What is Water Quality and how is it defined?

Candela Rocío Barbisan
Chemical engineer

The concept "water quality" refers to the physical and chemical characteristics present in the water, being regulated under standards that may vary from country to country. The set of characteristics within the title of "quality" refers to concentrations of compounds and properties that can be perceived, and depending on them the use of the resource.

parameters

There are different parameters measured or estimated to determine the quality of the water, among them: pH, dissolved solids, hardness (depending on carbonates of calcium and magnesium), oxygen and other dissolved gases, clay content, organic and inorganic matter content, concentration of different salts and minerals.

To determine the possibility of water, the quality must meet a series of requirements and contain certain amounts of compounds under certain acceptable levels, in order to ensure that the use that is given to it is appropriate and, in turn, at an industrial level, not to damage the equipment on which it is installed. used, where we introduce a new concept: not all water is exclusively for human consumption, for example, boiler feed water is not It is suitable for consumption, but it must meet a series of specifications to avoid corrosion in boilers due to high concentrations of dissolved oxygen. in her. Specifically in this case, the boiler feed water must be avid for gases, particularly oxygen, which is why certain treatments are required prior to entering the boiler. The same happens with different equipment that works with high temperatures. Likewise, these equipments must be fed with water of low hardness, given that at high temperatures favor the precipitation of carbonates that act as a film resistant to the transfer of heat. Without going any further, in certain cities of the world the water is harder than in others and it can be seen as forms the famous "scale" and adheres to the walls of thermoses, electric kettles and even taps domestic.

Therefore, the most common parameters to evaluate are:
– Smell, color and taste
– Transparency and turbidity
- Temperature
–pH
- Electric conductivity
– Hardness and content of calcium and magnesium carbonates
– Content of salts and minerals
– Dissolved oxygen and chemical oxygen demand
– Dissolved and suspended solids
– Bacteria (sulfate-reducing bacteria, acid-producing bacteria, among others)
– Coliforms
– Heavy metals
– Compounds of nitrogen, sulfur and phosphorus
– Free chlorine and hypochlorites.
– Pesticides and derivatives

There are many other factors to measure, however, depending on the utility of the resource, it is the exhaustive evaluation of each of them, because many of these parameters are not evaluated. on site and a sample must be collected in an appropriate manner. Additionally, many of them require sufficient time for their estimation, for example, microbiological parameters require an exhaustive study of colony formation and so on.

Technologies

There are many types of water, for example, hard water (with a high content of calcium and magnesium carbonates), and soft water. (those that go through a softening process such as filters, fixed beds, osmosis or exchange columns ionic). The latter are the most widespread method for softening water given their low cost and high performance. Unlike other processes, such as reverse osmosis, ion exchange columns require low or no energy consumption, since they are not They require a heating resistance and the highest cost is associated with the exchange resin and the process of regeneration of it when it runs out or is used up. saturates.

Regarding the quality of osmosis water, demineralized water is similar to the quality of tap water. distillation, the latter being avid for gases by undergoing thermal processes (for this reason, in principle, its pH is less); however, in relation to feed water – reject water – produced water, reverse osmosis is a more profitable and efficient technology. As for the other types of parameters, they are waters of similar qualities, depending on the type of distillation equipment that is used and the quality of the osmosis membrane used. In general, reverse osmosis membranes retain compounds such as nitrates and sulfates, but not organic matter, which increases their conductivity compared to, for example, distilled water. Unlike distillation equipment, reverse osmosis is a more compact equipment with yields between 93-98%.