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Bio-Digester vs Composter

Updated on January 13, 2020
Alexander Okelo profile image

Alexander is a professional engineer who specializes in the construction of affordable houses and structures using recycled materials.

Background

For decades, composting and decomposing of waste by the use of a digester has been a common way to treat waste. Previously, people preferred to use composting as a way of waste management because you could use the waste as a fertilizer for your crops.

Now, people have switched to eco-friendly methods; whether instead of releasing toxins, pathogens, and other harmful chemicals to the soil, anaerobic digestion takes place in a bio-digester and it outputs gas and clean water to use for agricultural and household purposes.

In this article, we shall take a look at the difference and similarities between decomposition used by the composter and anaerobic digestion used with bio-digesters. Keep reading it find out more.

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Similarities and Differences of Composter and Bio-Digester

Even though people embrace different realities when it comes to releasing of waste and the environment, it is always better to take a more in-depth look at the choices available. Here you shall read on some of the similarities and differences that exist with these two.

First off, you should know that both methods are energy-saving and can be sustained for an extended period. This means whichever option you choose for your home, whether it's an apartment or a shipping container home, you will be well served by either choice.

Now let's take a look at the difference between the two, in terms of advantages and the processes involved with either of them.

Composter

A composter uses a decomposing method known as an aerobic process (with oxygen). Under the layers of waste, the organisms are naturally oxidizing the organic matter with oxygen. This means that the nitrogen chemicals are turning to nitrates, sulfur to sulfates, and phosphorus to phosphates.

This process allows the organic matter to decompose in such a way that it produces the same chemicals used in manure hence very suitable for use in your farm as rich and nutritious fertilizer. This has been a very common process in the coast, especially for large industries. They would invest in making their own fertilizer to save on cost.

There is one disclaimer though because it is aerobic in nature, the oxygen used in the process shall release by-products such as carbon dioxide which is unhealthy and unsafe for the environment. This makes this method non-eco-friendly.

Besides that, it is a really good form of recycling as the products are safe to use in the soil.

Bio-Digester

On the other hand, a bio-digester uses anaerobic digestion to decompose waste. From the sealed off tanks, bacteria will eat ways the waste-producing gases and water as it's by-products, which is not only eco-friendly but also safe for the use at home.

This negative side of this system is that it is much slower than normal composting, but the result is far more useful. As the materials anaerobically decay it seeps methane, which is a key component to biogas, the gas recycled for household use such as cooking.

By-Products of Bio-Digester and Composter

From the process of anaerobic digestion, the bio-digester releases gases that can be used for home purposes; that is biogas.

Biogas

Renewable energy can substitute many of its fossil fuel counterparts. A long-lasting fuel that can be used to cook and even fuel vehicles as it's one of the cleanest and safest energy source.

Although it's a great substitute for fossil fuels, biogas is not widely used. This is due to the already established fossil fuel companies that sell countrywide, therefore many corporations are then reluctant to switch.

Adding to this there is little awareness of its potential. Being eco-friendly and cheap to produce, it could be what people need to fight global warming amongst other environmental disasters.

Water

Waste from the house can be either grey or black. Black contains all the solid content while grey includes the fats, and water from other household activities. This greywater is not usually best to be run through the digester because of its hazardous properties.

Nonetheless, the waste is taken to decompose to produce water for use around the home. After the toilet has been flushed, the black water will drop to the tank through a piping system and into the first chamber as elaborated above.

As for the grey matter, you can't really avoid grease and other hazardous materials from entering the tank. Hence, the grey waste will instead pass through a grease interceptor to get rid of fats, which can be harmful to the environment once emitted.

After the chemicals, fats, and other harmful substances have been sieved from waste, it then goes directly to the soak pit, which is the last chamber of the bio-digester. The digester will release the water to sink through the stones and into the ground for irrigation and other purposes.

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The Advantages and Disadvantages of Anaerobic Digestion vs Composting

Because we see both decomposing and anaerobic digestion as great ways to deal with waste management, here's a look at the advantages and disadvantages either one possesses over the other.

First off, both processes are very common as waste treatment plans for your home. The crucial difference is that composting is the decomposition of organic matter in the presence of air (oxygen) and anaerobic digestion (AD) is the decomposition of organic matter, without air (and most importantly oxygen) present. This then changes the process in such a way that they produce different by-products.

Here's a rundown for each process by listing the advantages and disadvantages of anaerobic digestion vs composting below:

Advantages of Anaerobic Digestion

Against the composter as a sewage and wastewater treatment scheme, the bio-digester has exhibited greater advantages. Let's take a look at some of these advantages;

  • It digests organic solids in an ecological way -- just like the shipping container homes are ecological, so are the bio-digesters.
  • It prevents human waste and untreated water from contaminating groundwater - before being exposed to the ground. The water had been treated to remove over 99% of pathogens.
  • It offers an alternative to the dumping of wastes into rivers, lakes, and fields in rural and semi-rural areas where there are no sewage systems.
  • The effluent from the bio-digester can be used to water plants in the form of irrigation.
  • The effluent is cleaner, more effective and easier to use than a septic tank because it doesn’t need to be emptied.
  • The effluent exhumes odorless, non-obnoxious, colorless air as compared to the end products of the toilets being used these days.
  • It doesn’t require the work and energy involved in relocating composting toilets every year.
  • It requires no further wastewater management or treatment.

