Air Gap Membrane Distillation Research Articles

Removal of copper sulfate from aqueous solution by air-gap membrane distillation process

The potential use of air-gap membrane distillation (AGMD) process for the removal of copper sulfate (CuSO4) from aqueous solution was examined. A series of experiments were conducted to investigate the effects of both operation parameters and module parameters, including hot feed temperature(T3), coolant temperature (T1), feed flow rate (F), feed salt concentration (cf), vacuum pressure (P), the rate of hollow fiber membranes and heat-exchange hollow fibers (Nm/Nd) and the length of the modules (L) on permeate water flux (J), gained output ratio (GOR), water productivity (PV), and salt rejection rate (R) in AGMD process. It was found that the performance of AGMD process could be enhanced, but permeate water quality was deteriorated by adding vacuum pressure. Moreover, J declined, but PV and GOR increased as L increased. With the increment of Nm/Nd, J decreased when operation parameters keep constant, PV and GOR showed different variation trends with different T1 values due to the insufficient cold energy. The highest CuSO4 rejection rate exceeded 99.95%, so AGMD process has potential for CuSO4 separation from aqueous solution.

Robust superhydrophobic electrospun membrane fabricated by combination of electrospinning and electrospraying techniques for air gap membrane distillation

Membrane pore wetting is the main problem hindering long term stability of permeate flux quality in membrane distillation (MD) applications. A superhydrophobic membrane with micro and nanostructured surface features can offer a unique solution to resolve this issue. Thus, a modified electrospun membrane was fabricated using a combination of electrospinning and electrospraying. The membrane surface hydrophobicity was enhanced by constructing a beaded structure from spraying a mixture of non-fluorinated alumina (Al2O3) nanoparticles (NPs) mixed with low concentration of PVDF polymer on an electrospun base membrane made from PVDF. The results revealed that a rough surface with a hierarchical structure can be constructed, which could not only enhance the membrane hydrophobicity, but also further enhance the permeate efficiency by improving parameters such as flux and rejection. Additionally, the membrane hydrophobicity could be further tuned by controlling the bead spinning volume. Our study shows that the modified membrane with 7.8 μm beads layer thickness has boosted the liquid entry pressure (LEP) by 61% from 15.5 psi and the water contact angle to 154°. The performance of modified membranes with different spraying volume (1–5 ml) along with the neat electrospun and commercial membranes were examined in an air gap membrane distillation (AGMD) application for 5 h using a 2.5 wt% of synthetic heavy metal solution as a wastewater model. Then, the optimized superhydrophobic membrane with 2 ml spinning volume (ES15–2) was further tested in comparison with the commercial membrane during long-term operations (30 h) using 3.5 wt% of mixed heavy metals. The flux was 18.67 LMH (l m−2 h−1) for modified membrane (ES15–2) compare with 12.62 LMH for commercial PVDF membrane during 30 h of long-term operation with feed and coolant temperature at 60 °C, 20 °C, respectively. The present superhydrophobic membrane fabricated by a combined electrospinning/electrospray method shows high potential for MD applications.

Experimental and mathematical study of air gap membrane distillation for aqueous HCl azeotropic separation

AbstractBACKGROUNDIn the present study, the feasibility of air gap membrane distillation (AGMD) process is investigated for breaking an azeotropic mixture. A test cell AGMD module with hydrophobic PTFE membrane was fabricated and HCl/H2O azeotrope (20.2 wt% HCl) was taken as feed. A mathematical model based on Stefan diffusion multicomponent molecular‐Knudsen mass transfer approach has been developed and validated with experimental data. The effects of different process parameters on total permeate flux, on selectivity and on breaking an HCl/H2O azeotrope mixture also have been studied. The feed side membrane surface temperature and membrane side condensing surface temperature were estimated by CFD modelling.RESULTSThe HCl selectivity obtained in the permeate was <1, which indicates that permeate flux is leveraged with water and a higher HCl concentration in the retentate was achieved relative to the permeate. The permeate flux decreased from 36 to 17 kg m−2 h−1 upon increasing the air gap from 3 mm to 11 mm at 50 °C feed temperature. The permeate flux increased from 4 to 28.5 kg m−2 h−1 upon increasing the feed temperature from 30 to 50 °C at 5 mm air gap.CONCLUSIONWith azeotropic feed, the maximum concentration of HCl achieved in the retentate was 30.8 wt% HCl (i.e. a hyperazeotropic solution) and in permeate was found to be 15.29 wt% HCl (i.e. hypoazeotropic solution). This indicates a strong possibility of using AGMD for azeotropic mixture separation. It also was observed that the permeate flux is affected mainly by feed temperature and air gap width. © 2018 Society of Chemical Industry

