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Review

Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation

by
Bharti Verma
1,
Chandrajit Balomajumder
2,
Manigandan Sabapathy
1,* and
Sarang P. Gumfekar
1,*
1
Department of Chemical Engineering, Indian Institute of Technology, Ropar 140001, India
2
Department of Chemical Engineering, Indian Institute of Technology, Roorkee 247667, India
*
Authors to whom correspondence should be addressed.
Processes 2021, 9(5), 752; https://doi.org/10.3390/pr9050752
Submission received: 24 March 2021 / Revised: 21 April 2021 / Accepted: 22 April 2021 / Published: 24 April 2021
(This article belongs to the Special Issue Design and Applications of Polymeric Flocculants)
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Abstract

:
Pressure-driven processes have come a long way since they were introduced. These processes, namely Ultra-Filtration (UF), Nano-Filtration (NF), and Reverse-Osmosis (RO), aim to enhance the efficiency of wastewater treatment, thereby aiming at a cleaner production. Membranes may be polymeric, ceramic, metallic, or organo-mineral, and the filtration techniques differ in pore size from dense to porous membrane. The applied pressure varies according to the method used. These are being utilized in many exciting applications in, for example, the food industry, the pharmaceutical industry, and wastewater treatment. This paper attempts to comprehensively review the principle behind the different pressure-driven membrane technologies and their use in the removal of heavy metals from wastewater. The transport mechanism has been elaborated, which helps in the predictive modeling of the membrane system. Fouling of the membrane is perhaps the only barrier to the emergence of membrane technology and its full acceptance. However, with the use of innovative techniques of fabrication, this can be overcome. This review is concluded with perspective recommendations that can be incorporated by researchers worldwide as a new problem statement for their work.

1. Introduction

The rapid industrial revolution has led to the release of heavy metals into the water streams. Even the slightest of exposure to these elements is believed to cause catastrophic consequences [1]. These elements have atomic weights of between 63.5 and 200.6 and have a specific gravity higher than 5 [2]. The life span of these elements in the ecosystem, owing to their property of bio-magnification, makes the situation worse. Therefore, heavy metal removal from industrial wastewater has become an immediate matter of concern worldwide. The most toxic heavy metals are Zinc, Chromium, Nickel, Lead, Cadmium, and Mercury. There are conventional methods to treat wastewater, such as adsorption [3], flotation [4], bio-sorption [5], coagulation [6], ion exchange [7], bioremediation [8], and electro-dialysis [9]. Although these have been well-established, restrictive environmental legislation, more extensive space requirements, labour-intensive operations, lower selectivity, lower separation efficiency, and the high cost of these conventional methods have resulted in the search for more promising and unconventional techniques. Membrane technology in industrial pollution abatement has attracted research interest worldwide due to its high efficiency, smooth operation, and less space requirements.
Membrane technology may help industrial effluents to stay within permissible standards. Treatment through membranes is highly effective and, therefore, a review of the research carried out up to now is quite imperative. There is no detailed paper that covers the application of all the pressure-driven processes in environmental applications and the implications of various parameters on the performance of the membrane process. This manuscript aims to provide a comprehensive perspective and review of the available literature. This will help researchers to identify the gaps and proceed accordingly. Figure 1 presents the comparison of various kinds of pressure-driven membrane technologies.

