DI Water Plants & Loop Systems

Water is an important raw material and auxiliary in the manufacture of cosmetic and pharmaceutical products. It also serves as a rinsing agent for the CIP cleaning of plant components and pipes – which is why DI water plants are among the key systems in production.

Water qualities at a glance

The individual industries place different demands on water quality. Common designations are:

• DI water – fully demineralised or deionised water
• PW – Purified Water
• HPW – Highly Purified Water
• WFI – Water for Injection

The electrical conductivity in µS/cm usually serves as the measure of purity for demineralised water. Conductivity meters record it directly in the plant.

How water treatment by reverse osmosis works

Reverse osmosis largely removes the dissolved substances from the raw water. A typical treatment chain looks like this:

1. 1FiltrationMulti-layer, cartridge, ultra- or microfilters remove particles and turbidity.
2. 2Activated carbonActivated carbon filters reduce oxidising agents and bind low-molecular organic contaminants.
3. 3SofteningCalcium, magnesium and divalent iron are exchanged for sodium ions – particularly important with hard raw water.
4. 4Reverse osmosisThe membrane separates the feed water into permeate (pure water) and concentrate.
5. 5EDI or 2nd stageElectrodeionisation or a second osmosis stage further reduces the residual salt content.
6. 6Buffer tankThe DI water is stored and distributed via the loop.

Because of the large internal surface of the resin bed, softening is the most critical element of the entire treatment chain in microbiological terms. Chemical disinfection during regeneration keeps germ counts at a tolerable level. However, hot-water sanitisable plants are increasingly being used.

In modern plants, reverse osmosis is the method of choice for desalination, as it offers numerous advantages over ion exchangers. As a membrane process, it is both a mechanical and a chemical filtration. The plant presses the feed water through a semi-permeable membrane at a pressure above the osmotic pressure.

This creates two streams: a concentrate containing the separated salts and impurities, and a permeate – pure water with a very low salt content. Reverse osmosis achieves excellent rejection rates for salts, particles, microorganisms and pyrogens. However, the membranes are sensitive to fouling, scaling and oxidising agents.

To reach the required conductivity, either a second stage or an electrodeionisation unit (EDI) follows. Both deliver lower residual salt contents and therefore a greater safety margin to the limit values.

Control and buffer tank

With single softening units, the control system should schedule regeneration at night. Thanks to pre-treatment, the yield of the reverse osmosis plant rises considerably – from approx. 50 % to approx. 75 %. The concentrated waste water flows into the drain, while the DI water flows into a buffer tank.

Sensors monitor the level of the buffer tank and act directly on the control system. If the level falls below the minimum, the reverse osmosis plant starts producing water. At maximum level, it stops again. In this way, the plant is optimally utilised.

Loop systems to the points of use

Loops run from the storage tank to the individual points of use. They prevent microbial growth caused by stagnant water. The loop passes all points of use, and manual or automatic valves direct the water to the consumers.

The following principles also apply to a hygienic loop system:

• connect all components compactly with minimal dead space and ensure all areas are flushed
• no connections with seal offset or threads in the loops
• preferably aseptic connections to DIN 11864; where hot-cold changes occur, sterile flange connections if possible
• low-dead-space T-diaphragm valves at the points of use
• sealing materials with FDA approval (Food and Drug Administration)
• passivation after completion of the loops and plant components

Disinfection, sanitisation and sterilisation

To keep the water free of germs, operators combine different methods. Sanitisation and SIP processes run in defined cycles. The plant must be designed for the respective method.

Pure steam sterilisation process

For pure steam sterilisation, all plant components must be completely drained. Steam traps with suitable check valves are required at the points of use and at the lowest points of the pipes. The condensate must drain safely, and nobody must be able to get injured on the hot lines.

For reliable venting, it is advisable to put the storage tank and pipe network under vacuum. Pure steam then flows in, and the temperature is controlled via the pressure. It is important that the pipes are also connected to the steam network. Only then does the steam flow all the way to the condensate drain points.

Temperature sensors at hard-to-sterilise points and at the condensate drains record the values and adjust the steam supply. As soon as all sensors reach the defined sterilisation temperature (e.g. 121 °C or higher), the sterilisation time begins. The prerequisites for this are:

• reproducibly controllable sterilisation processes
• stored and documented quality-relevant measured values
• a fully automatic sterilisation sequence
• SOPs for handling the individual sterilisation methods

Heating of water circuits

Leak-proof shell-and-tube heat exchangers heat the water circuit. To prevent microbial growth, hot water should be stored at 70–99 °C. Cold water, on the other hand, should stay below 18 °C. A recooler in the loop takes care of this.

Qualification of DI water plants

Qualification is required to meet the GMP requirements for water plants. It comprises the following steps:

• RA – Risk analysis
• DQ – Design qualification
• IQ – Installation qualification
• CAL – Calibration
• OQ – Operational qualification
• PQ – Performance qualification
• R – Report

The qualification work should already be clearly specified in the requirement specification.

SEEFRIED Verfahrenstechnik GmbH supports you both in the design and in the qualification of your DI water plant.

Frequently Asked Questions about DI water plants and loop systems

Which water qualities are used in pharma and cosmetics?

Common qualities are DI water (demineralised or deionised water), Purified Water (PW), Highly Purified Water (HPW) and Water for Injection (WFI). Purity is usually determined via electrical conductivity in µS/cm.

How is DI water produced by reverse osmosis?

After a filtration stage and, if required, activated carbon filtration and softening, reverse osmosis forces the water through a semi-permeable membrane. For very low conductivities, a second stage or electrodeionisation (EDI) follows. The purified water is stored in a buffer tank.

Why are loop (circular) pipelines used?

Loop pipelines keep the water constantly moving and prevent microbial growth caused by standing water. Typical materials are stainless steel 316L or PVDF with surfaces Ra < 0.8 µm, low-dead-leg diaphragm valves and sterile connections according to DIN 11864.

How often should a DI water plant be sanitised?

At least four times a year, usually by heating to 80 °C and circulating for one hour. Alternatives are pressurised hot water sterilisation at 110–130 °C or sterilisation with pure steam.

Which qualification do GMP water plants require?

Risk analysis, DQ, IQ, calibration, OQ, PQ and a final report. The qualification work should already be specified in the requirement specification.

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