °C to 90 °C, when the steam chamber temperature was fixed at 119 °C. Within the temperature range of the steam chamber, the specific energy consumption during the treatment process, with respect to the biphasic thermosiphon, remained practically unchanged between 0.58 kWh L-1 and 0.60 kWh L-1, when the feed temperature was 90 °C. The results proved the potential of the falling-film distillation technology assisted by heat pipes to be a promising proposal for removing salinity from produced water from oil extraction operations.

Development of Bench-Scale Direct Contact Membrane Distillation System for Treatment of Palm Oil Mill Effluent

The oil palm industries generate large amounts of effluent that can cause pollution and, as a result, pose serious threats to the environment. Recently, membrane distillation (MD) has been identified as a potential candidate for treatment of palm oil mill effluents (POME). This is because the release of POME at high temperature may reduce the need to preheat the effluent prior to operation. The objective of this article is to manufacture a bench-scale MD system and assess the performance of the system in POME treatment. This project started with the design of a process and instrumentation diagram (P&amp;ID) and continued with the fabrication part. Subsequently, the performance of the direct contact membrane distillation (DCMD) system was tested using POME as a feed solution. Three different feed temperatures (55 °C, 65 °C and 75 °C) were analyzed during the testing. The results obtained show that the permeate flux increased with the increase of feed temperature with the highest flux is 10.76 kg/m2.hr. More than 85% of pollutants including ammonia nitrogen, color, chemical oxygen demand (COD) and turbidity were rejected. This shows that the system is capable of treating POME and producing high quality permeate water.

Prediction of sulfuric acid solution in the vacuum membrane distillation process using Artificial Neural Network

This paper presented an effective approach utilizing Artificial Neural Network (ANN) to predict the vacuum membrane distillation (VMD) process of sulfuric acid solution. Firstly, mathematical models have been developed and the influence mechanisms of critical parameters on the transfer resistance in the VMD process were explored via a simulation process. Furthermore, an ANN model from the experimental data under actual working conditions, was developed and applied to simulate the effects of critical parameters on the VMD process performance including membrane flux and gained output ratio (GOR). The simulation results revealed that decreasing feed concentration or vacuum side pressure and increasing feed temperature or feed velocity would contribute to the reduction of total transfer resistance. Then, the operation data at multiple working conditions using actual sulfuric acid solution was divided into three sets (training, validation and test) to develop the ANN model. The trained ANN model was subsequently observed to have good agreement between the predicted and experimental data. From the subsequent simulations with various variable controls, increasing feed concentration or vacuum side pressure led to the declines of membrane flux and GOR, while increasing feed temperature or feed flow rate were helpful to improve membrane flux and GOR. Obviously, the developed ANN model performed well to predict the VMD process performance with minimum error, which could be effectively utilized to predict and optimize the VMD system for industrial wastewater treatment without performing a complicated, expensive and dangerous experimental test.

Numerical simulations of the effect on twisted spacer filaments on biofouling and scaling in the feed channel of reverse osmosis membrane modules

Overcoming biofouling and scaling in membrane-based separation processes is significant as it affects the permeate quality. In the present study, the effect of biofouling (on membrane only, spacer only, membrane as well as spacer) and scaling on the velocity field, pressure variation, solute residence time distribution and water flux in the reverse osmosis feed channel consisting of twisted spacer filaments is presented using numerical simulations. The twisted spacer filaments caused fluid mixing, which enhanced membrane performance. The biofouling on spacer filaments and/or membrane surfaces and scaling resulted in a narrower effective area for fluid flow, thus causing fluid acceleration and higher pressure drop. The study of solute residence time distribution for biofouling revealed that the breakthrough time decreased with residence time due to fluid acceleration. The observations of solute tracer movement revealed that the solute advection pattern broadened when the feed time for the solute tracer was increased. An irregular and heterogeneous pattern of solute tracer movement was observed in the reverse osmosis feed channel with biofouling which enhanced the flow dispersion and acceleration. The effect of feed temperature on the biofouling pattern was also observed. Biofouling reduced with temperature because the increased feed temperature improved biomass mobility. The water flux in the computational domain containing spacer with scaling was higher compared to the computational domain containing spacer with biofouling because biofouling reduced the membrane porosity, diffusion coefficient and increased flow resistance. The present study concludes that the twisted spacer can effectively reduce biofouling and scaling with improved water flux in reverse osmosis membrane modules.

