# Mesocosm Study of Chemical Treatments on Methane Emissions in Oil Sands Tailings Ponds – Part II: Illustrating the Relationship of Naphthenic Acids with Methanogenesis

## TL;DR

This study explores how chemical treatments affect methane emissions and naphthenic acid levels in oil sands tailings ponds.

## Contribution

The study demonstrates that Fe2(SO4)3 can reduce both methane production and naphthenic acid concentrations in tailings ponds.

## Key findings

- Fe2(SO4)3 reduced methane production and naphthenic acid concentrations.
- Oxidative transformation of classical naphthenic acids was observed.
- Fe2(SO4)3 shows potential as a chemical amendment for tailings pond cleanup.

## Abstract

Naphthenic acid fraction compounds (NAFCs) are primary
toxic components
in oil sands process-affected water. Chemical treatments in tailings
ponds can influence their concentration and composition, which may
affect their toxicity. It is therefore crucial to measure the levels
and distribution of NAFCs if there is any chemical treatment process
being implemented in the tailings ponds. In the literature, some potential
chemical treatment processes have shown promising results in terms
of methane inhibition, thus reducing fugitive greenhouse gas (GHG)
emissions from tailings ponds. However, little has been established
to date on how the methanogenesis process along with chemicals used
in the treatment affects the concentration and compositional characteristics
of the NAFCs in the tailings ponds. In this study, laboratory scale
bottle tests simulating oil sands tailings pond environments were
used to investigate joint outcomes of chemical treatments on methanogenesis
in relation to the concentrations and molecular level characteristics
of NAFCs. Among the four chemicals (Na2MoO4·2H2O, Fe2(SO4)3, Na2SO4, and Na3C6H5O7·2H2O) tested, Fe2(SO4)3 reduced both methane production and the concentration
of the NAFCs. There was also evidence for oxidative transformation
of classical naphthenic acids (i.e., O2-NAFCs) presented
in the study. These findings suggest the potential of using Fe2(SO4)3 as a chemical amendment for NAFC
attenuation and methane reduction to assist with the cleanup effort
for oil sands tailings ponds.