Study On Chemical Washing And Biodegradation Combined Treatment Of Coastal Oil Contaminated Soil With Rhamnolipid Seawater Solution

Petroleum contaminated soil is harmful to the biology,the treatment is a requirement of the sustainable development.Environmental friendly biosurfactant rhamnolipid(RL)has been used at homemade simulated oil contaminated soil(SOCS)for chemical washing with the purpose of make oil content quickly fell to upper limit of microbial remediation.Different solvent such as different salinity water and fresh water and different SOCSs firstly added water or curde oil have been compared,and soil particles microscopic models have been constructed.The results show seawater washing is more effective that water washing,and salinity(>2.5%)of seawater has little effect.SOCS firstly added water more suitable for chemical washing,one hand maybe it formed a layer of water film on the surface of soil particles,and made secend oil easier to remove,in the other hand,the moisture promoted the soil particles together,effectively reduce the contact area of oil and soil particles.In order to explore the influence of soil adsorption on oil washing,SOCS were prepared by two different particle sizes from the same soil,and the suitable process conditions were obtained by single factor optimization method.Experimental conditions,liquid/solid ratio = 4,RL concentration = 0.1g/L,stirring speed = 150r/min,mixing time =30min,temperature = 60℃ is suitable for SOCS with particle size <2mm,oil removal rate(ORR)is 60.8%.And experimental conditions,liquid/solid ratio = 3,RL concentration =0.1g/L,stirring speed = 210r/min,mixing time = 30 min,temperature = 70℃ is suitable for SOCS with particle size <2mm,oil removal rate(ORR)is 51.7%.In order to explore the influence of soil properties changes after washing on bioremediation,the influence of RL,organic matter,oil content and soluble salt content on bioremediation have investigated by adding salt-tolerant and high-efficiency oil-degrading bacteria A.The results showed that ORR could reach 60.3% by adding bacteria agent A,higher than 23.9% by natural degradation.Moreover,ORR could be improved to 65.8% by adding RL on the first day,and ORR could be further improved to 70.1% by adding 5%glucose.However,excessive RL will have a certain toxic effect and inhibit the progress of bioremediation.The excessive salt content(> 1.2%)in soil will have a certain inhibitory effect,while the oil content has little effect on ORR.Three factors and three levels of orthogonal optimization were performed on the SOCS applied bioremediaton of bacteria agent A after chemical washing.The results showed that the suitable bioremediation condition was pH=7,additive amount = 0.2%,N/Pis 10% and 1% of the oil content.The factors influencing the effect of bioremediation were ranked as: pH > bacteria additive amount > N/P content.By orthogonal optimization,the maximum ORR obtained in the experiment was 76.6%,the remaining crude oil was 0.7%of the dry soil mass.Chemical washing-bioremediation conbined technology was tested to reduce the oil content below the agricultural standard(0.3%).The results showed that the remaining oil content of SOCS after third-grade seawater RL washing and first-grade fresh water washing was 0.89%,and salt content was 0.57%,which was more suitable for bioremediation.Oil content after 35 d bioremediation is expected to meet the standard of agricultural soil below.