Wednesday, January 17, 2018

5 Anaerobic Digestion Problems to Avoid in Commercial Biogas Facilities

These Anaerobic Digestion problems are potentially serious, however, through the good management of modern commercial biogas plants they are easily avoided.

Avoidance of these problems through the use of monitoring equipment, and taking early corrective action whenever these problems begin to appear, is the routine day to day task of the experienced biogas plant operator.

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Now we will look at each anaerobic digestion process problem, one by one:

1 – Foaming

Anaerobic digestion foaming is one of the most common anaerobic digestion problems. It is an operational problem in biogas plants with negative impacts on the biogas plant’s economy and environment.

Foaming incidents can last from one day to three weeks, causing 20-50% biogas production loss, unless early corrective action is taken.

2 – Acidification

This second of our listed anaerobic digestion problems is more correctly referred to as “over-acidification”, because acidification is in itself an important stage in healthy anaerobic digestion.

It is one of the most expensive problems, and if not corrected, can in the worst cases can take months until the digester biology recovers, and digester performance is restored.

Nearly always an overload of the digester biology is the cause for an acidification. Frequently, the problem has nothing to do with the loading rate of the digester, and other factors are the root cause.

3 – Increasing Viscosity

Floating layers form and stirring and mixing flows deteriorate.

The result is poor material transport and defective degassing, this often also leads to elevated plant energy consumption and increasing wear and tear on agitator/ mixing equipment.

In extreme cases, if the condition is allowed to persist, major mixing pump damage, and complete production outages can occur.

4 – Increasing VFA and TIC Value

An increasing VFA (Volatile fatty acids) and at times also in the TIC (Alkalinity, total inorganic carbonate buffer) value, may occur when the organic loading rate (OLR) is increased above a long-term stable rate. The biogas process becomes unstable, due to accumulation of volatile fatty acids (VFA), and/ or a non-optimum elevated (alkaline) pH.

Biogas output is impaired if the accumulation of volatile fatty acids (VFA) is sufficiently elevated, resulting in a process slow-down and further VFA accumulation in a worsening cycle, unless the OLR is reduced.

5 – Low Methane Yield

Lower than anticipated methane yield is very often the first indication of other problems, so it is important to continuously monitor the percentage of methane and other gases such as hydrogen sulphide (H2S), as an early-warning of the need to make adjustments to the digester operation.

Low methane yield is merely a symptom of other problems, and is only included here for completeness.

Conclusion – Anaerobic Digestion Problems Seen in Commercial Biogas Plants

Taking expert advice from an AD process expert "troubleshooter", or the AD Plant's Construction Contractor's in-house process experts, as soon as first signs of anaerobic digestion problems appear, is the recommended solution.

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Please also comment below and tell us of any errors, your experience of AD process problems etc.

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