Self-Forming Dynamic Membrane BioReactors (SFD MBR) for municipal wastewater treatment: Relevance of solids retention time and biological process stability

A lab-scale Self-Forming Dynamic Membrane BioReactor (SFD MBR) equipped with a nylon mesh was operated for the treatment of real municipal wastewater under a volumetric loading rate of 0.9-1.1 gCOD L-1 d-1 and a flux of 61-68 L m-2 h-1. During an experimental period of more than 600 d, three runs were performed with different solids retention times (SRT of 15, 30, and 50 d). At the steady state, the system had always good biological and filtration performances, but the mesh clogging tendency and the solid removal observed varied with the SRT. Lower filtration performance, both in terms of permeate quality and productivity, was observed under unstable conditions for the biological processes, such as start-up and variations of the food-to-microorganism ratio. Higher SRT resulted in more stable biological process at the steady state, which positively affected the filtration performance even in front of organic load variations.