Seawater is a strategic resource today, given the increasing scarcity of fresh water in many parts of the world. However, its use in fast-growing sectors such as marine aquaculture and desalination requires a specialised technical approach, particularly when it comes to filtration. The particular physico-chemical properties of salt water pose unique challenges that require tailored technical solutions.
The specific challenges of seawater filtration
Corrosion: the invisible enemy of installationsThe specific challenges of seawater filtration
Seawater contains around 35 grams of dissolved salts per litre, mainly sodium chloride, but also sulphates, carbonates and metal ions. This complex chemical composition creates a highly corrosive environment that rapidly attacks conventional metallic materials. Chloride ions, which are particularly aggressive, can cause pitting corrosion on standard stainless steel, compromising the structural integrity of equipment in just a few months.
The temperature of seawater amplifies this phenomenon: every 10°C increase approximately doubles the rate of corrosion. In desalination or aquaculture installations in tropical zones, this problem becomes critical and can lead to costly production stoppages.
Marine biodiversity: a wealth that complicates filtration
Seawater is home to extraordinary microscopic biological diversity. Phytoplankton, zooplankton, marine bacteria and micro-algae form a complex ecosystem whose characteristics vary according to the seasons, currents and temperature. These living organisms tend to agglomerate and form biofilms on filtration surfaces, a phenomenon known as biofouling.
This biological clogging represents a major challenge, as it progressively reduces filtration efficiency and increases pressure drops. Traditional cleaning methods are often inadequate to deal with these stubborn organic deposits.
Mineral particles and their variability
In addition to organic matter, seawater carries mineral particles whose concentration and grain size vary considerably depending on the catchment area. Fine sands, clays, limestone particles and shell debris are all abrasive elements that can damage sensitive equipment in industrial installations.
The proximity of the coast generally accentuates this particulate load, particularly during storms or heavy swells, which resuspend marine sediments.
Critical applications: aquaculture and desalination
Marine aquaculture: preserving the quality of the farming environment
Modern marine aquaculture requires impeccable water quality to optimise the growth of farmed organisms and prevent pathologies. Filtration comes into play at several crucial levels in these installations.
Upstream, the raw seawater must be cleaned of its coarsest impurities to protect the circulation pumps and heat exchangers. This pre-filtration eliminates organic debris, jellyfish and other organisms likely to clog the hydraulic circuits.
Fine filtration then takes place to eliminate smaller particles and some of the microbial load. This stage is particularly critical in larval rearing, where the sensitivity of young organisms requires very high water quality standards.
Desalination: protecting reverse osmosis technologies
Reverse osmosis desalination plants represent one of the most demanding challenges in seawater filtration. The semi-permeable membranes used in this process are extremely sensitive to clogging and require feed water of exceptional purity.
Pre-filtration is the crucial stage that determines the lifespan of osmosis membranes. Insufficient filtration leads to premature clogging of the membranes, necessitating frequent and costly replacement. Conversely, too much filtration increases operating costs without proportional benefit.
Filtration systems must remove particles down to 3-5 microns while maintaining a high flow rate and stable pressure. This performance must be maintained over time, despite variations in raw water quality.
Innovative technical solutions for Hectron automatic filters
Corrosion-resistant materials
Material selection is the foundation of any sustainable seawater installation. Super-duplex stainless steel or titanium-based alloys offer exceptional resistance to marine corrosion, but their high cost limits their use to the most critical applications.
A more economical approach is to use mixed constructions combining resistant metal elements for the structural parts and engineering plastics for the elements in direct contact with the seawater. This hybrid design optimises the performance/cost ratio while guaranteeing sufficient durability.
Automatic filtration technologies
Automatic filtration systems represent a major advance for seawater applications. These technologies incorporate automatic cleaning mechanisms that remove deposits without human intervention, maintaining consistent performance.
The principle of sequential backwashing enables the filtering surface to be progressively decolmatized by locally reversing the direction of flow. This technique is particularly effective against biofouling, as it mechanically removes biofilms before they consolidate.
Full automation of these cleaning cycles drastically reduces maintenance requirements while optimising washing water consumption. The most advanced systems automatically adjust the frequency of cycles according to the pollution load detected.
The Hectron range includes two models suitable for operation in seawater (316 stainless steel body with rislan coating, plastic parts and Duplex stainless steel): the AG automatic filter, available from 3 microns, which can be used upstream of a cartridge filter to protect a high-pressure pump for reverse osmosis, and the AS automatic filter, which is more suitable for low-pressure operation and is more particularly suited to protecting exchangers.
Performance optimisation and preventive maintenance
Real-time monitoring
Modern installations incorporate continuous monitoring systems that monitor key filtration parameters: differential pressure, flow rate, turbidity and temperature. This data is used to anticipate maintenance requirements and optimise cleaning cycles.
Telemetry makes it possible to monitor isolated installations remotely, reducing operating costs while improving responsiveness in the event of a malfunction.
Appropriate maintenance strategies
The marine environment imposes particular constraints in terms of maintenance. Exposure to salt requires frequent inspections and specialised lubricants that are resistant to seawater.
Preventive planning is crucial to avoid unscheduled downtime. Experience shows that proactive maintenance generates substantial savings compared with emergency corrective action.
Conclusion
Seawater filtration for aquaculture and desalination is a constantly evolving technical field, where technological innovation is meeting the growing challenges of these strategic sectors. Corrosion control, biofouling management and performance optimisation are the three pillars of a successful approach, so Hectron has designed filters specifically for seawater, in a mixed metal/plastics construction for good corrosion resistance, offering solutions adapted to all the problems encountered as well as moderate maintenance costs.
