The majority of urban water plants use traditional conventional water treatment processes, whose main functions are turbidity removal, color removal and sterilization, and the removal of dissolved organic pollutants in water is limited. In recent years, domestic and foreign countries have developed some purification treatment technologies for contaminated water, which can be mainly divided into adsorption method, oxidation method, biological method and membrane method.
Activated carbon adsorption is a micro-pollution removal technology that was applied to production earlier. Its principle is to use the huge specific surface area of activated carbon to adsorb organic pollutants in water. The use of granular activated carbon is realized by an activated carbon filter bed, which is placed after the sand filter or replaces the existing sand filter bed. After the contaminated water passes through the activated carbon filter bed, organic pollutants are trapped in the activated carbon filter bed. However, due to the heavy pollution of water sources in my country, activated carbon will become saturated and invalid soon after use. When water pollution is serious, activated carbon can only run for a few weeks. The adsorption performance of activated carbon can be restored through regeneration, but the replacement of activated carbon is frequent and the regeneration cost is high. Powder activated carbon has low capital and equipment investment in application, and is flexible and convenient to use. However, activated carbon is difficult to recycle, and operating costs are relatively high during use, and it is only used during periods of severe pollution. In recent years, people have pre-coated powdered activated carbon on some carriers, which improves the utilization rate of powdered activated carbon and also improves the removal efficiency of organic pollutants.
Powdered activated carbon can gradually form biological activated carbon during operation, and microorganisms continue to biodegrade organic pollutants adsorbed on the surface of activated carbon, which can effectively extend the life of activated carbon. Pre-oxidation can improve the biodegradability of organic pollutants and extend the life cycle of activated carbon.
Oxidation decontamination method uses strong oxidants to decompose organic pollutants in water. The oxidation process generally has a good decontamination effect, has a wide range of applications, and is relatively widely used. At present, the oxidants that can be used for water supply treatment mainly include chlorine, chlorine dioxide, potassium permanganate, hydrogen peroxide and ozone. Their oxidation-reduction potentials under standard conditions are 1.36V, 1.50V, 1.69V, 1.77V and 2.07V.
Obviously, ozone has the highest oxidation-reduction potential (oxidation potential +2.07 V) among several oxidants that can be used for water treatment, so it has the strongest oxidizing property and strong adaptability to water quality. It has been widely used in developed countries. Used in water supply treatment. Ozone can oxidize and destroy a variety of organic pollutants in water, but it can only oxidize and decompose organic pollutants that contain unsaturated bonds or some aromatics in water. Quite a lot of stable organic pollutants (such as pesticides, halogenated organics and nitro Compounds etc.) are difficult to be oxidized and decomposed. Although ozone oxidation technology has been researched for many years in our country, it has been difficult to promote and apply in our country due to the large investment and high operating and management costs.
The ability of hydrogen peroxide to decontaminate is very low, but it has strong oxidizing ability under acidic conditions when combined with ferrous iron. Because it is difficult to adjust pH in water treatment, the application of hydrogen peroxide is limited. Chlorine dioxide has a strong disinfection ability, but it is reduced to chlorite when oxidized with organic matter, which has a destructive effect on red blood cells. Chlorine has a certain oxidizing effect on organic matter, and has been used as a pre-oxidant for water treatment for a long time. However, due to the effect of chlorine and a variety of organic pollutants in raw water, a series of halogenated organic compounds that are harmful to humans are generated, so it is pre-chlorinated Gradually restricted by countries. The Ministry of Construction is studying the chemical pre-oxidation decontamination technology, compared the relative decontamination efficiency of various chemical pre-oxidation technologies, and found that certain chemical pre-oxidation composite technologies have good effects on removing trace organic pollutants in water.
The use of photocatalytic oxidation to degrade trace organic pollutants in water is generally applicable to small water purification facilities, but the application equipment investment in large-scale water plants is relatively large.
Biological pretreatment technology is the use of microorganisms to metabolize and decompose organic pollutants in water before or during the conventional water treatment process to make them inorganic. During the “Eighth Five-Year Plan” and “Ninth Five-Year Plan” period, my country has carried out systematic research work on various biological pretreatment technologies, which shows that for water with high biodegradability, biological pretreatment can significantly remove ammonia nitrogen in the water, which has a negative effect on organic pollutants. Certain removal effect. Productive experiments have been carried out in South my country. When the organic pollutants in the water are highly biodegradable, the water quality can be significantly improved; but for the raw water polluted by industrial wastewater and low biodegradability, biological pretreatment is used to remove pollution Low efficiency. Biological pretreatment has limited effects in northern areas, especially low-temperature water. Due to low microbial activity and longer residence time, equipment investment is relatively large.
Membrane technology is a water supply treatment process developed in recent years. The role of the membrane in decontamination is to trap organic molecules in water to one side of the membrane through its small pore size and remove them from the water phase. The membranes with decontamination function mainly include nanofiltration membranes and reverse osmosis membranes. At present, membrane treatment technology has a large investment in equipment and high membrane replacement costs. It is generally only used for small-scale water purification facilities, and it is difficult to apply to large-scale water plants. In addition, while membrane filtration removes harmful components (micro-pollutants) in the water, it also removes inorganic ions in the water (such as reverse osmosis). Long-term drinking of high-purity water is not good for your health.
In short, there are still limited new technologies and equipment that can be promoted and applied in production to cost-effectively improve drinking water quality.