Direct N2O Research Articles

A Comparison of the Carbon Footprints of Different Digested Sludge Post-Treatment Routes: A Case Study in China

As the “carbon peaking and carbon neutrality” strategy advances, carbon emissions have gradually become a significant indicator in selecting and evaluating sewage and sludge treatment solutions. This study compared the carbon footprints of different digested sludge post-treatment routes, taking the Lu’an project in China as an example. Considering anaerobic digestion and digested sludge post-treatment options, the carbon footprints are as follows: 347.7 kg CO2 (land application) < 459.7 kg CO2 (composting-involved land application) < 858.4 kg CO2 (brickmaking). In general, land application was superior to brickmaking from the perspective of carbon footprints. The power consumption incurred by aerating and turning and the direct N2O and CH4 emissions during composting increase the composting-involved land application carbon footprint. However, digested sludge that is not subject to high-temperature sterilization and compost is phytotoxic and can be fetid, which is a limitation of its applicability. And the composted sludge has a lower N ratio and water content, so the same N input means more sludge usage, which is conducive to solving the disposal problem of large amounts of sludge. Thus, if possible, composting-involved land application should be a preference, and improvements to the technique are required to minimize energy consumption and direct N2O and CH4 emissions.

Effects of Straw Amendment in Combination with Synthetic N Fertilizer Addition on N2O, N2, and Their Stoichiometric Ratios in Three Different Agro-Ecosystems

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control < KNO3 < rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Tillage strategies optimize SOC distribution to reduce carbon footprint

Tillage methods and nitrogen (N) application are critical for soil organic carbon (SOC) sequestration and crop production. However, both tillage and N are the main contributors to the carbon footprint (CF) in agricultural production. A 6-year-long field experiment was conducted under a winter wheat-summer maize cropping system in Northern China to test how tillage methods (RT, annual rotary tillage; DT, annual deep tillage; and TT, RT applied annually with a DT interval of two years) and N rates (300 kg ha–1, N300; 225 kg ha–1, N225; 165 kg ha–1, N165) affect SOC sequestration, greenhouse gas (GHG) emissions, and annual grain yield. And, the CF was used to evaluate ecological sustainability. RT preferentially sequestrated SOC in the 0–10 cm soil layer. In the 10–30 cm soil layers, 2.87–3.82 and 1.85–2.53 Mg ha–1 greater SOC were respectively observed under DT and TT than RT, which was conducive to maximizing annual grain yield with less N application (N225) relative to traditional farming practice (RT-N300). Both increasing N rate and deep tillage resulted in obvious increases in the total GHG emissions. N fertilizer production and transportation were the greatest contributors, accounting for 40.4–47.0% of the total GHG emissions, followed by direct N2O and CH4 emissions (23.5–30.5%). TT-N225 significantly reduced CF (CF including SOC sequestration was 0.49 Mg CO2 eq ha–1 year–1 lower than DT-N225, and was 1.87 Mg CO2 eq ha–1 year–1 lower than RT-N300) and maintained high crop productivity while creating appropriate soil conditions and thus may be a much cleaner agricultural strategy in Northern China. And, the strategy of reducing N application in agricultural production by improving soil properties of the plow layer in this study can also be referred to in other ecological regions.

Impact of source-separation of urine on effluent quality, energy consumption and greenhouse gas emissions of a decentralized wastewater treatment plant

The impact of urine diversion on the biological treatment processes at a decentralized wastewater treatment plant (WWTP) was investigated. BioWin software was used for the simulations, and the model was firstly validated with data from a real WWTP. The simulations showed that upto 82 % N, 30 % P, 6% chemical oxygen demand (COD) load to the WWTP can be reduced by complete urine diversion but effluent N reduction was notable up to 75 % urine diversion. Under the current WWTP operating conditions, the simulations suggest that 33 % of aeration energy can be saved by 90 % urine diversion. Direct N2O and CO2 emissions in the treatment processes can also be reduced by 98 % and 25 % respectively. Indirect green house gas emissions can also be reduced by 20 %. Overall, the reduction in the discharge of nutrients and in the operation of blowers was found to contribute to a 22 % reduction in the operating costs (on energy consumption and nutrient discharge).

Modelowanie emisji podtlenku azotu i amoniaku w skali regionalnej oraz w Polsce

Celem badań była weryfikacja przyjętych w krajowych inwentaryzacjach emisji gazów cieplarnianych współczynników emisji bezpośredniej N2O i NH3 oraz oszacowanie emisji bezpośredniej i pośredniej N2O w systemach uprawy zwiększających sekwestrację węgla. Symulacje wykonywano przy użyciu modelu DNDC dla województw i Polski z użyciem dwudziestoletnich serii danych meteorologicznych. Stwierdzono, że symulowana emisja bezpośrednia podtlenku azotu dla Polski była zgodna z przyjętym współczynnikiem emisji. Symulowana emisja amoniaku była większa od przyjętego współczynnika emisji. Zastosowanie w symulacjach systemów uprawy zwiększających sekwestrację węgla organicznego, takich jak uprawa konserwująca oraz nawożenie obornikiem, zwiększało: wymycie i spływ powierzchniowy azotu oraz emisję bezpośrednią i pośrednią N2O. Wzrost tych emisji powinien być skompensowany z naddatkiem przyrostem ilości sekwestrowanego węgla organicznego w glebie, jeśli bilans emisji gazów cieplarnianych ma być ujemny.

Integration of in Situ FTIR Studies and Catalyst Activity Measurements in Reaction Kinetic Analysis

This paper describes a method to utilize DRIFT measurements with catalyst activity data in reaction kinetic analysis. The method is applied to construction and discrimination of reaction rate models for NO reduction with CO in the presence of oxygen over a Pd-containing three-way catalyst. DRIFT measurements have a special advantage to discriminate reaction rate models by comparing semiquantitative measurement of surface complexes to simulated surface coverages. Reaction kinetic models based on three different mechanisms (direct decomposition, bimolecular reaction, and N2O formation via isocyanate complex formation) were compared. Only minor differences between the models exist in the fitting of the models to measured gas-phase concentrations, whereas predicted surface coverages differ significantly from each other. The direct decomposition reaction model can most correctly predict the semiquantitative DRIFT measurements. Moreover, the explanation of the slow transient effects, detected on light-off exper...