The biodegradation of petroleum hydrocarbons in an upflow sludge-blanket/fixed-film hybrid bioreactor under nitrate-reducing conditions: Performance evaluation and microbial identification

The effects of inlet concentrations of total petroleum hydrocarbons (TPH), hydraulic retention time (HRT), salinity, and the presence/absence of nitrate on TPH biodegradation in a continuous upflow sludge-blanket/fixed-film hybrid bioreactor (UAnSFB) operated under nitrate-reducing conditions were investigated. The critical TPH loading rate was around 78 g/m3 h based on changes in TPH inlet concentration and around 60.5 g/m3 h based on changes in HRT. The TPH biodegradation was not significantly affected by amounts of NaCl up to 30 g/L. TPH biodegradation sharply decreased in UAnSFB from 99.7% in the presence of nitrate to 37.6% only 3 days after the nitrate was withdrawn from the influent. 16S rDNA fragment and phylogenetic analysis identified Stenotrophomonas maltophilia and Stenotrophomonas acidaminiphila in biofilm and Staphylococcus warneri and Bacillus cereus in the sludge blanket as the most abundant species. Accordingly, the UAnSFB is a promising bioreactor for the efficient biodegradation of TPH in saline media.