*3.3.1. Effect of anions*

increase in metal concentration will lead to a decrease of metal toxicity. An example is the work conducted by Said and Lewis [26] where an increase in metal concentration was respon-

**Figure 3.** Metal concentration impact on bioremoval inhibition pattern of organic pollutants, assuming (1) a direct or

Briefly, the existence of different patterns of responses of organic pollutants towards metals is possible to assume and that this variety of responses makes the understanding and prediction of metal toxicity in the environment more difficult, since these elements may influence both

Unless the models used to predict the influence of metals on the bioremoval of organic pollutants incorporate both the ecologic and physiologic effects of metals towards the pollutant-

As previously mentioned, despite the research concerning biosorption processes has been well documented in the literature, biosorption of different metal ions by different types of biological materials has been mainly conducted in single-metal solutions [21]. Information concerning biosorption studies in binary- [30–34], tertiary- [31–35] and quaternary-component solutions [36] is very scarce. Moreover, the use of different evaluation methodologies makes any attempt to draw any meaningful and universal conclusion very difficult and, on the other hand [37], the influence that anions may exert on the biosorption process of metal cations has been somehow neglected. *Nostoc muscorum*, a cyanobacterium indigenous from coal mining sites, was employed as biosorbent to decontaminate aqueous solutions containing Cd(II), Cu(II), Pb(II) and Zn(II) (5 or 10 mg/L) [38]. The results obtained in these experiments showed a maximum bioremoval of both Pb(II) (96.3%) and Cu(II) (96.4%) followed by Cd(II) (80.0%) and Zn(II) (71.3%) after 60 h of culture period. The bioremoval of Cd(II), Cu(II) and Pb(II) was maximum at 5 mg/L, whereas Zn(II) bioremoval has a maximum when all the four heavy metals were set at 5 mg/L. These

the ecology and physiology of the pollutant-degrading microorganisms.

degrading microorganisms, they may fail their main purpose.

sible for a decrease in 2,4-DME bioremoval.

60 Biosorption

linear relationship, (2) additional pattern 1 and (3) additional pattern 2.

**3.3. Biosorption in multi-metal solutions**

Three aspects related to the influence of anions on the biosorption processes are usually considered in the available literature: (i) the influence that the anion has on the maximum biosorption capacity of the sorbent, in single-metal solutions [39]; (ii) the influence of anion concentration on the biosorption of several metal ions, in multi-metal solutions [37–41]; and (iii) the nature of the biosorbent that can influence significantly the effect of the anion on the biosorption capacity [21].

The biosorption of four metals—Cr(VI), Co(II), Ni(II) and Zn(II)—by the *Aspergillus niger* fungus [40] revealed that the presence of anions such as NO3 − and SO4 2− did not significantly affect the biosorption performance of the four metals, whereas the presence of Cl<sup>−</sup> did negatively affect the biosorption performance of the four metals in multi-metal solutions.

Kuyuca and Volesky [42] studied the biosorption of Co(II) ions in the presence of SO4 2− and PO4 3− by the brown macroalga *Ascophyllum nodosum* and concluded that the presence of these anions did not reveal any influence on the biosorption performance, as opposite to the presence of NO3 − anions, that strongly inhibited the biosorption process. The opposite situation was observed in the biosorption of Zn(II) by the cyanobacterium *Oscillatoria angustissima* [41], and it was stated that the presence of SO4 2−, NO3 − and Cl<sup>−</sup> had the following biosorption inhibition order SO4 2− > Cl<sup>−</sup> > NO3 − .

The degree of inhibition for the biosorption of La(III), Cd(II), Pb(II) and Ag(I) cations, by the *Rhizopus arrhizus* fungus [43], usually followed the order EDTA > SO4 2− > Cl<sup>−</sup> > PO4 3− > glutamate > CO3 <sup>2</sup> <sup>−</sup> .

As referred previously, the influence of the anion on the biosorption capacity will vary depending on the metal ion oxidation state, as it was observed for the biosorption of Cr(III) and CR(VI) ions [44], with the following inhibitory orders SO4 2− > Cl<sup>−</sup> ≈ NO<sup>3</sup> − and NO3 <sup>−</sup> > SO4 2−.

