Establishing the lower thresholds for water sterilisation with shock waves and hot gas bubbles from the detonation of explosives in water

Water sterilisation requires the inactivation of waterborne pathogens, like E.coli, to such low levels that its use will not cause illness. Here, we examine a potential methodology for disinfecting water through the combined effect of hot expanding gases and shock waves from underwater explosions. Water pathogens located within the proximity of the explosive charge will be exposed to two different sterilisation conditions: firstly, the high-pressure shock wave moving within the fluid, and secondly, the expanding hot N₂, O_2, and CO₂ bubbles that are products of the explosion. To simulate the first case, we used a flyer-plate technique to understand the lower threshold for inactivation. We did this with a novel capsule design in a single-stage light gas-gun and observed 0.813 Logs of E.coli inactivation after subjecting an entire bacterial broth to a minimum pressure of 3.53 GPa thereby indicating a lower threshold for shock pressure-induced inactivation. For the second case, we show that hot gas bubbles from different explosive gaseous products at 150°C in a bubble column established the minimum gas temperature thresholds required to successfully inactivate E.coli. This work shows that any benefit of using explosives to sterilise water will principally come from the release of hot gaseous bubbles rather than the effect of the shock. This new approach could be used in conflict areas or remote locations with no access to standard sterilisation technologies or power.