Fouling (membrane technology)

In membrane technology, the English term fouling (dt. 'Pollution', 'vegetation') means the pollution of filter membranes. A distinction is made between fouling in general and biofouling in particular.

Fouling in general

In membrane technology, the process of ultrafiltration and microfiltration is very strongly influenced by the formation of the filter cake (formation of the top layer). The effect can be so strong that from an ultrafiltration , a microfiltration is. The minimization of this filter cake formation is the main reason (in addition to the pinch effect when filtering with hollow fibers ) for the application of the energy-consuming tangential flow filtration .

Biofouling

This is usually a very stubborn growth of bacteria that can lead to the membrane becoming completely blocked. When water is filtered in particular, the microorganisms preferentially accumulate on the membrane, as the nutrients are carried directly to them.

Inorganic fouling

Inorganic fouling or colloidal fouling is understood to mean an accumulation of non-organic particles on the membrane wall. These include particles such as silicates , types of earth, such as. B. clay (soil) and metal hydroxide, wherein, when inorganic fouling mainly aluminum - iron - or manganese - Hydroxide play a role. These are deposited on the membrane, but also in the membrane and can therefore only be removed to a limited extent by backwashing.

Combating fouling

The most common measure is backwashing. Here, already cleaned solution ( permeate ) is pressed back onto the raw side. As a result, in the ideal case, most of the filter cake flakes off and can be discharged from the filter element. This process is usually not enough to combat biofouling, as the bacteria hide in a layer of slime that often stubbornly covers the surface. In this case, only dry cleaning can help. Another option is treatment with all-metal catalysts as a pretreatment before the membrane process. Adding biocides hardly helps in this case, since the killed microorganisms also cover the membrane.

The economic importance of fouling in membrane technology

The formation of the top layer is a key component in filtration . It lowers the flow rate of the filter element and (depending on the composition of the feed ) requires permanent maintenance. The backwashing measures must be carried out 1/4 to 1/2 hour for heavily contaminated solutions, which represents a high energy consumption. In addition, the system is at a standstill at this point and cannot produce. The consumption of chemicals and the disposal of the cleaning solution also represent a cost burden.

literature

Robert Rautenbach: Membrane process Basics of module and system design . Springer, 1997, ISBN 3-540-61573-3 .

Individual evidence

^ Argyris Panagopoulos, Katherine-Joanne Haralambous, Maria Loizidou: Desalination brine disposal methods and treatment technologies - A review . In: Science of The Total Environment . tape 693 , November 2019, ISSN 0048-9697 , p. 133545 , doi : 10.1016 / j.scitotenv.2019.07.351 ( sciencedirect.com [accessed October 29, 2019]).
↑ S. Wilhelm: water treatment. Chemistry and chemical engineering . 7th edition, Springer, 2003, ISBN 978-3-540-25163-7 , pp. 126f.

[1] Argyris Panagopoulos, Katherine-Joanne Haralambous, Maria Loizidou: Desalination brine disposal methods and treatment technologies - A review . In: Science of The Total Environment . tape 693 , November 2019, ISSN 0048-9697 , p. 133545 , doi : 10.1016 / j.scitotenv.2019.07.351 ( sciencedirect.com [accessed October 29, 2019]).

[2] S. Wilhelm: water treatment. Chemistry and chemical engineering . 7th edition, Springer, 2003, ISBN 978-3-540-25163-7 , pp. 126f.