Troubleshooting

Many factors can inhibit the biological performance of the biogas plant. The operator must be aware of the frequent one:

Ammonia (NH3)

The effect of ammonia on digestion is influenced by temperature, inputs composition, pH and bacteria acclimation. The concentration should be kept under 2000 ppm for an optimal operation. However mesophilic digester can support more than 3000 ppm if they are well acclimate to ammonia. An excess of ammonia can cause digestion failure.

Oxygen

Anaerobic bacteria require very little oxygen in the environment you need below 0.1 ppm O2

VFA

The VFA concentration can off-balance the biology of the system and should me less than 2000 ppm

Salt

Salt accumulation can affect the digestion performance. Sodium concentration should be in the range 3500 to 5500 ppm

Heavy metal

Trace concentrations of heavy metal is benefit for bacteria but high concentration can be toxic for the digestion.

Heating

Temperature should not vary more than 1 °C, if there are any changes in the temperature check the heating system and the PLC program.

Automation

If any problem in the program or alarm are found, ask for technical assistance to repair any PLC bug.

Mixing

If a mixer or pump doesn’t work. Look in the user manual of the equipment for troubleshooting. Finally, ask for a technical assistance to repair any parts.

 


 

Problems

Most likely causes

Recommended action

Gas yield has dropped
  • Drop in quality of substrates
  • Drop of temperature
  • Compounds inhibition
  • Non-homogenous substrates
  • Drop of methanogenic bacteria
  • Assure substrates mixing and quality
  • Check heating system
  • Check level of potential inhibitor compounds
  • Add digestate from another digester if the methanogenic bacteria as drop
Methane concentration dropped
  • Drop in quality of substrates
  • Drop of temperature
  • Compounds inhibition
  • Assure substrates mixing and quality
  • Check heating system
  • Check level of potential inhibitor compounds
Foaming problem
  • A new substrates with high protein content has been added
  • Air in being introduce in digestion
  • Temperature is changing
  • ·Reduce or stop feeding
  • Analyses substrates
  • Reduce air introduction
pH dropped
  • Feeding rate is too high or variable
  • Operating temperature have change
  • Agitation is not working
  • ·Reduce substrates until system returns to normal
  • Used only manure until system returns to normal
FOS/TAC ratio has increased
  • ·VFA rate is too high
  • Change in feedstock
  • Lack of buffer
  • Compounds inhibition
  • Reduce OLR
  • Use more manure in the mixte