PVA/UiO-66 mixed matrix membranes for n-butanol dehydration via pervaporation and effect of ethanol

In this work, pervaporative mixed matrix membranes (MMMs) composed of porous UiO-66 filler newly-synthesized and poly (vinyl alcohol) (PVA) have been investigated for dewatering n-butanol (BuOH) from BuOH/H2O and BuOH/ethanol/H2O solutions. The influences of the filler loading, feed concentration and feed temperature on the membrane dehydration performance are investigated in detail in terms of pervaporation flux/separation factor, pervaporation separation index and component permeance/selectivity. It is found that with the increase in feed water concentration or temperature, total permeation flux across the MMM substantially rises while the dehydration separation factor decreases considerably. With the increase in feed temperature, pronounced increase in the driving force is resulted, yielding the decline in the partial permeance and water/n-butanol selectivity but increase in the component flux. As the water content increases, the water permeance and water/n-butanol selectivity are reduced while both BuOH flux and permeance increase. Over the filler loading range considered here, the MMM with 15 wt% UiO-66 has reached the largest pervaporation separation index of 2560 kg/m2·h at 70 °C and 10 wt% water in the feed. In the case of using 10 wt% ethanol for BuOH in the feed, the dewatering separation performance has varied substantially as compared to the binary feed, leading to reduced separation factor and elevated permeation flux for the 15 wt% UiO-66 filled MMM. In the meantime, the MMM has maintained excellent separation performance over a testing duration of 240 h. Our results show that pervaporative UiO-66/PVA MMMs have demonstrated great potential in practical BuOH dehydration applications.

Removal of ketoprofen from surface water in a submerged photocatalytic membrane reactor utilizing membrane distillation: effect of process parameters and evaluation of long‐term performance

AbstractBACKGROUNDThe increasing presence of contaminants of emerging concern, including pharmaceuticals, in the environment creates an urgent need for development of efficient technologies of water treatment. A promising solution could be the application of hybrid systems combining advanced oxidation processes and membrane technology. The presented investigations were focused on the treatment of simulated surface water contaminated with ketoprofen in a submerged photocatalytic membrane reactor utilizing direct contact membrane distillation (SPMR‐DCMD). The influence of operational parameters such as TiO2 photocatalyst concentration, feed temperature and aeration rate was examined. Moreover, the long‐term performance of the polypropylene membrane in the SPMR‐DCMD was evaluated.RESULTSIt was proved that the increase in feed temperature not only improved the permeate flux but also enhanced the degradation efficiency, despite a simultaneous decrease in dissolved oxygen concentration. Aeration of feed did not improve the photodegradation rate, but enhanced the product quality, especially with reference to removal of CO2, thus reducing the aggressive properties of water. The presence of TiO2 was proved to enhance the permeate flux. During 200 h of SPMR‐DCMD operation the conductivity of the distillate did not exceed 3 μS cm−1 (vs. 0.1–0.5 mS cm−1 in feed), showing a high quality of the product.CONCLUSIONThe obtained results revealed a significant advantage of SPMR‐DCMD over the systems utilizing pressure‐driven membrane processes. Permeate quality was very high and no negative effect of the fouling layer on system performance was found. Moreover, the applied membrane exhibited very good stability during long‐term operation. © 2023 Society of Chemical Industry (SCI).

