Quality of Water in Cleaning
Water forms an important part of the cleaning process. It removes the gross soils from various surfaces and in most cases does 30-80% cleaning itself. It also solubilises detergent and soil. This helps in the detergent’s contact with soils and cleaning. Water, then, rinses all the soils, detergents and makes the surface clean. In many cases, water quality may dictate what detergents are to be used for a particular process.
Important parameters of water
Composition of water changes from place to place and from source to source. Natural pure water is very rare. Most of the time water picks up various components from its surroundings and its nature changes. Rainwater picks up the particles from the atmosphere while river water picks up the organic and inorganic matters in it. Sometimes even clay is picked up by water, making it look different. The parameters of water which are important from cleaning point of view are as under:
- Appearance, taste, odour and clarity:Taste or odour in water is normally due to the presence of microorganisms, minerals, chlorine, hydrogen sulphide or other decomposed products. The foul smell indicates microbial contamination. Such water is not suitable for cleaning. In fact, it may soil the surface or even contaminate the already cleaned surface. Presence of clay or organic matter in traces can result in turbid water. Smell of rotten eggs indicates presence of sulphur reducing bacteria. Many times water is seen slightly coloured due to presence of iron or manganese.
- pH:The pH indicates the acidity or alkalinity of water. Presence of certain salts makes it more alkaline. However, in most cases it is between 6 and 8 and does not affect cleaning within this range.
- Hardness:The presence of calcium and magnesium salts in water makes it hard. This is the single largest factor to interfere in the cleaning process. Temporary hardness is due to bicarbonates of calcium and magnesium and permanent hardness is due to sulphates, nitrates and chlorides of Calcium and Magnesium. The main drawbacks of hardness are they precipitate on either heating or when pH is increased due to addition of alkali. The calcium salts which are soluble in normal water become insoluble at higher pH or at elevated temperatures and are thrown out of solution. The calcium or magnesium carbonates, being insoluble in water, precipitate out and form scales on the surface. We observe this everywhere. Some of the examples are scaling on heating surfaces, greying of white fabric and choking of pipes due to scales, etc.
The main disadvantages of hard water are:
- They react with detergent and a part of detergent gets consumed due to hardness. This results in excess use of detergent.
- They form soap scum and prevent effective removal of fatty soil. The calcium and magnesium salts from the water react with fatty acids in fatty soil to form Ca / Mg soap which is insoluble. This not only is difficult to dissolve in water, but forms a viscous insoluble layer on the surface of fatty soil making it extremely difficult to remove. Thus, removal of fatty soil is extremely difficult using hard water.
- It suppresses foam.
- The scales create problems in terms of making heat transfer more difficult, reduce pipe diameters and consume more chemicals. Scales also pose a threat microbiologically as they harbour bacteria and make surfaces difficult to disinfect.
Improve water quality for better cleaning
First of all, water has to be microbiologically safe. Treatment with chlorine is the most convenient and cheaper way of doing it. A quantity of 2ppm chlorine will almost make it fit for this job. There are other ways of treating as well.
A simple filtration through fine filters will remove most of the suspended solids and possibility the turbidity.
Use of chelating agents will take care of hardness; however, it is one of the costliest way of softening water. Conventionally, ion exchange technology is used to replace Ca and Mg by Na ions, thus converting hard water soft. The softening process does not change total solids much as only Ca or Mg gets replaced by Na ions.
If total solids are also very high, either demineralisation process is used. Here, both anions and cations are replaced by H and OH ions respectively. Alternately, reverse osmosis technique can be used to remove large dissolved solids load. However, in a system where total solids are high, a softening treatment is preferred prior to RO filtration in order to avoid scaling in the membranes.
The managers in charge of the cleaning processes need to understand the following critical facts:
- Ion exchange is the simplest and most cost effective way to remove hardness and can result in saving huge costs in detergents besides improving performances.
- The water used for rinsing has to be of good microbial quality or else, the already cleaned and sanitised surfaces could get contaminated again.
Finally, the following specs are recommended for water to be used for effective cleaning: