The physical–biological processes of petroleum hydrocarbons in seawater/sediments after an oil spill

The adsorption and desorption behaviors of dissolved petroleum hydrocarbons (DPHs) in a seawater–sediment system were investigated. Tidal flat sediment was used as the adsorbent, and crude oil was used as the adsorbate. The processes of adsorption and desorption at low concentration (<14.3 mg L−1) were described by the first-order kinetics model. The rate of desorption was slower than that of adsorption, and about 49% of the DPHs remained on the sediment. Therefore the potential risk of pollution would exist for a long time. The adsorption isotherms could be better fitted to the linear isotherm model than the Freundlich and Langmuir models. The adsorption process is a physical adsorption, because |ΔH| was 39.0 kJ mol−1 which is less than 42.0 kJ mol−1. The change in n-alkanes in the process was more obvious than the aromatics; the weathering loss rate was 25.56%, the emulsification loss rate of the dispersant was 0.65% and the microbial degradation rate was 15.46%. The results showed the degradation processes of petroleum hydrocarbons in tidal flats.