A relationship is established, using the least squares method, between the standard enthalpy of formation and the standard enthalpy of formation divided by the exothermic denitration decomposition peak absolute temper...A relationship is established, using the least squares method, between the standard enthalpy of formation and the standard enthalpy of formation divided by the exothermic denitration decomposition peak absolute temperature corresponding to β →0.展开更多
Denitrification losses measured by direct method (measuring the evolution of (N2+N2O)-15N) were compared with the apparent denitrification losses (calculated from the difference between the total N loss and ammonia lo...Denitrification losses measured by direct method (measuring the evolution of (N2+N2O)-15N) were compared with the apparent denitrification losses (calculated from the difference between the total N loss and ammonia loss), for fertilizers applied to flooded soils. The direct measured denitrification losses from potassium nitrate were 23.0%, 40.0%, and 63.1-79.7% of applied N in rice field, and in incubations of 7 cm deep layer of soil and 2 cm deep layer of soil, respectively; while the corresponding apparent denitrification losses were 96.0%, 98.4%, and 97.7-97.9%, respectively. In field experiments with urea, the direct measured denitrification losses ranged from 0.1-1.8%, which were much less than the apparent denitrification losses (41.3-45.7%). Such discrepancies were primarily due to the entrapment of the gaseous products of denitrification in the soil as revealed by the facts: (1) stirring the floodwater and the surface soil markedly increased the fluxes of (N2+N2O)-15N from urea or potassium nitrate applied to the flooded rice field, and (2) reducing the pressure in the headspace of the incubation bottle with the 7 cm soil layer during gas sampling decreased the discrepancy between the direct measured and apparent denitrifecation losses from 58.4% to 21.2%. The advantage of reducing the pressure in the headspace is that there is minimal disturbance of the soil. Further testing of this technique in rice field is needed to determine its effectiveness in releasing the entrapped gaseous products of denitrification so that denitrification losses can be quantified directly.展开更多
Reduction of nitrate by zero-valent iron is a highly exergonic reaction that has long been known to occur. Use of scrap iron filings (SIF) as the PRB (Permeable Reactive Barrier) material can be used to recycle certai...Reduction of nitrate by zero-valent iron is a highly exergonic reaction that has long been known to occur. Use of scrap iron filings (SIF) as the PRB (Permeable Reactive Barrier) material can be used to recycle certain by-products, and identify cheaper replacements for expensive conventional PRB materials, especially pure metallic iron. The feasibility of reductive denitrification of nitrate by SIF was studied by batch experiments. Operational parameters such as pH value, SIF dosage and initial concentration of nitrate were investigated. The removal efficiency of nitrate reached 80% under the conditions of pH of 2.5, nitrate initial con- centration of 45 mg/L and SIF dosage of 100 g/L within 4 h. Results indicated that nitrate removal is inversely related to pH. Low pH value condition favors for the nitrate transformation. Different from the results of others who studied nitrate reduction using iron powder, we found that there was a lag time before nitrate reduction occurs, even at low pH. Finally, the possible mechanism of nitrate reduction by Fe0 is discussed.展开更多
Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalp...Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalpine forest-grassland ecotone of the eastern Tibetan Plateau. Land uses consisted of 1) sparse woodland, 2) shrub-land, 3) natural pasture, 4)fenced pasture, and 5) tilled pasture mimicking a gradient degenerating ecosystem under grazing impacts. The NO3--N content was higher than the NH4+-N content. Comparing tilled pasture with fenced pasture showed that higher intensive management (tillage) led to a significant decrease of soil organic matter (SOM) (P ＜ 0.05) in the soils, which was in contrast to the significant increases (P ＜0.05) of DN, GN, N2O and CO2 flux rates. GN (excluding tilled pasture) and CO2 flux rates increased with a temperature rise, but DN and N2O flux rates normally reached their maximum values at 12-14 ℃ with tilled pasture (the highest management intensity) being very sensitive to temperature increases. There was a difference between net nitrification and GN, with GN being a betterindicator of soil nitrification.展开更多
This paper investigates the effect of using sodium citrate（NaC6H5O6·2H2O）as sole carbon source for nitrate removal from drinking water.With sodium citrate as sole carbon source, batch experiments have been cond...This paper investigates the effect of using sodium citrate（NaC6H5O6·2H2O）as sole carbon source for nitrate removal from drinking water.With sodium citrate as sole carbon source, batch experiments have been conducted to study the law of denitrification influenced by pH, C/N and temperature. Results show that a denitrification rate reaching 1.32 g NO-3-N /（g Biomass·d） was obtained when pH was at 7.5,C/N at 1.7（atom ratio）, and temperature from 20 ℃ to 30 ℃. The results also show that denitrification rate with sodium citrate as carbon source approaches to that with methanol as carbon source.展开更多
文摘A relationship is established, using the least squares method, between the standard enthalpy of formation and the standard enthalpy of formation divided by the exothermic denitration decomposition peak absolute temperature corresponding to β →0.
