Degradation of micropollutants in secondary wastewater effluent using nonthermal plasma-based AOPs: The roles of free radicals and molecular oxidants

Emerging micropollutants (mu Ps) appearing in water bodies endanger aquatic animals, plants, microorganisms and humans. The nonthermal plasma-based advanced oxidation process is a promising technology for eliminating mu Ps in wastewater but still needs further development in view of full-scale industrial application. A novel cascade reactor design which consists of an ozonation chamber preceding a dielectric barrier discharge (DBD) plasma reactor with a falling water film on an activated carbon textile (Zorflex (R)) was used to remove a selection of mu Ps from secondary municipal wastewater effluent. Compare to previous plasma reactor, molecular oxidants degraded micropollutants again in an ozonation chamber in this study, and the utilization of different reactive oxygen species (ROS) was improved. A gas flow rate of 0.4 standard liter per minute (SLM), a water flow rate of 100 mL min(-1), and a discharge power of 25 W are identified as the optimal plasma reactor parameters, and the mu P degradation efficiency and electrical energy per order value (EE/O) are 84-98% and 2.4-5.3 kW/m(3), respectively. The presence of ROS during plasma treatment was determined in view of the mu Ps removal mechanisms. The degradation of diuron (DIU), bisphenol A (BPA) and 2-n-octyl-4-isothiazolin-3-one (OIT) was mainly performed in ozonation chamber, while the degradation of atrazine (ATZ), alachlor (ALA) and primidone (PRD) occurred in entire cascade system. The ROS not only degrade the mu Ps, but also remove nitrite (90.5%), nitrate (69.6%), ammonium (39.6%) and bulk organics (11.4%). This study provides insights and optimal settings for an energy-efficient removal of mu Ps from secondary effluent using both free radicals and molecular oxidants generated by the plasma in view of full-scale application.

Automated summary

A novel cascade reactor design was used to remove micropollutants from secondary municipal wastewater effluent, and the parameters such as gas flow rate, water flow rate, and discharge power greatly influenced the performance of the reactor. The utilization of different reactive oxygen species was improved by introducing an ozonation chamber preceding a dielectric barrier discharge plasma reactor. This study provides valuable insights and optimal settings for an energy-efficient removal of micropollutants from wastewater.