Three-dimensional numerical simulations of methane gas migration from decommissioned hydrocarbon production wells into shallow aquifers

Three-dimensional numerical simulations are used to provide insight into the behavior of methane as it migrates from a leaky decommissioned hydrocarbon well into a shallow aquifer. The conceptual model includes gas-phase migration from a leaky well, dissolution into groundwater, advective-dispersive transport and biodegradation of the dissolved methane plume. Gas-phase migration is simulated using the DuMux multiphase simulator, while transport and fate of the dissolved phase is simulated using the BIONAPL/3D reactive transport model. Methane behavior is simulated for two conceptual models: first in a shallow confined aquifer containing a decommissioned leaky well based on a monitored field site near Lindbergh, Alberta, Canada, and secondly on a representative unconfined aquifer based loosely on the Borden, Ontario, field site. The simulations show that the Lindbergh site confined aquifer data are generally consistent with a 2 year methane leak of 2–20 m3/d, assuming anaerobic (sulfate-reducing) methane oxidation and with maximum oxidation rates of 1 × 10−5 to 1 × 10−3 kg/m3/d. Under the highest oxidation rate, dissolved methane decreased from solubility (110 mg/L) to the threshold concentration of 10 mg/L within 5 years. In the unconfined case with the same leakage rate, including both aerobic and anaerobic methane oxidation, the methane plume was less extensive compared to the confined aquifer scenarios. Unconfined aquifers may therefore be less vulnerable to impacts from methane leaks along decommissioned wells. At other potential leakage sites, site-specific data on the natural background geochemistry would be necessary to make reliable predictions on the fate of methane in groundwater

Determination, occurrence, and treatment of saccharin in water: A review

Saccharin (SAC) is an emerging contaminant, widely detected in the environment, with potential ecotoxicity risks to aqueous organisms and human beings. Wastewater treatment plants (WWTPs) are key sources and sinks of SAC, and play a vital role in eliminating SAC entering the environment. An overview is provided of the potential ecotoxicity of SAC, its occurrence in the aqueous environment, and its degradation performance in WWTPs. SAC treatments, including physical, chemical (mainly advanced oxidation processes AOPs), biological, and hybrid processes, and possible degradation mechanisms are also considered. Of the various SAC removal processes, we find that adsorption-based physical methods exhibit relatively poor performance in terms of SAC removal, whereas chemical methods, especially hydroxy radical-mediated oxidation processes, possess excellent capacities for SAC elimination. Although biological degradation can be efficient at removing SAC, its efficiency depends on oxygen supply and the presence of other co-existing pollutants. Hybrid aerobic biodegradation processes combined with other treatments including AOPs could achieve complete SAC reduction. Furthermore, novel adsorbents, sustainable chemical methods, and bioaugmentation technologies, informed by in-depth studies of degradation mechanisms and the metabolic toxicity of intermediates, are expected further to enhance SAC removal efficiency and enable comprehensive control of SAC potential risks