2. Results and Discussion

2.1. Ultrafiltration in Heavy Metal Removal

Ultrafiltration (UF) is the technique under membrane separation where the transmembrane pressure required is relatively low. This method aims to eliminate dissolved as well as colloidal particles. The major limitation of this type of pressure-driven process is the larger size of the pore. The pore size for UF lies between 2 nm and 50 nm [10]. The pore sizes are more significant than the metal ions in their hydrated forms.
Permeate fluxes are determined by varying applied pressure at a fixed temperature. The flux can be predicted by the following equation known as the Hagen- Poiseuille equation [11]:
J = P T R M + R F + R G
where J is the flux through the membrane (m3/m2.s), PT is the transmembrane pressure (N/m2), RM is the intrinsic membrane resistance (N.s/m3), RF is the fouling resistance, and RG is the resistance related to concentration polarization. RM can also be written as:
R M = 32 × Δ X × µ ε × d p 2
where dp is the mean diameter of the pore (m), µ is the viscosity of the fluid (N.S/m2), ΔX is the thickness of the membrane skin (m), and ε is the porosity of the surface of the membrane.
The performance of UF can be increased by adding micelles or polymers, which can aggregate the heavy metal particle. These are referred to as Micellar Enhanced UF (MEUF), and Polymer Enhanced UF (PEUF) (Table 1). Scamehorn first discovered MEUF for water remediation [12]. Figure 2 shows the process of micellar enhanced filtration. In the process of MEUF, the addition of surfactants either at levels equal to or higher than Critical Micelle Concentration (CMC), lead to the formation of aggregates called micelles. The solubility of metal ions in these micelles is higher and is dependent on electrostatic or Van der Waals forces. These micelles containing metal ions are then subjected to UF membrane, and thus pure water is achieved. The retention of these heavy metal bound micelles is subsequently obtained by using a UF membrane with a pore size smaller than the size of the micelle. To achieve maximum efficiency, surfactants having electrical charges are used worldwide. As an example, Sodium Dodecyl Sulphate (SDS), having a negative charge, is used to treat wastewater containing metal ions. The removal efficiency is dependent on various parameters, including the pressure which is applied, the concentration of the surfactant, the temperature of feed, the flow rate, and the concentration of the feed. Since the driving force itself is the pressure difference, it is evident that permeate flux will vary with applied pressure at a particular surfactant concentration. However, the applied pressure should be less than the maximum pressure the membrane can withstand [13]. pH also plays a vital role in the removal of heavy metals by MEUF. It was observed that the removal of Cr(VI) by MEUF using Cetyl Trimethyl Ammonium Bromide (CTAB) was maximum (90%) at a pH of 2 [14]. The surfactant to metal molar ratio is an essential variable in MEUF as the formation of micelles depends on the Critical Micelle Concentration (CMC). It has been reported that a rejection coefficient as high as 99% can be obtained by keeping the surfactant to metal molar ratio above 5 [15]. In some unusual cases, it has been observed that metal rejection coefficients as high as 90% could be achieved for Cd(II), Cu(II), Pb(II), and Zn(II) by using the concentration of surfactants less than the Critical Micelle Concentration [16]. This may be attributed to the breakage of aggregates into smaller aggregates at a much higher concentration than CMC. The removal of chromium has also been investigated by using Cetyl Pyridinium Chloride (CPC), and it was reported that the permeate concentration increased with feed concentration. The concentration was observed to increase beyond the Critical Micelle Concentration (CMC) of 43 mM [17]. The removal of Cr(VI) by using CTAB, aggregation was observed at a CTAB concentration of 0.72 mM [18]. Feed temperature is also an important parameter as the thermal expansion of the membrane as well as the viscosity of the solution is directly dependent on the temperature of the solution. Besides, Critical Micelle Concentration (CMC) is dependent on the temperature. A hybrid system containing MEUF and an Activated Carbon Filter (ACF) was employed to obtain 96.2% removal efficiency of Ni(II) [19].
Polymer Enhanced UF (PEUF) is also a plausible solution to wastewater treatment. (Table 2). In this method, a water-soluble polymer is added as a complexing agent with metal ions and forms a macromolecule. The molecular weight of the macromolecule is higher than the molecular weight cut off of the membrane. Therefore, the metallic ions, along with the complexing agent, are retained over the UF membrane. The most commonly used complexing agents are Polyacrylic acid (PAA) [39], Polyvinylamine (PVA) [40], Polyethyleneimine (PEI) [41], a copolymer of maleic acid and acrylic acid (PMA) [42], and humic acid [43]. The performance of this method is dependent on the type of metal to be removed and the type of polymer used. Besides, solution pH and the existence of other ions in the solution also affect the performance. The efficiency of this method is dependent mainly on the type of metal and polymer, the feed concentration, the pH of the solution, and the presence of other salts. It was reported that the rejection coefficient reduced from 90% to 32% when the Cr(VI) concentration in the feed was increased from 25 PPM to 400 PPM [44]. The optimum polymer/metal weight ratio for the selective removal of Ni(II) and Cu(II) by using complexing agent PEI were 6 and 3, respectively [45]. The polymer/metal weight ratio of 25 was observed to be the most suitable for the removal of Ni(II) and Cr(III) with removal efficiencies of 99.5% and 99.8%, respectively [46]. The solution pH also affects the performance of the system. The complete removal of Cr(VI) by PEUF using Poly(N,N dimethylaminoethyl methacrylate) was reported when the pH was kept at 4 [47].

