Start-up with or without inoculum? Analysis of an SMBR pilot plant

This study analysed a submerged membrane bioreactor (SMBR) start-up with the purpose of determining the best conditions to carry it out. In order to do this, a hollow fibre membrane module was installed in a submerged configuration in a pilot aerobic reactor. The experiment was then divided in two phases, lasting 65 days each. During phase 1, the pilot plant was started-up without inoculum of activated sludge and no sludge, withdrawal was performed. Conversely, in phase 2, the MBR pilot plant was started-up with sludge inoculum and the sludge concentration was kept constant. In both phases, the volumetric loading rate applied to the pilot plant was kept constant. The authors analysed the difference in carbon removal performances, the evolution of floc sizes and the fouling rate in both phases. The results confirmed that MBRs can be quickly and easily started-up, but the initial start-up strategy can influence membrane fouling. More specifically, the carbon removal performances were similar in both phases, while the fouling rate increased faster during the start-up without inoculum, especially in terms of irreversible deposition of soluble compost on the membrane surface and into membrane pores.