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Recirculating aquaculture system integration of bivalve culture for effluent nutrient composition reduction

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Amanda R. Myers (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Ami Wilbur

Abstract: Closed recirculating aquaculture systems (RAS) are a technological innovation that reduces the amount of water needed for culture by treating and reusing up to 90% of the total water volume daily. Such systems consequently produce substantially smaller volumes of effluent, though it is enriched in nutrients relative to effluent from flow-through or open systems. For RAS to emerge as a viable culture strategy, an economical and efficient method must be developed to reduce effluent nutrient concentrations before discharge. As part of a larger project evaluating biofilter effects on RAS effluent, this study focused on the effect of bivalve culture on the composition of southern flounder RAS effluent. This system produces 1270 L/day of effluent, with nutrient and suspended solids concentrations 20-100x that of ambient levels. Two trials were conducted using this effluent as a nutrient base for bivalves stocked in an upwelling system for four weeks. Trial I utilized raw effluent nutrients for two densities of oysters (Crassostrea virginica, (average shell height ± standard error = 63.4 ± 1.7 mm). Trial II utilized effluent inoculated with microalgae, Isochrysis galbana, as the nutrient base for two densities of clams (Mercenaria mercenaria, average shell height ± standard error = 16.7 ± 0.2 mm). Effluent nutrient composition (total nitrogen, total phosphorus, and total suspended solids) was analyzed from samples (collected twice weekly) taken before and after bivalve filtration. Change in shell height was quantified by measuring subsamples at the start and end of each trial. Oysters did not have a significant impact (Wilcoxon-Mann-Whitney Test, p>0.05) on the RAS effluent nutrient compositions in this flow-through integrated system. Clams, also, did not have a significant impact (Wilcoxon-Mann-Whitney Test, p>0.05) on the RAS effluent nutrient compositions. Significant change in shell height was not exhibited in the oysters (Wilcoxon- Mann-Whitney and Welch-ANOVA Tests, p>0.05) over the time course of Trial I. Over the course of Trial II, a significant change in shell height was exhibited within treatments (Low: p=0.01, High: p=0.049) and between clam densities (p=0.01). The magnitude of seawater dilution, high flow rates, and high suspended solids loads may have inhibited my detection of effluent composition reductions.

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Aquaculture--Water-supply, Bivalve culture, Bivalve culture--By-products, Bivalve culture--Waste disposal, Marine biotechnology, Sewage--Purification--Nutrient removal, Water--Purification--Biological treatment, Water reuse
Aquaculture -- Water-supply
Water reuse
Bivalve culture
Water -- Purification -- Biological treatment
Sewage -- Purification -- Nutrient removal
Bivalve culture -- Waste disposal
Bivalve culture -- By-products
Marine biotechnology