Valorisation Of Residues From Supercritical Extraction Into Value Added Products For Water Treatment.

Résumé: Onion seeds are generally considered organic waste and discarded. However, instead of throwing them away, we have identified ways to use this organic material and give it scientific and economic value by using it to remove pollutants. In our study, we experimented with this organic material to remove two types of dyes, namely methyl green and crystal violet, through two different processes: bio-coagulation and biosorption. This organic material was characterized by infrared spectroscopy (FTIR), Boehm's method, methylene blue index (3.04 mg/g), and iodine index (380.7 mg/g). It demonstrated its ability to retain small and large molecules. The adsorption of crystal violet with OSER follows second-order kinetics. Other mechanisms that can be applied include intraparticle diffusion, which postulates that the transport of molecules or ions in the pores of solid particles is a critical mechanism influencing the adsorption kinetics. In the bio-coagulation process, our biomaterial has proven its role both as a coagulant and in reducing the concentration of methyl green in aqueous solutions with an efficiency of 72% using a settling time of 30 minutes and at a natural pH of 5.5, without the addition of a flocculent. The second part focused on studying the adsorption of Crystal Violet under different parameters such as contact time, adsorbent mass, initial pH, temperature, and initial concentration. This organic material yielded excellent results over a wide range of these factors. The results indicated that the pseudo-second-order model controlled by intraparticle diffusion describes retention. The CV isotherm by the extraction residue is well described by the Freundlich, Timken, and Dubinin-Radushkevich models with correlation factors of 0.8, 0.99, and 0.98 respectively. Our OSER biosorbent was able to reduce the concentration of Crystal Violet from 50 mg/L to 1.07 mg/L with an efficiency of 97.348% at equilibrium time of 60 minutes, a temperature of 33°C, and a natural pH of 5.5.

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