|DAVIDSON, JOHN - Freshwater Institute|
|GOOD, CHRISTOPHER - Freshwater Institute|
|WELSH, CARLA - Freshwater Institute|
|SUMMERFELT, STEVEN - Freshwater Institute|
Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2011
Publication Date: 5/1/2011
Citation: Davidson, J., Good, C., Welsh, C., Summerfelt, S.T. 2011. The effects of ozone and water exchange rates on water quality and rainbow trout Oncorhynchus mykiss performance in replicated water recirculating systems. Aquacultural Engineering. 3:44:80-96.
Interpretive Summary: Fish culture systems that recirculate water allow greater control of the rearing environment, especially water temperature, minimize water use, and place wastes into a concentrated and relatively small volume effluent that is easier to treat. Scientists at The Conservation Fund's Freshwater Institute (Shepherdstown, WV) conducted three studies using six replicated systems that were either operated with and without ozone at various water exchange rates. The purpose was to determine if either ozonation of the recirculating water or a 10-fold difference in flushing rate would significantly improve water quality and fish performance and welfare. Results indicate that ozonation of recirculating water significantly reduced TSS, BOD, Cu, Fe, and color. Water quality within ozonated low exchange systems was similar to systems operated with 10-times more flushing. Fish grew significantly better within ozonated systems, compared to non-ozonated systems. Fish grew as well within ozonated systems as in non-ozonated systems operated with 10-times more flushing. These findings have identified processes to improve water quality control and fish growth and survival in production systems that must operate in environments where water use is restricted due to water availability or pollution abatement requirements. This accomplishment aligns with the NP 106 Aquaculture Program Components: Aquaculture Production Systems (Production Intensity) and Sustainability and Environmental Compatibility of Aquaculture (Water Use & Reuse).
Technical Abstract: Rainbow trout Oncorhynchus mykiss performance and water quality were evaluated and compared within six replicated 9.5 cubic meter water recirculating aquaculture systems (WRAS) operated with and without ozone at various water exchange rates. Three separate studies were conducted: 1) low water exchange (0.26% of the total recycle flow) with and without ozone; 2) low water exchange with ozone versus high water exchange (2.6% of the total recycle flow) without ozone; and 3) near-zero water exchange (only backwash replacement) with and without ozone. Mean feed loading rates for WRAS operated at high, low, and near-zero exchange were 0.40, 3.98, and 55.9 kilogram feed per cubic meter make-up water, respectively. Ozone significantly reduced total suspended solids, color, and biochemical oxygen demand and resulted in a significant increase in ultraviolet transmittance (%) (P < 0.10). Ozone also created ambient water quality within low exchange WRAS that was comparable to that of WRAS operated at high water exchange (P > 0.10). Additionally, dissolved copper and iron were significantly lower within WRAS operated with ozone (P < 0.10). Dissolved zinc was also consistently lower in WRAS operated with ozone, but not significantly (P > 0.10). In studies 1 and 3, total ammonia nitrogen and nitrite nitrogen were slightly lower within the ozonated systems, but were not always significantly lower. In all studies, ozone did not prevent nitrate nitrogen accumulation. At the conclusion of Study 1, rainbow trout growth was significantly greater within low exchange WRAS operated with ozone (P = 0.001). At the conclusion of Study 2, rainbow trout growth was similar between treatments (P = 0.581), indicating that fish grew equally as well within ozonated WRAS operated at 1/10th the flushing rate as the non-ozonated and high flushing control systems. Overall, ozone created an improved water quality environment within low and near-zero exchange WRAS that generally resulted in enhanced rainbow trout growth rates, survival, feed conversion, and condition factor.