Treatment of Dairy Manure Effluent Using Freshwater Algae in Outdoor Pilot-Scale Raceways: Algal Production and Nutrient Recovery

Authors: Mulbry, Walter; Kondrad Ingram, Shannon; PIZARRO, CAROLINA - UNIV OF MD; Westhead, Elizabeth

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2008
Publication Date: 5/19/2008
Citation: Mulbry III, W.W., Kondrad, S.L., Pizarro, C., Westhead, E.K. 2008. Treatment of Dairy Manure Effluent Using Freshwater Algae in Outdoor Pilot-Scale Raceways: Algal Production and Nutrient Recovery. Bioresource Technology. 99:8137-8142.

Interpretive Summary: The vulnerability of aquatic ecosystems and groundwater to nutrient pollution has forced increasingly stringent environmental regulations to be placed on dairy farms. Production of algae on wastewater nutrients could provide a holistic solution to nutrient management problems on existing farms. Previous laboratory scale studies using one type of algal treatment system (termed an algal turf scrubber) have shown rates of algal growth and nutrient recovery from dairy manure effluents. The general objective of this study was to extend those results to larger, outdoor treatment systems. The specific objectives were to determine how algal growth, nutrient removal efficiency, and elemental composition of turf algae grown in outdoor raceways respond as a function of seasonal changes in light and temperature, carbon dioxide supplementation, and different loading rates of raw and anaerobically digested dairy manure effluent. In these experiments, algal biomass was harvested every 4 to 12 days from replicate 30 square meter pilot-scale algal turf scrubber raceways using daily loadings of manure effluent corresponding to rates of 0.3-2.2 g total N (TN) and 0.08-0.42 g total P (TP) per day. Raceways were operated approximately 260 days each year (roughly April 1 to Dec 15) from 2003 to 2006. Mean algal productivity values increased from approximately 2.5 g dry weight per square meter per day at the lowest loading rate (0.3 g TN per square meter per day) to 20 g DW per square meter per day at the highest loading rate (2.5 g TN per square meter per day). Mean N and P contents in the dried biomass increased 1.5 to 2.0 -fold with increasing loading rate up to maximums of 7 % N and 1.4 % P. Although highly variable, algal N and P accounted for roughly 50% of input N and P.

Technical Abstract: An alternative practice to land spreading of manure effluents is to grow crops of algae on the nitrogen (N) and phosphorus (P) present in these liquid slurries. The objective of this study was to determine how algal productivity, nutrient removal efficiency, and elemental composition of turf algae grown in outdoor raceways respond as a function of seasonal changes in light and temperature, carbon dioxide supplementation, and different loading rates of raw and anaerobically digested dairy manure effluent. Algal biomass was harvested every 4 to 12 days from replicate 30 square meter pilot-scale algal turf scrubber raceways using daily loadings of manure effluent corresponding to rates of 0.3-2.2 g total N (TN) and 0.08-0.42 g total P (TP) per day. Raceways were operated approximately 260 days each year (roughly April 1 to Dec 15) from 2003 to 2006. Mean algal productivity values increased from approximately 2.5 g dry weight per square meter per day at the lowest loading rate (0.3 g TN per square meter per day) to 20 g DW per square meter per day at the highest loading rate (2.5 g TN per square meter per day). Mean N and P contents in the dried biomass increased 1.5 to 2.0 -fold with increasing loading rate up to maximums of 7 % N and 1.4 % P. Although highly variable, algal N and P accounted for roughly 50% of input N and P.