The response of nitrous oxide emissions to different operating conditions in activated sludge wastewater treatment plants in Southeastern Brazil (original) (raw)
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Nitrous oxide emissions were determined in three campaigns in the aeration tank of a full scale conventional activated sludge wastewater treatment plant. During these experiments, the carbonaceous organic matter (BOD and COD) removal was high and rather constant (97-98% and 93-96%). The results indicate that the concentration of total nitrogen in the influent wastewater, especially NH4+, and the aeration flow rate are key controlling factor of N2O emissions from the aeration tank. Nitrification was the major source of N2O, suggested by the behavior of DO concentrations, NO3-/NH4+ ratio and pH values along the six interlinked zones of the aeration tank. Excessive air flow intensified N2O transfer from the liquor to the atmosphere by air stripping.
Química Nova, 2013
Recebido em 26/1/12; aceito em 13/7/12; publicado na web em 29/11/12 This study investigated the emission of N 2 O during the sequential aerated (60-min) and non-aerated (30-min) stages of an intermittent aeration cycle in an activated sludge wastewater treatment plant (WWTP). N 2 O emission occurred during both stages; however, emission was much higher during aeration. Air stripping is the major factor controlling transfer of N 2 O from the sewage to the atmosphere. The N 2 O emissions exclusively from the aeration tank represented 0.10% of the influent total nitrogen load and the per capita emission factor was almost 3 times higher than that suggested by the IPCC for inventories of N 2 O emission from WWTPs. Figure 1S. The covered aeration tank of the wastewater treatment plant and the openings (A, B and C) through which all measurements were made
Factors controlling nitrous oxide emissions from a full-scale activated sludge system in the tropics
Environmental science and pollution research international, 2015
Despite interest in characterizing nitrous oxide (N 2 O) emissions from wastewater treatment plants (WWTPs) in several parts of the globe, there are few studies in tropical zones. This study focus on the contribution of the scientific knowledge of anthropogenic nitrogen greenhouse gas emissions to climate change in tropical countries, investigating factors controlling N 2 O emissions in a non-biological nitrogen removal municipal WWTP. In terms of operational parameters, dissolved oxygen (DO) concentrations displayed a biphasic impact on N 2 O production and emission, with the highest emission at DO of 2.0 mg O 2 L −1 . The low solids retention time of 3 days also played a significant role, leading to nitrite accumulation, which is an important trigger for N 2 O production during nitrification. Furthermore, other factor especially important for tropical countries, namely, temperature, also had a positive correlation with N 2 O production. Emission factors estimated for this study were 0.12 (0.02-0.31)% of the influent total nitrogen load and 8.1 (3-17) g N 2 O person −1 year −1 , 2.5 times higher than currently proposed emission factors. Therefore, the highly variability and dependence on operational parameters reinforce the use of a single emission factor is inadequate, especially for developing countries with limited or variable extent of biological wastewater treatment and in regions of the world with widely varying climate patterns.
Factors Affecting Nitrous Oxide Emissions from Activated Sludge Wastewater Treatment Plants—A Review
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Nitrous oxide (N2O) is a greenhouse gas contributing to ozone layer depletion and climate change. Wastewater treatment plants (WWTPs) contribute significantly to the global anthropogenic N2O emissions. The main factors affecting N2O emissions are the dissolved oxygen concentration (DO), the nitrite accumulation, the rapidly changing process conditions, the substrate composition and COD/N ratio, the pH, and the temperature. Low DO in the nitrification process results in higher N2O emissions, whereas high aeration rate in the nitration/anammox process results in higher N2O production. High DO in the denitrification inhibits the N2O reductase synthesis/activity, leading to N2O accumulation. High nitrite accumulation in both the nitrification and denitrification processes leads to high N2O emissions. Transient DO changes and rapid shifts in pH result in high N2O production. Ammonia shock loads leads to incomplete nitrification, resulting in NO2− accumulation and N2O formation. Limiting ...
