Denitrification Potential of Marsh Soils in Two Natural Saline-alkaline Wetlands

Little information is available on denitrification potential of marsh soils in natural saline-alkaline wetlands. The denitrification potentials of an open wetland in the floodplain(Erbaifangzi wetland) and a closed wetland(Fulaowenpao wetland) in backwater areas in Jilin Province of Northeast China were monitored by an anaerobic incubation at 30℃ for 25 days. Our results showed that the relative denitrification index(RDI) increased gradually with incubation time, and showed a rapid increase in the first 5 days of incubation. The RDI values declined quickly from surface soils to subsurface soils and then kept a small change in deeper soils along soil profiles over the incubation time. Denitrification proceeded much faster in the top 20 cm soils of open wetland than in the closed wetland, whereas no significant differences in RDI values were observed in deeper soils between both wetlands. The RDIs were significantly negatively correlated with bulk density and sand content, while a significantly positive correlation with clay content, soil organic matter, total nitrogen and phosphorous. The maximum net NO–3-N loss through denitrification in 1 m depth were higher in the open wetland than the closed wetland with higher soil pH values. Future research should be focused on understanding the influencing mechanisms of soil alkalinity.

Removal of AlN from secondary aluminum dross by pyrometallurgical treatment

A new process of AlN removal from secondary aluminum dross(SAD)by pyrometallurgical treatment with added cryolite was applied for solving the problem of recycling the secondary aluminum dross.The response surface methodology(RSM)was used to design experiments and optimize parameters.The results show that adding the appropriate amount of cryolite can effectively promote the oxidation of AlN in the SAD,and too much cryolite will reduce the promotion effect.The effects of roasting temperature and cryolite on the denitrification rate are the most significant(p<0.0001)followed by holding time.Predicted values of the denitrification rate are found to be in good agreement with experimental values(R^(2)=0.9894 and R_(adj)^(2)=0.9775),which confirms the validity of the model employed.The optimum conditions of roasting temperature of 750°C,holding time of 194 min,mass fraction of cryolite of 17.7%are obtained according to the quadratic model.Under these conditions,the maximum actual denitrification rate reaches 94.71%and the AlN content in the SAD is only 0.55 wt%.The unfired brick with compressive strength of 18.62 MPa(GB/T 2542−2012)was prepared based on the roasted SAD.

Experimental study on removal nitrogen oxide of flue gas by using solid absorbents

With the rapid development of modem industry and increase of consumption of the coal, petroleum and natural gas etc., emission of nitrogen oxide （NOx） from flue gas has air environment quality worsen day by day. This research work is experimental study on removal low concentration NOx of flue gas by using solid absorbents. The experiment result shown that denification rate by modified activated carbon is higher than that of modified zeolite and rectorite. Average denitrification rate is 65.47% and maximum denitrification rate is 95.82% for activated carbon; average denitrification rate is respectively as 43.29% and 36.18%, maximum denitrification rate is respectively as 87.51% and 79.47% for modified zeolite and rectorite. Experiment results indicated that NO adsorption process of activated carbon can be described by Freudlich adsorption mode, K=0.143 and n=2.842 and Freudlich adsorption isotherm equation is： q = 0.143MO^0.3519.

Sulfur-based autotrophic denitrification from the micro-polluted water

Eutrophication caused by high concentrations of nutrients is a huge problem for many natural lakes and reservoirs. Removing the nitrogen contamination from the low C/N water body has become an urgent need. Autotrophic denitrification with the sulfur compound as electron donor was investigated in the biofilter reactors. Through the lab-scale experiment,it was found that different sulfur compounds and different carriers caused very different treatment performances. Thiosulfate was selected to be the best electron donor and ceramsite was chosen as the suitable carrier due to the good denitrification efficiency, low cost and the good resistibility against the high hydraulic loads. Later the optimum running parameters of the process were determined. Then the pilot-scale experiment was carried out with the real micro-polluted water from the West Lake, China. The results indicated that the autotrophic denitrification with thiosulfate as electron donor was feasible and applicable for the micro-polluted lake water.

Effect of the C:N:P ratio on the denitrifying dephosphatation in a sequencing batch biofilm reactor(SBBR)

A series of investigations were conducted using sequencing batch biofilm reactor（SBBR） to explore the influence of C：N：P ratio on biological dephosphatation including the denitrifying dephosphatation and the denitrification process.Biomass in the reactor occurred mainly in the form of a biofilm attached to completely submerged disks.Acetic acid was used as the source of organic carbon.C：N：P ratios have had a significant effect on the profiles of phosphate release and phosphate uptake and nitrogen removal.The highest rates of phosphate release and phosphate uptake were recorded at the C：N：P ratio of 140：70：7.The C：N ratio of 2.5：1 ensured complete denitrification.The highest rate of denitrification was achieved at the C：N：P ratio of 140：35：7.The increase of nitrogen load caused an increase in phosphates removal until a ratio C：N：P of 140：140：7.Bacteria of the biofilm exposed to alternate conditions of mixing and aeration exhibited enhanced intracellular accumulation of polyphosphates.Also,the structure of the biofilm encouraged anaerobic-aerobic as well as anoxic-anaerobic and absolutely anaerobic conditions in a SBBR.These heterogeneous conditions in the presence of nitrates may be a significant factor determining the promotion of denitrifying polyphosphate accumulating organism（DNPAO） development.

Global sensitivity and uncertainty analysis of the VIP ecosystem model with an expanded soil nitrogen module for winter wheat-summer maize rotation system in the North China Plain

Accurately simulating the soil nitrogen(N)cycle is crucial for assessing food security and resource utilization efficiency.The accuracy of model predictions relies heavily on model parameterization.The sensitivity and uncertainty of the simulations of soil N cycle of winter wheat-summer maize rotation system in the North China Plain(NCP)to the parameters were analyzed.First,the N module in the Vegetation Interface Processes(VIP)model was expanded to capture the dynamics of soil N cycle calibrated with field measurements in three ecological stations from 2000 to 2015.Second,the Morris and Sobol algorithms were adopted to identify the sensitive parameters that impact soil nitrate stock,denitrification rate,and ammonia volatilization rate.Finally,the shuffled complex evolution developed at the University of Arizona(SCE-UA)algorithm was used to optimize the selected sensitive parameters to improve prediction accuracy.The results showed that the sensitive parameters related to soil nitrate stock included the potential nitrification rate,Michaelis constant,microbial C/N ratio,and slow humus C/N ratio,the sensitive parameters related to denitrification rate were the potential denitrification rate,Michaelis constant,and N2 O production rate,and the sensitive parameters related to ammonia volatilization rate included the coefficient of ammonia volatilization exchange and potential nitrification rate.Based on the optimized parameters,prediction efficiency was notably increased with the highest coefficient of determination being approximately 0.8.Moreover,the average relative interval length at the 95% confidence level for soil nitrate stock,denitrification rate,and ammonia volatilization rate were 11.92,0.008,and 4.26,respectively,and the percentages of coverage of the measured values in the 95% confidence interval were 68%,86%,and 92%,respectively.By identifying sensitive parameters related to soil N,the expanded VIP model optimized by the SCE-UA algorithm can effectively simulate the dynamics of soil nitrate stock,denitrification rate,and ammonia volatilization rate in the NCP.