Pharmaceutical water treatment requires removing contaminants from municipal drinking water to meet USP standards. There are two basic types of pharmaceutical water; water for topical use or cleaning (sterile purified water, or PW), or water for injection(WFI) which includes sterile water for irrigation and most sterile water for inhalation.
For PW, USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a total organic carbon or total oxidizable carbon (TOC) limit of 500 ppb (µg/L), and a bacteria-count limit of 100 cfu/mL.
For WFI, the USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a TOC limit of 500 ppb (µg/L), an endotoxin limit of 0.25 endotoxin units/mL and a bacteria-count limit of 10 cfu/100 mL.
The main difference between PW and WFI is the amount of bacterial contamination allowed, measured by colony count and by endotoxin level.
Every water treatment plant is unique, but may include a combination of these methods:
- Multimedia filtration: Multimedia filters are designed to remove the bulk of suspended contaminants whose size exceeds 10–30 µm.
- Activated carbon (AC): AC beds, also known as activated carbon filters, most commonly are used to remove chlorine and chloramine compounds from feed water. This filtration process protects downstream equipment such as RO membranes and IX resin beads from the damaging oxidizing action of chlorine and chloramine compounds.
- Ion Exchange (IX) units: IX technology exchanges undesirable feed water cations and anions with desirable cations and anions. Cations are positively charged atoms and molecules. Anions are negatively charged atoms and molecules. Cation IX units exchange undesirable feed water cations such as calcium, magnesium, lead, and copper with desirable hydrogen ions. Anion IX units exchange undesirable feed water anions such as chloride, sulfate, phosphate, and nitrate with desirable hydroxide ions. The resulting hydrogen and hydroxide ions then combine to form water.
- Distillation: Distillation units heat the feed water to its boiling point. Most dissolved and suspended contaminants remain in the water phase. The steam that is produced is condensed and typically meets WFI and PW standards.
- Reverse Osmosis (RO) water treatment: RO water treatment has become the standard at many pharmaceutical water treatment plants. RO technology can be a costeffective replacement for dual cation and anion IX units. RO systems reduce the need to use costly chemicals, especially those that are caustic, and they curtail the ever-increasing cost of regeneration waste disposal. The payback that results from using an RO system can be achieved in less than two years in some situations. An RO membrane system can remove as much as 98–99% or more of all dissolved contaminants and can remove essentially all suspended (particulate) contaminants. However, RO units require pretreatment to prevent scaling, fouling with living and nonliving particulate materials, and chemical attack, commonly by oxidizing agents.
- Softening: A softener is a type of IX technology that controls scaling in downstream equipment. A softener controls scaling by removing hard scale–forming cations such as calcium and magnesium and exchanging (i.e., replacing) these ions for nonscale- forming sodium ions. An older term, sodium zeolite softening, frequently is used to describe water softening.
- Cartridge filtration: Cartridge filtration or other prefiltration technology is used ahead of RO units to protect against fouling from suspended particles in the feed water. RO membrane systems may become fouled if sufficient suspended solids (particulate) removal is not accomplished. Typically, 1–5-µm nominally rated filter cartridges are used.
- Mixed-bed IX units usually are positioned after an RO subsystem. The effluent from a mixed-bed IX unit meets USP conductivity limits for PW and WFI.
- UV irradiation may be used for bacterial control.
- Electrodeionization (EDI): EDI units in many cases can cost-effectively replace mixed-bed IX units. The resin beads in EDI units do not require chemical regeneration by acid and caustic. EDI units are continuously regenerated electrically.