Removal of nitrate in aquaria by means of electrochemically generated hydrogen gas as electron donor for biological denitrification

A hydrogenotrophic denitrification reactor was designed for the removal of nitrate from aquaria. An average hydrogen gas transfer up to 130 mg per day from the gas to the water phase was accomplished by recirculating the water from the denitrification reactor over a separate trickling filter column with a volume of 1.3 l. During batch experiments removal rates up to 36 mg N/l reactor per day were recorded at a hydraulic residence time of 12 h. To avoid the need for storage of large volumes of hydrogen gas in aquarium or aquaculture applications, an electrochemical cell was used to generate hydrogen gas. During a 7 day aquarium test, a nitrate removal rate up to 18.5 mg N/l reactor per day was recorded at an influent NO3−–N concentration of 20 mg/l.