NITROGEN AND PHOSPHORUS REMOVAL RATES, AND NITRIFICATION WITHIN ALGAL TURF SCRUBBERS GROWN ON DAIRY MANURE

Authors: Westhead, Elizabeth; Pizarro, Carolina; Mulbry, Walter; WILKIE, ANN - UNIV OF FLORIDA

Submitted to: Journal of Applied Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2002
Publication Date: 12/1/2002
Citation: Westhead, E.K., Pizarro, C.X., Mulbry Iii, W.W., Wilkie, A. 2002. Nitrogen and phosphorus removal rates, and nitrification within algal turf scrubbers grown on dairy manure. Journal of Applied Phycology.

Interpretive Summary: Conservation and reuse of nitrogen (N) and phosphorus (P) 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 N and P 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 specific objectives of these experiments were to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in previous experiments. Anaerobically digested dairy manure was obtained from the USDA/ARS dairy research unit in Beltsville, Maryland. In laboratory scale ATS units using loading rates of approximately 1-2 g N and 0.16 to 0.33 g P per square meter per day, algal production ranged from 6-20 g dry weight. Nutrient content of the algal biomass increased with loading rate, ranging from 5-7 % and 0.8-1.3 % for N and P, respectively. Removal rates of ammonium-N and phosphate-P increased with manure loading rate as did rates of nitrate production. These results are similar to those obtained previously using anaerobically digested manure from the University of Florida. Although the two dairies use anaerobic digestors to treat their waste effluents, their effluents are quite different because of the type of bedding material used (sand versus sawdust)and manure collection method (flush versus scrape system).

Technical Abstract: Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. ATS units were grown under three manure loading rates ranging from 1.10 to 2.21 g N per square meter per day and 0.16 to 0.33 g P per square meter per day. Algal turfs were harvested at different age (3 to 7 days) to evaluate the effect of biomass and turf age on removal rates and nitrification. Rates of nitrogen and phosphorus removal and nitrate production were determined based on samples taken over a 5-hour period. The algal biomass was harvested at the end of the experiment for dry weight and nutrient content analyses. Algal production ranged from 6.3 to 19.6 g DW per square meter per day with the highest values corresponding to 3 to 5 days old turf and the highest loading rate. Nutrient content of the algal biomass increased with loading rate, ranging from 5.4 to 6.8 % (W/W) for N and 0.85 to 1.34 % for P. Removal rates of ammonium-N and phosphate-P increased with loading rate, ranging from 0.77 to 1.56 mg per liter per hour and 0.10 to 0.46 mg per liter per hour, respectively. Nitrification rates ranged from 0.13 to 0.65 mg nitrate-N per liter per hour and generally increased with loading rate, and residual concentrations of NH4 in the effluent before the 5-hr experiments. The highest nitrification rates (0.50 to 0.65 mg per liter per hour) were recorded in experiments where the effluent was not bubbled with carbon dioxide.