Biology subjects

Sabba, F.

Publications and source records attributed to Sabba, F..

3 recordsLinked to original sources

bioRxiv2024

Nitrous oxide production, mechanisms, and modeling from a denitrifying phosphorus removal bioreactor

Nitrous oxide (N2O) is a potent greenhouse gas produced as an unintentional, undesired byproduct in many nitrogen removal bioprocesses. Given the considerable challenges in managing N2O emissions from wastewater treatment, N2O could be reframed as a value-added product if intentionally generated and captured. This study assesses N2O production and mechanisms in a Coupled Aerobic-anoxic Nitrous Decomposition Operation with Phosphorus removal (CANDO+P) reactor. Optimal performance was achieved when the reactor was fed with a mixture of propionate and glucose, resulting in N2O was production up to 50% of influent nitrogen. Through 16S rRNA amplicon and shotgun metagenomic sequencing, we found that Candidatus Accumulibacter were the dominant phosphorus accumulating organism (PAO). Assembly of a high-quality metagenome-assembled genome showed that Ca. Accumulibacter encoded a full complete denitrification pathway from nitrite to nitrogen gas. We also found abundant populations of denitrifying glycogen accumulating organisms (GAO) and ordinary heterotrophic organisms (OHO). We also incorporated truncated denitrification pathways into a process model to predict N2O generation. N2O predictions were the most similar to observed results when the denitrification pathways of PAO, GAO, and OHO model populations reflected denitrification gene abundances from the metagenomic sequencing analysis. Our work demonstrates the feasibility of using non-VFA carbon for intentional N2O generation and provides broader insights into N2O generation and truncated denitrification pathways of denitrifying PAO and GAO.

microbiology↗

bioRxiv2019

Integrated Low-Energy and Low Carbon Shortcut Nitrogen removal with Biological Phosphorus Removal for Sustainable Mainstream Wastewater Treatment

While enhanced biological phosphorus removal (EBPR) is widely utilized for phosphorus (P) removal from wastewater, understanding of efficient process alternatives that allow combined biological P removal and shortcut nitrogen (N) removal, such as nitritation-denitritation, is limited. Here, we demonstrate efficient and reliable combined total N, P, and chemical oxygen demand removal (70%, 83%, and 81%, respectively) in a sequencing batch reactor (SBR) treating real mainstream wastewater (primary effluent) at 20{degrees}C. Anaerobic - aerobic cycling (with intermittent oxic/anoxic periods during aeration) was used to achieve consistent removal rates, nitrite oxidizing organism (NOO) suppression, and high effluent quality. Importantly, high resolution process monitoring coupled to ex situ batch activity assays demonstrated that robust biological P removal was coupled to energy and carbon efficient nitritation-denitritation, not simultaneous nitrification-denitrification, for the last >400 days of 531 total days of operation. Nitrous oxide emissions of 2.2% relative to the influent TKN (or 5.2% relative to total inorganic nitrogen removal) were similar to those measured in other shortcut N bioprocesses. No exogenous chemicals were needed to achieve consistent process stability and high removal rates in the face of frequent wet weather flows and highly variable influent concentrations. Process modeling reproduced the performance observed in the SBR and confirmed that nitrite drawdown via denitritation contributed to suppression of NOO activity.

bioengineering↗

bioRxiv2018

Comammox Nitrospira are the dominant ammonia oxidizers in a mainstream low dissolved oxygen nitrification reactor

Recent findings show that a subset of bacteria affiliated with Nitrospira, a genus known for its importance in nitrite oxidation for biological nutrient removal applications, are capable of complete ammonia oxidation (comammox) to nitrate. Early reports suggested that they were absent or present in low abundance in most activated sludge processes, and thus likely functionally irrelevant. Here we show the accumulation of comammox Nitrospira in a nitrifying sequencing batch reactor operated at low dissolved oxygen (DO) concentrations. Actual mainstream wastewater was used as influent after primary settling and an upstream pre-treatment process for carbon and phosphorus removal. The ammonia removal rate was stable and exceeded that of the treatment plants parallel full-scale high DO nitrifying activated sludge reactor. 16S rRNA sequencing showed a steady accumulation of Nitrospira to 53% total abundance and a decline in conventional ammonia oxidizing bacteria to <1% total abundance over 400+ days of operation. After ruling out other known ammonia oxidizers, qPCR confirmed the accumulation of comammox Nitrospira beginning around day 200, to eventually comprise 94% of all detected amoA and 4% of total bacteria by day 407. Quantitative fluorescence in-situ hybridization confirmed the increasing trend and high relative abundance of Nitrospira. These results demonstrate that comammox can be metabolically relevant to nitrogen transformation in wastewater treatment, and can even dominate the ammonia oxidizing community. Our results suggest that comammox may be an important functional group in energy efficient nitrification systems designed to operate at low DO levels.

bioengineering↗