Influences Of Nutrients Addition On The Biodegradation Of Diesel Oil In Seawater

Studies on the biodegradation of petroleum in marine environment by microorganisms are a new technology.Due to the low cost,in-situ degradation and no pollution products,it attracts more attention.The application of biodegradation technology is limited by the lack of nutrients,such as nitrogen and phosphorus.So adding nutrients,enhancing its proliferation ability and increasing the degradation efficiency play key roles in the application of biodegradation.The mixed petroleum degrading bacteria from oiled seawater on Dagang pier were isolated.Taken 0# diesel as object,we used NaNO₃,NH₄NO₃,urea and fish meal as nitrogen sources to assess the effectiveness of nutrient application to indigenous oil-degrading bacteria.The main results obtained from the experiment were listed as follows:1.Based on the results of experiments,we find that when adding NaNO₃ alone as nitrogen source.,the stimulation of biodegradation effect of diesel is much better than adding NH₄NO₃ alone.The degradation rate of samples are 65%and 15%.It is also showed that the NO₃^-—N is more easier to absorb for oil-degrading bacteria than NH₄⁺—N.2.According to the research,the effect on biodegradation of diesel oil by adding nitrogen alone is more complex than the mixed nitrogen:The former can stimulate the growth of oil-degrading bacteria and further more increase the degradation efficiency; the latter have both stimulation and inhibition;There would be great impact on microbial degradation effect of diesel when the same inorganic nitrogen source mixed with different organic nitrogen source.While adding nitrogen source alone,the highest degradation rates of diesel oil and the lowest are 65%and 7.88%,higher than control group where 6.55%of diesel oil was degraded.Mixing NH₄NO₃ with fish meal and urea separately as nitrogen source,the removal rate of diesel reaches 56.4% and 3.57%on condition that the ratio of N and P is 1.5:1,lower than the control group.3.The stimulation of different nitrogen source to the petroleum degrading bacteria is subject to environment.Take NH₄NO₃ for example,when temperature is 20℃,the biodegradation rate reaches 90%,but once the environmental temperature changes from 20℃to 10℃or 30℃,the biodegradation rate is less than 10%:In the same conditions,using NaNO₃ as nitrogen source,the biodegradation rate of diesel oil under 20℃and 30℃are above 50%,,in low temperature 17%diesel oil was degraded.4.The best nitrogen source is NaNO₃.The optimal condition was:oil density 0.15%,temperature 20℃,N:P 5:1,under which the removal rate of diesel oil is the highest 78%5.Analysis TN in treatment samples indicated there was corresponding relations between the changes of TN and the oil the degradation rate decomposing.Once the concentration of TN had been fallen,the degradation rate of experimental oil would be rising over time.