Methanotrophic denitrification of anaerobic effluent was evaluated in an up-flow fixed structured bed reactor (Up-FSBR), using polyurethane foam as support media. Methane was provided as the sole electron donor and carbon source to the Up-FSBR, fed with synthetic medium mimicking nitrified sewage pre-treated anaerobically and operated without temperature control or previous medium sterilization.. Anaerobic post-treatment with methanotrophic denitrification in tropical areas

Background: The use of methane as electron donor for denitrification addresses nitrogen removal in anaerobic effluents and can help to abate greenhouse gas emissions from wastewater treatment plants. However, applicable rates of methanotrophic denitrification were only reached under temperature controlled conditions, and in membrane bioreactors, which are not widely available in low-income countries. In this study, polyurethane foam was used as support media to an up-flow fixed structured bed reactor (Up-FSBR). Methane was provided as the sole electron donor and carbon source to the Up-FSBR, fed with synthetic medium mimicking nitrified sewage pre-treated anaerobically and operated without temperature control or previous medium sterilization.Results: The denitrification rate was 17.8 ± 13.6 mg N.day-1 and the average efficiency was 17.0 ± 15.1%, having reached 67.7%. Data dispersion is linked to the operation conditions, such as temperature variation that ranged up to 18oC in a 24 h period. The temperature variation caused a swallow in the metallic valves used in the methane input device, leading to a high fluctuation in methane availability and bubble size, influencing gas-liquid transfer. 16S rDNA sequencing revealed a complex interplay among aerobic methane oxidizers (10.8% of relative abundance), non-methanotrophic methylotrophs (7.0% RA), heterotrophic denitrifiers (14.3% RA), and microorganisms affiliated with the archaeal Methanosarcinales (13.2%). Conclusions: The Up-FSBR is a promising alternative for methanotrophic denitrification. The operation challenges are linked with methane input rather than with the reactor configuration. The Up-FSBR was efficient in selecting a microbial community that is capable of performing methane oxidation and heterotrophic denitrification.