Introduction

For more than 25 years membrane filtration processes are used as state of the art technology in many different applications e.g. seawater desalination and applications in food processing industry and biotechnology. With increasing costs for water and wastewater a rapidly increasing tendency of using membranes can be observed in Central Europe.

1.1 What is water?

Water in the definition of the terms of this topic can be sea water with high amounts of sodium chloride, surface water with varying amounts of minerals and organic ingredients like humic acids but as well normal potable water already treated water from the water works.

1.2 What is wastewater?

Wastewater can be the effluent water from an industrial company discharged to the sewer, this is known as "end of pipe" treatment. Here, a wide range of compounds are present in varying concentrations. Wastewater can also be water treated using biological processes. Here, bacteria, residues of flocculants and sewage sludge can present. Wastewater can also be a part of a production plant e.g. a washing machine or bottle washer. In this case an influence on the composition of the wastewater can be made and often not only the water can be reused but useful products, which can have an added value for use in the production process again.

1.3 Which membrane processes are in use?

Depending on the feed and quality demands of the filtrate any filtration process ranging from microfiltration up to reverse osmosis involving a wide variety of membrane materials can be found. If a laundry or a car producer wants to meet the consent limits for the discharge of wastewater a simple microfiltration or ultrafiltration unit may be appropriate. If they want to re-use the water a nanofiltration or a reverse osmosis plant is needed. The composition of the wastewater in terms of viscosity, turbidity, fibres and abrasive materials determines the type of membrane e.g. tubular, hollow fibre, flat sheet or spiral wound. The permeate quality, stability of the membrane, lifetime and amount of investment could determine if a ceramic or polymer membrane is chosen.

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