Cartridge Filters vs Filter Sheets

Depth vs Membrane Filtration (Volume Filters vs Surface Filters)

Generally, depth filtration (sheet filter for example) is used to remove the vast majority of particulates. ABSOLUTE PES membrane cartridges are used just before bottling to ensure yeast or bacteria removal. PP pleated cartridge filters are used ahead of PES to protect them from being overloaded. Also, PP cartridges are used in place of sheet filters for smaller volumes.

Filter Sheets are Volume (Depth) Filters

• High Dirt Loading Capacity
• Cannot be cleaned and reused. Made of paper (cellulose) so, once wet, they physically collapse in a relatively short time. (Filter sheets have a small amount of Polypropylene plastic strands to make them more sturdy).
• Generally broad filtration spectrum.
• Relativley inexpensive

Absolute PES Cartridge Filters are Membrane Filters. Membrane filters are used as a last step to ensure microbial stability. The most common absolute filters are

• PES 0.65 micron will remove all yeast from wine and beer.
• PES 0.45 micron will remove all yeast and all bacteria for wine and beer.
• PES 0.22 micron is used for sterile water production--for example for cleaning water in pharmaceutical industry, and also for spirits filtration. Its use has become more common for wine/beer, but in most cases does not provide an enhanced barrier against bacteria/yeast than 0.45 micron.

Membrane Filters are Surface Filters. In the simplest form, they are a thin layer of material (PES) with well defined and uniform hole sizes. Particulates smaller than the hole size pass through, anything larger than the hole size gets stopped on the surface of the membrane.

• >99.999% Efficiency (Absolute)
• Large Surface Area
• Sharp filtration spectrum (because hole size can be very well defined)
• Low Dirt Loading Capacity (a 10" PES membrane cartridge has about 1/5 the dirt holding capacity of a single 40x40 sheet)
• Can be cleaned and reused. There is a limit however.

High Efficiency PP Pleated Cartridge Filters have both depth and membrane filtration features.

• >95% Efficiency
• Large Surface Area
• Low Dirt Holding Capacity compared to filter sheets, but much larger than PES membrane cartridges
• Made of polymers and are quite durable so they have relatively long life.
• Relatively inexpensive compared to PES cartridges
• Can be cleaned and reused. There is a limit however.
• Sharp Filtration Spectrum and high efficiency. See Zeta Potential discussion below.

Dirt Holding Capacity (DHC) defines the volume (or weight) of particulates a filter medium can hold. The Dirt Holding Capacity of a Depth Filter is essentially the volume of the filter. For a 40x40 Filter Sheet, the Dirt Holding Capacity is ~0.5 liters. (40cm x 40 cm x 3.4 mm).

Filter Sheets filter by two other mechanisms. Although the amount of particulates trapped by these mechanisms may not be large, it is important to understand them because they present limitations.

• A filter sheet is also a surface filter. See the Porosity discussion below
• Electrostatic filtration --see Zeta Potential below

A filter sheet has two porosities. A filter sheet is composed of multiple layers of cellulose. Each layer has a porosity that is much larger than the porosity of the entire sheet.

The most important Porosity is the smallest particulate size trapped in the sheet. For example a 5 micron filter sheet will pass particles less than 5 microns and trap those larger.

The other Porosity is the pore size of the individual cellulose layers. A 5 micron sheet consists of layers of cellulose fibers that have much larger pores---about 25 micron. The multiple layers of 25 micron pores result in a much smaller porosity of the entire sheet.

Please note that we do not list this second porosity in the table of filter sheets because it leads to confusion amongst clients.

This 25 micron pore size is important because it tells you that the sheet will act as a 25 micron membrane filter also. In other words, if you flood a 5 micron filter sheet with particles larger than 25 micron, you will pack the surface and then the sheet cannot act as a depth filter. Or put another way, a 5 micron sheet is a depth filter--with high DHC--for particles between 5 and 25 micron. It is a membrane filter--with low surface area---for particles larger than 25 micron.

This is why you should not try to filter large particles through a plate and frame filter—it will plug up quickly.

What is Zeta Potential? Zeta Potential is the basis of another mechanism of filtration that is particularly important in depth filters (sheets for example). This mechanism of filtration is not size dependent—rather due to electrostatic forces. For example, negatively charged particulates (most particulates in wine or beer are negatively charged) stick to a positively charged surface layer on the filter medium. It is most important to understand that this mechanism only exists when the solution is flowing and it takes a moment to establish the mechanism when flow begins. When you stop the flow on a plate and frame filter, the particles held by the zeta potential are released. When you begin again, some will pass through the filter. This is why it is recommended to recycle the first bit of wine or beer.