文摘Denitrification losses measured by direct method (measuring the evolution of (N2+N2O)-15N) were compared with the apparent denitrification losses (calculated from the difference between the total N loss and ammonia loss), for fertilizers applied to flooded soils. The direct measured denitrification losses from potassium nitrate were 23.0%, 40.0%, and 63.1-79.7% of applied N in rice field, and in incubations of 7 cm deep layer of soil and 2 cm deep layer of soil, respectively; while the corresponding apparent denitrification losses were 96.0%, 98.4%, and 97.7-97.9%, respectively. In field experiments with urea, the direct measured denitrification losses ranged from 0.1-1.8%, which were much less than the apparent denitrification losses (41.3-45.7%). Such discrepancies were primarily due to the entrapment of the gaseous products of denitrification in the soil as revealed by the facts: (1) stirring the floodwater and the surface soil markedly increased the fluxes of (N2+N2O)-15N from urea or potassium nitrate applied to the flooded rice field, and (2) reducing the pressure in the headspace of the incubation bottle with the 7 cm soil layer during gas sampling decreased the discrepancy between the direct measured and apparent denitrifecation losses from 58.4% to 21.2%. The advantage of reducing the pressure in the headspace is that there is minimal disturbance of the soil. Further testing of this technique in rice field is needed to determine its effectiveness in releasing the entrapped gaseous products of denitrification so that denitrification losses can be quantified directly.
基金Project (No. 20407015) supported by the National Natural Sci-ence Foundation of China
文摘Reduction of nitrate by zero-valent iron is a highly exergonic reaction that has long been known to occur. Use of scrap iron filings (SIF) as the PRB (Permeable Reactive Barrier) material can be used to recycle certain by-products, and identify cheaper replacements for expensive conventional PRB materials, especially pure metallic iron. The feasibility of reductive denitrification of nitrate by SIF was studied by batch experiments. Operational parameters such as pH value, SIF dosage and initial concentration of nitrate were investigated. The removal efficiency of nitrate reached 80% under the conditions of pH of 2.5, nitrate initial con- centration of 45 mg/L and SIF dosage of 100 g/L within 4 h. Results indicated that nitrate removal is inversely related to pH. Low pH value condition favors for the nitrate transformation. Different from the results of others who studied nitrate reduction using iron powder, we found that there was a lag time before nitrate reduction occurs, even at low pH. Finally, the possible mechanism of nitrate reduction by Fe0 is discussed.
文摘Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalpine forest-grassland ecotone of the eastern Tibetan Plateau. Land uses consisted of 1) sparse woodland, 2) shrub-land, 3) natural pasture, 4)fenced pasture, and 5) tilled pasture mimicking a gradient degenerating ecosystem under grazing impacts. The NO3--N content was higher than the NH4+-N content. Comparing tilled pasture with fenced pasture showed that higher intensive management (tillage) led to a significant decrease of soil organic matter (SOM) (P ＜ 0.05) in the soils, which was in contrast to the significant increases (P ＜0.05) of DN, GN, N2O and CO2 flux rates. GN (excluding tilled pasture) and CO2 flux rates increased with a temperature rise, but DN and N2O flux rates normally reached their maximum values at 12-14 ℃ with tilled pasture (the highest management intensity) being very sensitive to temperature increases. There was a difference between net nitrification and GN, with GN being a betterindicator of soil nitrification.
文摘This paper investigates the effect of using sodium citrate（NaC6H5O6·2H2O）as sole carbon source for nitrate removal from drinking water.With sodium citrate as sole carbon source, batch experiments have been conducted to study the law of denitrification influenced by pH, C/N and temperature. Results show that a denitrification rate reaching 1.32 g NO-3-N /（g Biomass·d） was obtained when pH was at 7.5,C/N at 1.7（atom ratio）, and temperature from 20 ℃ to 30 ℃. The results also show that denitrification rate with sodium citrate as carbon source approaches to that with methanol as carbon source.
