Evaluation of Bacillus subtilis and coliphage MS2 as indicators of advanced water treatment efficiency

Abstract

The assessment of water treatment facilities for their efficiency using alternate indicators is of paramount importance. Current methods for assessing efficiency are limited by the specific characteristics of the microorganisms, such as their different sensitivities to disinfectants. A pilot study was carried out to compare different treatment scenarios for the future upgrade of the Sergio Cuevas Water Treatment plant (the largest in the Caribbean) in San Juan, Puerto Rico. The treatment units under investigation included a coagulation-flocculation-sedimentation unit, dual-media filters, micro-filtration units, intermediate ozone injection and contact columns as well as a biological filtration unit. The plant was challenged at different stages of treatment with Bacillus subtilis spores and MS2 coliphages in an attempt to test them as possible alternate indicators of treatment plant performance. These organisms were chosen because of their resistance to disinfection and desiccation, their low analysis costs and ease of detection. The removal of spores and coliphages by each treatment unit tested was calculated by seeding a known concentration (5-7 log10) of spores and coliphages and following the removal or disinfection rates. The seeded indicators were detected using traditional culture techniques. Ballasted clarification was shown to be highly efficient at removing 99.1% (approximately 3 log10) of the spores and 85.1% (approximately 0.86 log10) of MS2. Ozone treatment inactivated 80.37% (approximately 1.4 log10) spores and 99.95% (approximately 3.07 log10) coliphages. The coliphage inactivation rate obtained confirmed data obtained by previous studies indicating that MS2 was less resistant to ozonation than B subtilis spores. The membrane technology had the best efficiency in terms of physical removal of spores achieving over 99.9% (> 3 log10) removal. Coliphage removal mechanisms remain to be determined and will be a future focus of the study. Preliminary results indicate that aerobic spores and coliphages may be useful as indicators to determine the efficiency of different drinking water treatment technologies.

Bactericidal Effect of Solar Water Disinfection under Real Sunlight Conditions

“…A quantity of spore suspension (200 ml) was poured into sterile 500-ml Erlenmeyer flasks and placed in a water bath at 80°C for 15 min in order to eliminate vegetative cells (10,16). Afterwards they were kept at 4°C for subsequent bottle inoculation.…”

Comparison of the inactivation of Bacillus subtilis spores and MS2 bacteriophage by MIOX, ClorTec and hypochlorite

“…Indicator organisms can be used to assess the effectiveness of different drinking water disinfection technologies (Radziminski et al. 2002; Huertas et al. 2003; Young and Setlow 2003) and to eliminate the need to use pathogens.…”

Physico‐Chemical Processes

“…Rajala et al (2003) studied the removal of microbes from combined rapid sand filter with coagulants and ultraviolet irradiation processes. Huertas et al (2003) carried out experiments to evaluate the efficiency of advanced water treatment in removing indicator organisms Bacillus subtilis and Coliphage MS2. Jia et al (2003) investigated the distribution and variation of microcystins from a water resource to a water plant.…”