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Discussion Starter · #1 · (Edited)
Hello my fellow survivalists!

I really like the calorie calculator on this site! So I looked for other tools that either optimize me or my harvest.
Somehow I remembered, that one square mile of arable land has a much higher yield rate today than it did even just 200 years ago! So I started looking for simple tools to optimize a running processes and try their promises in real life!

Here is my observation:

Putting organic compounds into an airtight tank and letting it degrade for a while creates biogas.
Because biogas has a high methane content (between 60%-80%), it can be used as an energy source.

Simply put, some of the energy contained in organic matter such as food waste can be reclaimed and put to use. Because this process is very simple, as seen on videos on youtube, biogas production is commonly featured in off the grid communities. I recommend every autonomous community to have at least one biogas digester, as it allows unimpeded all year energy generation.

Unfortunately, the biogas yield depends not just on the input feedstock but also on a plethora of environmental conditions. Because my food waste and environmental conditions change often, my own biogas production was far from optimal.

So a couple of months ago, I started experimenting with technology from the industrial sector to optimize my biogas production.
The calculations from many online calculators did not yield usable results, as most of them assume that you operate an industrial scale plant where many environmental conditions are held constant. Some others required a running internet connection. And even others, are prohibitively expensive. As individual survivalists, we don't have this luxury!

Eventually, I settled on this. It contains all necessary features, works offline, is cheap and even at a discount right now (So go get it, folks!).

Before that, it took me one to two weeks to measure any changes I did to my biogas tank. This is time I do not have in an emergency. Now this process happens in mere seconds, which allows me to increase the biogas yield by experimenting digitally before committing to it in real life.

After these experiences, I consider such software now as essential.

My recommendation to all of you is to gear up on tools that optimize whatever process you are running. If it is digital, it does not increase the weight of your bag and everybody will notice the difference it makes, when you are able to power a generator in situations where others are not.

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I am curious. How much energy can you generate per pound of organic material. I hope you can express such as btu per pound. I would think it would depend on source of organic material, what would be the most efficient source of organic material. This could be rated by most btu/pound or alternatively, btu/acre based on probably yield. nudes...

And welcome

9 Posts
Discussion Starter · #8 ·
Hello nondakotagroer! :)

Let me answer each of your questions in more detail!

I would think it would depend on source of organic material,
You are right, it depends on the source of organic material, also called substrate in this context. For example, a banana has different characteristics than maize.
If you look at the declaration box of food in the supermarket, you'll often find something called calories. Calories are a unit of energy. We measure the energy value of a food by using something called a bomb caloriemeter. Even though you have things like dryness content, volatile solids and the like, you can use the calorie value on the box as a rough indicator on how much energy you might be able to extract from your substrate.

Beware, the actual value you extract depends on the process, like anaerobic digestion etc. you are using. But it nevertheless serves as a useful bound.

If we are using anaerobic digestion (some also call it anaerobic respiration), which leads to our biogas, we have many environmental factors that affect the biogas yield that can be obtained from your substrate.

Therefore, there is no best substrate that works under all conditions. In addition, as survivalists we ideally want to be able to recycle any arising organic waste instead of carefully cultivating specific feedstock for only this specific purpose (which many industrial scale plants are doing).

Roughly speaking, methane is formed by specific bacteria that generally only survives under no-air conditions. You can think of it as a zoo in micro scale. These bacteria need food, need suitable hospitable conditions and have to be protected from other competing bacteria. Because these bacteria are incredible small, we can only protect them indirectly by affecting the environmental conditions in which they live in.

These environmental conditions include but are not limited to: pH value of the (after hydrolysis now watery) substrate, alkalinity of the (after hydrolysis now watery) substrate, temperature, organic loading rate, bacterial growth and decay rates and more.
And the chemical composition of your substrate of course also has a major impact! In addition, a lot of these parameters are incredibly sensitive. For example, in some conditions even slight temperature variations might have a big impact on biogas yield.

Unfortunately, it takes around 10-20 days before you see any changes you conduct reflected in your biogas production yield. Because of the copious amount of environmental factors, experimenting in real life to find suitable substrate / environmental factors combinations would take years (if it is even possible for all combinations of environmental factors and substrate).

The industry has also recognized this, as they try to move away from purpose grown food and constant operating conditions. For them, this is sometimes forced by environmental regulations (why grow corn for biogas when you could eat it?) and concerns (food waste is a-plenty and sounds good to any politician).

So they invested heavily into simulation tools, capable of simulating the anaerobic digestion process digitally. This allows them to test hundreds of "digital biogas runs" a day to find the best course of action to maximize or minimize their target variables. And yes, not just maximization of biogas production but also minimization of biogas production is important. For example, in times of low energy need you want to slow down your process, basically treating your substrate as a battery.

Being the industry, these tools are usually very expensive. The industry leaders in this field, cost upwards of thousands of dollars per year (!)
But the benefits are clearly there, that's why they are ready to pay this amount.

