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Author Topic: Sustainable Farming  (Read 6082 times)

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Re: Sustainable Farming
« Reply #30 on: May 29, 2016, 05:23:16 pm »
Our recent discussion of methane digesters led me here.


The Shocking Carbon Footprint of Compost

Most people think of composting as a very "green" thing to do, but few realize that composting actually generates a significant amount of the potent greenhouse gases (GHG), methane and nitrous oxide.  Under current landfill regulations, requirements to exclude water minimizes the breakdown of organic matter and requirements to capture and burn methane mean that even that option has a better carbon footprint than composting (thanks to Fred Krieger for pointing out this advance in the landfill arena).  The even better option is anaerobic digestion which I will describe at the end of this post.

These Emissions Are Not A Scientific Surprise

To a microbiologist, it is not surprising that these gases would be generated during composting. Methane and nitrous oxide are formed by certain microbes when there is not enough oxygen available (anaerobic conditions). In the middle of a large-scale compost pile there are micro-sites without oxygen. This occurs even in a pile turned frequently for aeration. This is particularly true during the "hot" phase of the composting process which kills pathogens and weed seeds. During the period of very high oxygen demand, some parts of the pile will run short and the anaerobic organisms will make methane and nitrous oxide.

An Example

The graph above is based on one typical study of GHG emissions during composting (Hao et al 2001).  This was from active composting of cattle manure - a common procedure in which the pile is aerated by turning it frequently using a tractor (its fossil CO2 emissions are shown in green above.)

The first column represents how much carbon or nitrogen was emitted in various forms per metric ton (Mton) of manure. We can't even see the 0.19 kg nitrous oxide-N at this scale. Methane is 8.1 kg C and the fuel is 4.4 kg C.

The second column shows how much the emissions contribute to a net increase in greenhouse gases in the atmosphere (Carbon dioxide is "carbon neutral" because it was recently pulled out of the atmosphere by a plant - thus no net GHG contribution.  Methane and nitrous oxide are multiplied by 21 and 310 respectfully because of their higher radiative forcing potential).

The third column shows the GHG contribution per metric ton of finished compost (after 21% loss of mass - much as water).  The total "carbon footprint" of the compost is now 233.4 kg CO2-C/Mton.  For those more familiar with English units and expression as CO2 this would be 2167 lbs CO2/Ton.

How Much Compost Is Typically Used?

When compost is used in farming, it is normally applied in large quantities.  According to the University of California, Davis cost and return studies, a typical organic crop would receive between 2 and 10 tons of compost per acre.  Thus a mid-range use of 5 tons/acre would represent a carbon footprint of 10,833 pounds (CO2 equivalents).  This is without including the fuel footprint of hauling the compost to the field and spreading it.

How Big Is That Footprint?

To put this in perspective, the carbon footprint of this amount of compost used on one acre of a crop would be equal to the various other carbon footprints described below:
The carbon footprint of manufacturing 2,580 pounds of synthetic urea-nitrogen fertilizer (at 4.2 lbs/CO2 per lb)
The "embedded carbon footprint" of that urea for fertilizing 12.9 acres of corn at 200 lbs/acre
The complete carbon footprint of producing 5.7 acres of conventional corn (including fertilizer, crop protection chemicals, seed, fuel, nitrous oxide emissions from soil...)
The carbon footprint of burning the gas to drive a typical car 13,982 miles (at 25 mpg).
The carbon footprint of all it takes to produce 985 pounds of beef
The carbon footprint of growing, handling and transporting 9,641 pounds of bananas from Costa Rica to Germany
In other words, the footprint of the applied compost is shockingly large.  It is certainly not a practice one would want to see on a large scale.

Waste Is A Terrible Thing To Waste

Why bring this up?  Because there is a superior use for manures and other organic waste streams.  When waste is processed in an anaerobic digester,  most of the carbon in the is intentionally converted to methane, and then the methane is burned as a form of renewable energy.  The emissions are carbon neutral and the energy generated offsets fossil carbon use.  As with compost, the remaining fiber that is left after digestion can still be used for soil improvement or other uses.

