February 15-18, 2009 Washington State Convention Center Seattle ...

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IMPACT OF ATTACHED ALGAE, SUSPENDED BACTERIA, AND RE-AERATION ON
OXYGEN AND CARBON DIOIXIDE BALANCES IN SERIES RACEWAYS
John Colt, Barnaby Watten and Michael Rust
National Oceanic and Atmospheric Administration
Northwest Fisheries Science Center
2725 Montlake Blvd. East
Seattle, WA 98112 USA
john.colt@noaa.gov
In the design of raceways, the impact of algae, bacteria, and oxygen transfer is commonly ignored. In lightly loaded single-pass
salmon and trout systems, these processes may not important. Their impact has not been clearly documented in heavy loaded
serial reuse systems that are used in commercial facilities.
The impact of these parameters were evaluated in a 10-pass serial reuse system operated at a cumulative oxygen consumption
of 16.7 mg/L, elevation = 1,500 m, water temperature = 10°C, and water flow = 2,500 lpm. Oxygen consumption of suspended
bacteria was based on a kinetic constant (K 20C ) of 0.10 and a theta value equal to 1.135. The influent BOD 5 was assumed equal
to 2 mg/L and the BOD 5 production rate equal to 50 g/kg feed. The oxygen production and respiration rate of attached algae
were assumed to be 3.0 g oxygen/(m 2 •d) and 0.103 g carbon dioxide/(m 2 •d), respectively. The reaeration coefficient for oxygen
was based on the O’Connor-Dobbins film penetration model. The reaeration coefficients ratio for CO 2 /O 2 was equal to 0.81. A
triangular notch weir was used between raceways with a r 20 = 1.923.
The impact of attached algae, suspended bacteria, re-aeration, and weir aeration on oxygen and carbon dioxide balances are
presented below for the effluent from raceways 1 and 10 for both day and night conditions: Compared to gas transfer across the
air-water interface, the weir is a much more significant mechanism for gas transfer in raceways. During the day, attached algae
is a significant source of oxygen but has little impact at night. Attached algae significantly reduces the CO 2 concentrations during
the day, resulting in reduced metabolic pH depression and elevated un-ionized ammonia concentrations. Field testing and
verification is needed to confirm these findings.
Oxygen Balance in Raceways 1 and 10
Time #
Influent
DO
Fish Algae Bacteria
Re-
Aeration
Effluent
DO
Weir
To Next
Raceway
Day 1 9.456 -1.667 0.664 -0.0185 0.016 8.450 0.508 8.957
10 8.307 -1.667 0.664 -0.0330 0.051 7.332 0.980 8.302
Night 1 9.456 -1.667 -0.0084 -0.0185 0.026 7.855 0.785 8.573
10 7.432 -1.667 -0.0084 -0.0330 0.088 5.812 1.612 7.424
Carbon Dioxide Balance in Raceways 1 and 10
Time #
Influent
CO2 Fish Algae Bacteria
Re-
Aeration
Effluent
CO2 Weir
To Next
Raceway
Day 1 0.746 2.292 -0.9125 0.0254 -0.008 1.407 -0.177 1.285
10 3.479 2.292 -0.9125 0.0454 -0.082 4.504 -1.025 3.539
Night 1 0.746 2.292 0.0116 0.0254 -0.017 2.127 -0.374 1.818
10 5.634 2.292 0.0116 0.0454 -0.147 7.534 -1.856 5.723