Minimization of nitrous oxide emission in a pilot-scale oxidation ditch: Generation, spatial variation and microbial interpretation (original) (raw)
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Chemosphere, 2018
Ammonia-oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and NO-reducing denitrifiers were measured by quantitative real-time PCR (qPCR) in activated sludge samples from four full-scale wastewater treatment plants (WWTPs) in South Spain, and their abundances were linked to the generation of NO in the samples using multivariate analysis (Non-metric multidimensional scaling, MDS, and BIO-ENV). The average abundances of AOA remained in similar orders of magnitude in all WWTPs (10copies amoA/L activated sludge mixed liquor), while significant differences were detected for AOB (10-10copies amoA/L) and NO-reducers (10-10copies nosZ/L). Average NO emissions measured in activated sludge samples ranged from 0.10 ± 0.05 to 6.49 ± 8.89 mg NO-N/h/L activated sludge, and were strongly correlated with increased abundances of AOB and lower counts of NO-reducers. A significant contribution of AOA to NO generation was unlikely, since their abundance correlated negatively to NO emissions. AO...
Environmental Science & Technology, 2011
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.
Journal of water process engineering, 2020
Low dissolved oxygen operation has been adopted by water resource recovery facilities to reduce operating costs of activated sludge processes. However, the effects of low dissolved oxygen setpoint in aeration tanks on nitrous oxide emission and microbial community have rarely been addressed at full-scale activated sludge systems. This study for the first time monitored nitrous oxide emission as an anoxic/aerobic membrane bioreactor facility decreased dissolved oxygen setpoint gradually from 3.5 to 0.5 mg/L. Low dissolved oxygen operation retained efficient ammonia removal and increased total nitrogen removal efficiency from 21.4% to 50.1%. Nitrous oxide emission decreased from 0.65% to 0.15% of total nitrogen removal due to uninhibited last stage of heterotrophic denitrification and one-step nitrification. Low dissolved oxygen operation is hence an energy-saving strategy that promotes climate-friendly, efficient biological nitrogen removal. Moreover, this study diagnosed microbial communities in anoxic/aerobic membrane bioreactors of another full-scale plant which had been operated efficiently for years at an ultra-low dissolved oxygen level (0.2 mg/L). Microbial community was similar in all the bioreactors and simultaneous nitrification and denitrification was the main mechanism of nitrogen removal. Nitrospira, which may include complete ammonia oxidizing bacteria, was the only genus of autotrophic nitrifying bacteria. Simultaneous nitrification and denitrification and one-step nitrification by comammox bacteria in low dissolved oxygen operation led to low nitrite concentration and less nitrous oxide emissions from both anoxic and aeration tanks.
Journal of Bioscience and Bioengineering, 2014
Nitrous oxide (N 2 O) production and expression of genes capable of its reduction were investigated in two full-scale parallel plug-flow activated sludge systems. These two systems continuously received wastewater with the same constituents, but operated under distinct nitrification efficiencies due to mixed liquor suspended solid (MLSS) concentration and the different hydraulic retention times (HRTs). A shorter HRT in system 2 resulted in a lower nitrification efficiency (40e60%) in conjunction with a high N 2 O emission (50.6 mg-N/L/day), whereas there was a higher nitrification efficiency (>99%) in system 1 with low N 2 O emission (22.6 mg-N/L/day). The DNA abundance of functional genes responsible for nitrification and denitrification were comparable in both systems, but transcription of nosZ mRNA in the lower N 2 O emission system (system 1) was one order of magnitude higher than that in the higher N 2 O emission system (system 2). The diversity and evenness of the nosZ gene were nearly identical; however, the predominant N 2 O reducing bacteria were phylogenetically distinct. Phylogenetic analysis indicated that N 2 O-reducing strains only retrieved in system 1 were close to the genera Rhodobacter, Oligotropha and Shinella, whereas they were close to the genera Mesorhizobium only in system 2. The distinct predominant N 2 O reducers may directly or indirectly influence N 2 O emissions.
Recent advances in nitrous oxide production and mitigation in wastewater treatment
Water Research, 2020
Nitrous oxide (N 2 O) emitted from wastewater treatment plants has caused widespread concern. Over the past decade, people have made tremendous effort s to discover the microorganisms responsible for N 2 O production, elucidate metabolic pathways, establish production models and formulate mitigation strategies. The ultimate goal of all these effort s is to shed new light on how N 2 O is produced and how to reduce it, and one of the best ways is to find key opportunities by integrating the information obtained. This review article critically evaluates the knowledge gained in the field within a decade, especially in N 2 O production microbiology, biochemistry, models and mitigation strategies, with a focus on denitrification. Previous research has greatly deepened the understanding of the N 2 O generation mechanism, but further efforts are still needed due to the lack of standardized methodology for establishing N 2 O mitigation strategies in full-scale systems. One of the challenges seems to be to convert the denitrification process from a net N 2 O source into an effective sink, which is recommended as a key opportunity to reduce N 2 O production in this review.
