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Bioremediation for Sustainable Environmental Cleanup

impact on climate change, causes economic losses (mainly in agriculture and forestry) and offers a

significant health risk to humans (Cachada et al. 2014).

4.2 Techniques for Heavy Metals Removal

Heavy alloys are usually deleted from water solutions employing physicochemical techniques.

The following are the most prevalent methods:

• Infiltration

• Coagulation

• Chemical precipitation

• Ion exchange

• Membrane processes

Heavy metals can be removed using a single method or a combination of two or more methods.

Many factors influence the method selection, including effluent kinds, content and forms and

concentrations of elements to be removed, as well as the degree of removal required (Cachada

et al. 2014). Precipitation of metals in the form of hydroxides, which are then removed from

the solution during filtration or decantation, is the most common method for removing heavy

metals from industrial effluent. The presence of organic and inorganic compounds, as well as

temperature and pH, can all have a negative impact on the process’s efficacy (Chamekh et al. 2021).

Furthermore, handling moistened sludge raises costs. Another approach for removing heavy metals

is ion exchange. Ions bound to the ion-exchanger are transferred for ions present in the surrounding

solution in this process. Natural or synthetic ion-exchangers are available (Chen et al. 2019). The

solutions should be pre-treated before the ion exchange since impurities in the water can disrupt

the process. Membrane techniques can also remove heavy metals from wastewater. Contaminants

can be separated using these methods. Membranes are essential for water treatment efficiency.

A membrane is a thin partition that allows molecules to pass through it selectively. Natural and

manmade materials can be used to make membranes (Chen et al. 2020). They should have excellent

hydraulic efficiency, separation qualities, mechanical, chemical and heat resistance. Sorption on

activated carbon or zeolite is used to remove heavy metals. Activated carbon is used in adsorption

(present in granular of fine forms). Metals are removed from activated carbon’s surface, where they

are kept (Chojnacka 2010). The methods suggested are frequently time-consuming and costly to

implement. As a result, new, more cost-effective and easier technologies for heavy metal removal

are required.

4.3 Removal of Heavy Metals with Biosorption and Bioaccumulation

Since the turn of the century, there has been a growing awareness of the need to safeguard the

natural environment. It is necessary to develop new technologies for eliminating toxins from the

environment (Fabre et al. 2020). Biotechnological methods, which rely on the inherent characteristics

of microbes to adsorb and accumulate heavy metals, may be a viable alternative to physicochemical

methods. Heavy metals can be captured and accumulated by all microbial species in water solutions

(Fargasova et al. 2010). Heavy metal absorption is linked to a microbial mechanism that allows the

uptake of elements necessary for growth and metabolic processes. The ability of the biomass to

bind and accumulate harmful metals can be utilized to build efficient and cost-effective wastewater

treatment systems for the mining and electroplating industries (Flouty and Estephane 2012).

Biosorption and bioaccumulation are terms used to describe processes that use biomass to remove

metals (Figure 4.1).

Both approaches differ in terms of the mechanism that allows contaminants to be bound.

Toxins stick largely to the surface of the microbial cell wall when biosorption occurs, whereas

bioaccumulation allows pollutants to penetrate microbial cells (Gajda Meissner et al. 2020). As