Principles and advancements of air gap membrane distillation

Abstract In recent years, membrane distillation (MD) has evidently emerged as one of the promising separation processes, with increasing areas of application including but not limited to desalination, pharmaceutical and textile wastewater purification, food processing, concentration of aqueous solution, breaking azeotropic mixtures, and extraction of volatile organic compounds. Primarily, MD has been categorized on the basis of vapor collection and condensation arrangement methods. Among the various categories, air gap membrane distillation (AGMD), in which an air gap is maintained across the membrane and the cooling plate, turns out to be an important and efficient process. Lately, AGMD has received significant attention of researchers around the world which motivates the present work. This paper aims to review the work done so far concerning the AGMD in order to provide a holistic view that covers the principles and applications of AGMD, effect of process parameters, membrane parameters, mathematical modeling, fouling, temperature and concentration polarization, types of membrane module, energy consumption, recent developments in AGMD process, cost estimation, and heat integration with AGMD. To the best of our knowledge, the present work is the first attempt to exhaustively review the AGMD process.

Air gap membrane distillation for hypersaline brine concentration: Operational analysis of a full-scale module–New strategies for wetting mitigation

Membrane distillation (MD) is a thermal separation process which possesses a hydrophobic, microporous membrane as vapor space. A high potential application for MD is the concentration of hypersaline brines, such as e.g. reverse osmosis retentate or other saline effluents to be concentrated to a near saturation level with a Zero Liquid Discharge process chain. In order to further commercialize MD for these target applications, adapted MD module designs are required along with strategies for the mitigation of membrane wetting phenomena. This work presents the experimental results of pilot operation with an adapted Air Gap Membrane Distillation (AGMD) module for hypersaline brine concentration within a range of 0–240 g NaCl /kg solution. Key performance indicators such as flux, GOR and thermal efficiency are analyzed. A new strategy for wetting mitigation by active draining of the air gap channel by low pressure air blowing is tested and analyzed. Only small reductions in flux and GOR of 1.2% and 4.1% respectively, are caused by air sparging into the air gap channel. Wetting phenomena are significantly reduced by avoiding stagnant distillate in the air gap making the air blower a seemingly worth- while additional system component.

PVDF/h-BN hybrid membranes and their application in desalination through AGMD

A new procedure to produce poly(vinylidene fluoride)/boron nitride hybrid membrane is presented for application in membrane distillation (MD) process. The influence of hexagonal boron nitride (h-BN) incorporation on the performance of the polymeric membranes is studied through the present investigation. For this aim, h-BN nanopowders were successfully synthesized using the simple chemical vapor deposition (CVD) route and subsequent solvent treatments. The resulting h-BN nanosheets were blended with poly(vinylidene fluoride) (PVDF) solution. Then, the prepared composite solution was subjected to phase inversion process to obtain PVDF/h-BN hybrid membranes. Various examinations such as scanning electron microscopy (SEM), wettability, permeation flux, mechanical strength and liquid entry pressure (LEP) measurements are performed to evaluate the prepared membrane. Moreover, Air gap membrane distillation (AGMD) experiments were carried out to investigate the salt rejection performance and the durability of membranes. The results show that our hybrid PVDF/h-BN membrane presents higher water permeation flux (~18 kg/m2 h) compared to pristine PVDF membrane. In addition, the experimental data confirms that the prepared nanocomposite membrane is hydrophobic (water contact angle: ~103 degree),has a porous skin layer (>85%), as well competitive fouling resistance and operational durability. Furthermore, the total salt rejection efficiency was obtained for PVDF/h-BN membrane. The results prove that the novel PVDF/h-BN membrane can be easily synthesized and applied in MD process for salt rejection purposes.

