NITROGEN AND PHOSPHORUS REMOVAL RATES OF SMALL ALGAL TURFS GROWN ON DAIRY MANURE

Authors: Pizarro, Carolina; Westhead, Elizabeth; Mulbry, Walter

Submitted to: Journal of Applied Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2002
Publication Date: 12/11/2002
Citation: PIZARRO, C.X., WESTHEAD, E.K., MULBRY III, W.W. NITROGEN AND PHOSPHORUS REMOVAL RATES OF SMALL ALGAL TURFS GROWN ON DAIRY MANURE. JOURNAL OF APPLIED PHYCOLOGY. 2002.

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 test small sections of algal mats using different loading rates of anaerobically digested dairy manure. Algal turfs were grown in a laboratory-scale ATS unit (1 sq. meter) operated by recycling wastewater and adding manure effluents daily. Small subsamples of algal turfs of the same age were removed from the ATS unit and treated with different dilutions of manure containing 5-80 ppm ammonium-N (NH4-N). During the experiments, the pH was maintained between 7-7.5 to prevent ammonia volatilization. The rates we obtained with these small sections of algal mat were 1.4 g of NH4-N and 0.4 g of phosphorus per square meter per day and are equivalent to annual uptake rates of 5133 kg and 1467 kg per hectare for N and P, respectively. Use of the small sections allows us to conduct relatively rapid experiments and to run several experiments at once using similar algal samples. Both of these features will help us test and develop this technology more quickly.

Technical Abstract: Conservation and reuse of nitrogen (N) and phosphorus (P) from animal manure is increasingly important as producers try to minimize transport of these nutrients from farms. An alternative to land spreading is to grow crops of algae on the N and P present in the manure. The specific objective of this study was to evaluate the use of small sub-samples of algal turfs for determining N and P removal rates of attached algae under different loading rates of dairy manure. Algae were grown in a laboratory-scale algal turf scrubber (ATS) operated by recycling wastewater and adding manure effluent daily. Replicate sub-samples (0.032 square meters) of algal turf screens were removed and treated with five different loadings of anaerobically digested dairy manure containing 5 to 80 ppm ammonium-N (NH4-N) and 1 to 20 ppm phosphate-P (PO4-P) over a two hour incubation period. NH4-N removal rates were biphasic with a fast initial rate followed by a slower rate. Biphasic rates were more pronounced for loading rates of 5 and 10 ppm but less so for 20, 40 and 80 ppm NH4-N. PO4-P removal rates were linear throughout the incubation period for all loading rates. N and P removal rates increased with increasing loading rate and biomass. In incubations using 1% dairy manure daily NH4-N and PO4-P removal rates averaged 1.4 and 0.43 g per square meter, respectively.