Geochemistry Process Of AOX In Vadose Zone Of Sewage Irrigation Area

AOX (Absorbable Organic Halogens) as an important index of the environmental quality is use extensive in the world. As the same with other Organic Halogens, it has the carcinogenicity and mutagenicity. Sewage and industrial wastewater contain high concentration of AOX. Sewage irrigation as a measure to saving water was applicated in many areas, but also causes AOX pollutants to vadose.Vadose can remove pollutants from swage thouge the process of filtering, adsorption and degradation. Vadose which has been polluted will release contaminationto the groundwater again under the action of water infiltrate soon, the pollutants in vadose can also enters the body through transfer of plants. Because of the spatial variability and dynamic characteristics of water in vadose, the migration of pollutant is a complicated process.Now, China has a large sewage irrigation area, and many industrial and farm discharge wastewater without control, the vadose and groundwater face the risk of pollution.It is a direct threat to the local agricultural.production and people's living environment. So the geochemistry process of AOX in vadose zone of sewage irrigation area study is very meaningful for preventing pollution of groundwater and vadose.On the conditions of swage irrigation, the geochemical behaviour of AOX in the vadose area is complicated, in order to facilitate study, static experiment and indoor dynamic soil column experiment are both used in this paper to reaseach the static adsorption,the adsorption and desorption dynamics behavior of AOX in vadose.Static experiment analyze AOX soil adsorption and desorption behavior quantitatively and its adsorption and desorption model was established. Simulated the movement process of AOX in vadose on the two conditions:complex pollutant in swage and AOX is the only pollutant in the swage. Through this research confirmed which geochemical process play a main role for vadose to remove AOX of swage. This paper have implementated a pollution investigation of groundwater and vadose in the area where have a long-term sewage irrigation and analyzes the spatial distribution characteristic of AOX in vadose of sewage irrigation area.According to the experimental data and investigation, the conclusions are as follows: a. There are 19 surface water samples were collected in the east main canal of Xiaodian area, Beizhang and Taiyu waste canal. The indexes of total nitrogen and total phosphorus both exceed standard severely. The value of total nitrogen exceeds standard from 1 to 25 times and total phosphorus exceeds standard from 1 to 15 times. The maximum value of AOX is 1.52 mg/L, the minimum is 0.11 mg/L. Water quantity keeps under standard in the water flow direction of irrigation channel. Most heavy metal elements below theâ…£class of groundwater environmental quality standards (GB/T 14848-93) standard (â…£class in according to the agricultural and industrial water demands), which accord with the typical characteristics of sewage.b. Adsorption isothermal of AOX in soil can be fit by Linear and Freundlich isothermal adsorption model. Its kinetic adsorption rate can be fit by Langmuir secondary adsorption rate linear equation. If the soil particle is smaller and the content of organic matter is higher, then the adsorptive capacity of AOX is higher.c. The adsorption ability of AOX in soil is a kind of fast reaction. After one hour of the absorption experiment, adsorption capacity of soil for AOX is above 83 percent of the equilibrium adsorption. After 24 hours, it can reach absorption balance.d. In the process of wastewater irrigation, provide the source of carbon and nitrogen for microbe in soil can promote the microbial degradation of AOX and improve about 15 percent of depredate efficiency.e. In the research area, the background values of groundwater are less low, and AOX was not detected in local area. The contents of AOX and TOC in ground water have significant correlationship. AOX in the groundwater of long-term wastewater irrigation area was obviously higher than that of clean water irrigation area. According to the correlation analysis of the data from three boreholes in vadose zone, we found TOC has an important impact to AOX for spatial distribution feature in polluted vadose zone.In conclusion, it is the first time to investigate the pollution situation of AOX in soil of vodose zone and groundwater at Xiaodian irrigation area. According to the experimental data, we study the adsorption-desorption behavior of AOX in vadose zone by the quantitative analysis and analyze the mechanism of self-purification in vadose zone for AOX under the irrigation of complex components. The conclusions have an important significance for strengthening water resources management and groundwater pollution prevention.