Establishing suitable conditions for metals recovery from metal saturated Bacillaceae bacterium using experimental design

Abstract

In this study the response surface methodology (RSM) based on the Box-Behnken design model was applied to investigate the effect of parameter interactions that are suspected to influence the metal desorption process. The experiment was based on the four-variable-three-level design of parameters such as uptake time, pH of eluant, shaking speed during desorption, and volume of eluant. The metal-removal process was designed so as to enhance desorption and regeneration of biosorbent. The results show that all four of the variables influenced metal desorption from the biomass, and the experimental design allowed better observation of the interaction level of parameters suitable for the desorption process leading to optimum recovery and regeneration of biosorbent. Calculated P values (P = 0.0233 for nickel and P = 0.0203 for lead) confirmed the fitness of the model to the experiments conducted. The desorption process was found to be dependent on the type of mechanism involved during biosorption. Parameter settings of 20 min (level 1) uptake time, pH 5 (level 0), 50 ml (level 0) eluant, and 200 r min−1 (level 1) shaking speed, led to maximum response (55.72%) during metal release. X-ray elemental mapping profiles and graphical data recorded using transmission electron microscopy (TEM) showed binding of both nickel and lead to Bacillaceae bacteria, but most importantly preferential binding of lead; FTIR spectroscopy depicted involvement of active groups such as hydroxyl, amine, and carboxyl in the uptake of both metals. Biomass regenerated was more effective in the removal of lead than nickel, achieving up to 100% uptake of lead in the second cycle. Desorption of metal from biomass is very important for the recovery of metals, which is necessary for undiminished uptake in the next cycle of metal removal