Performance, energy and economic investigation of airgap membrane distillation system: An experimental and numerical investigation

Airgap membrane distillation (AGMD) is an efficient configuration employed widely for the solar membrane distillation desalination process. In the present work, 1-D Knudsen and molecular transport (KMT) model has been developed to investigate the performance of the flat sheet PVDF membrane. A new solution algorithm for the co-current and counter-current flow regime has been designed to solve the heat and mass transfer equations iteratively for a single-stage AGMD module. The feed temperature, feed flow rate, airgap size, salinity, membrane porosity and module length were varied and compared with experimental results. The increase in feed temperature from 40 °C to 80 °C resulted in 10.38 times increase in flux for co-current flow and 11.05 times for counter-current flow. The maximum permeate flux at 80 °C was 8.668 kg/m2h and 8.871 kg/m2h for the co-current and counter-current processes, respectively. Optimizing the feed temperature, flow rate, and membrane length using RSM suggests 80 °C, 1.528 LPM and 10 m as the optimum operating condition. An AGMD module of size 0.8 m width and 10 m length under the optimum operating condition exhibited a freshwater yield of 8.73 kg/h by consuming 24.98 kWh/m3 of specific energy, and the water production cost would be around $2.25/m3.

Research on High Flux Direct Contact Membrane Distillation Technology

The effects of membrane materials, membrane module structure and membrane distillation operation parameters on the performance of direct contact membrane distillation were investigated by using strontium chloride solution with Sr2 + concentration of 1g/L as test solution. The results showed that the flux of PTFE is the largest, PVDF is the second, PP is the smallest, and the rejection rate of PTFE decreases rapidly with the increase of running time, which indicated that PTFE is easy to be fouled, while PVDF is a better membrane material; When the packaging fraction of membrane module increases, the membrane flux decreases, but the water yield per unit time increases. Considering the economy and treatment efficiency, it is recommended to select the membrane module with packaging fraction of 11.42%; the increase of feed flow rate and temperature is beneficial to the increase of flux in DCMD process. The rejection rate is almost unaffected by the membrane module structure and operating conditions, and remains above 99.9%. This study is helpful to provide research direction for improving membrane distillation flux, and provide theoretical reference for membrane distillation technology to treat practical radioactive wastewater.

Preparation and characterization of PPO/PS porous membrane for desalination via direct contact membrane distillation (DCMD)

The non-solvent induced phase separation (NIPS) method was used to prepare novel polyphenylene oxide and polystyrene blend (PPO/PS) flat-sheet porous membranes. The performance of prepared samples was studied in a direct contact membrane distillation (DCMD) experimental set-up. The prepared membranes were characterized using field emission scanning electron microscopy (FESEM), attenuated total reflection Fourier transform infrared (ATR-FTIR), atomic force microscopy (AFM), and zeta potential. A number of other properties, such as porosity, contact angle, and liquid entry pressure (LEP), were measured. Permeate flux has also been evaluated at different feed concentrations (0, 3500, and 35000 ppm NaCl) and temperatures (0, 60, and 80 °C). According to the results, by increasing feed temperature from 40 to 80 °C and maintaining permeate temperature constant at 22 °C, the permeate flux was increased from 5.53 to 31.36 kg/m2h. Altering the feed concentration from 0 to 35000 ppm has resulted in a reduction of permeate flux from 31.36 to 27.87 kg/m2h. In all DCMD tests, high rejection was observed (99.9%). Moreover, the anti-fouling and anti-scaling properties of the prepared membrane were investigated. Anti-scaling properties were examined by adding CaCl2 and Na2SO4 to the feed solution; the permeate flux did not change significantly and rejection was maintained above 99.8%. Humic acid (HA) in feed solution led to fouling, resulting in a 20% reduction in flux, but the rejection was maintained above 99.4%. Furthermore, SDS and CTAB surfactants (below CMC) as foulant agents were added to feed and due to the wetting phenomenon, the rejection dropped to 99.11 and 99.28%, respectively, while permeate flux decreased very slightly after 4 h operation.

