Study On Emission Characteristics Of Air Pollutants From Open Burning Of Municipal Solid Waste

With the acceleration of industrialization and urbanization in China and rapid economic expansion,the amount of municipal solid waste?MSW?generated increases year by year.Due to its simplicity,convenience,and low transportation costs,open burning is very common in China.Different from the incinerators treatment,the open burning treatment causes a large amount of discharged pollutants because of the incomplete combustion result from low temperature and lack of oxygen.This study collected MSW samples from different urban functional areas.Pile–up burning and barrel burning were then adopted to handle these MSW samples as the simulation of the two most common open burning practices.A dilution sampling test system was used to test and analyze the emission and chemical components of gaseous pollutants and PM_2.5,and then an air pollutants emission factor database of open burning of municipal solid waste was established.On this basis,we obtained the activity levels of proportion of MSW burned openly and the per capita waste generation rate.Further,we adopted the“bottom-up”emission factor method to establish the emission inventories of air pollutants discharged from open burning of MSW of 361prefecture-levels cities in 2016.Using the modified combustion efficiency?MCE?to evaluate the combustion state of the combustion process,under barrel burning,it was discovered that the degree of smoldering is more significant than pile–up burning due to insufficient oxygen supply.That was to say,oxygen was the key factor of the MCE value and smoldering degree.During the combustion process,the CO₂,SO₂,and NO_x concentrations were positively related to the MCE,whereas the CO concentration was significantly negatively related to the MCE.Average emission factors of CO₂,CO,SO₂ and NO_x were discovered to be 1136.66,40.49,0.36 and 1.82 g kg^-1,respectively.The degree of smoldering in the combustion practice of barrel burning is more significant.Therefore,the emission factors of gaseous pollutants of different components generated by it are higher than by pile–up burning.The chemical composition of PM_2.5?carbonaceous components,water-soluble ions and heavy metal elements?was mainly determined by the composition of the MSW samples.OC was the main component of PM_2.5 generated by the open burning of paper,wood,textile?three kinds of combustible ingredients?and their mixture.EC was the main component?47.1%?of the PM_2.5emitted by open burning of rubber and plastics.Water soluble ions took up a large proportion?31.5%?of the PM_2.5 from open burning of wood solid waste.The average emission factors of PM_2.5,OC,and EC were 8.26,3.71,and 1.45 g kg^-1,respectively.Due to the higher degree of smoldering in the barrel burning,the emissions of PM_2.5,OC and EC generated by it were higher than by pile–up burning.The average emission factors of heavy metals are 1.10 mg kg^-1?As?,0.31mg kg^-1?Cd?,1.19 mg kg^-1?Pb?,0.52 mg kg^-1?Cr?,0.50 mg kg^-1?Ni?,2.40 mg kg^-1?Mn?,6.70 mg kg^-1?Cu?and 17.52 mg kg^-1?Zn?,respectively.And those findings indicated that the average release rate of heavy metals was 15.2%,which were mainly gathering in the bottom ash.The main water-soluble cation in the PM_2.5 was NH₄⁺,which accounted for an average of 19.4%of the total ions;the main anion was Cl^-,which accounted for 52.9%of the total ion.Additionally,SO₄^2-contributed an average proportion of 11.5%of total ions.The average ratio of NH₄⁺and Cl^-in PM_2.5 produced by the barrel burning was 1.4 times what produced by pile-up burning.In 2016,China's total annual emissions of CO₂,CO,SO₂ and NO_x from MSW incineration were 14613.69,520.50,4.56 and 23.33 ten thousand tons,respectively;the total annual emissions of PM_2.5,OC and EC were 106.52,47.63 and 14.72 ten thousand tons,respectively;the total annual discharge of heavy metals was 3742.77 tons,there into the total annual emissions of As,Pb,Cd,Cr,Mn,Cu,Zn and Ni were 136.26,146.79,38.40,63.79,297.29829.32,2169.60,61.32 tons,respectively.The discharges of open burning sources of MSW in the four provinces of Guangdong,Shandong,Jiangsu and Henan ranked the top four,accounting for10.8%,7.7%,7.5%,and 5.8%of the national total,respectively.