| Abstract | With increasing of water demand while fresh water resource is decreasing, concept of greywater reuse has been introduced in many counties. One issue needed to be addressed is that people may be infected by bacteria contaminated in greywater. The aim of this study would provide information of potential health risk to people at household level who would like to reuse greywater. Integrated Pathogen Flow Analysis (PFA) and Quantitative Microbial Risk Assessment (QMRA) model was used as a tool to quantify yearly risk in various mitigation scenarios. E.coli and Salmonella spp. were examined in separated greywater streams including: bathroom, laundry, and kitchen of two selected households in Pathumthani province, Thailand. The geometric mean concentration of E. coli were found 2.38E+04, 1.28E+04, and 1.71E+08 MPN/100 mL in bathroom, laundry and kitchen greywater, respectively, while Salmonella spp. was found 7.27E+01 MPN/100 mL in only greywater from kitchen. Highly E. coli concentration in kitchen greywater may result from food waste contamination. In addition, among greywater sources, pollution was mainly contributed from kitchen due to high concentration. The logarithm concentration of E. coli in all greywater streams was fit to logistic probability density function. However, Salmonella spp. was not fit to any PDF because the positive sample was found less than 30 samples. For bathroom and laundry streams, yearly infection risk of E.coli during irrigation and toilet flushed was estimated in range of less than 1 to 46 infections per 10,000 populations and 97 to 678 infections per 10,000 populations for reuse of treated and untreated greywater respectively. Moreover, in case people eat raw vegetable which irrigated by untreated greywater, they would posed mean infection in range 296 to 3,670 infections per 10,000 populations while it was determined to be less than 1 infection per 10,000 populations for vegetable irrigated by treated greywater. For kitchen greywater, people would be posed to infection risk from E. coli infection in range of 300-8,300 infections per 10,000 populations for all scenarios and Salmonella spp. in range 1 to 640 infections per 10,000 populations. It was clearly that prior to reuse greywater, it should be treated with disinfection relevant to reuse purpose. In order to minimize yearly infection risk of E. coli in bathroom and laundry greywater, the reductions of 1.8, 2.4, and 3.4 logs were needed for raw vegetable consumption, toilet flushed, and garden irrigation respectively. While for kitchen greywater need higher treatment performance than other two sources. In addition, reduce Salmonella spp. probability risk infection to an acceptable level; any disinfection system at 2.9 logs reduction should be installed. |