Garbage Incineration.

Municipal waste being incinerated.  Courtesy Wikipedia.

So,

It would seem that there is some kerfuffle in the Greater Toronto Area.  The ground has been broken on a garbage incinerator project, and the locals are certainly worked up about it.  While I will not pretend to be an expert on the subject, I do know some pertinent science that I am sure you, my monocled, Brandy-swirling readers would love to hear about.

I will freely admit that at first, burning garbage seems like a bad idea.  After all, many of us have thrown things onto a fire and seen the evolution of black pillars of foul-smelling smoke.  This, however, is far different from what goes on in a garbage incinerator.  You see, inside an incinerator, it is much easier to get up to high temperatures in an enclosed space than in an open fire pit.  Those of you who have used a chimney to ignite charcoal (or "cookin' biochar", as I am certain no one calls it) may be familiar with this effect.  The objective here is to achieve total combustion, where all carbon [or fuel, the garbage] is fully converted to carbon dioxide ["is fully oxidised"].  This is far better for our air than the results of impure combusion, which include much higher amounts of ash, soot [what I assume to be aerosolised/dispersed ash, really], and harmful products like carbon monoxide.  Fire pits see impure combustion when "smoky".  The combustion above appears to be very pure, by comparison.

The structure and synthesis of polystyrene. Wikipedia.

I will also admit that, in many cases, garbage incineration is often accompanied by the abandonment of recycling plastics.  They are necessary to fuel the blaze, and are included with the garbage.  This, too, sounds like a nightmare to the environmentalist.  I agree that in a perfect world, all plastic would be recycled forever.  Sadly, this is either not the case, or not possible.  Some classes of plastics would be easy to recycle.  Styrofoam, polymerized styrene [or "polystyrene"] is an example.  This is easily dissolved in the solvent acetone.  Acetone also has a very, very low boiling point.  It would be very easy to dissolve all those meat trays and packing chips, then boil off the solvent to have relatively unscathed polystyrene to reuse.  Unfortunately, as with other classes of plastics (water bottles, especially), this is not the case.  The manufacturing process for these types of plastics is inexpensive enough that the recycled product is too expensive for anyone to purchase.

The other challenge facing plastic recycling is the nature of the substance.  As can be seen above, plastics [polymers] are very long chains of some individual molecule [the monomer].  The recycling process must heat plastic so that it can be reformed.  Heating damages the bonds of the polymer, causing the plastic to degrade.  In fact, the reason that one rarely sees 100% recycled plastic products is that the structural integrity of recycled plastic is compromised, and it must be blended with new plastic so that the product may serve its purpose.  For the record, recycled metal does not share this problem, and I think it a fabulous idea, given the environmental costs of smelting metal.  Metal is also easily recovered in the incineration process.

A garbage incinerator in Vienna.  Source.

"Now see here!" You may demand.  "Won't this contribute to global warming?  Spewing out all that carbon dioxide?!"  This is an excellent point, and I am glad that you [might have] raised it.  It is true that greenhouse gas emissions will be added to with garbage incineration, however, it is much better than other emissions associated with dumps.  You may have seen torches burning outside of buried garbage dumps.  I know that I have near Carp, Ontario.  The reason for this is the venting of methane, a common byproduct of garbage disposal.  A methane leak is far, far worse than the leaking of carbon dioxide into the atmosphere.  The reason can be explained with very simple physical chemistry and math (you may skip the next paragraph if you are truly averse to it, though I find it interesting).

The surface of the Earth is heated by the Sun.  As can be seen in math here, the light that an object emits depends on its temperature.  The very hot Sun emits all colours of the rainbow, but the Earth is by comparison only lukewarm.  Objects at that temperature emit infrared (IR) radiation (this is how night and thermal cameras work).  Normally, a substantial amount of heat from the Earth is converted into IR and is lost to space.  Molecules, however, will absorb IR and begin to vibrate, blocking the exit of the heat into space.  This is the cause of the greenhouse effect.  Now, not all molecules are created equally.  The amount of IR that a molecule can absorb depends on how many ways that molecule can vibrate, known as vibrational modes.  The number of vibrational modes of a molecule depend only on the number of atoms.  Carbon dioxide has three atoms, and linear molecules follow the formula 3N-5, meaning it has 4 modes of vibration.  Non-linear molecules have 3N-6 vibrational modes, giving methane, a 5 atom species, 9 modes of vibration (or something like that).  Other math which I do not wish to get into demonstrates that this makes methane 21 times worse to have in the atmosphere than carbon dioxide.

We must also consider the issue of storage.  Many municipalities are running out of space for garbage, and it is much easier to bury the remaining ash of an incinerator than it is for the immense volume it started as.  Also, while most modern dumps are more or less sealed, leaks of contaminants are not impossible.  Many contaminants released by the incineration process can be captured before discharge into the air, meaning that, in my opinion, it is likely safer to incinerate garbage than it is to simply bury it.

Power transmission lines, because I discuss it below, and this certainly is a large block of text.  Source.

