Filtration and ultrafiltration: differences, applications and how to choose

The differences between filtration and ultrafiltration lie mainly in the size of the particles they can retain, the type of barrier used and the ultimate goal of the treatment. Although both technologies improve water quality, they are not always alternatives to one another: they frequently complement each other within the same treatment line. In this guide, we explain what each process removes, when it is best to use one or the other and what technical criteria must be reviewed before selecting a system for industry, hotels, agriculture, water purification, reuse or the protection of a reverse osmosis plant.

Quick reply: how do they differ?

Conventional filtration

Conventional filtration passes water through a mesh, cartridge, disc or filter bed. Its usual function is to retain sand, sediment, suspended solids and particles that can cause turbidity, blockages or wear in downstream equipment.

Ultrafiltration

Ultrafiltration uses membranes with much finer pores. As well as reducing turbidity and very small solids, it can act as a barrier against colloids, bacteria and other microorganisms. This is why it is used when more stable water quality or advanced pretreatment is required. In short: Filtration primarily removes particles; ultrafiltration adds a higher-precision physical barrier. The choice depends on the incoming water and the required output quality.

Key differences between filtration and ultrafiltration

• Mechanism: filtration uses granular media, meshes, discs or cartridges; ultrafiltration employs membranes.
• Separation level: Conventional filtration works with larger particles; ultrafiltration targets fine solids and colloids.
• Microbiological control: A conventional filter should not be considered a microbiological barrier. Ultrafiltration can retain bacteria and reduce the presence of microorganisms, although the complete system may require additional disinfection.
• Quality of water produced: Ultrafiltration usually offers lower and more stable turbidity in the face of variations in the source water.
• Operation: both technologies require cleaning and pressure drop control; membranes also require specific backwashing protocols and, depending on the application, chemical cleaning.
• Investment and consumption: Ultrafiltration typically requires greater investment and operational control. The decision should be based on the life-cycle cost, not just the initial price.

What problems does each technology solve?

Suitable problems for conventional filtration

• Sand, silt and visible particles.
• Turbidity caused by suspended solids.
• Blockage of pipes, nozzles and irrigation emitters.
• Protection of pumps, heat exchangers and process equipment.
• Reduction of the solids loading prior to cartridges, membranes or disinfection.

Problems suitable for ultrafiltration

• Fine and variable turbidity.
• Colloids that pass through conventional filters.
• Need for a physical barrier against bacteria and microorganisms.
• Advanced reverse osmosis membrane protection.
• Production of water of consistent quality for drinking, process or reuse.

Neither conventional filtration nor ultrafiltration alone removes dissolved salts. When the goal is to reduce salinity, conductivity or other dissolved compounds, a subsequent stage is usually required, such as reverse osmosis or another specific technology.

Can filtration and ultrafiltration be combined?

Yes. In waters with a high or changing solids load, a preliminary stage of screening, multimedia filtration, disc or cartridge filtration can protect the ultrafiltration membranes. In turn, ultrafiltration can provide stable water prior to a reverse osmosis plant, an industrial process or a disinfection stage. The right combination reduces fouling, extends the service life of the equipment and avoids sizing a technology to perform a function that could be solved more simply in an earlier stage.

How to choose between filtration and ultrafiltration

Selection should not be made solely on the basis of flow rate. At least the following criteria should be reviewed:

1. Origin of water: network, borehole, gallery, surface abstraction, seawater, treated wastewater or a mix of sources.
2. Characterisation: turbidity, suspended solids, particle size, organic matter, microbiology, salinity and seasonal variations.
3. Target quality: irrigation, industrial process, human consumption, reuse or reverse osmosis feed.
4. Flow rate and demand profile: continuous operation, peak consumption, shift production or temporary needs.
5. Space and installation conditions: technical room, marine environment, temperature, electrical availability and possibility of expansion.
6. Operation and maintenance: available staff, automation, wash frequency, rejection management and access to consumables.
7. Total cost: investment, energy, wash water, chemicals, spare parts, maintenance and production downtime.

A filterability test or pilot plant may be advisable when water quality varies significantly, the water contains complex organic matter, or the project requires strict performance guarantees.

Common applications

Industry and hotels

Filtration protects networks, tanks, exchangers, cooling towers and process equipment. Ultrafiltration is valued when the installation requires a more consistent quality, internal reuse or robust pretreatment prior to membranes.

Agriculture and irrigation

Mesh, disc or sand filters help prevent drippers and sprinklers from clogging. Ultrafiltration may be suitable when treating recycled water or where there is a high presence of fine solids and microbiological load.

Potabilisation and reuse

In surface or variable quality waters, ultrafiltration can form part of a multi-barrier system. The complete design must also consider disinfection, analytical control, and the health requirements applicable to the end use.

Ports, marinas and remote facilities

Marine environments and remote locations require robust, automated and easy-to-maintain equipment. Modular or containerised solutions can simplify transport, installation and future expansions.

Special criteria in the Canary Islands and projects in Africa

In the Canary Islands, it is common to work with desalinated water, wells, galleries and networks with different conditions between islands and installations. In West and North African projects, there may also be seasonal changes, long logistical distances or limited access to spare parts. These variables influence material selection, redundancy, the level of automation and the inventory of consumables. Location does not determine technology on its own. Water analysis, end use and actual operating capacity are the data that must guide the design.

Frequent errors when selecting treatment

• Choosing the equipment without representative water analysis.
• Confusing turbidity with salinity and expecting a filter to remove dissolved salts.
• Size solely based on the nominal flow rate, without considering peaks or backwashing.
• Disregard seasonal variations in the inlet water.
• Failing to provide space, drainage, consumable storage or maintenance access.
• Evaluate only the purchase price and not the operating cost over the lifespan.

Maintenance: what should be checked

In conventional filtration, head loss, backwash frequency, the condition of the filter media, and the replacement of cartridges or elements are checked. In ultrafiltration, flow rate, transmembrane pressure, membrane integrity, and the effectiveness of cleaning cycles are also monitored. Recording these parameters makes it possible to detect fouling, optimise consumption, and plan maintenance before water quality or production is affected.

Conclusion

Conventional filtration is an efficient solution for removing solids and protecting installations. Ultrafiltration provides finer separation and more stable quality when the process demands it. In many projects, the best answer is not to choose a single technology, but to combine them correctly. If you already need to move from analysis to a project, consult our professional water filtration and ultrafiltration solutions in the Canary Islands and Africa, where we explain the design, integration, installation and technical support service.