By the way, the microbes involved are reportedly facultative anaerobes, and this means they can survive oxygen exposure. Otherwise, you'd have a much larger challenge.

 

I'd place your entire "fermentor" inside an incubator, which is little more than a moderately insulated enclosure with a light bulb as a heat source, like people use for hatching eggs. A small fan would be nice but is probably not necessary. Fungi are very forgiving as long as you don't cook them.

Sunlight on a sunny day would be more than enough energy to hit 37°C, so if you expect to use passive solar, you'll need a shade to prevent cooking your ferment. Put the whole thing inside a regulated greenhouse.

If the thing cools off a little at night, but resumes 37°C operation during the day, is that bad?

Hi!

I think we've already thought of doing something like that but the idea seemed to be expensive? Or rather will cost more.
Hence, we resort into choosing to come up with a device than we can just attach to a container such as the "casserole".
Yes a sunny day would be more than enough BUT we'll have problem during the rainy season.
In order to speed up this fermentation/molding process, we intend to cut all possible "periods" were the fermentation process stops because the temperature drops.
That happens mostly at night but that's also possible during daytime and of course, when raining.
.
I hope I got your message right. I really have no idea for passive solar stuff and regulated greenhouse haha, sorry ..
But still, thank you for the response

 

By the way, the microbes involved are reportedly facultative anaerobes, and this means they can survive oxygen exposure. Otherwise, you'd have a much larger challenge.

Yeah, thank God it's like that!
The previous study we're supposed to do involved bacteria from sewage sludge and it's very complicated and focuses greatly on the chemical aspect and not on the electronics..
But back to the topic. I might have been focusing too much about fermentation in general I almost forgot about that. Thank you!

 

OK, well one problem is your 3.5V "specification". Let's say it's a cool rainy evening. Your fermentor might need, say, 20W to stay at 37°C. (Just a wild guess - you should try to determine for yourself what the real number is.) Delivering 20W from a 3.5V supply requires 20W/3.5V= 5.7A. I would say that's "a lot". A car battery cannot sustain that for more than a couple hours without serious discharge.

So I think insulation is critical to get the heat flux down under 5W or less. Insulation will also protect the ferment on a hot day.

I'm also thinking thermal mass would help to avoid any rapid change. Picture your casserole in a water bath inside an insulated cooler. Wrapped in foil and under a blanket. You could be sure of the water temperature as you seal it all up, and it would take very little extra input to counter the heat flux leaking out. My dad helped me grow crystals once when I was a kid - that's how we did it. It took days to cool off even without any heat input.

 

If this is a commercial product you might consider incorporating a custom constant temperature ceramic heaters, which are thermistors that are heaters that regulate their temperature.

One such part; they can be made in nearly any shape.
http://www.aliexpress.com/store/product/PTC-Heater-for-crimper-max-150W-12V/508447_1495145476.html

I've always loved these. It's such a brilliantly simple concept. No moving parts, no software, no extra joints to solder up for a control circuit, and the only power consumption is what's turned into heat. Brilliant!

 

OK, well one problem is your 3.5V "specification". Let's say it's a cool rainy evening. Your fermentor might need, say, 20W to stay at 37°C. (Just a wild guess - you should try to determine for yourself what the real number is.) Delivering 20W from a 3.5V supply requires 20W/3.5V= 5.7A. I would say that's "a lot". A car battery cannot sustain that for more than a couple hours without serious discharge.

So I think insulation is critical to get the heat flux down under 5W or less. Insulation will also protect the ferment on a hot day.

I'm also thinking thermal mass would help to avoid any rapid change. Picture your casserole in a water bath inside an insulated cooler. Wrapped in foil and under a blanket. You could be sure of the water temperature as you seal it all up, and it would take very little extra input to counter the heat flux leaking out. My dad helped me grow crystals once when I was a kid - that's how we did it. It took days to cool off even without any heat input.

I still have to read more though to fully understand as to how are we gonna do such..but I think that's great!
There's a high chance that that's achievable for our project and I don't think it'll be that expensive!
Actually, we've been wondering if it's okay to use just the casserole as the outermost material and then we put the next layers inside (Like that metallic net mentioned from other responses here).
And we've been contemplating similarities for our device's function with a rice cooker and a flat-iron but it's not really clicking.
I think that that approach is really great thank you very much!!

 

Again, with the container, if it's just hermetically sealed, what factor should we consider if we really have to turn it into vacuum?

You don't. If you buy a vacuum pump and cause a vacuum in the container, you will kill everything except spores. The natural air pressure on Earth is 14.7 P.S.I. That pressure is everywhere except in containers people make to keep the air out. I will bet this computer that the mold you grow did not evolve in a vacuum and will not flourish in a vacuum.

 

If you buy a vacuum pump and cause a vacuum in the container, you will kill everything except spores.

Interesting comment. Why are bacteria, including non-spore forming varieties, preserved under high vacuum?

@Pi Ya
You have received some valuable advice about how to make an incubator. There is still a lot unknown about the microbiology you are trying to accomplish. When I first read your post, I was struck with your need for 37°C. It is a common misconception that microorganism grow best at that temperature. In fact, even most human pathogenic bacteria and fungi grow best at lower temperatures. I was wondering whether you were doing something with organisms that actually prefer 37°C. Thankfully, you finally cleared that up in post #19. I suspect you really need a temperature around 30° or even lower. (If you think about organisms growing in water, how many bodies of water are at 37°C?)

