4 Ways to Filter Water for the Pharmaceutical Industry

For pharmaceutical manufacturers, filtration is an essential process. Water is a key ingredient in a massive range of pharmaceuticals — from pills to vaccines to inhalable solutions — and that water needs to be of a medicine-grade purity before it can be used. 

A guest post by Megan R. Nichols (STEM Writer)

There are several common approaches to water filtration that companies in the pharmaceutical industry use to ensure water purity. The particular pharmaceutical water system used, however, may change depending on a company's specific needs and the resources they have access to. Here are a few examples of the techniques they might employ: 

1. Single and Multiple Effect Distillation

Distillation is the use of evaporation to purify a liquid. It's how most desalination plants create drinking water from salt-filled seawater. In the pharmaceutical industry, three main types of distillation are used — single effect, multiple effect and vapor compression distillation.

Single and multiple effect distillation systems consist of numerous stages — anywhere from one to 14 — called effects. Unpurified water is fed into these effects, where it's heated by vapor in tubes, causing some of the water to evaporate. 

Microbiology book

The first effect occurs under extreme pressure. Each effect is a lower temperature and pressure than the last. Because the boiling point of water decreases as the pressure drops, it's possible to collect and use the vapor generated in one effect to boil water in the next. As a result, only the vapor in the first effect is generated by adding heat from an outside source to boil water.

As the vapor passes through the tubes, some of it cools and condenses into distilled water, which flows out of the system and is collected. 

Single and multiple effect systems are popular among pharmaceutical manufacturers for a few different reasons. They require few moving parts and use low power levels to create purified water. However, they can't be scaled down effectively. That means even the simplest effect distillation system takes up a significant amount of space, making them unworkable for smaller operations. 

2. Vapor Compression Distillation

Vapor compression distillation is distinct from multiple effect distillation but uses a similar process to create purified or drinking water. With a vapor compression system, heat is generated by putting water vapor under extremely high pressure levels. When the vapor is compressed, its temperature rises to the point where it can boil water.

This vapor is then passed into a reduced-pressure chamber, where it causes feed water to evaporate. The vapor produced by this process is removed from the chamber, cooled and then extracted from the system as distilled water.

Unlike multiple effect systems, vapor compression distillation works at smaller scales, making it practical for manufacturers that don't need to produce massive amounts of distilled water. However, vapor compression distillation does need significantly more power because electricity is required to keep the vapor hot and under high pressures. 

3. Ultrafiltration (UF)

Ultrafiltration is another approach that companies sometimes use in pharmaceutical water systems. With UF, manufacturers use one or more membranes to remove large molecules from water. The feed water is pumped into the system at high rates and under pressure, where it passes through a membrane filter or series of filters. The water, along with low-weight molecules — like soaps and salts — passes through, while macromolecules, typically oils and solids, are trapped by the membrane.

Because the membrane's pores are so small in size — around 0.01 microns — they can also capture microorganisms, like viruses and bacteria. Ultrafiltration is more effective at capturing unwanted compounds than microfiltration, but it's less effective than nanofiltration and reverse osmosis.

Ultrafiltration isn't typically used by itself, due to concerns that unwanted molecules will be left in the filtered water. However, using ultrafiltration first before another process, like reverse osmosis, helps to remove large molecules from the feed water that can damage more sensitive filters. 

4. Reverse Osmosis (RO)

Reverse osmosis, like ultrafiltration, is a filtration process that forces water through a membrane to strip out unwanted molecules and produce filtered water. The pore size in RO membranes is typically around 0.0001 microns but can be slightly larger in some applications. There is no widely used filtration method that uses stronger membranes.

The filters remove unwanted ions, molecules and microorganisms from feed water.

Because the filters used for reverse osmosis tend to be highly sensitive, reverse osmosis is typically not used by itself in a filtration process. In a case like this, before the water undergoes reverse osmosis treatment, the manufacturer will purify it with another approach — typically distillation or ultrafiltration. Reverse osmosis ensures extremely high-quality water. 

Filtered Water for Use in Pharmaceuticals

Purified water is an essential ingredient for many pharmaceuticals, meaning water purification technology is key to the pharmaceutical industry. Most manufacturers take advantage of a few popular methods. Various types of distillation, which use evaporation to separate water from solids, are common. Other approaches, like those that use filters to purify water, are also popular. However, the risk of damaging filters means that highly effective filtration systems — like reverse osmosis filtering — usually require additional pretreatment of feed water.

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)