Cartridge Filters

Specifications of PES and PP cartridge filters

Absolute vs High Efficiency vs Nominal
In practical terms, Absolute means all particulates below a specified size are removed. In quantitative terms, most mfgs employ the standard of >99.98% efficiency. PES cartridges exceed this standard. High Efficiency is typically reserved for filters of >90% efficiency. Nominal filters are typically 60-90% efficient.

What is BETA? Beta is simply another means of expressing efficiency. A filter of 99% efficiency allows 1 particulate out of 100 to pass. The Beta = 100. A filter of 99.98% efficiency lets 2 in 10,000 pass ( or 1 in 5000). Beta = 5000. So Absolute filters have Beta > 5000.

Flow Rates for Cartridge Filters
GPM = Gallons Per Minute
psid = pounds per square inch differential (i.e, the difference in the inlet and outlet pressure)
Rates are for a single 10" cartridge. A 30" cartridge will have 3 times the rate.

PES Cartridges

• Each cartridge is integrity tested
• No binders or adhesives used in production (hot-welded)
• Each filter is washed with ultrapure water
• Filter area for 10" cartridge: > 0.7 m² (7.5 sf)
• Maximum Working temperature 150 °F
• Cleaning procedure below: Do NOT backwash (reverse flow) PES filters
  
• Maximum Differential Pressure: Foward 60 psid at 25° C. Do not reverse flow PES cartridges.
  The maximum differential pressure decreases with increasing temperature.
• Wine/Beer Maximum Operating Differential Pressure: 30 psid
• pH range: 1-13

Immediately prior to use, rinse with sanitizer solution of choice.

PP High Efficiency Cartridges

• Each cartridge is integrity tested
• No binders or adhesives used in production (hot-welded)
• 0.22 and 0.45 micron are washed with ultrapure water
• Filter area for 10" cartridge: > 0.6 m² (6.5 sf)
• Maximum Working temperature 150 °F
• Cleaning procedure is the same as PES, except reverse flow is okay with PP cartridges.
• Maximum Differential Pressure: Forward 60 psid at 140° F
  Reverse 30 psid at 140° F
  The maximum differential pressure decreases with increasing temperature.
• Wine/Beer Maximum Operating Differential Pressure: 30 psid
• pH range: 1-13

Materials of contruction

PES
Media: Polyethersulfone
Support and Drainage Layers: Polypropylene
Core and Cage: Polypropylene and 316 stainless steel
Ends: Polypropylene

PP
Media: Polypropylene
Support and Drainage Layers: Polypropylene
Core and Cage: Polypropylene and PVDF
Ends: Polypropylene

Maximum Differential Pressure vs Operating Differential Pressure
Maximum Operating Differential Pressure depends upon the product. The maximum differential pressure for wine/beer (or other products with suspended particles) is 30 psid. The maximum differential pressure of 60 psid applies to applications such as water sterilization, in which the water does not have suspended particles.

Cleaning PES cartridges

Do NOT backwash (reverse flow) PES filters

Procedure 1. This procedure does not involve caustic or acid.
a)Forward flow with cold water for 5 minutes to remove product.
b)Forward flow with hot water (175° F) for 5 minutes.
c)Now recirculate with hot water for 15-30 minutes. Leave hot water in unit overnight.
d)Rinse with hot water for 2 minutest the next morning.
f) Air-dry cartridge and store in open to avoid mold growth. You can store the cartridge in the filter housing, but be sure to open the valves so air can penetrate.
Cleaning solutions should be filtered. Flow rate ~ 4 GPM per 10" cartridge.

If Procedure 1 is not effective, this procedure may be used.

Caustic is dangerous. Wear rubber gloves, boots, safety glasses and apron.

Procedure 2. Hot cautic cleaning
a)Forward flow with cold water for 10 minutes to remove product
b)Forward flow with hot caustic solution (140°-150° F) for 30 minutes. (1% NaOH). This is recirculation but discard the first gallon or so.
c)Forward flow (recirculate) with acid solution for 5 minutes. Any weak acid is suitable including vinegar.
d)Forward flow with cold water for 30 minutes. Do not recirculate in this step. You must be certain that all caustic and acid is removed.
f) Air-dry cartridge and store in open to avoid mold growth. You can store the cartridge in the filter housing, but be sure to open the valves so air can penetrate.

Cleaning solutions should be filtered.
Flow rate should be 4 GPM/10" cartridge for hot caustic. 4-10 GPM/10" cartridge for cold water and acid solution.