2.2. Nanofiltration for the Removal of Heavy Metals from Wastewater

Nanofiltration (NF) possesses properties between those of UF and Reverse osmosis (RO), and therefore the pore size is usually less than 2 nm, corresponding to an MWCO of 100–1000 Da [63]. The presence of surface functional groups and their dissociation provides charge to these membranes. NF membranes’ charge is highly dependent on solution pH. For example, typical polyamide NF membranes have an isoelectric point (IEP) between 3.5–5. At pH lower than IEP, amine groups and carboxylic groups are protonated (R-NH2+/RCOOH), which confer to the membrane a positive charge. Contrarily, at pH>IEP, NF membranes exhibit a negative charge because of the deprotonation of the above-mentioned functional groups (R-NH/R-COO−). In view of the fact that most of the heavy metals are cations, NF is of prime importance due to the separation achieved by the combination of steric effect and electrostatic forces [64]. Higher rejection of divalent ions, lower rejection of monovalent ions, and higher flux compared to RO membranes are some of the critical attributes of NF membranes. To reduce energy costs, NF is extensively used in the wastewater treatment processes and is currently trying to replace RO to make the processes more economically viable. The NF membranes separate the solute from the solution via two mechanisms. The first is known as ionic separation and corresponds to the separation based on the charge of solute in water. The second is known as sieving, which corresponds to the molecular weight of uncharged solutes. The non-sieving rejection mechanisms of NF are Donnan exclusion [65] and dielectric exclusion [66]. This is being explored to remove heavy metals from wastewater (Table 2) due to its ease of operation, reliability, and lower energy consumptions. The NF technique has been applied for removal of heavy metals such as Copper [67], Cobalt [68], Nickel [69], Zinc [70], Lead [71], Cadmium [72], Chromium [73], Arsenic [74] and mercury [75].
It was reported that As(V) removal increased with increased pH. The rejection increased from 74% to 88% when the pH was increased from 3.4 to 10. This could be explained by the fact that the monovalent ion H2AsO4− is dominant in the range of pH 4–6 while the divalent ion HAsO42− is dominant above pH 7. Owing to the large, hydrated radii of divalent ions, they are rejected by the membrane at a much higher rate. The As(V) removal increased with lower temperature. It was observed that at 15 °C, the arsenic removal was 95.4% which decreased to 93.1% on increasing the temperature to 40 °C. This is because of the increased diffusivity of arsenic with temperature [76]. In another study, it was observed that natural organic matter, humic acid, increased the rejection coefficient of As(V) by using NF membranes. The rejection coefficient for all four types of membranes was recorded to be higher than 94% [74]. Another study reported that the removal of Ni(II) ions increased with feed pressure and feed concentration. The maximum observed rejection coefficient of Ni(II) was 98.94% for an initial feed concentration of 5 PPM [77]. The efficiency of silver recovery was found to be 29%–59% for hybrid cyanidation and membrane separation [78]. Modification of NF membranes at the laboratory scale has also been done to increase their selectivity. A study reported removal efficiencies of 47.9, 44.2, 52.3 for Cu(II), Cd(II) and Cr(VI), respectively by the NF membrane modified by halloysite nanotubes (HNTs) functionalized with 3-aminopropyltriethoxysilane (APTES) [79]. Polyether sulphone (PES) NF membranes were grafted with poly- (amidoamine) dendrimer and showed outstanding performance with almost 99% removal efficiency for Pb(II), Cu(II), Ni(II), Cd(II), Zn(II), and As(V) [80]. Chelating polymers like poly- (acrylic acid-co-maleic acid) (PAM) and poly- (acrylic acid) (PAA) were adsorbed on the NF filtration membranes to treat Cd(II), Zn(II), Pb(II), Ni(II), Cu(II), As(V), and Cr(VI), and rejection coefficients of more than 98% were obtained for all the heavy metals [81]. Hollow fibre NF membranes have been fabricated using polybenzimidazole (PBI) and were investigated for their Cr(VI) removal capacity. The fabricated PBI membranes with Molecular Weight Cut Off (MWCO) of 525 Da showed 95.7% Cr(VI) removal [82]. The removal of Cr(VI) was also attempted by fabricating asymmetric NF membrane with poly- (m-phenylene isophthalamide) (PMIA). It was observed that 98% of Cr(VI) was removed at a pH of 8 with the fabricated membrane [83]. The presence of metal complexing polymer also played a crucial role in the application of membranes in the treatment of heavy metal. It was seen that with the addition of Bovine Serum Albumin (BSA), rejection coefficients of 93%, 99%, 93%, and 99% were obtained by employing a ceramic membrane with MWCO of 450 Da for Zn(II), Cd(II), Pb(II) and Cu(II), respectively [84]. The capillary UF properties were merged with capillary NF to achieve the desired separation of heavy metal from wastewater. This combined technique, called Direct Capillary NF (CNF), was employed to remove Pb(II), and 83% removal efficiency was obtained with the flux of 20 L/m2·h [85]. NF was also combined with MF, and the hybrid system was able to obtain 99% removal efficiency of Cr(VI) from aqueous solutions [86]. A dual-layer NF membrane was fabricated with an outer layer of polybenzimidazole (PBI) and a blend of polyethersulfone (PES) and polyvinylpyrrolidone (PVP). This membrane with an active area of 0.0037 m2 was employed to remove Cr(VI), Pb(II), and Cd(II). It was observed that 98% of Cr(VI) and 93% of Pb(II) were removed at pH of 12 and 2.2, respectively [87]. One study showed the laboratory scale development of an amphoteric hollow fiber NF membrane which was capable of removing 97% of As(V)) at a pH of 10 [88]. A positively charged membrane was fabricated by modifying NF membrane with hyperbranched polyethyleneimine (PEI) and removed 91.05% of Pb(II) at a pH of less than 8 [89]. A positively charged NF membrane was developed with the use of 2-chloro-1-methyliodopyridine and removed 96% and 95.8% of Cu(II) and Ni(II), respectively [90]. Nanotechnology has also come a long way since its development. Some researchers blended 0.5 weight% of cobalt ferrite nanoparticles in a polyethersulphone NF membrane and achieved rejection of 98%, 92%, and 88% for Cu(II), Ni(II) and Pb(II), respectively [91]. Beside, 1 wt% of cellulose nanocrystals functionalized by amine groups were also embedded in the PES membrane and the fabricated membrane removed 90% of Cu(II) ions [92]. A NF membrane Desal 5 DK was investigated for separating Cr(III) ions from acid solutions. It was evaluated that the Cr(III) concentration profile across the membrane is sensitive to the initial concentration of chromium as well as to the pore dielectric constant [93]. The performance of a semi-aromatic poly(piperazineamide) membrane was assessed for the removal of metals from copper metallurgical process streams. The membrane showed high metal rejections of more than 80%, and the high rejection values were associated with dielectric exclusion [94]. A research group studied the performance of extreme-acid-resistant duracid membrane for the valorisation of copper acidic effluent. The permeate flux and the feed water composition were varied, and it was observed that the metal rejection was more than 90% [95]. A novel nanocomposite membrane was developed for the removal of heavy metals, and its performance was compared to the polymeric membranes. It was concluded that while the polymeric membranes can exhibit a rejection from 77 up to 99%, the nanocomposite membranes can completely reject heavy metals (up to 100%) [96]. Table 3 summarizes the recent literature of various NF membranes used for heavy metal removal and their performance.

