| Increasing the scale of the intensive animal feeding operations(AFOs),which results in the increasing of the particulate pollution,by means of the reasonable intercepting measures can control the particulate pollution from the area source,so as to reduce the financial burden on atmospheric environment.Vegetative barriers(VB)showed the advantage of high efficiency,environment friendly,economical in the process of intercepting particulate matter(PM),which provides an effective solution to control the emission of PM from the AFOs.Some special branch-scale structures and micro-structures of vegetation play an important role in intercepting the PM,which provides a bionic prototype for the further design of artificial dust barrier.This study investigates the surrounding environment of the cattle feedlot and the laying hen house,in the background of ChangChun city,Jilin province.We build indoor low speed wind tunnel on the basis of the climate conditions of ChangChun city and the surrounding environment of the AFOs.The total height of the wind tunnel is 1.8 m,total length is 6.5 m.Wing velocity of the test section can be controlled continuously from 0 to 6 m s-1.We designed the method to simulate the PM source of AFOs.This method is mainly for the primary particle of the AFOs,the secondary particles are not in consideration.In addition,different sources of PM were identified through EDS tests.The elements of the cattle feedlot include C,N,O,Na,Mg,Al,Si,P,S,Cl,K Ca,of all the components,C,N,O,Si,Ca were the major components,with mean mass percentages of 30.4%,20.5%,36.5%,4.0%,3.1%,respectively.The elements of the laying hen house include C,N,O,Na,Mg,Al,Si,P,S,Cl,K,Ca,of all the components,C,N,O,K,Ca were the major components,with mean mass percentages of 34.67%,23.79%,34.44%,1.11%,1.89%,respectively.We tested the efficiency of the branch-scale structures of clove to the PM from the cattle feedlot,as a result,VB of clove with the surface area density(SAD)of ρ3 had the best efficiency to reduce the air flow,from 60% to 85%.When the velocity of air flow is V3,it had the highest efficiency,which is 88.2 ± 8.23%.With the increase of wind speed,the efficiency to reduce wind speed presents a trend of increasing.VB of clove has more efficiency to intercept the PM with a diameter smaller than 2μm,is suitable for intercepting ultrafine particles.VB of clove with the surface area density(SAD)of ρ3 had the most efficiency in the low wind speed,which can reach to 48.0± 6.0%.The micro-structures of clove and the particle deposition distribution on the leaf were observed through scanning electron microscope(SEM),as a result,more irregular “ridges” and apparent ditches of stripes distributed around or close to midrib and PM deposition also can be observed.The clove leaves have pinnate venation crossing the non-smooth surface with midrib in the center and many “ridge”-shape structures distributed on the surface which can increase the efficiency of PM deposition.The mean contact angle of clove leaves is 58.96 ± 4.04°,thus,clove leaves can be considered as hydrophilic surface,which have a characterize to capture more PM.We tested the efficiency of Mongolica shoot to the PM from the cattle feedlot,as a result,at the level of PⅡ with the wind speed of 0.9 m?s-1,PM1、PM2.5 and PM10 have the highest efficiency,which is 41.59%,26.41%,36.90%,respectively.And it showed more efficiency to PM1 than PM2.5 and PM10,which indicates that VB of Mongolica shoot have best efficiency to intercept PM1.Compared to the VB of clove to intercept PM from cattle feedlot,when the SAD was close to ρ1,the efficiency of the VB of Mongolica shoot just below the VB of clove,but the efficiency to reduce the wind speed is far less than the latter.Thus,in the process of the same number of PM,the former has a small wind resistance than the latter,which characterize is used to intercept the PM from AFOs,and it provides a solution for low resistance of bionic dust-controlling nets.The positive and negative of the Mongolica shoot needles before and after intercepting PM were observed through SEM,as a result,the micro-structure of the Mongolica shoot needles on the surface present a well organized “ridge” stripe band and porosity distribution,orderly arrangement with fuzzy structure distribution between the pores,a large number of PM are easier to deposit in this area,and on the back of Mongolica shoot needles deposit more PM than the positive.The contact angle of the positive is 51.57± 1.92°,while the negative is 78.22 ± 2.61°.More chemical composition of PM sources were detected in the back of the Mongolica shoot needles through EDS and XPS,which proved once more that Mongolica shoot needles deposit more PM in the negative than the positive.To investigate the air flow around the VB,the wind speed around clove and Mongolica shoot vegetation barrier were tested through wind tunnel,as a result,on the windward of VB,there is a decrease on the velocity of air flow.The velocity had an increase bypass the VB at the top of the lift air monitoring stations.Part of the air flow had a decrease after passing through the VB,there is significantly decrease in the back of the monitoring points of the VB,eventually it flow back into the back of the test section along the axial,and it presented a trend of recovery at the monitoring station which is far from the VB.In additional,under the level,the efficiency to reduce wind speed of Mongolica shoot VB is far less than clove VB,the highest efficiency is up to 28.3%.The efficiency of clove VB to intercept the PM from laying hen house is researched.As a result,at a level of PⅡ with wind speed of V3,clove VB with SAD ofρ3 had the wind speed reduced efficiency from 65% to 78%,which had the highest reduce efficiency when the wind speed is highest,showed the number of 78.0 ± 2.55%.Compared to the former test,clove VB had the same rule and trend of air flow when intercepting the PM from cattle feedlot or laying hen house,but for the air flow which contain the PM from laying hen house,the efficiency to reduce wind speed is just below the air flow which contain the PM from cattle house.Compared to the efficiency to intercept PM from cattle feedlot,clove VB showed lower efficiency on PM10 which came from laying hen house.The distribution and micro-structure characterize on the surface of clove leaves had been observed through SEM.As a result,there has a large number of small particle size accumulated on the fold area of the surface of clove leaves,especially more fine PM deposited in the disorder “ridge” stripe,but the coarse PM is little.Under the level of PⅡ,clove leaves accumulate more PM than the level of P?.The surface of clove belongs to hydrophilic surface,but the coarse PM which came from laying hen house is major generated from feed,which is organic compound particles and is poor hydrophilicity,as for the coarse PM which came from cattle feedlot is major generated from soil,which is inorganic compound particles and is soluble in water,good hydrophilicity,as a result,clove VB is more suitable for intercepting PM which came from cattle feedlot. |
PDF Full Text Request