Avocado seed as a natural coagulant for removing dyes and turbidity from wastewater: Behnken Box design, sustainable reuse, and economic evaluation

Abstract

In wastewater treatment, conventional coagulants are becoming very complex with environmental concerns. For this purpose, using an alternative natural coagulant such as fruit waste becomes essential. This study explores the potential of avocado seed powder as a novel biocoagulant for treating wastewater contaminated with dyes and turbidity. It was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Scanning Electron Microscopy coupling with Energy-dispersive X-ray spectroscopy, and X-ray fluorescence. The coagulation-flocculation process was optimized using a Box-Behnken design, evaluating the effects of coagulant dose (300–1000 mg. L−1), initial solution pH (3–9), and granulation (63–112 μm), on the removal of methylene blue, crystal violet, and turbidity. The response surface methodology revealed statistically significant quadratic models (R2 > 0.94) for maximizing pollutant removal. Under optimal conditions (1000 mg. L−1 dose, pH 9, 63 μm granulation for methylene blue; 950 mg. L−1, pH 7, 108 μm for crystal violet; 300 mg. L−1, pH 8, 63 μm for turbidity), avocado seed powder achieved maximum removal efficiencies of 94.34 % for methylene blue, 95.28 % for crystal violet, and 99.64 % for turbidity. Characterization techniques confirmed the involvement of avocado seed powder in the coagulation-flocculation mechanism. The biocoagulant has demonstrated significant reuse potential over five cycles. It also has a low estimated cost, of the order of 0.008–0.025 USD. m−3 as agricultural waste, compared with 1.5 USD. m−3 for aluminum sulfate. Overall, avocado seed is a sustainable and promising natural coagulant for wastewater treatment.