Olive mill wastewater reuse to enable solar photo-Fenton-like processes for the elimination of priority substances in mu
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RESEARCH ARTICLE
Olive mill wastewater reuse to enable solar photo-Fenton-like processes for the elimination of priority substances in municipal wastewater treatment plant effluents Ana Ruíz-Delgado 1,2 & Melina Antonella Roccamante 1,2 & Sixto Malato 1,2 & Ana Agüera 2 & Isabel Oller 1,2 Received: 25 February 2020 / Accepted: 12 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Olive mill wastewater (OMW) appears as an interesting and innovative natural alternative to synthetic chelating agents of iron in solar photo-Fenton processes at circumneutral pH due to its high polyphenol content, valorizing wastewater typically found in sunny countries. The aim of this work was the reuse of OMW for the elimination of other recalcitrant microcontaminants: terbutryn, chlorfenvinphos, diclofenac, and pentachlorophenol. Highly diluted OMW (1:1500) was employed to keep the iron in solution at circumneutral pH. Eighty percent degradation of microcontaminants was achieved, although the reaction rate was slow compared with conventional photo-Fenton process, due to Fe-polyphenol complex instability at neutral pH. At pH around 4 (considerable superior to the photo-Fenton optimal pH 2.8), Fe-polyphenol complex stability was promoted: solar UV energy required was 25 times lower to reach the objective of 80% microcontaminants degradation, which was attained in a single step, without coupling with other processes. Operating photo-Fenton at slightly acidic pH was proposed for the first time for possible reuse of treated wastewater in crop irrigation, requiring minimum pH adjustment by simply mixing it with natural wastewater. Keywords Advanced oxidation processes . Circumneutral pH . Contaminants of emerging concern . Olive mill wastewater reuse . Polyphenols . Wastewater valorization
Introduction Photo-Fenton process is one of the most investigated and applied advanced oxidation processes (AOPs) worldwide for the remediation of different types of wastewater. Such as other AOPs, photo-Fenton is based on the generation of hydroxyl radicals (Ameta et al. 2018; Rahim Pouran et al. 2015). In water, Fe3+ is hydrolyzed, forming different soluble aqua complexes at acidic pH (Lipczynska-Kochany and Kochany 2008). As pH increases to values higher than 3.5, Fe(OH)3 is formed with 100% speciation and at pH values around 5, it precipitates (Pignatello et al. 2006). This effect
Responsible editor: Vítor Pais Vilar * Isabel Oller [email protected] 1
Plataforma Solar de Almería-CIEMAT, Ctra. Senés km 4, 04200 Tabernas, Almería, Spain
2
CIESOL, Joint Centre of the University of Almería-CIEMAT, 04120 Almería, Spain
is considered a serious drawback for the wide application of the well-known photo-Fenton process under near neutral pH, limiting its use in wastewater treatment for microcontaminants where acidification is very often not a choice. Therefore, a great effort has been done in the last years to find alternatives to keep iron in solution at circumneutral pH (De la Cruz et al. 2012; De Luca et al. 2014; De Lu
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