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Introduction to microfiltration technologies

Spectrum of filtration

Microfiltration is one of the most common laboratory and industrial processes which is used to separate colloidal or suspended microparticles 0.1 to 10 μm in size as well as microorganisms from liquids and gases. Microfiltration occupies an intermediate position between ultrafiltration and conventional filtration (macrofiltration) without any clear-cut boundaries.

By the mechanism of particle retention, the filter elements produced by Technofilter are broken down into membrane elements (with surface retention prevailing), depth elements (with particle retention taking place mainly inside the filter media) and sorptive filter elements (with particle retention proceeding by adsorption mechanisms). Cartridge elements are operating in the dead-end mode (degree of conversion = 1). Filter elements are also classified either as HYDROPHOBIC (for the filtration of gases and liquids) or as HYDROPHILIC (for the filtration of liquids). By the type of filter material packing, filter elements are divided into pleated and unpleated. Depending on required filter capacity, filters are implemented as disks, capsules, minicartridges, or standard cartridges.

Efficiency of the filtration process

The filter elements produced by Technofilter can be used both for prefiltration and final filtration of liquid and gaseous media. The right choice of a filter is dependent not only on the required quality of the product, but also on the economic performance of the system in each specific case.

Upstream of membrane filters, depth filters are usually installed for prefiltration of process media.

Depth prefilters effectively reduce the bioload and remove most particles and colloid contaminants that can prematurely plug the final membrane filters, thereby improving their performance and service life.

The choice of the filtration system depends on specific characteristics of the medium being filtered and the specific process technology. The factors that should be taken into consideration include particle size distribution and particle concentration, viscosity, temperature of the medium being filtered, chemical and thermal stability of materials of construction used in fabrication of the filter and many others. That is why the process of designing a filtration system remains even now a ‘rule of thumb' method rather than an exact science.

Definitions of filtration terms

Clarification, the stage of processing intended to remove suspended particles before further treatment.

PREFILTRATION, the stage of processing intended to extend the service life of the downstream (final) filter.

FINAL (STERILIZING) FILTRATION, the stage of processing intended to produce filtrate having a preselected degree of purification, e.g., sterile.