Aeration and Heating Improve Slow Sand Filtration as a Disinfection System for Closed Hydroponic Systems
Aeration and heating were used to improve the disinfection activity of slow sand filtration of recirculating nutrient solutions in a closed hydroponic system. Filter performance was evaluated under different running conditions using <i>E. coli</i> elimination efficiency as an indicator of filter performance. Aeration with or without heating during filter 'ripening' increased filter performance so much as to obviate differences in performance associated with filtration rate. The filter reduced influent <i>E. coli</i> concentrations by nearly 3 orders of magnitude with aeration. Effluent <i>E. coli</i> concentrations from filters pre-circulated with aeration and heating were over 4 orders of magnitude lower than influent concentrations. Vertical distribution of viable <i>E. coli</i> in an effective slow sand filter which reduced <i>E. coli</i> concentrations from 10<sup>6</sup> cfu ml<sup>-1</sup> to less than 10<sup>2</sup> cfu ml<sup>-1</sup> was mostly in the Schmutzdecke (10<sup>6</sup>∼10<sup>7</sup> cfu g<sup>-1</sup>) and first 10 cm of the surface of the sand layer. High-performance filters did not eliminate <i>Ralstonia solanacearum</i> as effectively as <i>E. coli</i> or the fungal pathogens <i>Fusarium oxysporum</i> and <i>Pythium helicoides</i>.
- Environment control in biology
Environment control in biology 45(3), 179-187, 2007-09-30
Japanese Society of Agricultural, Biological and Environmental Engineers and Scientists