**2.2. Mechanisms of biosorption**

toxic effects to aquatic organisms, and human health. Their efficient removal from water and reduction of risk presents a new challenge for water managers and development of new water

The most problematic micropollutants in waters are heavy metals, pesticides, industrial chemicals and byproducts, personal care products, pharmaceuticals, and other substances that can be toxic to wild animals and humans at low concentrations. Currently, available wastewater treatment technologies are often expensive or ineffective [11]. Research results confirm that large amounts of conventional waste, including egg shells, bones, peat, mushroom, seaweed, yeasts, and carrots [12, 13] show the ability to effectively remove heavy metals from pickled water. Biosorption refers to a set of processes that involve physical and chemical adsorption, ion exchange, electrostatic interactions, complexation, chelation, and microprecipitation, that occur in the cell wall and precede the anaerobic or aerobic biodegradation processes. It is characterized by high selectivity and efficiency (high performance and low cost). Natural materials, such as marine algae or weeds, or industrial waste, such as excess activated sludge

Biological sludge wastewater treatment processes utilize biosorption and bioaccumulation as part of organic and inorganic pollutants, priority substances, heavy metals, and organic

The idea of using biomass in technologies to protect the environment originates at the early twentieth century when Arden and Lockett found that some species of living bacteria are capable of removing nitrogen and phosphorus from wastewater during aeration [14–16]. This process is known as activated sludge process. The removal mechanism has been explained in the context of bioaccumulation capacity. This phenomenon as well as the activation process itself has continued to be widely used. The break occurred in the late 1970s of the last century. Knowing the sequestration nature of biologically inactive biomass has led to a shift in

The interest in biosorption of organic and inorganic pollutants stems from the fact that these substances are toxic and can destabilize the food chain [18]. The absorption of substances by microbial biomass is generally referred to as biosorption. The mechanism responsible for this accumulation is complex and includes, among other processes, adsorption to the cell surface and/or absorption of the substances into various compartments of the microbial cell. Microbial cells have a disposition to concentrate chemicals from the aquatic environment. Therefore, it is necessary and important to understand the mechanisms and kinetics of biosorption, bioaccumulation and biodegradation processes, and their interactions that govern the fate of hazardous inorganic and organic pollutants in biological treatment of wastewater.

Biosorption is a physicochemical process that utilizes the mechanisms of absorption, adsorption, ion exchange, surface complexing, and precipitation processes. It is a spontaneous process

treatment technologies present a challenge for the scientific community [10].

or fermentation wastes, may be used as biosorbents.

2 Biosorption

pollutants/micropollutants removal mechanisms.

research from bioaccumulation to biosorption [17].

**2. Mechanisms and kinetics of biosorption**

**2.1. Biosorption and bioaccumulation**

Biosorption of heavy metals and organic compounds occur due to the physicochemical interactions between the metal and the functional groups present at the surface of the biosorbent. The processes involved include physical adsorption, ion exchange, and chemical sorption that are not related to metabolism. The cell walls of microorganisms consist mainly of polysaccharides, proteins and lipids and have carboxyl, sulfate, phosphate and amino groups to form bonds with metals, and their complexes. Such biosorption occurs relatively rapidly and can be reversible [19]. Various mechanisms of removal of heavymetal by activated sludge microorganisms are discussed in more details e.g. by Pagnanelli et al. [20].

Organic pollutants differ significantly in their structure. As a result, biosorption is affected by molecule size, charge, solubility, hydrophobicity, and reactivity. The biosorbent process can also significantly influence the type of biosorbent and the composition of wastewater [21].

The lipophilic nature of the hydrophobic compounds allows them to pass through cell membranes and absorb into the organic cell matrix. An important component of biosorption of organic pollutants may be absorption in cell membranes or lipid containing cell structures. Other mechanisms are involved in biosorption include surface adsorption, chemisorption, and complexation [22]. For more detailed information we refer the reader to the work Fomina and Gadd [21].
