Abstract
Persistent pharmaceutical pollutants (PPPs) have been identified as potential endocrine disruptors that mimic growth hormones when consumed at nanogram per litre to microgram per litre concentrations. Their occurrence in potable water remains a great threat to human health. Different conventional technologies developed for their removal from wastewater have failed to achieve complete mineralisation. Advanced oxidation technologies such as dielectric barrier discharges (DBDs) based on free radical mechanisms have been identified to completely decompose PPPs. Due to the existence of pharmaceuticals as mixtures in wastewater and the recalcitrance of their degradation intermediate by-products, no single advanced oxidation technology has been able to eliminate pharmaceutical xenobiotics. This review paper provides an update on the sources, occurrence, and types of pharmaceuticals in wastewater by emphasising different DBD configurations previously and currently utilised for pharmaceuticals degradation under different experimental conditions. The performance of the DBD geometries was evaluated considering various factors including treatment time, initial concentration, half-life time, degradation efficiency and the energy yield (G50) required to degrade half of the pollutant concentration. The review showed that the efficacy of the DBD systems on the removal of pharmaceutical compounds depends not only on these parameters but also on the nature/type of the pollutant.
Highlights
The availability of clean water is fundamental to the socio-economic development and maintenance of human health
Jones et al [71] and Sirés and Brillas [114] reported that the recalcitrant behaviour of pharmaceuticals in water is because after biodegradation, deconjugation, sorption, and photodegradation processes, up to 90% of pharmaceutical residues consisting of unmetabolised and metabolized bio recalcitrant fragments were still present in final effluents of water and wastewater treatment plants (WWTPs)
Non-thermal plasma based on dielectric barrier discharges (DBDs) usually referred to as silent discharges have emerged as novel remediation technologies and have been employed for various applications including ozone generation, control of gaseous toxins, and the demolition of carcinogenic compounds [153,154]
Summary
The availability of clean water is fundamental to the socio-economic development and maintenance of human health. To comply with stringent environmental regulatory frameworks and to reduce the pressure on existing limited clean water, alternative treatment techniques based on advanced oxidation processes (AOPs) need to be developed [10,25] These AOPs are viable technologies capable of decomposing biologically recalcitrant and persistent organic pollutants present in wastewater [26,27], accomplished using hydroxyl radicals as primary non-selective oxidants [28]. Non-thermal electrical discharge systems have been found very effective due to the generation of different molecular and ionic free reactive species, UV radiation, and shock waves at ambient conditions without chemical additives [43] The combination of these species forms a mixture of potent oxidants in the bulk solution that mineralises water pollutants in a short period [44,45,46,47]. This review highlights the abundance of various classes of pharmaceuticals in water sources and focuses on their removal by different DBD systems and configurations
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