Application of grape seed and Austrocylindropuntia mucilage for the simultaneous removal of azo dye and turbidity from synthetic wastewater: Optimizing experimental conditions using Box-Behnken Design (BBD)

The purpose of this study was to explore the potential of grape seed powder (GSP) as a natural coagulant and Austrocylindropuntia mucilage (AM) as a natural flocculant to efficiently eliminate both Congo red (CR) azo dye and turbidity from synthetic wastewater using coagulation-flocculation technique. The Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive spectra (EDS) mapping, and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize natural plants employed as well as sludge formed after coagulation-flocculation process. Moreover, response surface methodology (RSM) approach was established via Box-Behnken Design (BBD) to optimize a set of coagulation-flocculation conditions; including GSP dose, AM dose, initial pH, initial CR concentration, initial turbidity, and settling time. RSM-BBD results showed highest removal efficiency of 99.36 % and 95.74 % of CR and turbidity, respectively, achieved under optimum conditions of 0.45 mg L⁻¹ of GSP coagulant, 6 mL L⁻¹ of AM flocculant, at pH of 10, initial CR concentration of 5 mg L⁻¹, initial turbidity of 250 NTU, and after settling time of 120 min. The findings of this work revealed that there are multiple mechanisms involved in CR and turbidity removal, namely hydrogen bonding, electrostatic interactions, π-π interactions, and bridging effect.