Scholarly
    Communications Project


Document Type:Master's Thesis
Name:Jennifer Brooke Phillips
Email address:jephill2@vt.edu
URN:1998/00019
Title:Denitrification of Recirculating Aquaculture System Waters Using an Upflow Biofilter and a Fermented Substrate
Degree:Master of Science
Department:Environmental Engineering
Committee Chair: Dr. Nancy Love
Chair's email:nlove@vt.edu
Committee Members:Dr. Gregory Boardman
Dr. George Libey
Dr. John Novak
Keywords:aquaculture, denitrification, biofiltration, fermentation
Date of defense:December 17, 1997
Availability:Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.

Abstract:

The ability of an upflow, denitrifying biofilter using a fermentation generated carbon source to treat the high nitrate concentrations typically seen in recirculating aquaculture systems was studied using a synthetic nitrate wastewater supplied at two nitrate loadings, 1.13 and 2.52 kg NO3-N/m3/day. A supplemental carbon source was provided primarily through the fermentation of fish food which generated volatile fatty acids (VFA) in the form of acetic, propionic, isobutyric, n-butyric, 2-methylbutyric, 3-methylbutyric, and n-valeric acids. Acetic and propionic acids were the predominant constituents generated, while lower concentrations of the longer carbon chain butyric and valeric acids were produced. The VFAs proved to be a viable carbon source for the denitrification process as indicated by the ability of the biofilm to assimilate all of the constituents generated. Carbon limiting the system resulted in an increase in effluent nitrite and incomplete nitrate removal. During the low nitrate loading condition, influent COD to NO3-N ratios greater than 5 typically achieved high total nitrogen removals greater than 95%. This influent ratio corresponded with a COD to NOx -N consumption ratio of 4.62 0.28 mg/L as COD per mg/L as N for complete nitrogen removal. Under the high nitrate loading condition, influent COD to NO3-N ratios achieving high nitrogen removals showed great variability and did not correspond to a distinct value. The COD to NOx -N consumption ratios were often below stoichiometric values, which was attributed to the hydrolysis of influent fermentation solids captured within the column to generate a COD source not measured by filtered samples. The column biofilm kinetics were modeled using a half-order reaction rate and denitrification coefficients (k) of 0.70 0.02 (mg NOx-N/L)1/2 / min and 1.18 0.12 (NOx-N /L)1/2 / min were determined for the low and high nitrate loading phases, respectively.

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