Operating a biogas plant: Direct recirculation within the cycle
Anyone who operates a biogas plant is familiar with the problem: as soon as digestate or separated solids leave the plant, this results in emissions, transport effort and costs. Direct recirculation fundamentally solves this problem. The substrate, once introduced into the digestion cycle, never leaves it again – it is recirculated directly after separation. The result: a fully closed, emission-free system with measurable economic benefits for every biogas plant operator.
➔ The cycletherefore remains closed even with the separation of digestion products and slurry.
Separation or filtration in its original form, enhanced by the ability to keep digestate within a closed, emission-free cycle – this is possiblewith the Sepogant Direkt screw press separatorand the Returgant Direktbiomass recirculation filter !
The problem & the solution
Due to the new provisions of the TA-Luft, the separation and storage of digestate is permitted exclusively in enclosed spaces or under cover. This new regulation poses a major challenge for many agricultural businesses.
Direct substrate recirculationis the solution to this restriction.This method canbe integratedintothe biogas plant in various ways, thereby forming a holistic cycle. Our products, Sepogant Direkt and Returgant Direkt, offer different technologies for implementing this method.
TA-Luft 2021: What is changing for biogas plants
The stricter provisions of the TA-Luft stipulate that the separation and storage of digestate must take place exclusively in enclosed spaces or under cover. This new regulation poses considerable challenges for many agricultural businesses – particularly in terms of investment costs for new storage areas and structural measures.
Direct substrate recirculation is the most elegant solution to this requirement: as the solids and liquid phase do not enter the open air in the first place, the regulation is met from the outset without the need for additional construction work.
How direct substrate recirculation works
In direct recycling, substrate is extracted directly from the fermenter or post-fermenter. Immediately after separation, the pressed phase – that is, the fibre material that has not yet fully fermented (> 0.5 mm) – is returned to the fermenter or post-fermenter. This gives the material sufficient time to ferment completely.
This offers two key advantages:
Firstly, different feedstocks require different fermentation times – the recirculation ensures that the gas potential is fully utilised. Secondly, the entire logistical effort is eliminated: no collection, no reintroduction via the feeding system, and no transport between the separation point and the fermentation vessel.
Our products enable two technological approaches:
- Sepogant Direkt:a screw press separator that separates within the fermentation line
- Returgant Direkt:a biomass recirculation filter that pumps filtered substrate back into the digestion line
Both systems can be easily integrated into existing biogas plants.
+5 – 10 % higher gas yield: The benefits at a glance
| Benefit | Effect |
|---|---|
| ♻️ Closed-loop system | No digestate is released into the environment – completely emission-free |
| 📈 Higher gas potential | +5% to +10% through complete utilisation of the substrate |
| 🚫 No ammonia emissions | No losses during transport or interim storage |
| 💧 Substrate savings | Full utilisation of all raw materials |
| 🏗️ Reduced storage volume | Reduced need for digestate storage |
| ⚙️ Fewer agitators | Reduced need for agitators in the digestate storage facility |
| 🌡️ Saving process heat | Heat savings in the fermenter through an optimised cycle |
| ⏱️ Reduced working hours | No manual transport or handling required |
Sepogant Direkt & Returgant Direkt: your choice of technology
Depending on the plant configuration and operational requirements, two technologies are available. The Sepogant Direkt operates as a screw press separator directly within the digestion line and is particularly suitable for high throughput rates. The Returgant Direkt relies on filtration and recirculation, making it ideal for businesses seeking a particularly space-saving solution or wishing to retrofit existing plants.
Both systems are tried and tested, technically mature and are manufactured and supported by Biogastechnik Süd GmbH in Isny, Allgäu.
Enquire now about direct recirculation for your biogas plant
Would you like to operate your biogas plant in compliance with the TA-Luft guidelines, minimise emissions and, at the same time, get more out of your substrate? Get in touch – we’ll provide you with personalised advice on the Sepogant Direkt, Returgant Direkt and how best to integrate them into your plant.
