Control of organic loading rate using the specific methanogenic activity test during start-up of an anaerobic digestion system

The specific methanogenic activity test (SMA) was used to determine a suitable organic loading rate during the start-up phase of a crossflow ultrafiltration membrane anaerobic reactor system (CUMAR). The SMA test was immediately carried out after seeding the reactor with sludge taken from a municipal wastewater treatment plant digester in order to determine the most acceptable initial organic loading rate. The initial test results during the first week showed that the acetoclastic capacity of the reactor sludge, at an organic loading rate (OLR) of 1 kg COD/m3 • d, was found to be low which resulted in a very poor COD removal efficiency, i.e. 14%. Therefore the OLR was maintained at approximately 0.7 kg COD/m3 • d in the next two weeks of operation resulting in the COD removal efficiency of over 65% in the effluent. Based upon the SMA tests results, the OLRs were either increased or decreased in order to improve performance of the system and to achieve stable conditions which further resulted in an excellent organic matter removal, i.e. over 98% COD and almost 100% BOD removal at an OLR of over 1 kg COD/m3 • d. At this point the ratio of actual methane production (AMP) rate of the CUMAR system to potential methane production (PMP) rate determined from the SMA test was 0.45, which ensured that the CUMAR system could be loaded at higher organic loading rates for the remainder of the operating period.