Three-Dimensional Electrosorption for Pharmaceutical Wastewater Management and Sustainable Biochar Regeneration

Abstract

The adsorption capacity of a biochar (BC) obtained from pine wood residues was evaluated for its ability to remove two pharmaceuticals: fluoxetine (FLX) and sulfamethizole (SMZ). The material showed promising results in FLX removal, but a limited capacity in the case of SMZ. In order to improve these results, BC surface modifications were made by doping with nitrogen, as well as using acid, basic and electrochemical treatments. A three-dimensional electrosorption treatment proved to be the most effective, increasing the adsorption rate from 0.45 to 13.46 mg/g after evaluating different operating conditions, such as the electrodes used or the BC dosage. Consecutive cycles of BC use were performed through desorption and electro-regeneration techniques to test its capacity for reuse, and it was observed that application in the 25 mA electric field increased the useful life of the material. Finally, the effect of ionic strength was studied, highlighting that the presence of ions did not significantly affect the efficiency of SMZ removal, although a slight increase was observed at a high ion concentration, probably due to a salinization effect.

Keywords: biochar; fluoxetine; mechanisms; regeneration; sulfamethizole; three-dimensional electrosorption.

Figure 1

Physicochemical characterization of BC through (a) BET; (b) FTIR; (c) XRD; (d) Raman; (e) TGA and (f) ICP-OES.

Figure 2

EDS mapping of (a) carbon, (b) oxygen and (c) Calcium present in BC. (d) Micrography from BC at x2500 resolution.

Figure 3

(a) FLX (blue) and SMZ (orange) removal achieved by BC in 4 h of contact with dose of 10 g/L and pollutant concentration of 10 mg/L; and (b) FLX isotherm fittings to Langmuir, Freundlich and Redlich–Peterson models.

Figure 4

BC modifications for enhanced SMZ removal over 120 min of treatment with pollutant concentration of 10 mg/L and 10 g/L of adsorbent. BC was modified with 0.5 M C₃H₆N₆; 2 M H₂SO₄; 2 M NaOH and electric field was applied at 1.2 V. Letters represent different groups of the studied factor (modifications) significantly different from each other in relation to the response variable (removal). The group’s influence is ordered decreasingly, with A being the highest impact group, followed by B, C and D.

Figure 5

SMZ removal over 120 min according to (a) electrode material and (b) BC dose. (c) CV result after 5 cycles for doses of 0.8, 2.5 and 10 g/L BC. (d) Specific capacitance according to dose employed. Letters represent different groups of the studied factor (electrode effect and dose effect) significantly different from each other in relation to the response variable (removal and/or uptake). The group’s influence is ordered decreasingly. In case of removal, A is the highest impact group, followed by B, and C (if applied). In case of uptake, a is the highest impact group, followed by b and c.

Figure 6

Profile of SMZ uptake over time and related removal with 3D electrosorption using 0.8 g/L of adsorbent to remove 10 mg/L of SMZ at 1.2 V. (a) Kinetic adjustment PFO (dotted line) and PSO (continuous line) and (b) synergistic effect by comparison of adsorption, control at 1.2 V and 3D electrosorption.

Figure 7

Consecutive cycles of use after BC regeneration through desorption with ACN (orange) and electro-regeneration at 25 mA (green), 50 mA (blue) and 100 mA (purple). Letters represent different groups of the studied factor (regeneration) significantly different from each other in relation to the response variable (removal). A and B are the highest and lowest impact groups, respectively. Same letter in different regeneration methods implies no significant difference in response. Group A/B in the 3th use at 100 mA implies the treatment is equidistant from both groups due to its standard deviation.

Figure 8

(a) SMZ removal after 24 h of BC/3D-ES treatment with different molar ratios of pollutant and ions. Letters represent different groups of the studied factor (molar ratio) significantly different from each other in relation to the response variable (removal). A and B are the highest and lowest impact groups, respectively. Same letter in different ratios implies no significant difference in response. Ion concentration for molar rates of (b) 1:1; (c) 1:5 and (d) 1:10, at initial time (orange) and after 24 h (blue) of treatment.