天美传媒

Bioremediation; Adsorption

Introduction

The twentieth century is remembered as a time of exceptionally rapid civilised and technological advancement. Environmental issues were caused by industrialization, conflict, and extensive usage of synthetic xenobiotics and heavy metals on a massive scale [1]. A significant issue is the pollution of the environment by petroleum products, medicinal substances, chloro- and nitrophenols and their derivatives, polycyclic aromatic hydrocarbons, organic dyes, pesticides, and heavy metals. There are various ways in which these toxins get into the ecosystem. An illustration would be the leakage of millions of barrels of crude oil into the environment as a result of the military confrontation between Iraq and Kuwait. The cleanup of oil from the contaminated environment became the focus of various scientific investigations that were launched after the war. Accidental oil spills are one of the additional sources of crude oil in ecosystems. The British Petroleum company released around 2.8 million barrels of crude oil during one of the worst marine disasters that have occurred in Mexico in 2010. (BP). Other harmful pollutants found in soil include pesticides [2-5]. According to the USEPA, there were 2.36 million tonnes of pesticides used for agricultural purposes worldwide in 2007. Because pesticides are toxic to non-target organisms, when used in large quantities for extended periods of time in a small area, these compounds have a serious negative impact on local microflora and people. In addition, a large number of pesticide biodegradation's toxic byproducts are also priority pollutants. For instance, 2,4-dichlorophenol and p-nitrophenol, respectively, are the major metabolites of the biodegradation of parathion and 2,4-dichloropenoxy acetic acid. Numerous microbes have reportedly been shown to be capable of degrading a variety of contaminants. However, because microorganisms are sensitive to a variety of environmental variables, the pace of biodegradation is dependent on their physiological state. The resilience of microorganisms to harmful environmental effects is known to be enhanced by immobilisation [6-8]. The major goal of this study is to present and debate the most recent data regarding the role of natural carriers in the bioremediation processes carried out by immobilised cells. Immobilization techniques for bioremediation are also presented in the article.

Use of Bioremediation [9]

The concept of cleaning soil with microorganisms and triggering biodegradation processes in order to remove petroleum derivative contamination. The restoration of the natural and practical values of contaminated sites using microorganisms that can break down, change,or chelate different toxic compounds is known as bioremediation today. Microorganisms can degrade organic pollutants by cometabolizing with them or by using them as a source of carbon and energy. Heavy metals undergo transition from one oxidative state or organic complex to another; they are not physiologically eliminated or destroyed. Their toxicity is reduced and their water solubility is altered. Bioremediation is a permanent solution that can result in the degradation or transformation of environmental contaminants into harmless or less toxic forms. It is also more affordable, non-invasive, and environmentally friendly than conventional methods. It is possible to perform soil bioremediation onsite (in situ) or in a specially prepared area when transferring polluted soil is not an option, as is the case when contamination covers a large area, in situ technology is used.

Adsorption [10]

By physically interacting with the surface of water-insoluble carriers, microbial cells and enzymes are immobilised by adsorption. This technique, which is frequently used in bioremediation procedures, is efficient, quick, eco-friendly, and affordable. Weak bonds are formed to allow for adsorption to occur on a carrier surface. This is why using this method to immobilise GMMs is not recommended due to the high likelihood of cells leaking from the carrier into the environment.

Adhesion to a surface

Similar to physical adsorption, electrostatic binding on a surface reduces the likelihood of microorganism leakage. By washing the carrier's surface with a buffer solution, this technique creates a hydrophilic surface that can draw negatively charged cells or enzymes. Because covalent binding necessitates the presence of a binding agent, the process for immobilisation is different in this situation. Only chemically activated carriers that are rich in carbamate, amide, and ether bonds are suitable for immobilization. This technique is primarily used to immobilise enzymes because binding agents are frequently toxic to cells, which reduces microbial viability and activity. Covalent bonds have the benefit of being sufficiently strong to stop molecules from leaking into the environment.

Currently being held in a porous matrix

Bioremediation frequently uses entrapment of microorganisms, which is well recognised. Microbial cells can only migrate inside a carrier after being entrapped. Although the exchange of nutrients and metabolites may be constrained, this stops the cells from leaking into the surrounding environment. Physiologically different microorganisms are trapped in the heterogeneous carrier. In contrast to the starving cells found inside the carrier, the cells close to the surface display tremendous metabolic activity. Entrapment is a quick, safe, cost-effective, and adaptable technique. Environmental elements are shielded from entrapped bacteria. The ratio between the size of the carrier's pores and the size of the cells is the most crucial factor in the trapping of microorganisms when the holes are bigger than the immobilised cells.

Encapsulation

Encapsulation and entrapment are very similar, but in this instance, immobilised particles are kept apart from the outside environment by a semi-permeable membrane. The greatest benefit of this method is the significant defence it offers biological material against the harmful effects of the outside environment. Encapsulation is only occasionally used in ex situ bioremediation, though, because of the membrane's low permeability and the possibility that it will be harmed by developing cells.

Conclusions

Organic carriers, which are leftovers from the food and agricultural industries, are becoming more and more popular because they make excellent immobilisation materials. They all have a wide variety of functional groups, which has a favourable impact on the level of microbial colonization. Additionally, volcanic rocks with good sorption qualities and high mechanical resistance, such as expanded perlite and tezontle, are known as carriers. The use of carriers like corncobs and loofah sponges has been successful in bioremediation in situ, and the former has demonstrated the greatest support for pesticide biodegradation. Using carriers like bagasse, sawdust, expanded perlite, and tezontle has produced the best results in ex situ bioremediation. Although more research is needed, porous glass, cotton fibers, sunflower seed husks, and coco-peat all appear to be promising immobilisation materials.

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