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Energy: Biogas

Anyone who has spent time in a swamp, like the incredible Florida Everglades, knows what “biogas” is.  It’s the end result of natural processes that break down plant matter and return the nutrients back to the soil – and produce a lot of methane gas.   Capturing that process, improving it, and making use of the methane is a very old technology that has been in use in some form for centuries.

It also might very well be the future of energy around the world, especially with a few advancements and refinements.

The process of making biogas is known as “anaerobic digestion” because it digests any kind of cellulose or sugar based plant matter without air.  The work is done by bacteria that get the energy they need to survive in the process.  All that has to be done is to set up conditions that are ideal for them to thrive in a big tank and they are happy making methane.  The end result is that nearly all the carbon present is consumed, between 60-70% of it released as methane (CH4) and the rest as carbon dioxide (CO2).

Any source of “cellulosic” or woody material can be used – hay, paper, food, corn stalks, or what have you.  The bacteria are not fussy.

For a while, ethanol has been the renewable energy standard here in the US.  Growing fuel is an attractive alternative to emitting more “greenhouse gases” from carbon sources that have been dormant underground.  But biogas is much better than ethanol for the following reasons:

  • The chemical energy created is about 2.7 times greater.
  • Anaerobic digestion can be performed on a much smaller scale.
  • Capital investment is a tiny fraction of an ethanol plant.
  • All nutrients can be returned to the soil.
  • Any source of cellulosic material can be used.

The advantages over ethanol are impressive.  That’s why this process is being developed by many companies around the world and at every university Agricultural / Bioengineering department in the US.  On a personal note, I was part of a project to make biogas as a cooking fuel on a small scale for Haiti when I was in High School, and my grandfather had a small biogas system operating when he ran the Delaware County, Pennsylvania, sewage treatment plant 60 years ago.

If this technology is so well known and so great, why isn’t it more widely implemented?

Biogas is a very low quality methane produced at very low pressure.  Methane, as a very small molecule, does not form a transportable liquid easily or safely.  All of the reasons why natural gas is often flared off are amplified by the impure nature of biogas.

Most of the programs making biogas use it to create electricity, which of course can be transmitted anywhere.  But the efficiency of small-scale electrical production is low.

That’s why the ability to take methane, one carbon all by itself, and combine it into a larger chain in a cheap, simple process is so valuable.  Eight carbons strung together, as octane, is gasoline – concentrated chemical energy in an easily transported liquid form.  But even smaller molecules like propane (3 carbons) or butane (4 carbons) would be a major improvement.  The new technologies described earlier for making longer carbon chains from methane could revolutionize biogas into systems something like this one:

Note that there are still issues of scale – this whole plant may not make sense on a small farm, but might need to be part of a co-op that serves a whole community.  But the potential for these two technologies working together to provide a sustainable, carbon-neutral fuel that is economical and supports farms is undeniable.

How might this work?  Each digester could make up to 88 gallons of gasoline per ton of solid input.  It could use anything, including native plants that grow like (or as) weeds as part of a “fallow” season for a plot of land.  In a nation that consumes about 140 billion gallons of gasoline each year, that implies about 1.5 billion tons of plant or wood waste is needed – which happens to be about what we have around even before we deliberately grow crops just for fuel.

Note that hay is worth around $100 per ton, but the fuel that could be made from it in this process would be worth about $300.  There is a lot of room for the cost of the process.

The liquid fuels that could be produced by combining these technologies would have nearly limitless uses through the economy.  Transportation is one thing, but it’s worth noting that in Minnesota that is about 1/3 of our energy usage – the other needs being heat (also 1/3) and electricity.

While it is possible that a system like this would enable us to grow our transportation fuel, even perhaps export some, it is always beneficial to conserve as much as we can so that it is available for other uses.  And that’s what we’ll talk about next time.

24 thoughts on “Energy: Biogas

  1. I have heard of this before,but didn’t know it was so far along or so economical. This is breathtaking. To think we can make all of our gasoline from renewables really does change everything. I especially like how you are linking these techs together into a system.
    Doesn’t this also work on landfills? It would be great to make energy from garbage if we can.

