Midden Mini – Update

Finding it extraodinarily hard to find to time to write with everything thats going on (tours, workshops, Real Job, kids home, potato harvest, epic vacation planning)  but The Good Work is not suffering.  This post will be text only as I don;t have time to upload and edit the pics.

The main updates on the ‘Midden are that the pile is cooling – down to 110.  That is due as much to its age as to me tearing into it every week to tinker with the, now, primed digesters.   So lets talk about those digesters.  2 weeks ago I filled one of the 55 gallon drums with ground up box elders, and the other with ground up lambsquarter.  Why?  Both plants are prevalent and rather despised weeds hereabouts.   To those not sharing the local stereotypes on plants, that means that the biomass from those two plants can be had for free and in large amounts, or in the case of box elder, one can be paid to remove it from woodlots.  Nice.

The side by sides were to see if a more carbon rich (box elder) feedstock would screw things up.  Goal in biogas production is to shoot for normal composting C:N ratios of 25-30:1.  The box elder was likely closer to 40-50:1, the lambsquarter more like 20:1.  Jean Pain never measured, and I like flexible systems.  We *know* 25:1 will work, so lets push the envelope to see what happens.  Unfortunately, 2 of my 3 steel drum lids had the bungs rusted on (snapped a bung wrench trying to open it) so I can only seal one.  I choose the Box Elder.  Weeks went by with nothing.  Temps are good – 90-100 with digester feedstock at 95.  I should be cooking right along, but wasn’t, or if I was I wasn’t capturing it.  That meant I needed to reseal the barrel as the old gasket was, well, old or that the chemistry had gone wonky.  I sealed the barrel up with silicone and then I took a sample to a friend with lots of lab equipment including pH testers that give near instantaneous readings to within .01.  Results – the Box Elder batch was sour.  REAL sour : 4.8 !  Methane microbes like to be 6.8-7.4.  Oops.   Making methane is a delicate dance between acid producing bacteria and methane producing ones.  I don;t know enough about the bio-0chemistry, but my hunch is that the prevalence of carbon in this digester tilted the balance, but there are so many variables.

So I stopped by my friend who runs our local sewer utility and picked up 8 gallons of biosolids – the left over treated turds of our village.  Our municipality sterilizes the processed effluent with lime as not many bacteria live past a pH of 12.  So the left over solids are about 10.4 pH and are still high in organic matter.  3 gallons of slurry and had me up to 6.1 pH, so I threw in another 2 gallons and will test again tomorrow.  I also threw in another cu ft or so of compost to reinoculate it.  Why?  Because I have come to the same conclusion as Will Allen at Growing Power – that compost fixes nearly everything microbial- if you throw 500 billion bacteria, spread across 15000 different species it is rather likely the one you want is in there and will thrive if you set the environment up.  Fingers crossed.

Back to our story.  When I went into the lab today, I also tested the lambsquarter digester for pH.  This unit had a different odor to it, less sickly sour and more of a deeper, more robust putrescence.    It was also bubbling under the slime.  Huh.  Could that be methane?  The pH test of that looked much better – 7.10!  Right in the sweet spot. So I switched over the methane capturing lid and now the lambsquarter digester (#2) is sealed and plumbed to collect gas.  Perhaps I will have video up soon of itty bitty bubbles coming out the discharge tube.  If so, I will capture some and take them back to be tested at the sewer utility as they have equipment to test for methance gas quality.  And since I am using their Biosolids-  I now qualify as a test project so I get to use all their toys.  Awwww yeah.

Also staking out felling rights to several local woodlots and will likely be buying a chain saw or a wicked good axe to take down several hundred 3-5 yr old Box Elders for the next phase of the ‘Midden as we switch gear for hot water production, perhaps in September.  Problem is I will be out of town for half the month and I lost my “intern” to school so not sure if I want to start it before or after.  We’ll make it work.

MUCH more to come!


One Response

  1. I’ll be sure to learn all about the bio-chem (and C4/CAM photosynthesis mechanisms) in schrool and report back.

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