CONTROLLING DISINFECTION BY-PRODUCT FORMATION WITH GAC ADSORPTION AND POTENTIAL ROLE FOR UV-LEDS WITH CHLORINE

Abstract

The J. Douglas Kline Water Supply Plant (JDKWSP) is one of the main drinking water facilities in Halifax, Nova Scotia. The treatment process of JDKWSP is characterized by direct anthracite-sand filtration and chlorine disinfection. Natural organic matter (NOM) as one of the components impacting water quality has increased in Pockwock Lake, the water source of JDKWSP. Increasing NOM has required higher alum doses and higher chlorine demand, which shortens filtration efficiency and tends to produce more disinfection by-products (DBPs) in drinking water. The Centre for Water Resources Studies (CWRS) operates a pilot plant at JDKWSP for optimizing the treatment processes, where sedimentation was added followed by three parallel filters, the first being anthracite sand to mimic the full-scale facility. This study looked at using Granular Activated Carbon (GAC) applied in two of the pilot-scale filters for increasing the NOM removal rate and minimizing DBP formation. Specifically, the full-scale filtered water and pilot-scale filtered waters that were filtered by these three filters were analyzed for exploring the effect of sedimentation and GAC adsorption on NOM removal and DBP formation.

Ultraviolet light emitting diode (UV LED) disinfection was also investigated as a potential full-scale disinfection technology and was compared to current plant conditions using chlorine. DBP formation potential of THMs and HAAs was measured for UV exposed, chlorine exposed, and UV + chlorine exposed to understand the impact that UV disinfection has on mitigating DBP formation. UV Fluences of 20, 40, and 80 mJ /cm2 were used to characterize the optimal conditions for the Pockwock Lake water matrix.

This study identified that GAC filters were able to remove DBP precursor material and reduce DBP formation. Sedimentation did not help to remove NOM and lower DBP formation potential, but it can improve filtration efficiency and increase filter run times. Additionally, the UV fluences and the sequence of UV LED and chlorine did not significantly impact the formation of trihalomethanes (THMs) and haloacetic acids (HAAs).