or hiding the groups or exposing further sites to bind metals. Biosorptive performance has been boosted by carboxylation, phosphorylation, and amination of amine, carboxyl, and hydroxyl groups, saponification of ester groups, sulfonation, halogenation, oxidation, and so on (Wan Ngah and Hanafiah, 2008). Various biomasses, irrespective of their source, including pine bark, rose petals, spirogyra, walnut shell, rubber leaves, and sawdust, showed promising biosorption capabilities after alkaline pretreatment (Argun et al., 2009).
Desorption and Regeneration
The ability of biosorbents to recover after use is one of their most important achievements. Adsorbate is cleared off the biosorbent surface after use, and the biosorbent reverts to its original structure and efficiency (Adewuyi, 2020).Biosorbents’ economic value and sustainability are primarily determined by the number of cycles they can be reused. It is essential to develop an effective desorption method. High performance is not enough for a biosorbent; it also needs to be reusable. As a result, when choosing biosorbents, desorption and regeneration are the important processes to consider. Still, some of them are difficult to regenerate, making their long‐term usage doubtful since they would need to be discarded after a few cycles. Disposing of such materials can result in contamination of the environment. The separation of spent biosorbents and the regeneration and recycling of the medium after the sorption process are very significant.
Eluent utilization is now the most frequently used desorption mechanism. Choosing the right eluent is essential and depends on the form of biosorbent, adsorbent, and biosorption mechanism. A proper eluent should not harm or modify the biosorbent structure, it should be environmentally friendly and affordable, it should have a high level of adsorbing ability, it should not alter adsorbing or biosorbing substances, and it must be easily disconnected. To dislodge metal ions while concurrently replenishing the filled biosorbent, chemicals like hydrochloric acid and sodium hydroxide and chelators like EDTA have been utilized (Ahemad and Kibret, 2013).
Cost Evaluation
Approximating the cost of biosorption and biosorbents is a challenging process that is rarely published. Cost assessment depends on many factors that make generalization difficult. Variables such as process handling, storage, energy use, repair, optimization of process, rejuvenation, discharge, and desorption are considered when evaluating cost. The type of water or effluent to be treated, as well as the amount, will affect the cost. Capital costs and operating costs, on the other hand, are determined by the type and size of the treatment plant.
It is preferred to employ wastes as a substrate for processing biosorbents in order to lower process expenses. Agricultural waste, home trash, and industrial waste, such as bacterial drainage from fermentation, fungal waste from food manufacturing, and waste from other industrial processes, can all be used to make biosorbents. Waste management is a significant environmental issue, and using these wastes addresses the concern while also lowering the cost of manufacturing biosorbents for treating water.
Pretreatment of feedstock is one aspect that increases production costs. Certain products need to be pretreated before manufacturing, and additional pretreatment increases the cost of production. It is important to note that feedstock treatment should be efficient but also inexpensive and accessible. It is critical that the treatment plant be placed near the effluent source in order to reduce expenses.
The cost of disposal must also be taken into account in biosorption, as once the biomass is fully used in repeated cycles it must be substituted. However, it may be applied in other areas, such as particulate board processing, cement, biogas, etc.
Conclusion
Biosorption is a low‐cost treatment for complicated commercial wastewater with high volumes and low heavy metal concentrations. Metal ions in an aqueous solution are replaced for a counter ion bound to biomass in this process, classified as ion exchange. The efficacy of the various biosorbents is unquestionably essential to the biosorption technology's promising potential. Several types of biomass that are abundant and exhibit strong metal binding characteristics have been recognized. Many natural biomass biosorbents have been established from cellulosic and microbial origins, with effective biosorption features. But several of these biosorbents have shown poor efficiency. Surface changes made to biosorbents have helped enhance their metal‐binding characteristics, as is apparent from extensive research; however, the adjustments increase the average operational costs to match the cost of commercialized ion‐exchange resins. The existence of multifunctional groups on the biomass surface causes it to be non‐selective to a particular metal ion. The biosorbents' non‐selective and unspecific character, as well as their lesser resilience, pose a significant marketing challenge. The creation of biosorption models and the identification of biosorption mechanisms, as well as the identification of better and more selective biosorbents, are all key future research topics for biosorption technology.
References
1 Abbas, S.H., Ismail, I.M., Mostafa, T.M., and Sulaymon, A.H. (2014). Biosorption of heavy metals: A review. Journal of Chemical Science and Technology 3 (4): 74–102.
2 Abdi, O. and Kazemi, M. (2015). A review study of biosorption of heavy metals and comparison between different biosorbents. Journal of Materials and Environmental Science 6 (5): 1386–1399.
3 Acosta Rodríguez, I., Martínez‐Juárez, V.M., Cárdenas‐González, J.F. et al. (2013). Biosorption of Arsenic(III) from Aqueous Solutions by Modified Fungal Biomass of Paecilomyces sp. Bioinorganic Chemistry and Applications 2013: 1–5. doi:10.1155/2013/376780.
4 Adewuyi, A. (2020). Chemically modified biosorbents and their role in the removal of emerging pharmaceutical waste in the water system. Water 12 (6): 1551. doi:10.3390/w12061551.
5 Ahemad, M. and Kibret, M. (2013). Recent trends in microbial biosorption of heavy metals: A review. Biochemistry and Molecular Biology 1 (1): 19–26.
6 Al‐Asheh, S., Banat, F., and Mohai, F. (1999). Sorption of copper and nickel by spent animal bones. Chemosphere 39: 2087–2096.
7 Ali Redha, A. (2020). Removal of heavy metals from aqueous media by biosorption. Arab Journal of Basic and Applied Sciences 27 (1): 183–193. doi:10.1080/25765299.2020.1756177.
8 Anaemene, I.A. (2012). The use of Candida sp. in the biosorption of heavy metals from industrial effluent. European Journal of Experimental Biology 2 (3): 484–488.
9 Apinthanapong, M. and Phensaijai, M. (2009). Biosorption of copper by spent yeast immobilized in sodium alginate beads. Kasetsart Journal (Natural Science) 43: 326–332.
10 Arakaki, A.H., Vandenberghe, S., de Soccol, L.P. et al. (2011). Optimization of biomass production with copper bioaccumulation by yeasts in submerged fermentation. Brazilian Archives of Biology and Technology 54 (5): 1027–1034. doi:10.1590/S1516‐89132011000500021.
11 Aravindhan, R., Fathima, A., Selvamurugan, M. et al. (2012). Adsorption, desorption, and kinetic study on Cr(III) removal from aqueous solution using Bacillus subtilis biomass. Clean Technologies and Environmental Policy 14 (4): 727–735. doi:10.1007/s10098‐011‐0440‐7.
12 Arbanah, M., Najwa, M., and Ku Halim, K. (2013). Utilization of Pleurotusostreatus in the removal of Cr (VI) from chemical laboratory waste. International Refereed Journal of Engineering Science 2: 29–39.
13 Argun, M.E., Dursun, S., and Karatas, M. (2009). Removal of Cd (II), Pb (II), Cu (II) and Ni (II) from water using modified pine bark. Desalination 249: 519–527.
14 Arshad, N. and Imran, S. (2020). Indigenous waste plant materials: An easy and cost‐effective approach for the removal
