Case: More than two years of operation without cleaning the digester

16 September 2026 | VOGELSANG

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At one of Ronconi’s biogas plants, long fibres caused frequent operational problems and required the digester to be cleaned almost every month. At the second plant, the PreMix® solid matter feeder creates a homogeneous suspension, resulting in fewer disruptions and a higher specific gas yield.

Two biogas plants using the same biomass

Az. Agr. Ronconi is a family-run agricultural business in Marmirolo, Italy. The farm manages 900 hectares of land and has approximately 130,000 pigs and 2,000 dairy cows.

The company also operates two biogas plants, each with a capacity of 1 MW. Both plants use the same input materials: pig and cattle slurry, process water and a small quantity of silage. The main difference is how the biomass is fed and pre-treated.

Fibres caused frequent operational problems

At the first plant, solid materials were fed directly into the digester using a vertical mixer followed by a screw conveyor.

Ropes, fibres and other long-fibrous materials repeatedly became caught in the agitators. The digester therefore had to be opened almost every month so that the agitators could be removed and cleaned.

The agitators also required considerable energy to mix the biomass thoroughly. In addition, floating layers formed in the digester and reduced the gas yield.

Four process steps in one solution

For the second biogas plant, operations manager Giovanni Ronconi selected a PreMix solid matter feeder with a RotaCut RCX-58G macerator and a CC66-M1 progressive cavity pump.

A screw conveyor feeds the solid materials directly into the PreMix solid matter feeder, where they are mixed with liquid. Long fibres and coarse components are reduced, while heavy material is separated. The homogeneous suspension is then pumped into the digester.

This pre-treatment reduces the load on the agitators and prevents floating and sinking layers from forming in the digester.

Fewer disruptions and a higher gas yield

After more than two years of operation, Ronconi was able to compare the two systems. At the plant equipped with the PreMix solid matter feeder, there had been no need to open and clean the digester due to fibrous material.

Maintenance had been limited to replacing the cutting screen and blades in the RotaCut macerator. The progressive cavity pump had continued to operate without problems.

The PreMix solid matter feeder also uses less energy than the vertical mixer and reduces the energy required by the agitators. The specific gas yield has increased, allowing Ronconi to reduce the amount of silage without lowering daily biogas production.

“Maintenance requirements at the biogas plant are significantly lower with the PreMix solution. Energy consumption in the solid matter feeding system and the agitators has been reduced, while the specific gas yield has increased.” Giovanni Ronconi, Italy

Results for Ronconi:

More than two years of operation without cleaning the digester due to fibrous material
Fewer operational problems and a reduced workload
Lower energy consumption in the feeding system and agitators
No floating or sinking layers in the digester
Higher specific gas yield
Less silage required for the same biogas production
Minimal maintenance of the PreMix system

Learn more about the PreMix solid matter feeder and Vogelsang’s solutions for efficient biomass feeding and pre-treatment. Visit Vogelsang at Agromek 2026 in Hall K, stand K8000.