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Submitted to: Journal of Applied Phycology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/22/2008 Publication Date: 2/20/2008 Citation: Mulbry III, W.W., Ingram, S.K., Buyer, J.S. 2008. Treatment of Dairy and Swine Manure Effluents Using Freshwater Algae: Fatty Acid Content and Composition of Algal Biomass at Different Manure Loading Rates. Journal of Applied Phycology. 20:1079-1085. Interpretive Summary: Production of algae as a biofuel feedstock has been the subject of research for at least five decades and was a focus of the U.S. Department of Energy’s Aquatic Species Program (ASP) from 1979 to 1995. One conclusion of the ASP was that the most compelling systems would couple an algae-based wastewater treatment system to biofuel production from the resulting biomass. One assumption of this idea is that the entire system would be partially or entirely funded by the value of wastewater treatment. An additional assumption is that the wastewater-grown biomass would contain sufficient levels of fatty acids (FA) to compete with other potential feedstocks. Although there is renewed interest in the algal production of algae for biofuel, there are few reports of the biofuel potential of wastewater-grown algae. The objective of this study was to determine how the fatty acid (FA) content and composition of algae respond to changes in the type of manure, manure loading rate, and to whether the algae was grown with supplemental carbon dioxide. Algal biomass was harvested weekly from indoor and outdoor algal turf scrubber (ATS) units using different loading rates of dairy and swine manure effluents. The results showed that FA content values of the algal biomass ranged from 0.8 to 1.8% of dry weight and showed no consistent relationship to loading rate, type of manure, or to whether supplemental carbon dioxide was added to the systems. Using an approximate value of 1% FA (corresponding to values from the outdoor pilot scale ATS units using raw dairy manure), we estimate a feedstock cost of $130 per kg of algal FA (before extraction and processing). However, within the context of reducing nutrient inputs in sensitive watersheds such as the Chesapeake Bay, ATS treatment costs of roughly $11 per kg N compare very favorably with the costs of other agricultural nutrient management practices. Assuming that extraction solvents could be removed to an acceptable level in the extracted biomass, then sale of the extracted biomass as a slow release fertilizer could also provide a significant source of revenue. If the nutrient treatment and/or fertilizer values are included in the cost analysis, then the feedstock cost per kg FA would be significantly reduced. Technical Abstract: An alternative to land spreading of manure effluents is to grow crops of algae on the N and P present in the manure and convert manure N and P into algal biomass. The objective of this study was to determine how fatty acid (FA) content and composition of algae respond to changes in the type of manure, manure loading rate, and to whether the algae was grown with supplemental carbon dioxide. Algal biomass was harvested weekly from indoor laboratory-scale algal turf scrubber (ATS) units using different loading rates of raw and anaerobically digested dairy manure effluents and raw swine manure effluent. Manure loading rates corresponded to N loading rates of 0.2 to 1.3 g total nitrogen (TN) per sq. meter-day for raw swine manure effluent and 0.3 to 2.3 g TN per sq. meter-day. In addition, algal biomass was harvested from outdoor pilot-scale ATS units using different loading rates of raw and anaerobically digested dairy manure effluents. FA content values of the algal biomass ranged from 0.8 to 1.8% of dry weight and showed no consistent relationship to loading rate, type of manure, or to whether supplemental carbon dioxide was added to the systems. FA composition was remarkably consistent among samples and >90% of the FA content consisted of c14 to c18 fatty acids. |
