Scope

In any purified water system where low conductivity combined with low or zero bacteria performance is required, a well-designed purified water distribution ring main is an absolute requirement. To polish the purified water to low conductivity and achieve continual low bacteria levels the purified water must be kept recirculating. 

The purified water ring main will normally be fed from a purified water tank and stainless steel ring main pump. The ring main will feed to all the required points of use before returning to the purified water tank via a spray ball.

When I speak to engineers about the need for bacteria removal, sometimes I get asked about the role of free chlorine.

Water utility company's will typically add approximately 0.1 parts per million, (PPM) of free chlorine to the incoming water supply. This background level of free chlorine is added to inhibit and remove bacteria from the feed water.

When we purify water, however, the first thing we do is to remove the free chlorine with the water purification processes used. From there on if the wrong conditions are created bacteria cells can grow.

Waste water is becoming an ever-increasing and infinitely valuable water resource. Treated industrial waste water can be transformed into a product that can be used for numerous applications, including wash water, industrial process water, surface irrigation, wetlands and ground water recharge, to name but a few.

High levels of bacteria growth can be very difficult and exceedingly costly to resolve retrospectively.

In most cases this problem is a factor of system design and installation standards in the original installation.

In this article we will explain the common causes of bacteria growth in purified water systems and the effective means of bacteria prevention and removal.

Prevention is much better than the cure

The prevention of bacteria growth in purified water systems, in most cases, is a factor of good system design in the first place. Installation materials used are normally ABS, PVC, Polypropylene, PVDF or 316L stainless steel.

Installation standards are very important. By this we mean that all pipe work joints should be crevice free. Purified water should always be kept moving through a purified water distribution ring main. Flow rates are important as a working velocity of 1.5 to 2.0 meters per second should be achieved through the pipe work.