Available at: https://digitalcommons.calpoly.edu/theses/3252
Date of Award
3-2026
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Tryg Lundquist
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
Despite wastewater treatment and improved agricultural practices in many regions, eutrophication continues due to release of excess nutrients into waterways. Algae-based technologies such as engineered Flow Ways (FWs) might be advantageous in terms of lower cost and inputs while providing greater nutrient recovery. This thesis investigated the performance of algal monocultures and polycultures cultivated in pilot scale attached algal Flow Way (FW) systems treating nitrified, filtered municipal reclaimed water. The study evaluated differences in ash content, harvest productivity, and nutrient removal, including diel nutrient removal patterns. Three biomass harvesting intensities were compared with respect to productivity: a soft silicone brush, a notched squeegee, and a fully scraped method. Six FWs (30 cm wide × 7.62 m long) were operated at 12.9 L/min in recirculation. Two systems were inoculated with filamentous Tribonema minus, two with Uronema sp., and two with a polyculture of both species. Biomass production was quantified weekly over a 12-week period using total, volatile, and non-volatile solids analyses. Nitrate (NO₃⁻–N) and dissolved reactive phosphorus (DRP) concentrations were determined weekly. Results showed biomass ash content was similar in all FW. However, productivity differed by species when comparing the FWs: Uronema sp. had the highest mean harvest productivity (2.06 g/m²-d), followed closely by the polyculture (2.01 g/m²-d), while T. minus demonstrated poor attachment and the lowest productivity (1.26 g g/m²-d). Uronema sp. achieved the highest mean nitrate removal (38%), followed by the polycultures (34%) and T. minus (25%). Nitrate removal rates were higher overnight (0.022 g/m²-hr) compared to daytime (0.001 g/m²-hr) indicating denitrification. Phosphorus removal was substantial in all FWs, with Uronema sp. reaching 87% removal, polyculture 70%, and T. minus 66%. Phosphorus removal rates were higher during the day (0.027 g m²-hr) than at night (−0.006 g/m²-hr), indicating nighttime dissolution of phosphate precipitates. Harvest method greatly influenced biomass production rates when comparing the FW harvesting zones. The fully scraped technique resulted in the highest mean productivity between harvests (1.96 g/m²day), outperforming the notched (1.48 g/m²-day) and brushed (1.02 g/m²-day) methods. Overall, results suggest that Uronema sp. combined with a fully scraped harvest approach leads to the highest productivity and nutrient removal from reclaimed water, supporting improved species selection and operational strategies for future studies.