Nitrification in premise plumbing systems

Abstract

Monochloramine is increasingly used instead of free chlorine as a secondary disinfectant. Ammonia is introduced into water for monochloramine formation or by decay. Nitrification can have deleterious effects on water quality that may lead to regulatory violations. In this project water quality and influence of pipe material on the onset of nitrification and consequences of nitrification in premise plumbing were investigated. Also potential control strategies for nitrification were evaluated. Initially two types of copper coupons (new and old, i.e., pre-exposed to 0.1N NaOH solution) were used with water of two different carbon (2~4ppm) and ammonianitrogen (0.36~0.71ppm) concentrations. In the next experiment, pre-aged copper and PVC coupons were used with high carbon (4 ppm) and two ammonia concentrations (0.36 and 0.71 ppm). When all reactors showed complete signs of nitrification the ammonia concentration in low ammonia (0.36 ppm) feed reactors were raised to the high level (0.71 ppm). The PVC reactors were quicker in adjusting to this change. Next, the effect of copper ion, chlorite and chloramine on nitrifying simulated household plumbing systems was investigated. No significant effect of copper on nitrification was observed. Chlorite was not effective on the PVC system but inhibited the copper system at 20 ppm. Nitrification activity was also impacted significantly at a 5:1 ratio of chlorine to ammonia and ultimately stopped. To investigate the effect of nutrient conditions on metal release in a nitrifying system and the consequences of change in microbial population, influent humic and ammonia concentrations of two reactors of each set were raised to 8 ppm and 2.13 ppm respectively. Higher ammonia increased only the autotrophs while higher TOC increased only the heterotrophs. For all reactors alkalinity and pH decreased due to nitrification, with lesser effect on copper reactors. Increased TOC or nitrogen increased the copper concentration in the water. The microbial population was analyzed by PCR and DGGE. The biofilm community composition is influenced by nutrient condition and pipe material and environmental stress (chlorite or monochloramine). The presence of copper in the PVC reactor did not cause any impact on community composition.