Manipulation of particle microorganism association for improved UV disinfection of surface waters

Abstract

The performance of ultraviolet (UV) disinfection is subject to the quality of water supplied to the reactor, which could often be poor in facilities lacking adequate pre-treatment. Particulate matter in low-quality water can interfere UV disinfection by shielding microorganisms from light through particle-microorganism (p-m) associations. This study investigates Zeta Potential (ZP) manipulation as a pre-treatment to improve UV effectiveness by reducing p-m associations. ZP manipulation is hypothesized to free microorganisms from particulate attachments, increasing their UV vulnerability. Water samples from a drinking water treatment plant applying UV disinfection without pre-filtration were altered for ZP, achieving five different ZP levels. A protocol was developed to distinguish between viable microorganisms attached to particles and free-floating microorganisms. UV experiments were conducted to establish the relationship between UV efficiency and ZP. Results indicated that neutral ZP results in the highest p-m association and lowest disinfection achieved. Disinfection kinetic studies revealed that highly negative ZP enhanced UV efficiency as delivered UV dose increased due to dominant repulsive forces. This study demonstrated that optimizing ZP effectively controlled the degree of p-m association for both viruses and bacteria, which could be a viable approach for mitigating p-m association and leveraged for advancements in UV disinfection.