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Citation: Staszak, K.; Regel-Rosocka,
M. Removing Heavy Metals:
Cutting-Edge Strategies and
Advancements in Biosorption
Technology. Materials 2024,17, 1155.
https://doi.org/10.3390/
ma17051155
Academic Editor: Agata
Jakóbik-Kolon
Received: 1 February 2024
Revised: 25 February 2024
Accepted: 28 February 2024
Published: 1 March 2024
Copyright: © 2024 by the authors.
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materials
Review
Removing Heavy Metals: Cutting-Edge Strategies and
Advancements in Biosorption Technology
Katarzyna Staszak and Magdalena Regel-Rosocka *
Institute of Chemical Technology and Engineering, Faculty of Chemical Technology, Poznan University of
Technology, ul. Berdychowo 4, 60-965 Poznan, Poland; katarzyna.staszak@put.poznan.pl
*Correspondence: magdalena.regel-rosocka@put.poznan.pl
Abstract: This article explores recent advancements and innovative strategies in biosorption tech-
nology, with a particular focus on the removal of heavy metals, such as Cu(II), Pb(II), Cr(III), Cr(VI),
Zn(II), and Ni(II), and a metalloid, As(V), from various sources. Detailed information on biosorbents,
including their composition, structure, and performance metrics in heavy metal sorption, is presented.
Specific attention is given to the numerical values of the adsorption capacities for each metal, show-
casing the efficacy of biosorbents in removing Cu (up to 96.4%), Pb (up to 95%), Cr (up to 99.9%),
Zn (up to 99%), Ni (up to 93.8%), and As (up to 92.9%) from wastewater and industrial effluents. In
addition, the issue of biosorbent deactivation and failure over time is highlighted as it is crucial for
the successful implementation of adsorption in practical applications. Such phenomena as blockage
by other cations or chemical decomposition are reported, and chemical, thermal, and microwave
treatments are indicated as effective regeneration techniques. Ongoing research should focus on the
development of more resilient biosorbent materials, optimizing regeneration techniques, and explor-
ing innovative approaches to improve the long-term performance and sustainability of biosorption
technologies. The analysis showed that biosorption emerges as a promising strategy for alleviating
pollutants in wastewater and industrial effluents, offering a sustainable and environmentally friendly
approach to addressing water pollution challenges.
Keywords: biosorption; biomaterials; heavy metals; cutting-edge strategies; wastewater; industrial
effluents; nickel; cobalt; chromium; zinc; lead; copper; mercury; cadmium; arsenium
1. Introduction
Biosorption, a process that is gaining prominence as an eco-friendly and cost-effective
method, demonstrates remarkable potential in the removal of pollutants. This separation
operation is defined as a physicochemical and metabolically independent process that
enables certain biomasses of biological origin to accumulate heavy metals by binding
them to their cellular structures based on a variety of mechanisms, including absorption,
adsorption, ion exchange, surface complexation, and precipitation [
1
,
2
]. This technique
involves the utilization of various biological materials, including agricultural residues such
as crop residues, fruit peels, and other agricultural by-products, as well as microorganisms,
algae, and fungi. Such biobased materials serve as effective sorbents and exhibit the ability
to adsorb and accumulate pollutants from aqueous solutions. This process is gaining
attention as a sustainable alternative to traditional physicochemical methods of wastewater
treatment. It could be concluded that biosorption is part of broader bioremediation strate-
gies. Microorganisms and plants are used to adsorb and accumulate pollutants, helping to
restore the environment.
These biological approaches leverage the natural capabilities of certain organisms to
sequester, transform, or immobilize contaminants in soil, water, and air. Certain bacteria
and fungi have the ability to metabolize or transform pollutants into less harmful forms. For
example, certain bacteria and fungi have the ability to metabolize or transform pollutants
Materials 2024,17, 1155. https://doi.org/10.3390/ma17051155 https://www.mdpi.com/journal/materials
Materials 2024,17, 1155 2 of 21
into less harmful forms and sorb the derivatives. For example, bacteria such as Pseudomonas
and Bacillus species can degrade hydrocarbons and organic pollutants [
3
] and adsorb heavy
metals and other pollutants onto their cell surfaces, and their effectiveness can be influenced
by factors such as pH, temperature, and the presence of competing ions. In addition, specific
bacteria, known as metal-resistant bacteria, have the ability to survive in environments
containing high concentrations of heavy metals. These bacteria can accumulate metal
ions on their cell surfaces, making them suitable for biosorption applications in metal-
contaminated wastewater [
4
,
5
]. However, fungi, for example, white rot fungi, such as
Phanerochaete chrysosporium, are known for their ability to break down complex organic
compounds and their ability to sorb a wide range of pollutants [
6
,
7
]. The mycelial structure
of fungi provides a developed surface area for biosorption. Comprised mainly of natural
polymers such as chitin, cellulose, and proteins, mycelium constitutes a natural polymeric
composite material with a porous structure formed by tubular filaments known as hyphae.
Typically, hyphae range in diameter from 1 to 30
µ
m and can extend in length from a
few microns to several meters, contributing to the recognition of mycelium as one of the
largest living organisms on Earth [
8
,
9
]. Fungal mycelium can entrap and accumulate
heavy metals, making fungi suitable for the removal of metals from aqueous solutions.
Modification of fungal biomass with chitosan, a natural biopolymer derived from chitin,
enhances the biosorption capacity. Chitosan-modified fungi have been used for the removal
of metals, dyes, and other pollutants from wastewater [
10
]. Among the arguments in
favour of the use of bacteria and fungi are their high species diversity and their ability to be
adapted or engineered to combat specific contaminants. In addition, some microorganisms
have the ability to regenerate and continue biosorption after desorption, contributing to
the sustainability of the biosorption process [
11
]. On the other hand, the use of various
biological materials, such as biosorbents, especially agricultural residues, represents a
sustainable and cost-effective approach for the removal of pollutants from wastewater
and industrial effluents [
12
]. Agricultural residues are abundant, renewable, and often
considered as waste, which makes their repurposing for biosorption an environmentally
friendly solution. An excellent example is found in crop residues, biomasses from crop
harvesting, such as corn stalks, wheat straw, and rice husks, which are rich in cellulose
and lignin [
13
–
15
]. These materials have been successfully used as biosorbents for heavy
metals due to their structural components that offer binding sites for metal ions [
14
,
16
].
Sugarcane bagasse, the fibrous residue left after extracting juice from sugarcane, is another
example. The bagasse contains cellulose and hemicellulose and has been shown to be
effective in removing pollutants, such as dyes and heavy metals, from wastewater [
17
,
18
].
In addition, fruit peels are proposed as sorbents. For example, the peels of citrus fruits,
such as oranges and lemons, are abundant sources of pectin and other organic compounds.
Citrus peels have been used as biosorbents for the removal of heavy metals, dyes, and
organic pollutants from aqueous solutions [
19
–
22
], while banana peels, known for their
high cellulose and polyphenol content, have shown promise as biosorbents [23,24]. Other
agricultural by-products, such as shells and bran or nut shells, have also been tested for
their biosorption capacity. In addition to the fact that agricultural residues are found in
large amounts and are often considered waste, making them a viable source of biosorbents,
the issue of their renewability and the ease with which they can be modified to increase
their biosorption capacity through methods such as chemical modification establishes that
their use as biosorbents is consistent with sustainable practices and reduces dependence on
non-renewable resources. It is crucial to highlight that, in a number of cases, biowaste is
converted into activated charcoal and performs as a biosorbent in this altered form [
14
].
However, this review focuses only on native organic sorbents, specifically on biomaterials
derived from living organisms such as plants, fungi, and microorganisms, excluding
sorbents such as coal, fly ashes, and biochars.
