Carbon capture from controlled degassing of deep meromictic lakes: Insights to techno-economic and environmental feasibility, from the "killer lakes" in Cameroon.

Carbon dioxide (CO) accumulation and emission are well-known features of deep lakes, making them a significant unavoidable carbon source to the atmosphere. In the case of meromictic lakes, degassing devices are installed to controllably release through a pipe the CO trapped in the bottom waters. Otherwise, the gas is emitted diffusely at the air-water surface or accidentally through a limnic eruption when the saturation limit is reached. This controlled degassing operation gives rise to an end-of-pipe carbon capture opportunity that has yet to be explored. In the perspective of promoting negative emission technologies, as this is required to reach the near-term global carbon neutrality objective, this study outlines an end-of-pipe solid sorbent-based carbon capture technique that targets the CO released through controlled degassing of deep meromictic lakes. A direct air capture (DAC) system astutely dimensioned and optimised by the vacuuming of air enriched with CO from the controlled degassing of the lake is therefore proposed and its technical, economic, and environmental feasibility discussed based on the cases of lakes Nyos and Monoun in Cameroon. It resulted that, even on a small scale, capturing CO from lake degassing at 8 vol% (80,000 ppm) can achieve a life cycle cost of 15 bar-compressed CO between $200 and $350 t, two to three times less than that of conventional DAC depending on the energy source used, with potentially attractive marginal abatement costs of CO, especially if natural gas, hydro or solar PV are considered.