Investigating on plasma polymerization of polyethersulfone membranes by ethylene for membrane distillation

A novel hydrophobic membrane was developed by means of plasma polymerization of the polyethersulfone (PES) membrane using ethylene as the precursor to obtain appropriate performance in the membrane distillation (MD). The effects of plasma treating parameters including duration time, gas pressure, and power on the surface properties of the treated membranes as well as their MD performances were discussed. The surface properties of the treated samples were evaluated in terms of the surface morphology, chemistry, porosity and pore size, roughness, hydrophobicity, and Liquid Entry Pressure (LEP). The treated hydrophobic PES membranes with water contact angles of as high as 115° were obtained at high pressures and moderate powers. Response surface methodology was applied for modeling and optimization of the Air Gap Membrane Distillation (AGMD) system to separate benzene as a volatile organic compound from water. The plasma treated membranes showed fluxes at least as high as those of the commercial polytetrafluoroethylene (PTFE) membranes.

Membrane distillation process for concentration of nutrients and water recovery from digestate reject water

Abstract During low-solids anaerobic digestion (AD) of substrates with a high solids content, substrate dilution can be obtained by recycling the liquid phase (reject water) of dewatered digestate. However, this can lead to accumulation of compounds, which inhibits the AD process. This laboratory-scale study assessed the potential of thermally driven air gap membrane distillation (AGMD) for concentrating nutrients in the reject water and recovering process water suitable for use in AD. The results showed that the removal rate of COD, P, S, and K was >98% and the removal rate of total ammonia nitrogen (TAN) reached nearly 100%. The corresponding yield of recovered permeate water was >56%. The concentration of TAN and PO 4 -P in the recovered permeate was 2 h) at 60 °C inlet temperature and showed a 28% decline by the end of the experiment. There was no leaking, wetting, or fouling of the membrane over the entire three consecutive day’s test duration. Specific heat demand for AGMD ranged from 900 to 1300 kWh/m 3 without heat recovery and was as low as 66–170 kWh/m 3 with heat recovery. The performance results reported here highlight the potential and robustness of the AGMD process.

Simulation and experimental study of an AGMD membrane distillation pilot for the desalination of seawater or brackish water with zero liquid discharged

Our work consists in presenting the results of an invention for a membrane distillation system coupled to an efficient and robust water solar collector. This system produces potable water with high quality and a small percentage of brackish discharge independent of salinity of the water source. To optimize and characterize experimentally the installation unit of the air gap membrane distillation (AGMD). During the tests, brackish water was used, ranging from 4.2 to 12.5 g/l of salt. The results show that the permeate flux increases as the temperature and feed rate an increase, and the thickness of the air gap decreases (from 5.12 to 1.5 mm). Our AGMD system was modelled using Matlab programming on heat and mass transfer aspects. The 1D model is based on the transfer equations and correlations of the literature present in the membrane distillation pilot. The maximum permeate flux obtained was 7.4 kg /m2 h with the temperature of the hot fluid of 80 °C, a gap of 1.5 mm and water flow rates of 4.8 l/min for the hot chamber and cold. For all measurements, the maximum relative difference between the experimental results and the simulated results is observed at 10% errors. The results of low temperature hot fluids can be interested in the solar energy coupling project.

Experimental characterization and optimization of multi-channel spiral wound air gap membrane distillation modules for seawater desalination

Abstract An experimental characterization of the performance of two multi-channel spiral-wound air-gap membrane distillation modules at commercial-scale was carried out for seawater desalination. The only difference between them was the membrane surface areas: 7.2 m2 and 24 m2 and thus the length of the channels (1.5 and 5 m respectively). The influence of the main operating parameters (evaporator inlet temperature, condenser inlet temperature and feed flow rate) was quantified. It was observed that the trade-off between productivity and energy efficiency was mostly related to the heat recovery inside the module. This was affected by the operation and also by the design of the modules: the longer the channel, the better the thermal efficiency but the worse the productivity. Empirical models were derived for each module. Optimum values of the three operating parameters to simultaneously maximize permeate flux and minimize specific heat consumption were obtained using surface response methodology (RSM). In the longest module it was possible to find operating conditions that maximize the productivity without losing thermal efficiency, but in the shortest module a compromise had to be found between both.

