Multivariate optimization of the decolorization process by surface modified biomaterial: Box–Behnken design and mechanism analysis

Abstract

A natural biosorbent obtained from Pyracantha coccinea was modified with an anionic surfactant to facilitate its dye removal ability. Modified biosorbent was successfully employed for the decolorization of Methyl Violet (MV)-contaminated solutions. A three-variable Box–Behnken design for response surface methodology was used to examine the function of independent operating variables. Optimum pH and biosorbent amount were found to be 6.0 and 0.055 g, respectively. The effects of temperature and ionic strength on the dye removal performance of biosorbent were also investigated. A biosorption equilibrium was attained within 30 min and experimental data fitted well to the pseudo-second-order model. The Langmuir isotherm model fitted adequately to the equilibrium data. The maximum monolayer biosorption capacity of the modified biosorbent was found to be 254.88 mg g⁻¹. Good biosorption yields were also recorded in continuous biosorption system. Ion exchange and complexation could be suggested as possible mechanisms for the biosorption. The developed modified biosorbent was regenerated up to 80.30 % by 0.005 M HCl. At real wastewater conditions, it has 86.23 ± 0.21 and 94.51 ± 1.09 % dye removal yields in batch and column systems, respectively. Modified biomaterial can be used as an effective biosorbent for the removal of MV dye from aqueous solution with high biosorption performance.

Appendix

Kinetic and isotherm model equations

The pseudo-first-order equation;

$$ \ln \left({q}_{\mathrm{e}}-{q}_{\mathrm{t}}\right)= \ln {q}_{\mathrm{e}}-{k}_1 t $$

(5)

The pseudo-second-order rate equation;

$$ \frac{t}{q_{\mathrm{t}}}=\frac{1}{k_2{q}_{\mathrm{e}}^2}+\frac{1}{q_{\mathrm{e}}} t $$

(6)

$$ h = {k}_2{q_{\mathrm{e}}}^2 $$

(7)

The intraparticle diffusion equation;

$$ {q}_{\mathrm{t}}={k}_{\mathrm{p}}{t}^{1/2}+ C $$

(8)

which k ₁ is rate constant of pseudo-first-order biosorption (min⁻¹), k ₂ is the equilibrium rate constant of pseudo-second-order biosorption (g mg⁻¹ min⁻¹), q _e and q _t are biosorption capacity at equilibrium and at time t (mg g⁻¹), respectively, h is the initial biosorption rate (mg g min⁻¹), C is the intercept (mg g⁻¹), and k _p is the intraparticle diffusion rate constant (mg g⁻¹ min^−1/2).

Freundlich isotherm equation;

$$ \ln {q}_{\mathrm{e}}= \ln {K}_{\mathrm{F}}+1/ n \ln {C}_{\mathrm{e}} $$

(9)

Langmuir isotherm model;

$$ \frac{1}{q_{\mathrm{e}}}=\frac{1}{q_{\max }}+\left(\frac{1}{q_{\max }{K}_{\mathrm{L}}}\right)\frac{1}{C_{\mathrm{e}}} $$

(10)

$$ {R}_{\mathrm{L}}=\frac{1}{1+{K}_{\mathrm{L}}{C}_{\mathrm{o}}} $$

(11)

D − R isotherm model;

$$ \ln {q}_{\mathrm{e}}= \ln {q}_{\mathrm{m}}-\beta {\varepsilon}^2 $$

(12)

$$ E=1/{\left(2\beta \right)}^{1/2} $$

(13)

where q _e (mol g⁻¹) and C _e (mol L⁻¹) are the amount of biosorbed dye per unit weight of biosorbent and unbiosorbed dye concentration in solution at equilibrium, respectively, K _F (L g⁻¹) and n (dimensionless) are Freundlich constants, q _max is the maximum monolayer biosorption capacity (mol g⁻¹), K _L is Langmuir constant related to the energy of biosorption (L mol⁻¹), R _L is separation factor, C _o is the initial solute concentration (mol L⁻¹), q _m is the biosorption capacity (mol g⁻¹), β is the activity coefficient related to the biosorption energy, and E (kJ mol⁻¹) is the mean free energy.