Simple and Eco-Friendly Route from Agro-Food Waste to Water Pollutants Removal

Abstract

The current study reflects the demand to mitigate the environmental issues caused by the waste from the agriculture and food industry. The crops that do not meet the supply chain requirements and waste from their processing are overfilling landfills. The mentioned wastes contain cellulose, which is the most abundant carbon precursor. Therefore, one of the possibilities of returning such waste into the life cycle could be preparing the activated carbon through an eco-friendly and simple route. Herein, the carrot pulp from the waste was used. Techniques such as thermogravimetric analysis (TGA), elemental analysis (EA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and x-ray diffraction (XRD) were used to investigate the thermal treatment effect during the carbon material preparation. The development of microstructure, phase formation, and chemical composition of prepared material was evaluated. The obtained carbon material was finally tested for water cleaning from a synthetic pollutant such as rhodamine B and phloxine B. An adsorption mechanism was proposed on the base of positron annihilation lifetime spectroscopy (PALS) results and attributed to the responsible interactions. It was shown that a significant carbon sorbent from the organic waste for water purification was obtained.

Keywords: agriculture waste; carbon; carrot pulp; food waste; organic pollutants; sorption; water purification.

Figure 1

Structural formula of rhodamine B (left) and phloxine B (right) drawn using the molecule editor Avogadro [50].

Figure 2

Effect of weight loss (a) and color change (b) during the stabilization and carbonization processes of the carrot pulp.

Figure 3

Thermogravimetric analysis of carrot pulp stabilized and carbonized at temperatures between 50 and 800 °C.

Figure 4

(a) Effect of the temperature on the Raman spectra of carrot pulp (CP) treated at various temperatures. (b) I_D/I_G ratio of the pulps on temperature.

Figure 5

Fourier-transform infrared (FTIR) spectra of CP were processed at different temperatures in the range of wavenumber of 800–1900 cm⁻¹ (a) and 2500–3800 cm⁻¹ (b).

Figure 6

Scanning electron microscopy (SEM) microstructure of the heat-treated carrot in dependence on the temperature (a) 150, (b) 200, (c) 250, (d) 400, (e) 600, and (f) 800 °C.

Figure 7

X-ray diffraction (XRD) pattern of the heat-treated carrot in dependence on the heat treatment temperature.

Figure 8

Absorption spectra of the supernatant obtained by centrifuging the mixture of dye and CCP sample with the ratio of the amount of RhB to the mass of CCP sample of 1.60 µmol·g⁻¹ (a) and 0.40 µmol·g⁻¹ (b) and of PhB to the mass of CCP sample of 1.60 µmol·g⁻¹ (c) and 0.40 µmol·g⁻¹ (d) (all solid lines); absorption spectra of the RhB (a,b) and PhB (c,d) in water are displayed by dashed lines.

Figure 9

Evolution of RhB and PhB removal efficiency with time for the mixtures with the ratio of the amount of dye to the mass of CCP sample of 1.60 µmol·g⁻¹ (mixture I.) and 0.40 µmol·g⁻¹ (mixture II.).

Figure 10

Lifetime t₂ (a) and the relative intensity I₂ (b) for the CCP, rhodamine B, and their composite. 1—CCP measured in air, 2—CCP measured in vacuum, 3—RhB measured in air, 4—RhB measured in vacuum, 5—CCP/RhB measured in air, 6—CCP/RhB measured in vacuum.

Figure 11

FTIR results of RhB (magenta line) and the “composite” material CCP/RhB (blue line) in the range 600–4000 cm⁻¹.