Insights of microorganisms role in rice and rapeseed wastes as potential sorbents for metal removal

Rice and rapeseed agricultural wastes, as nonliving biomass, are proposed for heavy metal remediation in polluted effluents (chromium, cadmium, copper and lead). The physicochemical characterization of these biomasses shows that the surface of both sorbents is negatively charged (zeta potential), the surface area of sorbents is 4.39 and 40.7 (Brunauer-Emmett-Teller), and the main functional groups are carboxylic and hydroxyl (attenuated total reflection Fourier-transform infrared spectroscopy). The main purpose of this work is to evaluate the insights of microorganisms associated with these nonliving biomasses in the removal of heavy metals from synthetic aqueous solutions, adjusted at pH 4.0 (as the best acidic condition for the sorption process). The isolates (Bacillus genus in rice and Escherichia, Micrococcus and Staphylococcus genus in rapeseed) remove heavy metals from mentioned solutions, mainly in consortia, with contribution percentage over than 80% of total metals. In addition, when they are present in biomass, they provide an additional metal removal effect, especially in rapeseed biomass system and with multiple heavy metals aqueous solutions: i.e. Cr(III) removal, at 4 mmol/L, increases from 70 to 100%. This knowledge makes possible the use of the nonliving biomasses with no need for any special pretreatment against the microorganisms, prior to their use as metal sorbents that implies their good feasibility for application from an economical point of view.