Investigation Of Enhanced Oil Separation In Water And Biodegradation Mechanism

In recent years, oil slim in water derived from increasing oil spill accidents has been seriously threatened marine ecological environment. The technology of removing oil slim is one of the presently studying hotspots. The oil droplets dispersed from surface slicks caused by local flow and turbulence conditions aggregates with suspended mineral particles naturally and readily forming oil mineral aggregates (OMA), which enhance dispersion of spilled oil and decreases average oil droplet size by preventing the droplets recoalescence. This process is good for oil biodegradation. In this study, the influence of factors on OMA formation was investigated. Clay was modified and then used to form OMA with different oil. Models were developed for experimental data fitting and OMA formation mechanism was further discussed. Besides, the oil biodegradation facilitation by OMA was studied. The main conclusions of this dissertation are as follows:1. The study on OMA formation with sediment minerals from Yangtze Estuary and Hangzhou Bay found that particulate matter size distribution, organic matter content and concentration were important parameters, and light diesel and heavy oil only formed OMA with minerals with grain diameters less than3μm. High organic matter content of sediment was proved to be good for aggregation between particle and oil droplet. The OMA formation efficiency increased with the particle concentration. Oil droplet separated by different surfactant would have different OMA formation efficiency with mineral and cationic surfactant promote OMA formation.2. Different types of surfactant were used to modify the clay. CTAB modified clay has the higest aggregation efficiency with oil droplet. Acid pretreatment clay had better CTAB modifiy efficiency. The reaction equilibrium reached at6h with initial CTAB concentration of2g/L. The surface structure of clay before and after modified was studied with SEM. Modified clay (CTAB-B) has a more rough surface and more apparent structural channels features compared to original clay (Na-B). IR results showed that long carbon chain of CTAB was introduced to the surface of clay which confirmed the successful modification. TG curves of clays indicated that both CTAB-B and Na-B had preferable thermostability. CTAB-B had better hydrophobicity than Na-B. Zeta potential test result demonstrated that Na-B was negative charged and CTAB-B was positive charged.3. Light diesel and heavy oil OMA formation efficiency has increased sharply with modified clay. Under UV epi-fluorescence observation, it was found that there are three different structure types of OMA:droplet, solid and flake. OMA formed with CTAB-B and Na-B had different structure. Much more CTAB-B particles adhered to the surface of oil droplet, by which OMA formed with CTAB-B was more stable. The size of OMA formed with CTAB-B was wider ranged and the average of it was smaller.4. OMA formation efficiency increased with clay dosage. Maximum efficiency reaches at critical clay concentration and salinity. Surface property is the key factor for the aggregation. Surface modification increased the affinity between oil droplet and particle. OMA-particle concentration model was set up and the experimental data was linear fitted. Correlation coefficients of the model were more than0.9. The fitting results indicated that OMA formation efficiency was very low as the particle concentration was lower than50%of CS50, and OMA formation efficiency increased with particle concentration as which was more than50%of CS50. The increasing rate of efficiency with particle concentration went up with the model parameter n.5. The diameter of oil droplet decreased because of OMA formation with particle FX、 Na-B and CTAB-B. Meanwhile, larger rough surface provided by particles was beneficial for bacteria culture. Oil biodegradation was consequently enhanced by this process. Furthermore, oil biodegraded at the highest rate with addition of CTAB-B, and light diesel and heavy oil removal efficiency reached73%and79%in five days respectively. Yet increasing salinity restrained the microorganisms’ growth, the size of oil droplet decreased with increasing salinity by which oil biodegradation was facilitated. pH of the water was reduced due to organic acids produced by oil degradation. Na-B、CTAB-B played a important role on pH balance by adsorption of hydrogen ion. Most of the organics with short carbon chain in light diesel and heavy oil was removed and only a small fraction of residual oil with long carbon chain was left.The above results are helpful to understand oil dispersity in water, provide experimental data and theoretical basis to predict and model the transportation of spilled oil, and offer quantitative evidence that supports further development of practical operational oil removal techniques based on OMA formation.