Microbial Quality of Gray Water for Reuse

Abstract

As the scarcity of water and the price of municipal water inevitably increase, gray water reuse may become an inexpensive and viable alternative for such purposes as irrigation, lawn maintenance and water closet flushing. However, some problems do exist. The microbial and chemical content of gray water includes agents that may present public health problems. The purpose of this study was to determine the general microbial composition of gray water using standard plate counts and selective media at specific sites (shower/bath, wash cycle and rinse cycle of a clothes washing machine) and the general chemical and physical properties of gray water at these same sites (phosphate, ammonia, chloride, pH, TDS and turbidity). Samples were taken from a diverse group of families with and without children (1 ½ - 9 years). Standard plate count bacteria ranged from 10⁵ to 10¹⁰ colony forming units (CFU)₄/100 ml. Shower and bath water contained an average of 10⁴ to 10⁶ CFU/100 ml of coliforms. Failies with children produced wash cycle gray water containing 10⁶ CFU /100 ml of fecal coliforms. Ammonia concentrations varied proportionally with bacterial concentrations while phosphate varied inversely with bacterial growth. Bacterial numbers increased one order of magnitude during storage of gray water.