**1. Introduction**

Water quality policy over the world concerning trace pollutants is defined by environmental quality standards expressed in terms of concentrations in water (Canadian Environmental Quality Guidelines (CEQGs); EU [1, 2]), guidelines (CEQGs; (Environment Canada [3])), ambient water quality criteria (United States Environmental Protection Agency (US EPA), n.d. [4]), and peer reviewed literature on thresholds for effects on aquatic biota (e.g., No observable effect concentrations (NOECs); lowest observable adverse effects) is a major driver of continuing interest in these measurements as part of risk/exposure (Lepom et al. [5]) as well as trend assessments (Fliedner et al. [6]).

DOI: 10.5772/intechopen.78961

In Europe, the adoption of the water framework directive (WFD) [7] provides a policy tool that enables sustainable protection of water resources. WFD presents a positive example of complex legislative in water quality protection.

The Decision No 2455/2001/EC of the European Parliament and the Council of November 2001 [8] established the list of 33 priority substances or group of substances, including the priority hazardous substances, presenting a significant risk to water pollution or via the aquatic environment including risks to waters used for the abstraction of drinking water.

The WFD daughter Directive 2013/39/EU [1] extended the list of priority substances to 45, including priority metal species cadmium, lead, mercury, and nickel. It also stresses the need for the development of new water and wastewater treatment technologies to address the problem of pollution by priority and river basin specific pollutants.

Nowadays, micropollutants occurring in the environment are considered to be a serious problem [9]. Aquatic environment is polluted by a broad range of these compounds from various sources including industry, agriculture, and municipal wastewaters. Many of those compounds are present at low concentrations in the environment, but they still pose and

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

independent of the metabolism of microorganisms. In biotechnology, it is used to separate inorganic and organic substances from the solution using biosorbents. Biosorption is an impor-

Introductory Chapter: Biosorption

3

http://dx.doi.org/10.5772/intechopen.78961

Biosorption is defined as the passive adsorption of toxic substances by dead, inactive or biologically derived materials. Biosorption is a consequence of several metabolic processes independent of the cell membrane, the mechanisms responsible for the absorption of the pollutant

Bioaccumulation is defined as the phenomenon occurring in living organisms. More specifically, bioaccumulation is defined as the absorption of toxic contaminants by living cells or organisms. Compounds are passively or actively transported into cells, accumulated inside them, and they also enter the metabolic cycle through the cell membranes. Bioaccumulation

Both bioaccumulation and biosorption have certain advantages and disadvantages. In general, the use of living organisms is not suitable for continuous water purification processes from highly toxic organic/inorganic contaminants. If the concentration of the toxic substance is too high or the process step takes a long-time period, the accumulated substance quantity may reach partition equilibrium, or saturation. Due to the high accumulated pollutant concentration the metabolism of the organism will be disturbed and death may occur. This scenario can be avoided by using inactive, dead biomass. Moreover, if the sorption process is reversible, compounds may be desorbed back to the treated water if the concentration drops. To avoid desorption, a high sorption capacity has to be provided. This is not always feasible in processes applying living cells, because of various restrictions such as requirements of nutrients, aeration, maximum cell density, and so on. This is why we devote more attention

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

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,

tant process also in protecting the environment.

vary according to the type of applied biomass.

is therefore often dependent on cell metabolisms.

to biosorption than bioaccumulation.

**2.2. Mechanisms of biosorption**

et al. [20].

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 or fermentation wastes, may be used as biosorbents.

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

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 research from bioaccumulation to biosorption [17].

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.
