Pure water systems

By

Benjamin Slomka

Who needs pure water?

Reverse osmosis was developed by the NASA

for water recycling in the aerospace

The food industry

• Vine concentration to reduce transport costs

• Preparation of soft drinks

• To test the quality of products

Sea water desalination

In analytical laboratories

Electronic producer

Pharma producers

Cruise ships

Aquarium operators / fish tanks

What is pure water?

Typical pressures and pore sizes

Revers osmosis = final step?

• No reverse osmosis have not the ability to make the water pure enough.

• Water out of an reverse osmosis device still have a conductivity of 5µS/cm.

• To comparison pure water have a conductivity of 0,055 µS/cm; (18,2 MΩ).

Calculation of the conductivity; X

Analytical pure water types

In the GLP there exist a regulation for water of analytical grade. This regulation is written down in the „DIN ISO 3696„ or in ASTM (American Society for Testing and Materials).There differ three types of water.

Analytical types of water. Parameter Type 1 Type 2 Type 3

pH-value at 25 ºC- - 5,0 to 7,5

Spec. electric conductivity µS/cm 25 ºC, max. 0,1 1,0 5,0

COD (O2-) amount mg/l max.- 0,08 0,4

absorption at 254 nm and a length at 1 cm, max. 0,001 0,01 -

Dry weight 110 ºC mg/kg, max.- 1 2

Silica (SiO2-) amount mg/l, max. 0,01 0,02 -

Suggested application of type 3 water

- Washing of materials

- Preparation of buffers

- Water bathes

- and so on...

Suggested application of type 2 water

For all standard analytical measurements

Suggested application of type 1 water

For all critical applications like:

ICP-MS

HPLC-MS

AAS and others

Solvent preparation and dilutions

„Type 4“It exist one more type pure water of importance. The so called „pyrogen free water“. This is a water which is used in biological analysis. Pyrogen free means that these water have no content of:

Pyrogens: This are chemicals which causes immune

reactions and are possible grow inhibitors for

micro-organism

Nucleic acids: Its clear in PRC reactions you don´t

want disturbing genes

Nuclease; an enzyme which can cut DNA

How to get pure water?

How to get ultra pure water?

Ultra pure water is produced in ultra pure water systems. It is a combined system of different stations. An example for a possible system is:

Inflow (drinking water) softener reverse osmosis ion-exchanger/Elix pH-controller UV-

disinfecting ion-exchanger ultrafiltration 0,5 µm ultrafiltration 0,2 µm storage tank

SoftenerSoftener are the first step in an ultra pure water system.The function of a softener is the replacement of Ca2+ and Mg2+ against Na+. The aim of a softener is to protect the reverse osmosis membrane surface by precipitation of CaCO2 , MgOH2. The softener have no significant influence on TOC.

Reverse osmosisReverse osmosis is a non porous filtration method. This is the most important treatment step. It works with high pressures up to 100 bar. Reverse osmosis is a cut off in the range of 300 Dalton.

Ion exchanger / Elix

Ion exchanger remove the remaining ions from the water. This is done by resins that are optimally loaded with H+ and OH-

ions. Na+ and Cl- are also possible. The different to the softener is the salt concentration here are lesser.

In practise exist different types of ion-exchanger. There are

- the cation-anion exchanger,

- the mixed bed ion exchanger

- and the Elix.

Cation-, anion-exchanger

Mixed-bed ion exchanger

In a mixed-bed ion-exchanger the cation and anion resins are mixed in one tank. The theoretical description say this is the same like many ion exchanger in a row. The exchanging rate here is much more higher that in a normal ion exchanger. For condition the cation and anion resin the resin must be separated. This works gravimerical (cation-exchanger are lighter than water).

Elix

UV- Desinfection

-To avoid microbial grow is necessary to sterilise the water with a UV-lamp. Of course UV has no negative effect on the water like ozone, chlorine or other disinfectants.

-After this step two additional filtration's are following. This filters have a membrane with 0,5 µm and 0,2 µm pores.

-At least there is a additional resin which removes the last ions.

...but remember this was only an example in practise it can be much more easier.

Thank you for your attention!