Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/18/2001
Publication Date: N/A
Interpretive Summary: An alternative to land spreading of manures is to grow crops of algae on the nitrogen and phosphorus present in the manure. Compared to terrestrial plants, filamentous algae have exceedingly high growth and nutrient uptake rates. Moreover, they are capable of year-round growth in temperate climates, can be harvested on adapted farm-scale equipment, and yield a biomass that should be valuable as an animal feed supplement. The overall goal of this research is to evaluate and develop algal systems for recovering nutrients from animal wastes. The specific objective of these experiments were to test the effects of different loading rates of anaerobically digested dairy manure on nitrogen removal efficiency (by the algae) and nitrate production (an undesired bacterial process) within one type of algal production system (termed algal turf scrubbers or ATS). In laboratory scale ATS units, filamentous algae were grown and tested for their ability to remove nitrogen from dairy manure. In previous experiments using higher loading rates, the algae only used about half of the input nitrogen and bacteria in the system converted the rest of the nitrogen (which was mostly in the form of ammonium) into nitrate. Since the algae don't use nitrate as well as they do ammonium, we wish to minimize this bacterial process. In these experiments, we tested lower loadings of manure and found that algal uptake of nitrogen was improved and nitrate production was not detectable. These results are useful for understanding the dynamic competition of algae and bacteria for nitrogen within this system. As a practical matter, these results will also help in the design and operation of our field scale systems.
Technical Abstract: A potential alternative to land application of livestock manures for crop production is the production of algae to recover the nitrogen (N) and phosphorus (P) present in the manure. The specific objectives of these experiments were to test the effects of different loading rates of anaerobically digested dairy manure on nitrogen removal efficiency and nitrification within algal turf scrubbers (ATS). Laboratory-scale ATS units were operated by continuously recycling 220 liters of wastewater and adding manure effluents daily. The algal turfs contained mixed indigenous assemblages of benthic algae. The most abundant genera were Ulothrix, Oedogonium, and Rhizoclonium. Weekly harvest of algal biomass, and wastewater samples were analyzed for total Kjeldahl nitrogen (TKN), ammonium, nitrate, and elemental composition. In previous experiments with loading rates of 0.6-0.96 g total nitrogen (TN)/ sq. meter-day, algal nitrogen accounted for 42-50 % of input ammonium-nitrogen. Nitrate production accounted for the bulk of remaining input ammonium-nitrogen. Lower loading rates (0.24 and 0.48 g TN/sq. meter-day) tested here showed a higher removal rate where algal nitrogen accounted for 71% of input ammonium-nitrogen (56% of TN), and nitrate production was negligible. The disappearance of ammonium-nitrogen from wastewater in scrubbers measured over 4-5 hours showed initial rates of about 6 mg ammonium-nitrogen/hour-gram DW algae, corresponding to 3.7 g ammonium-nitrogen/sq. meter-day. This was followed by slightly lower rates, probably indicating limitation in carbon and/or micro-nutrients.