I must also discuss the issue of power.  Conventional dumps may use the methane generated by the garbage to spin a turbine and generate power, which seems like a fantastic idea.  Energy from our waste. However, garbage incineration offers a much higher amount of energy to us.  The fire from the incinerator can be used to generate steam from a boiler.  This would spin a turbine in exactly the same way as nuclear, coal and natural gas power plants do, but from a power source we are currently wasting. In a twist on this idea, a company called Plasco has found that heating and exposure to a plasma torch can produce refined syngas (mentioned previously in my biofuels post), which can then be used to make various other products and fuels.  It is also worth noting that steam-generating applications can route waste heat to nearby schools and hospitals to heat hot water, boosting the overall efficiency of the process.

With this in mind, I feel that garbage incineration is beneficial, and ultimately an opportunity.  It would lead to safer disposal of our waste, which is inherently invaluable.  Further, it represents an untapped energy source which could ease strain on our grid, and provide baseline electricity generation which most renewable fuels cannot (as the sun does not always shine, nor does the wind always blow).  I think that, if done properly, widespread incineration efforts would lead to a better tomorrow.

NM

Biochar.

Courtesy Wikipedia under GNU Licence Agreement

So,

An issue currently facing the scientific community is that of carbon capture and storage, CCS.  It is essentially trying to reverse what has been done over the course of a hundred-or-so years of burning fossil fuels.  Realistically speaking, storage is the easy part of CCS, in that there have been various proposals for very reasonable places to put captured carbon, including abandoned mines and the seafloor.  As an interesting aside, if one were to pump carbon dioxide to the bottom of the ocean, the pressure is so great that water molecules will align to form a "clathrate", a cage which will hold gases there indefinitely.  Carbon capture, however, has proven to be incredibly difficult and a challenge to the greatest minds of today.  Though I do not rank with those greatest minds, the subject of my honour's thesis was a theoretical study of carbon capture mechanisms using metal organic frameworks.  In case you were wondering, I studied copper II benzenetricarboxylate.  For now, these frameworks show great potential.  Unless some improvement is found, though, they will remain a terrible, terrible idea.  The problem here is that carbon dioxide is a very stable molecule, and is not all that easy to trap.

I hope to have at least conveyed that CCS is by no means a trivial problem.  That being said, I feel that a good solution may have been "discovered" recently.  I use parentheses because the technology is by no means new.  In fact many of you, while not adjusting your monocles and top hats, may have handled this technology.  You see, outside of the scientific world, this technology is known as "charcoal".  Biochar simply refers to charcoal when used for CCS and related purposes.  Please do not ask me why they couldn't call it charcoal.  Bioscientists go all goofy when they have the opportunity to name things.

I was recently introduced to this idea by a former environmental issues professor (he has a blog here).  Biochar has the potential to be an elegant solution to the problem of CCS.  Capture, the hardest part of CCS, is accomplished simply by growing woody or cellulosic biomass (trees, grass, what have you).  Storage is then rather easy, biochar may come in chunks, briquettes, full bricks, or even as a powder, but all that need be done is to bury it.  This scheme gives several advantages over other proposed methods.  For one, burying solids is very easy, especially when juxtaposed with methods proposing pumping carbon dioxide into abandoned mineshafts.  Other solids have been proposed, such as calcium carbonate.  The problem here is that while calcium carbonate (you know it as chalk and Tums' active ingredient), is a solid and very easy to deal with, simply burying it would affect soil pH, and widespread leaching could  be devastating.  Another benefit is that one would be burying carbon only, and not sacrificing an oxygen molecule for each carbon atom that must be stored, as would be the case with both carbonate or carbon dioxide storage.

In case you have furrowed your brow, wondering what the ecological effects of burying biochar would be, I believe I have an answer.  While I am by no means an expert, it is my opinion that no environmental harm would be done by burying this material.  My reason for this thinking is terra preta.  This term, which in Portugese means "black earth", refers to the enrichment of soil with biochar.  It would seem that infertile soil may be made fertile with the addition of biochar.  This effect may be noted to a depth of roughly two meters and is stable for timescales on the order of thousands of years.  It is an effect similar to that which switchgrass accomplishes with its extensive root system, but far more quick and direct.

A further benefit is that biochar is not difficult to produce.  It is the same process as charcoal, in fact, though perhaps with lower-grade feedstocks.  Plant matter is heated, causing it to give off water and syngas (carbon monoxide and hydrogen gas), the latter of which could be useful to heat subsequent batches of biochar.  The result is carbon (and potentially mineral) rich biochar.  I must admit, after learning of this, I became a little upset that my parents have been using a propane barbecue for years when charcoal is a far more sustainable technology.

Looking at this problem from a student's perspective, it all seems so simple and obvious a solution.  Biochar could be an excellent CCS solution, one which does not require teams of undergrads toiling away on computers, dreaming up theoretical mechanisms for accomplishing the same thing.  I suppose in an ideal world, switchgrass could be used not only for our heating and biofuel needs, but surplus could be set aside as biochar, which could sustainably reverse anthropogenic climate change.  Could the biochar even be redirected to fertilise our food crops?  The possibilities sure do seem endless.

