Xi BeiDou

Spatial structure characteristic analysis of corn stover during alkali and biological co-pretreatment using XRD

Dynamic variation in the spatial structure of corn stover during alkali and biological co-pretreatment was investigated by X-ray diffraction. The result for crystallinity and microcrystalline size of cellulose showed periodic changes during the pretreatment process. The dominant destruction periods of crystalline areas were mainly located at 3-5d and 7-17d, and prevailing destroyed amorphous areas mainly occurred at 0-2d and 5-7d. On day 7, the relative crystallinity and microcrystalline size reached 52.81% and 8.56 nm, respectively, which were the maximum and minimum values during the whole co-pretreatment. The results indicated that spatial structure change was not uniform with pretreatment time, and this was contributed to explore the vital time point of destruction during the alkali-biological pretreatment.

Application of stable isotope on nitrate pollution researches of surface water

Since nitrate contamination in surface water is an environmental problem in many regions of the world,methods to trace the source of nitrate and its transformation mechanisms are important for nitrate pollution control.Nowadays,stable nitrogen(15N) and oxygen(18O) isotope data can provide meaningful insight for tracing sources of nitrate and have been frequently used to identify nitrate source and its transformation mechanisms in surface water.However,the stable isotope methods have limitations because the complex fractionations caused by multiple N-cycling processes can change the original isotopic values.This review paper systematically summarizes the isotopic composition and its influencing factors of various nitrate sources,the techniques and progresses in research on nitrate sources identification,and load estimation and assessment of denitrification in different types of land-use watersheds using nitrate stable isotope methods.Based upon the previous researches about the application of stable isotope methods,we suggest that in the future it is important to treat a catchment as a unit and to apply several assisted indexes to study the variation of δ15N-NO3 and δ18O-NO3 in different sources under the combined effects of multiple factors.In addition,comparative studies should be conducted to assess the uncertainty between polluting source survey data and the results of model simulation,and to build a better load computational model.Finally,further studies should be made to investigate the scale and extent of denitrification in a catchment / river using the nitrate stable isotope methods,especially in the sediment-water system.