NITROGEN AND PHOSPHORUS REMOVAL RATES WITHIN SUBUNITS OF ALGAL TURF SCRUBBERS GROWN ON DAIRY MANURE

Pizarro, C., Westhead, E. K. & Mulbry, W. Agricultural Research Service, U.S.D.A., Beltsville, MD 20705‐2350 USA 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 different loading rates of anaerobically digested dairy manure on nitrogen removal rates. Algal turfs were grown in a laboratory‐scale ATS unit (1 m 2 ) operated by recycling wastewater and adding manure effluents daily. The most abundant genera of benthic algae in the ATS unit were Ulothrix, Oedegonium and Rhizoclonium. Replicate subsamples (0.04 m 2 ) of algal turfs of the same age were removed from the ATS unit and treated with different loads of manure containing 5–40 mg l ‐1 ammonium‐N (NH 4 ‐N). During the experiments, the pH was maintained between 7–7.5 to prevent ammonia volatilization. Ammonium‐N removal rates were biphasic, with a fast rate of 3.0–4.7 mg‐NH 4 ‐N hr ‐1 g ‐1 DW for the first 20–30 minutes, followed by a slower rate of 0.53–0.96 mg‐NH 4 ‐N hr ‐1 g ‐1 DW for the remainder of the 2 hour incubation period. The initial rates are comparable to laboratory scale ATS units and correspond to calculated removal rates of about 3 g NH 4 ‐N m ‐2 d ‐1 .