N_2O emissions from agricultural soils in the North China Plain: the effect of chemical nitrogen fertilizer and organic manure

An enclosed chamber technique was used to measure N 2O emissions from intensively agricultural soils of the North China Plain during the periods of 1995—1996 and 1997—1998, to reflect distinct components of winter wheat and summer maize growing seasons. The results showed that the continuous application of fertilizer in agricultural soils increased N\-2O emissions by a factor of 24.1—28.1, the calculated annual chemical N fertilizer\|transformed N\-2O\|N emissions was 0.67%. Our results indicated that the application of organic manure also had a significant influence on soil N 2O emissions, which combined with the use of chemical N increased about 20% in a year. It was calculated that there were about 0.11% N of organic manure transformed as N 2O N. Annual mean N 2O emission from our study area of fertilized soils was estimated to be 57.1 μgN 2O/(m 2·h). A weak correlation was also found between N 2O emissions and soil available nitrogen content NH + 4.

Yield Effect of Chemical and Soil Nitrogen on the Mid-season and Ratooning Hybrid Rice

Using hybrid rice Yixiang1577 as the material, the mid-season and ratooning hybrid rice yield variation was studied in Southem Sichuan at different levels of nitrogen fertilizer. The results showed that rice yield by using N fertilizer increased to the most significant level than no fertilizer ones, and the mid-season rice and rice yield by using more N fertilizer increased to the significant level than less fertilizer ones. The rice yield by using no fertilizer ones increased to the most significant level than some used fertilizer, and the ratooning rice and rice yield by using more N fertilizer decreased to the most significant level than less fertilizer ones. The rice yield by using some fertilizer increased to the most significant level than no fertilizer ones for mid-season＋rationing rice and rice yield by using some fertilizer had no obvious differences at different nitrogen levels. Therefore, application of fertilizer can improve yield of mid-season rice and mid-season＋rationing rice. Soil test results showed that nutrient contents in rice field in South Sichuan were very rich in nitrogen, which could provide more adequate crop growth potential soil nitrogen nutrition. The crops with a deep root system had stronger ability of utilization on soil nitrogen. Therefore, the ratooning rice used no or little N fertilizer had a high yield performance because they made full use of soil nitrogen with deep root system.

Effects of Chlorination on Soil Chemical Properties and Nitrogen Uptake for Tomato Drip Irrigated with Secondary Sewage Effluent

Chlorination is usually an economical method for treating clogging in drip emitters during sewage application. Appropriate assessment of the responses of soil and crop is essential for determining an optimal chlorination scheme. During 2008 to 2009, field experiments were conducted in a solar-heated greenhouse for tomato drip irrigated with secondary sewage effluent, to investigate the influences of chlorine injection intervals and levels on soil chemical properties and nitrogen uptake. Injection intervals ranging from two to eight weeks and injection concentrations ranging from 2 to 50 mg L-1 were used. A salinity factor and a nutrient factor were extracted from the pool of the nine soil chemical constituents using factor analysis method. The results demonstrated that chlorination practices increased the residual Cl in the soil, resulting in an increased salinity factor, especially for the frequent chlorination at a high injection concentration. Chlorination weakened the accumulation of nutrients factor in the upper soil layer. Nitrogen uptake of the tomato plants also was inhibited by the increased salinity in the upper soil layer caused by high chlorination levels. In order to reduce the unfavorable effect on soil chemical properties and nitrogen uptake, chlorination scheme with concentrations of lower than 20 mg L-1 was recommended.

Effects of COD/N ratio and DO concentration on simultaneous nitrification and denitrification in an airlift internal circulation membrane bioreactor

The effects of chemical oxygen demand and nitrogen(COD/N)ratio and dissolved oxygen concentration(DO)on simultaneous nitrification and denitrification(SND)were investigated using an airlift internal circulation membrane bioreactor(AIC-MBR)with synthetic wastewater.The results showed that the COD efficiencies were consistently greater than 90% regardless of changes in the COD/N ratio.At the COD/N ratio of 4.77 and 10.04,the system nitrogen removal efficiency became higher than 70%.However,the nitrogen remova...

