Application of Fixed-Bed Biofilm Reactors for the Treatment of Oil Sands Process Water

Lei Zhang
2019
The accumulation of huge amount of oil sands process water (OSPW) in tailing ponds has shown a serious threat to the local public health for their potential to contaminate surface and groundwater. Naphthenic acids (NAs) are considered to be one of the most important toxic compounds present in OSPW. Current physical and chemical NA degradation processes are still too expensive to be piloted; therefore, full-scale applications have not been assessed so far. With the advantages of ease
more » ... of ease construction, low energy input and robustness, the biofiltration process has been considered a promising approach for OSPW treatment. In this study, with the application of gravity as an important part of energy source, indigenous microorganisms based fixed-bed biofilm reactors were developed by using raw OSPW as influent process water and pure sand as media. Ultra performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS) detection showed that 21.8% of classical NAs could be removed from raw OSPW after 8 cycles of circulation through the established fixed-bed biofilm reactor with an equivalent hydraulic retention time (HRT) of 16 hours. With the combination of mild ozonation (with utilized ozone dose of 30 mg/L) pretreatment, the classical NAs in OSPW could be removed by 92.7% after the circulation of raw OSPW for eight times (with an equivalent HRT of 16 hours). Although both ozonation and biofiltration alone did not show degradation of oxidized NAs from raw OSPW, the combined process led to a 52.9% and 42.6% removal for O 3 -NAs and O 4 -NAs which were the dominant oxidized NA species in raw OSPW. With the advantage of high NA removal efficiency, the ozonation-biofiltration process is a promising approach for NA degradation. iii An innovative biofiltration-ozonation-biofiltration process was also developed and applied for the treatment of OSPW. By using the established fixed-bed biofilm reactor, a biofiltration pretreatment (with an equivalent HRT of 8 hours) showed consistent NA removal effect on raw OSPW as before, and it was found to benefit the following ozonation process for NA removal substantially. Through the biofiltration pretreatment, the ozonation (with utilized ozone dose of 30 mg/L) removal of classical NAs from OSPW improved from 32.1% to 84.8%, and the NA degradation efficiency improved from 0.1 mg NAs/mg O 3 to 0.3 mg NAs/mg O 3 . Compared with the biofiltration pretreatment, the post-biofiltration process showed higher degradation effect on oxidized NAs (removal ratio: 22.9% vs. 3.3%; removal rate: 0.4 mg/L/h vs. 0.1 mg/L/h). With biofiltration pretreatment, the utilized ozone dose is expected to be reduced to achieve the same NA removal as the ozonation of raw OSPW. With the high possibility to reduce the cost of ozonation, the biofiltration-ozonation-biofiltration process shows improved potential to be used in industrial applications. It is known that bacteria are the main players for petroleum hydrocarbons degradation and fungi are also potential organisms. 16S rRNA and 18S rRNA genes targeted sequencing revealed that Proteobacteria and Cryptomycota were the dominant bacterial and fungal phyla in the established biofilter. The dominant bacterial class was Alphaproteobacteria, the abundance of which decreased from 34.9% to 18.3% with depth, but the abundance of Anaerolineae increased from 1.5% to 8.3%. The changes in bacterial community structure along the biofilter suggested that the bioremediation of OSPW was achieved by aerobic and anaerobic combined degradation processes. Metatranscriptomic sequencing analysis showed that the functional abundance of aromatic compounds metabolism and organic acids degradation pathways in indigenous microbial community improved from 0.05% and 0.29% to 0.76% and 0.39% in the biofilter, iv respectively. The diverse microbial community structures and transcriptomic profiles might explain the effective degradation of NAs from different OSPW by biofiltration. Fixed-bed biofilm reactors were successfully developed and used for OSPW treatment in this study. The mild ozonation combined biofiltration process showed high efficiency on the removal of recalcitrant NAs from OSPW. Biofiltration pretreatment was observed to improve the ozonation efficiency on NA removal remarkably. The biofiltration-ozonation-biofiltration process also removed cyclic and aliphatic NAs from OSPW effectively. The diverse microbial communities along the fixed-bed biofilm reactors could alter their transcriptomic profiles for the effective degradation of NAs from different OSPW. With the advantages of cost-effective and high NA removal efficiency, the established biofiltration system is promising to be scaled up for OSPW treatment. v
doi:10.7939/r3-rkkd-b189 fatcat:ntr5mdd7dzcplextipzvyhewoy