Membrane filtration for process water treatment

Process water is water, which is used in industrial processes. In most cases, the raw water (e.g. drinking water, well water,…) can not be used directly but has to be treated before use. The target of the process water treatment is to protect technical equipment and machines from damages and wear (e.g. through corrosion or growth of biofilm). Depending on the specific application (e.g. cooling water in open cooling towers), the protection of the health of employees and the public is a goal of the process water treatment as well.

Process water is “pure water”. In contrast to that, we use the term “industrial process fluids”. These are fluids which are generally also water based but chemically altered to such an extent that they should not be regarded as “water” anymore. Typical examples is the treatment of degreasing baths and the treatment and recycling of lye (e.g. caustic soda).

Advantages of process water treatment

The effective and efficient treatment of process water allows the industry to achieve several economical and ecological goals simultaneously. In general, process water is used in (very) large quantities. Therefore, the potential for saving costs and protecting the environment through resource efficient treatment processes is enormous.

  • Protection of machines and equipment from damages and wear
  • Reduction of OPEX and maintenance costs
  • Stable production process without downtime
  • Protection of human health (employees and public)
  • Saving of fresh water
  • Saving of energy and chemicals
  • Reduced amount of waste water

Technologies for process water treatment

Depending on the characteristics of the raw water and the requirements of the process water, different technologies and processes can be applied individually or combined. However, in most cases, the treatment process consists of at least two of the following steps.

Membrane filtration – MF, UF, NF and RO

Like in other fields of application, membrane filtration is our strong point in the process water treatment as well. Most of the systems are microfiltration systems which use ceramic membranes. They can be used as first treatment step of the raw water for removal of particles and turbidity. At the same time they also remove oil and microorganisms (e.g. bacteria, algae, legionella) safely and therefore are suitable for an ongoing treatment of the circulating water as well.

  • Microfiltration (MF) for removal of turbidity, bacteria and oil
  • Ultrafiltration (UF) for removal of above mentioned contaminants as well as virus and higher molecular compounds
  • Nanofiltration (NF) for removal of dissolved substances
  • Reverse osmosis (RO) for production of DI water

Membrane filtration systems can be applied individually or combined (e.g. microfiltration as pretreatment prior to reverse osmosis).

Dosing of biocides and chemical additives

By means of (membrane) filtration, undesired substances are removed from the water. Frequently afterwards chemical additives are added to the water in a controlled way in order to create some positive properties of the process water. For example, biocide as to be added to open cooling water circuits in order to maintain the contamination with germs low (e.g. legionella).

  • Dosing of biocides and disinfectants
  • Dosing of corrosion inhibitors
  • Dosing of additives for hardness stabilizer
  • Adjustment of pH

Ion exchanger (IX)

Through ion exchange (abbreviated “IX”), specific dissolved substances can be removed from the water selectively or all positively or negatively charged ions can me removed in a non-selective way. In many cases, ion exchangers are combined with membrane systems for process water treatment. One example is the production of ultra pure water through a combination of reverse osmosis and demineralization by means of ion exchange.

Automatic blowdown / purge

In most of the process water circuits there the concentration of dissolved substances in the water increases over time. In case of open cooling water circuits, this increase in salinity is most significant. Through the evaporation of water (water vapor is almost pure water), the concentration of dissolved solids (e.g. salts, metals, minerals, organic compounds) in the remaining process water rises. If this concentration becomes to high, the process water develops negative properties. By means of an automatic and measurement of conductivity, the salinity of the process water can be controlled. When reaching a certain limit automatically a certain amount of water purged from the system and becomes waste water. The water lost through evaporation as well as the water lost through purge / blowdown has to be replaced with treated fresh water (makeup water).

Prozesswasser Industriebetrieb
Kesselspeisewasser