Biosorption has found applications in various industries and settings due to its ef-
fectiveness in removing pollutants from wastewater and industrial effluents. Biosorption
is often integrated with other water treatment technologies, such as membrane filtration
Materials 2024,17, 1155 3 of 21
and precipitation, to achieve a more comprehensive and efficient pollutant removal. For
example, biosorption is used to treat wastewater from the textile industry, where it helps to
remove various pollutants, including dyes and pigments [
25
–
28
]. The versatility of biosor-
bents makes biosorption a valuable tool for addressing the complex nature of pollutants
generated in textile processes. Furthermore, the leather industry, known for producing
effluents containing chromium and dyes from the tanning process, benefits from biosorp-
tion as a means of effectively removing these pollutants [
29
]. There are also examples in
which biosorption has been explored to treat municipal wastewater to remove pollutants,
such as organic compounds, nutrients, and heavy metals [
30
–
32
]. It can complement or
serve as an alternative to conventional treatment methods [
33
,
34
]. Biosorption can also be
applied to remove excess nutrients, such as phosphorus and nitrogen, from agricultural
runoff, helping to prevent eutrophication in water bodies [
35
]. Biosorption is also pro-
posed to remove heavy metals, such as lead, copper, cadmium, zinc, and cobalt [
36
–
38
],
in typical metal industries, such as mining, electroplating, and metallurgical processes.
These examples show that the application of biobased materials aligns with the overarching
goal of minimizing the environmental impact of industrial activities and contributes to
the sustainable management of wastewater from various industries, particularly leather
manufacturing and metal processing. Its versatility and eco-friendly nature positions
biosorption as a promising technology with the potential to contribute significantly to the
field of environmental remediation.
Despite the variety of the literature on biosorbents for heavy metal removal from
model (synthetic) solutions, there is a notable scarcity of studies that evaluate these materi-
als on real-world objects, such as wastewater and industrial effluents. This gap is significant
because the practical application of biosorbents requires a thorough understanding of their
performance under realistic environmental conditions. The majority of heavy metals are
found in water in cationic form, whereas chromium(VI) exists as oxyanions, with specific
species predominating depending on the pH level. At pH values between 0 and 6, the
predominant forms are Cr
2
O
72−
and HCrO
4−
, while CrO
42−
becomes dominant at a pH of
approximately 4.5, reaching its maximum concentration at pH values greater than 8 [
39
].
Furthermore, oxyanions of As(III) and As(V) are stable under a wide range of conditions
in aqueous solutions. H
2
AsO
4−
is predominant under oxidizing conditions at a pH less
than 6.9, whereas HAsO
42−
becomes dominant at higher pH levels. In addition, H
3
AsO
4
can be present in strongly acidic solutions, while AsO
43−
is formed under alkaline condi-
tions
[40,41]
. Heavy metal speciation in wastewater affects the interactions between metal
ions and biosorbents, but also the presence in real-world samples of complex matrices with
coexisting ions, organic matter, and various contaminants that influence the biosorption
process. The effectiveness of biosorbents can depend on factors such as pH, temperature,
and the presence of competing ions, underscoring the importance of studying them in
context-relevant environments. Investigation of biosorption from real solutions is crucial for
validating their performance, optimizing the process conditions, and ensuring the practical
applicability of biosorption for large-scale environmental remediation initiatives. Addition-
ally, such studies contribute to environmental impact assessments, examining potential
ecotoxicological effects and providing insight into the long-term implications of biosorbent
applications. Ultimately, bridging the gap between laboratory studies and real-world
applications is essential to advance the field and facilitate the responsible deployment of
biosorbents in diverse environmental scenarios. Therefore, the objective of this paper is to
provide a comprehensive review of the latest advances in biosorption processes specifically
tailored for the removal of heavy metals from wastewater and industrial effluents (for the
review methodology see Appendix Aand Supplementary Materials). In recent years, a
significant thrust of continuous research has been directed toward the enhancement of
biosorption efficiency through the development of new and improved biosorbents, the
optimization of process conditions, and the exploration of novel applications. This study
explores the innovative landscape of biosorption technology, focusing on cutting-edge
strategies for removing heavy metals from wastewater and industrial effluents. The paper
Materials 2024,17, 1155 4 of 21
presents novel insights into recent breakthroughs and advancements, shedding light on the
evolving nature of biosorption applications for environmental remediation. We provide a
comprehensive analysis, including an examination of various biosorbent systems, which
highlights the novel contributions in biosorption technology for tackling heavy metal
contamination in diverse industrial settings.
2. The Negative Impact of Heavy Metals on Human Health
Heavy metals are often defined as a group of metallic elements characterized by their
high density, atomic weight, and potential toxicity to human health. While some heavy
metals are essential for life in trace amounts (for example, Co is a constituent of vitamin B
12
),
excessive or prolonged exposure to certain heavy metals can have severe negative impacts
on various physiological systems. It is noteworthy that in the scientific literature the term
“heavy metals” has been diversely defined to even include metalloids, such as the non-metals
As and Se. As this has raised questions about the nomenclature of these elements, in this
review, we adopt the definition proposed by Ali and Khan [
42
], i.e., “heavy metals are naturally
occurring metals having atomic number greater than 20 and an elemental density greater than 5 g/mL”.
Some exemplary metals, such as cadmium, chromium, nickel, cobalt, lead, copper, and zinc,
have been selected from this group to consider the possibility of their biosorption. The only
exception among the metals considered is a very harmful contaminant, the metalloid arsenic,
the removal of which with biosorbents is also taken into account.
Table 1demonstrates the negative influence of the selected heavy metals frequently
reported in industrial effluents, as discussed in this review, on human health. It details
their industrial sources and the detrimental effects they can have on organs, tissues, and
overall well-being.
Table 1. The influence of the selected heavy metals on human health.
Metal Industrial Sources Negative Effect on Human Health Ref.
Arsenic Mining, smelting, pesticide manufacturing,
wood preservatives
Skin lesions, cardiovascular diseases, neurotoxicity,
developmental effects, diabetes, cancers
(skin, lung, bladder, liver, kidney) [43,44]
Cadmium Metallurgical, electroplating, mining
industry, manufacturing of paintings
Lung and kidney diseases; breast, lung, prostate,
nasopharynx, pancreas, and kidney cancers; fetal
growth restriction; skeletal damage [45–47]
Cobalt
Electroplating, metallurgy, mining,
superalloys “resistant to corrosion and
wear”, manufacturing industries,
rechargeable battery electrodes, nuclear
power plants, petrochemicals, electronics,
paints and pigments, chemical industry
Damage to liver, heart failure, asthma, allergy, bone
defects, hair loss, low blood pressure, nervous system
disorders, reduced thyroid activity (goiter), vomiting,
genotoxicity, risk for cancer
[38,48]
Copper Electroplating, metallurgical industry Kidney damage, anemia [49]
Chromium
(especially
Cr(VI)) Electroplating, tanning and mining industry Mutagenic and carcinogenic effects, kidney
dysfunction, lung cancer, and critical health impacts
like diarrhea, ulcers, and damage to blood cells [47,50,51]
Lead
Metallurgical, electroplating, metal finishing
industries, manufacturing of paints, storage
batteries, petroleum refining and drainage
from ore mines
Risk of lung, stomach, and bladder cancer; damage to
the kidney, nervous system, reproductive system, liver,
and brain; causing sickness during pregnancy, Pb can
also hamper fetal growth in the early stage
[45,52,53]
Mercury Metal smelting, coal production, waste
disposal, and chemical synthesis Neurotoxicity and nephrotoxicity, cognitive
impairment in children and fetal abnormalities [45,54]
Nickel Alloy production, electroplating, production
of nickel–cadmium batteries Allergy, cardiovascular and kidney diseases, lung
fibrosis, lung and nasal cancer [47,55]
Zinc Electroplating, hot-dip galvanizing,
metallurgy, production of batteries, pigments
Disorders to the immune system, prostate problems,
diabetes and macular degeneration [56,57]
Materials 2024,17, 1155 5 of 21
3. Development of Advanced/Modified Biosorbents
One key focus of current research is the creation and optimization of advanced biosor-
bents. This involves harnessing the potential of diverse biological materials, such as agricul-
tural residues [
12
,
13
,
24
,
58
], microorganisms [
5
,
58
], algae [
59
–
61
], and fungi
[6,62,63] (Table 2)
.
Researchers are actively working to identify and engineer biosorbents with enhanced affinity
and selectivity for heavy metals. This approach aims to maximize the efficiency of removing
pollutants from aqueous solutions while minimizing the ecological impact.
Table 2. Examples of biosorbent systems applied for heavy metal removal from industrial effluents.
Metal/Sorbent Source Result Ref.
