Date of Award

2024

Type

Thesis

Major

Master of Science

Degree Type

Master of Science in Natural Sciences - Environmental Science Track

First Advisor

Dr. Troy Keller

Second Advisor

Dr. Stacey Blersch

Third Advisor

Dr. Clifton Ruehl

Abstract

Freshwater nutrient enrichment from wastewater facilities and other sources can lead to freshwater eutrophication, a threat to global aquatic ecosystems. Mechanical and chemical ways to curb this threat are either too expensive or not sustainable, and thus, not feasible. Compared to mechanical and other methods, sustainable, inexpensive biological methods (for example, algal treatment systems) have therefore been developed for the removal of excess nutrients from wastewater. By design, secondary waste treatment facilities (WWTF) remove organics and solids and lower oxygen demanding substances; however, they may not remove enough nutrients to protect freshwater ecosystems in all cases. While algae-based biological methods have proven successful in treating primary and secondary wastewater, less is known about the use of algae in treating biodigester filtrate. Since biodigester filtrate is characterized by elevated concentration of ammonia and high pH, it may inhibit algae in algal treatment systems. An experiment was conducted to test the hypothesis that diluting biodigester filtrate concentration improves algal biomass production and nutrient removal in recirculating algal treatment systems. Three concentrations of biodigester filtrate were created with different volumes of secondary wastewater (1:7, 1:14, and 1:28 for high, medium, and low concentrations respectively). The results showed algae were inhibited by high concentrations of biodigester filtrate. One possible explanation for the result is ammonia/ammonium toxicity. To test this hypothesis, a second experiment that added ammonium chloride to diluted biodigester filtrate (target concentrations of 20mg/L, 40mg/L, and 80mg/L NH3-N for control, low and high treatments respectively) was conducted. Eight replicates recirculating floways of each treatment were operated for 21days. Total algal biomass production and nutrient removal were higher in control than in the elevated ammonium chloride treatments. Results from this study clearly demonstrate that ammonium toxicity is an inhibitory factor in algal productivity. This study shows the feasibility of using algal wastewater treatment systems to treat highly concentrated biodigester filtrate if the filtrate is diluted prior to treatment.

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