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Application of sunlight-mediated pretreatment for small water treatment systems

Fernando L. Rosario-Ortiz, University of Colorado, Boulder 
Roberto Rodriguez, University of Texas-Health Sciences Center at Houston 

Access to safe and inexpensive water sources is a fundamental need for communities around the world. In the case of rural and/or isolated communities, water treatment systems that make use of natural processes to improve water quality while minimizing chemical and energy inputs could serve as adequate solutions. These natural processes include sunlight-driven reactions that occur in surface waters. These reactions include inactivation of pathogens and also modifications of the chemical matrix which could improve water quality, such as potential decrease in disinfection byproduct formation upon chlorination of distributed water.

It is well known that upon irradiation of natural waters containing dissolved organic matter (DOM), a series of photochemical reactions occur which result in the formation of reactive intermediates (RI, see Fig. 1). These RI include excited state DOM moieties and reactive oxygen species (ROS), including singlet oxygen (1O2) and hydroxyl radical (HO•). The formation of these RI can impact different processes in natural systems, including photomineralization and degradation of organic pollutants (P). These RI can also aid in the inactivation of pathogens. Pathogens overall can be inactivated via both direct sunlight or indirectly by reactions with these RI.

In this project, we have conducted an evaluation of the efficacy of sunlight-driven processes for pathogen inactivation and DBP precursor modification. We have studied different pathogens and surrogates, including E. Coli, adenovirus, and MS2, using water samples collected from sites in Colorado and Puerto Rico. The results so far indicate that sunlight processes can result in up to 6.5 log inactivation for pathogens such as E. Coli, with lower inactivation for others. The differences are the result of the fundamental pathways by which the inactivation occurs. Overall, we have demonstrated that the utilization of retention ponds, where sunlight-driven processes could improve water quality, is an alternative for small systems. The process does not depend on any chemical usage making it a sustainable option. We are now examining more in detail the implementation of this process.