Optimization of the chromium (Cr) reduction from waterways using chemically and bacterially treated agro-waste.

Heavy metals, a major source of pollution in the environment, pose a substantial threat due to their non-biodegradability and ability to accumulate in living organisms, causing health problems. Recently, researchers have been searching for cost-effective and safe ways to remove heavy metals from polluted waterways using agricultural waste substitutes. The present study focused on the low-cost treatments for the reduction of chromium Cr metal from the effluent, wherein it has been found that chemically and bacterially treated agro-waste had increased heavy metal ion adsorption capabilities. A sequential optimization of the process parameters was attempted using Plackett-Burman design (PBD) and central composite design of response surface methodology (CCD-RSM) for the maximum reduction of the chromium metal from the effluent. A total of eight parameters were screened out using a 12-run PBD experiment. Out of the eight parameters, time, HCl, NaOH, and bacterial treatments were found to be significantly affecting the maximum reduction of Cr from the effluent. To investigate the interactions' effects of the chosen parameters, they were evaluated using CCD-RSM. Maximum 74% Cr reduction was achieved under the optimum treatment to rice husk of HCl 4.52 N, NaOH 3.53 N, bacterial suspension 7.41%, and with an interaction time 14.32 min using 30 run CCD-RSM experiment. A scanning electron microscope was used to confirm the effects of selected variables on the agro-waste for the Cr reductions, as well as a Fourier transform infrared spectrometer.