    • It’s very far along, and being implemented all around the world. I didn’t dwell on municipal waste (garbage) as much because something tells me that this being so centrally located it might make more sense to do this along with municipal sewage as a source of natural gas for heat. But the principle is the same.
      Landfills are NOT optimized to make methane by any stretch, but they do. And it’s being tapped. That same garbage can be sorted and the conditions optimized to make a LOT of methane if we want to!

  2. I just did a post in this and when I tried to post it, it went away and I was asked to log in again. I generally don’t have the time or patience to do this twice……


  3. I’m also having trouble, it’s jumping around when I comment. But this is very cool and it would be amazing if we could grow fuel. The most valuable resource in America is cropland, in a sense it would be a shame to waste it as long as the world is hungry but I can see that if we use the leftover waste it would be different.

    • We can, and do, feed a lot of the world. We currently have a lot of land raising corn for ethanol, so we would only have to change that over to a native grass (switchgrass grows well up here!) to make material for digesters. And let’s not forget America’s #1 crop – grass on people’s lawns! 🙂

  4. Take this as a reminder that there is nothing wrong with this great nation that can’t be fixed if we put our best minds to it. Things are bad now but there are better times ahead. I appreciate your optimism and desire to search for the way out & hope your message gets out!

    • You are very right. As Bill Clinton said, “There is nothing wrong with American that can’t be fixed by what is right with America.” I do believe that. It’s a matter of getting our priorities and values right.
      And I am doing my part to get the message out, but I appreciate all the help I can get!

  5. .The most valuable resource in America is cropland, in a sense it would be a shame to waste it as long as the world is hungry but I can see that if we use the leftover waste it would be different

  6. People, please, please:

    Cannot everybody in Minnesota recall the mindless cheerleading for corn ethanol, for garbage incineration, for poultry litter incineration, for “biomass” burning, for “District Energy”???? Even basically desirable industries such as wind and solar have their downsides. There ain’t no free lunch.

    Anaerobic digestion has a place in the scheme of things, but (1) the chemistry is not simple but extremely complex and temperature sensitive, (2) digestion generally does not work well for woody materials–as opposed to food waste, poop, etc, (3) the resulting offgas is contaminated with smelly and toxic reduced sulfur compounds, diluted with carbon dioxide, etc., blah, blah, blah.
    Further, there is no way that petroleum fuels can be replaced by biofuels at our excessive levels of consumption. We need a balanced look at these issues with the emphasis on the demand side (conservation and efficiency).

    One of the biggest problems is that when people start cheerleading for a new industry they haven’t done their homework on, and the promoters start handing around in the Capital bullshitting the pols and giving them money, we see exemptions from “environmental review,” “streamlined” permitting, and so on. Thus, the mechanisms we do have in place for considered evaluation of new ideas get neutralized. This has happened over and over again and we don’t seem to be learning.

    This is not to say that new ideas (AD is NOT a new idea, however) should be rejected out of hand, but that we need to get a lot smarter about them.

    • A lot of good points! Yes, biogas is far, far from new. It also does have its problems, especially in an urban area – which is why I left the municipal solid waste alone for now (although coupling it with an existing sewage treatment plant as a finishing step gets around many of the problems with smell, residuals, etc).
      Should we jump on this bandwagon and install digesters everywhere willy-nilly? Absolutely not! The ethanol example shows us a lot of what can go wrong, for sure, and I hope we learned from that. Note that in the diagram I included a “Water Recovery” step, which is absolutely essential to making this work safely and environmentally.
      What I am attempting to highlight, however, is that it is possible to make this stuff in scattered sites once we solve the transportation problem – which the previous post shows a tech that could do this. And the capacity is roughly what we need to be able to grow our own fuel, meaning that this could sustain the entire economy. That may be questionable, but stay tuned until tomorrow because conservation still plays a big role in our overall needs and capacity.
      But your caution is very well advised. The main difference between this and ethanol (or, for that matter, hydrogen) and their boosters working the halls of power far harder than the lab is that this has the support it needs to meet very tough standards in a practical, economical implementation. We should insist on very high standards.
      While there is a crisis today, moving to energy independence with a methane economy based on natural gas first is a critical step before we jump all over the potential for renewable energy from our farms. We have the technology and, more importantly, we have the time to implement it right. Whether or not we have the will to do it right is another dimension, and I agree with you that we have got to find it.

