Water Treatment for Cleanrooms: Deionized Water - Quality Standards and Engineering Solutions for FUNE and High-Tech Manufacturing
This article examines the requirements for water-treatment systems intended to produce deionized (demineralized) water used in cleanrooms in nuclear energy, pharmaceuticals, and microelectronics. It analyzes technological schemes such as reverse osmosis, ion exchange, and electrodeionization; the classification of water quality under ISO 3696, ASTM D1193, and pharmacopoeias (USP, EP, State Pharmacopoeia); and purity indicators including resistivity, total organic carbon (TOC), bacteriological purity, and endotoxin levels. Recommendations are provided for designing water-treatment systems for cleanrooms, including requirements for pipeline materials, quality control, and validation.
Introduction. Ultrapure Water as a Process Medium
For facilities using nuclear energy, pharmaceutical enterprises, and microelectronics production, ultrapure water is a critical technological resource. At NPPs, deeply demineralized (deionized) water is used for make-up of steam boilers, turbines, and heat-recovery boilers operating at pressures of up to 140 atm. In controlled access zones, the chemical composition of the primary- and secondary-circuit coolant must prevent corrosion of structural materials and accumulation of activated impurities.
In the pharmaceutical industry, water-quality requirements are even stricter. Purified Water and Water for Injection must not contain pyrogens, endotoxins, or microbial contamination. The latest GMP requirements state that pharmaceutical water must be at least of drinking-water quality, while the design, installation, operation, and maintenance of water-purification equipment must ensure compliance with established quality standards.
The microelectronics industry also imposes extremely stringent requirements: Type I water, with resistivity of 18.2 MOhm·cm, is used for final wafer rinsing and chip production, where even nanograms of impurities can cause rejects.
This article summarizes regulatory requirements for deionized-water quality, technological methods for obtaining it, and practical recommendations for designing water-treatment systems for cleanrooms.
Regulatory Framework for Deionized-Water Quality
Deionized (demineralized) water is classified under international and national standards. There are no uniform requirements for physical and chemical parameters; the required purity class is determined by industry regulations and the technological process.
1. Laboratory Standards: ISO 3696, ASTM D1193
ISO 3696:1999 (in Russia, GOST R 52501-2005) establishes three types of pure water for laboratory analysis:
• Type I (ultrapure water): resistivity >=18.2 MOhm·cm at 25°C, TOC < 50 ppb, no particles or bacteria. It is used in sensitive analysis, for preparation of standard solutions, and in microelectronics.
• Type II (deionized water): resistivity >=5 MOhm·cm at 25°C, TOC < 30 ppb. It corresponds to the requirements of general chemical or biological experiments.
• Type III (water produced by reverse osmosis): resistivity >=0.5 MOhm·cm. It is used for laboratory glassware, feeding distillers, and autoclaves.
ASTM D1193-06 (Reagent Water) establishes similar quality classes for laboratory-grade pure water.
2. Pharmacopoeial Standards: USP, EP, State Pharmacopoeia
Water-treatment systems in pharmaceuticals must comply with GMP. The United States Pharmacopeia (USP) distinguishes Purified Water, Water for Injection, and Highly Purified Water. Key indicators for Purified Water include conductivity <1.3 µS/cm at 25°C, TOC <500 ppb, and absence of bacterial growth.
In Russia, the State Pharmacopoeia (OFS.2.2.0020.15 'Purified Water') applies, as does the European Pharmacopoeia (EP), which regulates similar parameters. Reverse osmosis, electrodeionization, and distillation are specified as the main technological methods permitted for producing pharmaceutical-grade water.
3. Application at NPPs: Special Technical Conditions
The technology for producing deeply demineralized water at nuclear power plants is governed by RD 24.031.120-91, GOST 20995-75, SO 153-34.20.501-2003, and technical operation rules. Coolant-quality requirements directly depend on reactor type (VVER, RBMK, BN) and circuit pressure. Traditionally, distillation was used to produce water with specific electrical resistance of 0.2 MOhm·cm (specific conductivity of 5 µS/cm) from water with salinity up to 1000 mg/L, but since the 1990s ion exchange, reverse osmosis, and electrodialysis methods have become increasingly widespread.
Technologies for Producing Deionized Water
A typical water-treatment system includes sequential purification stages: preliminary mechanical filtration, softening, reverse osmosis, deionization (ion exchange), and final polishing (electrodeionization, UV sterilization, ultrafiltration).
1. Mechanical Filtration and Softening - Pretreatment
Removal of suspended particles, sand, rust, and chlorine is carried out on sand-carbon and cartridge filters. Water softening (Na-cation ion exchange) is necessary to reduce hardness before reverse osmosis and to protect membranes from calcium-carbonate deposits.
