Growth of benthic freshwater algae on dairy manures

A potential alternative to land application of livestock manures for crop production is the production of algae to recover 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 objective of this research was to evaluate algal turf scrubber (ATS) technology to remove nitrogen, phosphorus and chemical oxygen demand from raw and anaerobically digested dairy manure. Laboratory-scale ATS units were operated by continuously recycling wastewater and adding manure effluents daily. ATS units were seeded with algal consortia from a nearby stream and grown using dairy manures from two different dairy farms. Algal biomass was harvested weekly and dried prior to analysis for total Kjeldahl nitrogen, total phosphorus, and inorganic constituents. Wastewater samples were analyzed for total Kjeldahl nitrogen, ammonium, nitrate, orthophosphate, conductivity and chemical oxygen demand. Using a typical manure input containing 0.6-0.96 a total nitrogen day(-1), the dried algal yield was approximately 5 g m(-2) day(-1). The dried algae contained approximately 1.5-2% phosphorus and 5-7% nitrogen. Algal nitrogen and phosphorus accounted for 42-100% of input ammonium-nitrogen (33-42% of total nitrogen) and 58-100% of input total phosphorus, respectively.