A Microfluidic Atmospheric-Pressure Plasma Reactor for Water Treatment

Laila Patinglag,Louise M Melling,David Sawtell,Alex Iles,Kirsty J Shaw

doi:10.1007/s11090-019-09970-z

Abstract

A dielectric barrier discharge microfluidic plasma reactor, operated at atmospheric pressure, was studied for its potential to treat organic contaminants in water. Microfluidic technology represents a compelling approach for plasma-based water treatment due to inherent characteristics such as a large surface-area-to-volume ratio and flow control, in inexpensive and portable devices. The microfluidic device in this work incorporated a dielectric barrier discharge generated in a continuous gas flow stream of a two-phase annular flow regime in the microchannels of the device. Methylene blue in solution was used to investigate plasma induced degradation of dissolved organic compounds within the microfluidic device. The relative degradation rates of methylene blue were influenced by the residence time of the sample solution in the discharge zone, type of gas applied, channel depth and flow rate. Increasing the residence time inside the plasma region led to higher levels of degradation. Oxygen was found to be the most effective gas, with the spectra obtained using Liquid Chromatography-Mass Spectroscopy indicating the most significant degradation. By reducing the channel depth from 100 to 50 µm, the best results were obtained, achieving a greater than 97% level of methylene blue degradation. The microfluidic system presented here demonstrates proof-of-concept that plasma technology can be utilised as an advanced oxidation process for water treatment, with the potential to eliminate water treatment consumables such as filters and disinfectants.

Highlights

Conventional water treatment processes, such as filtration or coagulation followed by disinfection, fail to eliminate persistent contaminants from water sources effectively
The present study evaluated a planar microfluidic plasma reactor (MPR) for water treatment, based on the degradation of methylene blue (MB) as a model micropollutant due to its stability and resistance to breakdown by conventional methods [28,29,30]
A filamentary dielectric barrier discharge (DBD) regime was employed using copper electrodes aligned in parallel to the serpentine channel, with the glass of the microfluidic device acting as a dielectric barrier

Summary

Introduction

Conventional water treatment processes, such as filtration or coagulation followed by disinfection, fail to eliminate persistent contaminants from water sources effectively. Innovative continuous flow plasma reactors, such as falling water film reactors and reactors with radial flow, have been applied to increase plasma–liquid interfacial area to improve treatment efficiency [16, 17] In these systems thin films of water flow along the inner walls of a vertical cylindrical electrode and come into contact with plasma. Each device may only process a small volume at a time, larger volumes can be processed by operating multiple devices in parallel [27] For these reasons, the present study evaluated a planar microfluidic plasma reactor (MPR) for water treatment, based on the degradation of methylene blue (MB) as a model micropollutant due to its stability and resistance to breakdown by conventional methods [28,29,30]. The effect of residence time of the solution in the discharge zone, type of gas applied, barrier thickness and channel depth were evaluated

Materials and Methods

Results and Discussion

Evaluation of Degradation Potential

Conclusions