Phosphate and Nitrate Removal from Impacted Waters by Combined Physical-Chemical and Microbiological Transformations

Nutrient rich agricultural runoff is a major source of phosphorus (P) and nitrogen (N) loading to surface waters, resulting in eutrophication and harmful algal blooms. The most effective nutrient removal technologies often have cost, land, or operational requirements that limits use in the decentralized areas that need it most. This dissertation investigated combined physical-chemical and microbiological technologies for combined P and N removal from nonpoint sources. Chapter 2 investigated the combination of basic oxygen furnace (BOF) steel slag and woody mulch for P removal by mineral precipitation and N removal by microbial denitrification. When combined with mulch in column experiments, slag with high fines content achieved complete P removal under unsaturated conditions. Batch experiments showed that microbial denitrification occurred under the highly alkaline conditions created by steel slag, but the timescale differential between P and N removal was a critical barrier to combining these treatment technologies. Chapter 3 evaluated a field-scale slag filter to treat agricultural tile drainage and lab-scale column experiments to provide insight on field conditions that impacted P removal. Increases in alkalinity had negative influences on P removal through inhibition of P mineral precipitation by BOF slag, while blast furnace (BF) steel slag was less impacted by alkalinity due to primarily adsorptive P removal. Regeneration strategies were identified based on water quality and slag type.Chapters 4 and 5 explored biological ion exchange (BIEX) as an option for addressing the timescale offset identified in Chapter 1. In Chapter 4 columns fed with dissolved organic matter (DOM) were not regenerated and over 50% DOM removal was observed, with the primary mechanism of removal identified as secondary ion exchange (SIEX) between sulfate and DOM fractions with high affinities for ion exchange. Chapter 5 aimed to expand BIEX to N treatment through batch denitrification and adsorption experiments, which revealed a positive relationship between molecular weight of organic molecules and their ability to displace nitrate. This work shows that by having an improved understanding of impacted water characteristics, the information presented in this work can be used to select and implement effective treatment technologies for decentralized areas.