Saving the World… Dirty Jobs Edition

Right.  So saving the world isn’t all about cute seals, swanky organic clothes, and sexy Tesla electric cars.  We’ve built a gasifier that can burn just about any carbon source from wood chips to cow pies to straw if its pelletized.  We also have alot of diversity in our CSE which is one of its primary strengths.  Put those two together, add some beer and weird things are bound to happen.  So a few weeks ago we were talking about available local waste resources that could be potential feedstocks, and one of our members happens to run my town Wastewater Treatment plant…. You can see where this is going and I don’t blame you if you stop reading now.  But for those looking for ,erm, unique solutions to the coming energy crisis, please do read on!

This past Monday I got together with several of the more intrepid members of my CSE and met up at our local Sewage Treatment plant to see if we could find a better mix of the leftover sludge that wold burn.  Weeks ago we ran about 10#’s of sludge through the gasifier and the results were not the greatest – it was too wet and our plant treats the leftover solids with lime to kill off the ecoli, etc and the high mineral content didn’t agree with the gasifier -rock dust doesn’t burn so good.  


We hope that adding in some other carbon sources that the village has in abundance (chips and leaves) we can raise the carbon content and it will burn better.  Here is yours truly shlepping chips into the augers (BIG augers… like 18″ diameter!) that they use to move the Bio Solids around.

About the sludge.  Lets be clear about this: these are Class A Biosolids, which means they are clean enough to be certified for use as fertilizer for food crops if need be.  The Biosolids are thoroughly processed, and are now no more human waste than my finished compost is still a melon rind.  Still, I get it that its gross… 

 The issue is that due to the lime, it funks around with the soil PH if you add too much or too often.  


So we are sitting on alot of it.  Like enough to fill the All Purpose Room at my kids school – and that is just since November in a town of 2000 souls.   If we can get this crap (pun intended) to burn we could literally power the entire Municipal yard on sh/t.  [The jokes alone almost make this job worth it –they just never get old!] So that is why 5 relatively normal men are throwing perfectly good wood chips into an auger full of perfectly good Biosolids on a bright Monday Morning.  No one ever said saving the world was easy.

the-biosolid-recipe-resizeWe struggled to get the mix right for awhile.  The augers were set to move the Solids expeditiously filling each gap in the auger almost completely, so there wasn’t enough room to mix in the chips.  Once we slowed the intake of the sheets of drying solids, we were able to get something closer to a 50:50 mix of chips to processed waste which was our goal.  The scale of this study is getting significant, we are rapidly moving from backyard tinkerer to players on a municipal scale.  If we are able to make the recipe work, we could be only months away from setting up a test scale gasifier on site.  How exciting!  But I am getting ahead of myself.


The steam coming off the mixed pile shows how wet the mix still is – we estimate it to be over 70% moisture.  That is about 4x too wet to burn – we like our fuels to be in the 15-18% moisture range.  We were able to mix up this good sized pile in about 30 minutes, so the equipment is certainly efficient enough.  Next up will be to set up some solar stills to see how rapidly we can dry the mixture without any energy inputs, and then see if  it can burn well.  

In the mean time, we have 2 concerns.  The Biosolds are about 1-2% nitrogren and adding all that carbon will almost certainly turn this into a giant compost pile – the piles of pure BioSolids are already sitting at 90 F all winter on their own as a result of residual benign bacteria chewing on it – and we just inoculated our solids with all sorts of good bugs.  That would mean we would be losing carbon to the air in the exhalations of the bacteria until it dries.  If that becomes an issue then we will need to dry the Solids before we mix them to prevent the bacteria from firing up.  The second concern that many of us voiced is that in taking the wet BioSolid and mixing in leaves, straw, and chips we end up with a mixture that looks remarkably like cob.  Depending on the binding strength present in the sludge we may very well have just made a 2 ton impressionist sculpture on the municipal grounds when this all dries/hardens.  Let’s hope not!

This may end up being one of our more notable failures, but Edison managed to create 10,000 ways to *not* make a lightbulb so we are due for some flops.  But if we pull this off we may be on to something.  

