What Is Clear Mucus?

Water, with the chemical formula HO, is an inorganic substance composed of two elements, hydrogen and oxygen. It is non-toxic and drinkable. It is a colorless and odorless transparent liquid at normal temperature and pressure, which is called the source of human life. Water is one of the most common substances on the earth. It is an important resource for all life, including inorganic compounds and human beings. ^[1]

Water is a colorless and odorless liquid, and 72% of the earth's surface is covered by water. Although the content of water in the air is small, it is an important component of air. The density of solid water (ice) (916.8kg / m ³ ) is smaller than the density of liquid water (999.84kg / m ³ ), so ice will float on the water surface, and the volume of water will increase slightly when it freezes. Water reaches its maximum density (999.97kg / m3) at 3.98 ° C. Unlike other liquids, the maximum density appears at the melting point. Water molecules are polar, that is, the positive and negative charge centers of water molecules do not coincide, which makes water a good solvent. ^[2]

There are many different understandings of the origin of water on the earth, each with its own reason, but the truth of the matter remains to be seen by scientists to gather more objective evidence to unravel this mystery. As we all know, 71% of the earth's surface is covered by water. However, where the water on the earth comes from is still an unsolved mystery. ^[7]

Seawater desalination, also known as seawater desalination, is a technology and process for obtaining freshwater from seawater. Desalination can be achieved by taking out fresh water or removing salt from seawater. According to the classification of desalination processes, there are three main types of desalination methods: thermal, membrane and chemical methods. Thermal desalination technologies include multi-stage flash (MSF), multi-effect distillation (MED), pressure steam distillation (VC), and freezing. Membrane desalination technology includes

When we raise the temperature and pressure of water to a critical point (temperature 374.3 ° C, pressure 22.05 MPa), the water will be in a fluid state that is different from both gaseous and liquid and solid states-supercritical state. The state of water is called supercritical water (SCW). ^[13]

Supercritical water oxidation technology (Supercritical water oxidation) is a new advanced oxidation water treatment technology proposed by American scholar Modell in the mid-1980s. It uses water as a medium, a free radical reaction under supercritical conditions, and there is no resistance to mass transfer at the gas-liquid interface, which can increase the reaction rate and achieve complete oxidation. Compared with incineration, wet catalytic oxidation and other technologies, supercritical water oxidation has good solvent performance and transfer performance, which can completely destroy the structure of organic pollutants. It has complete oxidation of pollutants, less secondary pollution, and relatively low equipment and operating costs. And other advantages, is an efficient and environmentally friendly processing technology. ^[14]

Water development process

Modell developed a supercritical water oxidation treatment process at MODAR; from 1990, Gloyna developed and researched a supercritical water oxidation treatment process, and began to carry out industrial wastewater treatment research in May 1994. MODAR was acquired by General Atomics (GA) in 1996. General Atomics (GA) uses this technology to treat military waste. ^[14]

China has been engaged in the research of near (super) critical water oxidation treatment of waste water from the mid-1990s. From the simulation of small-scale equipment experiments to the development of medium-sized equipment, it also began to treat high-concentration industrial wastewater, such as Explosive wastewater and printing and dyeing wastewater have achieved very good treatment effects, but they have just started in engineering applications. There are many domestic patents on supercritical equipment, but due to its high cost, easy corrosion, salt deposition and other reasons, it is still difficult to achieve industrialized large-scale continuous operation. ^[14]

Water applications

As an emerging advanced oxidation technology, supercritical water oxidation technology has considerable advantages. It can completely destroy the structure of organic matter, and is theoretically applicable to any organic-containing waste. In terms of environmental protection, it is mainly used to treat high-concentration organic toxic refractory waste. ^[14]

(1) conventional wastewater field

Wastewater contains more and more toxic and harmful pollutants, with complex components and great harm. Many pollutants are difficult to biodegrade. The use of supercritical water oxidation technology can make toxic and harmful organics in wastewater open loop, bond breaking, substitution, and electronics. Transfer, etc., into small molecules that are easily degradable, or even directly into water and carbon dioxide, to achieve the purpose of treatment. ^[14]

SCWO (Supercritical Water Oxidation) has fast reaction speed and complete oxidative decomposition. Generally it only takes a few seconds to several minutes, even if the organic matter in the wastewater can be completely oxidized and decomposed, the removal rate can reach more than 99%. Therefore, supercritical has an irreplaceable role in the treatment of wastewater. ^[14]

(2) High concentration organic waste liquid

Wastewater containing high concentrations of ammonia nitrogen, phenol and chemical oxygen demand (COD) can be easily destroyed and decomposed during supercritical oxidation. In addition, when supercritical water oxidation technology is used to treat high-concentration organic waste liquid, under normal circumstances, when the organic matter concentration in the wastewater is> 2%, the heat released by its own reaction can maintain the thermal balance of the reaction process, thereby achieving an autothermal reaction. Further energy savings. Therefore, the SCWO technology is particularly suitable for the treatment of high-concentration refractory organic wastewater. ^[14]

(3) Solid waste (including sludge)

