REPOSITORY > RESULTS

Abstract

Water scarcity is becoming a greater issue worldwide due to ever-increasing anthropogenic activity. A dedicated effort is required to recover and maintain the purity of our water resources and has created an environment for developing better technologies to tackle this issue. Low-pressure gaseous plasma, consisting of a complex mixture of reactive particles, ions, and neutrals and emitting powerful radiation, is a versatile, environmentally friendly tool, serving many purposes in various industries. Among other features, it can also produce intense vacuum ultraviolet (V-UV) radiation, serving as a potential sterilisation technique since the photons have enough energy to disrupt molecular bonds, causing the degradation of pollutants. The issue, however, is that V-UV is strongly absorbed by almost all substances, most notably the oxygen molecules in the atmosphere. Therefore, its application to treat any material should entail a unique system where the V-UV is actually allowed to interact with the desired substance.
The main objective of this study was to construct a low-pressure plasma system as a source of V-UV radiation and evaluate its potential to treat liquid samples for the purpose of disinfection. Bacteriophage MS2 served as a model contaminant for studying disinfection efficiency since viruses are difficult to remove from contaminated water.
The literature review revealed that this kind of water treatment has never been attempted in the past. We initiated our research by constructing a pulsed DC plasma system and carried out systematic characterization of operating parameters for producing V-UV radiation. A special sample chamber was constructed to treat liquid samples with low-pressure plasma radiation, physically separating the different pressure environments while still allowing the V-UV radiation to reach the sample. Through a series of different experimental setups and conditions, hydroxyl radicals (OH●) were shown to be the primary inactivation factors, and the presence of O2 in the headspace of the sample greatly improved the inactivation efficiency due to the additional production of ROS (OH●, H2O2, O3).
Seeking additional information and improvement on the system, a radiofrequency inductively coupled low-pressure plasma system (RF ICP) was constructed and used for the same purpose. Similar conclusions were reached, namely that OH● is the primary factor for virus inactivation, whose production is significantly enhanced by more intense V-UV radiation, along with O2 being present in the headspace. Additionally, we subjected MS2 bacteriophage to V-UV treated water separately, whose poor inactivation demonstrated that short-lived ROS are primarily responsible for the observed inactivation. Expanding further, we utilised the RF ICP to treat other types of water pollutants, such as bacteria, antibiotics, and dyes, to showcase the method’s general applicability towards all types of contamination.
To conclude our work, we made some calculations and compared the energy efficiency of our system against standard disinfection methods, which provided some promising prospects for this technique.