We will see some water features especially in liquid state. To explain what happens in contamination and decontamination of water is important to know the features of water. Among others, pure water has the following:
• Colorless, odorless and tasteless.
• Density: 1 g/cm3 at 4 ° C
• Melting point: 0 ° C
• Boiling point: 100 ° C.
• Dielectric constant: 78.3
• pH = 7
• Very low electrical conductivity and high resistivity.
Liquid water is colorless, odorless and tasteless. Actually, water is considered colorless, but analyzed with a spectrophotometer a slight blue-green coloration is detected. Although the blue of sea is caused by reflections of the sky, this property of water contributes to blue color of sea, lakes and large bodies of water.
Other properties can be understood from two characteristics of the water molecule. One is, as we saw in the initial post of this blog, that has a dipolar character and other feature is the dissociation of water molecules (H2O) into protons (H +) and hydroxyl (OH-).
Both the melting point and boiling point are outliers with respect to the same series of hydrides oxygen due to its more pronounced dipolar character allowing links with hydrogen bridges. As a consequence of water’s melting point and boiling point higher than the rest of hydrides series, it can be found on Earth in three states (solid, liquid and vapor).
The high dielectric constant of water makes that the water has great ability to dissolve polar substances
Thus, the negative parts of the water molecule (Oxygen side) interact with positively charged substances and the positive part of the dipole (Hidrogen side) of the water molecule interacts with negatively charged substances.
In the following graph is represented as water dissolves salt (sodium chloride) and solvating ions of Na + and Cl- to form a solution.
In pure water, there is a very small part that is dissociated into protons (H +) and hydroxyl (OH-). This amount of dissociated water molecules are related with pH. Pure water has a pH of 7 which is considered neutral pH.
Water conductivity is very low due to the low dissociation presented. Pure water practically does not conduct electricity. However, the water that we find in nature always has other dissolved substances which make its conductivity high and therefore, we consider that water is a good conductor of electricity.
These are some of the characteristics of pure water. Nevertheless, water in nature hasn´t got the features described above on the same values that pure water, but the inclusion of other substances due to water ability of dissolving, transporting, reacting to form structures or compounds with other substances, it happens that some parameter, several or all are different.
Water in nature contains minerals and organics substances from plants, microorganisms, animals.
Although natural waters have different characteristics to pure water, tend to have constant characteristics that vary with the seasons, rainfall, etc. But we can say that they have an identity and characteristic parameters.
Wastewater, however is water that has been used by humans in any of its activities and has very different components, quantity or quality than original water had. This wastewater with these abnormal characteristics adversely affects the receiving environment and can cause serious effect on it (surface water, soil, air, groundwater, oceans) and living beings in general.
The wastewater treatment consists on removing the abnormal components of wastewater and obtaining water with natural features. When pollutants including on waste water are more closely included in the water or are smaller, is harder to debug, it require more investment and cost and is more difficult to control the systems of treatment.
Treatment of water require physical, chemical and biologic methods depending on the type of contamination containing wastewater and the degree of purification required.