Reverse Osmosis Filtration Buying Guide

Summary
In the liquid filtration process, the selection of filters and cartridges directly determines product quality, productivity and system maintenance costs. However, many companies designing filtration systems are often faced with poor filtration results or frequent filter changes. The answer is hidden in a key question, “How many filters do I need for my process?” This article will help you select the right filters and cartridges by exploring the various steps of fluid filtration in detail through eight core arguments, combined with data analysis and authoritative citations. Whether it's fluid characteristics, filtration goals, or flow requirements, this article will provide you with practical advice, enhanced with tables and data to inform your decision.


INTRODUCTION:
Why is filter selection so important?
In fields such as industrial production, food processing and water treatment, liquid filtration is a central part of ensuring product quality and process stability. According to the American Society of Filtration (AFS), more than 60% of industrial filtration problems stem from improper filter selection or insufficient quantities. Therefore, understanding the critical steps in the liquid filtration process and selecting filters and cartridges based on actual needs can not only improve efficiency, but also significantly reduce operating costs.

Here are 8 key arguments for selecting filters and cartridges in the liquid filtration process and their rationale.


Argument 1: Fluid properties determine filter type and quantity
The physical and chemical properties of the fluid are the starting point for filter selection. For example, a low-viscosity fluid for water treatment has very different filter requirements than a high-viscosity fluid for petrochemicals. High-viscosity fluids require larger surface area filters to maintain flow rates, while fluids with high particle loading, such as wastewater, require multi-stage filtration systems to avoid clogging.

Arguments and data:
According to Journal of Filtration Technology, high particle loading fluids (e.g., wastewater with up to 500 ppm of sand) have an average clogging time of 3 hours with just a single filter, while system run time can be extended to 24 hours with a combination of a prefilter plus a fine filter. Chemically aggressive fluids (e.g. acids with pH < 2) require PTFE filters to ensure durability.


Argument 2: Filtration Objective Defines Filter Element Micron Rating
Different filtration objectives require different micron ratings of filter elements. For example, bacteria control requires a 0.2 µm cartridge, while general particle removal can be achieved with a 5 µm coarse cartridge.

Arguments and data:
The following table shows how common micron ratings correspond to filtration objectives:




Micron Rating
Filtration Objective
Application Scenarios




0.2 µm
Aseptic filtration, bacteria removal
Pharmaceutical, drinking water


0.5 µm
Sterile filtration, bacteria removal
Food & Beverage


1 µm
Mostly bacterial capture
Industrial water treatment


5 µm
Coarse Particle Removal (e.g. yeast)
Brewing, Chemicals



According to the International Organization for Standardization (ISO) filtration standard, 0.2 µm cartridges have a bacterial retention rate of 99.999% in sterile filtration for high purity requirement scenarios.


Argument 3: Combination of prefiltration and fine filtration optimizes system efficiency
Prefilters protect downstream fine filters by removing larger particles and extending their service life. This multi-stage filtration strategy is especially important in highly contaminated fluids.

Arguments and data:
A case study published by 3M Filtration Division shows that the addition of a 5 µm prefilter in the treatment of industrial wastewater containing particles larger than 50 µm extends the replacement interval of 0.5 µm fine filters from 1 month to 3 months, saving approximately 40% in maintenance costs.


Argument 4: Choice of Nominal vs. Absolute Ratings Affects Filtration Accuracy
Filter pore size ratings are categorized as nominal or absolute. Nominal ratings have efficiencies of 60-95% for general applications; absolute ratings have efficiencies up to 99.98% for stringent sterility requirements.

Arguments and data:
In the case of 1 µm filters, for example, nominal ratings may allow 10% of 1 µm particles to pass through, while absolute ratings block almost completely, for use in the pharmaceutical industry. According to test data from Pall Corporation, absolute rating filters offer a 25% higher ROI than nominal filters in high-precision applications.


Argument 5: Choice of Filter Material Affects Durability and Compatibility
The chemical and physical properties of a filtration material determine how it will perform in a particular fluid. For example, polypropylene is suitable for general water filtration, while PTFE is better suited for aggressive chemicals.

Arguments and data:
The following table compares the properties of common filtration materials:




Materials
Advantages
Disadvantages
Application Scenarios




Polypropylene
Lightweight and economical

Not resistant to high temperatures


General water treatment


Nylon
Chemical resistant, high temperature resistant
Higher cost
Chemical, food processing


Nylon
Chemical resistant, high temperature
Higher cost
Chemical, food processing


Stainless Steel
High temperature and pressure resistance

Heavy, not suitable for acidic fluids


Oil, gas


PTFE
Chemically inert
Expensive
Acid and alkali filtration, gas treatment



According to Filtration & Separation Magazine, stainless steel filters last 3 times longer than polypropylene in high-temperature fluids (>150°C).


Argument 6: Flow Requirements Determine Filter Size and Quantity
Flow rate (in LPM or GPM) directly affects filter selection. Filters that are too small result in excessive pressure drop, while filters that are too large waste resources.

Arguments and Data:
Assuming a system handling 100 LPM of liquid and a pressure drop tolerance of 0.5 bar, a filter with a surface area of at least 0.5 m² is required according to the Filter Selection Guide from Sartorius. If the particle load increases by 10%, an additional parallel filter of the same size is required to maintain the flow rate.


Argument 7: Frequency of filter replacement affects total cost of ownership
Replacement frequency depends on pollutant concentration and filter capacity. A proper replacement schedule balances performance and cost.

Arguments and Data:
As an example, a filter with a capacity of 500 g needs to be changed every 3 months for a fluid containing 100 ppm particles. For an annual production of 100,000 liters, 4 filters/year would be required. If the contaminant level increases to 200 ppm, the replacement frequency increases to every 2 months, requiring 6 filters/year. This figure can be optimized by actual testing.


Argument 8: System testing and optimization are indispensable
While theoretical calculations are important, practical testing can further optimize filter selection. Changes in fluid viscosity or temperature, for example, may require adjustment of the number of filters.

Arguments and data:
GE Water Solutions has shown that adjusting filter combinations through laboratory simulation tests can increase system efficiency by up to 15 percent, while reducing filter usage by 20 percent.


Summary
The selection of filters and cartridges for the liquid filtration process is not simply a matter of quantity stacking, but requires comprehensive consideration of eight key factors, including fluid characteristics, filtration objectives, pre-filtration strategy, pore size ratings, material selection, flow rate requirements, replacement frequency, and system testing. Through scientific analysis and data support, companies can not only ensure product quality, but also optimize cost and efficiency. It is recommended to combine the selection guidelines from authoritative organizations (e.g. AFS or ISO standards) with field testing in practical applications to achieve the best filtration results.