As(III)
Fungal isolates, APR-1 (Aspergillus
niger) and APR-2 (Aspergillus spp.),
immobilized on Luffa aegyptiaca
(sponge gourd) (an agro-waste
as biosorbent)
Industrial sewage from different
regions of Davangere, Davangere
District, India
Conc. in mg/L 17,995.87 (As)
R in %: 53.94 and 52.54 for
APR-1 and APR-2
No results: regeneration, the possibility of
reuse, or further treatment of the biomass
[44]
As(V)
Chemically pretreated (NaOH)
unshelled Moringa oleifera seeds
Cassava wastewater, Nsukka, India
Conc. in mg/L: 1.81–5.42 (As),
0–0.05 (Pb), 0.06–0.78 (Mn),
0.31–0.82 (Ni), 0.35–0.61 (Zn),
0.03–0.06 (Cu), 0.09–0.35 (Cd),
0.06–0.35 (Cr)
R in %: 92.9 for optimal conditions: pH 4.0,
contact time of 30 min, and dosage of 2 g [64]
Cr(VI)
Aspergillus niger:cleaned with
distilled water, boiled with 0.5 M
NaOH for 15 min, rinsed with
deionized water, dried at 60 ◦C for
24 h, and ground
Mining wastewater was recovered
from a mine pit located in Abaja
community, Ebonyi State, Nigeria
Conc. in mg/L: 1.445 (Cr(VI)), 0.381
(Cr(III)), 0.537(Fe(III)), 0.840
(PO43−), 0.296 (SO42−), 0.01 (Cl−);
pH 6, relative density 1.09,
conductivity 18.7·10−6S/m,
turbidity 3.92 NTU, TSS 0.12 mg/L,
TDS 93.5 mg/L
qmax: 0.0574 mg/g
Conditions: 5 h contact time, biosorbent
dosage 2.8 g, 200 rpm agitation speed
No results: regeneration or
the possibility of reuse
[37]
Cr(III)
Cladodes of Oputinia ficus-inida
var. ‘Orelha de elefante’: washed
with water, cut into pieces with
dimensions of 3 cm ×3 cm ×1 cm,
then dried at 55 ◦C for 72 h
and ground
Tannery stabilization pond in Brazil
Conc. of Cr2O3in g/L: 1.55–1.72,
pH 7.25
R in %: 74.8 and 84.9 using 2 and 4 g of
biomass, respectively
qmax: 611.49 mg/g
Conditions: 60 min, without
correction of pH
No results: regeneration or the
possibility of reuse
[29]
Cr(VI), Ni(II)
Platanus orientalis bark: washed
with water, dried in sun for 3 days,
ground to a fine powder, and dried
in oven at 100 ◦C for 24 h
Modification of sorbent: acid
activation by 0.4 M HNO3and
ddH2O for 24 h (to increase the
surface area and to prevent the
elution of tannin compounds)
Plating industry, Tehran, Iran
Conc. in mg/L: 556.5 (Ni), 46.7 (Fe),
86.39 (Cr(VI)), 2 (Cu), 0.68 (Ag),
0.48 (Al), 0.47 (Sn), 0.44 (Pb),
0.35 (Ba), 0.18 (Sb), Hg (0.02),
<0.01 (As, Bi, Co, Cd, Mo)
R in %: 89.6 and 90.7 (Cr, with
non-modified and modified bark),
74.5 and 56.5 (Ni, with non-modified
and modified bark)
Conditions: for Cr, pH 5, 2 g/L of sorbent
dosage, 5 h; for Ni, pH 3, 2 g/L sorbent
dosage, 1.5 h
q in mg/g: 13.42 and 19.92 (Cr, with
non-modified and modified bark),
126.58 and 285.714 (Ni, with non-modified
and modified bark)
No results: regeneration or the
possibility of reuse
[65]
Materials 2024,17, 1155 6 of 21
Table 2. Cont.
Metal/Sorbent Source Result Ref.
Cu(II) and Pb(II)
Shrimp shells (without heads):
cleaned with water, dried at 70 ◦C
for 12 h, ground, biological pigment
and protein removed (mixed with
5 wt. %. NaOH and 1 wt. H2O2for
3 days at 30 ◦C), and
washed with water
Semiconductor electroplating
wastewater (Vizianagaram, Andhra
Pradesh, India)
Conc. of Cu and Pb = 25–460 mg/L
Maximum efficiency in % (R):
96.4 for Cu and 89.8 for Pb
Sorption capacity in mg/g (qmax):
5.78 for Cu and 5.39 for Pb
Conditions: pH 5 for Cu, pH 6 for Pb,
metal conc. 20 mg/L, biosorbent dosage
0.1 g and temp. 30 ◦C
No results: regeneration or
the possibility of reuse
[36]
Cu(II)
Red alga Gracilaria chilensis
Material pretreatment: dried alga
suspended in 0.2 M CaCl2at pH 5
for 4 h, then washed several times
with deionized water to remove
excess calcium, filtered, and dried
for 12 h at 60 ◦C
A solution obtained after leaching
with 1 M H2SO4of mining tailings
from an abandoned deposit in the
north of Chile and subsequent
Fe precipitation
Conc. in mg/L: 200 (Fe ions),
150 (Cu(II)), pH 1.5
Cu(II) qmax 0.311 mmol/g
No data for Fe ion sorption
35% Cu(II) desorption with 0.05 M H2SO4
[66]
Fe, Mn, Cr, As, Cd, Ni, and Pb
Opuntia ficus-indica mucilage:
washed with fresh water and liquid
soap before procedure of mucilage
extraction (heated at 40 ◦C, stirred
at 300 rpm for 4 h, filtered and
refrigerated at 4 ◦C for 18 h,
freeze-dried under vacuum
(0.04 mbar) for 6 days)
Yautepec River, Morelos, México;
sources of pollution: livestock,
agricultural, recreation, public and
industrial activities (automotive,
food, cosmetic, pharmaceutical,
colorant, textile, chemical,
agrochemical, and metallurgical),
ashes and gases from
Popocatépetl volcano
Conc. in µg/L: 4.3–14.7 (Cu),
0.2–9.5 (Cd), 3.7–13.4 (Cr), 0–44.1
(Ni), 9.3–80.8 (Pb), 7.4–19.6 (Zn),
3–405.9 (Mn), 44.5–1546 (Fe), 2–9.1
(As), pH 5.9–8.5, turbidity 0–3.4
NTU, conductivity 239–2628
µ
S/cm
R in %: 96 (Fe), 91 (Mn), 70 (As), 60 (Cr),
39 (Ni), 32 (Cd), 26 (Pb)
No results: regeneration or the
possibility of reuse
[67]
Co(II), Ni(II), Zn(II), Cu(II)
Serratia marcescens strain 16:
isolated from serpentine deposits
located in Moa (Cuba)
Synthetic solution based on
composition from residual liquor
WL from the company Moa Nickel
S. A. Cuba
Conc. in mg/L: 2 (Co(II)), 25
(Ni(II)), 15 (Zn(II)), (Cu(II))
R in % after four cycles in monometallic
systems: 60.9 (Co), 53.6 (Ni),
43.1 (Cu), 78.8% (Zn)
R in % after four cycles in multimetallic
systems: 39.7 (Co), 40.2% (Ni),
42.8% (Cu), 44.7 (Zn)
The monometallic system exhibited a
sorption capacity two to three times greater
compared to the presence of bi-metallic
and multimetallic solutions, q for
monometallic solution in mg/g: 2.3 (Co),
11.4 (Ni), 8.6 (Cu), 11.9 (Zn)
Conditions: contact time 2 h,
biomass 0.6 g/L
Desorption of metals and reuse: 0.1 M HCl
for desorption (90% after 10 min), several
times reduction in sorption
capacity after 4 cycles
[68]
Materials 2024,17, 1155 7 of 21
Table 2. Cont.
Metal/Sorbent Source Result Ref.