Applied and Environmental Microbiology, 2010
In contrast to most denitrifiers studied so far, Pseudomonas stutzeri TR2 produces low levels of nitrous oxide (N 2 O) even under aerobic conditions. We compared the denitrification activity of strain TR2 with those of various denitrifiers in an artificial medium that was derived from piggery wastewater. Strain TR2 exhibited strong denitrification activity and produced little N 2 O under all conditions tested. Its growth rate under denitrifying conditions was near comparable to that under aerobic conditions, showing a sharp contrast to the lower growth rates of other denitrifiers under denitrifying conditions. Strain TR2 was tolerant to toxic nitrite, even utilizing it as a good denitrification substrate. When both nitrite and N 2 O were present, strain TR2 reduced N 2 O in preference to nitrite as the denitrification substrate. This bacterial strain was readily able to adapt to denitrifying conditions by expressing the denitrification genes for cytochrome cd 1 nitrite reductase (Ni...
Nitrous Oxide Emissions from Wastewater Treatment Plants. A Balancing Act
Proceedings of the Water Environment Federation, 2009
Acknowledgement of the role of nitrification on the emission of N 2 O from wastewater treatment plants is generating a renewed interest in the subject. Actual emission factors for N 2 O in WWTP seem to be higher than previously estimated. The impact of temperature, dissolved oxygen, nitrites, nitrates, C/N, pH, ammonia, H 2 S is reviewed. It is argued that actual emissions from the plant are result of interactions among nitrifiers, denitrifiers and the stripping effect of aeration. Nitrifiers are mostly a source through the nitrifiers-denitrification pathway. Denitrifying bacteria can act as a source or a sink. Denitrifiers play a significant role in reducing emissions in anoxic tanks. Locations prone to nitrous oxide emission in treatment plants are proposed. The impact of dynamic conditions in the plant is emphasized. Emission measurement protocols need to account for the diurnal variability of N 2 O emissions in treatment plants due to changing influent and operational conditions. Steady state evaluation in the laboratory can not capture the effects observed in the field. Some trends observed in mixed cultures of bacteria in treatment plants can be explained based on fundamental studies in pure cultures, others are not. Increased nitrous oxide emissions at high dissolved oxygen concentration often seen in mixed cultures from treatment plants are not directly inferred from the behaviour of nitrifiers or denitrifiers in pure culture. The impact of potentially higher nitrous oxide emission factors on green-house-gas emissions from the plant is quantified. If current trends are confirmed in full scale facilities the wastewater sector would have a larger impact than previously estimated. Alternative strategies for nitrous oxide control are reviewed. The need to remove nutrients from the water environment might lead to a different type of pollution in the atmosphere; there is a need to balance and minimize the overall effect.
Nitrous oxide emission during wastewater treatment
Water Research, 2009
Nitrous oxide (N 2 O), a potent greenhouse gas, can be emitted during wastewater treatment, significantly contributing to the greenhouse gas footprint. Measurements at lab-scale and full-scale wastewater treatment plants (WWTPs) have demonstrated that N 2 O can be emitted in substantial amounts during nitrogen removal in WWTPs, however, a large variation in reported emission values exists. Analysis of literature data enabled the identification of the most important operational parameters leading to N 2 O emission in WWTPs: (i) low dissolved oxygen concentration in the nitrification and denitrification stages, (ii) increased nitrite concentrations in both nitrification and denitrification stages, and (iii) low COD/N ratio in the denitrification stage. From the literature it remains unclear whether nitrifying or denitrifying microorganisms are the main source of N 2 O emissions. Operational strategies to prevent N 2 O emission from WWTPs are discussed and areas in which further research is urgently required are identified.
Clean Technologies and Environmental Policy, 2015
The carbon source used for denitrification is a key factor in the reduction of nitrous oxide (N 2 O) produced from wastewater treatment plants because it affects denitrification activity. In this study, two laboratory-scale Modified Ludzak Ettinger (MLE) processes were operated with methanol and sodium acetate as the sole carbon sources. Removal efficiency of soluble nitrogen was not affected by carbon source, but the N 2 O emission rate from the acetate-fed MLE process (1.6 ± 0.6 lg N-N 2 O/min) was lower than that from the methanol-fed process (3.0 ± 0.7 lg N-N 2 O/min). This is supported by the batch experiment data showing the acetate-fed biomass had a higher N 2 O reduction rate of 10.3 mg/gVSS/h than that of the methanol-fed biomass (3.3 mg/gVSS/h). In the methanol-fed process, 34.9 % of the total bacteria was the genus Methylotenera, which is reportedly incapable of N 2 O reduction. The acetate-fed process enriched the genera Dechloromonas and Rubrivivax, potential N 2 O reducers, accounting for 12.2 and 15.9 % of the total bacteria, respectively. The results indicated that acetate is a suitable replacement for methanol for wastewater treatment plants interested in mitigating N 2 O emission from the MLE process.