J. Kanimozhi3, R. Devika1, and R. Balaji1
1 Department of Biotechnology, Aarupadai Veedu Institute of Technology, Chennai, Tamilnadu, India
2 Department of Chemical Engineering, Hindustan Institute of Technology and Science, Chennai, Tamilnadu, India
3 Department of Biotechnology, Kalasalingam Academy of Research and Education, Krishnankoil, Tamilnadu, India
Introduction
Water plays a significant role in the global economy. Water covers most (71%) of the Earth's surface, but water from fresh sources like rivers, lakes, and streams contributes only 3% to total water resources. Freshwater bodies provide water suitable for human consumption. About 70% of freshwater is expended on irrigation. In many countries, these natural resources are limited, and their unavailability poses significant social and economic concerns (Baroni et al., 2007). As the quantity of water decreases, water quality is also seriously declining due to industrial, municipal, and agricultural wastes. Contamination can arise from wastewater leaking from damaged pipes and the flow of industrial waste into water. This contaminated water poses a constant danger to public health in the form of water‐borne diseases (Arshad and Imran, 2020).
Heavy metal exposure is considered a major environmental concern and a hazard to human health among numerous contaminations in drinking water. Even in minute amounts, toxic metals can cause toxicity when they enter the body due to their non‐degradable nature. Mercury, nickel, arsenic, chromium, manganese, copper, zinc, and cadmium are the most widely intoxicating heavy metals (Jaishankar et al., 2014). The wastewater streams from plating, casting, painting dyes, batteries, mining, and farming are key contributors to heavy metals entering the ecosystem (Ibrahim and Mutawie, 2013). Because of their toxic effects, most heavy metals produce various issues, including kidney problems, brain activity difficulties, and nervous weakness. Sleeplessness, impatience, anemic, dizziness, and muscle pain are some of their hazardous symptoms (Fu and Wang, 2011).
Several techniques for the biosorption of toxic metals from effluent have been developed. They include ion exchange, evaporation, chemical precipitation, and membrane filtration. Activated carbon is by far the most common and widely utilized material for treating wastewater pollution. Materials that are used to prepare higher‐quality activated carbon cost more (Babel, 2003). In recent years, awareness has increased of the development of adsorbents to substitute for expensive activated carbon. The emphasis is on adsorbents that can bind to metal and remove undesirable heavy metals from polluted water at a low cost.
Biosorption and bioaccumulation are environmentally friendly solutions with benefits compared to traditional methods. Owing to their metal‐binding functional groups, abundant natural materials have been considered as viable biosorbents for eliminating heavy metals: for example, microbial biomass, agro waste, and industrial byproducts. Parameters such as pH, temperature, metal ion concentration, biosorbent dose, and agitation rate influence biosorption. After the removal of heavy metals, biosorbents can be regenerated and reused, thus making the process economical (Kanamarlapudi et al., 2018). This chapter provides a summary of some low‐cost biosorbents discussed in recent publications.
Biosorption and Its Mechanism
Biosorption is a simple physical and passive mechanism involving the attachment of biosorbates (metal ions) to the biosorbent surface (of biological origin) (Mrvčić et al., 2012). Simple operation, no demand for supplementary nutrients, low sludge production, lower operational cost, good performance, biosorbent rejuvenation, and no increase in chemical oxygen demand (COD) in water are all advantages of this technology that are major drawbacks of older technologies. Pollutants with parts per billion (ppb) toxicity can be eliminated by biosorption even at diluted concentrations. This process is especially important for removing heavy metals.
The first step in biosorption is to suspend the biosorbent in the biosorbate‐containing solution (metal ions). Equilibrium is achieved after incubation for a given period. The metal‐enriched biomass is separated at this point (Chojnacka, 2010). Biosorption is a dynamic mechanism in which sorbate binds to a biosorbent. Physical attachment of metal ions (Van der Waals interaction or electrostatic forces) or chemical binding (replacement of ions), chelation, precipitation, reduction, and complexation are all possible with a wide range of natural materials as biosorbents. The significant factors that control the biosorption process are (Park et al., 2010) as follows:
Nature of the biosorbent
Category of the biological ligand
Optimum parameters of sorbate and sorbent (temperature, pH, concentration)
Accessibility of binding sites
Biosorbents
Biosorbents are biological elements such as bacteria, agricultural wastes, and municipal byproducts employed in the passive removal of toxins from a system. They have been encouraged since they are made from renewable resources, they are cheap and biologically degradable, and they do not produce toxic compounds after being used. Since they are biological material, they include several functional groups that act as the driving force for hydrophobic interactions, which are mostly pH‐dependent during the sorption process. Biosorbent contains a range of functional sites, including carboxyl, imidazole, sulfuryl, amino, phosphate, sulfate, thioether, phenol, carbonyl, amide, and hydroxylate, in contrast with mono‐functional ion‐exchange resins. A large number of natural materials have been suggested as promising biological agents for removing pollutants from water. The sources can be inactive or dead microbial biomass, as well as living microorganisms. It is well understood how some biosorbents function, whereas others need more research. The toxicity of some of these biomaterials also requires in‐depth analysis (Adewuyi, 2020).
Biosorbents, unlike mono‐functional ion‐exchange resins, possess functional groups that can bind and sequester metal ions. The functional groups may be amide, carbonyl, imidazole, sulfhydryl, thioether, amine, sulfonate, carboxyl, imine, and phosphodiester. The ability of a biosorbent to bind metal ions is characterized as its biosorption capability and defined as the number of metal ions biosorbed per unit weight of the biosorbent. This can be stated by using the mass balance equation as shown here:
(2.1)
The metal's biosorption effectiveness (R %) is calculated using the following equation
(2.2)
where qe = total metal ions adsorbed by the adsorbent (mg/g); Ci = original metal ion concentration in the solution (mg/L); Ce = metal ion concentration in the solution (mg/L); V = medium volume (L); and m = quantity of biomass used during the process of adsorption (g) (Kanamarlapudi et al., 2018).
Types of Biosorbents
A wide range of materials available in nature can be used to remove metals from contaminated water resources as biosorbents. Biosorbents include microbial biomass (live and dead), plant and animal‐derived materials, industrial and agriculture byproducts, biopolymers, and so on. Biosorbents are a less expensive and more efficient way to remove metallic elements from aqueous solutions, especially heavy metals. Choosing the most effective biosorbent type from a wide range of promising and cheap biomaterials is a significant challenge. Biosorbents with the ability to bind metal ions with larger affinities
