High-rate denitrification using polyethylene glycol gel carriers entrapping heterotrophic denitrifying bacteria

This study evaluated the nitrogen removal performance of polyethylene glycol (PEG) gel carriers containing entrapped heterotrophic denitrifying bacteria. A laboratory-scale denitrification reactor was operated for treatment of synthetic nitrate wastewater. The nitrogen removal activity gradually increased in continuous feed experiments, reaching 4.4 kg N m^-3 d^-1 on day 16 (30 °C). A maximum nitrogen removal rate of 5.1 kg N m^-3 d^-1 was observed. A high nitrogen removal efficiency of 92% on average was observed at a high loading rate. In batch experiments, the denitrifying gel carriers were characterized by temperature. Nitrate and total nitrogen removal activities both increased with increasing temperature, reaching a maximum at 37 and 43 °C, respectively. Apparent activation energies for nitrate and nitrite reduction were 52.1 and 71.9 kJ mol^-1, respectively. Clone library analysis performed on the basis of the 16S rRNA gene revealed that Hyphomicrobium was mainly involved in denitrification in the methanol-fed denitrification reactors.