    • OK, back up a bit. Methane, released into the atmosphere, is a big absorber of sunlight and a greenhouse gas. When burned it makes carbon dioxide (CO2).
      If the methane is produced by plants that have absorbed CO2 in sunlight there is a complete “carbon cycle” that is very different from carbon that is pulled out of the ground and removed from the atmosphere.
      Would a lot of methane digesters put raw methane into the atmosphere? It’s worth thinking about, but I sincerely doubt it. Everywhere things rot methane is being released now. The process described captures it to put it to work in a human based carbon cycle. If anything, I would think that a system like this would result in less methane being released than what we have now.

      • There are too sorts of “rotting.” One is the aerobic (with oxygen) kind with carbon dioxide as the endpoint. Ordinary composting is this sort of chemistry., and can be seen as a slow form of combustion. The other is anaerobic (without oxygen) with methane as one of the endpoints. (But note that the process is very imperfect–typically about one-half of digester offgas is carbon dioxide.) Most crop residues, etc, decompose aerobically. We only get anaerobic naturally in swamps and other situations where the material is cut off from an air supply–but of course there are lots of swamps in the world. So if we use anaerobic digestion and burn the methane for fuel, the real endpoint–carbon dioxide–is the same but maybe we harvest some useful energy along the way. The net climate and energy impacts depend on what would have happened otherwise and aren’t all that easy to figure out. If we assume that some fossil hydrocarbons aren’t burnt, or that we captured methane that otherwise would have been generated naturally and not been contained, there may be overall benefits. (Methane in the atmosphere is considered to have 20-100 or so times the climate forcing impact of CO2, depending on the time scales we are looking at.)
        This is interesting stuff and I’m glad you are writing about it.

    • Alan, you’re right on here – I’m trying to start from zero with most people so bear with me on the details you already know! One astonishing thing, however, is that there has been a lot of research into anaerobic digestion and effluents of up to 70% methane have been achieved over a long run time. I don’t really understand how they got it that high, to be honest, but it has to be close to the max we’ll ever get. But it’s still impressive and makes this tech much more appealing.
      The real key is always to leave the carbon in the ground as much as we possibly can. Methane is a bad actor in the air, for sure, for many reasons beyond even greenhouse gases. We do not want it getting out, and strict standards around billions of reactors are going to be essential. But the tech is there and has great potential – given the other things that are developing as well!

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  9. In Europe all EU countries are required to regulate landfill operators through the landfill permits to ensure that all methane possible is collected and not allowed to vent to the atmosphere to add to the greenhouse effect. It sounds as if you would be in favour of that. Will all states someday also bring in a similar regulation do you think? I understand that some already do?

    • Landfills, as we know them, are not at all designed to produce methane – they are kept as dry as possible and not turned over in any way. The trash that is put there is not sorted based on its potential value as nutrition for the bacteria that could produce methane.
      Having said that, regulations requiring the methane from existing facilities to be captured is reasonable – and potentially profitable. It would be far more interesting to explore what it would take to turn municipal solid waste into a net energy producer using anaerobic digestion.
      You’ll note that I dealt with farm waste here, which is a pretty shameless punt on my part. The reason is that the waste or crops going into the system are pretty well known and start out separated well. Not so with municipal waste.
      I think it would be a great idea to start performing some small-scale experiments with municipal waste and seeing what we can reasonably do to turn it into a source of fuel. Requiring existing landfills, badly designed as they are for anearobic digestion, to capture what they can is very reasonable as well, IMHO. But it’s nowhere near ready for prime-time as a source of a city’s methane (currently natural gas).
      Yes, let’s do it! Make what we can with what we have!

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