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4 reasons why anaerobic digesters fail

John F. Katers and Ryan Holzem Published on 29 June 2015

In partial response to the energy crisis in the early 1970s, anaerobic digesters were installed at nearly 200 dairy farms across the U.S., only for the vast majority of these systems to shut down or fail after just a few years of operation.

However, with improvements in anaerobic digester technology, as well as a better understanding of the anaerobic digestion process, there was a resurgence of anaerobic digesters being installed on large dairy farms beginning in the late 1990s and continuing to this day.

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Despite these improvements, there continue to be failures of anaerobic digestion systems, several of which have attracted considerable attention in the media. These failures can generally be grouped into the following four categories:

  1. Poor design and equipment selection
  2. Lack of appropriate technical expertise
  3. Lack of maintenance
  4. Lack of commitment by the operator

These four categories will be discussed in more detail in the following paragraphs.

Design and equipment selection

With any large capital engineering project, it is important that the right technology and equipment are selected. Design and equipment selection for anaerobic digestion systems can include decisions related to the manure pumping and conveyance systems (noting that manure is different than municipal wastewater in this regard and equipment selection is more involved than just transferring technology from the wastewater or food processing industry), the operating conditions in the anaerobic digester tank (i.e., heating and mixing systems) and the gas cleaning and electrical generation equipment.

A failure of any one of these system components can result in digester upsets, reduced revenue generation or added capital costs to replace faulty equipment. Using a reputable vendor, with a track record of successful installations and operations is one way to avoid these issues, although each farm will have unique operating characteristics that should also be considered. Therefore, evaluating the technology from several different vendors would be beneficial.

Lack of technical expertise

Because the operation of an anaerobic digestion system is often not considered to be one of the core business functions of a dairy farm, there can be a lack of technical expertise in managing this type of complex manure treatment system. Although dairy farmers routinely manage other complex systems, and training programs on anaerobic digestion system operations are available, there is still a learning curve to be able to sustain steady-state operations of an anaerobic digester.

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The farm needs to balance the amount of work hours that will need to be dedicated to operating the digester with the costs associated with poor digester operations and digester downtime. One option to address this is to have an individual dedicated to the operation of the anaerobic digestion system, with a backup person available in case of vacations or other unplanned emergencies.

Routine maintenance

Similarly, given the seasonal nature of farming, there can be times of the year when the anaerobic digester may not receive the attention and careful maintenance that is required. Again, this can be associated with the view that anaerobic digestion is not a core business function of the dairy farm, and other activities like planting or harvesting can take priority over things like routine maintenance of the anaerobic digestion system.

As noted previously, having a person dedicated to the operation of the digester can address this issue, provided they are not pulled away when other priorities or emergencies arise on the farm. Again, the farm will need to balance the long-term consequences of inadequate maintenance with more time dedicated to digester maintenance.

Lack of commitment by the operator

Finally, a lack of commitment by the operator can also lead to anaerobic digester failure. Given the first three items described above, it should be obvious that there are many things that can go wrong with anaerobic digestion systems, each of which can test the commitment of the operator.

Therefore, the commitment of the operator is necessary, starting with the design of the anaerobic digestion system and continuing over the entire lifespan of the project. A long-term commitment from the operator is especially important when maintaining the consistency of the feed substrate, as this requires the operator to always understand what is being added to the digester and if any operational changes elsewhere on the farm (i.e., changes in feed) will impact the digester.

It is also extremely important for the operator to understand how the anaerobic digester will align with the goals and operation of the farm, particularly so there are no false expectations in terms of performance and benefits that the anaerobic digester can provide in terms of profitability, nutrient management, etc. Having this type of viewpoint allows the operator to see the big picture and remain committed to the long-term viability and benefits of the anaerobic digestion system.

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Although there are many reasons why digesters fail, there are also numerous success stories of digesters that have assisted farms in meeting triple bottom line requirements. Still, understanding the reasons why digesters fail prior to initiating an anaerobic digestion project can reduce the risk and anxiety associated with making this type of large capital investment.

It is far better to address problems before they occur through better design, technical knowledge and maintenance. It then becomes far easier to be committed to an anaerobic digestion system that is operating successfully. PD

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