4.4.2 Sizing of the digester

The purpose of this chapter is to practice how to size the digester and what information is required.

Min Average Temperature during the coldest month16.4°CClimate data
Retention time45daysBased on the BMP test at a temperature of 16°C
Total inflow rate3.72m3/dayCalculated in the previous exercise
Total organic loading rate34kgVS/dayCharacterisation study
Specific organic loading rate for fixed dome digester0.75kgVS/m3/dayLiterature values
Assumptions for Case Study

The first step is calculating the necessary hydraulic volume for digestion. This will be determined based on the retention time of 45 days from the BMP test.


VDGDigester Volume
IN TOTALTotal Inflow per daym³/day
HRTHydraulic Retention timedays

Before proceeding, we must verify that the digester volume is suitable for the organic loading rate (OLR). If the organic loading rate exceeds the recommended limit of 0.75kgVS per m3 of the digester volume per day, it is advised to expand the volume.

To calculate the organic loading rate per m3 of digester volume per day, we need to divide the total organic loading rate by the digester volume.


OLRSSpecific Organic Loading RatekgVS/m³/day
OLROrganic Loading RatekgVS/day
VDGDigester Volume