This avoids the confounding factors in data interpretation, such as changing source water quality. In pilot studies, designers are able to optimize the operating conditions of each individual stage of a multistage installation. The fouling of membranes has been one the primary impediments to their more widespread application in water treatment. The former is the more common. Membrane fouling occurs during an increase in transmembrane pressure to maintain a particular water flux or during a decrease in water flux when the system is operated at constant pressure.
Bacteria can also adhere to the membranes and create a biofilm.
Accurate tests to predict fouling still do not exist. They can then adjust pretreatment and chemical cleaning procedures. Fouling can be controlled by hydrodynamic and chemical methods, periodic backwashing, and chemical cleaning. Other methods include improving pretreatment and changing operating conditions. Membrane fouling rates are functions of the operating conditions such as water flux and recovery.