Water quality In order to evaluate the quality of water bodies, a series of water quality parameters and water quality standards are specified. Such as domestic drinking water, industrial water and fishery water quality standards.
The comprehensive characteristics of water under the environment, namely the physical properties and chemical composition of water. Water in nature is an extremely complex complex composed of various substances (soluble and insoluble substances). The dissolved substances contained in water directly affect many properties of natural water, making water quality better or worse.
There are many types of substances in water, including O2, N2, CO2, and H2S gases dissolved in water, Cl-, Na +, K +, Ca2 +, and Mg2 +; there are trace elements such as Br, I, and F; there are very few contents of Ra and Rn And other radioactive elements; there are mostly colloidal organic matter and suspended solid particles. They vary in content depending on environmental conditions. The water quality of different water bodies is different.
Generally speaking, the composition of river water depends on the type of rock and soil flowing through the area and the source of recharge. The salinity of rainwater recharged rivers is generally low, snowmelt recharge is slightly higher, and groundwater recharge is the highest. Except for the rivers in the inland, less rainy areas, which are strong or highly mineralized, most rivers in the world are moderately mineralized.
The chemical composition of lake water is simpler than that of river water, but the concentration of elements and compounds related to biological activities varies greatly. Under natural circumstances, the nature of the lake will change due to changes in climate or long-term salt balance.
Groundwater has more dissolved substances than river water, and it is often weakly mixed, which is not as uniform as surface water. Groundwater mostly exhibits weakly acidic, neutral, and weakly alkaline reactions, and the pH generally varies between 5 and 9. The salinity of groundwater generally increases with depth, and the ion composition changes from low-salinity freshwater types to highly-salinized saltwater types. The chemical composition of groundwater in various basins in China gradually changes from shallow to deep Increased, the water chemistry type transitioned from bicarbonate type to sulfate type and chloride type.
The chemical composition of seawater is extremely complex, and most of the chemical elements dissolved in seawater exist in an ionic state. Because the volume of seawater is large and can be well mixed, the local conditions have a small impact on the overall ocean, so there is a fixed procedure for the content of major ions, and the relationship between the numbers of various ions is relatively constant. Although the average salt content of modern seawater is roughly the same, it varies from sea area to sea level.
Different applications have different requirements for water quality. Drinking water has high requirements for water quality, and has stricter regulations on water physical properties, total mineralization, total hardness, and the content of bacteria and harmful substances.
Various industries have different requirements for water quality. For example, the textile industry cannot use hard water; the paper industry does not use water containing excessive iron; the cooling water of the open hearth or blast furnace has a large amount of suspended matter that can block the condenser; Will produce scale. Irrigation water requires that the water temperature is close to the soil temperature, and the salt content of the water quality should be lower than the critical mineralization. For example, the increase of soluble salts in water will cause the accumulation of soil salinity and cause soil salinization.
Large-scale hydraulic buildings have proposed a series of new problems for water quality research, such as the prediction of water quality and chemical dynamics of reservoirs, canals, and converted rivers. In addition, water quality research is of great value to medicine (such as the prevention and treatment of endemic diseases) and mining. With the development of the economy, natural water is polluted and water quality deteriorates, causing serious harm to human health and aquatic organisms, which has attracted great attention from governments around the world.