Five Tips for Optimal Digester Performance

Operating a well-designed anaerobic digester is not difficult, nor should it be time-consuming. If you can successfully take care of a house plant, a digester should not be a challenge. Yet, to achieve optimal performance some general knowledge on best practices for operation and maintenance can be helpful. Some common performance standards of successful digester performance include: how thoroughly a given volume of organic acids will be biodegraded, how much biogas will be produced, what level of pathogen destruction will be achieved and how much odor control can be expected.

The design and structure of an anaerobic digester play a central role in terms of performance, but proper operation and maintenance is critical to long-term success.

Here are our FIVE TIPS for optimal anaerobic digester performance:

  1. Temperature
    Anaerobic digestion efficiency is highly dependent on the temperature inside the digester. For a mesophilic digester, the optimum temperature range is between 98 and 102 degrees Fahrenheit. Maintaining consistent temperatures within this range will help promote healthy bacteria activity and, in turn, generate desirable biogas production.
  2. Quality Feedstock
    Many different organic waste streams could be quality candidates for anaerobic digestion. Examples include manure, domestic or commercial food waste, food processing (industrial) waste, ethanol stillage, glycerin from biodiesel production, and sewage sludge. However, no matter what material is used, you must consider the moisture content, pH and carbon-to-nitrogen ration of all materials. Consider feeding the digester as you would a cow or animal, making sure it receives a “balanced diet.” It is also extremely important that no bactericides or biogas inhibitors are added to the digester.
  3. Retention Time
    Hydraulic retention time (HRT) is the length of time the waste or feedstock remains inside the digester. Digesters are designed for certain retention times based on the type of feedstock. All of the waste must remain in the digester for the full retention time in order for the anaerobic bacteria to thoroughly break down the organic matter, convert it to biogas, and destroy pathogens. If the volume or type of feedstock differs from what the digester was designed for, the retention time may be altered, which can negatively impact the digester’s biogas production and pathogen reduction.
  4. Consistent Feeding
    Providing a quality feedstock or food source is vital for the health of the anaerobic bacteria inside the digester. Feedstocks must be added to the digester at frequent and consistent intervals. In addition, the composition of the feedstock should remain fairly constant. For example, suddenly introducing a large amount of an acidic waste stream could result in a loading shock to the bacteria. Loading shock can cause detrimental swings in digester temperature, drastic changes in material composition and bacteria kills.
  5. Equipment Maintenance
    Anaerobic digesters are a sophisticated combination of biological, mechanical and electrical processes. While it is not necessary to have advanced educational degrees to operate and maintain a digester, it is essential to have good management and maintenance practices in place to ensure proper design performance. Digester systems have failed due to lack of commitment and technical support from the digester operators. It is imperative that the recommended operation and maintenance schedules are followed, daily checks are performed and any operational issues are addressed in a timely manner.

For more information about digester performance, please contact DVO.