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The biological denitrification (BD) process represents an interesting solution to remove nitrate from water and as well as to close the natural nitrogen cycle. Potential applications are related to both groundwater denitrification and treatment of nitraterich effluents from reverse osmosis and ion-exchange processes. This paper presents the results obtained from a pilot-scale cotton-supported heterotrophic denitrification reactor (HDR) where cotton acts as both organic carbon source and supporting material for the growth of a denitrifier biofilm. A trickling sand filter (TSF) was inserted as post-treatment to remove TOC released by the HDR and to re-oxygenate the treated water. The system is evaluated for drinking water treatment. Nitrate removal efficiency of the HDR was over 90% for 85 mg/l of inlet nitrate concentration which is a mean groundwater value in many EU countries. The process maintained its high performance up to 358 mg of daily nitrate inlet with a maximum specific volumetric ratio of 24.5 gN/m3·d. A first-order kinetic value was shown for sequential nitrate-nitrite and nitrite-nitrogen gas transformations. For that, the kinetic constants of 2.6 l/d (K1) and 15.9 l/d (K2) were assumed. The TSF provided additional nitrification-aerobic denitrification at a rate of 20.7gN/m 3 ·d. Although both reactors showed high performances in terms of nitrogen removal, this plant configuration cannot assure an adequate TOC outlet concentration (>3 mg/l).

Cotton-supported heterotrophic denitrification of nitrate-rich drinking water with a sand filtration post-treatment