From that, you can see why anaerobic digestion is far much better for the environment and even for your housing project.

Disadvantages of Anaerobic Digestion

Unfortunately, not all that glitters is gold. It the process is undertaken in high scale or commercial industry, the level of investment needed to provide adequate by-products for recycling is substantially high. The size of the tanks have to be extra-large, the receiving end has to be frequently checked, and maintenance will be costly.

Finally, because it's on a large scale, you can't avoid the emission of pungent smells from the pit. This can cause discomfort and be respiratory problems for someone working so close to the machinery.

Advantages of Composting

Now that we've taken a look at the advantages of using the bio-digesters, let's see how composting can be advantageous to you as well.

  • The lower initial capital investment needed to start of a composting facility than is needed for an AD Plant - as explained above, in order to produce such efficient by-products, you will need high investment to cater to the purchase of the machinery.
  • A slightly lower level of training is needed to run a composting plant the is required for an AD Plant. Decomposition is basic science, you don't need to know about what bacteria is needed to decompose the organic matter. As long as oxygen is involved, the waste will transform itself into very useful fertilizer.
  • Reduces the cost of purchasing store-bought manure for your farming needs.
  • Easily sustainable.

With the composter, there is a neuter understanding of the process than with the bio-digester. People know that when the organic matter is exposed to oxygen it then decomposes to manure which resonates well with the soil for your agricultural needs.

Disadvantages of Composting

Now let's see the downside to this process.

  • Hard to maintain hygiene. The composter works in a slightly open environment compared to the digester. This is because air is necessary to pasteurize the organic waste to composted material. As the process continues, infectious agents can easily get in.
  • There needs to me great attention to small details such as self sanitation, and monitoring.
  • Composting requires the input of quite large energy inputs to fuel and operate the equipment needed to aerate and turn the compost piles.
  • Composting can also produce pungent odors that are disturbing to being around.

From the comparison above, anaerobic digestion wins for being an eco-friendly solution and being able to provide its own power to do this. Composting makes no contribution to reducing the carbon footprints of the businesses that use the composting process.

Large scale anaerobic digestion towers
Large scale anaerobic digestion towers | Source

Can One Play Alternative to the Other?

So we know most of you are constantly asking yourself if at all anaerobic digestion can act as an alternative to composting and vice versa. Well, similar to composting, in anaerobic digestion, used by the bio-digesters, the bacteria consume organic waste such as food scraps, silage, and animal waste and generate an environmentally benign by-product that can be used as a natural fertilizer.

Unlike composting, however, anaerobic digestion also produces biogas, which consists of about 2/3 methane (CH4). Natural gas is methane with a small number of other trace gases, so biogas can be used as fuel just like any other natural gas.

What’s the Main Difference Between Anaerobic Digestion and Aerobic Decomposition

It's only about the air exposed to the organic matter during decomposition. One is with and the other without oxygen, and both divert waste from the landfill. In terms of the end products, anaerobic digestion provides a better solution to renewable energy than with composting. Hence, safer and more efficient to use for your projects.

Shipping container homes have always stood by the term eco-friendliness. Hence, since then it has become very ubiquitous than before. For composting, many other areas are also trying to decompose waste by themselves. In various areas, we see even the food trucks are placing bins alongside their trucks for compost, recyclables, and trash.

This means the city is diverting an enormous amount of trash from the landfill to help meet its zero-waste goal and producing lots of compost in the process – a process that also produces a lot of carbon dioxide, as a result of using oxygen.

A few cities are taking an alternative, more expensive approach to divert this organic waste called anaerobic digestion and in the process also producing biomethane that is captured for use in electricity generation or used as a transportation fuel.

So in the end, it highly depends on what end product you want. It can guide the process of waste management you want to use.

Anaerobic Digestion vs Composting – Conclusion

There are various advantages to both anaerobic digestion and composting. From organic waste to decomposed waste used as fertilizers or digested waste that produces gases and water for home use. Both ways have exceeded their expectations scientifically allowing the waste management sector to prosper.

But to conclude, the preferred process is anaerobic digestion. This is because it is considered more sustainable than composting. The process of composting requires an energy input to carry out the process. The energy is used in the power needed to turn the compost piles during composting.

But on the other hand, anaerobic digestion produces biogas; a renewable energy source that burns cleanly and makes more energy than they consume to operate. Hence, the better, more sustainable solution.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Alexander Okelo

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