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Filling a Biogas Digester for Starting

Filling a Biogas Digester for Starting

Do you have a biodigester?

Filling a Biogas Digester for Starting: Congratulations! Conditions are good for biogas to save the world and you, the new owner of biodigesters, are at the forefront. But before you make biogas, you need to establish a community of microbes in the bamboo tank/bag/dome biodigester that you just built, bought, or inherited. Fortunately, establishing the microbes to carry out this process is simple if you know what you are doing. But before we get filling a biogas digester for starting, a few questions need to be answered:

Does the biodigester hold water where it needs to hold water?

Is your biodigester holding gas below design gas pressure?


Once these two important structural considerations have been established, the next steps are easy. There are some important materials to have on hand, as everything is sealed and structurally functional, a lighter, and a pH test. A lighter will mark when you start to produce a combustible gas. The pH indicates the health of the biodigester.

Problems in Filling a Biogas Digester for Starting

Optimal pH range: 6.8-7.5. For the most part, an anaerobic digester operates in a specific pH range (6.8-7.5). At this pH, the methane production activity eliminates the inhibitory by-products and inhibits the process. Incredibly low pH: below 6.0. During the filling of a biogas digester for starting, microbes that produce acid and hydrolyze can cause methanogens to grow, causing a drop in pH. If the pH drops below 6.8, methanogen growth will be inhibited and if the pH drops below 6.0, you may want to consider cleaning and restarting the biodigester.

This problem can be a result of using “hard water” to biodigester organic material that is too rich in protein or ammonia. Anaerobic digestion is carried out by a community of microbes that hydrolyze (turn solids into soluble), produce acids, produce acetate, and produce methane (methanogens). Several other by-products form an important part of the process. Understanding a little science can improve the boot process and help with troubleshooting. If you are new to filing a biogas digester for starting jargon or want a quick update, take a look at the glossary to familiarize yourself with some terms.

What kind of biodegradable are you?

This is a two-component question. There is considerable diversity in the design of biodigesters, and biodigesters can have many ways to get filling a biogas digester for starting. Most of the time, however, we will be dealing with tank and piston flow reactors, so we will focus on these until the end when more advanced designs will be discussed. An example of a continuous flow digester would be the Sausage or polybag digester, while most Indian-style floating domes and biodigesters would be tank reactors.

If you have a fixed-film or up-flow biodigester that covers anaerobic sludge, you probably know that these bioreactors will likely need a different start than piston flow or tank reactors. Booting from these different systems may be similar, although the installation, load speed and digester management may be different. What you are feeding the digester will affect the initial procedure used. Feeding consideration becomes especially important when deviating from the common raw material of pig/cow manure.


Manure feedstock, for example, tends to have larger populations of methane-producing organisms called methanogens (particularly “ruminated” mammals, ie cows, goats, sheep, etc.). Your food substrate may not be rich in methanogen-preferred places to live, whether it’s fresh food waste, a process by-product, or a host of other wastes, but don’t worry! It may be necessary to create a community of biodigesters (using one of several methods) before loading in the way the biodigester normally feeds. Knowing the type of biodigester and its power will help you put the following start-up methods into practice.

Filling a biogas digester for starting Slurry and “Idling” Biodigesters.

Getting to filling a biogas digester for starting with Biodigester Slurry and “Idling” Biodigesters

The simplest and safest way to start a tank buffer or biodigester flow is to simply fill it with the contents and/or sludge from another biodigester. Proximity and availability are the biggest issues with this process, but assuming availability the biodigester should be fed a reduced amount of substrate and the pH should be monitored, if possible, daily until the projected loading rate is quickly reached. This is especially true if they are filling a biogas digester for starting to run on a different substrate than the running biodigester.


