(399c) Photocatalytic Decomposition of Geosmin and 2-Methylisoborneol by M-InVO4/TiO2 with Visible Light In Recirculating Aquaculture Systems

Geosmin and 2-methylisoborneol (MIB) are odor and taste contaminants often found in drinking water and aquaculture systems.  They are tertiary alcohols produced by several classes of cyanobacteria and actinobacteria.  They have a strong odor which can be detected by humans at concentrations as low as 4-10 ng/L.  In addition, these compounds impart a gamey, off-flavor taste to aquaculture species. Although they are not a direct threat to public health, consumers frequently use smell as a primary indicator of safety. 

Conventional water treatment (coagulation/ flocculation/ sedimentation/ filtration) and chlorination are not effective in the removal of these compounds.  Powdered or granulated activated carbon is generally effective.  However, this usually requires high dosing rates and lose efficacy with increased water turbidity.  Ozonation, although effective in drinking water systems, has several limitations in recirculating aquaculture systems (RAS).  Dissolved organic material present in RAS rapidly depletes ozone, reducing the residual ozone concentration.  Furthermore, ozone residuals may cause gill adhesions and increased mortality rate in fish.  Because of these drawbacks, many aquaculture systems use fresh water purge to reduce geosmin and MIB concentrations.  Purge systems consume large quantities of fresh water and produce significant waste streams. 

Ideally, an effective removal system would balance water consumption, fish mortality, and operating cost.  TiO₂ is an effective photocatalyst for the decomposition of organic compounds.  It is inexpensive, photostable, and chemically and biologically inert. However, only the ultraviolet portion of the solar irradiation (amounting to ~4% of the incoming solar energy on the earth’s surface) is absorbed by TiO₂ due to its high intrinsic band gap (3.2 eV for anatase and 3.0 eV for rutile).  When combined with M-InVO₄, where M is a transition metal, photoinitiation is moved to the visible spectrum range via electron transfer.  In the present study, efficacy of M-InVO₄/TiO₂ is explored for visible-range photocatalytic decomposition of geosmin and MIB in recirculating aquaculture systems.