This study sought to determine the effects of different operating conditions, such as variable organic loading, different sludge retention times (SRTs) and airflow rates, limited dissolved oxygen (DO) concentrations and ammonium (NH4 +) shock loading on total nitrogen (TN) removal routes and nitrous oxide (N2O) emissions in a lab-scale activated sludge system. Short SRT (5 days) combined with very low DO levels (0.5 mg L-1) were responsible for lower TKN oxidation efficiencies and, consequently, negligible NO2-accumulation rates. These results suggest that nitrification efficiency was hampered by the oxidation of organic matter, with a large part of TN removed by sludge waste process. As the SRT increased (from 5 to 10 days) and DO was set to 1.0 mg L-1 , TKN oxidation rates and NO2-accumulation reached their maxima, which are thought to be the optimal conditions for both organic matter oxidation and partial nitrification. Under these conditions, gas transfer to the atmosphere became the preferential route for TN removal instead of incorporation into the sludge waste. However, N2O contribution is estimated as less than 5.6% (with respect to TN in the influent). Insufficient aeration and stress conditions (such as NH4 + shock loading) can cause limited DO conditions and NO2-accumulation, leading to higher amounts of emitted N2O. Therefore, the adequate control of DO concentrations is a key factor to avoid NO2-accumulation and consequently high N2O emissions.
Nitrous oxide emissions from the oxidation tank of a pilot activated sludge plant
Water Research, 2012
This study discusses the results of the continuous monitoring of nitrous oxide emissions from the oxidation tank of a pilot conventional wastewater treatment plant. Nitrous oxide emissions from biological processes for nitrogen removal in wastewater treatment plants have drawn great attention over the last years, due to the high greenhouse effect. However, even if several studies have been carried out to quantify nitrous oxide emission rates from different types of treatment, quite wide ranges have been reported. Only grab samples or continuous measurements over limited periods were considered in previous studies, which can account for the wide variability of the obtained results. Through continuous monitoring over several months, our work tries to fill this gap of knowledge and get a deeper insight into nitrous oxide daily and weekly emission dynamics. Moreover, the influence of some operating conditions (sludge age, dissolved oxygen concentration in the oxidation tank, nitrogen load) was studied to determine good practices for wastewater treatment plant operation aiming at the reduction of nitrous oxide emissions. The dissolved oxygen set-point is shown to play a major role in nitrous oxide emissions. Low sludge ages and high nitrogen loads are responsible for higher emissions as well. An interesting pattern has been observed, with quite negligible emissions during most of the day and a peak with a bell-like shape in the morning in the hours of maximum nitrogen load in the plant, correlated to the ammonia and nitrite peaks in the tank.
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.
Environmental Science & Technology, 2010
Despite recognition of the possible role of biological nitrogen removal (BNR) processes in nitrous oxide (N 2 O) emission, a measured database of N 2 O emissions from these processes at the national scale does not currently exist. This study focused on the quantification of N 2 O emissions at 12 wastewater treatment plants (WWTPs) across the United States using a newly developed U.S. Environmental Protection Agency (USEPA) reviewed protocol. A high degree of variability in field-scale measurements of N 2 O was observed, both across the WWTPs sampled and within each WWTP. Additionally, aerobic zones, which have hitherto not been considered in the USEPA approach of estimating N 2 O emissions, generally contributed more to N 2 O fluxes than anoxic zones from BNR reactors. These results severely qualify the conventional use of a single emission factor to "estimate" N 2 O emissions from BNR processes, solely by virtue of denitrification. Upon subjecting the nationwide data set to multivariate regression data mining, high nitrite, ammonium, and dissolved oxygen concentrations were positively correlated with N 2 O emissions from aerobic zones of activated sludge reactors. On the other hand, high nitrite and dissolved oxygen concentrations were positively correlated with N 2 O emissions from anoxic zones. Based on these results, it can be argued that activated sludge processes that minimize transient or permanent build up of ammonium or nitrite, especially in the presence of dissolved oxygen, are expected to have low N 2 O emissions.