Pb(II), Cu(II), Zn(II), Ni(II)
Gossypium hirsutum stems from
the fields of Khanewal, Pakistan:
dried for 15 days, washed with
water, dried at 50 ◦C, then ground,
washed with water, and dried in an
oven at 60 ◦C. Modification in the
solution of 0.2 M HCl and 0.2 M
NaOH separately
Industrial effluents from discharge
points (including textile and electric
cable manufacturers; tanneries; and
pesticide, pharmaceutical, and
fertilizer plants) in Multan, Pakistan
Conc. in mg/L: 3.7 (Pb), 3.9 (Cu),
6.3 (Zn), 2.5 (Ni)
R in %: 78.5 (Pb), 80.3 (Cu), 81.4 (Zn)
and 82.6 (Ni)
q in mg/g: 121.2 (Pb), 117.09 (Cu),
130.6 (Zn), 111.09 (Ni)
Conditions: 0.5 g sorbent, 30 ◦C,
pH 5.5, 30 min
Regeneration using 0.1 M HNO
3,
only from
model solutions, 5 cycles, with desorption
efficiency in % (92.9–85.4 (Pb),
93.2–86.1 (Cu), 92.5–85.9 (Zn),
93.8–84.8 (Ni))
[69]
Pb(II)
Lactic acid
bacteria: Limosilactobacillus
fermentum CN-005, Lactobacillus
fermentum CN-011
Simulated wastewater collected
from Taihu Lake, China, and spiked
with Pb(II) standard solution at five
levels: 12.92, 16.17, 17.70,
20.22, and 23.94 mg/L
Average sorption efficiency of Pb(II):
73.38% with CN-011, 74.15% with CN-005
No results: the possibility of reuse or
further treatment of the biomass
[70]
Zn(II), Fe(II), Pb(II), Cu(II)
Arthrospira platensis microalgae
cultivated in mining wastewater
Mining wastewater from surface
and underground
water in Huangshaping, Hunan
Province, China
Biosorption efficiency at
pH > 7.1: 93% SO42−, 99% Fe(II), 95%
Pb(II), 89% Zn(II), 94% Cu(II).
No results: regeneration, the possibility of
reuse, or further treatment of the biomass
[71]
Pb(II), Ni(II)
24 heavy metal-resistant fungi
isolated from different industrial
wastes from India (near areas of
different metal-fed industries)
Sewage, sludge, and effluents
collected from 23 different
industrial units located at different
locations in India
R in %: 93 for Pb using resistant fungi,
Aspergillus terreus and Talaromyces
islandicus; 91 for Ni using Neurospora crassa
and Aspergillus flavus; and 95 for Pb and Ni
using the fungal consortia
[72]
Zn(II)
Sawdust of Indian rosewood
from a timber industry,
Bathinda (Punjab), India
Sawdust-derived biosorbents:
after boiling (SDB), chemical
modification with formaldehyde
(SDF) and sulfuric acid (SDS)
A real electroplating industrial
effluent (Ludhiana, Punjab, India)
Conc. in mg/L: 26–46 (Zn),
0.14–1.86 (Cu), 0.05–1.76 (Ni);
37–540 ppm of sulfates,
pH 1.65–5.36
Zn(II) qeq: 35.72 mg/g (SDB), 43.74 mg/g
(SDF), 45.87 mg/g (SDS) at pH 6
Pore size of biosorbents in m2/g:
232.928 (SDB)
, 291.102 (SDF), 498.873 (SDS)
[57]
Zn(II)
Sugarbeet pulp and brown alga
Fucus vesiculosus from the
northern Atlantic coast of Spain in
small glass columns (2.5 cm inner
diameter and 40 cm length) or
F.vesiculosus in glass columns
(7.5 cm inner diameter and 100 cm
length)—a pilot plant
Continuous biosorption tests with
real effluents from Industrial
Goñabe (Valladolid, Spain)
Conc. in mg/L: 546 (Zn), 22.9 (Fe),
10.8 (Cr), 0.129 (Cu), 0.050 (Ni),
116 (sulfate), 2520 (chloride),
pH 1.45
At F. vesiculosus qmax = 0.94 mmol
Zn(II)/g at pH adjusted to 5
3 consecutive cycles of continuous
sorption–desorption (with 1 N HNO3) and
regeneration with deionized water
[73]
Algae have recently attracted attention as efficient and sustainable biosorbents for
metal removal due to their significant metal-binding capacity, relatively low cost, and
widespread availability in all water sources with diverse surface physiochemical properties.
These biosorbents are characterized by a large binding capacity related to the abundance of
macromolecules in the walls of algal cells, for example, polysaccharides, proteins, lipids,
and uronic acids, and sulfhydryl groups. The naturally dried biomass of the macro-green
alga Enteromorpha intestinalis has been proposed for the simultaneous removal of coexisting
contaminants, i.e., mixed cobalt ions and Congo red dye, from model solutions [
38
], and
the mechanism of Co(II) sorption on the complex algal material was considered. The
multipath binding mechanism of Co(II) biosorption by the surface of algal biomass engages
Materials 2024,17, 1155 8 of 21
functional groups on the cell surface (e.g., sulfhydryl, phosphate, carboxyl, thiol, and
amino groups) as cell surface binding sites on which metal ions sorb through physical
and/or chemical adsorption or ion exchange between metal cations and the cell surface
containing cations such as K
+
, Na
+
, and Mg
2+
. It is important to highlight that among the
four natural and cost-effective biosorbents, namely, macroalgae (Fucus vesiculosus), crab
shells (Cancer pagurus), wood chippings, and iron-rich soil, the crab shell and macroalgae
biosorbents exhibited higher sorption capacities for Cu(II) and Zn(II) from model solutions
containing high concentrations of metal ions compared to commercial biochar and activated
carbon [61].
Two new strains of lactic acid bacteria (LAB), namely, Limosilactobacillus fermentum
CN-005 and Lactobacillus fermentum CN-011, were identified for their high sorption capacity
and tolerance to Pb(II) [
70
]. These strains were utilized for the effective biosorption of Pb(II)
from simulated wastewater (Table 2). Further investigation also showed that several other
strains of lactic acid bacteria (Lactobacillus brevis) exhibit efficient sorption of Pb(II) from
model solutions [
74
,
75
]. It was indicated that the mechanism of biosorption is realized
through Pb(II) interactions with OH and -COO- functional groups on the walls of bacterial
cells and leads to the formation of PbO and Pb(NO3)2.
Also, fungi are known for their ability to adsorb and accumulate heavy metals, con-
firming their great ecological and economic importance for the sustainability of ecosystems.
This makes them potential biomaterials suitable for deployment as sorbents in various
environmental and industrial applications. The large surface area provided by the fun-
gal mycelium and spores is particularly advantageous for metal binding, making them
beneficial materials for efficient metal removal [
76
]. For example, Co(II) was sorbed from
water on three fungal biomasses: Paecilomyces sp., Penicillium sp., and Aspergillus niger [
77
].
Paecilomyces sp. showed the highest removal of Co(II), reaching 93% within 24 h of incuba-
tion in a model solution. Furthermore, the filamentous fungus Paecilomyces sp. was found
to successfully remove 100% of Co(II) from naturally contaminated water and soil after
4 days
of incubation. Similarly, Penicillium sp. and A. niger sorbed 96.4% during seven-day
contact. However, the challenges lie in the kinetics of biosorption and the competition with
other ions in the environment, rendering the application of fungi as biosorbents a complex
task. Moreover, as presented in [
78
], it is possible to isolate the multimetal-tolerant fungus
Aspergillus sp. for removing Zn, Fe, Se, and Ag nanoparticles, potential nanoscale metal
pollutants, from aqueous solutions. Optimal biosorption conditions were determined,
showing high biosorption percentages for two-day-old cells (91.7, 76.8, 52.2, and 39.3% for
selenium, silver, iron, and zinc nanoparticles), pH 7 (80.4, 82, 68.1, and 38.8% for Se, Ag,
Fe, and Zn-NPs), and specific contact times (10 min for Zn and Ag, 40 min for Fe and Se).
The results indicated significant removal efficiencies for zinc, iron, selenium, and silver
nanoparticles, with living fungal pellets outperforming dead biomass. However, dead
fungal biomass may be more practical for environmental applications.
Another approach to the development of advanced biosorbents involves various mod-
ifications of native biomaterials to improve the sorption efficiency and selectivity toward
the target metal ions or facilitate the separation of solid material from liquors. For instance,
magnetically modified peanut husks have been proven to enhance the sorption of Pb(II) and
Cd(II), as well as the separation of the sorbent. However, the strong interaction between
sorbates and magnetic sorbents has been found to reduce the efficiency of desorption,
hindering the regeneration of this modified biomaterial [79].
