**3. Biosorbents**

For several decades, biosorption has been referred to as perspective, low-cost biotechnology applicable in wastewater treatment. However, despite intensive research, significant advances in the knowledge of these complex processes and rich magazines and book publications, the practical application of this process and related technologies are not adequate so far [20].

Previous research has focused on testing the development of more suitable and available biological materials. The biosorbent materials used may be alive or deactivated microorganisms and their components, plant materials, industrial and agricultural wastes, and natural processing residues, e.g. wood, wood bark, and sea algae.

Both live and dead biomass can be used to remove hazardous substances. The inactive (sterilized, dried, and/or otherwise chemically treated) biomass benefits from no need of supplies of substrate, nutrients, eventually oxygen, which would otherwise be needed in order to maintain viable biomass during adsorption. Also, the toxicity of pollutants to be removed by biosorption poses no problem.

Biosorbents for the removal of toxic metals or organic pollutants mainly use biomass of bacteria, yeasts, fibrous fungi, algae, as well as wastes from food and pharmaceutical production, agricultural waste, and other polysaccharide materials. All biomaterials should demonstrate good biosorption capacity and affinity for all types of inorganic ions and organic compounds.

Important biosorbents of the fungus family include the filamentous fungi of the genus *Alternaria, Aspergillus, Rhizopus, Penicillium,* and the yeast *Saccharomyces cerevisiae* and *Saccharomyces carlsbergensis*. These microorganisms are widely used in the food and pharmaceutical industry and end up as waste that is available from individual free or low-cost production. Another important biosorbent to which attention is focused are marine algae, which are also biological resources. The algae include red, green and brown algae, with brown algae being among the excellent biosorbents, for example, *Chlorella vulgaris*.

This is due to the alginate content that is present in the form of gel in the cell walls. The macroscopic structure of the algae provides a conventional basis for the production of biosorbents suitable for the application of sorption processes. It should be noted that algae are not considered waste; in fact, they are the source for the production of agar, alginate and, carrageenan. This means that the choice of algae for biosorption purposes needs to be given the utmost attention.

From the majority of biosorption-related work, it follows that the pseudo-first order equation does not describe well-meaning values throughout the contact time. Generally, this equation is only applicable in the initial phase of the adsorption process. This is due to the fact that, using the linearized form of Eq. (6) it is necessary to know the value of the equilibrium adsorption capacity, which can be approximated by the extrapolation of experimental data for infinite time, i.e., the trial and error method. On the other hand, it is not necessary to know this value

In this context, it should be emphasized that using a non-linear method of determining the values of parameters of non-linear equations in general it is possible to avoid such errors in

For several decades, biosorption has been referred to as perspective, low-cost biotechnology applicable in wastewater treatment. However, despite intensive research, significant advances in the knowledge of these complex processes and rich magazines and book publications, the practical application of this process and related technologies are not adequate so far [20].

Previous research has focused on testing the development of more suitable and available biological materials. The biosorbent materials used may be alive or deactivated microorganisms and their components, plant materials, industrial and agricultural wastes, and natural

Both live and dead biomass can be used to remove hazardous substances. The inactive (sterilized, dried, and/or otherwise chemically treated) biomass benefits from no need of supplies of substrate, nutrients, eventually oxygen, which would otherwise be needed in order to maintain viable biomass during adsorption. Also, the toxicity of pollutants to be removed by

Biosorbents for the removal of toxic metals or organic pollutants mainly use biomass of bacteria, yeasts, fibrous fungi, algae, as well as wastes from food and pharmaceutical production, agricultural waste, and other polysaccharide materials. All biomaterials should demonstrate good biosorption capacity and affinity for all types of inorganic ions and organic compounds. Important biosorbents of the fungus family include the filamentous fungi of the genus *Alternaria, Aspergillus, Rhizopus, Penicillium,* and the yeast *Saccharomyces cerevisiae* and *Saccharomyces carlsbergensis*. These microorganisms are widely used in the food and pharmaceutical industry and end up as waste that is available from individual free or low-cost production. Another important biosorbent to which attention is focused are marine algae, which are also biological resources. The algae include red, green and brown algae, with brown algae

This is due to the alginate content that is present in the form of gel in the cell walls. The macroscopic structure of the algae provides a conventional basis for the production of biosorbents suitable for the application of sorption processes. It should be noted that algae are not considered

processing residues, e.g. wood, wood bark, and sea algae.

being among the excellent biosorbents, for example, *Chlorella vulgaris*.

for the use of the linearized form of the kinetic equation of the pseudo-second-order.

the modeling of process kinetics.

biosorption poses no problem.

**3. Biosorbents**

6 Biosorption

Scientists work mainly with brown algae using one of the best metal sorbents seaweed, Sargassum seaweed. They focus on the study of sorption properties and biosorption mechanisms. Biosorbents using algae, bacteria, fibrous fungi, and yeasts are also used for analytical techniques, specifically for solid phase extraction to determine metals present in trace amounts in different aqueous matrices [29].

Microbial biomass (bacteria, fungi, and micorrhagia) shows better results of biosorption of dyes than macroscopic materials (seaweed, squirrel crabs, etc.). The reason is the difference in cell wall and functional groups involved in dye binding. Many bacteria, fungi, and microorganisms bind different types of dyes.

The results of the study by Simionato et al. [9] show that the use of chitosan obtained from silkworm chrysalis is a viable alternative for the removal of blue remazol and black remazol five dyes from the wastewater of the textile industry. Potential biosorbents belonging to the class of bacteria include *Bacillus, Geobacillus, Lactobacillus, Pseudomonas, Streptomyces, Staphylococcus, Streptococcus,* and others.

