Evaluation of Ozonated Water for Sanitizing Recycled Greenhouse Irrigation Water

A cooperative agreement between Colorado State University and USDA-APHIS-PPQ-CPHST lab was funded in 2014 to test the ability of ozonated water to sanitize recycled irrigation water in greenhouses.   A custom built ozone generator supplied the ozonated water for the study.  A private microbiology lab prepared and analyzed the Bacillus subtilis spore samples used as the hard-to-kill surrogate for bio-contaminated water.  The study involved three factors: 1) two B. subtilis spore types (normal and super dormant spore samples), five ozonated water concentrations (0, 10, 15, 20 and 25 ppm), and three exposure times (5, 10, and 15 min.). Ozonated water was generated then added to the spore suspensions for each of the 30 treatments.  The Oxidation Reduction Potential (ORP) ranged from 511 to 980 mv for the four ozonated water concentrations. The percent spore inactivation ranged from 87 to 99.9%, across the 30 treatment combinations.  Increasing the ozonated water ORP and/or the exposure time increased spore efficacy.  Further increases in spore efficacy may be achieved by extending the exposure time, or using repeated ozonated water applications.