In turn, the chemical modification of potato starch powder through phosphorylation
using disodium hydrogen orthophosphate has yielded positive results in the sorption of
Pb(II) [
80
]. Native starch typically exhibits low sorption ability due to the lack of specific
functional groups on its surface. Consequently, an increase in the specific surface area (from
2.25 to 6.75 m
2
/g) and average porosity (from 55.48 to 61.44 Å) of the modified biosorbent
compared to the unmodified one can be attributed to these chemical modifications. In
addition, a shift in pH
PZC
from 5.64 to 2.01 was reported for phosphorylated starch, indi-
cating a stronger electrostatic attraction between negatively charged biosorbents and Pb(II)
Materials 2024,17, 1155 9 of 21
ions. Other modified starches include succinylated starches, starch-based composites and
nanoparticles, starch-based hydrogels, and cross-linked or carboxylated starches [81].
An improvement in the sorption capacity of Cd(II) (33.2 mg/g) and Pb(II) (116.7 mg/g)
was reported for citric acid- and Fe
3
O
4
-modified sugarcane bagasse (MSB) compared to the
unmodified sorbent [
82
]. The improvement was primarily attributed to an increase in the
number of O-containing functional groups (e.g., hydroxyl and carboxyl or Fe-OH groups)
and aromatic rings. Correspondingly, multiple mechanisms, such as surface complexation,
electrostatic attraction, and cation–
π
interaction, were involved in the sorption of Cd and Pb
by the modified sugarcane bagasse. Another method to enhance the sorption performance
of Cu(II) (138 mg/g) by providing abundant active sites is the functionalization of cellulose
surfaces with hyperbranched polyamide (HP) with a subnano 3D architecture [83].
4. Optimization of Process Conditions
To enhance the effectiveness of biosorption processes, researchers are studying the
optimization of various operational parameters. This includes fine-tuning factors such as
pH, temperature, contact time, and biomass concentration. Optimizing these conditions
is crucial to achieving the highest possible removal efficiency and ensuring the practical
applicability of biosorption in diverse industrial settings.
Generally, various mathematical and statistical approaches, including statistical design
of experiments (DOE) or central composite design (CCD) for response surface method-
ology (RSM) [
25
,
38
,
80
], are employed to optimize biosorption conditions. It is often ben-
eficial to use a combination of these methods to comprehensively understand interac-
tions between different variables and their impact on biosorption efficiency and indicate
optimal conditions.
Central composite design (CCD) was proposed to optimize biosorption of cobalt
ions on dry biomass from E. intestinalis algae [
38
]. The desirability function predicted a
maximum Co(II) removal yield of 85.35% with E. intestinalis under optimal conditions.
These conditions included an initial pH value of 10, a biomass concentration of 1.0 g/L,
an initial Co(II) concentration of 200 mg/L, and an incubation time of 20 min. Upon
experimental verification, a Co(II) removal rate of 80.22% was achieved, confirming a high
correlation between the experimental values and the predicted ones. This suggests that
the CCD approach effectively optimized the biosorption of Co(II) on algal dry biomass,
highlighting the reliability of the predicted optimal conditions. Furthermore, the Plackett–
Burman design (PBD), the statistical experimental design technique used in the field of
experimental design and optimization, particularly in the context of screening experiments
to identify significant factors that affect a process, could be used successfully, as presented
in [
84
]. The study revealed that the impact of various factors on Cr(VI) biosorption by
Streptomyces rochei ANH was as follows: pH, biomass concentration, and agitation speed
exhibited adverse effects on biosorption efficiency. However, factors such as incubation
temperature, contact time, initial metal concentration, and cell viability showed negligible
effects on metal removal.
Moreover, the incorporation of advanced computational techniques, such as artificial
neural networks (ANNs) and genetic algorithms (GAs), is proving to be highly effective
in further refining biosorption process optimization. ANNs, for instance, can model
complex, non-linear relationships between various operational parameters and biosorption
efficiency, which traditional statistical methods may not fully capture. They provide a robust
framework for predicting optimal conditions even in highly variable industrial effluents.
Similarly, genetic algorithms offer a unique approach by mimicking natural evolutionary
processes to find the best combination of operational parameters for maximum biosorption
efficiency. This technique iteratively alters a set of parameter values, akin to genetic
mutation and selection, to arrive at a near-optimal solution over successive generations. By
this means, GAs can efficiently search through a vast parameter space to identify the most
effective biosorption conditions. For example, in a study focusing on the biosorption of
heavy metals from industrial wastewater, an integrated approach using an ANN and a GA
Materials 2024,17, 1155 10 of 21
was implemented. The model efficiently predicted optimal pH, temperature, and contact
time, which resulted in a significant increase in biosorption capacity, demonstrating the
potential of these computational techniques in improving the efficiency and applicability
of biosorption processes. For instance, these models were successfully adapted for the
prediction of Pb(II) sorption using natural and treated Ardisia compressa K. leaves [
85
],
while the efficacy of artificial neural network (ANN) and adaptive neuro-fuzzy inference
system (ANFIS) techniques was explored for predicting the removal efficiency of heavy
metal ions (lead and nickel) from the active sludge of an industrial wastewater treatment
plant [
86
]. Experimental parameters, including the pH of the solution, contact time, initial
ion concentration, and temperature, were analyzed to determine optimal values. The
ANN utilized a multilayer perceptron network, while the ANFIS employed a Sugeno
fuzzy model for modeling. Comparison between experimental and predicted data yielded
satisfactory results, with correlation coefficients exceeding 98%, indicating high accuracy in
both models, although the ANFIS showed slightly superior performance over the ANN.
Optimal operating conditions were determined via optimization of the genetic algorithm,
leading to acceptable sorption efficiency values when treating a real sludge sample under
these conditions. These findings suggest that the proposed intelligent models serve as
reliable tools for predicting pollutant sorption efficiencies.
Furthermore, researchers are exploring the use of machine learning (ML) algorithms
for predictive modelling of biosorption systems. These algorithms can process large
datasets, learn patterns, and make accurate predictions about biosorption outcomes un-
der various conditions. This not only aids in understanding the complex dynamics of
biosorption processes but also helps in scaling up the technology for industrial applications.
For example, key parameters that affect Cr(VI) biosorption by immobilized Pseudomonas
alcaliphila, including immobilized bacterial cells, contact time, and initial Cr concentrations,
were identified using the Plackett–Burman matrix in [
87
]. A comparative analysis between
the rotatable central composite design (RCCD) and an artificial neural network (ANN) was
conducted to determine the most suitable model to maximize Cr(VI) biosorption. RCCD
experimental data were used to train a feed-forward multilayer perceptron ANN algorithm,
which demonstrated superior predictive accuracy compared to the RCCD in forecasting
optimal wastewater treatment conditions. Scanning electron microscopy revealed the pres-
ence of shiny large particles on the bead surface post-biosorption, while energy dispersive
X-ray analysis detected an additional peak of Cr(VI), confirming the role of immobilized
bacteria in Cr(VI) ion biosorption.
The integration of computational and mathematical methods with experimental re-
search is key to unlocking the full potential of biosorption technologies and their optimal-
ization. Such multidisciplinary approaches not only enhance the efficiency of biosorption
processes but also contribute to their scalability and sustainability, paving the way for their
broader application in environmental remediation and resource recovery.
5. Exploration of Novel Applications
The versatility of biosorption is continually expanding through the exploration of
novel applications. Researchers are investigating its efficacy in addressing emerging chal-
lenges and pollutants, thereby broadening the scope of its environmental applications.
These include the removal of specific pollutants prevalent in various industries, which
makes biosorption an adaptable and targeted solution for different environmental needs.
