Methanogenic Biodegradation of iso-Alkanes by Indigenous Microbes from Two Different Oil Sands Tailings Ponds

iso-Alkanes, a major fraction of the solvents used in bitumen extraction from oil sand ores, are slow to biodegrade in anaerobic tailings ponds. We investigated methanogenic biodegradation of iso-alkane mixtures comprising either three (2-methylbutane, 2-methylpentane, 3-methylpentane) or five (2-methylbutane, 2-methylpentane, 2-methylhexane, 2-methylheptane, 2-methyloctane) iso-alkanes representing paraffinic and naphtha solvents, respectively. Mature fine tailings (MFT) collected from two tailings ponds, having different residual solvents (paraffinic solvent in Canadian Natural Upgrading Limited (CNUL) and naphtha in Canadian Natural Resources Limited (CNRL)), were amended separately with the two mixtures and incubated in microcosms for ~1600 d. The indigenous microbes in CNUL MFT produced methane from the three-iso-alkane mixture after a lag of ~200 d, completely depleting 2-methylpentane while partially depleting 2-methylbutane and 3-methylpentane. CNRL MFT exhibited a similar degradation pattern for the three iso-alkanes after a lag phase of ~700 d, but required 1200 d before beginning to produce methane from the five-iso-alkane mixture, preferentially depleting components in the order of decreasing carbon chain length. Peptococcaceae members were key iso-alkane-degraders in both CNUL and CNRL MFT but were associated with different archaeal partners. Co-dominance of acetoclastic (Methanosaeta) and hydrogenotrophic (Methanolinea and Methanoregula) methanogens was observed in CNUL MFT during biodegradation of three-iso-alkanes whereas CNRL MFT was enriched in Methanoregula during biodegradation of three-iso-alkanes and in Methanosaeta with five-iso-alkanes. This study highlights the different responses of indigenous methanogenic microbial communities in different oil sands tailings ponds to iso-alkanes

Natural-based polymers for wastewater treatment

Natural and synthetic polymers have been long used in wastewater treatment. In this study, two positive charge polymers (natural and synthetic) were selected. These polymers were than tested for its ability to treat the wastewater with polymer dosages ranging from 1-20 mg/L. Both synthetic and natural have almost similar performance in turbidity removal. The highest removal rate of 90% was obtained at a dose of 20 mg/L. The removal of humic acid in demineralized water and wastewater was compared. Humic acid removal at 70% was reached in demineralized water, and 30% in wastewater. The removal of COD and phosphate is also reported

Long-Term Incubation Reveals Methanogenic Biodegradation of C₅ and C₆ <i>iso</i>-Alkanes in Oil Sands Tailings

<i>iso</i>-Alkanes are major components of petroleum and have been considered recalcitrant to biodegradation under methanogenic conditions. However, indigenous microbes in oil sands tailings ponds exposed to solvents rich in 2-methylbutane, 2-methylpentane, 3-methylpentane, <i>n</i>-pentane, and <i>n</i>-hexane produce methane in situ. We incubated defined mixtures of <i>iso-</i> or <i>n-</i>alkanes with mature fine tailings from two tailings ponds of different ages historically exposed to different solvents: one, ∼10 years old, receiving C₅–C₆ paraffins and the other, ∼35 years old, receiving naphtha. A lengthy incubation (>6 years) revealed <i>iso-</i>alkane biodegradation after lag phases of 900–1800 and ∼280 days, respectively, before the onset of methanogenesis, although lag phases were shorter with <i>n</i>-alkanes (∼650–1675 and ∼170 days, respectively). 2-Methylpentane and both <i>n</i>-alkanes were completely depleted during ∼2400 days of incubation, whereas 2-methylbutane and 3-methylpentane were partially depleted only during active degradation of 2-methylpentane, suggesting co-metabolism. In both cases, pyrotag sequencing of 16S rRNA genes showed codominance of Peptococcaceae with acetoclastic (Methanosaeta) and hydrogenotrophic (Methanoregula and Methanolinea) methanogens. These observations are important for predicting long-term greenhouse-gas emissions from oil sands tailings ponds and extend the known range of hydrocarbons susceptible to methanogenic biodegradation in petroleum-impacted anaerobic environments