3.4.4 Organic loading rate

The Organic Loading Rate (OLR) indicates the capacity of an anaerobic digestion (AD) system to convert organic matter into biogas. It quantifies the amount of substrate introduced into the reactor volume within a specific time.

The OLR is typically expressed in units such as kilograms of chemical oxygen demand (COD) or volatile solids (VS) per unit volume per day (e.g., kgCOD/m3/day or kgVS/m3/day). These units indicate the mass of organic material (COD or VS) applied to the system per unit volume (m³) of the reactor per day.

OLR is essential to ensuring the proper functioning of (semi) continuous AD systems, the “overfeeding” of the digester can lead to the accumulation of volatile fatty acids, resulting in system failure. The organic loading rate for unstirred (semi) continuous AD reactors is typically between 0.5 – 2kgVS or 1 – 2kgCOD per cubic meter of reactor volume per day.

Therefore, OLR (kg/m3/day) is an essential design as well as an operational parameter and is calculated as follows:


OLROrganic Loading Ratekg/m3/day
MSMass of Organic Substratekg/day
VRReactor Volume

The mass of organic substrate can be calculated by multiplying the concentration of organic substrate with the feedstock flow rate.


MSMass of Organic Substratekg/day
CSConcentration of either VS or COD
per cubic meter of feedstock