Until such a time as biochar seems like a terrible idea, I shall continue to hope and dream that it will be widely adopted.

NM

Biofuels.

So,

Biofuels have been in the news lately.  I feel as though a lot of people have strong opinions on the subject without a strong understanding of the subject matter.  It is my hope that some may stumble upon this post, don monocles and top hats, and be able to have informed opinions.

In this post, I will choose to focus upon the issues surrounding ethanol, as it is the most prevalent technology at the moment.  I realise there exists a plethora of other options, but they are not as well developed.  The reason that ethanol has been selected as a biofuel is that is comparatively non-toxic and as a liquid phase organic molecule, it blends well with gasoline.  It is also fairly easy to make, as we humans are no strangers to ethanol (go to your local liquor or beer store to see all the things we can do with it).  The first generation of biofuels was made primarily from corn.  The conversion takes three steps.  First, the starch from the corn is broken down into simple sugars either by thermal processes or enzymatic breakdown.  Second, the sugars are converted into ethanol by using yeast or some similar bacterium.  The third step, as I understand, is the most energetically demanding step of the three.  The ethanol must be distilled from the mix, which costs large amounts of energy.  Water is comparatively very difficult to boil, which must be done to extract the ethanol.

This would be fine if not for a few looming problems. The first is that corn is comparatively energy-intensive to grow, requiring a large amount of fertilizer.  The second is that corn requires good quality soil, and displaces farmland which could be used to grow food for humans (known commonly as the food vs. fuel economy).  This lowers the available land for growing food crops, and increases food costs.  Another major issue is the distillation step for processing, which requires very large amounts of energy.  In a class on applied chemistry, we were advised that industry will avoid distillation wherever possible because of the energy (and thus monetary) costs involved.  As a result of high fertilisation and energy costs, the energy input required for one unit of ethanol is often equal to the chemical potential energy stored in the ethanol, if not greater.  Put simply, that means that burning the gasoline directly would have been a better idea.  There would be no food vs. fuel economy and the energy would not have been wasted.  I must specify however, that this is the case with most corn ethanol, particularly in Canada and most of the United States.  Brazil can use this sort of method with sugarcane because of the warm climate.  The more temperate climates cannot accomplish these feats with corn or sugarcane, unfortunately.

There is a [not so-]simple tweak that would boost the efficiency of this process.  If the entire corn plant was used rather than just the kernels, the yield of ethanol would be greatly increased.  Cellulose is the woody material that makes up the majority of plant biomass.  Like starch, it is a long chain of sugar molecules. Unlike starch, cellulose is bonded in a way that makes it more difficult to break down without specialised processes.  You have experienced this personally, dietary fiber is mostly cellulosic material, and cannot be digested.

Ethanol derived from cellulose has been dubbed "cellulosic ethanol", and is described by federal governments as "second generation biofuels", with the first being ethanol derived from corn kernels.  A benefit from this technology is that the feedstock needn't be corn.  Rather, any number of agricultural products could be evaluated.  Ideally, it would not require large energy inputs, and would not displace croplands used for food.  I have my own ideas about what this feedstock would be, but that is another post in itself.    Ultimately, cellulosic ethanol could prove to be a sustainable technology for biofuel production.

In my opinion, cellulosic ethanol is not the ideal solution, but it is a good start.  I will freely admit that I am not an expert in the field, but I would like to offer my ideas without any solicitation whatsoever.  I feel that distillation is prohibitively expensive energetically speaking.  I also feel that the time required for fermentation of sugars should be a deterrent.  Rather, I would like to see a thermochemical (heat energy which begets chemical change) solution employed.  You see, cellulose can be thermally broken down into "syngas", short for synthesis gas.  The name of syngas was coined due to its original purpose, which was to make methanol.  Methanol, like ethanol, is a combustible, liquid alcohol.  Unlike ethanol, it is not suitable for human consumption.  Most sources prefer ethanol for this reason, but I would counter that no one wishes to drink gasoline.  Take that as you will.  In any case, syngas may be directly (and catalytically) converted to methanol with little to no energy inputs.  This means that, in theory, feedstocks could be converted to biofuels quickly and more efficiently than with distillation and fermentation.  While I cannot remember the exact source, but I saw a story on a chemical plant in the southern United States which was employing a similar solution.  The plant was thermochemical, but I believe it produced ethanol.  This is slightly more complicated than making methanol and will have lower energy yields, but in my opinion it is a better idea.  The most attractive aspect of this process in my opinion is the time required.  Rather than fermentation which could take weeks, a truckload of fuel can be ready in roughly ten seconds via thermochemical methods.

Now you, my monocled, brandy swirling, non-spambot audience know what I think about the current state of biofuels.  I believe my next post shall regard what I believe is the ideal feedstock.  I knew it would come, my obsession with it has yielded a large body of informal and scholarly sources of information on the subject, and I tend to gab to anyone willing to listen.  I can only assume you wait with bated breath for my next post.

Also, for the record, I think biofuels are a great idea.  Oil won't last forever.

NM