The future plan of sewage plant will be focused on the small-scale sewage facilities designed to treat 1000 to 2000m
3/day. Even if they are small-scaled, the removal of nitrogen and phosphorus is still regarded as critical issues to be solved, because there is not a few case that the treated water is discharged to important water area on environmental preservation or closed water area.
In this study, a new hybrid anaerobic-aerobic filter system for easy maintenance was used for the purpose of the nitrogen removal in a short retention time, and separation and concentration of sludge in a steady performance. The process flow included anaerobic filter → dissolved air flotation → aerobic filter (employing two media filters downflow method in which the upper bed was packed with plastic medium, and the lower bed was packed with anthracite), and the nitrified liquid was circulated to the anaerobic filter. The experiment was carried out with the pilot scale apparatus by using untreated sewage.
To increase the ability of nitrification and denitrification per unit volume, the fluidized bed using medium with a large specific surface area was proved effective. Moreover, high and steady performance in separation and concentration of sludge was achieved even when dissolved air flotation without adding any chemicals was used. In addition, the stability of treatment performance with respect to the change in quantities of the inflow sewage was confirmed.
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