Petroleum Contamination And Purification In Seawater-sandy Beach Interface

Marine oil pollution is one of the main problems in the world. After the oil was spilled into the sea, large amount of oil was removed by physical and chemical methods. However, residual oil pollutants will drift to the bank with the action of wave and tide. Biodegradation and adsorption are both presented in seawater-sandy beach interface, and oil desorption from sands would bring a potential pollution threat to sandy beach. Exploring the mechanisms of oil pollution and its purification in seawater-sandy beach interface is of great significance.First, the adsorption mechanisms of dissolved oil on sands and its influcing factors are studied using batch-scale device; second, experimental methods are established to assess the co-influnces of biodegradation and adsorption on oil pollutants, and their behaviors in seawater-sandy beach are explored; third, natural desorption and induding desorption of oil from sands are studied using static and dynamic experiments; fourth, nutrients type and its relative content suited to the oil degrading microorganisms are studied using batch-scale equipment, and the control index of nutrient amendment in the bioremediation of oil-polluted beach are proposed by improving the addition methods and establishing oil-polluted sandy beach model. The main results obtained from the experiment are listed as follows:(1) The adsorption of dissolved oil on sands fits the second-order kinetic model, and the equilibrium adsorption capacity is 1.69mg/g. The adsorption capacity increases with the decrease of particle size and environmental temperature, and with the increment of salinity of seawater. The isotherms can be described as Henry's equation, and the adsorption heat in the process is -26.9 kJ/mol that demonstrates the adsorption of dissolved oil on sands belongs to physical adsorption.(2) When adsorption and biodegradation are both presented in the system, oil removal efficiency on account of adsorption in early stages is up to 20%~25%, while the biodgradation process is relatively weak. The biodegradation processes begin to exceed and play an important role in the middle and end of the experiment. The adsorption of dissolved oil by sands reduces oil concentration in seawater effectively, and the half time of oil biodegradation decreases from 3 1.9d to 22.4d and 19.5d respectively, while about 19%~25.5% oil pollutants is transferred on sands.(3) Natural desorption of oil from beach sands is very difficult, and the change of salinity and the increase of turbulence do not have much influence on the desorption process. Adding oil degrading microorganisms can promote desorption process extremely. Compared to natural desorption, bacteria consortium 1 and 2 with rich nutrients increase the mount of oil released from sands about 6 and 14 times, and raise the velocity 1-10 times. Due to the biosurfactant secreted by bacteria consortium 2, the promote effect is remarkable.(4) Adding nutrients can increase oil biodegradation effectively. Under test conditions, petroleum degrading microorganisms (PDMs) tend to use NO3-N as N source, and the optimal N/P ratio is 10: 1. The control index of nutrient addition in the bioremediation of oil-pollutedbeach are studied by establishing sandy beach model, and it is regarded the optimal N, P nutrient concentration is 5mg/l and 0.5mg/l respectively.Considering the comprehensive influences of biodegradation, adsorption and desorption, much more attention has been paid to key factors of petroleum pollution and its purification. On the basis of batch-scale experiment, the nutrient type and ratio that oil degraders tend to use were studied. Furthermore, through simulated model equipment, the control index of nutrient addition in the bioremediation of oil-polluted beach are put forward, and offers a database for the study of oil pollution and its purification in the sandy beach.