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Title: RECOVERY OF DAIRY MANURE NUTRIENTS BY BENTHIC FRESHWATER ALGAE

Author
item WILKIE, ANN - SOIL & WATER DEPT/U OF FL
item Mulbry, Walter

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2001
Publication Date: 8/15/2002
Citation: WILKIE, A., MULBRY III, W.W. RECOVERY OF DAIRY MANURE NUTRIENTS BY BENTHIC FRESHWATER ALGAE. BIORESOURCE TECHNOLOGY. 2002.

Interpretive Summary: The vulnerability of ecosystems and groundwater to pollution has forced increasingly stringent environmental regulations to be placed on dairy farms. A current Best Management Practice is for the waste stream to be held in a storage pond before being applied to croplands and/or hay fields. However, in many cases, dairies have to resort to more intensive cropping in order to meet the nitrogen and phosphorus removal requirements. Harnessing the solar energy to grow algal biomass on wastewater nutrients could provide a holistic solution to nutrient management problems on existing dairy farms. An algal treatment system concentrates nutrients in algal biomass by cultivating algae in engineered ponds or raceways, increasing the value and manageability of the nutrients. The objective of this research was to evaluate the use of laboratory-scale benthic algae growth chambers (BAGCs) to recover N and P from raw and anaerobically digested dairy manure. BAGCs containing using natural mixtures of algae were operated by continuously recycling wastewater and adding manure effluent daily. Algal biomass was harvested weekly and dried prior to analysis for total nitrogen, total phosphorus, and inorganic constituents. Nutrient balance results show that most of the manure nitrogen, and nearly all of the manure phosphorus, was taken up by the algae. In the best case, algal biomass had a crude protein content of 44%. At a dry matter yield of 5.53 g/ sq.meter-day, this is equivalent to an annual N uptake rate of 1430 kg/ ha-year. Compared to a conventional corn/rye rotation, such benthic algae production rates would require 26% of the land area requirements for equivalent N-uptake rates and 23% of the land area requirements on a P-uptake basis.

Technical Abstract: The objective of this research was to evaluate the use of benthic algae growth chambers (BAGCs) to recover N and P from raw and anaerobically digested dairy manure. The BAGCs were seeded with algal consortia using water from a nearby stream. Benthic algae was initially established on 0.93 sq.meter screens of black polyethylene mesh at 22 C, illuminated with 175 W metal halide lights at a 16-hour photo period, and a flow rate of 110 L/min. Diluted waste in a 220 L plastic drum was recirculated by a submersible pump and flowed across a tipping bucket onto the screen prior to returning to the drums. BAGCs were operated in semi-batch mode by continuously recycling wastewater and adding manure effluent daily. Algal biomass was harvested weekly and dried prior to analysis for total Kjeldahl nitrogen (TKN), total phosphorus (TP), and inorganic constituents. Wastewater samples were analyzed for TKN, ammonia/ammonium, nitrate, soluble reactive phosphate, conductivity, and chemical oxygen demand. Using total nitrogen (TN) loading rates of 0.64-1.03 g/ sq. meter-day, the dried algal yield was 5.3-5.5 g/ sq. meter-day. The dried algae contained 1.5-2.1 % P and 4.9-7.1 % N. At a TN loading rate of 1.03 g/ sq. meter-day, algal biomass contained 7.1 % N compared to only 5.0 % N at a TN loading rate of 0.64 g /sq. meter-day. In the best case, algal biomass had a crude protein content of 44%. At a dry matter yield of 5.53 g /sq. meter-day, this is equivalent to an annual N uptake rate of 1430 kg /ha-year. Compared to a conventional corn/rye rotation, such benthic algae production rates would require 26% of the land area requirements for equivalent N-uptake rates and 23% of the land area requirements on a P-uptake basis.