Seriously, I wouldn’t sh/t you on this…


8 Responses

  1. You know you’re going to have to write a book when you get this all dialed in, right? Or at least a detailed pdf. I so admire what you and your group are doing.

    By the way, I recognize that it’s your blog and all, but…why “sh/t” and not “shit”? I’ve never understood why this textual fig leafing of cuss words is considered polite or at least acceptable, while baldly using the words themselves is seen as rude. Just wondering.

  2. Thanks Kate. Not sure, on one hand I figure my kids will be reading this in a few years, and I try to maintain at least the semblance of FCC regulations. I treat it as the humorous radio *bleep* of the u in f/ck which accomplishes about as much as my backslash. Its more tongue in cheek snickering than prudishness I suppose.

    A book… I am a little ways into one focused more on Sensible Living in Suburbia, and I guess a “memoir of an Eco Geek” could also work and would need to be less detailed. But TIME! I can type as fast as most, but with all the crap going on there is little time to sit and write for more than about 800 words at a time. I’ve thought about just a website with chapters on it that is constantly updated. But then that starts to sounds kinda like, um, this blog…. Which is why there are about 2-3 books mixed in the 275,000 words here.

    We’ll see. With the intentional de-cluttering of my life mayhap I will find 30-60 minutes a few nights a week for more structured writing than pounding out a post or two a week.

  3. Seems kind of odd to me to be burning fertilizer. The nitrogen is a form of embedded energy, whether it is fixed by legumes or a chemical plant.

    Phosphorous is also a finite resource- the NC legislature just agreed to let a phosphate mine eat another twenty five acres of coastal wetland…

    But our society is kind of phobic about recycling our nutrients.

    I bet that the ability to burn sewage sludge would help you win grants.

    I don’t mean to dis your efforts- I think that what you’re doing is f/cking awesome.

  4. Thanks Matt. I share your concerns that this may not be the best use for the sludge. But phosphorous loading in the soils here in WI is a huge pollution concern of our DNR, and with good reason. That means that large grain farmers can’t/won’t take much and given the size of the pile, we could supply the gardens of the state with fertilizer – and that is only if we could get past the stigma of putting processed human waste on their home grown veggies. I am not there yet, myself and am in no hurry to get there. If we switch to biomass agriculture, I see this as a possible fertilizer for that or fuel crops for ethanol – but again there is the phosphorous loading.

    The best way is likely to revamp the whole treatment process to avoid the lime, produce methane, and process the waste water in an engineered wetland that produces cattail feedstock for ethanol production- but that takes millions of dollars that the municipalities don’t have right now. Gasifying the sludge will offset a significant amount of CO2 in energy emissions, produce biochar for carbon sequestration, and further the science a bit while helping to legitimatize the technology for the region for the sum of under $50,000. That’s the hope at least. Coincidentally our group is applying for LOTS of grants right now – at least 2 are involving our ideas with wastewater treatment plants.

    We also sent the char from our first test burn for testing to see how much of the lime is still present – it may be possible to extract it, or use the char as a soil amendment.


  5. Is there still a concern with heavy metals in class A biosolids? Do you plan to scrub your exhaust, like with a catalytic converter?

  6. EWA,
    You bet it is a concern. Here is why we decided to move forward: our sludge has very little heavy metals left in it – significantly below industry average and way below EPA standards. But, it must be a consideration. This is another reason we are testing the char: we are not sure if they will go airborne, or condense in the char. In the char, it may very well be rendered essentially inert and be sequestered but we will need to get scientific conclusion of that.

    Once we have the results then a discussion must be begun – what is worse – the mercury etc emmisions of the 85%+ coal mix in our states electrical generation, or whatever we are sending up in our own. Are there concerns long term for the soil? Etc. There is no free lunch!

    Thanks for reading and adding to the discussion.


  7. Hi Rob,

    Looks like a fun project. I’d love to get the chance to swing by and see it sometime, and I know my brother would as well (that is, if we can pull him away from his precious DC down there in DeKalb). Shoot me an email if you get the chance, I had some other questions about some of your operations too.

    John Fox

  8. Love the updates. The phrase “we’re doing it for shits and giggles” comes to mind…

    BTW, I posted my One Stone Carbon Challenge today – your blog title was part of the inspiration for the name!

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