2.3. Reverse Osmosis in Heavy Metal Removal from Wastewater

The technique of reverse osmosis (RO) is the most efficient in terms of the contaminants it can separate from water. The semi-permeable membrane mostly allows water to pass and retains most of the pollutants. This technique accounts for more than 20% of the world’s desalination capacity [97]. The application of RO in the removal of heavy metals from wastewater is being investigated (Table 4). Low-pressure RO has been applied with a complexing agent to remove Ni(II) and Cu(II), and the removal efficiencies for both single and a mixture of ions achieved over 99% [98]. The complete removal of Ni(II) was obtained by employing the UF/RO hybrid system in the metal finishing industry [99]. A rejection coefficient as high as 99.9% was achieved for removal of Cr(VI) by employing a RO membrane at a pH of 8 [100]. The pH of the solution plays a crucial role in the removal of heavy metals by RO. Researchers obtained 91% removal of Cr(VI) at a pH of 3 [101]. For an initial feed concentration of 200 mg/L, 99% of Cd(II) was rejected by using RO from contaminated wastewater [102]. Commercially available polyamide ultra-low pressure reverse osmosis (ULPRO) and a NF membrane were employed to separate heavy metals. The rejection of heavy metals was achieved to be greater than 97% [103]. A study of the implementation of sequential stages of MF, NF and RO to separate noble metals from a gold mining effluent was carried out. It was observed that the retention of metals in the concentrates of MF and RO was above 95% [104]. Recovery of heavy metals such as Mn, Fe, Cu, Zn, As, Cd, and Pb was assessed using a volume retarded osmosis low-pressure membrane (VRO-LPM), and 95% rejection was obtained for all the heavy metals [105].
Table
Table 3. Review of literature concerning application of NF in heavy metal removal.
Table 3. Review of literature concerning application of NF in heavy metal removal.
Characteristics of MembraneHeavy Metal TargetedInitial Metal Concentration (mg/L)pHPressure (bar)Removal Efficiency (%)Ref
Flat organic membranes
MWCO = 1000 Da
Permeability = 1.6 × 10−3 L m−2 s−1 bar−1 		Ni(II)
Cu(II)		691.21476.1
72.6		[106]
Polyamide membrane supported by diaminobenzenesulfonic acid (DABSA)
MWCO = 500 Da
Permeability = 11.8 L m−2 h−1 bar−1
Negative charged		Cr(VI)46094 >99[107]
Chitosan/polyvinyl alcohol/montmorillonite clay membrane
Active area = 0.00385 m2		Cr(VI)5071(84–88.34)[108]
PAN/Sulfonated Polyarylene ether benzonitrile
MWCO = 300 Da
Permeability = 7.62 LMH.bar−1		Pb(II)
Cd(II)		1000(2–5)694.6
95.1		[109]
Spiral wound Polymeric membrane (NF270–2540)
Active area = 2.6 m2
Negatively charged
MWCO = (200–400) Da		Co(II)
Ni(II)		20(3.4–5.6)
3.4		6
10		100
91.94		[110]
Polyamide membrane (NF270)
Active area = 0.00076 m2.
The surface of the membrane is positively charged for pH less than 4 and negatively charged for a higher value. 		Cd(II)
Mn(II)
Pb(II)		10001.5499
89
74		[111]
Polyamide membrane
Active area = 0.47 m2
Isoelectric point is at pH 3.3–4		Pb(II)
Ni(II)		15.56–886
93		[112]
