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Anaerobic digestion isn’t a new process. According to ADBA it’s one that’s been around for hundreds of years- their timeline states that an anaerobic digester was built in 1859 at a leper colony in India. It’s a proven technology and one that benefits the environment. However, safety and efficiency are important and there are always ways to improve the process. We discuss just three ways below:
As a confined space full of potential deadly gases, digester tank safety should be the number one priority when it comes to making the best use of your AD tank. If not, the risks are serious with deaths and injuries being reported cross the globe related to slurry and confined spaces. Documents published by organisations such as, US EPA (2011) and Safe Work Australia (2019) set out some clear guidelines to ensuring hazards are managed. These include but aren’t limited to:
- Ensuring Personal Protective Equipment (PPE) is supplied and fitted correctly to the user
- Carrying out regular visual integrity inspections of above-ground biogas components
- Carrying out preventative maintenance
- Prohibiting electrical work to be carried out by non-licensed electrical workers
There must also be adequate training for everyone carrying out inspections or working around a digester tank. All these safety measure ensure that you can make best use of your digester, and more important ensure the safety of every person involved.
It’s a very simple concept- the more space you have in the digester, the more biogas can be produced. With sludges often comes stubborn rag and grit which can accumulate in all stages of wastewater processes, including anaerobic digestion. This type of material can include eggshells, bone, lime, ash, glass and various other inert high-density materials. Grit settles in the digester, reducing the capacity in the tank and therefore decreases the digester’s efficiency.
The short-term issues associated with this include reduced throughput and pump blockages, while the long-term effects are even more problematic. Over time, grit causes excessive wear and reduced capacity in the digester, which means that cleanouts are essential to ensure maximum biogas generation.
The most common way that cleanouts currently take place is by shutting the digester down for anything from a few days to a week to excavate the accumulated rag and grit. The extracted materials are then usually transported off site where they are processed or disposed of. The removal tanker will return several times until the full load has been removed.
By processing the materials on site, cleanouts become much shorter, sometimes lasting only one day. As well as that, transport costs are significantly reduced as all materials are dealt with in-situ. By doing everything in the one place at the one time, cleanouts are more efficient, and operators can experience maximum uptime.
Anerobic digestion is an extremely useful process, and one that has been proven over many years. There is no denying its benefits, however to optimise the process, we can continue to do more to make digester cleaning and biogas generation safer and more efficient.
We’d love to hear more of your tips on making the best use of digester tanks. Get in touch with us on LinkedIn if you have some to share!
 US EPA (2011) Common Safety Practice for On-Farm Anaerobic Digestion Systems. [Accessed online 03/06/2019] https://www.epa.gov/sites/production/files/2014-12/documents/safety_practices.pdf
 Safe Work Australia (2019) Model WHS Regulations. [Accessed online 31/05/2019] https://www.safeworkaustralia.gov.au/system/files/documents/1902/model-whs-regulations-15-january-2019.pdf