Optimization of the pulsed electric field decontamination method in continous flow

Abstract

Summary form only given. Wastewater from hospitals carries large number of pathogenic and increasingly antibiotic resistant bacteria, which could spread in the environment. The pulsed electric field (PEF) treatment of wastewater as a non-chemical disinfection method is a suitable alternative method for reducing this bacterial freight. In the literature it was figured out, that continuous flow PEF treatment reduces more effectively bacterial contamination than batch reactor treatment. One explanation is that the heat generated during the PEF treatment in a continuous flow reactor is positively affecting the bacterial reduction. Depending on the PEF treatment energy, outlet temperatures of more than 70degC were achieved. Consequently, bacterial reduction depends on the initial wastewater temperature and on the electrical dissipated treatment energy. In our study we analysed the bacterial reduction depending on temperature. Filtered wastewater samples (from a wastewater purification plant) were inoculated with the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Enterococcus</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">faecium</i> (BRE; Strain 211, Mainz) and exposed to different PEF treatments at 40, 50 and 60degC. The lethal treatment temperature of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Enterococcus</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">faecium</i> by heat treatment over 3-4 min is around 56degC. Treatment with 60degC for the same duration provokes a bacterial reduction of 4 log. Simultaneous treatments of inoculated wastewater samples with PEF and heating (40, 50 and 60degC) reduced the bacterial contamination over the expected effect, calculated as a sum of effects induced from both treatments. This is an indication for a synergistic effect induced through the simultaneous treatment with PEF and heat. In all experiments the specific energy was kept constant by adjusting the number of pulses. At 2degC, the bacterial reduction saturates already for PEF treatments with specific energies higher than 120 J/ml. At higher temperatures (over 40degC), the bacterial reduction increased until the complete reduction (over 8 log) was achieved at 60degC. To separate the thermal effect from the PEF effect, samples were treated first with PEF in a batch chamber and afterwards, about 30 s later, by heating over 4 min. No significant variation of the efficiency of bacterial reduction compared to the simultaneous treatment was found. These results show that the duration of cell membrane damage, is far longer as the assumed healing time (mus-range). This finding can be used for further optimization of the PEF treatment in continuous flow.