Anaerobic digesters require a substantial, initial capital investment and are non-trivial to operate, but they are clearly the best way to deal with most organic waste streams.  They also pay for themselves over time.  Modern municipal water treatment facilities tend to have these digesters as do some large-scale dairies and CAFOs (confined animal feed operations).

The largest onion processor in California (Gills Onions) installed a digester for its substantial stream of trimmings.  Gills eliminated a troublesome odor and disposal issue, they now offset much of their energy demand, and they are ahead financially after paying back the initial investment. This is a great example of how "doing the right thing" from a greenhouse gas perspective can also be a sound, bottom-line option.

You are welcome to comment here and/or to email me at savage.sd@gmail.com.  For notifications of future posts you can follow me on twitter ( @grapedoc )

References on GHG emissions during composting:

•Hao, X., Chang, C., Larney, J., Travis, G. 2001. Greenhouse gas emissions during cattle feedlot manure composting. Journal of Environmental Quality 30:376-386.    •Osada, T., Kuroda, K., Yonaga, M. 2000 Determination of nitrous oxide, methane, and ammonia emissions from swine waste composting process.  Journal of material cycles and waste management 1:51-56    •Hellebrand, H.1998. Emission of nitrous oxide and other trace gases during composting of grass and green waste. Agric. Engng Res. 69:365-375     •Sommer, S., Holler, H.2000. Emission of greenhouse gases during composting of deep litter from pig production – effect of straw content. The Journal of Agricultural Science 134_327-335    •Hao, X., Chang, C., Larney, F. 2004. Carbon, nitrogen balances and greenhouse gas emission during cattle feedlot manure composting.  Journal of Environmental Quality 33:37-44    •Jackel, U., Thummes, K, Kampfer, P. 2005. Thermophilic methane production and oxidation in compost. FEMS Microbiology Ecology 52:175-184. (looking for microbes which might help reduce the methane emissions from composting)     •Hellmann, B., Zelles, L., Palojarvi,A, Bai, Q. 1997.  Emission of climate-relevant trace gases and succession of microbial communities during open-windrow composting.  Applied and Environmental Microbiol 63:1011-1018

What I got from this is that composting, a process most of us think of as being pretty green, has a big carbon footprint. The author makes the case that methane digesters are carbon neutral and a far superior way to deal with the carbon waste stream.

Palloy said, as I understood him, that methane digesters produce a lot of CO2.

So, from a carbon emissions standpoint, what is the trade-off on these practices? I'd like to know.

I suppose one has compare composting and methane digesting to the carbon footprint of the dominant agricultural practices of the day, which we all know, have a huge carbon footprint. It gets a little complicated to get to the real facts.

Help, anyone? JD? Palloy? AGelbert?

I take absolutely everything Palloy says with a grain of salt. Palloy is, after all, that fine fellow that said Greece had a "valuable" resource with all that COAL they have, back when people were talking about Greece getting carved up by the oligarchic neoliberal greedballs. The last time I checked, coal is a terribly polluting substance that emits a lot of CO2, among other pollutants. So, to even bring it up as an "energy resource" evidences a deliberate lack of perspective on the real costs for we-the-people of pollutants from energy sources.

Eddie, where I am going with this is that we MUST engage in apples to apples comparisons here when we talk of Methane digesters. As you probably know already, methane harvesters don't just use animal feces as the input; they can use other waste material from crops and food waste that is generally used in composting. The fertilizer residue from a methane harvesting operation is perfectly usable as high quality fertilizer. So, there is a synergy going on between methane harvesting and composting. It does not have to be an either/or situation.

Back to Palloy's perspective free point ("methane digesters produce a lot of CO2::)) about methane and CO2".

Eddie, as you said, "The author makes the case that methane digesters are carbon neutral and a far superior way to deal with the carbon waste stream".

In order to understand where the author is coming from, you must look at the same land use situation involving crops and animals WITHOUT a methane harvesting operation.