Comparison between dual-layer (superhydrophobic–hydrophobic) and single superhydrophobic layer electrospun membranes for heavy metal recovery by air-gap membrane distillation

A novel approach to enhance membrane performance using electrospinning fabrication technique for recovery of heavy metals using air-gap membrane distillation is described. Accordingly, a comprehensive study was accomplished to fabricate a unique electrospun dual-layer membrane (ESD) with an upper superhydrophobic layer and hydrophobic electrospun support layer and compare with a superhydrophobic electrospun single layer membrane (ESS). Superhydrophobic alumina nanoparticles (Al2O3) were embedded in a low polymer concentration of polyvinylidene fluoride (PVDF) to produce superhydrophobic ESS and top layer of ESD using electrospinning technique, while a mat with different concentrations of PVDF were used as hydrophobic electrospun support layer. In this study, dual layer membranes were fabricated in two sets. In the first set, layer thickness was varied by changing the spinning volume of the top and support layer with maintain total spinning volume, while in the second set the fibre diameter of the support layer was varied by changing the polymer concentration. Moreover, the electrospun membranes were characterized in terms of membrane performance such as: permeate flux, heavy metal rejection and energy consumption; wettability performance such as liquid entry pressure (LEP), and water contact angle (WCA); membrane structure such as mean with maximum pore size and porosity; membrane integrity such as mechanical and thermal integrity. The heavy metal rejection was >99% for all single and dual layer membranes when filtering artificial wastewater (Pb, Cd, Cr, Cu, Ni). When compared with single layer electrospun membrane made from spinning 16 ml PVDF, dual layer membrane made from the same spinning volume exhibited some improvement, such as higher permeate flux above 23 l/m2∙h (LMH) when filtering 2500 ppm concentration heavy metal feed water. Additionally, both sets of dual layer membrane demonstrated better mechanical performance and slight reduction of LEP compared with single layer electrospun membrane.

Boron evaporation in thermally-driven seawater desalination: Effect of temperature and operating conditions

The volatilization of boron in thermal desalination processes, namely multi-stage flash (MSF) and air-gap membrane distillation (AGMD) was investigated for the first time. This phenomenon was observed at feed temperatures above 55 °C in both studied processes. In simulated MSF process with two feeds, model boric acid and Red Sea water, boron concentration in distillate increased with feed temperature increase from 55 °C to 104 °C because of the increase in boric acid vapor pressure. Salinity and pH were the main factors controlling boron evaporation. The achieved boron concentrations in simulated MSF process were consistent with those measured in distillate samples collected from commercial MSF plants. The AGMD process also revealed a strong influence of operating temperature on boron removal. However, unlike MSF process, the boron concentration in AGMD permeate decreased with the feed temperature increase from 55 °C to 80 °C due probably to increase in vapor production and corresponding permeate dilution. When AGMD was operated in concentrating mode at a constant feed temperature of 80 °C, permeate boron concentration increased with process time due to concentration polarization and membrane fouling. A 10% flux decline observed after 21 h was attributed to CaCO3 scaling on the membrane surface.

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

The thermal performance of air gap membrane distillation (AGMD) desalination is dominated by heat and mass transfer across the air gap between the membrane and the condensing surface. However, little is known about the impact of condensate flow patterns in some design variations of the air gap. In this study, air gap membrane distillation experiments were performed at various inlet temperatures, varying module inclination angle, condensing surface hydrophobicity, and gap spacer design to identify the effect of each on the permeate production rate and thermal efficiency of the system. Additionally, this study is one of the first with enhanced visualization of flow patterns within the air gap itself, by using a transparent, high thermal conductivity sapphire plate as the condenser surface. System-level numerical modeling is used to further understand the impact of these flow regimes on overall energy efficiency, including flux and GOR. A brief review of membrane distillation condensation regimes is provided as well. For tilting the AGMD flat-plate module, permeate flux was barely influenced except at extreme positive angles (> 80°), and moderate negative angles (< −30°), where condensate fell onto the membrane surface. The surface with the hydrophobic coating (for dropwise condensation) was shown to have better droplet shedding (with very small nearly spherical droplets) and fewer droplets bridging the gap. Superhydrophobic surfaces (for jumping droplet condensation) were similar, with much smaller droplet sizes. Such surfaces could improve AGMD efficiency while avoiding flooding, as better performance (2x higher GOR) is reached with much smaller gap sizes (<0.2 mm) than currently attainable gaps with filmwise condensation (>1 mm). Meanwhile, the hydrophilic surface for small gap sizes (< 3 mm) often had pinned regions of water around the hydrophilic surface and plastic spacer. Overall, the various results imply that the common assumption of a laminar condensate film poorly describes the flow patterns in real systems for all tilt angles and most spacer designs. Real system performance is likely to be between that of pure AGMD and permeate gap membrane distillation (PGMD) variants, and modeling shows that enhanced condensing in air gaps may improve system energy efficiency significantly, with strong relative advantages at high salinity.

