Insights on Carbonaceous Materials Tailoring for Effective Removal of the Anticancer Drug 5-Fluorouracil from Contaminated Waters

Engineered pine nut shell derived activated carbons for improved removal of recalcitrant pharmaceuticals in urban wastewater treatment

Novel powdered activated carbons (PACs) from pine cones and pine nut shells (PNSs) were tested for the competitive adsorption of pharmaceutical compounds (PhCs) in spiked (100 µg/L) secondary effluent and mixed liquor from an urban wastewater treatment plant. Steam activated PNS77, with hierarchical pore structure and 1463 m²/g of BET area, outperformed the commercial benchmark (WP220, mineral origin) for PhCs and dissolved organic matter (DOM) control. PNS77 attained the highest adsorption capacity and rate in synthetic and real wastewaters. Competitive adsorption isotherms revealed the detrimental effect of direct site competing DOM on PhC removal. The PhCs' adsorbability increased with their hydrophobicity, regardless of the water matrix. Kinetic data allowed inferring that indirect competition due to pore constriction/blockage appeared to occur only in mixed liquor. Adsorption isotherm data modelling for ng/L range revealed 80 % removal of carbamazepine and diclofenac would be achieved dosing 8-15 mg/L PNS77 to secondary effluent, while for mixed liquor the dose must be doubled to balance the increased competition. Hydrophilic sulfamethoxazole required a higher dose (34-44 mg/L), lower in the mixed liquor. PNS77 hierarchical pore network and basic surface chemistry minimized DOM direct site competition, requiring lower doses in practical applications for wastewater treatment.

Active-chlorine-mediated oxidation of 5-fluorouracil on a hierarchically ordered macroporous RuO2 electrode

A hierarchically ordered macroporous RuO₂ electrode (HOM-RuO₂) was fabricated to enhance in situ active chlorine production in an electrochemical system intended for treatment of pharmaceutical active compounds (PhACs). The unique structure of HOM-RuO₂ resulted in a decrease of the chlorine evolution potential, a large electro-active area available for in situ conversion of Cl^- to active chlorine, and hence improved the active chlorine production by 40%. 5-Fluorouracil (5-FU) was used as a target pollutant to explore the performance of the HOM-RuO₂ for PhACs degradation based on the in situ generated active chlorine. The results showed that the reaction rate of active-chlorine-mediated oxidation of 5-FU produced using the HOM-RuO₂ was 18.4 times higher than that in the case of hydroxyl radicals (OH)-initiated oxidation using a PbO₂ electrode at 30 mA cm^-2. The effects of current density and initial solution pH on the 5-FU removal were investigated. The mechanism of 5-FU degradation was proposed taking into accounts both active chlorine production, and change of the speciation of 5-FU caused by pH variations. The dominant degradation products observed for the degradation of 5-FU using the HOM-RuO₂ were lactic acid, propanol, acetic acid, urea and other small molecules, but no chlorinated products were detected. These study demonstrates the promise of the HOM-RuO₂-based electrochemical systems for the active-chlorine-mediated treatment of recalcitrant pharmaceuticals found in wastewater.

Specific adsorbents for the treatment of OMW phenolic compounds by activation of bio-residues from the olive oil industry

A series of adsorbents was developed by physical (CO₂) and chemical (KOH) activation of two bio-residues: olive stones (OS) and wood from olive tree pruning (OTP). The physicochemical properties of such materials were determined and correlated with their adsorptive performance in the removal of phenolic compounds of olive mill wastewater (OMW). Adsorption isotherms and kinetics of single phenolic acids, as well as the kinetics for competitive multi-compound adsorption, were fitted by applying different models, though Langmuir and pseudo-second order models fitted better the experimental results, respectively. The intraparticle diffusion model pointed out that mesoporosity reduces the influence of phenolic compounds' restrictions in the external film diffusion of the adsorbent particle-solution interphase, but adsorption capacity linearly increases with the micropore volume accessible to N₂ at -196 °C (and also with BET surface area), while diffusion into ultramicropores (<0.7 nm, determined by CO₂-adsorption) is slow and presents minor influence on the total adsorption capacity. After saturation, thermal regeneration of spent adsorbents allows the removal of adsorbed products, enabling the reuse of samples whilst maintaining a significant performance.