Polyethersulfone Membrane
Area = 0.00001256 m2
Membrane fabricated with 0.5 wt% magnetic graphene based nanocomposites		Cu(II)205492[113]
Thin-film composite.
Area = 0.024 m2
The isoelectric point is 3.6.
Membrane surface is negatively charged		Pb(II)1505.82599[114]
Polyamide thin film composite membrane
MWCO = 400
Zeta potential = −36.8 mV		Cr(VI)
As(V)		0.188.18(25–95)[115]
NF 300
Active area = 2.5 m2		As(V)0.015 to 0.0255099.8[116]
Aromatic polyamide membrane
MWCO = (200–300)
Water permeability = 2.4 × 10−8 m3/(s.m2.kPa)		As(V)0.27.510>94[74]
Thin film composite membrane (NF 2)
Active area = 0.01 m2		As(V)0.150–0.252711.76(97–100)[117]
NF Hollow fibre membrane
MWCO = 520 Da
Isoelectric point = 6.6
Pure water flux = 47.5 L/(m2.h)		Ni(II)
Cr(VI)
Cu(II)		142.23
121.23
56.55		2.31494.99
95.76
95.33		[118]
Polyamide composite membrane
MWCO ranges between 150 and 300
Effective area = 0.00572 m2		Cu(II)2304.56.8998.1[119]
Thin-film Composite membrane
Area = 0.0036 m2		Pb(II)400 330 97.5[120]
Thin-film composite membrane (AFC 40)
Effective area = 0.024 m2		Co(II)100 325 97[64]
NF 300 membrane
Effective area = 0.015 m2		Cd(II)
Ni(II)		5 52097.26
98.90		[121]
Polyamide membrane (NF270)
Membrane surface area = 0.0012 m2
Isoelectric point = 3.3		Cu(II)25,000(3–10)3099.5[122]
Negatively charged microporous NF, Nanomax50Cu(II)200 < 4.53 66[123]
NF spiral-wound membraneCu(II)50 53.8 >95[124]
Polyamide membrane (NTR 729HF)
MWCO = 700
pH 6.5
Effective membrane area = 0.006 m2		As(V)
As(III)		0.5(5–9)0.1–581
57		[125]
Polyamide thin film composite (NF90- 2540)
Active surface area = 2.6 m2
MWCO = 200 Da		As(V)0.1 86>90[76]
Composite polyamide spiral wound membrane(NFI)
Membrane area = 0.75 m2
Pure water permeability = 3.20 L/hm2 bar		Cr(VI)1000 5–8 99[73]
Table
Table 4. Review of literature concerning application of RO in heavy metal removal.
Table 4. Review of literature concerning application of RO in heavy metal removal.
Characteristics of MembraneHeavy Metal TargetedInitial Metal Concentration (mg/L)Operating ConditionsPressure (bar)Removal EfficiencyRef
TFC spiral wound membrane
Active area = 1.95 m2
Allowable operating pH range = 4–11
Max operating temperature = 45 °C
Max feed turbidity, NTU = 1
Max feed SDI = 5		Cu(II)
Ni(II)		500 Na2EDTA was added as a chelating agent at pH 55.0699.5[126]
Disk membranes
Polyamide selective layer is supported on the polysulfone layer		Cu(II)20–100 Addition of Sodium dodecyl sulphate increased the removal efficiencyLow pressure 70–95[127]
Polyamide thin film composite membrane
MWCO = N.A
Pure water permeability = 0.75 L m−2 d−1 kPa−1
pH range = 3–10
Zeta potential = −4.5 mV		Cr(VI)
As(V)		0.1 85.13>90[106]
Polyamide membrane
Active area = 0.014 m2		As(V)0.1 10–4099.75[128]
Brackish water membrane
Active surface area = 0.014 m2		As(III) pH 9.6 4099[129]
SWHR membrane (Filmtec)As(V)
As(III)		0.2pH 4
pH 9.1		10–3596.8
92.5		[130]
Polyamide spiral wound membrane
Membrane surface area = 2.5 m2
pH range = (4–11)		Cu(II)
Cd(II)		500 1398
99		[131]
SE and MPF44 NF membranes
Active membrane surface area = 0.0028 m2		Cu(II)2 M 35>95[67]