Several studies have recently been carried out to develop cheap sorbents from industrial and agricultural waste. Partial attention was paid in particular to crab shells, activated sludge, rice husks, egg shells, mosses, and lichens. The results showed that, in particular, crab shells have excellent sorption abilities in relation to arsenic, chromium, cobalt, and nickel.

A preferred biosorbent material is activated sludge. There are a large number of binding sites on the cell walls of microorganisms, which are predominantly composed of polysaccharides, proteins, and lipids. This is due to the high biosorption capacity of activated sludge. The amount of excess sludge produced mostly outweighs the possibilities of its use and represents one related problem of wastewater treatment. Thus, this biosorbent is reely available and low-cost.

Authors [30–32] disclose the advantages of using aerobic and anaerobic deactivated sludge to remove dyestuffs and hazardous effluent from wastewater. Qiu et al. [33] presented the results of research into the use of active aerobic and anaerobic sludge for sewage treatment.

The extent of biosorption depends on the type of biomass [34]. In the past, biosorbent phenomena have often been found to bioaccumulate highly hydrophobic organic substances directly depending on the lipid content of biomass. However, non-polar substances have been found to accumulate in organisms according to the distribution equilibrium between the medium and the lipid content of the organism [35]. Other authors found the opposite phenomenon to track DDT [Dichloro-Diphenyl-Trichloroethane or 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)-ethane] adsorption by different soil fractions [36]. Some soil fractions were first extracted with ether and ethanol to remove lipid-like substances. Absence of lipid-like materials did not decrease, on the contrary, increased DDT adsorption with soil, indicating that other substances other than lipids may also play a role in biosorption. A similar finding was obtained by monitoring the adsorption of chlorites with microbial biomass [37]. Bacterial biomass with the highest lipid content among the observed samples had the lowest biosorption capacity. Further, it has been found that in different samples of fibrous fungi biomass, despite the similar lipid content in the cells, the biosorption capacity varied within a wide range. Interestingly, however, it was found that the biosorption capacity of different biomass samples depended directly on the amount of total organic carbon released during the contact of biomass with the pollutant. However, this phenomenon is not elucidated, it can only be assumed that the biosorption capacity increases with the growing proportion of cells destroyed in the medium, which correlates with the total organic carbon content released into the medium. Cell fragments have a larger surface and thus a higher sorption capacity [38]. The authors further found that the biosorption capacity of active and deactivated (inactive/dead) biomass is almost the same for highly biodegradable pollutants.

Most dyes are of synthetic origin. They are characterized by an aromatic structure, greater stability, and a worse biodegradability. They can affect the processes of photosynthesis in the aquatic environment to toxicise the aquatic ecosystem [44, 45]. Research results [44–46] show that there is a wide range of microorganisms, including bacteria, fungi, and algae, which are capable of biodegradation or bioaccumulation of azo dyestuffs in wastewater by anaerobic/

Introductory Chapter: Biosorption

9

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

For the modeling and optimization of processes using sorption on the activated sludge, the necessary is knowledge about the sorption of organic matter to the sludge. Modin et al. [47] compares primary, anaerobic, and aerobically activated sludge as biosorbent materials. Biosorptive capacity values were determined, process kinetics was studied, and some characteristics of sorbed organic matter were studied. Biosorption of dissolved organic substances occurred almost immediately. This was followed by a slower process that corresponded to firstorder kinetics. Biosorption of undissolved particles also corresponded to first order kinetics. However, there was no immediate sorption, but the particles were released during mixing.

Biosorption is used for wastewater treatment since the beginning of the last century, when the activation process was discovered. Controlled withdrawal of excess sludge together with significant participation of biosorption a bioaccumulation processes enable intensification of organic pollutants, nitrogen, and phosphorus removal. Bioaccumulation is usually an active process that is part of the metabolism of microorganisms. Biosorption is a passive process of adsorbing pollutants on the surface of microorganism cell walls. This leads to a decrease in the concentration of these substances in the purified water. However, such contamination remains a part of the activated sludge and its re-release to the environment is dependent on further treatment with the excess sludge produced, especially if the biosorption of these

An increasingly serious challenge is dangerous (organic) and so-called emerging pollutants, e.g. pesticides, estrogens, personal care products, or pharmaceuticals. These can be removed in the wastewater treatment plant by biotic and abiotic processes, or they can pass through the sewage treatment plant to the recipients without any significant change. In the context of minimizing the production of excess sludge, its disintegration prior to the process of biological stabilization and degradation of biosorbable pollutants on activated sludge, the combined

The solubility of the pollutant is an important property affecting biosorption. The inverse relationship between water solubility and accumulation of organic molecules with biomass was found [9]. In general, the different types of biomass observed had a greater biosorption capacity for less soluble pollutants. Organic molecules accumulate better in microbial biomass, the higher the biomass-water distribution coefficient (octanol-water model system), but as already mentioned above, there is no direct correlation between biosorbent capacity and

If the contaminant dissociates in the aqueous phase (on a weak acid or a weak base), sorption of the dissociated and non-dissociated forms can take place with different sorption coefficient values for both forms [15]. The effect of the initial concentration of the pollutant on the rate of biosorption was monitored. After 10-fold increase in the initial concentration of the pollutants

processes of biosorption and chemical oxidation, e.g. using ozone.

aerobic processes.

substances is reversible.

lipid content in biomass.
