Enhanced Bioremediation Of Petroleum Contaminated Soil Using Aged Refuse

With the rapid development of petrochemical industry,the soil pollution caused by oil production,storage,transportation and leakage accident is becoming more and more serious.Oil pollutants not only damage and destroy soil,but also directly harm the human through food chain.Compared with physical and chemical method,bioremediation is more cost-effective,thorough and eco-friendly.Hence,it is becoming the mainstream restoration method of petroleum-contaminated soil.But there are still many disadvantages in bioremediation,such as poor effect of natural degradation and long repair cycle,and it is difficult to repair heavy petroleum-contaminated soil.Some research enhanced bioremediation by adding exogenous bacteria agent,surfactant,and artificial aeration and so on.But the cost of these measures is too high.The biodegradation capacities of petroleum contaminants are affected by many physicochemical and biological factors.Therefore,it is difficult to achieve effective bioremediation of petroleum-contaminated soil if only a single bioaugmentation or biostimulation approach is used.To improve the effectiveness of bioremediation,researchers often implement several bioaugmentation and biostimulation measures simultaneously,which substantially increases the cost of bioremediation.Therefore,it is a problem of widespread attention at home and abroad that how to further improve the effect of bioremediation,expand the scope of the bioremediation applications,and decrease the cost of bioremediation.Aged refuse(AR)has high porosity,high moisture retention,and abundant organic matter in addition to essential nutrients for microbial growth.AR also provides additional microbial biomass and diversity for soil.It is a kind of waste with huge reserves and shallow burial depth,which is convenient for mining and utilization.The basic ideas and solutions of these problems were proposed in this paper that enhancing the in-situ bioremediation of petroleum-contaminated soil using AR from landfill.We conducted a lab-scale experiment and monitored changes in physicochemical properties,residual petroleum contents,enzyme activities,microbial biomass and microbial community structure and other factors in treatments to study the effect,application scope and the underlying mechanisms of AR on petroleum degradation.Then the treatments of enhanced phytoremediation by AR were studied to further improve the removal of total petroleum hydrocarbons(TPH).Finally,the method of enhanced bioremediation of petroleum-contaminated soil using AR was evaluated,and its safety was also analyzed.The main conclusions of this paper are as follows:The optimal bioremediation conditions of petroleum-contaminated soil enhanced by AR are as follows:aerobic condition,8 years landfill age AR,15%soil moisture content,25?temperature and 50%AR mass fraction.No tillage measures were required during bioremediation.Aerobic treatment showed the highest total petroleum hydrocarbon(TPH)removal rate but the lowest toxicity,indicating its highest effectiveness.Aerobic condition favored the biodegradation of small molecular petroleum pollutants.The removal rates of alkanes,alkenes,aromatic hydrocarbons and aromatic hydrocarbon derivatives were the highest and the added pollutants after remediation were mainly cyclanes,halogenated and nitrogen heterocyclic organic matter.In contrast,anaerobic condition favored the biodegradation of high molecular petroleum pollutants.The removal rates of cyclanes,cycloalkane derivatives and nitrogen heterocyclic organic matter were the highest and the added pollutants after remediation were mainly branched alkanes,cyclanes and oxygenated cyclic organic matter.Aerobic treatment had higher total microbial activity and more petroleum hydrocarbon degrading bacteria than anaerobic treatment,while in contrast anaerobic treatment had higher soil microbial diversity and more petroleum hydrocarbon derivative degrading bacteria.TPH removal effect was best in 5%TPH level soil(89.83%).When the TPH content was less than 5%,the ecotoxicity of petroleum pollutants was low.TPH content increase could result in more abundant carbon sources and energy for microorganisms,which could improve the quantity and activity of soil microorganisms,and thus improve the TPH removal rate.When the TPH content was greater than 5%,TPH removal rate decreased with the increase of TPH concentration due to the toxic effect of petroleum pollutants.The dominant bacteria and fungi in the five treatments were both Nocardia and Zopfiella,respectively.Nocardia proportion increased with TPH concentration rise,while Zopfiella proportion was opposite.AR amendment enhanced the bioremediation of petroleum-contaminated soil not only via biostimulation but also by bioaugmentation.In terms of biostimulation,AR addition significantly reduced soil ecotoxicity,substantially improved soil porosity,water holding capacity,cation exchange capacity,humus content,organic matter levels,nutrient levels and nutrient availability,and also made soil p H more neutral.All of the above changes in soil physical and chemical properties improved the living environment of soil microorganisms comprehensively,and thus improved the number and metabolic activity of soil microorganisms.The TPH removal rate of treatment amended by sterilized AR(Exp-SAR,74.64%)was much higher than that in natural attenuation control(22.40%),which proved that adding AR was an effective biostimulation measure.In terms of bioaugmentation,the number of microorganisms in AR was much larger than that in the test soil,and AR contained a variety of petroleum-degrading bacteria.AR addition markedly increased soil FDA hydrolytic activity and dehydrogenase activity,as well as the diversity and quantity of petroleum-degrading bacteria.The TPH removal rate in treatment amended by AR was 15.19%higher than that by in Exp-SAR,which proved that adding AR was an effective bioaugmentation measure.84kinds of petroleum degrading bacteria were isolated from AR,including 70 kinds of proteobacteria,11 kinds of bacteroides and 3 kinds of actinomycetes.After bioremediation,there were few C₇-C₂₂ alkanes remained in the soil.TPH degradation rate was increased by 10times with AR addition.AR enhanced phytoremediation further improved the remediation effect of petroleum-contaminated soil.With AR addition,the tolerable TPH concentration of alfalfa increased from below 3%to above 10%.The optimum plant of phytoremediation with AR addition was alfalfa.Compared with AR enhanced bioremediation,AR enhanced phytoremediation not only further increased FDA hydrolytic activity,dehydrogenase activity,latter polyphenol oxidase activity and bacterial diversity in soil,but also improved the proportions of bacteria that could degrade PAHs,PCBs,cyclanes and heterocyclic oil pollutants.TPH removal rate in alfalfa+AR test was 7.80%higher than in AR enhanced bioremediation.There were 25 strains isolated petroleum degrading bacteria which were only belong to alfalfa+AR test.They were belonged to Rhodococcus,Mycobacterium,iii1-15,Chryseobacterium,Ignavibacteriaceae,AKYG1722,Hyphomicrobiaceae,Parvibaculum,Rhodospirillaceae,Sphingobium,Novosphingobium,Sphingopyxis,Achromobacter,Giesbergeria,Methylophilales,Aquicella,Pantoea,Acinetobacter,Aeromonadaceae,Luteibacter and Arenimonas,respectively.There were 5strains isolated petroleum degrading bacteria were identified to species.The heavy metal contents of used AR meet the current standard screening values of I level construction land and orchard land.Adding AR can reduce the migration of petroleum pollutants in soil,and oil migration in soil decreased with the increase of AR mass fraction.Compared with other bioremediation methods,AR enhanced bioremediation has the following advantages:lower costs,better effect,shorter repair time,wider application range,simple process,easy to manage,facilitating in situ large-scale application.In addition,this study not only provided an economical and efficient bioremediation method for petroleum-contaminated soil,but also realized“treating pollution with waste”,which provided a new way for recycling AR.Hence,the bioremediation of petroleum-contaminated soil amended by aged refuse has high environmental and economic benefits.