Nutrients impact on methanogenesis in end-pit lakes

Establishment of end pit lakes (EPL) is considered a viable potential strategy to reclaim huge volumes of oil sands fluid fine tailings (FFT) under a water column. However, ebullition of biogenic gases primarily methane from underlying FFT might affect the trajectory of EPL reclamation. We investigated the influence of nutrients (nitrogen; N and phosphorus; P) on methanogenesis and the resulting flux of chemical constituents from FFT to cap water. Anaerobic 10 L columns filled with FFT capped with process water were spiked with mixture of labile hydrocarbons (n-alkanes, iso-alkanes and monoaromatics from C6-C10) representing fugitive hydrocarbons in FFT. Some spiked columns were amended with N or N and P. HCN columns generated highest methanogenic activity followed by HC and then HCNP columns metabolizing spiked hydrocarbons at different rates. Indigenous FFT Clostridia with both acetoclastic and hydrogenotrophic methanogens metabolized hydrocarbons to methane at different rates creating methanogenic activity in the order HCN>HC>HCPN indicating methane inhibition with the addition of P. Geochemical processes in FFT associated with methanogenesis followed same order in transforming FFT minerals, mobilizing ions and trace elements in FFT porewater, densifying FFT and inducing chemical flux to cap water. The results provide novel information about nutrients effect on methanogenesis and associated chemical flux to predict the sustainable management of EPL.