Winter 2021
Kelly Slabicki
Clean drinking water is a basic human necessity and a daily goal of the City of Wilmington’s water utilities. Wilmington aims to provide safe and aesthetically pleasing drinking water to its 110,000 consumers. The City has two water treatment plants: the Porter Filter Plant and the Brandywine Membrane Plant. Both plants source their water from the Brandywine River, which is one of Delaware’s few surface water sources. Throughout the treatment process, the City uses a coagulant to settle out large organic material before filtration. Chlorine is used as a disinfectant to eliminate microbial life in the water and a chlorine residual is maintained throughout the distribution system. Total organic carbon is a complex assortment of carbon-based organic compounds that are naturally occurring in raw water sources, most specifically in surface water. Organic carbon sources include byproducts from algal blooms, leaf decay, and upstream watershed runoff. While total organic carbon is not harmful to human consumption by itself, the combination of total organic carbon with chlorine disinfection causes disinfection byproducts. Disinfection byproducts are grouped into total trihalomethanes and haloacetic acids and pose potential carcinogenic effects with extended consumption above maximum contaminant levels.
This thesis evaluated the total organic carbon removal success at Porter Filter Plant and Brandywine Membrane Plant over a three-year period between 2017 and 2019. This thesis encompassed multiple storm events and varying seasonal effects. Porter Filter Plant showed more successful total organic carbon removal and had lower raw water total organic carbon than Brandywine Membrane Plant did. This thesis evaluated various water quality parameters as indicators of raw water total organic carbon and found that ultraviolet-254 and turbidity samples could be reliable proxies. Strong seasonal changes were observed with increased total organic carbon, turbidity, and disinfection byproducts in the summer months. During three of twelve sampling events in the thesis, Wilmington exceeded maximum contaminant levels for total trihalomethanes and/or haloacetic acids. Immediate and long-term recommendations were made in this thesis. Operational improvements such as increased analysis can be done. Brandywine Membrane Plant’s raw water source can be improved. In the coming decades, alternative water treatment processes like ultraviolet disinfection should be considered. In light of climate change and ever-changing weather extremes, these recommendations will allow the City of Wilmington to minimize disinfection byproduct production and continue to provide its customers with safe drinking water.