High voltage water treatment in recirculating systems

Water recirculation systems may require disinfection to reduce levels of bacteria that grow in the system. The levels often need to be maintained below maximum values specified by local or National government standards. Residual chemical disinfection methods are usually used to achieve this. An alternative method is to apply a high voltage to the water to reduce levels of bacteria in the recirculation stream. A theoretical model for the bacterial levels using this technique is presented. The model shows that a treatment device need not be highly effective in reducing bacteria levels in one pass. A lysing rate of 99% works as well as one of 100%. The most efficient system is one with a high recirculation flow rate rather than a high individual lysing rate. These ideas are validated by experimental testing on the bacteria E. coli using a point-of-use treatment device energised by a switch-mode power supply (SMPS). Levels of these bacteria in a closed-loop system were reduced by nearly 5 log within 15-20 min of operation. Also, the effectiveness of high voltage on the viability of Legionella was tested using a 50 Hz AC supply. In this case the high voltage exposure reduced the viability by 99.7%. Hence this high voltage treatment method may have applications in air conditioning systems.