Submitted to: Journal of Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 13, 2003
Publication Date: December 16, 2003
Citation: WESTHEAD, E.K., PIZARRO, C.X., MULBRY III, W.W., WILKIE, A.C. PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED DAIRY MANURE.. JOURNAL OF PHYCOLOGY. 2003.
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 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. As daily loading rates increased from 0.8 to 3.6 grams of total nitrogen per day, algal production increased from 7.6 to 16.2 grams dry weight per day, and algal N and P content increased from 4 to 7% and 1 to 1.5%, respectively. In the best case, algal biomass grown on dairy manure had a crude protein content of about 44%. At a dry matter yield of 16 g/ sq.meter-day, this is equivalent to annual uptake rates of 4090 and 876 kg/ ha-year for N and P, respectively. Compared to the N and P uptake of a conventional corn/rye rotation, an algal scrubber system operating 8 months of the year would require only about 13% of the land area to utilize the equivalent dairy manure N and P.
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. Previous studies in our laboratory on manure from two different dairy farms showed that removal by periphyton grown on ATS (algal turf scrubber) units accounted for 33-42% of input TN (total nitrogen) and 58-100% of TP (total phosphorus). However, high nitrification rates led to high nitrate levels in treated effluent of the digested manures. Algal production was about 5 g per sq. meter per day. 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, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 umol photons per sq. meter per sec) and manure loading rates ranging from 0.8 to 4.9 g TN and 0.13 to 0.77 g TP per sq. meter per day. Algal production, removal of N and P from effluent, and nutrient recovery in algal biomass were studied. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia and Cyclotella sp.) partially replaced the filamentous green algae at relatively high manure loading rates, and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6 (± 2.71) to 19.1 (± 2.73) g DW per sq. meter per day. N and P content of algal biomass generally increased with loading rate and ranged from 2.9-7.3% and 0.5-1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42-47%). The maximum removal rates of N and P per unit algal biomass (mg per g per sq. meter per day DW) were 70 and 13, respectively. Recovery of nutrients in harvested algal biomass accounted for up to 31-52% for N and 30-59% for P. P-removal appeared to be uncoupled with removal of N at higher loading rates, suggesting algal potential for accumulation of P may have already been saturated. Comparing results with previous studies in this laboratory, it appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the ATS units.