| The oil leakage in the process of oil exploration,such as wellhead oil leakage,pipeline perforation and blowout could combine with soil and result in the ground oily sludge.The oliy sludge has the characteristics of wide contamination range,compositional complexity,which lead to the high difficulty in treatment.The difficult volatile components of oil could interact with soil particles,damage the soil structure,reduce the soil fertility,and affect the survival of microorganisms in the soil.These induce the degradation or even death of vegetation in the contaminated sites,grain crop and destroy of the ecosystem.Rainfall leaching and replenishment effect can migrate the oily pollutants from the soil and surface water to the groundwater,leading to the lost of drinking function for groundwater.More seriously,this could also cause serious damage to the local industrial and agricultural production,ecological and human body health.Daqing is the most typical petrochemical city.820 thousand acres of oil field extends across Daqing main city,Honggang,Datong,Zhaozhou,Zhaoyuan and other counties and districts,accounting for about 25% of the Daqing territory.The pollution problems of the ground oily sludge have become increasingly serious.To explore the suitable treatment technologies for the oil pollutions in Daqing oilfield,the comprehensive treatment technologies for ground oily sludge and groundwater were studied in laboratory and engineering application.The oil content in the sludge is instability,meanwhile heavy oil content is usually high.Stable emulsified oil is easily formed in the presence of micro-sized inorganic particles,which makes it more difficult to treat the oily sludge.Aim at this question,the basic characteristics of the oily sludge was firstly evaluated.Suitable chemical cleaning agent for the modification of oily sludge was determinated based on indoor experimental study.The results show the best proportion of rhamnolipid surfactant to compound sodium silicate was 200:700.When the cleaning time wass 40 min,1% addition of cleaning agent was 1%,the hot water temperature was 60 ℃,the best treatment efficiency was obtained.After the dewatering of the modified sludge,the flocculating agent was optimized.It is found that when the weight ratio of inorganic flocculating agent PFS to organic flocculating agent WT-1 was 400:80,the Zeta potential was lowest and the best flocculating performance was achieved.The simulation experimental results of high-temperature pyrolysis showed that the highest oil recovery and system stability can be realized with 6 wt% Ca O as catalyst at 550 ℃.Based on the laboratory experiments,the treatment process of mechanical hardening and tempering-chemical heat washing under a high temperature-centrifugal dewatering-pyrolysis system was carried out in engineering application.In order to achieve harmless treatment of sludge,the time of high temperature thermochemical washing was controlled within 40 min,1% dosage to cleaning agent was added,and the water temperature was 60 ℃,1% compound flocculant was used,the speed of dewatering centrifuge was 2500 r/min and the pyrolysis temperature was 550 ℃.After treatment,the oil content was reduced to less than 3%.The treatment cost of oily sludge was estimated to be about 1520.20 yuan per ton.Based on the field research,lab analysis and the traditional hydrogeology theory,the soil and groundwater pollutions in the contaminated sites were evaluated.Continuous monitoring results of the contaminated cites for 12 months showed that the average content of the total petroleum hydrocarbons content(TPH)in the groundwater was as high as 5.26 mg/L,the content of the main petroleum pollutant(alkane)was up to 90%.The Benzene content ranged from 0.3 to 0.6 mg/L,xylene content varied from 0.3 to 0.6 mg/L and naphthalene content ranged from 0.05 to 0.45 mg/L.All of them exceeded the standard of drinking water for III types of directly dispersed water sources stipulated in GB/T 14848-2017.Petroleum pollutants in site groundwater exhibited a dynamic change both in time and space.During the monitoring period,TPH concentration was generally on a downward trend and the characteristics of time variation of TPH was that the contents was highest in summer and decreased in winter.Along the runoff path in groundwater,the concentration of petroleum gradually decreased.The attenuation was controlled by many factors,such as the migration of water current,adsorption,volatilization and biodegradation.Formed in contaminated oil pit as a center,upstream pollutants migrated to downstream and pollution halos expanded outwards from northeast to southwest in the site groundwater.The decrease of top-down trend in the longitudinal direction was found,while the content of TPH in clay layer of downstream of sludge pit was lower,the content of TPH was higher when closed to the groundwater surface.It demonstrated that the oil pollution entered the groundwater through vertical infiltration and horizontal diffusion.Based on the research of oil migration in soil,migration of pollutants was influenced by convection,diffusion and interaction between oil and water on account of the characteristic of soil porous medium.Based on the thermodynamic equilibrium and kinetic equation of porous medium,the migration model of petroleum,the distribution of pollutants was determined,and the risk assessment was put forward.Based on the modelling results,it is urgent to carry out the treatment of oil pollution,especially for aromatics.Based on the remediation mechanism of fortifying AS by rhamnolipid under the condition of the one dimensional in-situ simulation in laboratory,the experimental results showed that the increases of permeability of porous media and gas injection rate was beneficial to the remediation of pollution.Under the same aeration flow rates,air saturation of AS technology in groundwater was in inverse proportion to the size of medium.However,after treatment by 200 mg/L rhamnolipid,the air saturation in groundwater has positive correlation with the particle size of the medium particles.The existence of rhamnolipid improved the treatment efficiency of AS technology.Accrodingly,the in-situ treatment was carried out in the contaminated sites for 20 d.Through monitoring the water quality,water level and dissolved oxygen of monitoring wells around aeration wells,it was found that the affect area of single gas-injection well is about 8 m,the TPH in groundwater decreased by 85% within the subregion and petroleum pollution of groundwater was below 1 mg/L.The concentration of all kinds of petroleum pollution was decreased in different degrees,especially for aromatics.Assisted by the air injection,groundwater environment changed from anaerobic to aerobic,the redox parameter(Eh)increased significantly,and the activity of superoxide dismutase and catalase increased slightly.These suggest that surfactant enhanced AS technology can promote aerobic bio-degradation around the gas-injection wells to some extent.After remediation,the health risk of pollution has also been greatly reduced and the goal of remediation has been achieved. |
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