Biosorption techniques are employed in bioremediation processes to remove contaminants,
such as heavy metals and organic pollutants, from soil. Microorganisms and plants are
utilized to absorb, degrade, or sequester contaminants from the soil matrix, contributing to
soil remediation efforts. For example, rapid urbanization and agricultural intensification
contribute significantly to the generation of municipal solid waste (MSW), necessitating
economically viable innovations for reducing heavy metals to non-toxic levels. For such
problems, Manna et al. [
63
] proposed efficient fungi isolated from sewage sludge for a
biofiltration strategy, using them to remove substantial heavy metals from contaminated
Materials 2024,17, 1155 11 of 21
MSW compost. Trichoderma viride- and Aspergillus flavus-based biofilters exhibited high
removal rates for Pb (>40%) and Cd (>20%), while Aspergillus heteromorphus was more
efficient in removing Cu and Cr (20%). Biofilters based on Trichoderma viride,Aspergillus
heteromorphus,Rhizomucor pusillus, and Aspergillus flavus demonstrated effectiveness in
mitigating the toxicity of Zn (30%) and Ni (>30%). Differential minimum inhibitory concen-
trations, HM uptake, and biosorption capacities among fungi contributed to variations in
biofilter efficacy. In addition, biosorption techniques are applied in air filtration systems to
remove volatile organic compounds (VOCs), odors, and other pollutants from indoor and
outdoor air. Biofilters containing microbial cultures or activated carbon filters enhanced
with microorganisms are used to capture and degrade airborne contaminants [
62
]. Biosorp-
tion is also utilized in biological leaching processes for metal recovery from ores. Certain
microorganisms are capable of selective binding to target metals, facilitating their extraction
and recovery from mineral ores through bioleaching techniques [88].
6. Engineered Microorganisms and Nanomaterials
An exciting frontier in biosorption research involves the development of engineered
microorganisms and nanomaterials tailored for enhanced biosorption capabilities. Through
genetic modification and the incorporation of nanoscale materials, researchers aim to
improve the selectivity, capacity, and overall performance of biosorbents. This cutting-edge
approach holds promise for pushing the boundaries of biosorption technology and opening
up new possibilities for efficient heavy metal removal.
There is a noticeable trend for the isolation of bacteria that are resistant to heavy metals
from the environment. For example, a heavy metal-tolerant bacterium, Oceanobacillus
profundus KBZ 3-2, isolated from mine waste (from the abandoned Kabwe Mine, Zambia)
showed a high removal efficiency for Pb(II) (97%) and a lower efficiency for Zn(II) (54%) [
89
],
while the Cd-resistant bacterium Bacillus subtilis KC6 screened from Cd-contaminated soil
sampled from an abandoned open-air pyrite mine (Xingwen, Sichuan Province, China)
showed a reduction in cadmium of up to 86% [90].
The genetic engineering trend is also noticeable. For example, the bacterium Pseu-
domonas putida has been genetically modified to express metal-binding peptides on its cell
surface, enhancing its ability to sorb heavy metals from contaminated water. Moreover,
genetic engineering techniques have been used to engineer Escherichia coli strains with
enhanced metal-binding capabilities, making them effective biosorbents for the removal
of heavy metals from wastewater. As presented in [
91
], these synthetic bacterial cells and
magnetic nanoparticles could be used to remove Cd(II) and Pb(II) with over 90% efficiency
and could be recycled by artificial magnetic fields. This bioengineering effort involves the
integration of a synthetic metallothionein and a green fluorescence protein-encoding (GFP)
reporting gene into these bacteria, facilitating the expression of a fusion protein aimed at
heavy metal biosorption. Additionally, the use of magnetic nanoparticles (MNPs) coated
with polyethylenimine (PEI) and diethylenetriaminepentaacetic acid (DTPA) is discussed
as a method for enhancing the recruitment and recovery of these bacterial cells after heavy
metal remediation tasks. These MNPs were designed to interact with the modified bacteria,
facilitating magnetic separation and preventing the release of engineered genetic materials
into the environment. Magnetic nanoparticles have emerged as a highly effective solution
for the removal of metal ions from various environmental matrices. This innovative ap-
proach leverages the unique properties of NPs, specifically their magnetic characteristics, to
facilitate the easy and efficient separation of metal ions from contaminated water sources.
7. Deactivation and Regeneration of Biosorbents
The issue of biosorbent material deactivation and failure over time poses significant
challenges in the practical application of sorption processes for pollutant removal. Al-
though biosorbents initially exhibit promising sorption capabilities (see Table 2), their
long-term performance can be influenced by various factors, leading to deactivation and
reduced efficacy. The majority of works on the use of sorbents, however, do not describe
Materials 2024,17, 1155 12 of 21
this problem. Biosorbents typically have a finite number of binding sites available for
adsorption. Over time, these binding sites can become saturated as the biosorbent accu-
mulates pollutants, decreasing its capacity to sorb additional contaminants. For example,
as shown in the work on the removal of iron and phosphorus from a model solution by
mango leaf biosorbents [
92
], the deactivation of biosorbents is attributed to the reversible or
irreversible chemisorption of iron and phosphorous molecules to active sites. This reduces
the number of sites available for the adsorption reaction. The poisoning may occur as a
result of highly sorbed feed impurities, making the regeneration of poisoned materials
challenging. The authors showed that the highest desorption rate, reaching 93.15%, was
observed using 0.05 M HCl. However, the use of HNO
3
with the same concentration as the
eluent resulted in even more efficient desorption, reaching 94.56%. The sorption of iron and
phosphorus on the regenerated biosorbent remained consistent for the first three cycles,
maintaining a level of 97.38%. Subsequently, in the fourth cycle, a decrease was observed,
reducing to 82.36%.
Furthermore, the surface of biosorbents may experience fouling due to the accumu-
lation of impurities, organic matter, or other substances present in treated water. This
fouling can lead to a decrease in the active surface area and, consequently, a decline in
the sorption performance. For example, in the case of seawater purification, algae are
typical biofouling microorganisms. In this case, it is proposed to prepare a biosorbent with
antifouling properties, such as a 3D reticular antifouling sorbent based on polyethylen-
imine and guanidineacetic acid, for the extraction of uranium from seawater [
93
]. The
material demonstrates high sorption and regeneration performance with a sorption ca-
pacity of 414.93 mg/g. Moreover, the new sorbent effectively inhibits the interaction
between Closterium venus and material surfaces in antibiofouling assays. Hydrochloric acid
(0.4 M)
is also proposed as a regenerative agent for a biosorbent based on the brown alga
Sargassum polycystum
for the removal of cadmium and zinc from a model solution [
59
]. The
maximum adsorption capacities (q
max
) were 105.26 mg/g and 116.2 mg/g for Cd and Zn,
respectively, and the biosorbent demonstrated significant efficiency over five consecutive
cycles of the sorption–desorption process using 0.4 M HCl, with a decrease in efficiency of
approximately 5% over the five cycles.
Not without significance is the type of material that is used as a biosorbent. The
structural integrity of biosorbent materials may degrade with time due to aging processes,
affecting their sorption capabilities [
94
]. Structural changes, such as the degradation of
cellulose in agricultural residues, can reduce the overall effectiveness of a biosorbent [
95
].
In the case of microorganisms used as biosorbents, the formation of biofilms on their
surfaces can occur over time. Although biofilms can initially enhance sorption, they can
also create a protective layer that hinders further sorption or promotes the detachment
of microorganisms from the surface. For example, because living biofilms are dynamic
communities of microorganisms, such that biofilm properties change over time, they
affect the biosorption behavior [
96
]. Thus, biofilm incubation time on a geotextile was
investigated in Cu(II) biosorption. The results showed that the biofilms incubated for one
day exhibited the highest biosorption capacities in different Cu(II) concentrations, ranging
from 4 to
119 mg/g
. However, biosorption capacity decreased as biofilm development
progressed, with the lowest capacities observed on day 21 of incubation (0.75 to 61 mg/g).
This reduction in biosorption capacity, according to the authors’ opinion, was attributed to
the dominance of a monolayer in Cu(II) biosorption. Although increasing the incubation
time led to increased biofilm mass, inner layers became less active in biosorption, resulting
in a decrease in the surface-to-mass ratio of biosorption. However, the biosorption capacity
increased between days 21 and 28 due to the dispersion stage of biofilm development, where
some parts were detached and released into the bioreactor solution. This was supported
by the lower mass of biofilms harvested on day 28 compared to day 21, indicating the
appearance of the dispersion stage during this period.
Also, the sorption efficiency for heavy metals (Pb, Ni, Cd, and Hg in model solu-
tions) using the biomass of brown algae (Padina gymnospora), green algae (Cladophoropsis
Materials 2024,17, 1155 13 of 21
membranacea), and red algae (Hypnea hamulosa) depends on time. The duration of contact
between the biosorbent and sorbate might not directly influence biosorption capacity, but
it serves as a constraining factor. With extended time, the biosorbent can exhibit its full
sorption potential, showcasing its maximum capacity. At a specific duration, the sorbent
achieves saturation, indicating complete occupation of its binding sites [60].
