Methods of sequestering CO.sub.2 from a gaseous source of CO.sub.2 are provided. Aspects of the methods include employing an alkali enrichment protocol, such as a membrane mediated alkali enrichment protocol, in a CO.sub.2 sequestration protocol. Also provided are systems for practicing the methods.

An ocean alkalinity enhancement (OAE) system that reduces atmospheric CO.sub.2 and mitigates ocean acidification by electrochemically processing feedstock solution (e.g., seawater or brine) to generate an alkalinity product that is then supplied to the ocean. The OAE system includes a base-generating device and a control circuit disposed within a modular system housing deployed near a salt feedstock. The base-generating device (e.g., a bipolar electrodialysis (BPED) system) generates a base substance that is then used to generate the ocean alkalinity product. The control circuit controls the base-generating device such that the alkalinity product is supplied to the ocean only when (1) sufficient low/zero-carbon electricity is available, (2) it is safe to operate the base-generating device, and (3) supplying the alkalinity product will not endanger sea life. Modified BPED systems include features that facilitate autonomous system operations including enhanced maintenance cycle operations and a reduced reliance on external fresh water sources.

A platform for sequestering carbon dioxide using a body of water is described. The platform has a vessel for holding solid metal hydroxide and for exposing the solid metal hydroxide to a flow of water to create a solution of a metal hydroxide having a pH level. The solution containing metal hydroxide is released into the body of water, causing a reaction with the carbon dioxide present in the body of water, thereby producing metal carbonate/bicarbonate, thus sequestering the carbon dioxide. A choice of the metal in the metal hydroxide, a rate of the releasing the solution containing the metal hydroxide into the body of water, and a flow rate of the flow of water so that to substantially maintain the solution containing the metal hydroxide at the pH level that is defined as environmentally safe and not changing chemistry of seawater. A corresponding method is also provided.

Injecting CO2 that is diluted within water, into a coal seam, which allows for the sequestering and control of downhole CO2 within connected fractures without damaging the subterranean formation.

A method for scrubbing flue gas, comprising: providing a rotating packed bed device onboard a ship or an offshore floating vessel; mixing seawater with the flue gas under centrifugal force in the rotating packed bed device to prevent blow-by and produce a scrubbed flue gas having low sulfur; and discharging the scrubbed flue gas; wherein the scrubbed flue gas has less than half of the sulfur that was originally present in the flue gas before the mixing. Also, a system for scrubbing the flue gas according to the method described. Also, a marine ship, comprising: an engine that combusts HSFO; a rotating packed bed device, in a hull or funnel of the ship, comprising a rotating shaft and a porous material that mixes seawater with flue gas and reduces sulfur in the flue gas; and a connector from the engine and the rotating packed bed device.

A membrane module includes a housing. The housing includes a housing, comprising: a first plurality of porous hollow fiber membranes, and a second plurality of porous hollow fiber membranes different from the first plurality of porous hollow fiber membranes. The first plurality of porous hollow fiber membranes has a first length, and the second plurality of porous hollow fiber membranes has a second length that is at least 1.1 times greater than the first length. The membrane module can be used in separation methods, such as membrane distillation methods.

An ocean alkalinity enhancement (OAE) system that reduces atmospheric CO.sub.2 and mitigates ocean acidification by electrochemically processing feedstock solution (e.g., seawater or brine) to generate an alkalinity product that is then supplied to the ocean. The OAE system includes a base-generating device and a control circuit disposed within a modular system housing deployed near a salt feedstock. The base-generating device (e.g., a bipolar electrodialysis (BPED) system) generates a base substance that is then used to generate the ocean alkalinity product. The control circuit controls the base-generating device such that the alkalinity product is supplied to the ocean only when (1) sufficient low/zero-carbon electricity is available, (2) it is safe to operate the base-generating device, and (3) supplying the alkalinity product will not endanger sea life. Modified BPED systems include features that facilitate autonomous system operations including enhanced maintenance cycle operations and a reduced reliance on external fresh water sources.

An air cleaning system for removing carbon dioxide from polluted air and generating oxygen as a biproduct. A plurality of diatoms in water are held within a transparent vessel. Polluted air is injected into the water and is aerated with nanobubbles. The flow of air into the vessel is regulated to control the flow of nutrients to the diatoms. A light source provides light to permit the diatoms to use photosynthesis to consume the pollutants in the injected air and generate oxygen as a biproduct. The generated oxygen diffuses or bubbles out of the solution and is released from the system back into the atmosphere. A method of treating polluted air and generating oxygen as a byproduct using the air cleaning system is also provided.

Disclosed is a method for fast and cost-efficient preparation of ikaite crystals. The method comprises contacting an alkaline aqueous solution, which comprises carbonate and bicarbonate ions, with a water solution, which comprises Ca.sup.2+, at a temperature not exceeding 15° C., wherein contact between the alkaline aqueous solution and the water solution takes place at a permeable or porous surface, through which either solution is fed to the other at a flow rate facilitating formation of ikaite crystals. Also disclosed is system for carrying out the ikaite preparation process. The process and system provides a cost efficient and effective means for capture and storage of carbon dioxide.

The disclosure provides a method of treating flue gas that has one or more components. The method comprises passing a solution through both a magnetic field and an electric field to form an activated solution. The method also comprises contacting the activated solution with the flue gas so that the one or more components of the flue gas are at least partially absorbed by the activated solution to form a residue solution.