Glycerol-driven Denitratation: Process Kinetics, Microbial Ecology, and Operational Controls

Abstract

Denitratation, the selective reduction of nitrate to nitrite, is a novel process when coupled with anaerobic ammonium oxidation (anammox) could achieve resource-efficient biological nitrogen removal of ammonium- and nitrate-laden waste streams. Using a fundamentally-based, first principles approach, this study optimized a stoichiometrically-limited, glycerol-driven denitratation process and characterized mechanisms supporting nitrite accumulation with results that aligned with expectations. Glycerol supported selective nitrate reduction to nitrite and near-complete nitrate conversion, indicating its viability in a denitratation system. Glycerol-supported specific rates of nitrate reduction (135.3 mg-N/g-VSS/h) were at least one order of magnitude greater than specific rates of nitrite reduction (14.9 mg-N/g-VSS/h), potentially resulting in transient nitrite accumulation and indicating glycerol's superiority over other organic carbon sources in denitratation systems. pH and ORP inflection points in nitrogen transformation assays corresponded to maximum nitrite accumulation, indicating operational setpoints to prevent further nitrite reduction. Denitratation conditions supported enrichment of Thauera sp. as the dominant genus. Stoichiometric limitation of influent organic carbon, coupled with differential nitrate and nitrite reduction kinetics, optimized operational controls, and a distinctively enriched microbial ecology, was identified as causal in glycerol-driven denitratation.

Mainstream partial denitrification‐anammox in sand and expanded clay deep‐bed polishing filters under practical loading rates and backwashing conditions

“…However, both filters confirmed selection of known PdN‐related genera. Thauera , one of the most commonly reported genera in PdNA systems, was identified to be responsible for nitrite accumulation (Baideme et al, 2021; Cao et al, 2019; Chen et al, 2021); thus, it might have contributed to PdNA in the filters. The relative abundance of Thauera was not significantly different in both filters ( p = 0.39) (Figure 3).…”

Metagenomic assessment of nitrate-contaminated mine wastewaters and optimization of complete denitrification by indigenous enriched bacteria

“…The cultures containing NO 2 − and glucose as sole N-and C-sources, respectively, also demonstrated the gradual removal of NO 2 − from 2,500 mg/L to 548 mg/L (78% removal), which concurs with reports made by Yao et al (2020) that denitrifiers can reduce NO 2 − directly and not as a biogenic product of NO 3 − reduction. In denitrification studies in which glycerol was used as a cheaper carbon source from the biodiesel production plant, NO 2 − accumulated as a terminal byproduct of the denitrification process (Baideme et al, 2017), and for further removal of NO 2 − by denitrification, C/N ration was readjusted to circumvent NO 2 − accumulation from 1.8 to 3.5, as was performed in studies conducted by Carneiro and Foresti (2017) when running up-flow bioreactors with glycerol as a sole C-source. Biochemical utilization of the three carbon (glycerol) and six carbon (glucose) molecules as energy sources depends on the bacteria using them for denitrification and their energy demands as the two molecules get biodegraded at different rates.…”