Search Results (2)

This study evaluates the effects of carbon, nitrogen, and sulfur dopants on the photocatalytic activity of TiO₂ for degradation of oxytetracycline (OTC) and chemical oxygen demand (COD) removal from licorice extraction plant wastewater (LEPW). Three novel visible-light-responsive nanostructures, including L-Histidine-TiO₂, L-Methionine-TiO₂ and L-Asparagine-TiO₂, were successfully synthesized. The results showed that the modification of TiO₂ with these three amino acids made the catalyst active in the visible light region and reduced the recombination rate of e⁻/h⁺ pairs according to PL analysis. The photodegradation efficiency of L-Histidine (2 wt.%)-TiO₂ was 100% and 94% for OTC and COD, respectively. It showed the highest photocatalytic activity under illumination, compared to L-Methionine (1.5 wt.%)-TiO₂ and L-Asparagine (2 wt.%)-TiO₂. Synthesized composites were characterized with SEM, XRD, FTIR, DRS, and PL analyses. The biological oxygen demand to COD (BOD₅/COD) ratio for treated LEPW was determined to be 0.5–0.6, confirming the enhanced biodegradability of the treated effluent. The effect of the independent variables, namely, initial concentration of OTC and COD, catalyst dosage, irradiation time, pH of solution, and light intensity, on the photocatalytic process was evaluated by Response Surface Methodology (RSM), and the optimum value of each independent parameter for maximum degradation of OTC and COD by L-Histidine (2 wt.%)-TiO₂ was determined. The radical trapping experiment was performed with various scavengers in order to propose a photocatalytic mechanism, showing that hydroxyl radicals were the main active species. L-Histidine (2 wt.%)-TiO₂ showed a stable and reusable structure even after four cycles of COD removal under the following optimal conditions of [COD]: 300 mg/L, [catalyst]: 1 g/L, light intensity: 25 W/cm² at pH = 4 after 180 min irradiation. Full article

In this work, the use of polymeric ultrafiltration and nanofiltration membranes was investigated in order to recover glycyrrhizin and phenolic compounds from licorice wastewaters. Filtration experiments were performed on a laboratory scale using four polyamide thin-film composite membranes (GK, GH, GE, and DK, from GE Osmonics) with different molecular weight cut-offs (from 150 to 3500 Da). The permeate flux and retention values of glycyrrhizin, the total polyphenols, the caffeic acid, the total carbohydrate, and the total antioxidant activity as a function of the transmembrane pressure (TMP) and weight reduction factor (WRF) were evaluated. In selected operating conditions, the membrane productivity decreased in the order of GK > DK > GH > GE, with a similar trend to that of water permeability. Glycyrrhizin was totally rejected by selected membranes, independently of TMP and WRF. For the other antioxidant compounds, the retention values increased by increasing both of the parameters. According to the experimental results, a combination of membranes in a sequential design was proposed as a viable approach to produce concentrated fractions enriched in bioactive compounds and purified water from licorice wastewater. Full article