2.4. Fouling of Membranes

Despite its potential in the treatment of wastewater, there are certain limitations that prohibit the application of membranes in large-scale operations. The most challenging of all limitations arise from membrane fouling caused by different inorganic salts, which decreases permeate flux and increases feed pressure. The quality of the product is bad, and the life of the membrane is shortened [132]. The impacts of various model foulants on the performance of RO and NF membranes has also been studied. It was observed that organic foulants such as humic acid and sodium alginate caused the most severe drop in permeate flux [133]. The research was conducted to evaluate the cost of fouling in full-scale RO and NF installations, and it was found that the cost of fouling in RO plants was around 24% of operational expenses. The cost for early membrane replacement accounted for the significant portion of the total cost. It was concluded that cleaning-in-place automation could save up to 3% of operational expenses [134]. A surface-patterned alumina ceramic membrane with a porous gradient structure was fabricated to improve the anti-fouling ability [135]. The effect of gradient profile in ceramic membranes on fouling was also studied by a research group, and it was found that gradient profile reduced membrane resistance and fouling [136]. A hydrogenated TiO2 membrane with photocatalytically enhanced anti-fouling was developed for the treatment of surface water. It was observed that upon UV irradiation, the hydrogenated TiO2 membrane showed 60% higher humic acid removal efficiency as compared to the pristine TiO2 membrane [137].

