Performance of a moving bed-membrane bioreactor treating saline wastewater contaminated by hydrocarbons from washing of oil tankers

This work analyses the performance of a moving bed-membrane bioreactor (MB-MBR) in the treatment of saline wastewater contaminated by hydrocarbons from washing of oil tankers with seawater (slops). In order to allow a biomass acclimation, a gradual increase in salinity and total petroleum hydrocarbons (TPHs) were adopted during six experimental phases. The results showed that acclimation of heterotrophic strains to TPHs occurred during Phase IV (30% by volume of slop). This is confirmed by an evident increase in the biological removal efficiencies of chemical oxygen demand, total organic carbon and TPHs. In particular, the TPHs removal efficiency increased from about 8% up to the range of 35–70%. No inhibition of the ammonia oxidizing bacteria (AOB) was noted except for Phase VI (100% by volume of slop) characterized by a collapse of ammonium removal efficiency from about 95% to about 21–24%. An accumulation of nitrite at the end of Phase IV, suggested an inhibition of nitrite-oxidizing bacteria (NOB), while a simultaneous “salt-in” of bromide indicated the acclimation of the same strains to salinity. Moreover, the hydraulic performance showed a high increase in total resistance to filtration (RT) during the pseudo-stationary phases (from Phase I to Phase III) and during Phase VI, due to the high salinity and hydrocarbons concentration. The results showed that the MB-MBR system has high potentiality for the treatment of saline oily wastewater.