A new solar photo-Fenton strategy for wastewater reclamation based on simultaneous supply of H2O2 and NaOCl

Phenomenological insights into the occurrence and abatement of disinfection by-products in the novel solar chlor-photo-Fenton process

For the first time, in-depth phenomenological insights were investigated into the formation/degradation of chlorination disinfection by-products (DBPs) during the treatment of actual secondary effluents by the novel solar chlor-photo-Fenton (CPF) process for disinfection and organic microcontaminant removal. To this aim, the influence of solar irradiance and reagents involved in the process (ferric nitrilotriacetate, hydrogen peroxide, and sodium hypochlorite) was assessed at lab scale and further verified in raceway pond reactors operated in continuous flow in terms of DBP degradation, to guarantee the safety reuse of the treated water and thus the implementation on a larger scale. The results were highly encouraging, the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) being negligible compared to legislative limits (30 and 60 μg/L; 26- and 3-fold lower for THMs and HAAs, respectively). Solar CPF excels at reducing DBP concentrations, achieving levels of just 6.12 µg/L of THMs and 15.6 µg/L of HAAs, significantly lower than the 27.7 µg/L of THMs and 105 µg/L of HAAs produced by conventional chlorination. These findings proved the capacity of this novel strategy to notably mitigate DBP formation through the synergy of sunlight and HO•-induced oxidation while allowing simultaneous disinfection and microcontaminant removal.

Model-based scenario analysis to support the operation of solar photo-Fenton plants

Model-based tools applied to wastewater management have been identified as an emerging solution to address the associated challenges related to the optimization of the technologies, meeting more restricted water quality standards. Thus, for the first time, the demonstration of the solar photo-Fenton process for microcontaminant removal in the operating environment of a model-based tool is reported. This tool aids in determining the right cost-effective seasonal strategy for a 37-m2 demonstration-scale photoreactor operating in a rural wastewater treatment plant. It was developed using a model tuned adequately with experimental data obtained at lab scale and then validated in the solar photo-Fenton demonstration plant, proving its reliability, and enveloping a robust operation. Imidacloprid removal was the treatment target, and reagent concentrations were 0.1 mM for ferric nitrilotriacetate and 0.73 mM for hydrogen peroxide. According to the model-based tool, to attain the maximum treatment capacity, the best operating conditions were a liquid depth of 20-cm, and hydraulic residence time of 45 and 60-min in summer and winter, respectively, augmenting the treatment cost by 25% (0.49 €∙m-3 vs. 0.65 €∙m-3). This model-based tool allows the control and optimization of the technology to be improved, while promoting its attractiveness in the market.

Optimization, kinetics, and pathways of pharmaceutical pollutant degradation using solar Fenton technique

Solar Fenton is an important and extensively used advanced oxidation process (AOP) to degrade pharmaceutical pollutants. The objective of this study was to evaluate the performance of simultaneous degradation of the mixed pollutants (amoxicillin, acetaminophen, and ciprofloxacin) for an aqueous solution using the solar Fenton process. Operating parameters such as pH, iron doses, H2O2 doses, pollutant concentrations, and time were studied. From the experimental results, the ideal conditions were obtained for the removal of mixed pollutants such as pH 3, Fe2+ 0.04 mM, H2O2 4 mM, the concentration of the mixed pollutants 5 mg/L, solar radiation 400 W/m2, and time 10 min, respectively. The pseudo-first-order kinetics were utilized to investigate the degradation efficacy of the mixed pollutants. The result of the study indicates that the degradation efficiency was > 99% for the mixed pollutants. A maximum of 63% mineralization was observed, and hydroxyl radical scavenger effects were studied. The best optimal conditions were applied to assess the spiked wastewater (municipal wastewater (MWW) and hospital wastewater (HWW)). The highest elimination rates for AMX, ACET, and CIP were observed as 65%, 89%, and 85% for MWW and 76%, 92%, and 80% for HWW, respectively. The degraded by-products were detected by LC-ESI-MS in the water matrix (aqueous solution and spiked wastewater), and ECOSAR analysis was performed for the transformed products. The study concluded that the solar Fenton technique is promising and effective for the removal of mixed pollutants from the water matrix.

Integrated AI-driven optimization of Fenton process for the treatment of antibiotic sulfamethoxazole: Insights into mechanistic approach

Antibiotics, as a class of environmental pollutants, pose a significant challenge due to their persistent nature and resistance to easy degradation. This study delves into modeling and optimizing conventional Fenton degradation of antibiotic sulfamethoxazole (SMX) and total organic carbon (TOC) under varying levels of H2O2, Fe2+ concentration, pH, and temperature using statistical and artificial intelligence techniques including Multiple Regression Analysis (MRA), Support Vector Regression (SVR) and Artificial Neural Network (ANN). In statistical metrics, the ANN model demonstrated superior predictive accuracy compared to its counterparts, with lowest RMSE values of 0.986 and 1.173 for SMX and TOC removal, respectively. Sensitivity showcased H2O2/Fe2+ ratio, time and pH as pivotal for SMX degradation, while in simultaneous SMX and TOC reduction, fine tuning the time, pH, and temperature was essential. Leveraging a Hybrid Genetic Algorithm-Desirability Optimization approach, the trained ANN model revealed an optimal desirability of 0.941 out of 1000 solutions which yielded a 91.18% SMX degradation and 87.90% TOC removal under following specific conditions: treatment time of 48.5 min, Fe2+: 7.05 mg L-1, H2O2: 128.82 mg L-1, pH: 5.1, initial SMX: 97.6 mg L-1, and a temperature: 29.8 °C. LC/MS analysis reveals multiple intermediates with higher m/z (242, 270 and 288) and lower m/z (98, 108, 156 and 173) values identified, however no aliphatic hydrocarbon was isolated, because of the low mineralization performance of Fenton process. Furthermore, some inorganic fragments like NH4+ and NO3- were also determined in solution. This comprehensive research enriches AI modeling for intricate Fenton-based contaminant degradation, advancing sustainable antibiotic removal strategies.

