Evaluating the performance of a lab-scale water treatment plant using non-thermal plasma technology

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 U = 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.