German Engineering Meets Indian Manufacturing:

How Varibull Paddle Agitator

Solves the Biogas Mixing Problem at Scale

Rajesh Ayyappasur & Manoj M

In daily life, mixing is easy—stirring tea, whisking eggs – take a spoon or fork and work away for a few seconds.

But, when the “bowl” becomes an anaerobic digester larger than 6,000 m³, that simple act turns into an engineering challenge. Layers form, temperatures fluctuate, solids settle, and microorganisms refuse to work efficiently unless the environment is perfectly blended.

That’s why good mixing is a critical pillar of biogas production. It ensures uniform distribution of feedstock, stable temperatures, intimate contact between microbes and substrate, and the elimination of dead zones. Poor mixing directly translates to reduced methane yield and unstable plant performance.

Designed for large-scale digesters, Varibull’s slow-speed paddles sweep through the tank at just ~10 rpm, maintaining biological integrity while ensuring powerful circulation. With only 12 hours* of daily operation, it achieves outstanding performance at remarkably low operating costs.

In October, GPSR and Proweps teams visited Biogastechnik Süd GmbH’s facility in Isny im Allgäu, Germany.

How Varibull Outperforms Other Mixing Technologies

Slurry Pumping & Circulation

High power draw, heavy wear from sand and fibres, and poor internal homogenisation are common issues in most mixing technologies. Varibull avoids abrasive flow paths and delivers complete, uniform internal mixing.

Biogas Bubbling

Most technologies are suitable only for thin, low-solids systems, and cause channeling rather than mixing, wasting energy compressing gas. Varibull’s mechanical sweep breaks scum layers, setting the entire digester in motion.

High-Speed Propeller Agitators

With high-speed agitators, common issues are high shear damaging microbes, limited mixing patterns, and frequent maintenance due to high rpm. Varibull’s low-speed, high-torque design provides broad-flow mixing without straining the equipment — or the microbes.

Varibull combines German engineering with Indian manufacturing to meet demands of modern biogas plants — quietly, efficiently, and built for the long run.

*Depends on plant parameters