Enhancing disinfection and microcontaminant removal by coupling LED driven UVC and UVA/photo-Fenton processes in continuous flow reactors.

For the first time, the sequential combination of UVC-LED (276 nm) and photo-Fenton/UVA-LED (376 nm) process has been assessed in continuous flow mode for wastewater reclamation according to the new European Regulation for reuse in agricultural irrigation (EU 2020/741). The results show that it is possible to obtain water quality class B (Escherichia coli ≤ 100 CFU/100 mL) by UVC-LED irradiation alone, operating the system with a hydraulic residence time (HRT) of 6.5 min and liquid depth of 5 cm in the case of secondary effluents with low Escherichia coli load (8.102-3.1.103 CFU/100 mL). As for high bacteria concentrations (1.2-4.2.104 CFU/100 mL), HRTs longer than 30 min are required. The bacterial load has not influenced decontamination, removing 18 ± 4 % of microcontaminants. Coupling the UVC (30-min HRT and 5.0 cm liquid depth) and the UVA/photo-Fenton (60-min and 15-cm liquid depth) systems allows 58 ± 4 % of real organic microcontaminants to be removed, in addition to achieving water quality class B.

Thermochemical valorization of greenhouse cucumber, tomato and pepper as biofuel.

Agricultural residues adequate managing contributes to reduce CO2 emissions and easy the circular economy. In this paper, cucumber, tomato and pepper greenhouse crop residues were characterized both chemically and energetically to potential of waste as a biofuel. When compared to other herbaceous and woody biomass, the data show higher moisture, ash and chlorine contents. The gross calorific values of these residues are in the same range as the herbaceous biomass (14.92 MJ/kg), with net values of 13.71, 14.58 and 15.73 MJ/kg for cucumber, tomato and pepper, respectively. The study also included other not common elements, finding the highest values for calcium (13-25 mg/kg) and potassium (23-30 mg/kg). To date, empirical correlations have been defined to predict the CV as a function of total C content (expressed as % in dry weight) for these residues individually. The empirical correlations obtained had maximum absolute errors (MAE) of 0.11, 0.32 and 0.58 % for cucumber, tomato and pepper whereas the marginal mean bias errors (MBE) were 0.016, 0.002 and 0.004 %, respectively, which confirms the value of using this method to determinate the gross calorific value of these residues. The correlations shown provide a useful tool for developing energy production processes based on crop residues, that would appear to be an interesting source of renewable energy to produce heat.

Phenomenological study and application of the combined influence of iron concentration and irradiance on the photo-Fenton process to remove micropollutants.

The presence of low concentrations of persistent pollutants in waters (µg/L or ng/L), also called micropollutants, brings as a consequence the need to apply advanced oxidation treatments for their removal. The successful application of solar-driven photo-Fenton to treat highly polluted wastewaters (g/L and mg/L of pollutants) has prompted its application to lowly polluted effluents. However, a decrease in contaminant concentration may involve an alteration in the intrinsic process phenomenon, which until now has only been widely studied at the milligram-per-litre level or higher with this process. The aim of this research was to study the combined influence of the operating variable (iron concentration) and the environmental variable (irradiance) and application on the photo-Fenton process at pH2.8 when removing micropollutants. For this purpose, experimentation was carried out at laboratory and pilot plant scales with a biocide mixture of acetamiprid (ACTM), thiabendazole (TBZ) and imazalil (IMZ) (100 µg/L each) as the model pollutant. Results indicated that above 15 WUV/m(2) and a light path length of 5 cm (the most commonly used path for this type of application) iron concentration limited the process and there was irradiance excess under these conditions. On the other hand, and given the circumstances of irradiance excess, a higher light path length (10 cm) was assessed. Results showed that path lengths wider than 5 cm are recommended since more wastewater volume could be treated with a higher process rate per surface unit.

Economic evaluation of a combined photo-Fenton/MBR process using pesticides as model pollutant. Factors affecting costs.

The aim of this paper is to carry out an economic assessment on a solar photo-Fenton/MBR combined process to treat industrial ecotoxic wastewater. This study focuses on the impact of the contamination present in wastewater, the photochemical oxidation, the use of an MBR as biological process and the plant size on operating and amortization costs. As example of ecotoxic pollutant, a mixture of five commercial pesticides commonly used in the Mediterranean area has been used, ranging from 500 mg/L to 50mg/L, expressed as dissolved organic carbon concentration. The economic evaluation shows that (i) the increase in pollution load does not always involve an increase in photo-Fenton costs because they also depend on organic matter mineralization; (ii) the use of an MBR process permits lower photochemical oxidation requirements than other biological treatments, resulting in approximately 20% photo-Fenton cost reduction for highly polluted wastewater; (iii) when pollution load decreases, the contribution of reactant consumption to the photo-Fenton process costs increase with regard to amortization costs; (iv) 30% total cost reduction can be gained treating higher daily volumes, obtaining competitive costs that vary from 1.1-1.9 €/m(3), depending on the pollution load.