Many biodigester construction manuals are so fond of this method that they recommend filling a biogas digester for starting an “inoculum” or “seed” before building the biodigester! This can be done in several ways. One way is to fill a 55-gallon drum with one part manure and one part water and allow it to develop a community of microorganisms for anaerobic digestion. It is a good idea to monitor the drum’s pH from time to time to make sure the slurry has developed correctly; you certainly want to check the pH before adding the sludge to a biodigester.

A biodigester can be “inactive” (i.e., left alone for, for example, a growing season) and then restarted in the same way (by reducing the amount of substrate and monitoring the pH). The combustibility of the gas is important to monitor during the start-up phase; however, combustibility is rarely an issue when using anaerobic sludge.

Carbon dioxide is produced in the early stages of the anaerobic process, and it is important to know when it fills a biogas digester for starting to produce methane as this is the likely point of stability for the biodigester (i.e., acids are removed as quickly as they are produced).

The “beginning of the water”

Assuming the unavailability of sludge and biodigester contents, the next simplest method to filling a biogas digester for starting would be Water Start. The instructions are simple: fill the biodigester with water and load it with manure at a normal charge rate. The idea is that water will dilute inhibitory intermediates (acids) and by-products until the methane-producing population has time to recover. This can often be done without much monitoring or hassle.

The drawbacks are that the process can take time and is limited to substrates with a large population of methane-producing organisms, such as fresh manure. Some manure that may not be applicable may include poultry and possibly human dung. This method should be considered especially for plug-flow biodigesters.

Manure is a popular use for anaerobic digestion, but, as previously mentioned, it is certainly not the only use. To fill a biogas digester for starting that will degrade food waste, it is good to feed the biodigester with manure, as described above with starting water. As soon as the filling a biogas digester for starting to produce methane (check this by turning on the gas), it begins feeding food waste at a slower rate, slowly increasing to the intended feed rate.

Cultural enrichment and beginning

In a very general sense, filling a biogas digester for starting an anaerobic biodigester is to provide a population of methanogens to remove the inhibitory byproducts of the faster-growing hydrolysis and acid production processes. Remember that anaerobic digestion is done by a community of hydrolyzing microbes, acid producers, acetate producers, and methane producers.

There are several ways to start a biodigester, and here we will discuss some of the lesser-used methods. Basically, you can load the filling of a biogas digester for starting with a population of methanogens from an environment where they already exist.

Methanogens can be found in aqueous soils (marshy soils), aquatic sediments, animal rumen, thermal springs, anoxic zones in the ocean, various body parts of many organisms, landfills, and other anaerobic environments. Of these, two have commonly been used to start an anaerobic biodigester and usually in the laboratory.

Rumen and landfill leachate are some common methods of filling a biogas digester for starting in the laboratory. Due to toxicity issues with landfill leachate, the rumen is a preferable source of a methanogenic population.

Filling a Biogas Digester for Starting

Ruminant animals are defined as animals that soften food with their first stomach; examples could be cows, goats, sheep, buffaloes, and llamas. You can get a rumen in a slaughterhouse or if a dairy science unit is available on a fistulated cow. The rumen content of a cow can contain one-half to one-quarter of the methanogenic population of anaerobic sludge in a continuous-flow tank or manure digester.

To start a tank or plug flow biodigester with a rumen, the contents of one rumen must be removed to fill 10% of the volume of the biodigester and the other 90% with tap water (any water except distilled or deionized).

Feed the biodigester at the calculated rate and in a few days, you would expect the biogas to be produced. You will need to add 10% of methanogenic sludge to 10% of the initial volume of the biodigester sludge. You can also enrich a crop to degrade a specific compound of interest, such as cellulose (woody material). A similar rule of thumb inoculation of 10-20% volume (depending on how quickly you want the process to proceed) works well with starting anaerobic batch processes (as opposed to continuous feeding), however, this is another operational consideration and beyond the scope of this guide.

Beginning of Slurry (batch process).

