Organic Load

The organic loading is one of the most important parameters operating an anaerobic digester.

 

The organic loading provides information on nutrient supply levels of the microorganisms involved, overload or undersupply of the system as well as resulting technical and process control measures to be taken. Furthermore it gives an indication on biological degradation of the substrates i.e. it describes the efficiency of the anaerobic digester.

Organic load is defined as the amount of volatile organic dry matter entering the anaerobic digester over time - measured in pounds (lbs) per ft3 digester volume and day.

To ensure a stable digestion process and an optimum biogas output of the anaerobic digester system a consistent feeding regime allowing a constant organic load between 0,12 and 0,3 lbs/ft3 d is required.

 

For example: Irregular feeding intervals or overloading the digester leads to an imbalanced microbial system.

Acid forming bacteria have a higher growth rate than methanogens. Therefore, they respond faster to changes in substrate concentration. Production of long chain fatty acids and acetic acid is increased immediately and leads to a drop in pH.

Methanogens don't tolerate pH values below 6, have a much lower growth rat and cannot keep up as well in removing acetic acid and hydrogen.