Introduction

The high performance of membrane technology has been proven in recent years in a wide range of fields, such as chemical industry, medical technology, drinking water treatment, biotechnology and environmental technology. The German work groups of the DWA (ATV-DVWK 2000a, b, 2002a, b; DWA 2005) have provided excellent reports on the application of membranes in the field of wastewater treatment. Also, the Chemical Engineering School at the RWTH Aachen has provided important knowledge of fundamentals and applications in the whole area of membrane technology (Rautenbach and Albrecht 1981, 1989; Melin and Rautenbach

The continuous development of membrane materials and membrane design on the one hand and the knowledge of operational management on the other hand have fostered the growth of membrane technology in wastewater treatment. Many questions have yet to be answered, however, especially in activated sludge systems:

• How can we best implement membranes in activated sludge systems?

• Do we need primary settlers if we use a membrane activated sludge process?

• Which membrane modules and operating modes are effective and energy efficient?

• Is it possible to perform nitrification and phosphate elimination in combination with membrane processes?

The number of membrane processes installed for the treatment of municipal wastewater is rather low but steadily increasing. In Germany, several large membrane processes for wastewater treatment plants (>11000 inhabitants) are in operation or being planned (MUNLV 2003). The largest one (for 80000 inhabitants; about 1900 m3 h-1) has been in operation since 2004 in the wastewater treatment plant (WWTP) at Nordkanal (DWA 2005). The biggest industrial membrane process in biological wastewater treatment for a flow rate of about 200 m3 h-1 has been in operation near Dortmund since 2004 for the treatment of wastewater from the pharmaceutical production plant of Schering AG (Achtabowski and Neuhaus

Industrial wastewater treatment plants are often characterized by low flow rates and high pollutant concentrations. The benefit of using membranes is the possibility to reuse water in different qualities and the gain of reusable material as well as environmental aspects integrated in the production process. Examples for treatment of water and wastewater with membranes are given in Table 12.1.

Membrane processes have different targets, such as meeting the guidelines of wastewater quality standards, the recovery of components or the reuse of the treated water. In the field of municipal wastewater treatment, micro- and ultrafiltration processes are predominantly applied with the target of avoiding the need for a secondary clarifier, increasing the bacterial concentration in activated sludge process or producing an effluent free from suspended solids. In industrial wastewater treatment and water reuse, nanofiltration and reverse osmosis are preferentially used.

Table 12.1 Examples of membrane processes in wastewater and polluted river water treatment (MUNLV 2003).

Municipal, commercial and industrial applications

Micro- and

MBR for treatment of:

ultrafiltration

- municipal, pharmaceutical

- rendering plant

- food industry wastewater

- landfill leachate

Tertiary filtration of treated wastewater

Treatment of distillery wastewater

Treatment of electro dip coating water, oil-in-water emulsions and

degreasing-processes in metal industries

Reuse of concentrated water-soluble lacquers

Pretreatment for production of boiler feed water

Treatment of polluted river water with integrated precipitation

Elimination of phosphate, iron and manganese

Nanofiltration

Elimination of specific compounds like EDS in wastewater

Desalination of wastewater

Discoloring of wastewater in textile and cellulose industries

Concentration of landfill leachate

Reverse

Concentration of CaSO4 from mine-drainage water

osmosis

Recycling of silver from washing water in photo industry

Treatment of wastewater in textile-dye industry

Concentration of washing water in cellulose industries

Reuse of phosphor acid

Treatment of chlorine water

Treatment of landfill leachate

Desalination

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