Journal of Water Process Engineering 60 (2024) 105073 Available online 21 March 2024 2214-7144/© 2024 Elsevier Ltd. All rights reserved. Photochemical activation of persulfate for enhanced co-degradation of alkyl-esters of p-hydroxybenzoic acid in water Maria Antonopoulou a, * , Zacharias Frontistis b , Lelouda-Athanasia Koronaiou c, d , Dimitra Lambropoulou c, d a Department of Sustainable Agriculture, University of Patras, GR-30131 Agrinio, Greece b Department of Chemical Engineering, University of Western Macedonia, GR-50132 Kozani, Greece c Laboratory of Environmental Pollution Control, Department of Chemistry, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Greece d Center for Interdisciplinary Research and Innovation (CIRI-AUTH), Balkan Center, GR-57001 Thessaloniki, Greece A R T I C L E INFO Keywords: Parabens UV-C/persulfate Transformation products Water matrices Toxicity ABSTRACT The simultaneous degradation of a mixture containing 1 mg L  1 each of ethylparaben, methylparaben, and propylparaben using the UV-C/persulfate process was investigated. The degradation of these three parabens showed a similar decay pattern, resulting in >90 % reduction in <10 min. The system was capable of removing the parabens across a wide pH range; however, its efficiency was optimum at pH 6. The presence of sulfates, nitrates, and chlorides hindered slightly to moderately the removal of parabens, while a more significant decrease was observed in the presence of bicarbonates. Conversely, the addition of humic acid significantly reduced the apparent kinetic constants. In experiments conducted in environmentally relevant matrices, the observed efficiency was in the order of ultrapure water > drinking water > lake water > secondary effluent. Twelve transformation products were identified in different water matrices using high-resolution mass spec- trometry coupled to liquid chromatography. Toxicity measurements conducted using Scenedesmus rubescens across different matrices revealed that despite the formation of more toxic compounds during the initial stages of the reaction due to oxidation of parabens and matrix constituents, the system has the potential to significantly reduce the observed toxicity (to <10 %) after 180 min. Electric energy consumption using all the studied aqueous matrices was also evaluated which was found to increase using polluted water matrices. 1. Introduction In recent years, several chemicals have been detected in water and other environmental samples in traces, but they have been blamed for creating significant problems for humans and animals [1,2]. One of these classes of substances is called endocrine disruptors because of their negative impact on the endocrine systems of organisms, which can lead to significant side effects [3]. This category includes compounds such as parabens, which are widely used as preservatives and in a number of personal care products due to their interesting properties [4]. Residual amounts of various parabens such as methylparaben (MeP), ethylparaben (EtP) and propyl paraben (PrP) have been detected in surface waters and especially MeP and PrP are considered as ubiquitous pollutants in the aquatic systems all over the world [5]. In a recent re- view by Vale et al. (2022), the concentrations of parabens detected in aquatic systems have been compiled and were in the range of ng L  1 to μg L  1 [6]. Based on their review the highest concentrations detected in surface water were 170,870, 30,500 and 52,100 ng L  1 for MeP, EtP and PrP, respectively [[6] and references therein]. For the removal of parabens from wastewater, a large number of technologies have been examined, including techniques such as adsorption [7], photocatalysis [8–11], electrochemical oxidation [12,13], UV/H 2 O 2 [14], catalytic activation of persulfate [15] and ozonation [16]. However, each process suffers from certain drawbacks, such as the regeneration or disposal of adsorbents [17], the low effi- ciency in some cases, and the need for separation in heterogeneous photocatalysis [18]. Other challenges include the high energy costs, the requirement for conductivity, and the possibility of generating toxic species in electrochemical oxidation [19], as well as the potential for- mation of bromate and the handling of off-gas residuals in ozonation [20]. On the other hand, processes based on the use of UV radiation appear * Corresponding author. E-mail address: mantonop@upatras.gr (M. Antonopoulou). Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe https://doi.org/10.1016/j.jwpe.2024.105073 Received 16 December 2023; Received in revised form 17 February 2024; Accepted 25 February 2024