3. Conclusions

Membrane processes are the best available techniques for water and wastewater treatment. The capability of separating a wide variety of components from the aqueous stream makes membrane technology one of the most promising methods available. A great deal of research has been done on heavy metal removal by ultra-filtration using surfactants and complexing agents. There is no literature available on separation by using a hybrid system of MEUF and PEUF for heavy metal removal. Although work has been done on the application of nanotechnology in membrane processes, little has been done on their application in the removal of heavy metals from wastewater. The nano-filtration membranes have been modified by using specific materials to enhance their selectivity. The combination of nanoparticles and nanocomposites with membranes seems to be a research gap. Besides, the fouling of the membrane is a significant limitation in the application of membranes in wastewater treatment. New fabrication techniques of membrane development, such that fouling of the membranes can be controlled as well as mitigated, are highly recommended.

Author Contributions

Conceptualization, B.V. and C.B.; methodology, B.V.; software, B.V.; validation, B.V. and C.B.; formal analysis, B.V.; investigation, B.V.; resources, C.B.; data curation, B.V.; writing—original draft preparation, B.V.; writing—review and editing, S.P.G. and M.S.; visualization, B.V.; supervision, C.B., S.P.G., and M.S.; project administration, C.B.; funding acquisition, C.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Processes 09 00752 g001 550
Figure 1. Various pressure-driven membrane processes.
Figure 1. Various pressure-driven membrane processes.
Processes 09 00752 g001
Processes 09 00752 g002 550
Figure 2. Process of Micellar Enhanced Filtration.
Figure 2. Process of Micellar Enhanced Filtration.
Processes 09 00752 g002
Table
Table 1. Various membranes in wastewater remediation.
Table 1. Various membranes in wastewater remediation.
Membrane MaterialCharacteristic of MembraneHeavy Metal TargetedSurfactant/Complexing Agent UsedOptimum Pressure (Bar)Surfactant Concentration (mM)Initial Concentration (mg/L)pH% RemovalReference
CeramicMWCO = 210 kDaNi(II)
Co(II)		Sodium dodecyl sulphate2.8 0.02510 753
51		[20]
PAN MembraneArea = 0.00124 m2As(V)Cetyl Pyridinium Chloride (CPC) 1 5 17–896.9[21]
Polyether sulphoneMWCO = 6000 g mol−1
Area = 0.3 m2
TMP <= 0.15 MPa		Cd(II)
Zn(II)		Sodium dodecyl sulphate0.72.1550 92–98[22]
Amicon regenerated celluloseMWCO = 10 kDaCd(II)
Zn(II)		Sodium dodecyl sulphate313.9
14.2		23 99[23]
PolycarbonateTMP = 250 kPaNi(II)Sodium lauryl ether sulphate 2 9.2 98.6[24]
Polyether sulphoneMWCO = 10 kDa
Area = 9.6 cm2
Permeate flux = 150 L.m2/h at 0.35 MPa		Cu(II)
Cd(II)
Zn(II)
Pb(II)		Sodium dodecyl sulphate 8(50–300)>3
>3
3–10
3–10		99[25]
Polyether sulphoneMCO = 10 kDa
Area = 32.15 × 10−4 m2		Cd(II)Rhamnolipid2.768.04607.892[26]
CeramicMWCO = 1 kDaZn(II)Sodium dodecyl sulphate0.810 2 99[27]
Polyacrylonitrile (PAN)MWCO = 300,000
Area = 4.8 m2		Zn(II)Sodium dodecyl sulphate20.21 19.32784.67[28]
Polyether sulphoneMWCO = 10 kDa
Area = 1.6 m2		Cd(II)
Cu(II)		Sodium dodecyl sulphate3 60 0.37
0.41 		85
81		[29]
PolysulphoneMWCO =10 k Da
Area = 0.014 m2		Cr(VI)
Cr(III)		Rhamnolipid0.70.0210 698.7
96.2		[30]
Regenerated CelluloseMWCO = 10 kDa
Are a= 0.0013 m2		Cu(II)
Cd(II)
Zn(II)
Ni(II)
Mg(II)		nonaoxyethylene oleylether carboxylic acid (RO90)330.439206.5>95%[31]
