Cadmium Removal from Synthetic Wastewater using Seed Biomass Biosorbent: A Bench-top Reactor Investigation


 The cadmium ion concentration in drinking water is frequently found higher in different part of the world as per international recommendation. It is crucial to reduce concentration in water by sustainable and environmentally friendly means. We tested the biomass of Jamun (JP) and Amaltash (AT) seeds to remove cadmium from synthetic wastewater cost effectively. The biomasses were characterized by functional groups (FTIR), crystalline structures (XRD), and elemental analysis (ICP) techniques. Experimentation the optimization study has been carried out by using Design-software 6.0.8. Response surface methodology has been applied to design the experiments where we have used three factors and three levels Box-Behnken design (BBD). Cadmium removal ability of bio-sorbents were evaluated in bench-top reactor and optimized at various solution pH, adsorbent dose, and cadmium concentration in synthetic wastewater. At initial cadmium concentration 2 mg/litre, pH 6, adsorbent dose 60 mg and stirring speed 300 rpm the cadmium removal was ~95% and ~93% from synthetic wastewater by JP and AT seed biomass, respectively. The adsorption behaviour of cadmium ions well explained following Temkin model (AT r2=0.988; JP r2=0.984) and maximum adsorption capacity 3.88 mg g−1 (JP) and 4.54 mg g−1 (AT) after 70 minutes under optimal set of condition and proved to be an efficient and eco-friendly bio-sorbent for cadmium removal.


Adsorption isotherm
Three classical adsorption isotherm models namely Langmuir, Freundlich and Temkin em-89 ployed in present investigation is given below: (1) 91 Plotting the data Ce/qe versus Ce, using this equation, the values of qm and b0 is calculated 92 from the slope and intercept of the linear plot. 93 The experimental data were also fitted to Freundlich isotherm which assumes that adsorbent 94 surface is heterogeneous and each adsorption site varies in respect to their bond energy. As per 95 Freundlich model of adsorption, sorption energy exponentially decreases with occupying the 96 sorption sites of the adsorbent [Freundlich et al. 1906].
between 0 to 1, and represents the measure of adsorption intensity. If, this value is more than 101 1, indicates a co-operative adsorption (Foo et al. 2010). 102 The generalized linear form of Temkin adsorption model can be expressed by equation given 103 below (Temkin et al. 1940). A plot between qe and ln (Ce) gives a straight line and we can find 104 the value of KT and bT from the slope and intercept, respectively.
The KT is Temkin isotherm coefficient (L.g -1 ), and is temperature T(K),bT is a coefficient 107 associated to the heat of sorption (J/mol). surface at time t (qt) was calculated using equation (7) given below: Where qt is the sorption capacity at time t (mg.g -1 ), Volume of solution in liter is represented 118 During the investigation we tested pseudo-1 st order, pseudo 2 nd order, intra-particle and Elovich 119 models for best curve fit for adsorption data.

120
The pseudo-1 st order model of Lagrange is expressed as given below (Farhan et al. 2012): A graph plot between log (qe-qt) versus t gives a straight line. The value of k1and qe can be 123 estimated from the slope and intercept of regression line.

125
The pseudo 2 nd -order model is depending on sorption ability of the solid phases, which have 126 been utilised for calculating chemisorptions kinetics.

207
In the Table 2 and figure 3, we have comparatively represented different kinetic parameters for 208 the Pseudo-first-order, pseudo-second-order, intra-particle and Elovich models for JP and AT  Investigational data were evaluated to observe the finest adsorption isotherm that describes the 223 adsorption method on these two selected bio adsorbents. To explain adsorption isotherms mg/g, respectively, which are veryclose to the experiment results and much higher than previ-237 ously reported biomaterials given in Table 3. It might be interpreted that the sorption techniques 238 followed the Freundlich and Tempkin models whereby heterogeneous adsorption took place 239 on the adsorbent surface.   Clearly, we observed higher Cd removal at dose 60 for both the case and further experiments 259 were conducted at this dose for kinetic study.

260
In the Table 3  The pH value of the solution strongly affects the removal of cadmium from waste water.

293
From figure 8 and 9 it can be depicts that the percentage removal of cadmium is initially 294 increasing as on increasing the solution pH and it gets maximum value at pH 6 than decreases.  figure   299 6, figure 9 (a and b) (for AT bio-adsorbent) and figure 8 (a and b) (for JP bio-adsorbent). A 300 sharp increase in the cadmium removal has been observed by increasing the solution pH from 301 3 to 6 as shown in figure 6, and afterwards it decreased. The maximum cadmium ions adsorp-302 tion was achieved at pH 6 and it was the optimum pH for cadmium adsorption on the JP and 303 AT seed bio-adsorbents as shown in the figure 8 and 9 of statistical study. At the optimal pH, 304 the elimination efficiency was around 95% for JP and 93% for AT, respectively. Similarly, at 305 low pH the target molecules were considered stable and percentage removal ranged between