Presentation Summary
UV AOP performance is strongly influenced by water matrix kinetics, ammonia, and hydraulic conditions. This presentation examined limitations of conventional CCP control and demonstrated adaptive, algorithm‑based strategies that account for chloramine formation and HRT variability, reducing instrumentation reliance, energy use, shutdown risk, and improving robustness and regulatory compliance overall operation.
Presentation Overview
UV advanced oxidation (UV AOP) has become an essential component of advanced wastewater treatment and there continues to be discussions on how these systems are maintained and operated. Multiple UV AOP control strategies are currently employed in California, including fixed critical control point (CCP) approaches, combined UV dose–oxidant dose product methods, and strategies with flexible dose methods that instead target log removal of specific micropollutants. Subtle variations in water parameters can significantly and unexpectedly hinder treatment performance with any control philosophy but with a clearer understanding of the water matrix kinetics, operation with flexible dose targets can simplify UV AOP operation and make it more robust.
Ammonia (NH₃) is an example of a parameter that impacts UV AOP operation. It promotes monochloramine (NH2Cl) formation that reduces UV transmittance (UVT) and competes with target contaminants for the free radicals generated during UV AOP. This “radical scavenging” behavior cannot be directly monitored and may fluctuate even in high‑purity reverse osmosis (RO) permeate, necessitating dynamic adjustment of UV and oxidant dose targets. For instance, an unforeseen 0.5 ppm increase in NH concentration due to unexpected upstream RO breakthrough can increase the amount of sodium hypochlorite needed to achieve desired free chlorine levels by 100%. Further, UV intensity and power costs can also double to achieve UV dose targets at the lower UVT brought on by NHCl formation. Traditional CCP‑based control schemes often plan for these events by implementing fixed ammonia setpoints, which when exceeded can result in total plant shutdown. A more adaptive approach that is reviewed in this presentation—incorporating ammonia’s influence directly into algorithmic control logic—represents a more resilient strategy for stable operation.
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The hydraulic retention time (HRT) between when oxidants are injected and the UV bulbs also plays a critical role. As flow through a UV AOP system varies, the HRT changes correspondingly, affecting the extent of reactions upstream of the UV, including but not limited to the conversion of NH2Cl to dichloramine (NHCl2). Online instruments are often used in CCP-based controls to monitor these kinetic reactions but are challenging and time consuming to maintain and calibrate. Further, maintaining a HRT of the treated flow that is consistent with the HRT to the instrumentation is very difficult as flow demands change. An alternative can be a control philosophy that mathematically accounts for upstream reaction kinetics and since less instrumentation is needed, deliver a more rapid treatment response.
Effective UV AOP operation demands a detailed understanding of water matrix effects that subtly but significantly alter treatment performance. Variability in ammonia concentrations and oxidant‑water kinetics can increase dose requirements, disrupt control schemes, and reduce treatment efficiency. Incorporating these dynamics into adaptive control strategies enhances system resilience, minimizes unnecessary shutdowns, and supports consistent regulatory compliance while enabling operators to optimize performance across changing hydraulic and water quality conditions.
Learning Outcomes
Learners gained a practical understanding of how water matrix kinetics influence UV AOP performance and control reliability. The presentation equipped participants to compare common UV AOP control strategies and recognize their limitations under variable water quality and hydraulic conditions. Attendees learned how ammonia, chloramine formation, UV transmittance, and hydraulic retention time interact to drive oxidant demand, energy use, and system stability. By the end of the session, learners were able to apply adaptive, algorithm‑based control concepts that reduce reliance on complex instrumentation, minimize shutdown risk, and improve operational resilience and regulatory compliance in advanced treatment systems.
UV Solutions
To address water supply and quality challenges, many providers are turning to advanced water treatment processes to enable wastewater reuse and drinking water remediation. TrojanUV systems support these efforts by treating water to stringent standards, using UV advanced oxidation to break down specific contaminants like 1,4-dioxane and NDMA, ensuring the water is high-quality and useable.
