Vermicompost Promotes Soilization Of Waste Water-based Drilling Fluid Solids

Due to the increasing production of waste water-based drilling fluid after drilling in oil and gas fields,and the existing treatments like solidification method have the problem of occupying a large amount of land resources.Therefore,developing an environmental friendly technic for processing the waste water-based drilling fluid has become a trend.In addition,after the activated sludge process is applied to the treatment of municipal sewage,the amount of residual activated sludge is more and more.At present,the method of using earthworms to treat sludge and using the nutrient-rich vermicompost which is obtained after the treating of sludge as soil or fertilizer has a large number of researches.Based on this,it is found that the high solid content of the waste water-based drilling fluid can be used as the soil,but there is a deficiency of the nutrient substances.The residual active sludge has rich nutrients but its soil structure is poor,the utilization of the effective nitrogen and phosphorus is poor,so that vermicompost which are formed by the transformation of the residual activated sludge through the earthworms can overcome the defects of the sludge.Therefore,it is proposed for the first time that the solid phase of waste water-based drilling fluid after solid-liquid separation could be transformed into soil to plant plants based on the theory of soilization.Vermicompost was added to the solid phase of waste water-based drilling fluid to ensure that the soil contained suitable nutrients for the good growth of plants.The main results of the experiment were as follows:(1)Different proportion of vermicompost was added to the solid phase of waste water-based drilling fluid for planting the landscape plants—ipomoea aquatica forsk and ryegrass.The results showed that when the ratio of the solid phase of the waste water-based drilling fluid to vermicompost was 1:8,the percentage of germination for ipomoea aquatica forsk and ryegrass was 36.67%and 56.67%,respectively.While,the proportion was 1:10,the percentage of germination was 70.00%and 80.00%,respectively.It also showed that the proportion was 1:8,the soilization of the solid phase of waste water-based drilling fluid could realize,and plants could grow well.(2)The mixed ratio with the solid phase of waste water-based drilling fluid and vermicompost was designed in 1:0,1:8,1:10 and 0:1,their soil bulk density,specific gravity and porosity was determined.The results showed that the solid phase of waste water-based drilling fluid whose bulk density was 1.27 g/cm3 and porosity was 54.88%,the soil was hardened.The vermicompost has the good soil porosity whose bulk density of the soil was 0.48 g/cm3 and porosity was 73.76%.When the mixed ratio of solid phase of waste water-based drilling fluid and vermicompost was 1:8 and 1:10,the soil bulk density decreased to 0.55 g/cm3 and 0.54 g/cm3,and porosity increased to 72.04%and 73.62%,respectively.In the result,the vermicompost could improve the soil structure of solid phase of waste water-based drilling fluid.(3)The mixed ratio with the solid phase of waste water-based drilling fluid and vermicompost was designed in 1:0,1:8,1:10 and 0:1,whose soil organic matter,total nitrogen and other forms of nitrogen,total phosphorus and other forms of phosphorus of the soil were measured.The results showed that the content of soil organic matter,total nitrogen and total phosphorus for the solid phase of waste water-based drilling fluid were all increased since the adding of vermicompost,which were 43.16%,3.59 g/kg and 0.85 g/kg in 1:8,49.93%,3.75 g/kg and 1.18 g/kg in 1:10,respectively.In addition,the content of nutrient which could be absorbed and utilized by plants showed a decreasing trend,which indicated that the mixed soil in 1:8 and 1:10 showed that the soil had enough nutrients for plant growth and utilization.(4)The mixed ratio with the solid phase of waste water-based drilling fluid and vermicompost was designed in 1:0,1:8,1:10 and 0:1,whose contents of heavy metals(including Cd,Cr,Cu,Ni,Pb and Zn)in the soil before and after planting ipomoea aquatica forsk and ryegrass were measured.The results showed that after planting,the contents of heavy metals in soil,the biotoxicity and the types of organic pollutants were all decreased.It was indicated that the mixture of solid phase of waste water-based drilling fluid and vermicompost could effectively reduce the content of pollutants so that it had a good quality of the soil environment.Therefore,this treatment technology is an environmentally friendly and pollution-free method.