Entransy performance analysis of the sulfuric acid wastewater treatment process using a vacuum membrane distillation system

Industrial sulfuric acid wastewater treatment using vacuum membrane distillation (VMD) technology has attracted worldwide attention. However, high energy loss and low membrane flux seriously hinder the industrialization of VMD technology. This paper novelly introduced an entransy theory to improve the VMD system performance. Mathematical models were built and verified via an experimental setup. System performance was investigated through the experiment and simulation from entransy dissipation standpoint. Experimental results indicated that an excellent separation performance with a membrane flux of 1.8 kg·m−2·h−1 and condensate conductivity within 20 μS·cm−1 were obtained at feed concentration of 10 %, feed temperature of 353.0 K, feed velocity of 1.0 m·s−1and vacuum side pressure of 24 kPa. Moreover, a thermal efficiency of 57.8 % was obtained with an entransy dissipation resistance of 0.00012 K·W−1. Simulation results showed that decreasing feed concentration and vacuum side pressure or increasing feed temperature and feed velocity decrease entransy dissipation resistance and improve heat transfer capability. More importantly, the prediction model of entransy dissipation resistance was established by a multiple linear regression method, and influence degrees of operation parameters on entransy dissipation resistance were obtained by a single factor analysis method. These findings are beneficial to optimize the VMD system in the future.

Membrane fouling in thermophilic aerobic membrane distillation bioreactor treating hospital wastewater

In the membrane distillation bioreactor (MDBR) process, flux increases with increasing feed temperature, but the presence of microorganisms limits the feed temperature. Also, the accumulation of cells and other substances on the membrane surface can affect the efficiency of MDBR. In this study, hospital wastewater was treated by thermophilic activated sludge MDBR. In the MDBR, the initial flux was 7.87 L‧m−2·h−1 and the stable flux was 3.88 L‧m−2·h−1. The particle size, zeta potential and hydrophobicity of the activated sludge in MDBR were 2.25 µm, −14 mV and 24%, respectively. In addition, EPS (extracellular polymeric substances) and SMP (soluble microbial products), having a significant effect on membrane fouling, were determined to be 201.50 mg·L−1 and 669.35 mg·L−1 in MDBR, respectively. Contact angle, FTIR (Fourier transform infrared), SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectroscopy) measurements were also made on a virgin membrane and used membrane. Analysis of EDX, SEM and F-TIR showed that the membrane fouling was caused by CaCO3 and EPS.

Ammonia recovery from anaerobic digestion effluent by aeration-assisted membrane contactor

The ammonia recovery from anaerobic digestion (AD) effluent offers a low cost and low carbon footprint strategy for N recovery. To enhance ammonia recovery performance, the aeration-assisted membrane contactor (MC) process was presented with aeration applied on the feed side. The ammonia recovery performance with different pH adjustment methods and operating parameters were tested. Results illustrated that a high ammonia mass transfer coefficient (Kov = 4.85 ×10−7 m/s) could be achieved in the aeration-assisted MC. With the increase in air flow rate from 0 L/min to 0.6 L/min, the Kov increased from 1.21 × 10−7 m/s to 4.85 × 10−7 m/s by about 300%, and the ammonia separation factor (St) increased from 5.75 to 8.91 by about 55%. Additionally, the Kov increased sharply with the increase in feed temperature. Notably, the ammonia removal efficiency can reach 82% after 6-h experiment, which might be due to the large contact area of membrane contactor and the high mass transfer efficiency caused by the optimal conditions. The greenhouse gas (GHG) emission evaluation showed that compared with that of Haber-Bosch process (4.2 kg-CO2 eq/kg-N), the GHG emission of aeration-assisted MC was 1.86 kg-CO2 eq/kg-N under room temperature. The aeration-assisted MC can provide a high-efficient and low GHG-emission ammonia recovery process.