Nitrate removal effectiveness of fluidized sulfur-based autotrophic denitrification biofilters for recirculating aquaculture systems

Laura Christianson, Christine Lepine, Scott Tsukuda, Keiko Saito, Steven Summerfelt

Research output: Contribution to journalArticlepeer-review


There is a need to develop practical methods to reduce nitrate-nitrogen loads from recirculating aquaculture systems to facilitate increased food protein production simultaneously with attainment of water quality goals. The most common wastewater denitrification treatment systems utilize methanol-fueled heterotrophs, but sulfur-based autotrophic denitrification may allow a shift away from potentially expensive carbon sources. The objective of this work was to assess the nitrate-reduction potential of fluidized sulfur-based biofilters for treatment of aquaculture wastewater. Three fluidized biofilters (height 3.9m, diameter 0.31m; operational volume 0.206m3) were filled with sulfur particles (0.30mm effective particle size; static bed depth approximately 0.9m) and operated in triplicate mode (Phase I: 37-39% expansion; 3.2-3.3min hydraulic retention time; 860-888L/(m2min) hydraulic loading rate) and independently to achieve a range of hydraulic retention times (Phase II: 42-13% expansion; 3.2-4.8min hydraulic retention time). During Phase I, despite only removing 1.57±0.15 and 1.82±0.32mg NO3-N/L each pass through the biofilter, removal rates were the highest reported for sulfur-based denitrification systems (0.71±0.07 and 0.80±0.15gN removed/(L bioreactor-d)). Lower than expected sulfate production and alkalinity consumption indicated some of the nitrate removal was due to heterotrophic denitrification, and thus denitrification was mixotrophic. Microbial analysis indicated the presence of Thiobacillus denitrificans, a widely known autotrophic denitrifier, in addition to several heterotrophic denitrifiers. Phase II showed that longer retention times tended to result in more nitrate removal and sulfate production, but increasing the retention time through flow rate manipulation may create fluidization challenges for these sulfur particles.

Original languageEnglish (US)
Pages (from-to)10-18
Number of pages9
JournalAquacultural Engineering
StatePublished - Sep 1 2015
Externally publishedYes


  • Autotrophic
  • Denitrification
  • Fluidized biofilter
  • Mixotrophic
  • Recirculating aquaculture
  • Sulfur

ASJC Scopus subject areas

  • Aquatic Science

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