Water turbidity is one of the essential parameters to be controlled in drinking water treatment. This optical measurement, expressed in NTU (Nephelometric Turbidity Units), reflects the presence of suspended particles that cloud the water and can compromise its sanitary quality. Understanding the issues surrounding turbidity and the technologies available to reduce it is crucial to guaranteeing optimum drinking water quality.
Understanding turbidity: a key indicator of water quality
Turbidity results from the presence of various particles in water: organic matter, clays, silts, micro-organisms and corrosion residues. These particles, ranging in size from a few microns to several hundred microns, scatter light and give water its cloudy appearance.
French and European standards set strict thresholds for water intended for human consumption. Regulations require turbidity levels of less than 2 NTU at the treatment plant outlet, with a recommended target value of less than 1 NTU. There are several critical factors behind this requirement:
Firstly, high turbidity can mask the presence of pathogenic micro-organisms and reduce the effectiveness of disinfection treatments, particularly UV. Suspended particles can also act as a support for bacteria and viruses, protecting them from disinfectants. Secondly, in organoleptic terms, turbid water is immediately perceived as undrinkable by consumers, which can compromise product acceptability.
Reference technologies for reducing turbidity
Several technological approaches are available to effectively treat turbidity in drinking water. Each solution offers specific advantages, depending on the application context.
Coagulation-flocculation
This chemical technique remains the benchmark for large-scale treatment plants. It consists of destabilizing colloidal particles by adding coagulants (aluminum sulfate, ferric chloride), then promoting their aggregation into settleable flocs using flocculants. Although effective, this approach requires rigorous management of reagents and generates sludge to be treated.
Filtration membranes
Ultrafiltration and microfiltration use semi-permeable membranes to retain particles. These technologies offer an absolute physical barrier and guarantee consistent quality, but require protection against clogging and entail significant investment and operating costs.
Granular media filtration
Sand or anthracite filters are a tried-and-tested solution, particularly for tertiary treatment. However, they require regular backwashing and can present performance problems in the event of significant variations in particle load.
Automatic filtration: an innovative response
Faced with the limitations of traditional technologies, automatic filtration using metal or textile screens is emerging as a solution that is particularly well-suited to today’s challenges. This technology combines filtration efficiency, low maintenance and autonomous operation.
Hectron automatic filters: performance and versatility
Hectron, a French manufacturer specializing in automatic filtration solutions since 2004, offers two main ranges of high-performance turbidity filters: the AG and AS ranges.
AG range: versatility for pressurized networks
AG range automatic filters are designed to operate on networks with pressures in excess of 2 bar. Their versatility makes them the solution of choice for many drinking water treatment applications.
These filters offer an exceptionally wide filtration range, from 0.5 to 500 microns, enabling precise adaptation to the specific needs of each installation. For turbidity reduction, the 1 to 3 micron thresholds are particularly effective, making it easy to achieve regulatory targets of less than 1 NTU.
The AG range can handle considerable flow rates, up to 340 m³/h, while maintaining operating pressures from 2 to 16 bar. The suction boom cleaning system ensures optimum cleaning efficiency with reduced water consumption, typically representing less than 2% of the flow treated.
A concrete example illustrates this performance: at the Seythenex treatment plant (74), operated by Veolia, an AG300-E 1 to 3 micron filter treats 18 m³/h of slightly turbid catchment water, guaranteeing quality in compliance with standards for the village’s water supply.
AS range: low-pressure expertise
The AS range responds to a specific problem: effective treatment at very low pressure. These filters can operate with as little as 0.6 bar of upstream pressure, a unique feature that makes them particularly suited to heat pump exchanger protection applications or gravity-fed installations.
With a filtration range from 6 to 500 microns and flow rates of up to 340 m³/h, the AS range of automatic filters offers the same treatment performance as the AG range, but under reduced pressure conditions. This capacity opens up new installation possibilities, particularly in networks where available pressure is limited.
The automatic unclogging system, triggered by pressure differential, maintains constant performance without human intervention. This autonomy is a major advantage for isolated or hard-to-reach installations.
Operational benefits of Hectron solutions
Using Hectron automatic filters for turbidity reduction offers several decisive advantages over conventional technologies.
The absence of consumables is a first major economic and environmental advantage. Unlike cartridge or bag filters, no components need to be replaced on a regular basis, significantly reducing operating costs and environmental impact.
Minimal maintenance is a second operational advantage. The automatic cleaning system ensures autonomous operation, limiting intervention to periodic checks and annual preventive maintenance.
ACS (Attestation de Conformité Sanitaire) certification, available on the entire range, guarantees regulatory compliance for drinking water applications. This certification, mandatory for all equipment in contact with water intended for human consumption, simplifies administrative procedures and ensures sanitary compliance.
Selection and sizing criteria
The choice between the AG and AS ranges depends mainly on the hydraulic conditions of the network. For pressures above 2 bar, the AG range offers the greatest versatility. On the other hand, for low-pressure applications, or when pressure drop must be minimized, the AS range is the optimum solution.
Sizing depends on the flow rate to be treated, the quality of the raw water and the quality objectives to be met. For effective turbidity reduction, a filtration threshold of 1 to 3 microns is generally recommended, enabling output performance of less than 0.5 NTU.
Protective integration of other technologies (UV, reverse osmosis, ultrafiltration) may require finer filtration thresholds, down to 0.5 microns, to optimize the efficiency and service life of downstream equipment.
Conclusion
Turbidity control is a fundamental issue in drinking water treatment. Hectron’s AG and AS automatic filters offer a modern, efficient technological response, combining filtration performance, operating autonomy and low environmental impact. Their ability to adapt to the specific constraints of each installation, whether in terms of pressure, flow rate or water quality, makes them the solution of choice for professionals keen to optimize their treatment facilities while guaranteeing exemplary water quality.
