| Disinfection has historically been done using chlorine. However, in recent years, it has been determined that use of chlorine is detrimental to the ecosystem because, the chlorinated effluent contains carcinogens, the residual chlorine is toxic to organisms in the receiving waters, and the chlorine is acutely hazardous to plant operators. Ultraviolet light (UV) is a disinfection system which does not have these problems and is now seriously considered to disinfect drinking water and treated sewage. At the start of this study, UV had not been used in Hawaii to disinfect waters. The goal of this study was to evaluate different UV systems designed to disinfect different types of waters. The UV disinfection systems were evaluated based on the UV systems ability to disinfect multiple indicator microorganisms which were selected to represent waterborne pathogens from different genera, and are structurally diverse. The indicator microorganisms used for this study includes: total heterotrophic bacteria, fecal coliform, E. coli, enterococci, C. perfringens, hydrogen sulfide bacteria, Bacillus spp., F RNA bacteriophages. The two sources of water evaluated in this study were cistern water (rainwater collected for household use) and treated sewage. Four UV systems evaluated in this study were: (1) two commercially available electrically powered UV system, (2) an experimental solar powered UV system, (3) a pilot, and (4) two full-scale UV systems manufactured by Trojan Technologies Inc., to disinfect treated sewage water.;The results of field testing the electrically powered and pilot solar powered UV disinfection systems showed that these systems are capable of disinfecting clear cistern water to microbiological levels suitable for drinking. The electrically powered UV system is suitable for individual homes in developed countries while the solar powered UV system is suitable for remote areas without electricity. The results of this study also showed that testing water for H;The pilot UV system which used a single bank of UV lamps was effective in inactivating the six different microbial indicators naturally present in secondary treated sewage effluent even when the lamps were never cleaned for seven weeks. The susceptibility ranking of microbial indicators to the plant chorination system and UV system was similar (E. coli ;In summary, the concept of multiple microbial indicator system, for disinfection system evaluation, provides useful information for comparison and prediction of health risks associated with the use of disinfected waters. |
