Phyto-microbial Combination Remediation Of Water-based Drill Cutting Wastes From Offshore Oil Field

Nowadays,petroleum is one of the most important resources for human society.With the increasing demand for petroleum,offshore drilling platforms are increasing because the ocean is rich in petroleum resources.Water-based drill cutting wastes are generated in petroleum exploration.These oily solid wastes are often taken back to dispose on the land.Improper disposal of these drill cuttings will absolutely lead to the soil contamination.Petroleum hydrocarbon and other organic pollutants not only affect the normal function of the soil,decrease the environmental quality of the soil,and enrich in plants or animals,but also threaten human's health through the food chain.Therefore,oily sludge and waste drill cuttings are listed in the national list of hazardous waste,and their emissions are strictly limited.In this paper,the aims were to(1)evaluate the remediation effective of petroleum hydrocarbon from water-based drill cutting wastes by using of different plant-microbial system in a laboratory scale and in a pilot scale;(2)explore the changes of rhizo-microbial abundance and activity in different rhizosphere systems during the remediation.The main original conclusions of this dissertation were drawn as bellow:(1)By determining properties and content of pollutants of water-based drill cutting wastes,it was found that water-based drill cuttings wastes were alkaline(pH=9.1),moderate salinity(0.45%),the contents of Cr?Mn?Ni?Cu?Zn?Cd and Pb were 8.12?450.57?8.28?54.90?52.90?0.77 and 148.77 mg/kg,respectively.The main pollutant,however,was petroleum hydrocarbons.Its content was 27.59±4.77 g/kg.Therefore,petroleum hydrocarbons were the target for plant-microbial remediation.(2)According to the different proportions,waste water-based drill cuttings mixed with uncontaminated soil.Four plants,ryegrass(Lolium perenne L.),tall fescue(Festuca arundinace),alfalfa(Medicago sativa L.)and white clover(Trrifolium repens L.),were selected to evaluate their seed germination and growth under the different soil proportion.It was found that the germination and grow of ryegrass and alfalfa were more tolerance than other two plants under propotion of 1:1.As the result,ryegrass and alfalfa were determined as the testing plant.(3)Through pot experiment,the result showed that the removal rate of total petroleum hydrocarbon was ranged from 53%to 70%by using plant-microbial system,and this system also has a better removal to refractory compounds,such as polycyclic aromatic hydrocarbons.The removal rates of polycyclic aromatic hydrocarbons in all bioremediation treatments were exceeded 50%,and the removal rates of naphthalene and phenanthrene and fluoranthene(2-3fuse-ring)were higher than any other polycyclic aromatic hydrocarbons.Within a short time,plant can significantly increase the abundance of bacteria,and improve the activity of bacteria Dehydrogenase activity in growing plant was 237%higher than other treatments.Ryegrass made the number of total heterotrophic bacteria increase from 102 cfu/g to 107 cfu/g.Alfalfa,on the other hand,seems to specifically increase the number of microorganisms capable of degrading more complex hydrocarbons.The number of petroleum hydrocarbons degradation bacteria in alfalfa's rhizosphere was increased from 102 MPN/g to 105 MPN/g,and the number of polycyclic aromatic hydrocarbons degradation bacteria was increased from 102 MPN/g to 104 MPN/g.In addition,plants and their rhizosphere microorganisms can change the soil pH during the processes of plant growth and metabolism of pollutants in rhizosphere.Hence,based on results of pot experiment,a pilot scale experiment can be carried out in order to evaluate the bioremediation effect of petroleum hydrocarbon from water-based drill cutting wastes outside laboratory.(4)During the 120 days bioremediation process in this pilot test,the result showed that the removal of total petroleum hydrocarbon from waste water-based drill cuttings by rhizosphere remediation was significant high than that by non-rhizosphere.Alfalfa's rhizosphere removed a little higher level than ryegrass's,and the removal rate of such two plants were reached 95%and 94.1%,while removal in non-rhizosphere was only 77%.Moreover,the average content of total petroleum hydrocarbon in alfalfa's rhizosphere decreased from 7029.47 mg/kg to 297.76 mg/kg,and it was significant lower than the Chinese soil environment quality standard(GB15618-1995)3000 mg/kg.In addition,this pilot test was also found the same conclusions with the laboratory experiments about changing abundance and activity of microorganisms,and decreasing the soil pH.In a word,the technology of plant-microbial combination can be used to deal with water-based drill cutting wastes from offshore oil field,and make it harmless.