Another critical aspect concerning industrial effluents is the impact of relatively high
concentrations of metal ions in real solutions, often reaching hundreds of milligrams to even
several grams of heavy metals per liter. This leads to rapid saturation of the biosorbents
with metals. Once saturation occurs, the sorption process must be interrupted, and a
desorption operation followed by a subsequent washing step is necessary to regenerate
the biosorbent for reuse while maintaining its sorption capacity. Overcoming biosorbent
saturation is a challenge to ensure the continuous operation of waste treatment plants
required by industries to decontaminate their effluents. In 2008, a patented solution for
Cu(II) recovery from mining effluents was proposed, involving pretreatment of the liquor
with conventional methods (e.g., precipitation by increasing pH, conventional solvent
extraction, or emulsion liquid membrane extraction) to reduce high amounts of metal
ions before treating the effluents with continuous biosorption on microorganisms (Bacillus,
Pseudomonas,Klebsiella,Enterobacter, or mixtures of microorganisms that form biofilms
isolated from the natural environment) immobilized on a fixed bed [
97
]. Laboratory tests
showed that the efficient recovery of Cu(II) from leached tailings from an abandoned
deposit in the north of Chile was possible using biomass of the red alga Gracilaria chilensis.
The sulfuric leachate contained 224 mg/L of Cu(II) and 602 mg/L of Fe ions, prompting
selective precipitation of iron hydroxide as a pretreatment step. This resulted in a pH of 1.5,
with 150 mg/L Cu(II) and 200 mg/L of Fe ions in the final composition of the solution used
for the biosorption, with a maximum adsorption capacity for Cu(II) of 0.311 mmmol/1 g
reached by the red alga [66].
Moreover, biosorption processes are often sensitive to variations in environmental
conditions, such as pH and temperature [
98
]. Fluctuations in these factors can alter the
structure and functionality of the biosorbent, resulting in reduced sorption efficiency over
time. This is especially important when applied to real wastewater. On the other hand, it
has been pointed out that keeping biomass in a harsh environment for a long time would
cause it to respond to harsh conditions, produce mutants, and probably spread genetic
resistance to the next generation [99].
Certainly, various phenomena can simultaneously deactivate biosorbents. For exam-
ple, brewer’s spent grain (BSG) exhibited an affinity for heavy metal cations in the following
sequence: Mn(II)
≈
Zn(II) < Ni(II) < Cd(II) < Cu(II) < Pb(II). However, it was observed
that the functional groups of BSG lose their effectiveness in successive sorption–desorption
cycles either due to blockage by other cations or chemical decomposition resulting from
repeated contact with a 0.1 M HCl solution. Following each sorption–desorption cycle, a
5–10% decline in Cu(II) removal was indicated, ultimately resulting in a complete loss of
sorption properties after the sixteenth cycle [15].
Although reusability is a desirable characteristic of biosorbents, challenges may arise
in the desorption and regeneration processes. Over successive cycles, biosorbents may lose
their effectiveness, and attempts to regenerate them may be insufficient in restoring their
initial sorption capacity. Implementing effective regeneration techniques, such as chemical
treatment [
69
], can help mitigate the deactivation of biosorbents and extend their opera-
tional lifespan. Among the proposed solutions are modifications of biosorbent materials
through physical or chemical means. Such solutions can enhance their resistance to fouling
and environmental changes, improving their long-term stability. Regeneration concerns
depend both on the material from which the sorbent is made and on the reagents that
are used in the regeneration process. For example, the regeneration of a modified biosor-
bent, PD-Fe
3
O
4
@carboxymethyl chitosan (PD stands for poly(methacryloxyethyltrimethyl
ammonium chloride), after Cu(II) and Cr(VI) sorption indicates a noticeable decrease in
sorption performance during the initial recycling cycle, followed by minimal changes in
Materials 2024,17, 1155 14 of 21
subsequent regeneration cycles. This decline may stem from challenges related to the
regeneration of groups located at the base polymer chain. Interestingly, the desorption
performance improved significantly when a mixture of NaOH and NaCl solutions was used
compared to a single NaOH solution. The recovery efficiency of the mixed solution reached
83.7%, with a corresponding adsorption capacity of 138.3 mg/g. This improvement could
be attributed to increased competition between Cl
−
and Cr(VI) for adsorption sites on the
PD-Fe
3
O
4
@CCS surface, confirming that electrostatic interaction and ion exchange serve as
primary driving forces for Cr(VI) adsorption [
100
]. Also, studies of the regeneration of the
chitosan-based biosorbent with Fe
3
O
4
NPs have emphasized both the decrease in arsenic
sorption capacity and the possibility of regeneration for up to five cycles [
101
]. The results
indicated a gradual decrease in the removal efficiency from 99.5% to 95.0% for As(V) and
from 99.0% to 92.5% for As(III). Regeneration of the sorbent was efficiently achieved using
a 0.1 M NaOH solution, which neutralized the surface groups of the chitosan, weakening
the bonding forces between the sorbent surface and the arsenic species, thereby facilitating
the release of arsenic species and the regeneration of the biosorbent for subsequent reuse.
Moreover, combining biosorption with complementary technologies, such as membrane
filtration or flotation and sedimentation, can create hybrid systems that address the limita-
tions of biosorbent deactivation [
58
]. It was reported that a solution of NaOH is the most
effective regenerating agent for desorbing Pb(II) from a low-cost biosorbent, such as Citrus
grandis (Pomelo) leaves [
22
]. Furthermore, it enhanced the sorption capacity for up to four
sorption–desorption cycles. The ability to desorb and regenerate can be attributed to the
removal of wax and fats by the alkaline solution, which results in the exposure of surface
functional groups and their deprotonation, thereby increasing the electrostatic attraction
between the negatively charged surface of pomelo leaves and Pb(II) ions.
Understanding and addressing the issue of biosorbent material deactivation and
failure over time is crucial for the successful implementation of sorption in practical appli-
cations. Ongoing research should focus on the development of more resilient biosorbent
materials, optimizing regeneration techniques, and exploring innovative approaches to
improve the long-term performance and sustainability of biosorption technologies. An
exemplary illustration of this approach has been demonstrated in the development of
biosorption of Zn(II) from industrial effluents using F. vesiculosus from the laboratory scale
to a pilot plant [
73
] (see Table 2). Pilot tests with wastewaters in the sorption–desorption
regeneration cycle indicated that the treatment of diluted electroplating effluents originat-
ing from a spent zinc bath (1–100 mg/L Zn(II)) containing traces of other metals led to an
increase in the column service time.
Most of the reported biosorption research is focused on the removal of heavy metals
from model solutions. However, there are a few studies exploring the application of
biosorbents in real systems. Table 2provides examples of the removal of Cu(II), Pb(II),
Cr(VI), Cu(II), Ni(II), and Zn(II) from actual industrial effluents.
Based on Table 2, a visualization capturing the key findings and providing a compari-
son of percentage removal values among different metals, expressing sorption efficiency,
is shown in Figure 1. Cd(II) removal is not shown in the figure, as there was only one
percentage removal value found in the literature.
The visualization of adsorption efficiency demonstrates that various native organic
biosorbents can remove metal ions such as Cu(II), Pb(II), Cr(III), and Cr(VI) from industrial
effluents the most effectively (Figure 1). In spite of the efficient removal of the variety of
heavy metals from industrial wastewater, to the best of our knowledge, there are neither
working pilot nor industrial plants using native organic biosorbents.
Materials 2024,17, 1155 15 of 21
Materials 2024, 17, x FOR PEER REVIEW 15 of 22
Most of the reported biosorption research is focused on the removal of heavy metals
from model solutions. However, there are a few studies exploring the application of bi-
osorbents in real systems. Table 2 provides examples of the removal of Cu(II), Pb(II),
Cr(VI), Cu(II), Ni(II), and Zn(II) from actual industrial effluents.
Based on Table 2, a visualization capturing the key findings and providing a com-
parison of percentage removal values among different metals, expressing sorption effi-
ciency, is shown in Figure 1. Cd(II) removal is not shown in the figure, as there was only
one percentage removal value found in the literature.
Figure 1. Comparison of removal of heavy metals with biosorbents.
