Microaerophilic Activated Sludge System for Ammonia Retention toward Recovery from High-Strength Nitrogenous Wastewater: Performance and Microbial Communities

Abstract

A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activated sludge (CAS) with aerobic and settling compartments. Low dissolved oxygen (DO) concentrations (<0.2 mg/L) and short solids retention times (SRTs) (<5 days) eliminated nitrifying bacteria. The two parallel MASs were successfully operated for 300 days and had ammonia retention of 101.7 ± 24.9% and organic carbon removal of 85.5 ± 8.9%. The MASs mitigated N 2 O emissions with an emission factor of <0.23%, much lower than the default value of CAS (1.6%). A short-term step-change test demonstrated that N 2 O indicated the initiation of nitrification and the completion of denitrification in the MAS. The parallel MASs had comparable microbial diversity, promoting organic carbon oxidation while inhibiting ammonia-oxidizing microorganisms (AOMs), as revealed by 16S rRNA gene amplicon sequencing, the quantitative polymerase chain reaction of functional genes, and fluorescence in situ hybridization of β-proteobacteria AOB. The microbial analyses also uncovered that filamentous bacteria were positively correlated with effluent turbidity. Together, controlling DO and SRT achieved organic carbon removal and successful ammonia retention, mainly by suppressing AOM activity. This process represents a new nitrogen management paradigm.

Pilot-Scale Evaluation of Poultryponics: Insights into Nitrogen Utilization and Food Pathogen Dynamics

“…This increase is most likely due to mineralization of organic nitrogen (ammonification) as evidenced by the high influent total nitrogen (TN) compared to inorganic nitrogen concentrations (Table ). The anaerobic conditions in the holding tank likely favored heterotrophs that enzymatically degrade components like urea, free amino acids, and nucleic acids to NH 4 –N. , …”

“…Nitrification is the biological transformation of ammonium nitrogen to nitrite by ammonia oxidizing bacteria (AOB) and subsequently into nitrate by nitrite oxidizing bacteria (NOB) . However, heterotrophs that mineralize ammonium nitrogen from waste effluents with high organic nitrogen loads (such as PPW) often outcompete nitrifying bacteria for oxygen at low dissolved oxygen (DO) concentrations (DO < 0.2 mg L –1 ) due to the latter’s low oxygen affinities compared to heterotrophs …”