Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Low concentration peroxymonosulfate and UVA-LED combination for E. coli inactivation and wastewater disinfection from recirculating aquaculture systems Wanhe Qi, Songming Zhu*, Abubakar Shitu, Zhangying Ye, Dezhao Liu College of Biosystems Engineering and Food Science, Zhejiang University, Yuhangtang Road 866, Hangzhou 310058, PR China ARTICLE INFO Keywords: Advanced oxidation process Sulfate radicals PMS UVA-LED RAS disinfection ABSTRACT Under Minamata Convention restrictions, mercury-free UV source was in need for ultraviolet disinfection in recirculating aquaculture systems (RAS). Ultraviolet emitting diodes (UV-LEDs) seemed a potential mercury-free UV source and had gained increasing attention in water disinfection. In this study, a mercury-free UVA-LED and low concentration peroxymonosulfate (PMS) combination was proposed for E. coli (CGMCC 1.3373) inactivation and real RAS wastewater disinfection. Results showed that UVA-LED and low concentration PMS combination enhanced E. coli inactivation over UVA-LED alone. A synergistic effect on E. coli inactivation with synergy factor of 58.7 % was found when combining UVA-LED irradiation with 1 mg/L PMS. Kinetic rate constant increased by up to 139 % by UVA-LED and 1 mg/L PMS combination, which implied the required UV fluence to 2-log E. coli inactivation was saved up to 42 %. Also, UVA-LED and 1 mg/L PMS combination showed disinfection potential for real RAS wastewater treatment. Mechanism study revealed that the Cl - , · OH and SO 4 ·- played important roles and · OH was dominant radical in saline solution by UVA-LED/PMS process compared to that in phosphate buffered solution(PBS). The E. coli inactivation was caused by UVA-LED irradiation and reactive species gen- erated in UVA-LED/PMS system. Our study provided a potential strategy to introduce the mercury-free UV-LED into RAS and a better understanding of UVA-LED/PMS disinfection process. 1. Introduction Growing demand for food with increasing world population drove technology innovation in food production [1]. Aquaculture, an emer- ging major food-production sector globally, accounted for over 50 % of the total fish supply for food [2]. Increasingly more stringent regula- tions on aquaculture wastewater discharge and fewer suitable aqua- culture lands, had led to the development of recirculating aquaculture systems (RAS) as a sustainable alternative to conventional aquaculture systems [3]. RAS possessed many advantages such as decreased en- vironmental impacts, low water consumption, high fish yield and re- duced land use, providing a controlled environment for fish growth [4]. In practice, high fish stocking density and feeding rate were main- tained in RAS, which led to the high loads of organic and inorganic compounds (e.g. fish metabolic wastes) accumulation that potentially created a favorable environment for the growth of opportunistic pa- thogenic microorganisms [5–7]. To tackle this issue, ultraviolet (UV) irradiation or ozone was adopted as a disinfection method to prevent the introduction and accumulation of fish pathogens in RAS [8]. Ozone was a strong reactive oxidant and had been proven useful in bacteria inactivation and disease control in RAS [9–11]. However, ozone dis- infection byproducts formation, ozone dosing and toxicity of residual ozone to fish limited its wide use in RAS [5,12]. So far, UV irradiation had been reported to be effective in bacteriological control and left no toxic residuals in treated water [8,13]. In China, UV irradiation units were more commonly installed for water disinfection in RAS [14,15]. Generally, UV irradiation was divided into three spectral bands: UVA (400-315 nm), UVB(315-280 nm) and UVC(280-100 nm) [16]. Due to the DNA-damaging effect of UVC, the low-pressure (LP) mercury-vapor lamp (monochromatic emission at a wavelength of 253.7 nm) was frequently used in RAS [8]. China as one of 128 coun- tries had signed the Minamata Convention on Mercury, which came into force on 16 August 2017, aimed at reducing mercury use in pro- ducts and processes by 2020 [17]. Under this circumstance, there was an urgent need for mercury-free UV source in RAS. The newly emerging UV LEDs might be an alternative option in RAS. UV-LED had several unique advantages such as no mercury, no warm up time, design flex- ibility due to small size, emission at specific wavelength, low energy https://doi.org/10.1016/j.jwpe.2020.101362 Received 10 January 2020; Received in revised form 5 May 2020; Accepted 8 May 2020 ⁎ Corresponding author. E-mail address: zhusm@zju.edu.cn (S. Zhu). Journal of Water Process Engineering 36 (2020) 101362 Available online 10 June 2020 2214-7144/ © 2020 Elsevier Ltd. All rights reserved. T