Redirecting methane for a novel biological nitrogen removal process using methanotrophic mixed culture in a sequential batch reactor

Abstract

Wastewater treatment plants (WWTP) are focusing more on water reuse and resources recovery where it is equally important to meet the discharge requirements and recover higher-value resources. Methanotrophs can be employed as a stepping-stone to consolidate such shift in WWTPs’ perspective by exploiting the untapped biogas and dissolved methane generated from anaerobic treatment of sludge and/or wastewater. Methanotrophic sludge can be used in multiple resources recovery processes such as biopolymers and single-cell proteins production. Fortunately, methanotrophs can couple nitrogen removal by methane utilization. Thus, this research investigates methane redirection for methanotrophic-based nitrogen removal enriched from activated sludge. Different phases allowed evaluation of the nitrogen removal capacity of the methanotrophic culture in a sequential batch reactor. When removing ammonium by assimilation, the ammonium removal efficiency (ARE) was 98 ± 1%. Under elevated ammonium concentration and mainstream-like conditions, the ARE was 89 ± 5% and 87 ± 7% and the ammonium conversion to nitrate was 87 ± 11% and 87 ± 7%, respectively. This study is the first to maintain stable nitrate accumulation using methanotrophic mixed cultures. Despite attained in batch experiments, the maintenance of nitrification-denitrification activity using the same sludge found to be challenging. This study successfully demonstrates the potential of using methanotrophic bacteria as an alternative for nitrogen removal.