Bioremediation Of Petroleum Hydrocarbon Contaminated Soil

Since petroleum hydrocarbons are hard to degrade,and are known to produce carcinogenic,teratogenic and mutagenic effects,their accidental release can pose significant threat to the ecosystem and public health.The restoration of petroleum hydrocarbon contamination is therefore of great importance to the protection of the environment.Bioremediation,as an augmented version of the natural process,has the advantages of being cost effective,environmentally friendly,and implementable in situ without causing secondary pollution.It has thus become mainstream in petroleum hydrocarbon contamination remediation.This research is a case study of the bioremediation of a solid waste management unit(SWMU)in northern California.Experiments including indigenous bacteria isolation,functional consortium construction and greenhouse simulation study were performed to bioremediate the contaminated soil.30 bacterial strains were isolated from the contaminated soil through enrichment with petroleum hydrocarbons as the sole carbon source.16 S rDNA sequencing indicated that the strains belonged to 3 phylum and 13 genera,among which Proteobacteria were the major phylum,and Serratia and Pseudomonas were the dominant genera.Crude oil depletion experiment showed that Serratia proteamaculans S1BD1,Alcaligenes sp.OPKDS2,Rhodococcus erythropolis OSDS1,Rhizobium sp.PNS1 and Pseudomonas sp.BSS9BS1 achieved the highest depletion efficiencies of 67.99%,63.65%,54.92%,52.97% and 41.75% respectively.Bioemulsifier production of Rhodococcus erythropolis OSDS1 and its promotion of petroleum hydrocarbon depletion were investigated.The results showed that R.erythropolis OSDS1 produced an extracellular bioemulsifier with stable emulsification effect,with about 90% emulsification activity maintained after 168 h under room temperature.Among different petroleum hydrocarbons,the bioemulsifier had the strongest effect on diesel,followed by mineral oil/crude oil,and finally,gasoline.The depletion efficiencies of petroleum hydrocarbons were significantly improved with the addition of bioemulsifier.Pleosporales sp.32 achieved the highest degradation efficiencies for diesel(56.57%)and crude oil(84.80%)respectively when the concentration of emulsifier was 5g/L and 1.25g/L.Bacteria and fungus(R.erythropolis OSDS1+Pleosporales sp.32)co-culture system also improved the depletion efficiencies of petroleum hydrocarbons.The depletion efficiencies of diesel and crude oil were 64.43% and 80.17%,respectively,which were much higher than that achieved by individual strains(bacteria: 20.80% and 25.43%;fungus: 24.33% and 38.40%).The presence of bioemulsifier significantly increased the depletion efficiencies of C16 to C35 and PAHs in crude oil.Five petroleum hydrocarbon degrading bacterial strains with high depletion efficiencies and complementary depletion characteristics,including S.proteamaculans S1BD1,Alcaligenes sp.OPKDS2,R.erythropolis OSDS1,Rhizobium sp.PNS1 and Pseudomonas sp.BSS9BS1 were selected to construct a high efficiency bacterial consortium PHDc.It achieved 85.26% depletion efficiency for crude oil in 15 days,which was much higher than that of individual strains.Furthermore,PHDc significantly increased the depletion efficiencies of compounds > C16 and relatively more complex compounds like branched alkanes and PAHs in crude oil.Through PCR,this study successfully amplified alkane hydroxylase gene(alkB)from the consortium,further verifying the presence of petroleum hydrocarbon degrading enzymes.Five petroleum hydrocarbon degrading bacteria with plant growth-promoting properties were used to construct a plant growth promoting bacterial consortium PGPBc.Among these five,Pseudomonas sp.PFS1 and BSS3B2 produce IAA,S.proteamaculans SIBD1 and Alcaligenes sp.PKS1 solubilize phosphate,while Bacillus sp.strain PSS2 and Pseudomonas sp.strain PFS1 produce siderophore.The effects on seed germination and plant growth of saltgrass by this consortium were explored.The results showed that PGPBc had no observable effect on the germination of saltgrass seeds,but significantly promoted the subsequent growth of germinated seeds.When PGPBc inoculation is completmented with potting soil amendment,both the germination and growth of saltgrass in the contaminated soil were significantly improved.The germination rate was as high as 75%,while the biomass was 6.6 fold of the blank control.Finally,a six-month bioaugmentation-assisted phytoremediation was conducted under greenhouse conditions,leveraging the constructed petroleum hydrocarbon degrading bacterial consortium,plant growth promoting bacterial consortium and saltgrass.The results showed that the combined use of plant and microbes significantly improved the depletion efficiency of petroleum hydrocarbons in the contaminated soil to 50.25%.Petroleum hydrocarbon degrading bacteria can be used with saltgrass to facilitate the bioremediation of contaminated soil.This study first reported the ability of Serratia proteamaculans strain S1BD1 in solubilizing phosphate,the promotion of petroleum hydrocarbon degradation by the emulsifier of Rhodococcus sp.OSDS1 was also explored,and a series of bioremediation experiments were carried out.The outcomes from this research provided solid foundations for the implementation of large-scale bioremediation at SWMU.