Basic explanation:

Water treatment refers to the physical and chemical measures taken to make water quality meet certain standards of use. The minimum standard for drinking water is set by environmental protection departments. Industrial water has its own requirements. Physical characteristics such as temperature, color, transparency, smell and taste are the basic criteria for judging water quality.

Purpose of water treatment:

The purpose of water treatment is to improve water quality to meet specific standards. Depending on the method used, water treatment can be categorized into physical, chemical, and biological treatments. Based on the object or purpose, it can be divided into two main categories: water supply treatment and wastewater treatment. Water supply treatment includes both drinking water and industrial water treatment; wastewater treatment is further divided into domestic sewage treatment and industrial wastewater treatment. Among these, those closely related to thermal technology include boiler feedwater treatment, makeup water treatment, turbine main condensate treatment, and circulating water treatment, all of which fall under the category of industrial water treatment. Water treatment plays a crucial role in advancing industrial production, enhancing product quality, protecting the human environment, and maintaining ecological balance.

Water treatment methods:

Water treatment encompasses both sewage and drinking water treatment. In some regions, sewage treatment is further divided into two categories: sewage treatment and reclaimed water reuse. Commonly used water treatment chemicals include polyaluminum chloride, polyaluminum ferric chloride, basic aluminum chloride, polyacrylamide, activated carbon, and various filter media. The effectiveness of water treatment can be assessed by water quality standards. Water treatment involves processing raw water (source water) to meet the quality requirements for finished water, whether it is for domestic use, industrial use, or discharge. When the processed water is intended for domestic or industrial use, it is referred to as water supply treatment; when it is for wastewater treatment, it is called wastewater treatment. The primary goal of wastewater treatment is to ensure that the treated wastewater is either discharged into water bodies or land, or reused (see wastewater disposal and reuse).

In circulating water systems and water regeneration treatment, raw water is wastewater and finished water is water. The process has both water treatment and wastewater treatment properties. Water treatment also includes the treatment and final disposal of wastewater and sludge produced during the treatment process (see sludge treatment and disposal), and sometimes the treatment and discharge of exhaust gas.

Water treatment methods can be summarized in three ways:

① The most common is to obtain the required water quality by removing part or all of the impurities in the raw water;

② By adding new components to the raw water, the required water quality is obtained through physical or chemical reactions;

③ The processing of raw water does not involve the removal of impurities or the addition of new components.

Impurities in water and treatment methods:

Impurities in water include coarse materials, suspended solids, colloids, and dissolved substances. Coarse materials include floating aquatic plants, garbage, large aquatic organisms, sand and gravel from wastewater, and large pieces of debris in rivers. In water supply projects, coarse impurities are removed by the facilities of the water intake structures and are not included in the scope of water treatment.

In wastewater treatment, the removal of coarse impurities is typically part of the water pretreatment. Suspended solids and colloids include sand, algae, bacteria, viruses, and other non-soluble substances present in the water or generated during the treatment process. Dissolved substances include inorganic salts, organic compounds, and gases. There are various methods for removing impurities from water, and the effectiveness of these methods can be roughly categorized by the size of the impurities. Due to the significant differences in the types and concentrations of impurities in raw water compared to the allowable levels in treated water, the water treatment processes vary significantly.

For domestic water (or urban public water supply), raw water from high-quality sources, such as well water or well-protected water reservoirs, only needs to be disinfected to become potable water. Raw water from ordinary rivers or lakes must first remove turbidity-causing impurities like silt before disinfection. Raw water with more severe pollution also requires the removal of organic pollutants. Raw water containing iron and manganese, such as some well water, must have these elements removed. Domestic water can meet the water quality standards for general industrial use, but industrial water often requires additional processing, such as softening and desalination.

Water treatment development process:

In ancient times, without advanced water treatment technology, people used simple methods like simple screens and natural sedimentation to reduce the spread of diseases through water. Over time, they discovered that sand could filter out fine suspended particles, leading to the development of chemical coagulation pretreatment.

As human civilization continues to advance, the waste generated by humans and the extensive destruction of the environment have led to severe water pollution. When various infectious diseases spread through water, causing many people to fall ill or die, people realized the critical importance of water treatment. This realization has driven the gradual development of water treatment technologies.

It has been found that simple chemical and physical methods are inadequate for treating this type of wastewater, making the development of new water treatment technologies urgently needed. Scientists worldwide have started researching water treatment methods, starting with wastewater aeration experiments, followed by the biological film method, then artificial biological treatment methods, and now advanced technologies such as targeted ion exchange and electrochemical methods.

Due to the rapid economic development in recent decades, it has become evident that traditional water treatment methods can no longer meet societal water demands. As a result, biotechnology has been introduced into water supply processes. Moreover, with the rise of water resource crises, the reuse of wastewater has gained attention. To improve water quality and enhance the environment, ecological principles-based technologies, such as land irrigation and oxidation ponds, have also been developed.