Procedure 3. Alternative cleaning procedure using cold caustic:

a)Forward flow with cold water for 10 minutes to remove product
b)Soak overnight--up to 12 hours-- in caustic solution (1% NaOH)
c)Soak in acid solution for one hour (any weak acid including vinegar)
d)Forward flow with cold water for 30 minutes. Do not recirculate. You must be certain to remove all caustic and acid.
f) Air-dry cartridge and store in open to avoid mold growth. You can store the cartridge in the filter housing, but be sure to open the valves so air can penetrate.

Cleaning solutions should be filtered.
Flow rates should be 4-10 GPM/10" cartridge.

Cleaning PP cartridges

The cleaning procedure for PP cartridges is the same except you can reverse flow through PP cartridges. Be careful not to exceed the maximum pressure for reverse flow.

Filter Sheets—Specifications

General guidelines for depth filtration (i.e., plate and frame filtering with filter sheets)

How many gallons can I filter before changing filter sheets?
Typically 10-15 gallons for each 20x20 sheet.
Typically 40-60 gallons for each 40x40 sheet.
But, this assumes your wine is clean and you are polishing. The results can be much less if you have cloudy wine.
Stop filtration and change sheets when the pressures become too high. You can still push wine through the sheets at higher pressure but you are not filtering effectively.

Washing

• Even though we use raw materials of excellent quality and take special care in the production and converting process, the filter sheets can initally transfer scents and flavours. As a result, it is necessary to filter cold water through the filter sheets to wash them. This will eliminate all the small fibres and mineral particles that can become detached during the placement of the sheets.
• The water used for washing should be neutral (pH=7) or slightly acidic.
• If you cannot wash with water, we recommend recycling the first few gallons of filtered wine.
• Stopping and starting. If filtration is stopped, then the first volumes of wine upon restart should be recycled.

Filtering
We recommend recycling the first volumes of filtered wine or liquid. In order to achieve a good filtration quality we advise not to exceed the these maximum values.

Maximum flow rate recommended for each surface

• Coarse filtration 1000 l/hm2 (This equates to 43 gallons/hour for each 40x40 sheet and ~10 gallons/hour for each 20x20 sheet.)
• Clarification 500 l/hm2 (This equates to 21gallons/hour for each 40x40 sheet and ~5 gallons/hour for each 20x20 sheet.)
• Sterilisation 350 l/hm2 (This equates to 15 gallons/hour for each 40x40 sheet and ~3.5 gallons/hour for each 20x20 sheet.)

Differential Pressure recommended:

• Coarse filtration: maximum differential pressure 2,5 bar (36 psi)
• Clarification: maximum differential pressure 2,0 bar (30 psi)
• Sterilisation: maximum differential pressure 1,2 bar (18 psi)

Exit Pressure
It is important that the filter is full of liquid and empty of air. Therefore, it is essential that the exit pressure gauge (if present) be at a minimum pressure of 0,2 - 0,3 atm (this can be easily achieved by closing slightly the exit valve).

Inserting Filter Sheets

• Each filter sheet has a directional flow which allows the product to pass through. The filters have both a smooth and a porous (topographically rough) side. The product must go in from the rough (porous) side and must exit from the smooth. The smooth side has a fine checkerboard woven appearance. The rough side looks like a foamy milk surface.
• Loading the filters sheets. The sheets alternate, rough, smooth, rough, smooth.... for 20x20 filter: Working from the pump side of filter. 1st sheet--rough faces pump. 2nd--smooth faces pump. 3rd--rough faces pump. 4th--smooth faces pump. ....
• The order is reversed for 40x40 filters. The first sheet is smooth, then rough, smooth, ...
• To understand why this is so, please examine the plates carefully to understand the flow of the wine through the filter.

Filter surface area in m² x No. of filter sheets x recommended flow = liters filtered per hour.

20x20 filters have 0.04 m² surface area

40x40 filters have 0.16 m² surface area

Ex 1. If you use 30 of the V12 filters (20x20) , then you can filter
0.04 x 30 x 1000 = 1200 liters/hour. (300 gallons/hour).

Ex 2. If you have 2 hours to filter 400 liters using the V16 filters (20x20), then
200 liters/hour to be filtered. Divide by recommended flow of 1000 liters/hr-m² yields 0.20 m². Each filter is 0.04 m², so you will need 5 filter sheets.

Ex. 3. KAPPA 5 with 30 sheets. This is 4.8 m2. 4800 liters/hour. (1270 gallons/hour). This is 21 gallons/minute.