Solid waste and sludge produced in wastewater treatment process are rich in organic matter such as fat, protein, cellulose and sugar, as well as a variety of toxic and harmful organic pollutants and heavy metal ions. Its composition is complex and analysis and processing are difficult. The traditional treatment methods are mainly landfill methods. However, there are problems that the treatment effect is not good and secondary pollution is easy to occur. The application of supercritical water oxidation technology not only makes the treatment effect of hazardous waste more significant, but also reduces the cost. At a temperature of 370 to 650 ° C and a pressure of 22 to 26 MPa, the sludge treatment rate reaches more than 99%, and the final products are carbon dioxide and water. ^[14]

Water engineering applications

The supercritical water oxidation technology in the United States has developed rapidly. A large-scale industrialized device has been built and has achieved very good treatment results and economic benefits. As early as 1994, the SCWO (Supercritical Water Oxidation) plant designed by the United States MODEC company for the German pharmaceutical complex could process 5 to 30 tons of organic matter per day. ^[14]

In 1995, a SCWO unit capable of processing a variety of long-chain organics and amines was built in Austin, USA. Japan has also entered the pilot stage of supercritical water research. In 1997, Japan's Mitsubishi Heavy Industries and Tohoku Electric Power Company jointly established a set of pilot plants for the treatment of waste plastics with a processing capacity of 500 kg / d. Kobelco's supercritical water oxidation system was introduced in 1997 from the United States and developed in cooperation with Sweden. It was completed in 2000 with a maximum capacity of 1.1 t / h. SCWO water treatment unit with a processing capacity of 5.7m / d was completed in Sweden in 1999. The German Daimler Chrysler company has built a SCWO unit dedicated to the treatment of e-waste. ^[14]

Sanmenxia High-definition Environmental Protection Technology Co., Ltd. has been engaged in the research of supercritical water oxidation treatment of wastewater in China since 1998, and has carried out small-scale tests on a variety of chemical wastewater. The current pilot plant is 300L / d. Some domestic companies have developed a set of supercritical continuous devices that specialize in the treatment of high-concentration chemical waste liquids, with a water volume of 900 to 1000 L / d. At present, the largest daily production capacity in China is 3.6t. ^[14]

Water problems and improvements

(1) Corrosion issues

SCWO (Supercritical Water Oxidation) operating conditions are very harsh, high temperature and pressure, and extreme pH values (pH = 12), making the equipment extremely corrosive. Studies have shown that the main reasons for corrosion of SCWO stainless steel reactors are high temperature and oxidants. Acids produced when handling organics containing halogens, sulfur or phosphorus can cause severe corrosion in the reactor. The strongly alkaline (pH> 12) aqueous solution is highly corrosive to nickel alloys under supercritical temperature and oxidation conditions. ^[14]

For the acid products produced in the SCWO process, at least one material can adapt to its corrosiveness, but this material has no anti-corrosion ability to other acids. Therefore, by selecting and separating raw materials or applying different materials to different parts of the reactor for different raw materials, corrosion can be minimized. Near the critical point of water, the corrosion rate of the alloy increases exponentially with temperature. As the temperature rises, the corrosion rate increases, but when the temperature exceeds the critical temperature, the corrosion rate decreases with increasing temperature. Therefore, the development of high-performance and high-pressure resistant reactor materials, the study of nickel-based and titanium-based alloy coatings and other composite anticorrosive coatings, and the optimal design of reactors are important ways to prevent corrosion by supercritical water oxidation. ^[14]

(2) The problem of salt deposition

Most salts are more soluble at room temperature, but very low in supercritical water. When the temperature reaches a supercritical state, due to the greatly reduced solubility of the salt, a large amount of precipitates are precipitated, and the deposited salt will cause the reactor to be blocked, causing the equipment to fail to operate normally. The problem of salt deposition has become one of the important issues in the application of supercritical water oxidation. ^[14]

The best way to overcome the clogging problem is to minimize the salt concentration in the wastewater. Low-concentration salt-containing wastewater can be successfully treated by a special reactor, while high-concentration salt-containing wastewater is best treated by other methods, or pre-salted in the front part of the reactor, and then subjected to SCWO reaction. Or study the reactor integrated desalination and continuous slagging system. For example, if the bottom of the reactor is designed as a funnel and a salt discharge port is installed, the salt can be deposited on the bottom and the salt and slagging can be discharged in time. ^[14]

Water application prospects

Compared with the wet oxidation method and incineration method, the supercritical water oxidation technology has low operating cost for waste treatment, requires less floor space, and has lower operation and maintenance costs, and has certain industrial application value. ^[14]

Moreover, the technology has a wide range of applications, simple operation processes, and can be applied to the treatment of a variety of toxic and hazardous substances; the treatment efficiency is high and thorough, and the organic matter can be completely oxidized to carbon dioxide under appropriate temperature, pressure and short residence time, Non-toxic and harmless small molecule compounds such as water, nitrogen and salts, the treatment rate is above 99. 99%; homogeneous reaction, fast reaction rate, short residence time, average residence time is less than 1min. The reactor is simple in structure, small in size, small in area, and saves costs; if the concentration of organic matter in the treated wastewater is> 2%, the heat generated by the reaction can be maintained by the oxidation reaction itself, without external supply The heat saves energy. If the concentration of pollutants is high, the reaction can release more oxidation heat, and the heat can be recovered and reused. ^[14]