2. Reverse Osmosis - Barrier Purification
Water under pressure is passed through a semipermeable membrane that retains up to 99% of dissolved salts, bacteria, viruses, and organic molecules. Reverse osmosis substantially reduces the load on ion-exchange resins and increases their service life.
3. Ion Exchange - Deep Deionization
Water deionization (demineralization) is the key process that removes ions of inorganic salts. It is performed by passing water through columns filled with two types of ion-exchange resins:
• Cation exchanger R-H: binds metal cations (sodium, calcium, magnesium, iron), releasing H+ ions in exchange.
• Anion exchanger R-OH: binds anions of acid residues (chlorides, sulfates, nitrates, silicates), releasing OH- ions in exchange.
The resulting H+ and OH- ions combine into neutral H2O molecules. The ion-exchange process is reversible: exhausted resins are regenerated by passing acid solutions through the cation exchanger and alkali solutions through the anion exchanger.
To obtain deeply demineralized water with resistivity up to 18 MOhm·cm, two-stage H-OH ionization schemes are used. Mixed-bed resin filters (MBF - cation and anion exchangers in one column) are also used for final polishing to ultra-high resistivity.
4. Electrodeionization (EDI) - Reagent-Free Deep Demineralization
Electrodeionization is a technology combining ion exchange and electrodialysis. Under the influence of an electric field, ions are drawn out of the water stream through ion-exchange membranes, while the resin inside the chambers is continuously regenerated by water dissociation into H+ and OH- ions. EDI units produce water with resistivity >18 MOhm·cm without the use of chemical reagents.
For EDI systems, it is critically important to ensure high inlet-water quality, usually after reverse osmosis, so that membranes and resins are not contaminated.
5. Final Polishing for Ultrapure Water (Type I)
• UV lamp with wavelengths of 185 nm and 254 nm: reduces TOC by oxidizing organics to CO2 and provides sterilization by destroying bacteria.
• Ultrafiltration (UF): a capillary membrane removes pyrogens, endotoxins (lipopolysaccharides from gram-negative bacterial membranes), and nucleic-acid fragments.
• Membrane or vacuum degassing: removal of dissolved oxygen, nitrogen, and CO2.
For ultrapure water (18.2 MOhm·cm at 25°C, TOC <3 ppb, endotoxins <0.001 EU/mL, bacteria <0.01 CFU/mL), all listed modules are mandatory.
Design of Water-Treatment Systems for Cleanrooms
When implementing water-treatment systems at nuclear and pharmaceutical facilities, the following principles must be considered:
• Pipeline materials: high-purity polymers (PVC-C, PP, PVDF) or electropolished 316L stainless steel. In pharmaceuticals, welded joints are made by automatic orbital welding with surface-cleanliness control (Ra <0.6 µm).
• Minimization of stagnant zones: there must be no dead legs in pipelines (design according to ASME BPE requirements); the recirculation pump must provide turbulent flow (velocity >1.5 m/s) to prevent biofilm formation.
• Quality control (online monitoring): resistivity/conductivity meters, TOC sensors, and bacteriological analyzers (ATP metering).
• Validation (in pharmaceuticals): qualification of water-treatment and distribution systems (IQ/OQ/PQ). Periodic sampling of water in the loop is performed to control chemical and microbiological purity.
Conclusions
A reliable water-treatment system for producing deionized water is an integral part of the engineering infrastructure of NPPs, pharmaceutical plants, and microelectronics production facilities. The choice of technological scheme (ion exchange, reverse osmosis, EDI) and water-purity class (Type I/II/III under ISO 3696, Purified Water/Water for Injection under pharmacopoeias) is determined by the regulatory requirements of the specific technological process.
TechAtomStroy performs turnkey design, supply, installation, and commissioning of water-treatment systems for cleanrooms of any category, including closed-loop deionized-water systems with quality control (conductivity, TOC, bacteria). All work is performed in compliance with GMP requirements where necessary, nuclear-industry standards, and Rostechnadzor requirements.
To obtain a commercial proposal for designing and building a water-treatment system for your facility, send a technical specification indicating the required water-purity class, capacity, and industry-specific conditions to the commercial department of TechAtomStroy LLC through the feedback form on the website. A cost estimate, work schedule, and feasibility study for selecting the optimal technological scheme will be prepared.
This material was prepared on the basis of ISO 3696:1999, ASTM D1193-06, the State Pharmacopoeia of the Russian Federation (OFS.2.2.0020.15), USP, EP, and nuclear-industry regulatory documents (RD 24.031.120-91, PTE).