Date of Award

12-2018

Degree Name

MS in Civil and Environmental Engineering

Department/Program

Civil and Environmental Engineering

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Tryg Lundquist

Advisor Department

<--Please Select Department-->

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

Two sets of triplicate pilot algal raceway ponds (1000-L, 0.30-m deep, paddle wheel mixed) were operated for 14 months at a California wastewater treatment plant to treat wastewater and generate algal-bacterial biomass as biofuel feedstock. Two experiments were run to determine the effect on biomass productivity of (1) hydraulic residence time (HRT: 2, 3, 4, or 4.5 days) and (2) feeding schedule (18 small pulses during 8 AM-4 PM [diurnal] versus 20 large pulses during 4 AM-12 AM [diel]). The target productivity was at least 20 g volatile suspended solids per m2 of pond per day. Additional output variables were followed during the experiments: treatment performance and the effectiveness of biomass harvesting though bioflocculation. Productivity was consistently higher in ponds with a 2-d HRT versus longer HRTs. Average productivity for the 2-d HRT ponds and the variable-HRT ponds (3.6-d average HRT) were 30.1 and 23.4 g/m2-d, respectively. Productivity data collected during the feed regime experiment were highly variable, and average productivities were the same at 26 g/m2-d. During both experiments, both pond sets exceeded the target of 20 g/m2-d on an annual basis. During the hydraulic residence time experiment, the average pond productivity throughout the HRT experiment for the 2-d HRT and 3-d HRT ponds were 30.1 and 23.4 g/m2-d, respectively. Settling efficiency was high for both 2- and 3-d HRT ponds with average turbidity removal of 87-89%. However, total ammonia nitrogen (TAN)

concentrations in the 2-day HRT pond effluent were 50-94% higher than in the 3-d HRT pond effluents, although effluent TAN concentrations in both ponds were approximately the same during mid-summer. Furthermore, effluent biochemical oxygen demand (BOD5) concentrations were similar, with the supernatant of Imhoff cones settled for 24 hours containing 24-27 mg/L BOD5 (81-92% removal). In general, the 3-d HRT ponds provided better treatment than the 2-d HRT ponds. During the feeding regime experiment, no productivity or BOD5 removal differences were evident. However, the 3-d HRT ponds had consistently 8 mg/L more effluent TAN than the 2-d HRT ponds.

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