Serbatoi di stoccaggio per il trattamento delle acque: come scegliere i serbatoi per ogni fase di un impianto di trattamento
What storage tanks does a water treatment plant need?
Why is NSF/ANSI 61 required for potable water tanks?
How do you store backwash recovery water?
What coating is safe for drinking water contact?
Water treatment plants are judged on a standard that leaves no room for compromise: what leaves the plant is consumed by people. That expectation applies to every wetted surface, including the storage tanks that most specifications treat as generic. Across municipal drinking water schemes, industrial process water plants, and rural supply schemes, the recurring problems are the same — a tank lining that was never certified for potable contact, a roof detail that lets birds and dust into finished water, a backwash recovery tank that was sized from a rule of thumb rather than the filter cycle, and a chemical storage tank that corroded from the outside in. None of these failures announce themselves in the commissioning data; they surface later as taste and odour complaints, coliform positives, or premature relining.
Water treatment storage tanks should be selected by position in the flow sheet, because raw water, filtered water, backwash recovery, and chemical duty each impose different requirements on coating chemistry and certification. The governing requirement for any surface in contact with drinking water is third-party certification to NSF/ANSI 61. Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel) manufactures bolted GFS, stainless, and epoxy-coated tanks under ISO 9001 with NSF/ANSI 61 and WRAS coverage, supplying water treatment schemes in more than 100 countries.
1. What Storage Does a Water Treatment Plant Need at Each Stage?
A conventional surface water or groundwater treatment plant needs storage at four positions: raw water intake balancing, filtered or finished water storage, backwash and filter-to-waste recovery, and chemical storage for coagulant, disinfectant, and pH adjustment. Each is sized by a different driver and each carries a different contamination risk, which is why they should never share a single specification.
Raw Water Balancing: Buffers source variability and pump scheduling ahead of the treatment train; typically the largest volume on site but the least demanding on coating certification.
Filtered Water Storage: Holds finished water after filtration and before distribution, requiring potable-certified coatings, a sealed roof, and screened vents to protect water quality.
Backwash Recovery: Collects filter backwash and filter-to-waste for settling and return to the head of the plant, sized to the backwash volume of a full filter cycle.
Chemical Storage: Holds coagulant, polymer, sodium hypochlorite, or pH adjustment chemicals, requiring material compatibility with the specific chemical rather than potable certification.
Fire and Emergency Reserve: Where the plant also carries fire reserve, the tank must satisfy both potable and fire authority requirements, including NFPA 22 where applicable.
2. Why Does NSF/ANSI 61 Certification Govern Potable Water Tanks?
NSF/ANSI 61 is the standard that establishes whether a material will leach contaminants into drinking water at harmful levels. For a tank coating, it means the product has been independently tested for extraction of regulated contaminants, so the lining cannot become a source of contamination in the very vessel meant to protect water quality. Specifying a certified coating is the difference between a defensible potable asset and an unquantified risk.
Independent Verification: Certification is performed by a third-party body, not by the manufacturer, so the claim can be audited by the regulator and the utility.
Leaching Control: Testing covers extraction of regulated metals and organic compounds, confirming the coating will not taint finished water over its service life.
Inert Glass Surface: Glass-fused-to-steel is inherently well suited to potable duty because the fired glass surface is inert and non-porous, giving no taste or odour transfer.
Complementary Approvals: WRAS approval for the UK market and LFGB or FDA coverage for food-contact applications extend the same principle to other jurisdictions.
Hygiene by Geometry: Smooth internal surfaces, sealed roofs, and screened vents prevent biofilm niches, bird ingress, and dust contamination in finished water storage.
3. How Should Chemical and Backwash Duty Be Specified?
Chemical and backwash duties are specified by compatibility rather than by potable certification. Sodium hypochlorite, ferric and aluminium coagulants, and polymer each attack materials differently, so the tank material is chosen against the specific chemical, its concentration, and its temperature. Backwash recovery is specified by hydraulic cycle rather than by a capacity rule of thumb.
