Microfiltration is a membrane solids separation technique used to remove particles and suspended solids from colloidal and suspended solutions with particle sizes ranging from 0.05-10 microns. There are two main types of microfiltration systems - cross flow microfiltration and dead end microfiltration. Microfiltration membranes are made from materials like ceramics, metals, and polymers and are commonly used to remove microorganisms, particulates, and reduce turbidity from water and other liquids.

1. MICROFILTRATION
Cross-flow microfiltration

2. Microfiltration
The microfiltration process is a membrane solids separation technique that
can be used to remove particles and suspended solids from for colloidal and
suspended solutions.
Two distinct flow configurations are commonly employed for microfiltration
systems, Cross Flow Microfiltration and Dead End Microfiltration.

3. • Particle size in the range of 0.05-10 microns. On molecular weigh basis , the particles
are separated or rejected. Passage of particles through membrane is usually a
function of particle geometry (i.e; particles shape and size).
• Microfiltration is suited to separate larger sizes, such as suspended solids, particulates,
and microorganisms and reduction of turbidity . Commercially available
microfiltration membranes are made from a variety of materials including organic
polymers, such as polypropylene, ceramics and metal alloys. systems are operated at
much lower feed pressures than reverse osmosis or ultra filtration due to the greater
effective pore size.

4. The Dead-end Process
• The complete feed flow is forced through
the membrane and cumulated solids are
trapped on the surface of the membrane
until backwashing is performed.
• During backwashing, accumulated solids are
flushed away from the membranes and are
collected for disposal. Backwash volumes
typically represent roughly 2 to 5 percent of
the total influent feed stream.

5. Factors influencing performance are;
• Raw water characteristics
• Trans-membrane pressure
• Temperature
• Regular monitoring and maintenance.
Pretreatment
A self backwashing 100 um strainer is often necessary to protect the membranes and
moderate particulate loading. Depending on the raw water, a coagulant such as ferric
chloride may be added to form pin flocs and help improve rejection.

6. Cross-Flow Microfiltration:
With cross-flow filtration a constant turbulent flow along the membrane surface prevents the
accumulation of matter on the membrane surface. The membranes used in this process are
commonly tubes with a membrane layer on the inside wall of the tube. The feed flow
through the membrane tube has an elevated pressure as driving force for the filtration
process and a high flow speed to create turbulent conditions.

7. • The process is referred to as "cross-flow", because the feed flow and filtration flow
direction have a 90 degrees angle. Cross-flow filtration is an excellent way to filter
liquids with a high concentration of filterable matter. In cross-flow microfiltration
(CFMF), the suspension is pumped tangentially over the filtration medium.
• Clear liquid permeates the filtration medium and is recovered as the permeate,
while the solids accumulate at the filtration barrier to form a fouling layer, or cake.
• The cake, constituting an increase in hydraulic resistance, decreases the permeate
flux.
• The tangential suspension flow tends to limit the growth of the cake termed as
sweeping.
• Correspondingly, after an initial rapid decrease, the permeate flux levels off and
either attains a steady-state, or exhibits a slow, long-term decline with time.

8. Examples of micro filtration applications
They are;
• Cold sterilization of beverages and pharmaceuticals
• Clearing of fruit juice, wines and beer Separation of bacteria from water (biological
wastewater treatment)
• Separation of oil/ water emulsions
• Pre-treatment of water for nano filtration or Reverse Osmosis
• fermentation, broth clarification
• pre-treatment of water for nanofiltration