Industrial effluents from various sectors have become a matter of major environmental concern. The treatment of wastewater in recent year plays a significant role in order to remove the pollutants and to safeguard the water resource. The conventional wastewater treatment is considered costlier and associated with problem of sludge generation. Biosorption methods are considered as the potential solution due to their economical efficiency, good adsorption capacity and eco-friendliness. In this review, an extensive list of biosorbents from algae, bacteria, fungi and agricultural byproducts have been compiled. The suitability of biosorbents towards the eradication of heavy metals, textile dyes and phenolic compounds were highlighted. It is evident from the literature survey of recently published research articles that the biosorbents have demonstrated outstanding removal potential towards the wastewater pollutants. Therefore, biosorbents from the source of dead microbial and agricultural byproduct can be viable alternatives to activated carbon for the wastewater treatment.

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This study focuses on the use of novel Enteromorpha sp. macroalgal biomass (EMAB), for the biosorption of hexavalent chromium from aqueous solutions. The biosorbent was characterized by Fourier transformer infrared spectroscopy, energy dispersive spectroscopy, and scanning electron microscopy techniques. The effect of experimental parameters such as pH, initial concentration of Cr(VI) ions, biosorbent dosage, and temperature were evaluated. The maximum biosorption capacity for Cr(VI) was observed at pH 2.0. The modeling of the experimental data at equilibrium was performed using two parameter isotherm models. Both Langmuir and Freundlich isotherm equations better fitted the equilibrium data. A contact time of different initial Cr(VI) concentrations was about 160 min to attain biosorption equilibrium. The kinetic data were fitted by models including pseudo-first-order, pseudo-second-order, and intraparticle diffusion. The pseudo-second-order and intraparticle diffusion kinetic models adequately described the kinetic data. Moreover, the thermodynamic parameters indicated that the biosorption process was spontaneous, endothermic, and increased randomness in nature. The results showed that EMAB could be used as an effective biosorbent for the removal of Cr(VI) from aqueous solution. List of symbols A TTemkin isotherm equilibrium binding constant (L mg -1 ) b T Temkin isotherm constant (J mol -1 ) b L Langmuir isotherm constant (L mg -1 ) C 0 Initial Cr(VI) concentration (mg L -1 ) C e Cr(VI) concentration in solution at equilibrium (mg L -1 ) E Mean biosorption energy E (kJ mol -1 ) K F Freundlich constant (L g -1 ) K Dubinin-Radushkevich model constant (mol 2 kJ -2 ) K j Jovanovic isotherm constant (L g -1 ) k 1Pseudo-first-order rate constant (min -1 ) k 2 Pseudo-second-order rate constant (g mg -1 min -1 ) k id Intraparticle diffusion rate constant (mg g -1 min -1/2 ) k c Equilibrium constant m Amount of biosorbent (g) n F Freundlich exponent Q 0 Monolayer coverage capacity (mg g -1 ) Q m Maximum adsorption capacity (mg g -1 ) in Dubinin-Radushkevich model q mj Maximum adsorption capacity in Jovanovic model (mg g -1 ) q e Amount of Cr(VI) ions adsorbed per unit mass of biosorbent (mg g -1 ) R Gas constant (8.314 J mol -1 K -1 ) R L Separation factor V Volume of the solution (L) DG°Gibbs free energy (kJ mol -1 ) DH°Enthalpy (kJ mol -1 ) DS°Entropy (J mol -1 K -1 ) ePolanyi potential

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