Laboratory Evaluation of Dunaliella tertiolecta as a Candidate Algal Species for Tertiary Wastewater Treatment of Nitrogen and Phosphorus-Laden Effluents Impacting Marine Environments
Dunaliella tertiolecta was evaluated to determine the effectiveness of utilizing the algal species to reduce the nutrient load of saline wastewater during tertiary treatment. Nutrient uptake studies performed using f/2-Si medium illustrated that Dunaliella tertiolecta favored phosphate uptake over nitrate-nitrogen. Over a 7-day observational period, total phosphorus concentration was reduced by over 97% and the kinetic rate of uptake observed was approximately 0.5 - 1 mg/L/day. Daily nitrate-nitrogen concentrations were highly variable and a model could not be determined to predict uptake behavior. In heavily concentrated nutrient loads, the algae still favored phosphate uptake. However as the nutrient load increased from 4X to 32X, the percent reduction in total phosphorus concentration decreased linearly; biomass was reduced by over 20% for cell cultures containing the heaviest concentrated nutrient loads. Since immobilized microbe bioreactor treatment was not successful in significantly reducing nitrate-nitrogen and phosphate present in the landfill leachate, Dunaliella tertiolecta was used in simulated high-rate algal ponds to assimilate the nutrients. Simulated HRAP treatment greatly reduced (p-value < 0.05) the nitrogen-ammonia nutrient load in both leachate samples; the kinetic rates of uptake averaged 1.61 mg/L/day during week 1 and 0.48 mg/L/day during week 2 for the collection pond leachate. The kinetic uptake rates averaged 0.61 mg/L/day and 0.12 mg/L/day during week 1 and week 2 respectively for the holding tank leachate. However, since Dunaliella tertiolecta favored nitrogen uptake in the form of nitrogen-ammonia, nitrate-nitrogen uptake was significantly (p-value > 0.05) suppressed until nitrogen-ammonia concentrations were lowered. On average, the kinetic uptake rate observed for nitrate-nitrogen was 0.04 mg/L/day. Phosphate uptake also appeared to be suppressed by the presence of nitrogen-ammonia; total phosphorus concentrations increased linearly over the 14-days, but during week 2 the increase in concentration began to plateau as nitrogen-ammonia uptake decreased. Since Dunaliella tertiolecta had the ability to assimilate nutrients from heavily concentrated environments, it is likely that the marine algal species would be an ideal candidate for tertiary treatment of saline wastewaters when nitrogen-ammonia is present at extreme concentrations; in order to see significant overall reductions at such concentrations, the retention time would have to exceed 14-days.
Advisor:Jack N. Losso; Ralph J. Portier; Aixin Hou
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:03/27/2007