The decycling of digestate
Nature's inheritance.
The natural/geologic processes of our planet have never shown any lack
of ability in regard to the production of remarkable results. Amongst
their great many outstanding achievements they have extracted carbon
dioxide from the atmosphere, caused carbon to enter and remain within
anaerobic environments and enabled this carbon to enter states of
fossilisation -- but here's a thought -- if nature used to be able to do
all this in the past, maybe she's still got what it takes to do the
same kind of thing today.
There is no doubt about nature's potential to do the job. All she
needs is the opportunity to get it done - or, to be more specific, all
she needs a suitable quantity of carbon based material that gets
buried in a suitable way.
Going to waste.
The extent to which carbon based materials go to waste is staggering -
let us count the ways: there's the sewage, the food waste, the animal
waste, the waste paper, the other forms of naturally produced organic
waste and, to make mention of a curious side issue, a wide range
synthetically produced carbon based waste materials as well. There's a
phenomenal load of rubbish to be dealt with and it all needs to be
dealt with in appropriate ways.
The challenge of digestion.
There are, however, complications associated with a simple burial of
waste as a whole range of microbes will typically get buried along
with it. These microbes will continue consume everything they can and
for as long as they are able. One way to stop them is through the use
of an anaerobic environment and yet, even when the oxygen runs out, a
remaining content of hydrogen will enable methanogenic microbes to
continue to hydrate carbon and generate methane.
Methane is a notably destructive substance. It is an extremely potent
"greenhouse gas" that, over the time period of 100 years, would have
25 times the impact on the global temperature as an equivalent initial
quantity of carbon dioxide and, if that wasn't enough, it also seems
to have it in for itself. It possesses the remarkable ability to
oxidise without burning to an extent in which atmospheric methane only
takes about seven years for half its carbon content to get initiated
into the more dauntingly resilient dioxide community. Never-the-less,
from our point of view it is much better for methane to burn out than
to fade away. The great thing is that it burns really well, better
than any other carbon based fuel.
Controlled digestion.
The best way that methane can be controlled is through the application
of anaerobic digestion technologies. They work in a wonderfully simple
way. Waste materials are injected into the top of a large sealed drum,
microbial digestion does what it does best in the middle, relatively
solid digestate material is squeezed out at the bottom and natural
bubbles rise up all around.
The main complication is the simultaneous production of a small but
significant quantity of Hydrogen Sulphide (otherwise variously known
as: Sulphur Hydride; Sulphurated Hydrogen; Hydrosulphuric Acid; Sewer
Gas; Stink Damp; Rotten Egg Gas; Brimstone or H2S). Hydrogen sulphide
may easily be regarded as a smelly cousin of water and, as sulphur and
oxygen both possess the ability to bond with other atoms at non
typical angles, hydrogen sulphide and water can be considered to share
some of the same eccentricities. The big difference, however, is that
hydrogen sulphide is quite obnoxious and, mainly for the sake of the
machinery within which natural gas may pass, is excluded on a routine
basis.
Digestate.
At present farmers will may typically pay something like the costs to
get the digestate from a processing plant and onto their fields upon
which it can then act as a medium grade fertiliser within an obviously
aerobic environment and I have assumed that, from this point, the
entire carbon content of the digestate will eventually end up being
returned into the atmosphere. It's not a great deal of carbon but it
all adds up. Digestate materials are assessed to contain a modest 4.5%-
9% carbon content while crude oil, at a different extreme, will
typically boast a carbon content of something in the region of 95%.
This means that anything up to 21 units of digestate would need to be
decycled in order to to counteract the carbon print of a single unit
of crude oil.
Plastics.
Carbon can also be found (at widely noted levels of abundance) within
various forms of plastic. The current practice within anaerobic
systems is for the plastic materials to raked out of the mix. An
alternative, depending on the extent of the environmental effects that
various plastics may exhibit within various environments, would be to
leave certain and perhaps all forms of non styrofoam plastic in a
deposition mix. Instead of raking them out they might be chopped up.
The small remaining pieces of plastic would be unable to trap
significant quantities of natural gas and would be able to take yet
more carbon out of the equation.
Sedfill.
The next question relates to where to put all the waste.
Landfill might always be used but I'd like to present the more
controversial suggestion of digestate materials being buried at sea.
An immediate mechanical question may be raised in relation to ways in
which the digestate materials might be encouraged to sink. Digestate
materials, like all forms of biological matter, will likely have
something like the equivalent density as water and yet would need to
sink within bodies of water that would typically possess a heavy salty
content. A bit of ballast may be easily added. For instance, if
anaerobic digesters might be built in locations downhill from major
population centres in near proximity to navigable stretches of water
then it may be possible to add aquatic sediments directly into the
digestate mix. Sediments might even be added at a suitable stage of
the digestion process should that be possible or into the digestate
product at a later stage but, if this were to happen, a further dose
of natural gas might need to be released at a later stage.
