Why is there low biogas production?

Low biogas production is one of the most common problems in rural biodigesters. Often, the system appears to function normally, but biogas generation falls short of expectations due to malfunctions in the internal agitation of the biodigester.

In most cases, the cause is not in the biodigester design or the volume of waste available. The problem usually lies in an operational aspect that goes unnoticed: the lack of adequate agitation.

In this article, we explain how the absence or inefficiency of the agitator reduces biogas production and what can be done to correct this.

Why a biodigester might produce less biogas.

Biogas production depends on a precise biological process. Anaerobic bacteria need to be in constant contact with organic matter to break it down and release methane.

When this connection is interrupted or impaired, the system's efficiency drops—even if everything seems to be working normally on the outside.

Without proper agitation, three factors directly compromise low biogas production:

Crust formation on the surface

Without internal movement, the lighter matter rises and forms a solid, compact layer on the surface of the tank.

Furthermore, this crust acts like a lid: it traps the biogas that should be captured and blocks some of the biological activity.

Consequently, there is a decrease in the volume of biogas available for use.

Accumulation of solids at the bottom of the tank.

At the same time that the crust forms on the surface, the heavier material settles to the bottom.

This creates a layer of solids that bacteria cannot reach and digest efficiently.

In practice, some of the substrate's energy potential is not converted into biogas.

Dead zones inside the biodigester

Between the surface crust and the bottom sediment, internal regions are formed where substrate movement is minimal.

These areas are called dead zones.

As a result, part of the volume in the biodigester ceases to contribute to biogas production.

How to identify low biogas production

Before concluding that the agitator is the cause of low biogas production, it's worth noting some important signs:

• progressive decline in biogas production
• A crust is visible on the surface of the biodigester.
• fluctuation in production without change in management
• biofertilizer of inconsistent quality
• agitator missing, undersized, or without maintenance

If more than one of these signals appears in the system, there is a high chance that agitation is the operational bottleneck.

The impact of low biogas production on the property.

The loss of efficiency caused by inadequate agitation is not just operational; it also directly affects the financial return on the property.

Among the main impacts are:

• less energy generated
• greater dependence on external sources
• biofertilizer with lower agronomic value
• increased need for cleaning and maintenance
• greater consumption of time and labor

In short, a poorly agitated biodigester costs more to operate and produces less output.

How does the agitator improve biogas production?

A properly sized agitator keeps the biomass in continuous motion within the tank.

That way:

• The surface crust stops forming.
• the solids remain in suspension
• dead zones disappear
• the internal temperature remains uniform
• The process becomes more stable and predictable.

Furthermore, correcting low biogas production requires evaluating the biodigester's agitation system.

AGTO manufactures two models of agitators for biodigesters, developed for different substrate profiles.

Killermix — for liquid substrates

Killermix was developed specifically for swine manure and other substrates with up to 6% of solids.

Furthermore, its installation can be done without the need to empty the biodigester.

Its stainless steel construction ensures corrosion resistance and a long service life.

Thormix — for substrates with a high solids content

Thormix was designed for systems with denser substrates, such as cattle manure and agro-industrial waste.

Therefore, it delivers efficient homogenization even under the most demanding conditions.

In addition, it is available in power ratings from 10 to 25 HP to meet the needs of medium and large-scale systems.

When to inspect or replace the biodigester agitator.

If the biodigester already has an agitator, but production remains below expectations, several points need to be evaluated:

• correct sizing of the equipment
• Preventive maintenance up to date
• Proper positioning of the agitator
• correct operating mode

These factors directly influence the system's efficiency.

Your biodigester can produce more

Low biogas production is rarely an unsolvable problem. In most cases, the cause is related to inadequate agitation.

Correcting this point means:

• generate more energy
• improve substrate utilization
• to produce higher quality biofertilizer
• increase operational stability

The biodigester is already installed. The correct agitator makes it work to its true potential.