Comparison of the removal of 21 micropollutants at actual concentration from river water using photocatalysis and photo-Fenton

Simulation-based process optimization of full-scale advanced wastewater treatment systems using powdered activated carbon

This study extends a previously developed competitive modeling approach for predicting the adsorption of organic micropollutants (OMPs) on powdered activated carbon (PAC) in full-scale advanced wastewater treatment. The approach incorporates adsorption analysis for organic matter fractionation, assumes pseudo-first order kinetics and differentiates between fresh and partially loaded PAC through fraction segregation. Validation through full-scale measurement campaigns reveals successful model predictions of OMP removal, underestimating, however, diclofenac removals by 15-20%. Based on model testing, the impact of excess PAC return to the biological stage enhanced OMP removal, reaching up to 15% improvement for benzotriazole, carbamazepine and metoprolol, but no evident improvement of diclofenac removal. Intermittent PAC dosing revealed rapid process response, where organic matter concentration increased within 2 h after PAC cut-off. The simulation-based study demonstrated that during rain events, the overall OMP removal efficiency in the entire wastewater treatment plant was reduced by approximately 50% due to a shift of OMP concentration and a shortened hydraulic retention time in the biological and adsorption stages. Testing of various PAC dosing strategies revealed potential PAC savings of 10-15% compared to inflow-proportional dosing by using predefined OMP removal grades or maximum allowable effluent OMP concentrations as criteria for PAC dosing.

Structured photocatalytic systems: photocatalytic coatings on low-cost structures for treatment of water contaminated with micropollutants-a short review

The persistence of many micropollutants in water and wastewater is of great concern to the contemporary scientific community. Several types of advanced techniques such as heterogeneous photocatalysis are being used for the degradation of micropollutants in waters from domestic, industrial, and agricultural activities. Thus, structured photocatalytic systems are a great alternative in the development of photocatalytic reactors and continuous water treatment systems, as they present good autonomy during the treatment process. Many aspects such as type and geometry of the catalytic structure to be developed must be carefully chosen for the proper functioning of the system, as well as the best routes by which the photocatalysts will be immobilized. In this sense, this work brings the main photocatalytic coating techniques in low-cost structures for the treatment of water and wastewater contaminated with micropollutants. The methodologies and synthesis parameters that can influence the final result of the coating were highlighted, as well as the ability to reuse photocatalysts and methods for pretreating the structural surface. The dip-coating technique was the most reported among the current works due to its simplicity and, predominantly, the pretreatment techniques of the structure are still cleaning the surface with water, soap, and also some alcohols.

Degradation and mineralization of erythromycin by heterogeneous photocatalysis using SnO2-doped TiO2 structured catalysts: Activity and stability

Heterogeneous photocatalysis was used for the degradation and mineralization of erythromycin (ERY), with a consequent production of carboxylic acids. For that, a series of TiO₂ and Ti_1-xSn_xO₂ structured catalysts, namely M1 to M5, was prepared using the washcoating method, with the catalytic coatings being deposited onto stainless steel meshes. Besides, the catalytic activity of the prepared systems was compared to that of the commercial mesh (CM). The results showed that the prepared TiO₂ structured catalyst (M1) presented better ERY oxidation than the CM one, what was associated to the higher catalyst load and to the anatase/rutile ratio. Considering the Sn-doped structured catalysts, for M2, M4 and M5 catalysts, lower ERY mineralization and high formation of carboxylic acids were found, when compared to the M3 catalyst. The improved M3 activity was attributed to the formation of a staggered gap (type II heterojunction), providing better charge separation. In this situation, a high generation of hydroxyl radicals is obtained, resulting on a higher ERY mineralization. By the obtained results it is possible to determine that the addition order and the type of Sn compound added in the washcoating process, affects the catalytic activity due to the formation of a solid solution and to the type of produced heterostructures. The M3 catalyst also showed high stability in long-term tests up to 44 h of reaction. The results provide insights into the development of an inexpensive structured catalyst production method and its influence in the stability of the photocatalyst, as well as in its applicability on water/wastewater treatment.