Available at: https://digitalcommons.calpoly.edu/theses/1234
Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Water cost is one of the key deterrents in making algal biofuels a feasible alternative to traditional petroleum fuels. Research into recycling of algal media was conducted in a laboratory setting at the California Polytechnic State University in San Luis Obispo. A growth assay was created to allow for algal cultures, specifically Ward’s Chlorella sp., to proliferate in sealed culture vessels. Bold’s Basal Medium (BBM) was selected as the media due to its extensive use with freshwater algal strains. However, this medium can limit algal growth through nutrient limitation and it became necessary to augment the original recipe. 50mM of sodium bicarbonate was added to the media in order to buffer the purging of 100% CO2 into the culture vessel. The resultant pH of the CO2 saturated media was 6.25. The elemental? composition of Chlorella vulgaris was compared with the nutrient content of BBM to estimate possible nutrient limitations which could occur throughout growth (Oh Hama, 1988). From this analysis, the nitrogen and phosphorus concentration in BBM was augmented by a factor of three (BBM3N3P). Further, vitamins, specifically cyanocobalamin, thiamine HCL, and biotin, were incorporated after conducting a comparison growth study with BBM 3N3P. The average maximum specific growth rates for the normal BBM and for the vitamin-enhanced BBM were 0.689 +/- 0.0818 and 0.887 +/- 0.1901 (mean +/- std. deviation) per day, respectively. This difference was proved significant by a t-test with a p-value equal to 0.041. A standardized methodology for conducting a regrowth potential experiment was outlined by the research. One phase of this methodology included reintroduction of nutrients consumed during the first round of growth. Prior to continuing with this methodology the effect of supplementing trace metals and micronutrients into the culture was investigated. At a p-value of 0.0956, there was no significant difference between BBM 3N3P + vitamins and the same media with eight times the trace metal and micronutrient concentration. This allowed for up to seven rounds of regrowth with no inhibition caused from the restoration of these nutrients. A final regrowth was conducted on BBM 3N3P + vitamins + 50 mM bicarbonate. A significant difference existed between both the Round 1 and Round 2 cultures, as well as between the Round 2 cultures and their respective controls. This signified the possible release of allelochemicals by the Chlorella sp.. A preliminary investigation into the possible use of anaerobic digester effluent as a primary source of nutrients for algal cultures was also conducted. The digestate (diluted 50% v/v with a saline make-up) grew significantly faster than the controls (p-value<0.001). Further, after the introduction of trace metals and micronutrients the digestate columns outlived the control columns increasing the feasibility of using digestate to supplemental algal cultures.