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Farmers Are Using Food Waste to Make Electricity (npr.org)
99 points by Bhilai 3 days ago | hide | past | web | favorite | 38 comments

This is fun cause I've got a side project going on that does this, but without decomposition, and with direct electrochemical conversion. It uses solid oxide fuel cells, which can not only consume hydrogen, but can also generate electricity from the CO->CO2 oxidation. My current work is on developing a gliding arc plasma reactor that can take solid waste and convert it to syngas, which is then desulferized and fed directly into the SOFC. I'm hoping to build a 5-10kw system partnering with an SOFC manufacturer.

I'm a sailor and I'm targeting the sailing cruiser community with it, although I recognize potential markets elsewhere. The idea is that when you are remote, in locations where supply chains and infrastructure are undeveloped, it is incredibly risky to rely on ICEs for auxiliary propulsion and electricity. You may not have access to gasoline or diesel in the quantities or narrow quality specification that ICEs require. And you certainly don't have access to fuel when you are at sea on a long passage. This system would allow you to use pretty much any conventional fuel, but it would also allow you to use biowaste, garbage paper and plastic (including ocean plastics), wood pellets, and even wet biomass like seaweed (the moisture content reduces efficiency, but is still net positive for energy generation). And it can produce energy on demand, instead of waiting around for it to decompose and produce methane.

Have you checked out molten salt oxidation? https://en.wikipedia.org/wiki/Molten_salt_oxidation

Is that real? Because that would not be quite enough to power a DeLorian, but still come amazingly close!

(you must be getting this reaction a lot)

That is fascinating and could be a real game-changer. Would you care to share more about this?

I'm using some of the research done by Drexel's Plasma Lab [0] as inspiration for the reactor design. There are lots of plasma reactors out there, in research as well as commercially available, but most of them are focused on breaking down gaseous or liquid matter. The research I've seen at Drexel was the first I've come across that focused on solid fuels. I have a friend who was an atomization engineer for a rocket fuel company who has some pretty good ideas for handling solid fuels that we're going to experiment with. But at least we know it is already possible.

As far as the desulfurization and SOFC is concerned, we're not even close to that stage yet. Desulfurizers are pretty common, but most SOFC designs tend to be extremely large and heavy, more suitable for stationary generation. I'd like to work with NASA's Bi-Electrode Supported Cell concept, which has power densities suitable for transport applications [1], even better than most diesel engines. They are actively licensing the technology non-exclusively, so maybe we could get a license and produce it ourselves, but this is all bootstrapped so that is probably out of reach in the short term.

[0] https://drexel.edu/nyheiminstitute/researchlabs/plasma-energ...

[1] https://technology.nasa.gov/patent/LEW-TOPS-120

Have you considered working with S4 Energy/InEnTec to commercialize (they previously were a JV with Waste Management)? They've done some work in large scale gasification.

InEnTec looks interesting, looks like they're already working on plasma gasification. One of the problems I have run into with a lot of companies that I've contacted is that most of them are only interested in industrial scale systems, and have no interest in small scale production. Definitely worth getting in touch though.

This is a very common technique that has been in use for decades at farms all over the world. You can see these dome-shaped containers when you drive through the countryside in western Europe. The first Wikipedia entry (2002) mentions that it's a popular process in the Netherlands and Denmark. https://en.wikipedia.org/w/index.php?title=Biogas&oldid=2064....

My memory is fuzy on the details, but I think this is something to do with Mad Cow Disese (BSE) being caused indirectly by the old practice of feeding food waste (containing meat) back to animals as pigswill.

When this was banned suddenly there was a lot more food waste, and also animal feed became more expesnive, and anaerobic digestion emerged as a solution to both problems.

In Australia some farms installed these as a response to the carbon tax. I believe they got taxed on escaping methane if they let it decompose in the air, so it was a double win, turning a tax liability into a profit centre.

Australia doesn't have a carbon tax though!

