TREATMENT OF SWINE MANURE EFFLUENT USING FRESHWATER ALGAE: PRODUCTION, NUTRIENT RECOVERY, AND ELEMENTAL COMPOSITION OF ALGAL BIOMASS AT FOUR MANURE LOADING RATES

Authors: WESTHEAD, ELIZABETH - USDA, ARS, ANRI, AMBL; Pizarro, Carolina; Mulbry, Walter

Submitted to: Journal of Applied Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2005
Publication Date: 3/30/2006
Citation: Westhead, E., Pizarro, C.X., Mulbry III, W.W. 2006. Treatment of swine manure effluent using freshwater algae: production, nutrient recovery, and elemental composition of algal biomass at four effluent loading rates. Journal of Applied Phycology. 18:41-46.

Interpretive Summary: Conservation and reuse of nitrogen and phosphorus from animal manure is increasingly important as producers try to minimize transport of these nutrients off-farm. An alternative to land spreading is to grow crops of algae on the nitrogen and phosphorus present in the manure. The general goals of our research are to assess one algal production technology, termed algal turf scrubbers (ATS) to recover nutrients from animal manures. The objective of this study was to assess algal growth, nutrient removal, and elemental composition of the algal biomass using different loading rates of raw swine manure. As daily loading rates increased from 0.25 to 0.47 grams of total nitrogen per day, algal production increased from 6.8 to 11.1 grams dry weight per day, and algal nitrogen increased slightly from 3.6 to 3.9%. However, at higher effluent loading rates algal production increased only slightly and then declined. At the loading rate of 0.47 liters per sq. meter per day (corresponding to peak production level) the concentrations of individual components in the algal biomass were (in mg per kg): 250 (Al), 4800 (Ca), 0.31 (Cd), 1100 (Fe), 4.0 (Pb), 2350 (Mg), 100 (Mn), 5.85 (Mo), 7,600 (K), 140 (Si) and 450 (Zn). At these concentrations, 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 effluents presents an alternative to the current practice of land application. The objective of this study was to determine how algal productivity, nutrient removal efficiency, and elemental composition of algae changed in response to different loading rates of raw swine manure effluent. Algal biomass was harvested weekly from two laboratory scale algal turf scrubber units using four manure effluent loading rates (0.25, 0.43, 0.70 and 1.2 liters per sq. meter per day) corresponding to daily loading rates of 0.3-1.3 g total N and 0.05 and 0.27 g total P per day. Mean algal production values increased from 6.8 g dry weight per sq. meter per day at the lowest loading rate (0.25 liters of effluent per sq. meter per day) to 12.3 g dry weight per sq. meter per day at 0.47 liters of effluent per sq. meter per day. However, at higher effluent loading rates algal production increased only slightly and then declined. Mean N and P contents in the dried biomass increased roughly 1.4-fold with increasing loading rate up to maximums of 5.2% N and 1.5% P at 1.2 L m-2 d-1. Biomass concentrations of Al, Ca, Fe, K, Mg, Si, and Zn increased only slightly up between the loading rates of 0.25 and 0.70 liters per sq. meter per day but then in increased significantly at the highest loading rate. Concentrations of Cd, Mn, Mo generally increased with loading rate. The Pb concentration did not increase significantly with loading rate. At the loading rate of 0.47 liters per sq. meter per day (corresponding to peak production level) the concentrations of individual components in the algal biomass were (in mg per kg): 250 (Al), 4800 (Ca), 0.31 (Cd), 1100 (Fe), 4.0 (Pb), 2350 (Mg), 100 (Mn), 5.85 (Mo), 7,600 (K), 140 (Si) and 450 (Zn). At these concentrations, heavy metals in the algal biomass would not be expected to reduce its value as a soil or feed amendment.