Study On The Formation,Strengthen And Dynamic Change Of Oil-Particulate Aggregates(OPAs)

With the increase of oil demand and transportation,marine oil spill accidents occur frequently,which cause extensive and long-term adverse effects on the natural ecological environment and human social security.After the oil spill,the suspended particles will interact with the oil to form Oil-particle aggregates(OPAs)under the hydrodynamic action in the ocean.OPAs can form naturally in a few of minutes,accelerate the deposition of oil to the sea floor and promote the biodegradation,which play an important role in the removal of oil spills.Biochar(BC)is cheap,easy to obtain and has strong adsorption capacity for oil.So it is of great significance to study the strengthening effect of BC on OPAs and its removal mechanism for oil to promote the removal of marine oil spill.In this paper,the variation of the size,morphology,compactness,settling rate and oil trapping efficiency with shaking time of Oil-Kaolin aggregates(OKAs)and Oil-Bentonite aggregates(OBAs)were studied by using two types of clay particles,kaolin and bentonite,as the research objects.The EPS components and functional group were measured.The effects of bacteria and different suspended particles on the formation of OPAs were analyzed.On this basis,the morphology and oil trapping efficiency of stregthening OPAs(S-OPAs)generated under the action of BC were studied.The influence of BC on the formation of OPAs was analyzed.The EPS components and functional groups of S-OPAs were determined.The diversity of bacterial population structure in S-OPAs was also studied by high-throughput sequencing.Compared with OPAs,the effect of BC on the community structure and diversity of OPAs was analyzed.The main conclusions are as follows:(1)OPAs were more diverse in morphology and larger in size under natural bacterial conditions.OKAs can be divided into compact massive,dendritic and loose chopped,while OBAs can be divided into granular,flaky and hairy globular,with a maximum diameter of several hundreds of ?m.A large number of bacteria,oil and kaolin aggregate were attached to the surface and outer pores of S-OPAs formed by BC addition,and the surface of S-OBAs are smooth with little aggregates.(2)The settling rate of OPAs increased with the decrease of D2 value under natural bacterial conditions.Compared with OKAs,OBAS were more loose(the D2 value of OKAs was 1.32 on the 18 th day,the D2 value of OBAs was 1.26 on the 18 th day),and the settling rate is higher(the settling rate of OKAs was 0.39mm/s on the 18 th day,and the settling rate of OBAs was 2.75mm/s on the 18 th day).(3)Under natural bacterial conditions,OKAs and OBAs had better oil removal effects than aseptic conditions,and the oil trapping efficiency increased by 108.34% and 101.29%,respectively.In addition,the oil trapping efficiency of OBAs is far less than OKAs.Compared with OBAs,EPS of OKAs had higher protein and polysaccharide content,and the protein/polysaccharide ratio was higher.The higher the protein/polysaccharide ratio,the greater the oil adsorption capacity of OPAs.(4)High-throughput sequencing showed that compared with OBAs,the bacterial community of OKAs had higher richness,diversity and evenness.The dominant bacteria of OKAs were Alcanivorax(50.43%),Sphingomonas(10.87%),Oceanicaulis(10.11%),Brevibacterium(9.80%)and Sphingopyxis(5.01%),respectively.The dominant bacteria of OBAs were Alcanivorax(51.37%),Sphingomonas(12.64%),Brevibacterium(9.88%)and Sphingopyxis(5.92%),respectively.BC changed the bacterial community structure of S-OPAs,increasing the richness and evenness while decreasing the diversity.Acinetobacter with low abundance enriched on S-OPAs,and the proportion of Alcanivorax,Sphingomonas,Brevibacterium decreased.(5)Adding BC can shorten the oil absorption balance time and improve the oil absorption rate of OPAs.S-OPAs had better oil removal effect because it's great oil capture ability.After adding BC,the oil removal rate of OKAs and OBAs increased from 16.48% and 8.90% to 74.30% and 76.03%,respectively.However,the increased concentration of kaolin had a negative impact on the oil-capturing performance of S-OKAs.Therefore,BC is more suitable to be applied in the sea with lower concentration of kaolin to remediate the oil spill pollution.