Ultra-filtration Facilities

Ultra-filtration (UF) is a proven procedure for the separation of fine, undissolved particles with particle size down to approx. 0.2 µm. The particles to be separated could be solids matter (Dispersions) or liquids (Emulsions). Various ultra-filtration membranes in varied module designs can be suitable as per the type of separation requirement. For the separation of stable oil in water emulsions e.g. ceramic membranes are preferable as pipe modules. For the extraction of potable water from surface water, hollow fiber modules with cellulose acetate membranes have especially proven themselves.

The underlying principle in case of phase separation of emulsions or dispersions is the outlay of work. The separation process takes place in so-called cross flow procedure at the membrane surface. Cross flow means the emulsions to be separated flow lateral to the membrane surface with higher flow speed, whereby the build-up of a filter cake by the shear force arising is minimized.

The task for the separation process in the ultra-filtration module is executed by a pump. The components of the raw water (Feed) to be purified are separated through the pore size of the membrane as per their molecule size. The dissolved particles pass through the pores of the membrane and build the permeate. The undissolved particles flow further at the surface of the membrane and are known as residue.

In order to withstand the pump pressure, the membrane is located on a pressure-resistant supporting material. Membranes are mostly fitted in a permeate main collector designed in a tubular form. As per the requirement at the flow rate, several membranes can be integrated in a main collector. A unit with the arrangement of membranes is known as ultra-filtration module unit.

Selection of membranes and their arrangement takes place considering the required performance, feed quality and purity specifications.

The permeate yield is primarily restricted by the tendency of the residue to build sediments, which can lead to blocking of membranes. Prevention of membrane blocking is one of the main problems at the layout of a facility.

If the firm dispersion or emulsion (Feed) is extracted by the ultra-filtration plant from the permeate, a higher concentration of muddy stuff accrues in the residue. Dewatering can be carried out until the fine particles to be separated are concentrated to such an extent that that they agglomerate. From a previously firm emulsion for instance oil can be separated by gravitational force separation or the solid particles of dispersion can be separated by sedimentation subsequently.

Areas of Application

Drinking- and process water treatment from surface water

Low pressure ultra filtration is gaining more and more importance at the treatment of drinking- and process water from surface water. In order to utilize the commercial benefit of such facilities fully, all the components at the process must be adjusted with each other in an optimum manner.Sectors of industry with high water consumption always cover their requirement from surface water. Chemical plants, steel works, paper mills and, above all, power stations are, therefore, frequently found by the rivers or seas. Particularly river water shows seasonal fluctuating load of muddy stuff and bacteria and must be treated for use in the industrial operations.A combination of chemical and physical process steps through sand filtration, coagulation, precipitation and sedimentation is used at the conventional treatment of surface water. Additional process steps (e.g. ozonisation) are required in order to attain a complete decontamination of surface water. Disadvantage of the conventional treatment process is that the seasonal fluctuations at the river water composition and the river water temperature affect the quality of the generated pure water. These fluctuations can be only partly offset by increased dose of chemical additives. Relatively high operating costs is the consequence.The industry has recognized membrane technology at the treatment of surface water as particularly residue-poor technology. Ultra-filtration functions purely as physical separation process and delivers a clear and germfree permeate independent of the raw water quality. Therefore, ultra-filtration is also particularly well suitable as pre-treatment level for desalination with the help of reverse osmosis. Following are the advantages of ultra-filtration:

  • High permeate quality (clear, germfree and haze-free), almost independent of raw water quality.
  • Extension of the holding time of subsequent reverse osmosis or ion exchangers by lower Silt Density Index (SDI).
  • "Single step process", i.e. simple facility design, easy to automate by modular construction. In case of increase in the water requirement, UF blocks can be upgraded easily.
  • No increase in salinity of the water by coagulants.
  • Residue-poor procedure as the concentrate can be diverted back in the river.
  • In order to ensure the efficiency of membrane process, the specific permeate flow must be maintained at high level over years without the cleaning cycles being reduced further.   Membrane polymer, hollow fiber structure, module design and the mode of operation of the module must be adjusted to each other in an optimum manner in order to ensure secure operation of the filtration facility.

 

Process- and waste water treatment


Ultra-filtration facility is also used in process- and waste water treatment.

The problem can be versatile. The process water to be treated can include e.g. oil, solids and/or corrosion products, which are to be removed through ultra-filtration. Process water holding time can be, thus, extended, chemical products cut down in this way and the process water can be treated until it is in accordance with the waste water discharge conditions.

However, other applications are also possible and must be clarified in individual cases. Finally it deals with increasing the economic and ecological requirements for an operation through systems engineering.

We provide for experimental purpose two different pilot ultra-filtration facilities (once with hollow fiber modules, once with ceramic modules). The ultra-filtration facility with hollow fiber module is mounted mobile on a tag. UF permeate yield upto 95% as per muddy stuff content in the feed water can be attained. The modules are back-flushed periodically and the back-flush durations are variable.

Our ultra-filtration test facilities have already been installed successfully in a few well-known companies. The test results have contributed in a crucial way towards process design.