Biogas production is an effective way to reduce waste and turn it into a useful and environmentally friendly energy source. But the nutrient-rich digestate is often overlooked as an effective fertilizer.
What is Biogas digestate?
Biogas is a renewable fuel produced almost exclusively from biomass residues and waste. The raw material used to produce the gas can be anything from food waste and energy crops to residues from wastewater treatment plants or agricultural and forestry residues.
Biogas is produced through anaerobic digestion – a process in which bacteria break down organic matter in an oxygen-free environment. This is done in a sealed container called a reactor where the organic matter sits for about 3 weeks.
Biogas production is an effective way to reduce waste and turn it into a useful and environmentally friendly energy source. It can replace much of the fossil fuel, reducing greenhouse gas emissions. However, it’s often overlooked that biogas plants also produce another product that is at least as valuable as renewable energy due to its nutrient and organic matter content: digestate. The digestate contains all the nutrients (phosphorus, nitrogen and potassium) present in the waste during the process, making it an excellent fertilizer for agricultural crops.
Why dry Biogas digestate?
Biogas digestate is moist, so not only can it be difficult to store, as bacteria and molds can grow on it, but it can also cause strong odor emissions, and the toxins and spores formed can be a hazard to workers. The weight and size that moisture adds to the digestate also makes it more difficult to handle and causes unnecessary water transportation.
The feedstocks for biogas production are also often fibrous, making them difficult to mix and meaning that some of the energy is locked up in the fibers. Drying can eliminate these problems by sterilizing the digestate and making it easier to handle and store. The drying of digestate from biogas plants opens up new possibilities, since dried digestate can be transported inexpensively and thus distributed over longer distances on fields.
Dried digestate also emit significantly fewer greenhouse gasses than moist digestate and are therefore even more environmentally friendly. However, the drying of digestate is associated with some difficulties due to the specific properties of the starting material. Some drying processes can even lead to a deterioration in the fertilizing effect of the digestate by reducing valuable nutrients.
Exergy dryers for digestate
There are many benefits to drying the digestate rather than leaving it wet, but the key to these benefits is choosing the right dryer. In most cases, the dryer is the most expensive and energy-intensive stage in the production process and could have a negative impact on the environment due to emissions generated during drying.
The Exergy pressurized superheated steam dryer have the lowest energy consumption compared to other conventional dryers on the market. As an added benefit, the excess steam generated in the drying process can be recovered and reused as energy or heat for use in other processes. It completely sterilizes the digestate due to the high temperatures present in the steam environment, but in a very short and precise time.
Instead of using hot air or gas in the dryer, which often leads to uneven drying, nutrient degradation and oxidation of the product, our dryer can improve the product quality. The ExergyPSSD® can also be easily integrated with other processes for energy optimization and have no emissions into the atmosphere, making it even more environmentally friendly.
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