The visualization of adsorption efficiency demonstrates that various native organic
biosorbents can remove metal ions such as Cu(II), Pb(II), Cr(III), and Cr(VI) from indus-
trial effluents the most effectively (Figure 1). In spite of the efficient removal of the variety
of heavy metals from industrial wastewater, to the best of our knowledge, there are nei-
ther working pilot nor industrial plants using native organic biosorbents.
8. Conclusions
Biosorption has emerged as a promising strategy for mitigating pollutants in
wastewater and industrial effluents, providing a sustainable and environmentally
friendly solution to water pollution challenges. Ongoing research shows some pathways
in this field to develop future technological advancements to enhance the effectiveness
and applicability of biosorption in the future. While research on the utilization of bio-
materials has experienced growth in recent years, much of it still revolves around model
solutions. Furthermore, from an industrial perspective, untreated biomass does not yet
appear to be considered as an attractive sorbent, unlike activated carbon or biochars de-
rived from various biomass sources, which are commercially produced and could serve
as alternatives to synthetic sorbents. Although the efficacy of metal recovery with acti-
vated carbon has been demonstrated to be highly efficient, its high cost and challenging
regeneration present obstacles for treating large volumes of effluents or very diluted so-
lutions. In such instances, native organic biosorbents are likely to be proposed as an al-
ternative solution for effluent treatment. Certain types of algae, such as brown algae (e.g.,
Fucus vesiculosus), stand out as promising biosorbents. Algae have demonstrated signifi-
cant potential due to their natural abundance, developed surface area, and ability to ac-
cumulate metals and other pollutants effectively. Additionally, agricultural by-products
Figure 1. Comparison of removal of heavy metals with biosorbents.
8. Conclusions
Biosorption has emerged as a promising strategy for mitigating pollutants in wastewa-
ter and industrial effluents, providing a sustainable and environmentally friendly solution
to water pollution challenges. Ongoing research shows some pathways in this field to de-
velop future technological advancements to enhance the effectiveness and applicability of
biosorption in the future. While research on the utilization of biomaterials has experienced
growth in recent years, much of it still revolves around model solutions. Furthermore,
from an industrial perspective, untreated biomass does not yet appear to be considered as
an attractive sorbent, unlike activated carbon or biochars derived from various biomass
sources, which are commercially produced and could serve as alternatives to synthetic
sorbents. Although the efficacy of metal recovery with activated carbon has been demon-
strated to be highly efficient, its high cost and challenging regeneration present obstacles
for treating large volumes of effluents or very diluted solutions. In such instances, na-
tive organic biosorbents are likely to be proposed as an alternative solution for effluent
treatment. Certain types of algae, such as brown algae (e.g., Fucus vesiculosus), stand out
as promising biosorbents. Algae have demonstrated significant potential due to their
natural abundance, developed surface area, and ability to accumulate metals and other
pollutants effectively. Additionally, agricultural by-products like rice husks, coconut shells,
and sugarcane bagasse have shown promise as biosorbents due to their porous structures
and chemical compositions conducive to adsorption processes.
A critical aspect involves optimizing various parameters, such as pH, temperature,
biomass concentration, and contact time, to enhance biosorption efficiency, especially for
the treatment of real industrial wastes that are challenging due to their complex compo-
sitions. Additionally, the regeneration of biosorbents poses a challenge due to potential
damage during desorption processes or energy-intensive procedures and also due to the
need to ensure the continuous operation of plants. Looking ahead, future perspectives
involve ongoing research and development efforts aimed at refining biosorption processes,
improving selectivity, and innovating new biosorbents. Furthermore, the integration of
biosorption with complementary treatment technologies holds promise for achieving com-
prehensive and efficient wastewater treatment systems. The incorporation of emerging
technologies, such as artificial intelligence and nanomaterials, has the potential to revo-
lutionize biosorption techniques, providing more precise and efficient pollutant removal.
Collaboration among academia, industry, and government agencies will be crucial in fully
realizing the potential of biosorption to address modern environmental challenges.
Materials 2024,17, 1155 16 of 21
Supplementary Materials: The following supporting information can be downloaded at: https://doi.
org/10.5281/zenodo.10702893, PRISMA 2020 flow diagram for the review; Figure S1: Cluster analysis
of semantic web using VOSviewer software version 1.6.19. ref. [102] is cited in Supplmentary File.
Author Contributions: Conceptualization, K.S. and M.R.-R.; methodology, K.S. and M.R.-R.; writing—
original draft preparation, K.S. and M.R.-R.; writing—review and editing, K.S. and M.R.-R.; visual-
ization, K.S. and M.R.-R.; supervision, K.S. and M.R.-R.; project administration, K.S. and M.R.-R.;
funding acquisition, K.S. and M.R.-R. All authors have read and agreed to the published version of
the manuscript.
Funding: The research was funded by the Polish Ministry of Science and Education, grant number
0912/SBAD/2410.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: No new data were created or analyzed in this study. Data sharing is
not applicable to this article.
Conflicts of Interest: The authors declare no conflicts of interest. The funders had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or
in the decision to publish the results.
Appendix A. Methodology of the Bibliometric Analysis
To conduct the bibliometric analysis, the search engines employed included PubMed,
Scopus, and Google Scholar. The investigation utilized specific keywords for the search pro-
cess, such as combinations of biosorption with heavy metals, cobalt, nickel, lead, chromium
cadmium, zinc, arsenic, wastewater, and industrial influents.
The exclusion criteria included manuscripts written in languages other than English,
articles that were inaccessible, and those published before 2019 (with exceptions made for ar-
ticles crucial to the presentation of foundational studies on the applications of biosorption).
At the same time, to maintain originality and precision, the search specifically targeted
research articles, with a deliberate exclusion of review articles. Consequently, items featur-
ing titles containing terms such as ‘review’, ‘meta-analysis’, or ‘overview’ were omitted,
except in a few instances. A PRISMA flow diagram detailing the count of identified articles,
screened entries, eligibility assessments, and inclusions or exclusions in the final analysis,
along with the rationales for article exclusions, is available in the Supplementary Materials.
Description of the method used for the systematic literature review:
A. Planning
A.1 Initial idea formulation
Biosorption for the removal of heavy metals: addressing challenges, exploring oppor-
tunities, examining perspectives, and charting research directions.
A.2 PICOC
Population: Biosorption.
Intervention: Use of biosorption for removal of heavy metals from wastewater.
Comparison: The development of biosorbents for use in real sludge.
Outcomes: Treatment support, separation efficiency, and real conditions.
Context: Challenges and opportunities associated with the applications of biosorbents
in heavy metals removal.
B. Research questions
What biosorbents can be used to remove heavy metals from wastewater?
What is the efficiency of the biosorption process?
For which real wastewaters can biosorption be used?
What modifications and improvements are proposed?
What research directions are being pursued?
What challenges are linked to the application of biosorption processes for the removal
of heavy metals?
Materials 2024,17, 1155 17 of 21
C. Digital library sources
Google Scholar, Scopus, and PubMed.
D. Inclusion and exclusion criteria
Inclusion: Results obtained by searching using biosorption with heavy metals, cobalt,
nickel, lead, chromium cadmium, zinc, wastewater, and industrial influents.
Exclusion: Articles published before 2019 and those categorized as reviews, with a few
exceptions made for studies providing fundamental insights into the issues raised.
E. Quality Assessment (QA) checklist
E.1. Ensure that:
The search strategy was accurately delineated. The inclusion and exclusion crite-
ria were suitable and clearly defined. The studies chosen aligned well with the
research question.
The selected papers demonstrated high quality, characterized by robust design and ex-
ecution.
The data were pertinent and thoroughly described. The methods used for paper inclu-
sion were fitting and well documented. The consistency of the results was sufficiently
assessed and presented.
E.2. Data extraction form
By metals: Cobalt, copper, nickel, lead, chromium cadmium, zinc, and arsenic.
By wastewater: Metal industries: mining, electroplating, and metallurgical processes;
textile industries; and the leather industry.
E.3. Conducting
Studies were gathered using the Mendeley reference management tool as a database
resource.
E.4. Study selection and refinement
The literature items were scrutinized for duplicates and filtered based on the exclusion
and inclusion criteria outlined earlier, resulting in a curated set of articles chosen for
the study.
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