Air gap and water gap multistage membrane distillation for water desalination

The performances of multistage air gap membrane distillation (MS-AGMD) and water gap membrane distillation (MS-WGMD) systems are experimentally investigated and compared using three-stages systems for different operating conditions. Parallel, series, and mixed stage-connections are considered. The flux of MS-WGMD is more than double the flux of MS-AGMD. The parallel stages-flow connections produced higher output flux than series connections (15% on average for MS-WGMD and 10% on average for MS-AGMD). The MS-AGMD system is found to be more sensitive to changes in the feed temperature and gap width than the MS-WGMD system. The effect of feed flow rate on permeate flux is higher than the coolant flow rate. The series stage connections are more sensitive to the change in hot and cold flow rates than the parallel connection; particularly the feed flow rate. The productivity of the three-stages system is almost three times the single stage system. The calculated specific electric energy consumption ranged from 5 to 10 kWh/m3 and it values for MS-WGMD system are lower than that of MS-AGMD system, and decreases with increasing the feed temperature.

Graphene quantum dots modified polyvinylidenefluride (PVDF) nanofibrous membranes with enhanced performance for air Gap membrane distillation

This study investigates the potential of novel graphene quantum dots (GQDs)/polyvinylidene fluoride (PVDF) nanofibrous membranes for water desalination via air gap membrane distillation (AGMD) process. Different contents of GQDs were loaded in/on nanofibrous membrane for obtaining the desired structure for AGMD process. The resultant GQDs/PVDF nanofibrous presented a slight decrease in water contact angle and considerable increase in liquid entry pressure of water (LEPw). The sample containing 0.25 wt.% GQDs exhibited porosity of >90%, LEPw of >135 kPa, mean average surface roughness of 189.24 nm and water contact angle of >125°. Furthermore, the BET analysis exhibited that the mean pore diameter and effective surface area of nanofibrous membrane were modified at presence of GQD. AGMD experiments indicated that the higher water flux of 17.6 kg/m2 h and salt rejection of about 99.7% were achieved for GQD3P membrane containing 0.25 wt% GQDs compared to neat PVDF nanofibrous membrane with water flux of about 14.7 kg/m2 h and salt rejection of about 94.5% (partial wetting occurred after 4 h) during filtration of 3.5 wt.% NaCl solution for 8 h under feed and permeate temperatures of 60 °C and 20 °C, respectively. Eventually, GQD3P exhibited the water flux of 10.8 kg/m2h and reliable salt rejection of >99.5% over 60 h experiment.

Flux-enhanced PVDF mixed matrix membranes incorporating APTS-functionalized graphene oxide for membrane distillation

Air gap membrane distillation (AGMD) is an emerging desalination technology with the potential to meet the challenge of global water scarcity due to its low cost and high thermal efficiency compared to other processes. However, despite the potential of AGMD, a lack of appropriate membranes limits its commercial application. Therefore, this study was focussed on the fabrication of high flux, robust membranes for the purification of artificial sea water by incorporating graphene oxide functionalized with 3-(aminopropyl)triethoxysilane (APTS) into PVDF polymer solutions. Successful functionalisation of GO with APTS was confirmed with XPS and FTIR. It was shown that the addition of GO and GO-APTS enhanced the permeate flux by 52% and 86%, respectively, compared to pure PVDF. The best performing membrane contained 0.3 wt% GO-APTS (with respect to PVDF) and had a flux of 6.2 LMH (L m−2 h−1) whilst maintaining perfect salt rejection (>99.9%). These improvements were attributed to increased surface and bulk porosity, larger mean pore size and hydrophilic interactions owing to the functional groups of GO and GO-APTS. These membranes are evidence of the potential that GO and related materials have as nanocomposite fillers in high performance desalination membranes.