Winery and olive mill wastewaters treatment using nitrilotriacetic acid/UV-C/Fenton process: Batch and semi-continuous mode

In this work, both red and white winery wastewaters (WW) and olive mill wastewater (OMW) were submitted to a treatment by Fenton-based processes (FBPs). The main aim was to evaluate the most efficient and economic process. Initial tests, resorting to a batch reactor, demonstrated that UV-C/Fenton (λ = 254 nm) was the most effective process. Operational conditions such as pH, H2O2 and Fe2+ concentrations revealed to have a superior influence within dissolved organic carbon (DOC) removal as well as regarding the reactor's energy consumption. As a means to prevent iron precipitation, the addition of nitrilotriacetic acid (NTA) was tested. With experimental conditions pH = 3.0, [H2O2] = 194 mM, [Fe2+] = 1.0 mM, [NTA] = 1.0 mM, radiation UV-C (254 nm), time = 240 min, the kinetic rate related with DOC removal showed a kredWW = 0.0128 min-1 > kOMW = 0.0124 min-1 > kwhiteWW = 0.0104 min-1 and both the WW and OMW achieved the Portuguese legal limit values for wastewater discharge. Furthermore, comparative experiments were performed in a semi-continuous reactor, being that the results put in evidence that the concentration of H2O2 added and the flow rate of reagents' addition (F) had a significant effect on the efficiency of the reactor. Under an optimum experimental procedure pH = 3.0, [H2O2] = 97 mM, [Fe2+] = 1.0 mM, [NTA] = 1.0 mM, radiation UV-C (254 nm), F = 1 mL min-1, time = 240 min, there were observed higher DOC removal kinetic rates (kOMW = 15.20 × 10-3 min-1 > kredWW = 11.64 × 10-3 min-1 > kwhiteWW = 11.57 × 10-3 min-1) and a cost ranging between 0.0402 and 0.0419 €/g.DOC. These results showed that semi-continuous reactors have the potential to be applied to large scale treatments, with low reagents consumption and reduced energy requirements.

Continuous flow operation of solar photo-Fenton fused with NaOCl as a novel tertiary treatment

A novel strategy based on solar photo-Fenton mediated by ferric nitrilotriacetate (Fe3+-NTA) combined with NaOCl in continuous flow mode for wastewater reclamation has been studied. Escherichia coli (E. coli) inactivation attained ≥ 5 log10-units, meeting the most restrictive EU 2020/741 target (10 CFU/100 mL), and 75% of organic microcontaminant total load was removed. As a remarkable finding, trihalomethanes (THMs) concentration was insignificant, complying by far with the Italian legislation limit. To attain these results, first the effect of liquid depth on E. coli inactivation and imidacloprid (IMD) removal from spiked municipal effluents was evaluated in continuous flow pilot-scale raceway pond reactors at 60-min hydraulic residence time with low reagent concentrations (0.10 mM Fe3+-NTA, 0.73 mM H2O2 and 0.13 mM NaOCl). Disinfection was due to the bactericidal effect of chlorine. In contrast, liquid depth notably influenced microcontaminant removal, highlighting that operation at 10-cm liquid depth allows achieving treatment capacities higher than at 5 cm (16.50 vs 28.20 mg IMD/m2∙day). Next, the monitoring of THMs was carried out to evaluate the generation and degradation of disinfection by-products, along with the removal of actual microcontaminants. These promising results draw attention to the treatment potential and open the way for its commercial application.

Continuous solar photo-Fenton for wastewater reclamation in operational environment at demonstration scale

For the first time, a continuous flow solar photo-Fenton demonstration plant has been assessed for wastewater reclamation according to the EU 2020/741 regulation. The treated water qualities achieved under two operating strategies (acidic and neutral pH) in a 100-m2 raceway pond reactor were explored in terms of liquid depth, iron source, reagent concentrations, and hydraulic residence time over three consecutive days of operation. The results obtained at acidic pH showed removal percentages of contaminants of emerging concern (CECs) > 75% and water quality classes B, C and D according to EU regulation at both assessed operating conditions, with treatment capacities up to 1.92 m3 m-2 d-1. At neutral pH with ferric nitrilotriacetate (Fe3+-NTA), 50% of CEC removal and only water quality class D were achieved with the most oxidizing condition assessed, giving a treatment capacity of 0.80 m3 m-2 d-1. The treatment capacities obtained in this work, which have never been achieved with solar water treatments, demonstrate the potential of this technology for commercial-scale application.