Water is the basic element for all living organisms on earth. Moreover, water fulls a large number of different functions for human activities such as drinking water, in households, agriculture, industrial applications and transport. The latter also refers to transport our waste to treatment plants. This wastewater is mechanically and biologically treated in wastewater treatment plants (wwtp's) resulting in a good effluent water quality, whereby biodegradable organics, nitrogen, phosphate and suspended solids are removed to a large extent. The resulting wwtp effluent is normally discharged to surface water, but can also be used as a water source for other applications. One of the techniques to upgrade wwtp effluent to a higher water quality is membrane filltration. By using ultrafilltration membranes an excellent basic water quality can be achieved, without suspended solids, bacteria, large macro-molecules and mostly all pathogenic organisms. The advantages of ultrafilltration are the relatively high ux, low trans membrane pressure and low energy costs, applying the dead-end mode. A major drawback in the use and operation of ultrafilltration is membrane fouling, which is a natural consequence of the membrane separation process. Membrane fouling affects the filtration properties directly and therefore limits the overall process performance. In order to understand membrane fouling mechanisms, it is of great importance to know which components contribute to membrane fouling and how these foulants are attached to the membrane surface and connected to each other. In this thesis the physical and chemical mechanisms of membrane fouling during dead-end ultrafiltration of wwtp effluent have been investigated in order to optimise process conditions, pre-treatment and membrane cleaning.