Biodigester on the property: what you need for the system to really work.
Investing in a biodigester is a strategic decision. But many producers discover, after installation, that the system doesn't deliver what it promised—and that the problem wasn't with the biodigester itself, but with what was lacking around it.
A biodigester operates within a system. It depends on quality substrate, adequate operating conditions, and equipment that ensures the efficiency of the biological process. Without these elements, the investment exists—but the return does not.
In this article, we detail what is needed for a biodigester to function with real efficiency — from the basic structure to the equipment that makes all the difference in the outcome.
Sufficient and constant volume of substrate
The biodigester needs regular feeding to function. The anaerobic digestion process is carried out by bacteria that depend on a constant flow of organic matter to remain active and productive.
Properties with very small herds or irregularly generated waste have difficulty keeping the biodigester operating at its ideal efficiency range. The system's size needs to be compatible with the available substrate volume—neither oversized nor undersized.
Points to note:
The daily volume of waste generated by the herd needs to be calculated before installation.
The hydraulic retention time — the period that the substrate remains in the biodigester — needs to be respected to guarantee complete digestion.
– Abrupt variations in the input volume destabilize the biological process and reduce biogas production.
Control of solids content in the substrate
The solids content of the substrate entering the biodigester has a direct impact on the efficiency of the process and the lifespan of the equipment.
Very dense substrate — with a high solids content — hinders internal movement, overloads the agitator, and can compromise homogenization. Very diluted substrate reduces the organic load available to bacteria and decreases the potential for biogas production.
The solids separator is an important tool in this control: by separating the solid fraction before it enters the biodigester, it allows adjusting the solids content of the substrate and optimizing the digestion process. The effluent entering the system becomes more homogeneous and easier to work with.
Each type of waste — swine, bovine, agro-industrial — has distinct characteristics that need to be considered in the design and operation of the system.
Stable temperature inside the biodigester.
The bacteria responsible for anaerobic digestion are sensitive to temperature. The mesophilic range—between 30°C and 40°C—is where the process occurs most efficiently. Below or above this range, bacterial activity decreases and biogas production diminishes.
In regions with harsh winters — as is the case in much of southern Brazil, where pig and cattle farming are more intensive — the drop in temperature is a critical factor for the performance of the biodigester.
What contributes to thermal stability:
– Proper covering of the biodigester, which retains the heat generated by the biological process.
– Regular agitation, which distributes heat evenly throughout the tank's volume.
– In some systems, active heating of the substrate — especially in colder climates.
Agitation plays a dual role here: in addition to homogenizing the substrate, it distributes the temperature evenly, preventing cold zones within the tank where bacterial activity would be reduced.
Efficient and continuous agitation is the defining element of performance.
Of all the elements that make up an efficient biodigester, agitation is the one that most directly impacts the daily operation results.
Without proper agitation, the biomass inside the tank stratifies: crust on the surface, sediment at the bottom, dead zones in the middle. The biological process loses efficiency, biogas production drops, and the biofertilizer becomes of inconsistent quality—even if everything else in the system is functioning correctly.
With the right agitator, the substrate remains homogeneous, the bacteria have constant contact with the organic matter, and the biogas produced can escape from the fermenting mass without hindrance. The result is a system that operates in a stable and predictable manner.
AGTO manufactures two models of agitators for biodigesters:
Killermix — for substrates with up to 6% solids
Developed for swine manure and liquid substrates. Installed via a 300 mm diameter pipe, without the need to empty the biodigester. Features a 100% stainless steel structure, high-performance SIC mechanical seal, and internal bearings for greater stability. High corrosion resistance and low maintenance cost.
– Thormix — for substrates above 6%
Designed for systems with higher solids content — bovine manure, agro-industrial waste, or denser biomass. Available in power ratings from 10 to 25 HP, with a stainless steel structure and high operational stability for demanding conditions.
Choosing the right model depends on the type of substrate, the volume of the biodigester, and the operational conditions of the property—and this decision deserves specialized technical attention.
Biogas capture and utilization system
The biogas produced inside the biodigester needs to be captured, stored, and used efficiently. Without a proper capture system, some of the production is simply lost—and the return on investment decreases.
The basic elements of a rain catchment system include:
– Waterproof cover for the biodigester, which retains the biogas produced and prevents losses to the atmosphere.
– Gasometer or biogas reservoir, which stores the produced gas and ensures a stable supply even during periods of lower production.
– Purification system, when biogas is used in engines, generators or will be converted into biomethane — for the removal of moisture, hydrogen sulfide (H₂S) and CO₂.
– End-use equipment, such as boilers, generators, engines or burners, adapted to operate on biogas.
The efficiency of the harvesting system depends directly on the quality of biogas production—and biogas production depends on agitation. This chain of dependencies shows why each element of the system matters.
Preventive maintenance and continuous monitoring
Even a well-designed and installed biodigester with the right equipment still needs preventative maintenance to maintain its performance over time.
The most important monitoring points are:
– Biogas production: abrupt variations indicate instability in the process — a problem with the substrate, temperature, or agitation.
– Agitator condition: seals, bearings, and motor require periodic inspection. An agitator with delayed maintenance loses efficiency before showing obvious signs of a problem.
– Cover integrity: small leaks in the tarp or collection structure can represent significant losses of biogas.
– Periodic analysis of biofertilizer: to check the concentration of nutrients and calibrate the application in the crops.
Preventive maintenance costs less than corrective maintenance. And in a biogas system, unplanned downtime has an immediate impact on energy production and waste management.
The biodigester is the system. The agitator is what makes it work.
An efficient biodigester doesn't depend on a single element—it depends on a well-designed, well-installed, and well-operated system. Suitable substrate, stable temperature, efficient collection, and regular maintenance.
But of all the components that make the system work, agitation is the one that most directly defines the day-to-day result. It keeps the biological process active, the biogas flowing, and the biofertilizer of good quality.
Those who invest in a biodigester but forget about the agitator are only investing half as much.
Does your biodigester have the right agitator?
AGTO manufactures the Killermix and Thormix agitators — developed for the realities of Brazilian rural producers, with a 100% stainless steel structure, low maintenance costs, and specialized technical support. Our team analyzes your system and recommends the ideal model for your substrate and volume.
Get in touch and speak with an AGTO specialist.
