Nitrification and denitrification processes for mitigation of nitrous oxide from waste water treatment plants for biovalorization: Challenges and opportunities

Abstract Nitrous oxide (N 2 O) is a potent greenhouse gas. Even though its emissions is much lesser than CO 2 but its global warming potential (GWP) is 298 times more than CO 2 . N 2 O emissions from wastewater treatment plants was caused due to incomplete nitrification or incomplete denitrification catalyzed by ammonia-oxidizing bacteria and heterotrophic denitrifiers. Low dissolved oxygen, high nitrite accumulation, change in optimal pH or temperature, fluctuation in C/N ratio, short solid retention time and non-availability of Cu ions were responsible for higher N 2 O leakage. Regulation of enzyme metabolic pathways involved in N 2 O production and reduction has also been reviewed. Sequential bioreactors, bioscrubbers, membrane biofilters usage have helped microbial nitrification- denitrification processes in succumbing N 2 O production in wastewater treatment plants. Reduction of N 2 O negativity has been studied through its valorization for the formation of value added products such as biopolymers has led to biorefinery approaches as an upcoming mitigation strategy.