THAT is the apples to apples comparison required that fossil fuelers cleverly avoid like the plague.  When you DO NOT harvest that truly NATURAL (as opposed to Fracked gas methane product) gas, it goes up into the atmosphere unburned as a GHG (greenhouse gas) and stays there for about a month or so before it degrades. During that month or so, it is over 80 times as powerful as a GHG as the CO2 and water vapor that would BE THERE in its place if it had been collected and then burned for energy at ground level.

The fossil fuelers will calmly bean count every f u c k i n g BTU of fossil fuel energy you use in farming and animal husbandry to, OF COURSE, LOWER the ERoEI of Renewable Energy products like ethanol. Never mind the MUCH GREATER energy inputs required to make the world's 5% of ethanol obtained at oil refineries... Oh, but to them, ethanol is ethanol. Just look at Hess's Law and we can all go back to sleep. LOL!

Back to CH4 (methane), IF you do NOTHING on your farm or with your herd's feces, you are ADDING to global warming. SO, when you set up a methane harvesting operation, you are SUBTRACTING from the GHG carbon footprint of your farm.

This is just CFS (common F'n Sense)!

As to getting to the "Carbon Neutral" or "Carbon Negative" point we all need to get to, the hairsplitters defending the fossil fuel industry will drive us all bananas with bean counting about the FOSSIL FUEL BASED energy to make every screw, panel, tank and pipe in the methane digester to try to talk their way around the FACT that CH4  from those harvesters requires NO FLARING and is therefore CLEAN and CHEAPER than CH4 from oil and gas operations.

Simply put, the fossil fuel industry CANNOT COMPETE on a dollar for dollar AND ERoEI basis with truly NATURAL gas. SO, they make up a lot of studiously sounding bullshit bean counting stuff to snow people into believing the reverse.

Eddie, apples to apples carbon footprint calculations aimed to justify a "carbon neutral" award to CH4+ fertilizer equipment (you can compost without capturing the CH4 but it makes more ERoEI sense to compost AND capture the CH4 while you compost) requires that you a priori state that you will have X amount of animals, Y amount of crops and Z amount of machinery.

Once you have that, you have to compute what amount of  CH4 and CO2 would be emitted by all the life forms down to the microbial level on your land if you, your animals and your machinery were not there.

THAT is your baseline for Carbon Neutral. It is possible that, if your spread is mostly grassland, that it would be Carbon Negative, as the autotrophs there would actually be sucking more GHG(s) out of the atmosphere than the microbes and other life forms there are putting into it.

THEN, with all your stuff in position, you do the math. You CAN give the fossil fueler bean counters the finger by NOT using gasoline for your machines. E85 or Renewable Energy based ethanol would be throw a wrench in their claims that you NEED a lot of fossil fuels to do your stuff.

Methane digester plastic parts CAN be made from carbohydrate based, rather than hydrocarbon based, feed stock. That would also help towards your goal.

I realize all this detail is boring.  

But I add it here because I am weary of seeing so many context and perspective free statements tossed around by supporters of the unsustainable dirty energy status quo every single time real world Renewable Energy, carbon neutral, cost competitive THREATS to the fossil fuel industry products, like methane digesters, are discussed. 

The bottom line for methane digesters/harvesters is that, all things being equal, they LOWER your carbon footprint massively because you will eventually BURN the CH4 that would have floated into the atmosphere.

And if every farm in this country did that, the Fracking industry would go BELLY UP.     
ANY argument from the fossil fuelers (whether they claim to support Renewable Energy or not) about methane digesters "not being cost effective for energy production or environmentally friendly"  trotted out as a excuse to avoid putting in these Renewable energy, pollution free CH4 capturing devices is total, unadulterated bullshit.

I'll dig up some info on truly NATURAL gas collecting devices (like the ones the Germans are using) to justify the points I have just made.  8)

« Last Edit: May 29, 2016, 09:02:59 pm by AGelbert »
Rob not the poor, because he is poor: neither oppress the afflicted in the gate:
For the Lord will plead their cause, and spoil the soul of those that spoiled them. Pr. 22:22-23


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