The software I linked includes the fundamental equations and is suitable probably around 80%-90% of the tank sizes and configurations we have as preppers face and is cheaper than many take-away meals. I recommend it.

This could be rated by most btu/pound or alternatively, btu/acre based on probably yield.
Correct. In the next post I am going to do an example calculation for you.

9 Posts
Discussion Starter · #9 · (Edited)
The following calculations are long winded, in order to be as transparent as possible. In addition, this also helps to catch any errors or hidden assumptions.

For the international audience, I am going to use SI units. Non SI are in brackets.

Let's use the example of corn. According to this page, 164 g (~5,78 oz) of sweet yellow corn contains 177 calories.

This is equal to around 4518 J per 1 kg (4518 J per 2,20462 lbs), which translates to around 0.001255 kWh per 1 kg (0.001255 kWh per 2,20462 lbs).
Putting this into perspective, according to Wikipedia an iPhone 13 Pro Max has a 0.01675 kWh battery. Therefore, 1 kg (2,20462 lbs) of this specific type of corn contains as much energy as is required to charge an iPhone 13 Pro Max from zero to 7 %.
If you do not like to think in phones, you could see it this way: Because the specific heat of water is 4182 J/kg°C, our 1 kg (2,20462 lbs) or sweet yellow corn contains as much energy as is required to heat 1 liter (0,264172 gallon) of water by around one degree Celsius (1.8 Fahrenheit).

It is recommended, that adults consume around 2000-2500 calories per day.
At first glance, our first rough calculations appear to indicate, that there is a moderate energy content in our food that can be harvested. But here comes the kicker: You can put any organic waste into your digester. A single leftover Big Mac contains already up to 550 kcal. If you live near a city, just prowl the garbage bins at night around a McDonalds and you'll find dozens of them.

And if you live rural, just collect any organic material you find: All the uneaten food, plants but also manure from your livestock. Through advances in technology, it is even possible to prepare wooden biomass for use in a biogas digester.
And wood in many situations readily available.

Looking at it from this lens, the organic material that can be utilized for biogas production is often available in abundance or at least enough.

But there is one major downside: Randomly putting organic material into a tank might lead to suboptimal performance that can even virtually bring to a halt the methane production process. We therefore should be careful and conservative when feeding the biogas digestion tank with new material. In best case, we try to simulate the repercussions of introducing a new organic material by simulating it beforehand.

Let us continue with the example of crop, more specifically let us investigate the silage.
According to this page, at some times of the year silage has an energy density of around 11.0MJ/kgDM (DM for dry matter I suppose).

So how much of this energy can we harvest through anaerobic digestion?

In order to simulate estimate the methane yield of silage, we first of have to translate the characteristics of this substrate into the language of chemistry. These characteristics are encoded by the chemical oxygen demand (COD). You can calculate or measure COD values of most organic materiel. If you are using a known substrate, you thankfully do not have to do this yourself but rely on substrate tables as found here.

You can input these values and more values into your software framework of choice. I am using the aforementioned BioNet for this purpose, but other tools should be similar.

I will not mention the values of all the other environmental variables (pH etc.) in this example.

My first simulation run over 20 days yields a cumulative Methane (also called CH4) production of around 4.4 molCH4 per m^3 (4.4 molCH4 per 35.3147 ft^3).

Slope Rectangle Plot Font Parallel

As methane has a molar weight of 16.04 g/mol, this is equivalent to 70.57 g CH4 per m^3 ( 0.15 lbs CH4 per 35.3147 ft^3). As methane has an energy density of –55.5 MJ/kg, this yields to 3.916 MJ per kg. That is equivalent to around 1.087 kWh per m^3 (1.087 kWh per 35.3147 ft^3).
That is quite a lot of energy, you can heat a lot of water with that. But still, we are some ways off from our theoretical upper bound. Can we improve?

Using simulation software again, we can adjust some of the many parameters. For example, the organic loading rate right now is set to 3. Let us see what changes if we slightly change the organic loading rate to 2.8

Rectangle Slope Plot Font Parallel

As we can see, the gaseous methane output has increased to 4.51 molCH4 per m^3 (4.51 molCH4 per 35.3147 ft^3). Doing the same calculations as before, this is equivalent to 4 MJ per m^3, or equivalently, 1.11 kWh per m^3 (1.11 kWh per 35.3147 ft^3).

If we further want to optimize our process, we turn our attention to the other process variables.

Because there are so many environmental parameters (over 30) there is no way we can optimize all of them by hand.
But we can let the software do it for us.

In the example above, by just changing the organic loading rate by 0.2 days (4.8 hours) we gain an additional 0.014 kWh.
Recall that an iPhone 13 Pro Max has a 0.01675 kWh battery. Only tiny adjustments allow us to charge one additional telephone. I would not have seen this if I had to look at a physical reactor. That's why I consider such software essential.
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