Influence of membrane properties on fouling in MBRs

The membrane bioreactor (MBR) applies membranes for separating activated sludge and the purified water in the activated sludge process used for wastewater treatment. Membrane fouling occurs by activated sludge material depositing on the membrane surface or inside the membrane pores. The subject of this thesis is to identify optimal membrane properties which reduce membrane fouling. Chapter 2 introduces the improved flux-step method (IFSM): a new experimental protocol which is able to compare the influence of many different membrane properties on fouling and fouling reversibility. Chapter 3 describes the use of the IFSM for five different polymeric membrane materials with varying membrane properties. The objective is to elucidate the influence of different membrane properties on fouling in order to find the optimal membrane that suffers the least from membrane fouling. In Chapter 4 the IFSM is applied for the same membranes as in Chapter 3, but now in two other activated sludge mixtures. The objective is to determine whether the different feed properties influence the optimal membrane properties. Chapter 5 describes relaxation and backwashing experiments to elucidate which cleaning method is more effective for flat-sheet membranes. The amount of irreversible fouling which is not removed by the cleaning methods is determined at an equal net flux for both cleaning methods. Chapter 6 describes a pioneering study with corrugated membranes to decrease fouling in MBR. Corrugated membranes have a larger membrane surface area and can lead to more turbulence at the membrane-liquid interface. The fouling behavior of corrugated membranes is compared to regular smooth membranes. Chapter 7 presents the main conclusions of the work in this thesis, together with the outlook for each addressed fouling topic.