Combined organic coagulants and photocatalytic processes for winery wastewater treatment

Due to the consumers demand for quality wines, washing and disinfection operations are necessary in wine productions, leading to the generation of large volumes of winery wastewater (WW) with a high organic content which has the potential to cause irreversible environmental impacts. The aim and novelty of this work is the production of natural organic coagulants (NOCs) to be applied in coagulation-flocculation-decantation (CFD) process. To complement this treatment process, it is also aimed the performed a photo-Fenton process, combining hydrogen peroxide (H2O2) and potassium persulfate (KPS). The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) showed that NOCs are carbon-based materials with adsorption capacity. Under the best operational conditions, NOCs achieved a turbidity removal between 86.2 and 98.9%, a total suspended solids (TSS) removal ranging between 85.0 and 94.9% and a dissolved organic carbon (DOC) removal ranging between 14.1 and 44.9%. To degrade the DOC present in the WW, different advanced oxidation pro-cesses (AOPs) were tested. Results showed that KPS-photo-Fenton, under the best operational conditions [Fe2+] = 2.5 mM, [KPS] = 1.0 mM, pH = 3.0, radiation UV-C mercury lamp (254 nm), agitation 350 rpm, temperature 298 K, reaction time 240 min achieved a DOC removal of 91.2 and 96.8%, with a H2O2 consumption of 156.9 and 199.0 mM, respectively for red and white WW. With application of combined CFD-KPS-photo-Fenton process, it was observed an increase of DOC removal with lower H2O2 consumptions. The energy consumption of the photosystem was evaluated by application of electric energy per mass (EEM). The application of KPS-photo-Fenton process achieved an EEM of 0.308 and 0.0309 kWh/g/L DOC, with a cost of 2.05 and 2.59 euro/g/L DOC respectively for red and white WW. The combination of CFD-KPS-photo-Fenton decreased significantly the costs of treatment and the treated wastewater achieved the Portuguese legal values for wastewater discharge. This work shows that NOCs are a promising technology that can be an alternative to traditional metal salts, the combination of sulfate radicals with hydroxyl radicals can achieve high DOC removal and the combination of CFD with KPS-photo-Fenton process can decrease the operational costs.

Automated summary

Due to the consumers' demand for quality wines, the production of winery wastewater with a high organic content poses potential environmental impacts. This study introduces the production of natural organic coagulants and their application in the coagulation-flocculation-decantation process, accompanied by a photo-Fenton process using hydrogen peroxide and potassium persulfate. The results demonstrate effective removal of turbidity, total suspended solids, and dissolved organic carbon from the wastewater. Furthermore, the combination of the two processes reduces operational costs and ensures compliance with wastewater discharge standards.