Efficient and low-cost water purification based on innovative, functional membrane coating
In cooperation with Italian partners, Karlsruhe University of Applied Sciences recently developed a new type of anti-fouling coating on membranes with scalable retention to improve the quality of purified water while reducing the costs involved in cleaning, maintaining and replacing the membranes. Pore sizes and thus separation efficiency and chemical properties of the novel PBM coated membrane surface can be individually adjusted to the composition of the water to be purified. The PBM coated ultrafiltration membranes were successfully tested in membrane bioreactor (MBR) systems using real wastewater.
The method was developed for coating membranes which are used in the field of industrial wastewater treatment.
A new type of anti-fouling coating with scalable retention helps to improve the quality of purified water while reducing the costs involved in cleaning, maintaining and replacing the membranes. The coated membranes can also be used in membrane bioreactor (MBR) systems.
In recent years, membrane technology has been increasingly used for water treatment. However, conventional membranes are prone to fouling, which has a negative impact on both filtration effectiveness and water flow during the filtration cycle. Therefore, membranes need to be replaced or chemically cleaned in order to remove deposits and bacteria, entailing costs and delays. Membrane quality represents the major bottleneck towards further development, in particular when using MBR systems for process wastewater treatment. This is due to the fact that time-consuming and costly membrane cleaning has a significant impact on both ecological and economical process efficiency. In order to achieve satisfactory results, it is often necessary to post-treat water, in particular wastewater from the pharmaceutical, cosmetics, textile and paper industries. Moreover, requirements on process water purity are becoming stricter and water, in general, is a commodity that is becoming scarcer and even more precious.
In cooperation with Italian partners, Karlsruhe University of Applied Sciences recently developed a method that is based on the properties of polymerizable bicontinuous microemulsions (PBM). It provides commercial membranes with a novel coating, making their hydrophilic surface a lot less prone to fouling. At the same time, pore sizes and thus separation efficiency and chemical properties of the membrane surface can be individually adjusted to the composition of the water to be purified. PBMs are characterized by the formation of a network of oil and water channels at the interface between the two immiscible liquids. Oil channels can be polymerized, building the membrane matrix. The aqueous phase remains unchanged. Since microemulsion has the tendency to organize itself in stable structures depending on the mixing ratio, it is possible to adjust and control the size and distribution of the pores on the membrane surface in the nanometer range. By adding nanoparticles to the PBM, functional elements, such as nanocatalysts, can be embedded in the membrane surface.
Summary of the field test results
The PBM coated ultrafiltration membranes as described in the invention were tested in MBR modules using real wastewater from a textile factory. Textile wastewater usually contains strong dye concentrations and a lot of low biodegradable substances.
Compared to conventional, commercially available MBR systems that were tested in parallel, the membranes as described in the invention achieved a higher and more stable flow rate, which was also due to reduced fouling. The following conclusions can be drawn from this outcome:
- the annual cost of chemicals involved in chemical cleaning of the membranes is reduced by 30 %,
- annual investment cost decreases by 20 %,
- annual operating cost (chemicals, energy) is reduced by 30 %.
Additionally, the membranes as described in the invention were tested with wastewater from an olive oil mill. This type of wastewater often leads to membrane fouling.
A test carried out at the same time, using conventional, commercially available MBR systems, confirmed that membranes as described in the invention are less prone to fouling. The result:
- COD removal efficiency increased by 13 % and
- reduced need for chemical cleaning.
Additionally, the membranes as described in the invention were tested with wastewater from a factory producing cosmetics products.
Compared to conventional, commercially available MBR systems that were tested in parallel, the membranes as described in the invention helped to
- increase COD removal efficiency by 17 % and more specifically
- achieve higher permeate quality.
- Long membrane lifetime / longer service life
- Significant savings thanks to less need for cleaning
- Anti-fouling properties
- Customized properties of the active or reactive membrane layer
- Improved retention due to adjustable pore sizes of dye molecules or biological contaminants, for example
- According to the invention, it is possible to apply the coating to conventional membranes
- Membranes were successfully tested in the field, using wastewater from the textile and cosmetics industries as well as from an oil mill (cf. page 2)
Production of membranes for use in the treatment of industrial waste water.