It's been a running theme over the past decade's various changes in Prime Ministers. A bit of a rundown https://www.afr.com/politics/federal/how-the-coalition-becam...

Edit: oh oops. I'd forgotten it had actually existed for a while

Not sure if you know this and are joking, but for the benefit of others, it got introduced and revoked by a following government:


Semi-related, one comparison I'd like to see is pre-sliced fruit in plastic containers versus the whole fruit.

These regularly get attacked as signs of how wasteful we are (which I generally agree with) and people defend them because people with various kinds of physical impairments might find it hard to peel a fruit.

But I think if you recycle the skins/seeds/waste properly in a factory, wrap it in lightweight plastic and account for the reduced shipping weight, then you might come out ahead even if you ignore the benefits of eating more fruit.

One of the many complex decisions that a carbon fee might simplify by guiding people towards doing the right thing at every step in the process.

Puuh i think you overestimate the usable energy from pulp. Honestly anaerobic digestion works best with simple sugars. More complex carbohydrates and proteins and their turnover to methane depends on the digestability by the used bacteria. This is also why corn is a major feed for digesters in central Europe.

Cellulosic biomass may not have the hydrogen necessary to break down into methane reliably, but that doesn't mean it can't be used. It can be burned directly or turned into pellet fuel quite easily.

Presliced apples in plastic bags are very common in the US.

Also in use since the 80's in various African countries... http://www.songhai.org/index.php/en/home-en/16-songhai/190-b...

The Songhai Center does a full carbon cycle re-use. An interesting place to visit too!

A previous comment on HN went something along the lines of "what is going to happen in the summer when we've built solar/wind/etc to fulfill this winter months needs?"

I started researching energy storage. Creating liquid fuels from electricity would be handy for storage. There are processes, but getting CO2 and H2 to create hydrocarbons is currently very energy intensive. On the CO2 side, I think biogas can help this out. biogas is 25-50% CO2. In biogas upgrading, CO2 is considered a waste product (with purer methane the desired output). CO2 from this source looks noticeably less energy intensive than direct air capture.

I know biogas can be done on the small scale (e.g. homebiogas.com). My research focused especially on liquid fuel creation that could work in someone's backyard. I haven't found it. "High‐Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode" [0] was an exciting find, dampened after reading how well ethanol stores.

I mostly became convinced that existing oil, gas, and chemical companies will maintain dominance producing many of the same outputs, from a different (renewable) set of inputs.

[0]: https://onlinelibrary.wiley.com/doi/full/10.1002/slct.201601...

Looks like you've been going down a similar path as me. Unfortunately, liquid fuels from pure electricity is extremely energy inefficient. For example, the fischer tropsch process will consume the hydrogen that you've split with precious electricity, and only half of that will make its way into the fuel, the other half of ends up converting back into water. And that is before you figure out how to get CO2 in concentrations high enough to be cost effective.

You might want to check out plasma reforming. It's the path I'm currently on, although targeted for a different end product.


Yeah, FT looked insane, which is one of the reasons the linked paper was so attractive. Ethanol from CO2, electricity, and water at ambient temperature and pressure.

I mostly think I have to be doing some chemistry/math wrong, based on how not terrible the energy efficiency is. I'd love corrections or reading material, as this is not a knowledgeable area for me. - 2 CO2 + 9 H20 + 12e- -> C2H5OH + 12 OH- = 0.084 V - over voltage of 1.2 V is best - 1kWh @ 1.2V yields 30 moles electrons - 30 moles electrons has theoretical yield 2.5 moles ethanol = 0.146 L ethanol - reduced to appx 116ml ethanol due to selectivity - 116ml ethanol has raw energy of 778 Wh, probably 550 Wh recoverable with Combined Heat and Power

I think 55% round trip efficiency for energy-dense long term storage would be big. Of course, this isn't that (math is partially based on theoretical bests, ethanol isn't long term, CO2 capture and material movement not accounted for).

Thanks for the plasma reforming tip!

