Year Established: 2012 Start Date: 2012-03-01 End Date: 2013-12-31
Total Federal Funds: $63,992 Total Non-Federal Funds: $127,984
Principal Investigators: Julian Fairey, Wen Zhang
Abstract: Disinfection byproducts (DBPs) are formed by reactions between disinfectants (e.g., free chlorine) and dissolved organic matter (DOM), which is ubiquitous in lakes and rivers. DBPs are formed during chlorination of drinking water year-round, but on balance form at higher concentrations in the summer months when algal communities are more active. Continued nutrient enrichments of nitrogen (N) and phosphorus (P) are expected to increase primary productivity and shift the phytoplankton community composition to predominately cyanobacteria in both suspended and sessile growth, but these impacts on DOM properties and hence DBP formation and control remain largely unknown. Additionally, climate change maybe a potent catalyst for further expansion of these blooms, as high nutrient loadings and rising water temperatures favor cyanobacteria over other phytoplankton species such as diatoms and green algae. At present, the four drinking water treatment plants (DWTPs) on the Beaver Lake reservoir are struggling to meet the current and pending DBP regulations. The largest of these DWTPs – the Beaver Water District, Lowell AR – is currently in the process of switching pre-oxidants (e.g., from free chlorine to chlorine dioxide) in an attempt to curb DBPs. Here, we propose a series of nutrient enrichment mesocosms on Beaver Lake to study the impacts of phytoplankton biomass and algal speciation on physicochemical DOM properties and DBP formation and control. The results of this study will be of vital importance to the four DWTPs on Beaver Lake as they develop strategies to meet current and pending DBP regulations. The objective of this proposal is to determine the effects of nitrogen (N) and phosphorus (P) nutrient enrichments on Beaver Lake reservoir DOM quality and the subsequent impacts on DBP formation and control. The work plan consists of quarterly batch mesocosm nutrient-enrichment studies and DBP formation and control experiments. The Beaver Lake reservoir, the primary drinking water source for the 500,000 residents of Northwest Arkansas, was selected as the sampling location for this one-year project. Sampling will occur at the intake structures of the four DWTPs approximately 8 times throughout the year, with emphasis on the algal growing season (April-September, 2012). Experiments will include (1) phytoplankton community composition in water column (the relative numbers of diatoms, green algae, cyanobacteria, and other more rare forms) and dominant species in biofilms, (2) algal biomass (chlorophyll-a [Chl-a] and total phosphorus [TP]), and (3) DBP formation and control. The net result will be an improved understanding of the future water quality of Beaver Lake reservoir and critical information that can be leveraged by the four DWTPs to help make more informed decisions regarding disinfection regimes and DOM-removal processes for DBP control. This project will advance the science of DBP research and benefit end-users (e.g., consulting engineers, water utilities, etc.) through development of a conceptual framework to (1) evaluate long-term changes in DBP formation due to perturbations in source water, (2) assess changes in physicochemical DOM properties driven by continued nutrient enrichments and weather-related events, and (3) select and optimize DBP-precursor removal strategies based on source water DOM properties.