Author
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Westhead, Elizabeth |
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Pizarro, Carolina |
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Mulbry, Walter |
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Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/15/2004 Publication Date: 11/2/2004 Citation: Mulbry, W.W., Westhead, E.K., Pizarro, C.X., Wilkie, A. 2004. Treatment of dairy manure effluent using freshwater algae: elemental composition of algal biomass at different manure loading rates. Journal of Agricultural and Food Chemistry. 52:7293-7296. Interpretive Summary: Cultivating algae on nitrogen (N) and phosphorus (P) in animal manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. However, the use and value of the algal biomass as a feed or soil supplement depends, in part, on whether the biomass contains any harmful components. Previous research has shown that freshwater algae can accumulate heavy metals to levels far above levels found in their aqueous environment. The objective of this study was to determine how the composition of algae changes using different loading rates of anaerobically digested flushed dairy manure. Algal biomass was harvested weekly from laboratory scale algal turf scrubber (ATS) units using four different manure loading rates. N and P contents in the dried biomass both increased 2-fold with increasing loading rate up to maximums of 6.6% N and 1.3% P, at 6 liters of manure per day. Above this loading rate, N and P contents reached plateaus or decreased slightly. The contents of most other elements showed similar 2-fold increases up to maximums at a loading rate of 6 liters of manure per day, followed by decreases above this loading rate. The maximum concentrations of individual components in the algal biomass were (in mg per kg): 1200 (aluminum), 9300(calcium), 0.4(cadmium), 65(copper), 650(iron), 5.0(lead), 2400(magnesium), 260(manganese), 3.0(molybdenum), 16,300(potassium), 230(silicon) and 350(zinc). Levels of heavy metals in the algal biomass would not be expected to reduce its value as a soil or feed amendment. Technical Abstract: Cultivating algae on nitrogen (N) and phosphorus (P) in animal manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. However, the use and value of the algal biomass as a feed or soil supplement depends, in part, on whether the biomass contains any harmful components. Previous research has shown that freshwater algae can accumulate heavy metals to levels far above levels found in their aqueous environment. The objective of this study was to determine how the composition of algae changes using different loading rates of anaerobically digested flushed dairy manure. Algal biomass was harvested weekly from laboratory scale algal turf scrubber (ATS) units using four manure loading rates (2,4,6, and 9 liters of manure per square meter-day). These rates correspond to daily loading rates of 0.8-3.7 g total N and 0.12'0.58 g total P. The harvested algal biomass was dried at 70 C and ground prior to elemental analysis. N and P contents in the dried biomass both increased 2-fold with increasing loading rate up to maximums of 6.6% N and 1.3% P, at 6 liters of manure per day. Above this loading rate, N and P contents reached plateaus or decreased slightly. There was considerable variation in the elemental composition of the algal biomass, but contents of other elements showed similar 2-fold increases up to maximums at a loading rate of 6 liters of manure per day, followed by decreases above this loading rate. The maximum concentrations of individual components in the algal biomass were (in mg per kg): 1200 (aluminum), 9300(calcium), 0.4(cadmium), 65(copper), 650(iron), 5.0(lead), 2400(magnesium), 260(manganese), 3.0(molybdenum), 16,300(potassium), 230(silicon) and 350(zinc). Levels of heavy metals in the algal biomass would not be expected to reduce its value as a soil or feed amendment. |
