Available at: https://digitalcommons.calpoly.edu/theses/1544
Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Biomass growth of the alga Nannochloropsis oceanica, cultivated outdoors in six pilot-scale raceway ponds, was monitored over the course of 1.5 years, at two different dilution regimes each season, to establish the effects on algal biomass productivity and concentration of dilution rate, pond water temperature, and solar radiation. The 4.5-m2 ponds were located in a mild, mid-latitude, coastal region (central California). Experimental conditions were operated in duplicates or triplicates with a consistent artificial seawater medium, pond depth, pH range, paddle wheel mixing speed, and replete nutrient conditions for the duration of the study. Two cultivation regimes were used to regulate pond biomass concentration: batch growth and a three-times-per-week dilution with a resulting dilution rate of 0.21/d. For the ranges of input variables tested, productivity (g/m2-d) was positively correlated to both pond water temperature and solar radiation. However, the data scatter in the correlations was substantial, indicating the existence of other major influences on productivity. A dilution regime consisting of three dilutions per week and a dilution rate of 0.21/d resulted in the higher productivities compared to batch cultivation for all seasons tested. With high light intensity (200-300 W/m2) and warm water (18.3oC daily average), the highest productivity was 11.4 g/m2-d with a resulting biomass concentration of 0.15-0.20 g/L. With low light intensities (150-200 W/m2) and cool water (16.6oC daily average), the highest productivity was 6.9 g/m2-d with a resulting biomass concentration of 0.10-0.15 g/L.