Friday, 13 November 2009
An environmentally friendly economical viable pilot scale recirculating mariculture operation consisting of an algae based biofilter system for transforming mariculture wastes into high quality valuable products, thereby providing an incentive for coastal aquaculture systems to recycle the effluents and protect the coastline environment, was developed. Specifically, A 1600 L Black Sea Bass (Centropristis striata) aquaculture re-circulating system with a high fish stocking density was developed and the rate of ammonia removal from the aquaculture water; the amount of non-planktonic algal (cyanobacteria) biomass produced, and the performance of the system as a high density fish operation were assessed. The use of seaweed (gracilaria sp) a potentially commercial product was also investigated as an alternative or to compliment the algae biofilter. The use of biofilter containing algae and/or seaweed maintained consistent water quality (pH, temperature, salinity, ammonia, phosphate, nitrate and dissolved oxygen) in the recirculating system over a two months research period. Like the algae, the seaweed removed most of the nitrite and ammonium from the water, but left behind high levels of phosphate and nitrate, thus signifying a low uptake of those nutrients. It was also found that live Tilapia was an effective feedstock for the growth of the Black Sea Bass. The wastewater from the Tilapia feedstock was recirculated and used to grow organic vegetables, including but not limited to lettuce, herbs, tomatoes and cucumbers in a hydroponic system. The carbohydrates and lipids content of the algae were determined before and after use in the recircilating system. A 75% yield of carbohydrates from the filamentous algae and a 50% yield of carbohydrates from the single-cell algae was obtained. A 3% yield of lipids from the filamentous algae, and a 6% yield of lipids from the single-cell algae was also observed. The production of sugars from the dried algae (with the aid of a solid acid catalyst) and subsequent conversion of the sugars to bioethanol through fermentation, was investigated. Fermentation of the algae was done at 25 degrees C and brewers yeast in a fermentation device. Potential revenue generation from the sale of the fully grown Black Sea Bass, the organic vegetables, the seaweed and the biethanol coupled with the zero or low coastline discharge of environmental contaminants (ammonia etc) from this mariculture operation was assessed for economic viablilty. Details of the technical operations will be presented.
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