Study On Air Stripping As An Emergency Treatment Technology For Removing Volatile Organic Compounds In Source Water

Volatile organic compounds are some complex and widely distributed substances,which have serious ecological and health hazards. The processes of productionmanufacture and transportation are the potential pollution risks for the source water.This research is focused on the air stripping as an emergency treatment technologyfor removing volatile organic compounds. Eight typical volatile organic compoundsare chose as the research objects. They include four halogenated hydrocarbons(chloroform, bromodichloromethane, dibromochloromethane, bromoform), twoalkenyl halides (trichloroethylene, tetrachloroethylene) and two benzene series(benzene, toluene). The bubble aeration is performed in the unpacked tower. Theresearch includes the following results.(1) The models of air stripping for the removal of volatile organic compounds werebuilt. The basic static air stripping model is C/C0=exp(-G·q), where q is gas-waterratio, stripping coefficient G is related to the Henry’s constant. The first, second andthird order dynamic model of air stripping were built on the basis of static model.Both static and dynamic stripping tests results were consistent with the theoreticalmodels.(2) The parameters of air stripping process were determined. The mass transferprocess of air stripping includes two zones, mass transfer zone and equilibrium zone.The height separating the two zones is defined as the equilibrium height h*, where theconcentration of pollutants between the gas phase and the liquid phase reachesequilibrium. The equilibrium height h*could be determined as the strippingcoefficient varied with different air stripping depths. For2.55L/(h·cm2) aerationintensity, the tested equilibrium heights of chloroform, bromodichloromethane,dibromochloromethane, bromoform, trichloroethylene, tetrachloroethylene, benzene,toluene, were about25-35cm,30-50cm, lower than10cm, lower than10cm,40-50cm,40-50cm,30-40cm,30-40cm respectively. The predictive equilibrium heightscalculated from the overall mass transfer coefficient were consistent with the testsresults. In engineering applications, the stripping depth should be more than50cm in order to make full use of the gas.(3) The corresponding tests were carried out to evaluate the removal effects. Whenthe concentration of pollutants between the gas phase and the liquid phase reachesequilibrium, the stripping coefficient has the same number with the Henry’s constant.For20℃waterin the equilibrium zone, a50%removal rate for chloroform,bromodichloromethane, dibromochloromethane, bromoform, trichloroethylene,tetrachloroethylene, benzene, toluene corresponds to a gas-water ratio about5.5,9.2,20,39,2.2,1.3,3.7,3.3, an80%removal rate corresponds to a gas-water ratio about13,22,46,89,5.2,3.0,8.5,7.7and a90%removal rate corresponds to a gas-waterratio about18,31,66,128,7.4,4.3,12,11.(4) The technical and economic feasibility of air stripping were analyzed.1.0m3air costs0.0096Yuan, at2m wind pressure. The systems of air stripping technologywere designed preliminary for different water conditions, such as rivers, diversioncanal and lakes.