Optimization of the Environmental Condition for the Removal of n-Propylbenzene and Isopropylbenzene in Seawater by Rhinomonas reticulata S6A Based on Response Surface Methodology

N-propylbenzene (n-PBZ) and isopropylbenzene (i-PBZ) are considered hazardous and noxious substances, and once leaked into the sea, they will cause serious harm to the marine ecosystems. Our previous study has found that the removal rate of n-PBZ and i-PBZ at a concentration of 5 mg/L by Rhodomonas reticulata S6A within 7 days were 34.6% and 38.8%, respectively. To further clarify the suitable environmental conditions for the remediation of propylbenzene-contaminated seawaters, the effects of salinity, temperature and light intensity on the removal of n-PBZ and i-PBZ from seawater by R. reticulata S6A were investigated in this study using response surface methodology (RSM) based on the Box-Behnken design. The results indicated that light intensity and temperature were the key factors affecting the removal of n-PBZ and i-PBZ, respectively. Additionally, the interactions between temperature and salinity, as well as temperature and light intensity, were found to be significant. The optimal environmental condition for the microalga to remove n-PBZ was as follows, salinity 27.2, temperature 25.1 ℃ and light intensity 237.9 μmol/(m²·s) with a measured removal rate of 51.2%. The most suitable environmental condition for removing i-PBZ was as follows, salinity 28.4, temperature 25.5 ℃ and light intensity 580.8 μmol/(m²·s) with a measured removal rate of 54.6%. The removal rate prediction model constructed based on the experimental results could be used to estimate the bioremediation effect in propylbenzene-contaminated seawaters, providing a decision-making basis for determining the appropriate occasions and times for using the microalga.