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

In order to improve the anaerobic digestion efficiency of waste activated sludge（WAS）,a pretreatment procedure should be carried out so as to disrupt the microbial cell structure,thus releasing intracellular organic matters.In this paper,a corona discharge triggered by a DC voltage was employed to pre-treat WAS for various time periods under different temperatures.The magnitude of the DC voltage was 4 k V at both negative and positive polarities.The changes in the soluble chemical oxygen demand,phosphorus and nitrogen content,and p H value within the WAS were utilized to estimate the pretreatment performance of the DC corona.It was found that with increasing treatment time,the pretreatment efficiency tends to be reduced.With increased temperature,the pretreatment efficiency appears to be better.It is suggested that the oxidative species and the active particles generated in the corona discharge play an important role in disrupting the microbial cell structure,which is dependent upon the treatment time and the temperature.

Effects of bimetallic catalysts on synthesis of nitrogen-doped carbon nanotubes as nanoscale energetic materials

Well aligned nitrogen-doped carbon nanotubes （CNx-NTs）, as energetic materials, are synthesized on a silicon substrate by aerosol-assisted chemical vapor deposition, Tungsten （W） and molybdenum （Mo） metals are respectively introduced to combine with iron （Fe） to act as a bimetallic co-catalyst layer. Cor- relations between the composition and shape of the co-catalyst and morphology, size, growth rate and nitrogen doping amount of the synthesized CNx-NTs are investigated by secondary and backscattered electron imaging in a field emission scanning electron microscope （FESEM） and X-ray photoelectron spectrometer （XPS）. Compared to pure iron catalyst, W-Fe co-catalyst can result in lower growth rate, larger diameter and wider size distribution of the CNx-NTs; while incorporation of molybdenum into the iron catalyst layer can reduce the diameter and size distribution of the nanotubes. Compared to the sole iron catalyst, Fe-W catalyst impedes nitrogen doping while Fe-Mo catalyst promotes the incorporation of nitrogen into the nanotubes. The present work indicates that CNx-NTs with modulated size, growth rate and nitrogen doping concentration are expected to be synthesized by tuning the size and composition of co-catalysts, which may find great potential in producing CNx-NTs with controlled structure and properties,

Ambient photolysis frequency of NO2 determined using chemical actinometer and spectroradiometer at an urban site in Beijing

The photolysis frequency of NO2, j（NO2）, is an important analytical parameter in the study of tropospheric chemistry. A chemical actinometer （CA） was built to measure the ambient j（NQ） based on a high precision NOx instrument with 1 min time resolution. Parallel measurements of the ambient j（NO2） by using the CA and a commercial spectroradiometer （SR） were conducted at a typical urban site （Peking University Urban Environmental Monitoring Station） in Beijing. In general, good agreement was achieved between the CA and SR data with a high linear correlation coefficient （R2 = 0.977） and a regression slope of 1.12. The regression offset was negligible compared to the measured signal level. Thej（NO2） data were calculated using the tropospheric ultraviolet visible radiation （TUV） model, which was constrained to observe aerosol optical properties. The calculated j（NO2） was intermediate between the results obtained with CA and SR, demonstrating the consistency of all the parameters observed at this site. The good agreement between the CA and SR data, and the consistency with the TUV model results, demonstrate the good performance of the installed SR instrument. Since a drift of the SR sensitivity is expected by the manufacturer, we propose a regular check of the data acquired via SR against those obtained by CA for long-term delivery of a high quality series ofj（NO2） data. Establishing such a time series will be invaluable for analyzing the long-term atmospheric oxidation capacity trends as well as O3 pollution for urban Beijing.

Enhancing nitrogen removal from low carbon to nitrogen ratio wastewater by using a novel sequencing batch biofilm reactor

Removing nitrogen from wastewater with low chemical oxygen demand/total nitrogen （COD/TN） ratio is a difficult task due to the insufficient carbon source available for denitrification. Therefore, in the present work, a novel sequencing batch biofilm reactor （NSBBR） was developed to enhance the nitrogen removal from wastewater with low COD/ TN ratio. The NSBBR was divided into two units separated by a vertical clapboard. Alternate feeding and aeration was performed in the two units, which created an anoxie unit with rich substrate content and an aeration unit deficient in substrate simultaneously. Therefore, the utilization of the influent carbon source for denitrification was increased, leading to higher TN removal compared to conventional SBBR （CSBBR） operation. The results show that the CSBBR removed up to 76.8%, 44.5% and 10.4% of TN, respectively, at three tested COD/TN ratios （9.0, 4.8 and 2.5）. In contrast, the TN removal of the NSBBR could reach 81.9%, 60.5% and 26.6%, respectively, at the corresponding COD/TN ratios. Therefore, better TN removal performance could be achieved in the NSBBR, especially at low CODfrN ratios （4.8 and 2.5）. Furthermore, it is easy to upgrade a CSBBR into an NSBBR in practice.