Evaluation of Fertilizer Additions to Stimulate Oil Biodegradation in Sand Seashore Mesocosms

Effects of fertilizer additions for oil degradation were examined in sand seashore mesocosms. Within 37 days, up to $85\%$ removal was achieved by the addition of slow-release type fertilizer (SRF) with the initial degradation rate of 423.3 mg oil $(kg sand)^-1\;day^-1$. The removal was mostly of biological origin based on the changes of $C_17$ /pristane and $C_18$/phytane ratios from 2.60 to 0.81 and from 3.55 to 1.29, respectively. The addition of oleophilic fertilizer (Inipol EAP22) was less effective and resulted in the removal of $64\%$ of the added oil ($3\%$, v/v) with a lower initial degradation rate. Petroleum-degrading bacteria had achieved a value of $1{\times}10^8$ CFU $(g sand)^-1$ at Day 3 and this peak exactly coincided with the initial degradation in the SRF-treated mesocosm. In this mesocosm, surface tension values were decreased drastically during Days 3 and 8, suggesting that microbially-produced surface-active agents actively enhanced the oil degradation rate and cell proliferation. Although the Inipol-treated mesocosm appeared to show significantly enhanced oil degradation compared to that of the untreated control mesocosm, Inipol was found to be less effective than SRF in enhancing a true oil-degrader when compared under similar experimental conditions.