Another possible way to start an anaerobic digester is to fill it with 5-20% manure and water and then leave the mud in a sort of “batch” process. When biogas starts to evolve from the sludge, you can start feeding the biodigester at the recommended rate. Care and monitoring of pH must be considered because using the “batch” start method can easily overload and unbalance the biodigester, causing a drop in pH. In a variation of starting with the paste, you can start using an empty biodigester and add the paste little by little.

A floating dome should be considered (e.g., will a watertight seal be produced on the first edition?). This filling a biogas digester for starting option can be particularly desirable if your biodigester is prone to leaks. A similar process is used when creating an inoculum for the biodigester before construction, as mentioned in the filling of a biogas digester for starting and idle section.

Effects of temperature

You know (hopefully!) that temperature affects the amount of organic material that can be loaded into a biodigester, but did you know that temperature impacts also begin? In general, methanogens can grow (given the available substrate) acid-producing organisms at higher temperatures, while at lower temperatures, acid-producing organisms can outperform methanogens.

This means that filling a biogas digester for starting at a lower temperature, such as in the mountains, can be more difficult and more prone to collapse than starting a biodigester in a low-lying tropical environment. One solution might be to increase the dilution, switching to a safer technique such as starting with water or reducing the loading speed at startup.

Role of nutrients in filling a biogas digester for starting

Nutrients play an important role in anaerobic sludge formation and their availability can facilitate the overall anaerobic digestion process. Nitrogen, Phosphorus, Sulfur, Calcium, Magnesium, Iron, Nickel, Cobalt and Zinc are recommended supplements for an anaerobic digester.

Many fertilizers contain these compounds, and if filling a biogas digester for starting a tank or buffer flow system (one that does not have long anaerobic sludge retention times), a nutrient supplement can speed up the start-up process. Nutrient supplements can also help start some biodigesters where nutrient precipitation occurs. Supplementing your influencer with a nutrient-rich substrate such as food waste.

The types of systems that can be subject to nutrient deficiency can be substrates rich in one type of organic matter, metals that can corrode and “precipitate” nutrients, the use of iron-rich water that can bind some nutrients a combination of these factors. However, before blaming a failed filling of a biogas digester for starting toxicity issues or nutrient deficiency, I should point out that they should be a last resort, as they probably are not the problem.

How long will that take?

Well, the answer to that question, for the simpler designs mentioned earlier, is complicated. The filling of a biogas digester for starting time depends on the temperature, the initial microbial concentration, the microbial concentration in the raw material, and the availability of nutrients. That said, in a hot climate, using the dung of a ruminated mammal, using any of the methods mentioned above, a filling a biogas digester for starting in a few days up to a maximum of a few weeks.

In any case, there is something wrong with your startup method if you are filling a biogas digester for starting a simple biodigester and it takes more than a month (the only exception might be exceptionally cold weather, where you would probably want to provide some active or passive form. however, heating or anaerobic digestion would not be appropriate).

You can also guess and add nutrients, maybe some carbohydrates or try to speed up the start procedure with other methods (DO NOT try to raise the temperature just to start, you will break the digester when it goes into normal operation).

The only downside is that your “accelerated” solution, which you have never tried, could collapse, or inhibit the biodigester. The start-up time for more advanced projects will be discussed in the next section of filling a biogas digester for starting.

Biofilm and the start of granulation

This section for most readers can be skipped or read for interest. This is not an instruction guide, but rather a filling a biogas digester as a starting point for starting a “sludge retention” anaerobic biodigester. Some anaerobic bioreactors will retain sludge for various benefits such as extremely low hydraulic retention time (<6 hours reported), increased methane content, low biodigester volume, resistance to stressors, ease of idling, faster “digestion” rate, less or no sludge in the effluent.

However, while a simpler biodigester can take up to 2 weeks to start a biofilm, a granular sludge biodigester can take 4 months or more. Simpler designs and processes also eliminate some expensive materials such as pumps and fluid carriers. The mentioned mechanisms of microbial fixation and granulation are not fully elucidated, but a lot of work and research has been done to study these processes.


