Evaluating the Performance of a Lab-Scale Water Treatment Plant Using Non-Thermal Plasma Technology

Stefan Schönekerl,Astrid Weigert,Karsten Backhaus,Christel Pfefferkorn,Katharina Wellner,Richard Pörschke,Stephan Uhlig,André Lerch

doi:10.3390/w12071956

Abstract

In this study, a lab-scale plant was designed to treat water in continuous flow condition using non-thermal plasma technology. The core was an electrode system with connected high-voltage (HV) pulse generator. Its potentials and limitations were investigated in different experimental series with regard to the high-voltage settings, additions of oxygen-based species, different volume flow rates, and various physical-chemical properties of the process water such as conductivity, pH value, and temperature. Indigo carmine, para-Chlorobenzoic acid, and phenol were chosen as reference substances. The best HV settings was found for the voltage amplitude Û = 30 kV, the pulse repetition rate f = 0.4–0.6 kHz, and the pulse duration tb = 500 ns with an energy yield for 50% degradation G50, which is of 41.8 g∙kWh−1 for indigo carmine, 0.32 g∙kWh−1 for para-Chlorobenzoic acid, and 1.04 g∙kWh−1 for phenol. By adding 1 × 10−3 mol∙L−1 of oxygen, a 50% increase in degradation was achieved for para-Chlorobenzoic acid. Conductivity is the key parameter for degradation efficiency with a negative exponential dependence. The most important species for degradation are hydroxyl radicals (c ≈ 1.4 × 10−8 mol∙L−1) and solvated electrons (c ≈ 1.4 × 10−8 mol∙L−1). The results show that the technology could be upgraded from the small-scale experiments described in the literature to a pilot plant level and has the potential to be used on a large scale for different applications.

Highlights

In research and application, various approaches for the elimination of persistent substances in polluted water, such as biological, chemical and physical based or combined techniques were discussed
The O2 addition even resulted in an increase of more than 50% in the degradation of para-Chlorobenzoic compared to the results under identical HV conditions without O2 addition (Figure 7a)
The O2 addition even resulted in an increase of more than 50% in the degradation of para-Chlorobenzoic acid (Figure 7b)

Summary

Introduction

Various approaches for the elimination of persistent substances in polluted water, such as biological, chemical and physical based or combined techniques were discussed. Over the past few years, the investigation on advanced oxidation processes (AOP) as a physical-chemical method has increased considerably. Water treatment using non-thermal plasma (NTP) technology is a relatively new technology within various types of AOP. In related experimental set-ups, strongly oxidizing agents are produced within non-thermal plasma in ambient atmospheric pressure and brings them into contact with the water to be processed quasi simultaneously. A strong short-existing electric field is generated by high-voltage (HV) pulses with high repetition rates between HV electrode(s) and ground electrode(s) in the presence of dielectric(s). Electrons are accelerated due to the short-pulsed energy supply to the space located in the gap between

Objectives

Methods

Conclusion