Advanced Oxidation Processes and Non-Thermal Plasma for the Removal of Emerging Contaminants in Water

Tizaoui, C. and Ni Y.
College of Engineering, Bay Campus, Swansea University, UK



The occurrence of emerging contaminants (ECs) commonly known as micropollutants or trace contaminants into the aquatic environment has become an important issue due to the negative effects that these substances cause to aquatic species and humans. Examples of ECs include steroid hormones, pharmaceutical and personal care products, pesticides and surfactants. Conventional wastewater treatment plants were not designed to specifically remove ECs, which makes them a major source of these substances in the environment. New treatment technologies are therefore required to address this emerging problem. This paper discusses the application of two novel oxidation techniques for the removal of estrogenic contaminants in water. An ozone-based process termed as liquid/liquid-ozone (LLO) used a solvent that was initially charged with ozone before being reacted with the wastewater. After reaction, the solvent was separated from the wastewater and recycled back for further ozone loading. Non-thermal plasma (NTP) used high electrical voltage to generate a cocktail of reactive species that efficiently degraded the contaminants. Both techniques have been found effective to degrade potent estrogenic hormones (Estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2)). Particularly the LLO process has shown significant cost savings as compared to conventional gas/liquid ozone processes.


Emerging contaminants, estrogens, liquid-liquid extraction, non-thermal plasma, oxidation, ozone.


The widespread occurrence in water bodies of micropollutants, also termed as emerging contaminants (ECs), has triggered over the past years increased concerns regarding exposure of human and aquatic species to these substances (Luo et al. 2014; Klatte et al. 2017; Tijani et al. 2013). This is because exposure to ECs, despite being found at low concentrations, resulted in effects such as disruption of the endocrine system, reduction in sperm count in males (Swan et al. 1997; Uzumcu et al. 2004), intersex in fish (Harries et al. 1997; Jobling et al. 2009), cancers (Bergman et al. 2013) and proliferation of antimicrobial resistance genes (Malik et al. 2015; Guardabassi et al. 1998). ECs exist in water bodies at very low concentrations ranging from sub-ng/L to few mg/L and cover a vast and expanding list of anthropogenic and natural substances (e.g. steroid hormones, pharmaceuticals and personal care products, pesticides, plasticizers, and many other substances). Because of their extremely potent effects, the natural and synthetic steroidal estrogens, are of major concerns. They originate principally from human excretion, are ubiquitously spread in almost all waters, and they can cause upon exposure to them effects such as disruption of the endocrine system. Although the topic of micropollutants occurrence in the environment has been raised as an issue as early as the 1950s (Fisher et al. 1952), only recently that it has gained significant interest from the scientific community, water industry, regulatory bodies and the media. This is largely due to the recent advancement in analytical instrumentation which provided the tools necessary to accurately measure and identify these substances, commonly found at extremely low concentrations. The main source of ECs in the aquatic environment is effluent discharge from wastewater treatment plants (WWTPs). This is because conventional WWTPs were designed to reduce mainly the parameters BOD and suspended solids rather than to remove specific substances such as ECs. Development of new technologies to efficiently and economically remove MPs from wastewater is hence very important to the wastewater industry since regulations aimed at controlling the discharge of selected ECs have started to emerge (Audenaert et al. 2014; Carvalho et al. 2015). This paper will discuss two novel technologies used to remove potent estrogenic hormones including Estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in water. The first of the two technologies was liquid/liquid-ozone (LLO) process which used a solvent that is immiscible in water and has high capacity for ozone absorption to extract and degrade the estrogens. The solvent was recycled in the process so it was recharged with ozone and used again. A second process used non-thermal plasma (NTP) to generate a cocktail of reactive species that efficiently degraded the contaminants. NTP was produced by applying high voltage between two electrodes.

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