Comparison of Partial and Full Nitrification Processes Applied for Treating High-Strength Nitrogen Wastewaters: Microbial Ecology through Nitrous Oxide Production

Abstract

The increasing regulatory demands to achieve greater nutrient removal from wastewater treatment plant effluents, while minimizing infrastructure investments and operating costs, has resulted in the development of several innovative biological nitrogen removal (BNR) processes. Partial nitrification based processes such as the single reactor system for high ammonium removal over nitrite (SHARON 1 ) and its variants are attractive for treating high-strength nitrogen waste streams such as anaerobic digestion reject water or centrate, owing to their reduced consumption of energy (for aeration) and organic carbon (for denitrification). Indeed, separate treatment of centrate via partial nitrification is one of the options for limiting nitrogen discharges to Jamaica Bay in New York City 2 and is part of PlaNYC, a sustainability plan for New York City targeted for 2030.The energy and carbon savings of partial nitrification processes for nitrogen removal are by virtue of restricting ammonia oxidation to nitrite rather than to nitrate. On the other hand, nitrite is a known trigger for nitrous oxide (N 2 O) and nitric oxide (NO) production via nitrification 3,4 and denitrification 5,6 pathways. Full-scale measurements also point to nitrite as a factor in N 2 O production.7,8 Low (but not zero) dissolved oxygen concentrations were initially implicated as a significant factor for N 2 O and NO emissions from nitrification.9-11 However, the production of N 2 O by nitrifying bacteria under aerobic conditions has also been shown. 3,4,12,13 Recent reports suggest that N 2 O and NO emissions by ammonia oxidizing bacteria are related to imbalances in their metabolism and gene-expression patterns. 14,15 Given that the greenhouse impact of N 2 O is about three hundred times that of carbon dioxide 16 and both N 2 O and NO contribute to ozone layer depletion, 17 it needs to be determined whether N-removal processes based on transient nitrite accumulation are systematically greater contributors of N 2 O and NO than full nitrification based processes. The mechanisms of such differential N 2 O production from partial and full-nitrification systems at the microbial level also need to be understood. Therefore, the overarching goal of this study was to compare the microbial ecology, gene expression, biokinetics, and N 2 O emissions from a lab-scale bioreactor operated sequentially in full-nitrification and partial-nitrification modes. It was hypothesized that operation in partial nitrification mode would result in higher N 2 O and NO emissions than operation in full nitrification mode. It was additionally hypothesized that the high emissions of the gases would parallel the sustained elevated expression of the genes coding for their production. ABSTRACT: The goal of this study was to compare the microbial ecology, gene expression, biokinetics, and N 2 O emissions from a lab-scale bioreactor operated sequentially in full-nitrification and partial-nitrification modes. Based on sequencing of 16S rRNA and ammonia monooxygenase subunit A (amoA) g...

Distribution of Human-Specific Bacteroidales and Fecal Indicator Bacteria in an Urban Watershed Impacted by Sewage Pollution, Determined Using RNA- and DNA-Based Quantitative PCR Assays

“…The application of rRNA-based assays to detect active bacteria has proven useful in several studies (18)(19)(20)(21). In a previous study, we demonstrated that the detection frequency of rRNA-based assays were in better agreement with the culture based detection of E. coli and enterococci in surface waters than that of rRNA genebased assays, suggesting that rRNA signals were associated to active bacterial populations (27).…”

“…These results demonstrate that targeting rRNA via RT-qPCR may provide up to 1,000-fold greater sensitivity over corresponding rRNA gene targets. Indeed, the higher sensitivity of RT-qPCR technique compared to qPCR have been reported for quantification of bacteria in natural and engineered systems such as human gut (28), marine sediments and grasslands (50,51), environmental waters (27), and activated sludge processes (21,52). Thus, in our study, the increased detection of fecal bacteria markers via rRNA-based signals suggests that RT-qPCR assays may be better suited for tracking and quantifying active fecal bacteria in environmental waters when the targeted groups are present at relatively low levels.…”

“…However, one disadvantage of RNA based detection is that it may be difficult to equate rRNA copy numbers to actual cell densities due to the strong correlation of rRNA expression with physiological state of the cell. RNA-based reverse transcription-qPCR (RTqPCR) assays have been utilized in a number of microbiological studies, such as the detection of bacterial contamination in blood (19), subdominant bacteria in human intestines (20), and assessment of nitrification in wastewater treatment (21).…”

The Effect of Influent Characteristics and Operational Conditions over the Performance and Microbial Community Structure of Partial Nitritation Reactors

“…The different characteristics of AOB and NOB have been studied in order to develop strategies for NOB control in partial nitritation systems. These are based on temperature, dissolved oxygen, hydraulic retention time (HRT) and solid retention time (SRT), or free ammonia (FA) and free nitrous acid (FNA) concentrations, among others [14,24,35,36]. When 50% ammonium is oxidized under steady-state conditions, partial nitritation reactors have a relative abundance of 64% AOB and less than 5% NOB [37].…”

Identification of nitrous oxide emissions from green areas of Chihuahua City irrigated with treated wastewater

“…Higher nitrous oxide concentrations in the samples were located at the root zone in all the lysimeters. An example of the results from lysimeter 3 (L3), watered with a nitrogen fertilizer solution, is shown in Table 2 ( Ahn et al, 2011).…”