Membrane fouling

Under fouling (german dirt, mold ) is understood in the membrane technology, the pollution of filter membranes. A distinction is made between general fouling, and biofouling in particular.

Fouling generally

In the process of membrane technology greatly through the filter cake formation ( fouling ) is influenced at ultra-and microfiltration. The effect may be so strong that in a micro- filtration, ultrafiltration. The minimization of this filter cake formation is the main reason (besides the pinch effect in filtration by means of hollow fibers) for the application of energy-intensive cross-flow filtration.

Biofouling

This is usually a very stubborn growth of bacteria, which can lead to complete blockage of the membrane. Especially in the filtration of water samples, the micro-organisms to store preferred to the membrane, because the nutrients are executed directly contribute to them.

Inorganic fouling

Among inorganic fouling and colloidal fouling refers to an accumulation of non-organic particles to the membrane wall. These include particles, such as silicates, soil types, such as Clay ( soil type ) and metal hydroxide, wherein the inorganic fouling mainly aluminum, iron or manganese hydroxides play a role. These attach to the membrane, but also in the membrane and are therefore to be removed by backwashing limited.

Combat fouling

The most common measure is to backwash. This purified solution ( permeate) is already pushed back on the raw side. This ideally bursts from the largest part of the filter cake and can be discharged from the filter element. To combat biofouling, this process does not usually sufficient, since the bacteria hide in a layer of mucus, often very persistent, the surface occupied. In this case, usually only helps dry cleaning. Another option is the treatment with all-metal catalysts, as a pretreatment prior to the membrane process. Addition of biocides hardly helps in this case, since the killed microorganisms occupy the membrane.

The economic importance of fouling in membrane technology

The layer formation is a key component in the filtration. It reduces the flow capacity of the filter element and makes it (depending on the feed composition) of a continuous maintenance necessary. The Rückspülmaßnahmen must be performed every hour for strongly contaminated solutions 1/4 to 1/2, which is a high energy consumption. In addition, the system has stopped at this time and can not produce. Also, the chemical consumption and disposal of cleaning solution represent a cost burden