Polysulphone MWCO = 1 kDa
Area = 0.004 m2		Ni(II)Sodium dodecyl sulphate2.51610797%[32]
Polyacrylonitrile (PAN)MWCO = 100 kDa
Area = 0.07 m2		Ni(II)
Zn(II)		Sodium dodecyl sulphate112.75 23796.3
96.7		[33]
PolysulphoneMWCO = 10 kDa
Area = 0.004 m2		Ni(II)Sodium dodecyl sulphate18101199[34]
PolysulphoneMWCO = 10 kDa
Area = 0.3 m2		Cd(II)Sodium dodecyl sulphate0.380.45 97[35]
Polyether sulphoneMWCO = 5 kDa, 10 kDa, 30 kDa
Area = 0.00096 m2		Cd(II)Sodium dodecyl sulphate1 4 10 90[36]
Polyether sulphoneMWCO = 8 kDa
Area = −0.005 m2		Cd(II)Sodium dodecyl sulphate 7.3350 98.4[37]
HydrophilicMWCO = 10 kDaCu(II)polyoxyethylene Octyl phenyl ether (Triton-X) plus Sodium dodecyl sulphate 2.0961.29
5.67		9.2592[38]
Polyether sulfoneMWCO = 10 kDa
Area = 0.003019 m2		Cd(II)
Cu(II)
Pb(II)
Zn(II)		Sodium dodecyl sulphate19 10 >90[16]
Table
Table 2. Effect of environmental chemistry on the removal of heavy metals by membranes.
Table 2. Effect of environmental chemistry on the removal of heavy metals by membranes.
MembraneCharacteristic of Membrane (MWCO)Heavy Metal Surfactant/Complexing Agent UsedOptimum Pressure (bar) Surfactant ConcentrationInitial Concentration (mg/L)pH% RemovalRef
Ceramic15 kDaCu(II)Poly (acrylic acid) sodium3 1 wt%1604–599.5[48]
Ceramic15,000 g/molCr(III)Polyvinyl alcohol (PVA) 1 wt%925>90%[49]
Polyether sulphone10 kDaPb(II)
Cu(II)
Fe(III)		Polyvinylamine20.1 wt%25 799
97
99		[40]
Ceramic10 kDaCu(II)Poly (acrylic acid) 0.4 wt%160 5.599.5[50]
Ceramic10 kDaCu(II)
Zn(II)		Partially ethoxylated polyethyleneimine (PEPEI)3 0.06 wt%90.626Selectivity ratio Cu(II)/Zn(II) = 12.31[51]
Polyether sulphone10 kDaCd(II)Poly (ammonium acrylate)2 3.71 × 10−4 mol/L466.3299[52]
Cellulose10 kDaCu(II)
Zn(II)		Poly (acrylic acid)3 2 × 10−3 mol/L46597
75		[53]
Thin Film Composite3.5 kDaNi(II)Chitosan28 2 × 10−2 mol/L0.0725.490[54]
Polyether sulphone10 kDaHg(II)Polyvinylamine20.05 wt%10 >90[55]
Polyether sulphone60 kDaCu(II)Polyethylenimine (PEI)1.7 25 mM230394[56]
Polysulphone8 kDa, 15 kDaCd(II)Poly(ammonium) acrylate2 46498[57]
Ceramic10 kDaCr(VI)poly(diallyldimethylammonium chloride) (PDADMAC)4 0.1 wt%50 999[58]
Polyethersulphone10 kDaCu(II)
Ni(II)
Cr(III)		Carboxy methyl cellulose1 1 g/L10 797.6
99.1
99.5		[59]
Polyether sulphone10 kDaHg(II)Polyvinylamine20.1 wt%10 6–799[60]
Ceramic10 kDaCu(II)Partially ethoxylated polyethylenimine (PEPEI)4 0.06 wt%208 mg Cu/g PEPEI697[61]
Ceramic10 kDaPb(II)Poly(acrylic) acid (PAA)4 0.036%100 6100[62]
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Verma, B.; Balomajumder, C.; Sabapathy, M.; Gumfekar, S.P. Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation. Processes 2021, 9, 752. https://doi.org/10.3390/pr9050752

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Verma B, Balomajumder C, Sabapathy M, Gumfekar SP. Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation. Processes. 2021; 9(5):752. https://doi.org/10.3390/pr9050752

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Verma, Bharti, Chandrajit Balomajumder, Manigandan Sabapathy, and Sarang P. Gumfekar. 2021. "Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation" Processes 9, no. 5: 752. https://doi.org/10.3390/pr9050752

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Verma, B., Balomajumder, C., Sabapathy, M., & Gumfekar, S. P. (2021). Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation. Processes, 9(5), 752. https://doi.org/10.3390/pr9050752

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