Interactions between Nitrification, Biofilms, and Engineered Responses in Drinking Water Distribution Systems
Authors:   , Bradley Tyler Christopher , Sales Christopher 
Published: January 2024

Providing safe drinking water is the core mission of drinking water providers and requires balancing numerous potential challenges to accomplish this mission successfully. A key challenge in maintaining high quality drinking water in chloraminated water systems is nitrification. Nitrification is a biochemical process where bacteria in the water and biofilms of a system, primarily ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), oxidize ammonia to nitrite and then further to nitrate. In chloraminated drinking water systems, nitrification is a detrimental process that can cause rapid loss of disinfectant residual and potentially result in increased bacterial regrowth and regulatory violations. The goal of this dissertation is to increase understanding and improve the effectiveness of water systems' responses to nitrification events. One of the most important elements in effectively managing nitrification in a drinking water system is how quickly the water system recognizes that nitrification is on-going and can respond. To that end, a novel data-driven method is proposed for developing site-specific action levels for total chlorine within a drinking water system. This method utilizes historical total chlorine data, which is readily available for all chloraminated systems, to isolate the "falling limb" of the curve and then calculate action levels based on only this portion of the total chlorine trend. Isolating the falling limb of the curve allows the action levels to be based solely on the portion of the curve where nitrification is beginning and proliferating. In this research, we demonstrate that this method helps provide action levels that can alert water systems to the initial start of nitrification and to the onset of severe nitrification more effectively than previously proposed methods. While nitrification effects the chemistry of the bulk water in drinking water systems, the process is largely taking place and being seeded by the biofilms that grow within these systems. One of the challenges of studying biofilms within drinking water systems is that most coupon designs don't simulate the position and curvature of a pipe wall. In this dissertation, we utilize two *in-situ* biofilm samplers, one installed directly into the main in the street and the other installed into the building plumbing of a dedicated sampling shed within the Philadelphia Water Department's system. Using these biofilm samplers, the spatiotemporal heterogeneity was assessed within a single sampler, between samplers small distances apart (in the street vs in an adjacent building), and in different buildings within the same service area. This research demonstrates that there are significant differences between biofilms that grow in different samplers and in different buildings, but there are minimal differences between biofilm samples that are collected from within a single sampler. This research acts as a springboard for the use of the samplers for testing of varying conditions to assess the impacts of a controlled variable without the concern of any differences potentially being caused by natural variation within the samplers. A common mitigation strategy for nitrification within a water system is the use of conventional flushing, specifically point flushing and continuous flushing. Using the biofilm samplers, the impacts of these two flushing techniques on the biofilms that seed the nitrification process was assessed. Results show that neither of these flushing methods resulted in significant changes in the biofilm's microbial community. Furthermore, this research confirms that the use of these conventional flushing methods should be used primarily as an early response to nitrification rather than as a method to address severe nitrification.