Organic Matter Removal via Biological Drinking Water Filters: Removal Efficiency Based on Quantifiable System Factors

Terry, Leigh Gilmore

Graduate Thesis Or Dissertation

Organic Matter Removal via Biological Drinking Water Filters: Removal Efficiency Based on Quantifiable System Factors Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/1544bp405

Abstract

Biodegradable organic matter (BOM), found in all surface waters, is a challenge for drinking water utilities as it can lead to distribution system bio-regrowth, react to form disinfection by-products, or be a specific compound of concern. Drinking water utilities face the challenge of removing BOM to meet increasingly stringent regulations, often at higher costs and operational complexity. Biofiltration can be an efficient treatment technology to remove BOM from the influent water, but should be optimized to achieve maximum removal performance. The objectives of this dissertation were to evaluate and model the impacts of biologically active filter (biofilter) design and operation on BOM removal as measured by dissolved organic carbon (DOC). Operational and water quality parameters, i.e. extended empty bed contact time (EBCT), temperature, biomass acclimation and distribution, and natural organic matter concentration and origin (microbial, terrestrial and wastewater effluent), were evaluated to determine impacts on biofilter performance. A novel bench scale methodology was developed in Chapter 2 that incorporated a batch reactor and a single-pass flow through reactor that allowed arduous pilot scale experiments to be replaced with streamlined bench scale testing, which could expedite biofilter implementation in drinking water utilities. In Chapter 3, a model derived from Monod kinetics was developed for biological filters based on EBCT and a single biomass measurement from the top of the filter. The model was developed for the control of DOC and successfully applied to predict DOC removal. Biomass activity, adenosine triphosphate (ATP), measurements were a direct function of temperature, yet biomass concentration, phospholipid measurements, were not a function of temperature in the range of 5 °C to 22 °C. Pilot scale work in Chapter 4 found acclimation of the ‘fresh’ media in terms of DOC removal and activity occurred over a two-month time frame. Chapter 4 and Chapter 5 found extended EBCT of a biofilter and higher temperatures improved the performance of biofilters for controlling DOC, yet influent DOC did not impact DOC removal directly. Biomass activity, ATP, was highest at the top of the filter and decreased with increasing filter depth. Chapter 5 bench scale work found biofilters were robust in removing DOC from microbial, terrestrial and wastewater effluent sources and reduced DBP precursors. In chapter 6, a life cycle assessment model was used to compare conventional filtration and biofiltration. Biofiltration had lower environmental impacts than conventional filtration for average U.S. source waters by about 25%. Chemicals, in particular alum and caustic soda, had the largest contributions to environmental impacts. The most effective way to substantially decrease negative environmental impacts of either filtration system is to optimize chemical doses. Higher temperatures can support greater DOC biodegradation, which increases the environmental benefits of biofiltration, and higher levels of biodegradation can also be achieved at lower temperatures when biofilter parameters are optimized.

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