The containers of digestate, weighed down by any suitably dense
substance, could then be shipped or otherwise floated out to sea to
locations in which they might then be caused to descend down to the
sea floor.
One potentially ideal situation for the deposition of the digestate
materials might involve the anchoring of a suitably equipped container
ship above a deposition site. This ship would then be able to act as a
base for the direction of a remote controlled vehicle on the sea floor
whose main purpose would be to dig trenches into which the digestate
might be accommodated. Containers of digestate materials could then be
guided into place either through the movement of a suitably sized loop
of cable that could be attached both to the remote controlled vehicle
and to both ends of the ship. An alternate method of container
deposition could involve the use of forms of submersible equipment
that might guide individual containers of digestate on their way.
These submersible guides could be simply equipped with ballast tank
capable of being variously be filled with water or air, fins to permit
a controlled path of descent and accent, a sensor to monitor the
location of the remote controlled vehicle below and its designated
docking station above and a programmed ability not to crash into
anything on the way. As long as the trench digging remote controlled
vehicle was able to let the submersible guides know where it was then
if, for instance, the ROV might be digging its way in an easterly
direction then the submersible guide would simply aim to deposit its
cargo at a safe distance to the west. The trench digging remote
controlled vehicle might also be directed in such a way in which it
may additionally be able to cover over previously dug sections of
trench. All it would need would be the capacity to deposit the
excavated sedimentary materials on just one of its sides and also be
able to cut its path on a spirally bound course or simply to go up and
down like a farmer might in plowing a field. The remote controlled
vehicle would be able to cover its tracks by either method.
However, dependant on the assessed experience that digestate type
medium grade fertilisers may have on the sea bed and similarly
dependant on the assessed need to reduce quantities of carbon dioxide
entering the atmosphere and, of course, dependent on cost, it may
decided that other means may also be used for the deposition of
digestate onto the sea bed. Any boat that had spare capacity when
heading out to sea would have a potential capability to take some
digestate with it and, amongst others, there are plenty of fishing
vessel and oil tankers that might do the job. The people operating
these vessels are often brave souls performing lonely jobs but, all
the same, it may be time for them to give something back.
Thermostasis.
It may be conceived that the decycling process described may be able
to provide some relief from the severity of the carbon crisis and
perhaps there may be more. Depending on both the potential implication
or the decycling method and manner in which the energy industries
choose to operate, it may perhaps be possible for the deposition rate
of digestate carbon through decycling activities to surpass the
extraction rate of fossilised carbon. If that could happen then the
result would be this - a control of the climate would be in our hands.
Within this eventuality a target carbon content for the atmosphere
would need to be chosen and yet it may be conceived that different
people may have different preferences with regard to their ideal
temperature for the earth. Obviously we are currently a very long way
from having any form of control of the climate and yet I would still
like to say this. Perhaps an atmospheric carbon content similar to the
carbon content of the atmosphere in the 1960s may present an initially
suitable target.
Cooler climates present a range of advantages with regard to the
welfare of a wide variety of current forms of terrestrial life. There
is, however, a bigger picture. Warmer temperatures may, at some stage,
present us with possibilities for the preparation of our planet for
its longer term capacity to support life. The problem is that the
arctic regions of our planet contain huge quantities of our old friend
methane saturates a variety of materials such as peat in regions such
as those towards the poles. Its a time bomb. When the ice finally
melts, which - due to the fact that the sun seems to be slowly yet
relentlessly heating up - it will, the carbon will naturally end up
being released into the atmosphere. There will be advantages for all
our futures if situations can be orchestrated within which the carbon
might be dealt.
The high temperature climate would, however, be quite literally awash
with disadvantages. A higher temperature atmosphere would have greater
ability to hold on to an occasionally high level of water content.
Water vapour presents problems in two significant ways. It has a
greater reflective potential than any of the other abundant form of
"steamhouse gas" and yet the water vapour content of the atmosphere
has an unsettling potential to "change like the weather". Global
warming, on its own, might not have been so bad. It actually sounds
quite nice. Its the related concept of global poaching, its
potentially erratic weather and its oppressively muggy skies that may
represent a broader indication of the phenomena.
Generational inheritance.
It should also be noted that the decycling process has its
limitations. For instance, it has a limited ability to affect the fuel
crisis. Fossil and nuclear fuels are finite in nature and need to be
protected for the future. The wind, however, cannot be overfarmed,
wood can always be burnt and geothermal, solar, wave and perhaps other
water driven sources of energy can be tapped without limit.
It is especially at Christmas that parents may desire to give their
children the earth. With a continued application of effort it may
actually be possible to do just that.
Merry Christmas.
Greg
A version of this text receiving intermittent updates is posted on the
Attempts at Survival website at attempts.org.uk/decycling
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