Performances of air gap and water gap MD desalination modules

Abstract Membrane distillation (MD) is a promising thermally-driven membrane separation technology for water desalination. In MD, water vapor is being separated from the hot feed water solution using a micro-porous hydrophobic membrane, due to the difference in vapor pressures across the membrane. In the present work, experiments are conducted to compare the performance of water gap membrane distillation (WGMD) and air gap membrane distillation (AGMD) modules under the main operating and design conditions including the feed and coolant temperatures, membrane material and pore sizes, and the gap width. Results showed that the WGMD module produced higher fluxes as compared to the AGMD module, for all test conditions. The feed temperature is the dominant factor affecting the system flux. The permeate flux increases with reducing the gap width for both water and air gap modules. However, WGMD module was found to be less sensitive to the change in the gap width compared to the AGMD module. The PTFE membrane produced higher permeate flux as compared to the PVDF membrane. Bigger mean pore diameter enhanced the permeate flux, however, this enhancement is marginal at high feed temperatures. With increasing the feed temperature, the GOR values increase and the specific energy consumption decreases.

Boron removal from geothermal water by air gap membrane distillation

In this study, boron removal from geothermal water with an air gap membrane distillation (AGMD) system was examined. The utilization idea of the waste heat sources in geothermal power plants for membrane distillation process is the basis of this research. During the study, six different types of commercial membranes were used and the influence of operating parameters such as feed temperature and velocity, coolant temperature and velocity and air gap distance on the permeate flux and rejection performances were investigated. First, the operating parameters were optimized and the experiments were performed with three different saline water concentrations (0.1–1.5–3% (w/v)). Then, the effect of boron concentration on permeate flux was investigated by using a synthetic geothermal water. Finally, a real geothermal water was used for the determination of AGMD system performance and min. 99.5% boron removal efficiency was achieved for all membranes. The results showed that permeate water boron concentrations were <0.5 mg/L for all membranes which are in accordance with irrigation standards. As a result, the air gap width, feed velocity and temperature were found as dominant factors affecting the permeate flux. And also, it was observed that feed water boron concentration did not affect permeate water flux.

Hierarchical Composite Membranes with Robust Omniphobic Surface Using Layer-By-Layer Assembly Technique

In this study, composite membranes were fabricated via layer-by-layer (LBL) assembly of negatively charged silica aerogel (SiA) and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FTCS) on a polyvinylidene fluoride phase inversion membrane and interconnecting them with positively charged poly(diallyldimethylammonium chloride) (PDDA) via electrostatic interaction. The results showed that the PDDA-SiA-FTCS coated membrane had significantly enhanced the membrane structure and properties. New trifluoromethyl and tetrafluoroethylene bonds appeared at the surface of the coated membrane, which led to lower surface free energy of the composite membrane. Additionally, the LBL membrane showed increased surface roughness. The improved structure and property gave the LBL membrane an omniphobic property, as indicated by its good wetting resistance. The membrane performed a stable air gap membrane distillation (AGMD) flux of 11.22 L/m2 h with very high salt rejection using reverse osmosis brine from coal seam gas produced water as feed with the addition of up to 0.5 mM SDS solution. This performance was much better compared to those of the neat membrane. The present study suggests that the enhanced membrane properties with good omniphobicity via LBL assembly make the porous membranes suitable for long-term AGMD operation with stable permeation flux when treating challenging saline wastewater containing low surface tension organic contaminants.

The Performance of an AGMD Unit Coupled with a Water Solar Collector the Experimental Validation for Desalination of Seawater

Our work consists in presenting the results of an invention for a membrane distillation system coupled to an efficient and robust water solar collector which produces potable water with high quality and a small percentage of brackish discharge independent of salinity of the water source. The air gap membrane distillation (AGMD) model for the modules has been developed. This model is based on mathematical equations that describe the heat and mass transfer mechanisms of a single-stage AGMD process. It can simulate AGMD modules in regimes. The theoretical model was validated using in AGMD under different operating conditions and parameters. The predicted water vapor flux was compared to the flux measured at five different feed water temperatures, two different feed water salinities. The model was then used to study and analyze the parameters that have significant effect on scaling-up the AGMD process such as the effect of increasing the membrane length, and feed and coolant flow rates. The model was also used to analyze the maximum thermal efficiency of the AGMD process