  1. What is a biogas digester, and what is its purpose?

    A biogas digester is a device or system that breaks down organic waste materials in an oxygen-free environment to produce biogas, a mixture primarily composed of methane and carbon dioxide. Its purpose is to generate renewable energy and convert organic waste into useful byproducts.

  2. How do I fill a biogas digester initially?

    To start filling a biogas digester, you need to introduce a mixture of organic waste and water into the digester tank. This waste can include food scraps, animal manure, agricultural residues, or energy crops. The waste should be finely chopped or shredded and mixed with water to form a slurry before being added to the digester.

  3. What is the ideal feedstock ratio for filling a biogas digester?

    The ideal feedstock ratio depends on the type of waste being used, but a common guideline is to maintain a carbon-to-nitrogen (C/N) ratio between 20:1 and 30:1. This ensures a balanced microbial activity for efficient biogas production. Different feedstocks have different C/N ratios, so it is important to mix them in appropriate proportions to achieve the desired ratio.

  4. Can I add multiple types of waste to the biogas digester?

    Yes, it is possible to add multiple types of waste to the biogas digester. Mixing different feedstocks can enhance the nutrient balance, increase biogas production, and improve the stability of the digester. However, it is important to consider the C/N ratio and the characteristics of each waste to ensure a well-balanced and efficient process.

  5. What temperature should the digester be maintained at during the filling process?

    The optimal temperature for biogas production typically ranges between 35°C and 40°C (95°F to 104°F) for mesophilic digesters and between 50°C and 55°C (122°F to 131°F) for thermophilic digesters. It is crucial to monitor and maintain the digester’s temperature within the recommended range to promote the activity of the microorganisms responsible for the anaerobic digestion process.

  6. How long does it take for the biogas digester to start producing gas?

    The start-up time can vary depending on various factors such as temperature, feedstock characteristics, digester design, and microbial activity. In general, it can take anywhere from a few days to several weeks for a biogas digester to start producing significant amounts of gas. During the initial period, microorganisms need time to establish and adapt to the environment.

  7. What should I do if the biogas digester does not start producing gas?

    If the digester does not start producing gas within a reasonable time frame, there may be several reasons. Check the temperature to ensure it is within the optimal range. Verify that the feedstock is mixed properly and the C/N ratio is suitable. If necessary, consider adjusting the pH level, which should ideally be between 6.5 and 7.5. If problems persist, consulting an expert in biogas digester systems is recommended.

  8. Can I add additional waste to a biogas digester once it is already operational?

    Yes, you can add additional waste to an operational biogas digester. It is common practice to continuously feed the digester with organic waste to maintain a steady biogas production. However, it is important to maintain the appropriate feedstock ratio and avoid sudden or excessive changes in the composition or quantity of waste, as it can affect the digestion process and gas production.

  9. How frequently should I check the digester's progress during the filling phase?

    During the filling phase, it is advisable to monitor the digester’s progress regularly. This includes checking the temperature, pH level, gas production, and the overall digestion process. Initially, daily monitoring may be necessary, but as the digester stabilizes, you can gradually reduce the frequency to weekly or bi-weekly checks.

  10. Are there any safety precautions to consider while filling a biogas digester?

    Yes, there are several safety precautions to consider while filling a biogas digester. Firstly, ensure proper ventilation to prevent the buildup of potentially harmful gases. Take caution when handling and storing organic waste, as it may contain pathogens. Also, Additionally, follow safety guidelines for working with equipment, such as pumps and mixers. It is recommended to familiarize yourself with local safety regulations and seek professional guidance if needed.

3 thoughts on “Filling a Biogas Digester for Starting”

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  2. Hello I am starting a bio digester in an IBC container. To start i used a 3:1 ration of water to cow manure. We placed these materials in another tank to be able to monitor the ph level. One question i still have is, how much of the Bio digester needs to be filled with the initial starting Sludge.

  3. Pingback: Constructional details of Biogas generation Plant

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