## *3.3.2. Effect of the ionic concentration*

Considering the limited number of active sites present on the biosorbent surface, it is accepted that the biosorption capacity of the biosorbent towards a specific pollutant (metal or not) in a multicomponent solution is inferior to the one in single-component solutions; therefore, the contaminants will compete for the active sites, available for sorption [44].

This is the case of the amount of Cr(VI) biosorbed per unit weight of *Rhizopus arrhizus* that decreased with the increase of Fe(III) concentration as an antagonistic effect [45, 46].

exploitation, which so often is the primary underlying principle for such investment and work [18, 19, 21]. Despite the incontestable progress made over decades of research, most of the biosorption studies are still conducted at a laboratory scale and involve (i) the characterization of a selected sorbent, which will sorb a given contaminant from solution, (ii) the study of the effect of physico-chemical parameters may have on biosorption and (iii) the use of metals. Considering that the majority of elements present in the periodic table are classified as metals, the potential number of 'original' research is most likely beyond comprehension, especially if coupled with the gigantic number of microbial species, strains and metabolites/derived substances. It is therefore expected that the output of publications related to biosorption shows no sign of decreasing and will be increased due to the continuing number of new journals,

Biosorption of Multicomponent Solutions: A State of the Art of the Understudy Case

http://dx.doi.org/10.5772/intechopen.72179

63

It is also logical to infer that several technical and scientific issues should be solved in order to meet the industrial demands and bring the biosorption technology into commercialization.

• Although a large number of biological materials are available, it is still essential to find and/

• It is necessary to elaborate, improve and/or simplify the mathematical models used to de-

• To achieve the best biosorption performance, it is crucial to identify the biosorption mecha-

• To obtain the best biosorption performance, it is essential to identify the biosorption mech-

• Biosorption studies should also be conducted at a pilot or industrial scale and with multicomponent solutions or, if possible, real effluents and wastewaters. This will allow to understand the interactions between all the sorbents and the sorbate and thus optimize the

• Although there is a significant number of patents and publications available, the biosorption process has been so far mainly performed at a laboratory scale. Up-scale of the bio-

• In order to apply the biosorption technology at an industrial scale, economic analyses are

• Additional attention should be paid to the application of biosorption technology in product

• The use of similar and universal evaluation methodologies allows to draw meaningful and

• Eradicate the poor and misleading communications, and the use of loose terminology, which is associated with the great complexity of biosorption phenomena, has intricated the process of prioritizing fundamental scientific and commercial tasks and of creating clear

necessary to estimate the overall cost of the sorbent and biosorption process.

including those that are web based [18, 19].

scribe the multicomponent systems.

sorption processes should be enhanced.

separation, recovery and purification.

universal conclusions [21].

information for the industry.

Based on this, several future perspectives can be made:

or prepare more economic, efficient and selective sorbents.

nism underlying relatively to the class of biosorbents used.

anism in relation to the general group of the selected biosorbent.

biosorption process, promoting its future commercialization.

Fagundes-Klen et al. [47] observed that the amount of Zn(II) biosorbed by *S. filipendula* in the presence of high concentrations of Cd(II) decreased significantly (56.8 %) when comparing the biosorption results achieved in single-metal solution. These results are easily explained by the reduced number of coordination, the ionic radius and the higher ionization potential of Zn(II).

It is therefore worth noting that as the ionic concentrations become higher, there is a growing force able to overcome the mass resistance transfer of metal ions through the biosorption process. The published data [48] showed that even though lead ions (Pb2+) have higher affinity than copper (Cu2+) to be biosorbed by an algae belonging to the genera *Gelidium* uptake, Cu2+ uptake was higher than Pb2+ uptakes due to the higher initial concentration of Cu2+. Similar results described the biosorption of Pb2+ and Cu2+ by pine cone shells [49]. When binary solutions were tested, the uptake of both metals was significantly inhibited, revealing an antagonistic effect.
