New nano-biomaterials for the removal of malachite green from aqueous solution via a response surface methodology

The development of new biomaterials for the remove of organic contaminants from wastewater has attracted much attention over the few past years. One of the most cost-effective approaches is to produce new high value biomaterials from low value solid agricultural biowastes. In this work, sugarcane bagasse and agricultural waste rich in reducing sugars, acted as both a green bioreductant for graphene oxide (GO) and a sustainable supporter for the immobilization of Burkholderia cepacia. Therefore, this new biomaterial which contained both reduced graphene oxide (RGO) and Burkholderia cepacia, was cable of initial adsorption of malachite green (MG) and its subsequent biodegradation. After 60 h, immobilized Burkholderia cepacia degraded more MG (98.5%) than a cell cultured Burkholderia cepacia (87.7%) alone. Raman spectroscopy confirmed that GO was successfully reduced by bagasse and that consequently a composite (B-RGO) was prepared. SEM indicated that Burkholderia cepacia was well immobilized and kinetics studies showed that the adsorption of MG onto the developed composite fitted a pseudo-second order kinetics model (R² > 0.99). Biodegradation of MG, was confirmed by the detection of appropriate degradation products such as N, N-dimethylaniline and 4-(Dimethylamino) benzophenone using GC-MS, UV and FT-IR, and via best fit first-order biodegration kinetics. Furthermore, a response surface methodology (RSM) was applied to the removal process by varying four independent parameters using a Box-Behnken design (BBD). Optimum MG removal (99.3%) was achieved at 31.5 °C, with an initial MG concentration of 114.5 mg L^-1, initial pH of 5.85, and an adsorbent dosage of 0.11 g L ^-1. The excellent removal efficiency indicated that agricultural waste derived reduced graphene oxide bio-adsorbents have significant potential for the removal of dyes such as MG from industrial wastewaters.