Characteristics of underground water sources

1.1 Introduction to groundwater

– Water is a very necessary role and need in human and biological life, it participates in all activities of natural processes and affects all changes of organisms on earth, without water. there will be no life. As society develops, people’s need for water is also increasing.

– Therefore, water sources used in human activities are divided into many different types: water for drinking needs requires high quality, ensuring it does not affect human health; Water sources used for bathing and washing may have lower requirements. In addition, our country is an agricultural country, so the demand for water for agricultural production is very large; Besides, water is also used for industry, transportation and other activities. Water used to supply domestic and production needs has very different qualities, including surface water and groundwater. These water sources hardly meet quality requirements; Therefore, it is necessary to know their composition and properties to proceed with treatment to achieve quality requirements and meet the purpose of water use. For water supply purposes, people often use underground water sources, so many underground water treatment technologies have been applied to meet human life needs.

– Groundwater has been exploited and used by humans for thousands of years. Through the ages, in all parts of the world, humans have created many different methods to exploit underground water, using all kinds of energy (animal power, human power, wind power, water power, etc.) Solar,…). Today, worldwide about 60% of drinking water, 15% of household water and 20% of irrigation water come from underground sources. In most arid regions of the world, groundwater is the main source of water. In addition, it also provides at least 20% and sometimes more than 30% of the total volume of water used in industrial countries. Currently in the world, people exploit about 600 – 700 billion m3 of groundwater every year, more than any other resource exploited from soil cages. In Vietnam, underground water resources are relatively abundant, many places have good water quality that can be exploited for direct use without needing treatment.

1.2 Characteristics, composition and properties of underground water sources

1.2.1 Groundwater characteristics in Vietnam

– Vietnam is a country with underground water sources that are quite rich in reserves and quite good in quality. Groundwater exists in holes and cracks in soil and rock formed during the sedimentation period or by permeation from surface water, rainwater… Groundwater can exist several meters above the ground. meters to several tens of meters or hundreds of meters.

– Groundwater is a part of the hydrological cycle that enters soil and rock systems from the ground or surface water and for a long time groundwater is considered a “clean water source” – can be used for drinking. drinking activities. In fact, this water source often contains concentrations of elements much higher than potable water standards, notably Fe, Mn, H2S,… so groundwater needs to be treated before distribution and use. use.

1.2.2 Characteristics of groundwater

a. Temperature

Water temperature is a quantity that depends on environmental and climatic conditions. Temperature affects water treatment processes and consumption demand. Surface water often has a temperature that changes depending on the environment. The temperature in surface water sources in the South is relatively stable (26 to 29 oC).

b. Color degree

Color is usually colorless. The color is caused by the presence of humic acid substances. Insoluble Iron and Manganese compounds make the water reddish-brown, Humic substances cause yellow color. The commonly used color measurement unit is platinum – cobalt. The apparent color in water is usually caused by suspended substances in the water and is easily removed by filtration. Meanwhile, to remove the true color of water (created by dissolved substances), combined physical and chemical measures must be used.

c. Turbidity

Usually changes by season. Turbidity units are usually mgSiO2/L, NTU, FTU. Suspended solids content is also a quantity correlated to water turbidity.

d. Taste

Taste in water is often caused by chemical compounds, mainly organic compounds or products from material decomposition processes.
Depending on the composition and content of dissolved mineral salts, water can taste salty, sweet, acrid, bitter…

e. Viscosity

Viscosity is a quantity that represents the internal friction force, generated during the movement between liquids. This is the main factor causing pressure loss. Therefore it plays an important role in the water treatment process. Viscosity increases as the content of dissolved salts in water increases and decreases as temperature increases.

f. Electrical conductivity

Water has poor electrical conductivity. The conductivity of water increases with the content of dissolved minerals in the water and fluctuates with temperature. This property is often used to evaluate the total dissolved mineral content in water.

1.2.3 Chemical properties of water source

a. PH

pH is an index that characterizes the concentration of H+ ions in a solution, often used to indicate the acidity and alkalinity of water.

