Fallacies on the Number of Stages (Part 1)

Nowadays, the belief is that, “the longer the stages the cleaner the water”. So many set ups were being advertised with the highlights of the number of stages.14, 16, 18, 21, 23, 26, 29 etc.

Question is that, are the number of stages would guarantee you, to have the safest drinking water?

Allow me to present the basic units used in a typical water treatment design for water station.

1) Multi-media depth filter (MMDF) – Fiber reinforced plastic (FRP) tank with either automatic, manual or semi-automatic valve with media elements inside. This unit is used to trap particulates or suspended solids from the water through depth filtration. When we talk of depth filtration, it means that filtration happens from top to the bottom of the major filter media which is the Anthracite Coal probably 1 ft3.

Volumes for 1054 tank size and below it are layers of sand and gravel that acts as a supporting bed to prevent the major filter media from collapsing. It can either be 3, 4 or seven layers depending on the designer’s desired height. Let us say we settle for 3 layers supporting bed and Anthracite coal on top, we will be having 4 layers for the MMDF unit. We have 4 layers but function is one.

Trapping of particulates but it is projected as four stages. We have to establish that when we talk of stages, it refers to the gradual enhancement of water in terms of quality as it passes through the said stages. Now talking of MMDF, how many enhancements do the water undergoes? Four stage enhancement or just one? So is it right to say 4 stages or 4 layers single stage?

2) Carbon tank- same concept as the MMDF but the difference is the major filter media, Granular Activated Carbon is used as top layer. Some are saying that there are layers of bituminous carbon, lignite carbon and granular activated carbon but actually functions of bituminous and lignite are the features of Granular Activated Carbon (GAC) sabi nga same banana.

It is designed to remove foul taste, odor, color caused by organic contaminants and any carbon based substance or derivatives. Again it has 4 layers, so how many stages does a carbon tank have? Four or one?

3) Water Softener Tank- same concept as that of MMDF and Carbon Tank but again the difference is the major filter media which is the Resin (Cation resin for calcium, magnesium and iron adsorption) Designed to remove hardness from the water.

So again it has 4 layers but single function which is to convert hard water into soft water by removing calcium and magnesium from the water via ion exchange process(next time I will be discussing the concept of ion exchange).So again, how many stages does a water softener tank has? Four or one?

4) RO sediment pre-filter- you can use 5 micron and 1 micron or just 5 micron sediment filter. However some are using 20,10,5 and 1 micron .We assumed that we will be using 5 and 1 micron sediment filter. So for this segment we use 2 stages.

5) Reverse Osmosis system-Designed to remove salt and other minerals from the water. This is again one stage.

6) Polishing carbon- .We can use either one or two carbon block filters. For our discussion, we use 2 carbon blocks so that means to say, we have 2 stages of polishing carbon. The first carbon block is intended to remove organic contaminants that the water might have while inside the product tank and the second carbon is for further enhancement in terms of taste and appearance.

7) Ultra Violet Sterilizer-eliminates disease causing micro-organisms by emitting ultra violet rays while water is passing through the reaction chamber. This is again a single stage process.

Here is the summary:

MMDF – 1 stage
Carbon Tank- 1 stage
Water Softener- 1 stage
RO pre filter- 2 stages
RO- 1 stage
Polishing carbon- 2 stages
UV- 1 stage

Total number of stages: 9 stages

Next time, I will be discussing the analysis and interpretation of the concept presented.

- Orly Shanghai