Pumping water uphill is another one. A lot of farms ditch water off the property in wet months and then irritate with precious well water during dry spells. If you’re on a slope, or build a tower, you could use excess electricity to pump water from a pond to a higher point. The receiving tank becomes a battery, and the energy can be released with gravity to irrigate during droughts.

Biogas you can also use it to run vehicles it has cleaner exhaust emissions compared to other fuels Gasoline/Diesel. Farmer could and probably will run their tractors off Biogas. Because farmers like to experiment, its available and decision paths to get it into action are short.

No need to experiment, this is already done commercially on a massive scale.

"Stockholm Vatten's sewage treatment works produce 4.1 million m³ of biogas annually, but have the capacity to double this amount." [1]

[1] http://www.stockholmvattenochavfall.se/en/water-and-wastewat...

I worked for an entity that eventually got rolled into the subject of the NPR article.

We looked into compression/cleaning for biogas, but both the capital requirement and ongoing operational cost was too high for the gas volume produced by the farm.

Not too unrelated, composting can generate heat around 60°C. Could save some heating

I used to work in AD/Composting and the issue I've read about with compost heat recovery was the cost of the recovery system (compost piles are very large) and short equipment life span due to damage by loaders/environmental degradation.

The most consistent use of compost heat has been to ensure proper pathogen reduction in certain waste materials such as wastewater byproducts. A popular example of this is called a 'dutch tunnel' (add 'composting' to that if you google it) where you have a pretty robust, loader accessible composting container which largely self-heats for pathogen reduction. I use the term 'largely self-heats' because there are aeration/mixture characteristics that are required for proper temperature development.

Searching EPA 40 CFR 503 is a good introduction to the process, because there is been a lot written about it and you can easily find guides/introductions.

There are some permaculturists out there, like Ben Falk, who have built radiant heaters by running coils through compost piles.

Unanswered question, where does the remaining waste from the plant go? Surely not all of the mass is converted into gas. And with 1000 tons per day, there should be a lot of waste to dispose off somewhere.

Anaerobic biodigesters are very common here in Germany. The residue is a really good fertilizer that can be applied to the fields. At least here in G the nitrogen application from this has to be documented and subtracts from the N fertilizer budget farmers are allowed to apply.

The only downside is that to the best of my knowledge, those installations tend to be designed without storage in mind, running the generator at whatever time is convenient thanks to flat feed-in rates. Making them dispatchible would be by far the single lowest-hanging fruit in the whole field of grid storage.

(Correct me if I'm wrong, I'd love to be)

They provide such a minuscule amount of power that I'm not sure whether making them dispatchable is worth the effort.

Take a look at https://energy-charts.de/power.htm : pumped storage peak discharge hardly ever reaches a level of contribution as high has biomass and that is basically all the non-fossil dispatchability that we have. Meanwhile, biomass is running as baseload more stubbornly than even nuclear.

Making the biomass contribution dispatchible would be huge.

Changes in regulation in G require operators to upgrade generator capacity in order to utilize gas storage to produce electricity at peak demand and not flat all the time.

Is that change already in place? Do you have any links or keyword suggestions for a bit of news googling? (German would be fine for me, but English is obviously preferable for the benefit of other readers)

It is already in place since Jan 2017 I think. Energieeinspeisegesetz is the relevant keyword. But this redesign of the regulation is really complicated with a lot of different cases and exceptions. No concise summary in english I'm afraid.

edit: fixed typo

Thanks, 2017 was already quite useful for narrowing down search results.

Pre-existing requirements for the seasonal storage of manure on dairy farms (primarily because you aren't supposed to spread manure in the winter) means that many dairy farms already have large manure storage lagoons/tanks. These are adapted into digestate storage tanks when the system is installed, although the additional food waste volume can result in additional storage volumes being required. What is nice about some of the manure storage tanks is that you can sometimes just add a 'ring' onto them to increase storage volume.

the digestate is then spread on farm fields using similar methods/equipment used to previously spread manure.

It's used as fertilizer on the fields.

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