Study On The Transport Law Of Typical Sewage In Soil In Rural Areas Of Gansu Province

Gansu Province,as a large northwest province focusing on the development of agricultural industrialization,has a vast rural area,lack of water resources and a large rural population base.The domestic sewage in rural areas of Gansu Province is mainly kitchen,bathroom and washing.Its composition is simple and the content of harmful substances such as heavy metals is low.At present,the discharge mode is relatively random,which has caused certain pollution to soil and even groundwater.At the same time,the use of pesticides in rural areas has exacerbated the pollution to soil and groundwater.Therefore,in order to speed up the process of building a beautiful countryside,it is of great significance to study the migration law of typical sewage in Loess in rural areas.The model of combining indoor test and software simulation was used to explore the migration law of typical sewage in rural areas of Gansu Province.The basic parameters of soil hydraulic parameters and solute transport were obtained by indoor experiments.Through the soil column comparison experiment with clean water,domestic sewage with different concentrations,glyphosate and chlorothalonil as the infiltration liquid,the indexes such as cod,ammonia nitrogen,pesticide glyphosate,pesticide chlorothalonil concentration,water yield and p H value of each soil column were monitored and analyzed.Using hydraus-1d software,combined with various parameters obtained in the laboratory and simulated solute transport process,the measured values are fitted with the simulated values.The main conclusions are as follows:(1)Through the indoor Na Cl leaching experiment,the distribution curve of soil concentration along the process and the variation curve of salt concentration at the observation point with time are obtained.Then,according to the basic theory of dispersion,the dispersion coefficient and dispersion degree of the tested loess are obtained.The dispersion coefficient is 0.35cm2/min and the dispersion degree is 17.5cm.(2)Through the experimental study of indoor domestic sewage soil column,we can get:(1)change of water output: in the unsaturated stage of soil column,the water output of soil column shows a trend of slowly decreasing at first and then slowly increasing.From the numerical point of view,the water output of low concentration sewage soil column is always greater than that of high concentration sewage soil column.In the saturation stage of soil column,the water output of the two soil columns decreased first and then changed stably.In the process of clean water infiltration,it first increases slowly with a small amplitude.After the soil column is saturated,the water output decreases,and then it is in a stable state.In the whole infiltration process,the water output of clean water soil column is greater than that of low concentration sewage soil column.(2)Change of p H value: with the increase of infiltration time,p H first shows a downward trend,and then shows a slight fluctuation state.When the soil column is saturated,the p H value suddenly increases until it is consistent with the inlet liquid,and the outlet p H of the clean water soil column is greater than the inlet p H value.(3)Change of cod: the COD in the effluent of the two soil columns decreased rapidly at first,then decreased slowly,increased suddenly on the 31 st and 34 th days of infiltration,and then increased slowly.(4)Change of ammonia nitrogen: during the initial infiltration,the ammonia nitrogen content in the effluent is only less than 15%.With the infiltration experiment,the ammonia nitrogen content in the effluent begins to increase rapidly until the high concentration sewage soil column and low concentration sewage soil column infiltrate to43 days and 46 days respectively,and the ammonia nitrogen content in the effluent reaches more than 95%.With the continuous adsorption saturation of loess particles,the content of ammonia nitrogen in effluent is small and shows a relatively stable trend.(3)Through the indoor experimental study of typical pesticide soil column,it can be obtained that:(1)during the initial infiltration process,the concentration of glyphosate in the effluent of soil column is basically 0%.After the soil column is saturated,the content of glyphosate in the effluent increases greatly.After increasing to a certain extent,the content of pesticide changes little,reaching a state of equilibrium and stable change,and the concentration in the effluent reaches 89%.(2)The adsorption capacity of Loess Column for chlorothalonil is far lower than that of glyphosate.In the process of infiltration,the concentration of chlorothalonil in the outlet water decreases to 4.7% at a very slow speed.After the soil adsorption is saturated,the concentration of chlorothalonil in the outlet water increases to 79.6%.However,due to the powder shape of chlorothalonil,it is easy to accumulate on the surface of soil column,and its concentration in the outlet water is always lower than that in the inlet liquid.(4)The solute transport process of pollutants in loess is numerically simulated by using hydraus-1d software,and the reliability of the model is verified.The measured data obtained from the indoor test are used to verify the model.The fitting effect of the model is evaluated through three indexes: root mean square error,relative error and coincidence index.It is considered that the fitting effect is acceptable,can effectively reflect the pollutant transport situation in the region,and the model is reliable.