The pH of water is related to the presence of certain metals and gases dissolved in the water. At pH < 5, depending on geological conditions, some water sources may contain Iron, Manganese, Aluminum in dissolved form and some gases such as CO2, H2O exist in free form in water. In addition, when pH is increased and oxidizing agents are added, metals dissolved in water turn into precipitates and are easily removed from water by sedimentation.

b. Alkalinity

– Total alkalinity is the total content of Bicarbonate ions, Hydroxides and anions of salts of weak acids. Because the amount of these salts in water is very small, they can be ignored.

– At a certain temperature, alkalinity depends on the pH and the content of free CO2 gas in the water.

– Bicarbonate alkalinity contributes to buffering the aqueous solution. The water source has high buffer properties. If chemicals such as alum are used during the treatment process, the pH of the water will change little, so chemicals used to adjust pH will be saved.

c. Stiffness

Water hardness is a measure of the amount of Calcium and Magnesium ions in the water. Using water with high hardness in daily life will cause waste of soap because Calcium and Magnesium react with fatty acids to form insoluble compounds. In production, hard water can create scale in boilers or cause precipitation that affects product quality.

d. Oxidation

The degree of oxidation is a quantity to roughly assess the level of pollution in a water source. That is the amount of oxygen needed to oxidize all organic compounds in water. The oxidant commonly used to determine this indicator is potassium permanganate (KMnO4).

e. Nitrogen-containing compounds

– The process of decomposing organic matter produces ammonia, nitrite and nitrate. Therefore, these compounds are often considered indicators used to identify the level of contamination of water sources. When first contaminated, in addition to high value indicators such as oxidation level and ammonia, there is also a little nitrite and nitrate in the water. After a while, ammonia and nitrite are oxidized into nitrate.

– High nitrate concentration is a good nutritional environment for algae and seaweed to grow, affecting the quality of water used for domestic use. Children drink water with high nitrate levels which can affect the blood (methaemoglo binaemia). According to World Health Organization regulations, nitrate concentration in drinking water must not exceed 10 mg/l.

f. Phosphorus compounds

In natural water, the most common is phosphate. This is a product of biological decomposition of organic matter. The source of phosphate introduced into the water environment is from domestic wastewater, wastewater from some industries and fertilizers used in fields. Phosphate is not a chemical toxic to humans, but the existence of this substance in high concentrations will hinder the treatment process, especially the active ingredients of sedimentation tanks. Phosphate concentration in unpolluted water sources is usually < 0.01mg/l.

g. Chloride

Chloride makes water taste salty. This ion penetrates into water through the dissolution of mineral salts or is affected by salinization of underground aquifers or in rivers near the sea. Using water with high chloride content can cause kidney disease. In addition, water containing a lot of chloride is aggressive to concrete.

H. Iron

Natural water, mainly groundwater, can contain iron with concentrations up to 40 mg/l or higher. With iron content higher than 0.5 mg/l, water has an unpleasant fishy smell, yellows clothes when washing, and damages products of the textile, paper, film, and canned food industries. Precipitated iron deposits can clog or reduce the transport capacity of water pipes.

i. Manganese

Like iron, manganese is often present in groundwater in the form of Mn2+ ion, but at relatively low concentrations, rarely exceeding 5 mg/l. However, manganese content in water greater than 0.1 mg/l will cause harm in use, just like the case of water containing high iron content.

j. Aluminum

When it contains a lot of dissolved aluminum, the water is often clear blue and tastes very sour. Aluminum is toxic to human health. Drinking water with high aluminum content can cause brain diseases such as Alzheimer’s.

1.2.4 Microbiological criteria

– In natural water there are many types of bacteria, viruses, algae, algae and protozoa, which enter the water from the surrounding environment or live and grow.

developed in the country. Some disease-causing organisms must be removed from the water before use.

– Several microbial indicators of fecal pollution can be used to assess contamination from garbage, human and animal feces:

✓ The typical coliform group is Escherichia Coli (E.Coli)
✓ The typical Streptococci group is Streptococcus Faecalis
✓ The typical group of Sulfite-reducing Clostridia is Clostridium Perfringents

1.3 Water supply standards after treatment

After treatment, the water supply meets QCVN 01-1:2018/BYT – National technical regulations on water quality.