Whether your AD plant is brand new or has been constructed for years, the feedstock still has to be suitable for the process. If we don’t get the right feedstock in the process it can lead to damaging results to the digester microbes and the biogas yield.
In this article, we cover what to look for in your feedstock and how suitable it will be for your digester. After all, if you get the wrong medium it will start causing havoc in the digester and ultimately ruin your profit margins.
How do we Ensure Suitable Feedstock?
Biodegradability
The biodegradability is essential to know as you need to know the optimal breakdown periods of the contents. If a digester was designed to suit manure, but there was heavy fats or fibrous materials then the set-up would be wrong.
Feedstock Mixing, HRT & OLR
Equally, the feedstock has to be suitable for the process as a whole. If the medium has an extremely high organic loading rate, then the digester won’t be stable if it has been designed for manure like applications. The method of mixing has to be suitable. There are many ways a digester can be mixed to ensure the continuous breakdown of the feedstock and prevent the digester from becoming unstable.
Efficient & Robust Microbial Population
Microbial populations play an important role in the digester. Having the right balance can lead to a biochemical process that is efficient enough to allow the breakdown of the medium as needed but is stable enough to withstand slight changes in the process variables without then becoming volatile.
Feedstock Temperature, Alkalinity, pH & VFA’s
As mentioned in previous articles, there are many process variables in the world of AD. The main process indicators are commonly taken from the temperature of the system (Mesophilic or Thermophilic), the pH of the digester and the VFA profiles within the digester. Different feedstocks will have different requirements from a system. Some may need to be at a higher temperature or given their biological makeup they may need a slightly altered pH to allow optimal degradation. These are all considered when the system is designed.
Toxic & Inhibitory Substances
Co-digestion can lead to two different types of feedstock helping each other to break down more efficiently. As one feedstock may have higher acidity or levels of metals that the other feedstock needs more of to break down efficiently. However, sometimes the feedstocks can inhibit the gas production process due to their nature. Heavy metals, biocides and solvents can cause havoc inside the digester.
Reference – Roots Organics Ltd.
