Mitigation of Emerging Contaminants in Treated Wastewater Using Non-thermal Air Plasma

Conventional water treatment processes often fail to effectively remove Chemicals of Emerging Concern (CECs), resulting in their continuous discharge to receiving waters and driving the need for advanced tertiary or quaternary treatment strategies. This study investigates cold atmospheric pressure air plasma in a falling film reactor as a potential treatment approach for the mitigation of CECs in treated wastewater effluents. The removal efficacy of thirteen structurally diverse CECs was evaluated under different plasma generation conditions and solution matrices, including ultrapure water and treated municipal wastewater. Characterisation of plasma-generated reactive species in both the gas and liquid phases revealed the formation of O 3 , N 2 O and NO 2 in the gas phase, leading to the production of OH, H 2 O 2 , NO 2 - and NO 3 - in the treated solution. The concentrations of these species varied significantly with plasma power and water matrix composition, directly influencing pollutant removal performance. Targeted LC-MS/MS analysis demonstrated >90% removal of erythromycin and diclofenac in both matrices, whereas caffeine (35–48%) and triclocarban (47–65%) were the most recalcitrant compounds under the conditions examined. Removal of the remaining compounds was strongly dependent on the water matrix and discharge power, with many compounds exhibiting substantially higher removal in the wastewater matrix. Evaluation of removal energy efficiency for selected compounds yielded G 50 values of up to 1.60 g/kWh for triclosan, 0.60 g/kWh for bisphenol AF, 0.44 g/kWh for carbamazepine and 0.31 g/kWh for diclofenac across the investigated matrices, indicating that the process compares favourably with several established advanced oxidation technologies.