Vorsana

The extraction of dissolved gases and volatile compounds from water is called degassing or stripping. Degassing is important for high energy cavitation, which is effective for disinfection and crystallization. High energy cavitation has enormous energy -- there is even some preliminary evidence of nuclear fusion in deuterated acetone due to cavitation. Any extra noncondensible gases in cavitation bubbles act as a cushion, preventing a rapid and energetic implosion to produce the shock waves and microjets that destroy microbes. Therefore degassing upstream of any cavitation treatment is good.

The cavitation bubbles may be induced by electrical and physical forces. Pulsed electric fields cause streamers to propagate in the water, forming cavitation bubbles where dissolved gases evolve. This is called electrohydraulic cavitation. Shear cavitation is where the water rips apart due to mechanical stresses.

Degassing is an important treatment step in pollution abatement, and a need exists for non-chemical and easily scalable means for degassing large flows of process water or wastewater.

Process water may contain volatile compounds, or odorants, such as ammonia, acetone, methylethylketone (MEK), and volatile organic compounds (VOCs). The odorants must either be stripped out or cracked before further use of the water or its discharge to the environment. Preferably, the degassed water should also be cooled before further use. Therefore, atomization, which provides increased surface area for evaporative cooling and for residual dissolved gas evolution, is desirable in process water treatment.

Municipal wastewater may contain dissolved noncondensible gases, including hydrogen sulfide (H₂S, commonly known as sewer gas), dissolved residual chlorine (Cl₂) from chlorination, ammonia (NH₃), methane (CH₄), nitrous oxide (N₂O), and nitrogen (N₂). In addition, there may be VOCs, including cyanide species, which must be extracted before discharge to the environment or recycling. The volume of municipal wastewater streams (typically hundreds of million of liters per day) presents a daunting challenge, and excludes complicated low-flow devices and methods that depend on adding and mixing in chemicals to react with the dissolved gases. Biological methods, such as using microorganisms to convert ammonia to nitrogen gas, require very large investment and a large footprint, and they only work on one gas. Wastewater reclamation cannot be feasible unless the gas stripping problem can be solved by an inexpensive and high-throughput mechanical degassing device such as the Vorsana Degasser.

Ammonia in discharges of wastewater has been linked to the decline of fish populations, but tertiary treatment to remove ammonia is prohibitively expensive. For example, Sacramento, California, estimates it will cost $1 billion to upgrade their wastewater treatment, which discharges 146 million gallons per day, to remove the ammonia that is killing the fish in the Sacramento River Delta. Ammonia is a precursor for the formation of cyanide, and a strong odorant.

Residual dissolved chlorine from conventional disinfection may combine with organic matter in the environment or other dissolved gases to produce carcinogenic disinfection by products (DBPs). DBPs have been implicated in rectal cancer, bladder cancer, miscarriage, birth defects, and fetal growth restriction. A need exists to move away from the use of chlorine as a disinfectant and to extract any residual chlorine remaining.

Methane is of recent concern for wastewater treatment plants because it is a potent greenhouse gas, 23 times more potent than carbon dioxide, and because its capture and combustion in power generators increases the energy efficiency of the plant. Another reason to extract methane from wastewater is because it can combine with other dissolved gases to create deadly compounds. Methane combines with residual chlorine to make chloroform, a possible carcinogen. Methane can also combine with ammonia in wastewater to form hydrocyanic acid (also known as prussic acid, the active ingredient in the Nazi death camp poison gas Zyklon B).

Other cyanide compounds are: cyanogen (NCCN), which becomes hydrogen cyanide (HCN) in water, and has a boiling point of -20.7 ^oC; cyanogen chloride (13.8 ^oC); and acetone cyanohydrin (82 ^oC). Note that all of these have lower boiling points than water (100 ^oC), i.e. they are volatile organic compounds. All cyanide species are considered to be acute hazardous materials and have therefore been designated as P-Class hazardous wastes. The remediation target for cyanide in wastewater is one microgram per liter (one part per billion), which is unattainable with presently known treatment technologies, even ultrafiltration, which at best can get to ten parts per billion. Other noxious volatile organic compounds (VOCs) in municipal and industrial wastewater are benzene, toluene, and xylene; collectively, these are referred to as BTX. Like cyanide, BTX are much more volatile than water, have lower viscosity, and have lower density (approximately 0.87 g/cm³ compared to water which is 1 g/cm³). VOCs are very potent greenhouse gases and should be captured rather than vented to the atmosphere.

Dissolved dinitrogen gas (N₂) causes algae bloom and fish die-off downstream, as well as 'blue baby' syndrome in humans. Nitrogen gas in municipal wastewater comes from microbial decomposition of waste and ammonia, and denitrification of wastewater is an important step in treatment. Dinitrogen gas extracted from wastewater may be harmlessly released into the atmosphere.

In any degassing process, it is recognized that high agitation greatly aids gas evolution. An example of this is the shear cavitation induced by shaking a soda bottle. The high turbulence (Re ~ 10⁶) known to exist in von Karman swirling flow may provide excellent agitation for degassing.

In the McCutchen Processor, the stripped gases are extracted continuously through a multiscale tree network of radial vortices sustained by radial counterflow bretween counter-rotating centrifugal impellers. The residence time between the impellers can be as long as required, and the separation effects in fine scale vortices can be collected because the turbulence is directionally oriented. It can be scaled to handle large flows and does not involve chemicals, catalysts, membranes, or the other expensive and ineffective conventional approaches.

By David J. McCutchen and Wilmot H. McCutchen