Filterability and Sludge Concentration in Membrane Bioreactors

The Thesis entitled “Filterability and Sludge Concentration in Membrane Bioreactors” aims at explaining the relation between Mixed Liquid Suspended Solids (MLSS) concentration, the amount of solids in the wastewater being treated, also designated as sludge, and filterability, being the ability of the sludge to be filtrated through a membrane, in a wastewater treatment system designated as Membrane Bioreactor (MBR). An MBR is a wastewater treatment system that combines an activated sludge process with a filtration process relying on membranes to separate sludge from clean water. The clean water produced by an MBR, also designated as permeate, is largely disinfected and has extensive reuse potential. The experimental procedures described in this thesis took place in 4 full-scale MBRs and 4 pilot-scale MBRs scattered across Europe. The relation between MLSS and filterability was explained through the sludge structure resulting in the definition of optimal MLSS concentrations for design and operation of municipal MBRs, information that was unclear until today. Improved MBR design and operation control would be achieved by placing the membrane in aeration tanks, intended for removal of carbon materials and nutrients, and operating at the lowest possible MLSS concentration. Additionally, a straightforward methodology was defined to verify membrane integrity and permeate MBR quality