Diatom Chaetoceros calcitarans MZB-1 for degrading propylbenzenes in seawater: Cultivation conditions, degradation kinetics, and influencing factors

Accidental leakage of petrochemical products (such as C9 aromatics) containing propylbenzenes (PBZs) during maritime transport poses severe threats to marine ecosystems. In this study, a PBZs-degrading diatom, Chaetoceros calcitrans MZB-1, was isolated from the seawater close to Quangang Port, Fujian Province, China, where a serious spill of C9 aromatics previously occurred several years ago. The optimal growth conditions for this alga were pH 8.5, salinity 10 ‰, temperature 25 °C and light intensity 60 μmol/(m²·s). At the optimal inoculation density (1 × 10⁶ cells/mL), removal efficiencies of two PBZs, namely n-propylbenzene (n-PBZ) and isopropylbenzene (i-PBZ), were 68.6 % and 44.6 %, respectively, within 7 days. The elimination of each PBZ over time followed the first-order kinetic model. After adding 750 mg/L and 500 mg/L of NaHCO₃ into the F/2 medium, the removal efficiencies of two PBZs increased to 70.8 % and 51.2 %, respectively. These results showed that alga MZB-1 could be more effectively used for bioremediation of PBZs-contaminated seawater than the one previously isolated.