Digester Mixing Solutions with Landia GasMix and Stirrer

Better biogas plant substrate mixing during fermentation is great news for a biogas operator. The importance of “creating a stir” in the fermentation tanks of fully mixed bio-reactors is huge. It provides better biogas yields and improved process stability. And, this is becoming much better understood.

Many AD plant clients around the globe are discovering that although it takes some of the power from the plant to run the mixer equipment it pays to do it. The additional yield of biogas will pay back with substantially more biogas power than well-designed specialist mixer equipment consumes.

This realization is all part of the industry trend toward higher biogas yields and reduced cost.

Digester Mixing Solutions

Efficient mixing in anaerobic digesters enhances gas production and reduces sludge volume. Various approaches—mechanical, hydraulic, or gas recirculation—can be used to circulate and agitate the digester contents.

Mechanical Mixing

There are several mechanical methods to mix digester contents:

Hydraulic Mixing

• Overview: Relies on gravity or pumps to recirculate the digester’s contents.
• Advantages:
  • Cost-effective: Typically requires less energy, making it economical.
  • Ideal for Small-Scale Digesters: Suitable for setups where simpler operations are preferred.

Gas Recirculation

• Principle: A portion of the biogas produced is captured and then injected back into the digester.
• Benefits:
  1. Enhanced Mixing: Bubbles generated by reintroduced gas help stir contents.
  2. Improved Contact: Increases interaction between microorganisms and organic matter, boosting digestion efficiency.

Digester Design Considerations

• Structural Features: Incorporating baffles, inclined walls, or multiple inlets and outlets can establish natural circulation patterns, further aiding mixing.
• Goal: Optimize flow paths to ensure uniform distribution of microorganisms and nutrients.

The Landia Gasmix is unique because it combines hydraulic mixing with gas recirculation (sparging).

Biogas Mixing Creates a Stir in China

The rest of this post was first published in June 2015. It is still 100% true and relevant today so we have provided it below for your information:

A scan of world news on this subject revealed that biogas operators, and researchers, from China to Malta are investing in biogas reactor mixing equipment.

Landia GasMix deployed and mixing at top Chinese bioenergy research institute

In the first news release we have here, the Landia GasMix system has been installed as a research tool. This has been done in order to discover achievable “best practise” biogas production data, for feedstocks consisting mainly of rice straw and liquid pig manure.

In the second a new completely mixed biogas reactor was successfully fitted with a biogas recirculating gas sparge system installed centrally in the top of the circular fermentation tank, to provide good mixing. And, in the third another proprietary mixing system was installed for process improvement purposes.

In our final release, it is clear that water treatment companies are also retrofitting enhanced mixing systems, and in this case the system (with other optimizations included) is said to be 3 times quicker to achieve the required biogas output, than a standard plant, as a result.

Now let's get started. Read the following to understand why good reactor tank mixing is so important:

1. More gas, less maintenance with Landia GasMix at leading Bioenergy Research Institute in China

Landia's GasMix digester mixing system has been deployed in one of China's most important comprehensive educational institutions. It is used to test various feedstocks and determine the best strategies for optimizing the AD process.

The University of Nanjing's Bioenergy Research Institute, which is located in the ancient capital of six dynasties in eastern China, has been experimenting with rice straw as a feedstock.

The Landia GasMix is externally installed, which improves the 300m³ digester at the pilot plant substantially.

This makes routine maintenance far easier than attempting to reach typical propeller mixing systems inside the digester. Because of the need to empty the tank, this inefficient design always results in substantial downtime, as well as health and safety concerns.

Mr. Zhang Yabing, Manager of the biogas plant at Nanjing’s Bioenergy Research Institute, commented:

“Not only is the entire mixing system of the Landia GasMix mounted outside the digester, the power consumption is also low and the cutting system of the chopper pump cuts straw into smaller particles”.

He continued:

“As an added bonus, it has also turned out that biogas production is much higher than expected”.

The university's biogas plant has an 18.5 kW Landia GasMix, which is extremely energy efficient because it only takes a brief operation period to mix the entire digester, around 20% of the time.

GasMix may be regarded as a better than energy-neutral mixing system since it genuinely mixes the whole contents of the tank for maximum efficiency. The enhanced biogas output exceeds the energy used by the mixing system.

The Importance of Digester Mixing

Anaerobic digestion is a biological process where microorganisms break down organic matter in the absence of oxygen, producing biogas primarily composed of methane and carbon dioxide. For this process to be efficient, maintaining a uniform environment within the digester is essential. Here's why digester mixing is indispensable:

1. • Uniform Substrate Distribution: Proper mixing ensures that the organic material, known as substrate, is evenly distributed throughout the digester. This prevents the formation of dry spots or clumps that can hinder microbial activity.

• • Temperature Regulation: Anaerobic microorganisms thrive within specific temperature ranges. Effective mixing helps maintain consistent temperatures, thereby optimizing microbial performance.

• • Nutrient Availability: Mixing facilitates the continuous supply of nutrients and removal of inhibitory by-products, sustaining the metabolic activities of the microbes.
  • Prevention of Sedimentation: Without adequate mixing, solid particles can settle at the bottom, leading to sludge accumulation that reduces the digester’s capacity and efficiency.

Digester Mixing – Frequently Asked Questions

Q1: How does digester mixing affect biogas production?

Effective mixing ensures uniform substrate distribution, maintains optimal microbial activity, and prevents sedimentation, all of which are critical for maximizing biogas yield.

Q2: Can GasMix and Stirrer systems be retrofitted to existing digesters?

Yes, their mixing solutions are designed to be versatile and can be adapted to integrate with various existing digester configurations.

Q3: What is the typical lifespan of GasMix and Stirrer systems?

With proper maintenance, their systems are built to last several years, providing reliable performance throughout their operational life.

Find out more here.

We hope that you agree that the evidence we have provided in this article shows that biogas plant substrate mixing during fermentation is creating a “stir”, or at least a lot of action from AD Plant Operators!