Water treatment can also be greatly inproved by the use of organized turbulence in radial counterflow. Besides the pressing problems of desalination, there is also the growing problem of methane and cyanide contamination in water.
is a greenhouse gas, 23 times more potent than carbon dioxide, that is emitted
by municipal sewage plants, industrial wastewater, and manure slurries.Next to carbon dioxide, methane is the most
serious contributor to global climate change.
municipal wastewater treatment plants capture methane (natural gas) from
anaerobic digesters and burn it to dry sludge or to produce electricity.However, much escapes from sewage settlement
ponds.We need to find a way to strip
methane from wastewater.
Methane combines with ammonia in
wastewater to produce hydrocyanic acid (aqueous hydrogen cyanide, HCN, also
known as prussic acid, the Nazi poison Zyklon B).Commercially, this is known as the BMA
process.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 1:g/L (one part per billion),
which is unattainable with presently known treatment technologies, even
ultrafiltration, which at best can get to 10 :g/L and are prohibitively
Cyanide is the anion CN-.In water, the cyanide anion grabs off a
hydrogen atom and becomes hydrogen cyanide (HCN).The boiling point of hydrogen cyanide is 26o
C, which makes it highly volatile.HCN
has a density of 0.687 g/cm3, which is much less dense than water,
and therefore HCN can be separated from water by density as well as by
volatility.Other cyanide compounds are:
cyanogen (NCCN), which becomes hydrogen cyanide (HCN) in water, and has a
boiling point of -20.7o C; cyanogen chloride (13.8o C);
and acetone cyanohydrin (82o C).Note that all of these have lower boiling points than water (100o
C), i.e. they are volatile organic compounds (VOCs).Lowering the pressure can cause them to boil
off and be captured.
Other noxious volatile organic
compounds (VOCs) in municipal and industrial wastewater are benzene, toluene,
and xylene; collectively, these are referred to as BTX.Like the cyanide compounds, these 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.
Mercury in wastewater is a very
dangerous pollutant which collects in fish, and eventually in people, causing
serious health effects.Fortunately,
mercury can be turned to vapor by lowering the pressure, like the VOCs.
Dissolved noncondensible gases in
wastewater include hydrogen sulfide (H2S, commonly known as sewer
gas), dissolved residual chlorine (Cl2) from chlorination, nitrous
oxide (N2O), methane, and nitrogen (N2) from
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
denitrification of wastewater so as to extract nitrogen gas is an important
step in treatment.Dinitrogen gas is
harmless in the atmosphere, but nitrous oxide (N2O) is a very potent
greenhouse gas, 296 times worse (molecule for molecule) than carbon
These noncondensibles separate from
the water (evolve) under low pressure, like VOCs and mercury.But stripping VOCs, mercury, and dissolved
noncondensible gases from wastewater and capturing them is a major unsolved
problem.We have a simple, non-chemical
solution at Vorsana, which is to cause the gases to evolve through
anisotropic turbulence.Large flows can
easily be handled, and the equipment is low tech.