Lake Sealing by andrewjlockley

Thanks for the proposal! 1) What would keep the methane bubbles from floating off the surface, particularly when surface tension has been reduced by surfactants? 2) How long are these bubbles expected to persist at the surface before they are lost by various pathways (winds, evaporation, buoyancy)? Given this, what might you envision a workable system for monitoring and methane capture to look like?

This would seem to be potentially applicable in a fairly localized way, unless there were some natural process that would then destroy the foam and the methane inside without having to gather the bubbles. For example, might some type of fish eat the bubbles and use the methane as food, thus oxidizing it? Perhaps an appropriate composition of the surfactant might promote the process--or would be need genetically modified fish?

To address the concerns raised in correspondence, I'll list and respond to them here. How will methane be recovered from the foam? A) Highly concentrated methane foams are flammable (even if aqueous), as can be seen from flaring bubble rafts made in the chemistry lab (a popular high school demonstration). If the methane entering the foam is dilute, or if the foam has time to exchanges gases with the atmosphere by diffusion through the bubble wall, ignition may no longer be possible. B) Centrifuges can be used to treat the foam. A device structurally similar to a spin drier can be continuously loaded with foam, with methane recovered from the drum centre and detergent-rich water recovered from the drum walls (or through holes within these walls). C) Heating the foam, perhaps using microwave radiation, will cause water to boil off the bubble surface and cause the bubbles to burst. If the foam is heated by contact from below the formation of steam bubbles may occur, which will collapse on cooling. (The above applies only to aqueous foams.) Methane is lighter than air. Will the foam fly away? No. The bubble matrix makes methane foam heavier than air. You can try this with a biological methane source in your bubble bath, or a fossil methane source in a chemistry lab sink. No flying foam will be observed. The surfactant would presumably be a hydrocarbon of some type. Where might it come from and what would be involved in generating it? The foam may be an aqueous surfactant, or an oily foam. The worldwide detergent (surfactant) industry operates at a large scale (~10Tg yr-1). Non-biodegradable detergents were routinely produced, until legislation controlled their manufacture. Recommencing these manufacturing processes will not be problematic. Typical low-biodegradability anionic detergents are alkylbenzenesulfonates with branched alkyl groups, and these represent candidates for experimentation. Manufacture is commonly by the following process "benzene is alkylated by long chain monoalkenes (e.g. dodecene) using hydrogen fluoride as a catalyst. The purified dodecylbenzenes (and related derivatives) are then sulfonated with sulfur trioxide to give the sulfonic acid. The sulfonic acid is subsequently neutralized with sodium hydroxide." The above assumes an aqueous solution. A non-polar (oily) foam may be preferred, which would float on top of the lake surface, leaving the water body below uncontaminated. However, an oily foam would have its own environmental impact, and care would need to be taken to skim off the oily layer from water exiting the lake. Would surfactant be recycled, or would it be consumed in the combustion or use of the methane? Very limited oxidation may occur in combustion of aqueous foams, but the surfactants in aqueous solution would generally not burn. If an oily foam was used, this would likely be fully flammable, until emulsified with water (by wave action, etc.). In that CH4 is food for some types of species, would not it be expected that organisms would be seeking to get at the methane, or for that matter, the surfactant, and so might this all really be equivalent to creating a scum covering the lakes? A scum cannot retain methane gas. Only a foam can do that. Would scum formation on methane emitting lakes not happen naturally? It may be the case that some methanotrophs do tend to create foaming agents naturally, but I am not aware of this phenomenon. Generally, large-scale foam rafts are not seen covering lakes naturally. Might the foam be gathered and used as an energy source? Yes, the foam could be collected and separated, using a variety of methods, as detailed above. What other effects on the lake would be expected from doing this? Detergents would affect the physics and chemistry of lake water, and would have significant effects on ecosystems. Considering Sodium dodecylbenzenesulfonate: The salt has an LD50 of 2.3 mg/liter for fish, about 4x more toxic than the branched tetrapropylenebenzenesulfonate Would the light inhibition hurt the lake and its natural ability to deal with methane, etc.? The foam itself would affect the ecosystem, by the mechanism of light reduction, and by inhibiting the transfer of oxygen into the lake. These effects would result in additional methanogenesis. However, the longevity of the increase would depend on the flux of water-borne biomass into the lake. Without photosynthesis, or a feedstock material, methanogenesis would cease. Could the covering be done by aircraft, or what would be required? Surfactants can be sprayed onto lakes using crop spraying or fire fighting planes. Surface vessel distribution, or a fixed piping supply, could also be used. What potential problems exist with the idea? The main risks are A) ecosystem damage B) diffusion of Methane through bubble wall into atmosphere - possibly leading to low flammability / purity C) if recovery instead of flaring is sought: economic cost of capital equipment and maintenance D) scaling across many lakes with low methane fluxes in each E) degradation or outflow of surfactants from waterbody, and associated pollution