Study On The Emulsification And Biodegradation Efficiency Of Oil Spills Under The Action Of Dispersants

Dispersant is widely used in the pollution treatment of oil spill as an emergencymeasure, however, use of dispersant is influenced by various factors (salinity,temperature, pH, marine hydrodynamics, level of weathered crude oil), and thereexists a phenomenon of adding excess dispersant in the actual treatment of oil spill. Infact, oil is emulsified and dispersed into water only, it doesn’t diappear actually andneed to be removed under the action of petroleum-degrading microorganisms in theend. So, it is of great significance to study the emulsification and biodegradation of oilspill that influenced by adding dispersant.Light crude oil and heavy crude oil were choosed in this article. Factors affectingthe efficiency of emulsification of the crude oil were studied first, such as the amountof adding dispersant, environmental conditions (salinity, temperature, pH, mixedenergy of seawater) and level of weathered crude oil, and then Plackett-Burman(PB)and Box-Behnken Design(BBD) test were applied on these factors, optimal conditionsof crude oil emulsification were obtained in the end. Secondly, choose mixedpetroleum-degrading microorganisms which were obtained through enrichment andacclimation as strains used in the bioremediation. The effect of changing the amountof adding dispersant in the biodegradation of crude oil was studied through batchswirling flask tests; and the effect of adding nutrient as well as different types ofnutrient and N/P ratio on bioremediation of crude oil emulsified by dispersant werediscussed also. The results are as follows:(1) Emulsification of various crude oil are in slightly different because of its ownphysical properties,light crude oil is more easily to be emulsified than heavy crude oil.(2) Under the effect of a single factor, amount of adding dispersant20%~30%,salinity30‰, higher temperature, neutral pH, higher mixed energy of seawater andlower level of weathered crude oil will be advantageous to the emulsification of crudeoil, and that can reach standard of dispersant emulsification (10min emulsificationrate is more than20%). (3) When different factors interact with each other, level of weathered crude oil,the amount of adding dispersant, mixed energy of seawater and salinity become moresignificant on effecting dispersant emulsification, and influence degree reduce in turn,then make sure the most optimal operating condition is: level of weathered crude oil0%, amount of adding dispersant28.90%, mixed energy of seawater150rpm/min,salinity31.27‰, and the emulsification rate reaches42.20%at the moment.(4) Adding dispersant is beneficial to growth and reproduction of microorganismand biodegradation of crude oil, but it doesn’t mean the more the better. When amountof adding dispersant is10%, effect on the growth and reproduction of microorganismis not extraordinarily obvious, the degradation rate of crude oil is37.58%; Whenamount of adding dispersant is40%, it isn’t conducive to the growth and reproductionof microorganism, and may as well the one without dispersant (the degradation rate ofcrude oil is28.04%); when the amount of adding dispersant is20%and30%, growthand reproduction of microorganism is promoted and the efficiency of degradation ofcrude oil is better, the degradation rate of crude oil is44.61%and42.90%.(5) Adding niutrient to the crude oil emulsified by dispersant will remarkableenhance the biodegradation rate of crude oil, and it was influenced slightly differentby various types of nutrient. Inorganic nitrogen source was much easier to be usedthan organic nitrogen source by microorganisms, and compared with ammoniumnitrate, nitrate nitrogen is more likely to be used, at this time, the amount ofmicroorganisms is the larger and the efficiency of biodegradation of crude oil is better.There is a wide concentration range that could improve the biodegradation of thecrude oil emulsified by dispersant. Keeping concentration of P at2mg/L, when theN/P ratio was6:1or8:1, proliferation of microorganism improved fast and so was thethe biodegradation rate of crude oil, the degradation rate of crude oil is78%and70.26%.