As for the atmosphere in which you grow these organisms, I suspect air with or without added CO2 will be most effective when you consider all of the organisms in your milieu. Another important constituent of most systems is humidity. You probably don't want a condensing atmosphere (i.e., 100% humidity), but you almost certainly want something greater than 60% (e.g., 70% to 80%). I cannot conceive of a need for a vacuum, but potentially you may need reduced oxygen concentration, which can easily be done by adding CO2 or nitrogen.

Rather than continue with a lengthy discussion of all of the possibilities that have been used as starter inoculums, will you please list the organism you intend to co-cultivate?

John

 

Interesting comment. Why are bacteria, including non-spore forming varieties, preserved under high vacuum?

I thought any bio-matter that (therefore) contains water would be ruptured when exposed to a vacuum. Maybe they freeze the subject matter first? I don't think that will fix it. That still wouldn't stop sublimation. Are cell membranes so strong because of their small size that the difference in pressure can't exert enough force to break them?

Internet search confirms, "50% to 65% survival" under vacuum conditions.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC546782/

Still, I don't believe a mold grower would intentionally vacuum his specimens to promote faster growth.

Oh...you already said that.
"I cannot conceive of a need for a vacuum,"

 

I thought any bio-matter that (therefore) contains water would be ruptured when exposed to a vacuum. Maybe they freeze the subject matter first? I don't think that will fix it. That still wouldn't stop sublimation. Are cell membranes so strong because of their small size that the difference in pressure can't exert enough force to break them?

You thought wrong.

John

 

Yeah, there's no such thing as a "vacuum sterilization" process. If only it were that easy. Microbes would scoff at you.

On the other hand, I've seen a lot of culture storage banks and none were under vacuum. Sealed lyophils - freeze dried cultures in vials - are common but they are not under vacuum.

 

There is still a lot unknown about the microbiology you are trying to accomplish.

Therein lies the crux of this project, in my opinion. The goal is a mixed culture under composting conditions; hot, moist, solid substrate, and plenty of nutrients. But with limited oxygen so that the fermentation goes anaerobic.

I'm skeptical of the science and validity behind the claims supporting the goal, but that's OK.

 

Yeah, there's no such thing as a "vacuum sterilization" process. If only it were that easy. Microbes would scoff at you.

All these years I thought using a vacuum pump on Freon systems was leaving them sterile. Oh the anguish! So many critters being condensed and evaporated, hundreds of times a day. I hope the S.P.C.A doesn't find out.

Sorry. I'm feeling a bit silly right now.

 

Quite all right.

And for what it's worth, "sterile" is a little like "vacuum" or absolute zero. Easy to understand in abstract but cannot be attained without great difficulty.

 

Hello,

If you want to more about the microbiology, have a look at the links of this page of the EDUCYPEDIA:
http://educypedia.karadimov.info/education/biology-virusinfo.htm

Bertus

 

Therein lies the crux of this project, in my opinion. The goal is a mixed culture under composting conditions; hot, moist, solid substrate, and plenty of nutrients. But with limited oxygen so that the fermentation goes anaerobic.

Exactly. EM-1 is a registered trademark, so there have arisen various microbial starter inoculums with other names. One recipe I came across was simply Sacchromyces cerevisiae (aka brewers yeast), Lactobacillus plantarum (an aerotolerant lactobacillus)and a Rhodopseudomonas (grows with or without oxygen, chemotropic). Other organisms have been used, but the article I read (http://www.hawaiihealingtree.org/how-to-make-your-own-em-1-inoculant-and-bokashi/ ; not my usual source for scientific information ) said they are no longer in use but gave no reason. Presumably, they were more difficult to grow or not as non-pathogenic as need be for this application.

I'm skeptical of the science and validity behind the claims supporting the goal, but that's OK.

I share that skepticism based on reading some pretty wild claims; however, the concept of using an inoculum to control the character and smell of compost may be valid.

A simple incubator can be made with a foam cooler (or similar), light bulb, circulator fan, and temp controller. More specific suggestions were given above. Be sure to have a source of humidity. A tray of water in the bottom of a closed incubator works well. That tray needs to be changed and cleaned periodically, as it will become colonized with various bacteria you may not want in a defined inoculum.

As for sterility, I also agree. It is probably easier to attain than space vacuum or absolute zero, but harder to prove.

John

 

Good Day Everyone!

@jpanhalt -- Thank you for that clarification! Yes, we thought that it's always 37 degrees because that's what we've read. Well then we have to search more about it. We've also thought of asking a professor whose expertise is microbiology but we're still waiting for a reply from a friend. From what I've read about the mixture, aside from dirt, it contains 3 microbes: Lactobacilli, yeast/fungi, phototropic bacilli.
And yes, EM-1 is the commercial mixture that know about but we're not sure if that's what are we also going to use. We still have to discuss some matters with the people from the site of our research locale. The bokashi that we're going to use will come from them. If ever that it came from a different source, we have to have it tested to prove what microbes it contain.
@#12 @wayneh -- Thank you for that discussion about vaccum! Then vacuum shouldn't be the right term to be used for our projects design. Claiming sterility could be hard we'll find ways as how to support that aspect in our project.
@bertus -- I've checked the site you just shared and the previous ones too. I think I've never visited them before when we were still doing the preliminary researches for our project. Thank you very much they're great help!

Thank you very much for all the advice and suggestions!
It's really amazing how professionals discuss about a certain matter...
I feel so humbled... and so inspired to study harder!!
From what I've read, it's kinda lot of information to process..
But I will take note of it all and discuss it with my group mates.
For the meantime, that will be the next step.
Because to be honest I wasn't quite sure if I have answered the questions properly )
Again, thank you very much and ultimate goodwill to you all!