Journal of Applied Phycology 13: 301–306, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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Growth of benthic freshwater algae on dairy manures Walter W. Mulbry1∗ & Ann C. Wilkie2 1 United
States Department of Agriculture, Agricultural Research Service, Soil Microbial Systems Laboratory, Building 001 Room 140 Beltsville Agricultural Research Center-West, 10,300 Baltimore Avenue, Beltsville, MD 20705, USA 2 Soil and Water Science Department, P.O. Box 110960, University of Florida, Gainesville, Florida 32611-0960, USA (∗ Author for correspondence; phone 301-504-6417; fax 301-504-8370; e-mail
[email protected]) Received 24 January 2001; revised 27 February 2001; accepted 27 February 2001
Key words: algal turf scrubber, benthic algae, dairy manure, nitrogen, phosphorus
Abstract 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 g 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. Abbreviations: ATS – algal turf scrubbing (or algal turf scrubber); DRU – Dairy Research Unit; USDA – U.S. Department of Agriculture; UF – University of Florida
Introduction Conservation and reuse of nitrogen (N) and phosphorus (P) from animal manures is increasingly important as producers try to minimize transport of these nutrients off-farm. However, the current practice of land-spreading manures is limited in its effectiveness for the following reasons: 1. the application window is relatively short during the growing season; 2. large amounts of N are lost during manure storage and spreading;
3. large areas are generally needed to spread these manures (which increases the likelihood of offsite nutrient transport by volatilization, runoff and leaching). An alternative to land spreading is to grow crops of algae on the N and P present in the manure. There is considerable literature on the treatment of municipal wastewater in high rate ponds (Nurdogan & Oswald, 1995) and on the treatment of swine and dairy manures by particular algal genera, such as Spirulina (Arthrospira), Phormidium, Chlorella and Scenedesmus (Blier
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Figure 1. Diagram of laboratory-scale algal turf scrubber (adapted from Adey & Loveland, 1998). ATS effluent is continuously pumped into the wave surge bucket from a plastic drum below (not shown). The bucket fills, tips over approximately every 15 s, and the effluent washes over the turf screen before draining into the drum below to be recycled. Water depth over the mesh is 1–2 cm. A metal halide lamp is located approximately 42 cm above the growing turf.
et al., 1996; Lincoln et al., 1996; Olguin et al., 1997). The use of benthic algae for wastewater treatment is less characterized, but such systems have a number of potential advantages over suspended algal systems (Hoffmann, 1998). The purpose of this study was to assess the ability of one benthic algal production technology, termed algal turf scrubbing (ATS), to recover nutrients from three types of dairy manure wastes. ATS technology was first developed by Adey and coworkers to purify water for microcosm research on shallow water reefs (Adey & Hackney, 1989). Algal turfs, short mats of benthic algal filaments, vary widely in species composition depending on water quality (Adey & Hackney, 1989; Adey et al., 1993; Adey & Loveland, 1998), but despite this variation are uniformly capable of high sustainable production rates if harvested often. The essential elements of the ATS system are a solid support for the growth and harvest of benthic algae, wave surge, and optimal light (Figure 1). Turf algae are typically grown on polyethylene mesh in laboratory-scale ATS units and on nylon netting on pilot and field-scale scrubbers. Frequent wave surge created by a dumping bucket prevents development of boundary layers that limit nutrient and metabolite exchange, as well as preventing light shielding of interior portions of the algal turf (Adey & Loveland, 1998). Small-scale algal scrubbers are used in aquaria, in a variety of mesocosms, and for the commercial production of coral reef organisms (Adey & Loveland, 1998). Large-scale scrubbers are in commercial use for treating wastewater generated by Tilapia aquaculture operations (Adey & Loveland, 1998). The ATS
scrubs the water of nitrogen and phosphorus to levels suitable for reuse and generates algal biomass that is fed back to the fish. Adey and coworkers have also conducted research on the use of the ATS system for P removal from agricultural runoff (Adey et al., 1993), the remediation of trichloroethylene contaminated groundwater (Adey et al., 1996) and for N and P removal in tertiary treatment of municipal wastewater (Craggs et al., 1996a). Our overall research goals are to adapt and evaluate the ATS system to remove N, P, and other constituents from different dairy manures, and in the process conserve these elements in an algal biomass that can be used as a feed supplement or other high value product. The specific objectives of this study were to evaluate algal growth and determine nutrient balances using raw and anaerobically digested manure from two different types of dairy operations.
Materials and methods Dairy manure Three dairy manure wastes were used in this study. Two of the manure wastes used were the solidsseparated anaerobic digester influent (undigested manure) and anaerobic digester effluent (digested manure) collected from the Dairy Research Unit (DRU) of the USDA facility in Beltsville, Maryland (USDA) and stored at 4 ◦ C prior to use. Anaerobically digested manure was collected from the University of Florida’s DRU in Gainesville, Florida (UF), shipped overnight to Maryland, and stored at 4 ◦ C prior to use. The manures from the USDA and UF facilities differ significantly (Table 1) because the USDA DRU uses a scrape system for cleaning the barns while the UF DRU uses a flush system (Wilkie et al., 1995; Wilkie, 2000). The USDA and UF DRUs also use different types of animal bedding (sawdust and sand, respectively). In both systems, the manures are subjected to a solids separation step followed by anaerobic digestion of the separated liquids. Because of the differences in dilution, the USDA digested manure has a 10–11-fold higher content of N and P compared to the UF digested manure. However, the TN/TP ratios of both digested manures are similar (ca 10). The USDA undigested manure has a much lower TN/TP ratio (ca 4) compared to that of digested manure because of significant precipitation of P with solids during anaerobic digestion.
303 Table 1. Characteristics of manures used in this study
USDA undigested USDA digested UF digested
NH4 -N (mg L−1 )
Organic-N (mg L−1 )
NO3 -N (mg L−1 )
TN (mg L−1 )
TP (mg L−1 )
Conductivity (mS cm−1 )
COD (mg L−1 )
N:P ratio
306 1620 178
904 751 47