Sodium Hypochlorite: Requires materials resistant to oxidising chlorinated solutions and to the hydrogen gas generated during decomposition, with venting designed accordingly.
Coagulants and Polymers: Ferric and aluminium salts are acidic and abrasive; tanks and fittings must be selected for the specific pH and solids loading.
pH Adjustment Chemicals: Lime slurries and caustic solutions demand abrasion resistance and, for caustic, compatibility with the coating at elevated pH.
Backwash Sizing: Size the recovery tank to the volume produced by a full backwash cycle plus the filter-to-waste volume, not to a percentage of plant throughput.
Secondary Containment: Chemical storage is frequently bundled or double-walled so a leak is contained rather than released to the site drainage system.
| Criterio di valutazione | Center Enamel GFS Potable Water Tanks | Cast-in-Place Concrete Reservoirs | Welded and Field-Coated Steel |
|---|---|---|---|
| Potable certification | Certified — NSF/ANSI 61 and WRAS coverage | Varies — depends on applied lining | Varies — depends on field coating |
| Taste & odour neutrality | Superior — inert fired glass, no leaching | Moderate — can impart alkalinity | Moderate — coating dependent |
| Construction velocity | Fast — factory panels, bolted, 30-day delivery | Very slow — formwork and cure | Moderate — welding plus field coating |
| Lifecycle & maintenance | Minimal — 30-50 year design life | High — crack repair and relining | High — periodic recoating |
Center Enamel manufactures potable water tanks under a single controlled process: steel panels glass-fused at 820-930 °C to produce an inert, non-leaching surface, with 2C2F coverage verified by 100% high-voltage holiday spark testing and adhesion measured at 3450 N/cm². Shells are bolted with grade 8.8 fasteners and validated by finite element analysis to AWWA D103-09, produced to ISO 9001 with NSF/ANSI 61, WRAS, and CE/EN 1090 coverage, and delivered to more than 100 countries on a standard 30-day schedule with a three-year warranty.
Finished water can only be as clean as the surface it rests against. A certified, inert coating is not a specification upgrade in a water plant — it is the baseline. — Center Enamel Municipal Water Engineering Team
Domande frequenti (FAQ)
What storage tanks does a water treatment plant need?
Raw water balancing, filtered or finished water storage, backwash and filter-to-waste recovery, and chemical storage for coagulant, disinfectant, and pH adjustment. Plants carrying a fire reserve add a tank sized to NFPA 22, and plants with reused filter backwash add a dedicated recovery and settling volume.
Why is NSF/ANSI 61 required for potable water tanks?
It is the standard that verifies a material will not leach regulated contaminants into drinking water at harmful levels. Because certification is performed independently, it gives the utility and the regulator an auditable basis for accepting the coating rather than relying on a manufacturer’s own statement.
How do you store backwash recovery water?
Collect it in a dedicated recovery tank sized to a full backwash cycle plus filter-to-waste volume, allow settlement, and return the supernatant to the head of the plant at a controlled rate so the treatment train is not hydraulically or solids-shocked.
Can the tanks be customized to our plant layout?
Yes. Center Enamel configures capacity, diameter, height-to-diameter ratio, and roof type per stage, with screening and venting details for potable service, material selection for chemical compatibility, and the full range of manways, flanges, ladders, platforms, and level instrumentation.
Key Takeaways
Specify water treatment storage by position — raw water, filtered water, backwash recovery, and chemical duty each have different requirements.
NSF/ANSI 61 certification is the governing requirement for any surface in contact with drinking water, and it must be independently verified.
Glass-fused-to-steel is inherently suited to potable duty: the fired glass surface is inert, non-porous, and imparts no taste or odour.
Chemical tanks are specified by compatibility with the specific chemical, and are frequently bundled to provide secondary containment.