Industrial waste water | Chromaticity

Chromaticity (chromaticity) is the color of water, refers to the soluble substances in the water or colloidal substances appear like yellow and yellowish brown degree. The chromaticity of water is divided into two kinds: surface color and true color. Surface color refers to the color of water without removal of suspended matter, including the color produced by dissolved matter and indissolved suspended matter. True color refers to the color of water after the removal of suspended matter, which is produced only by soluble colored substances. Clean or very low turbidity of water, the true color and surface color close; The difference between industrial wastewater and domestic sewage with deep coloring and more suspended matter is great.

Physical and chemical tests of water quality usually measure only true color. Clean natural water is colorless and transparent when the water layer is shallow, and light blue or light green when it is deep. Natural water often presents different colors is caused by the decomposition of organic matter in water and contains inorganic matter, the most common is the color of organic complex produced by the decomposition of natural organic matter.

For example, plant organic matter dissolved in water will make the water pale yellow, even brown yellow; Water with high iron compounds is yellow; Hydrogen sulfide in water is oxidized to release sulfur, which can make water light blue; The black color of some swamp waters due to the combination of tannic and gallic acids in plants with iron salts; The presence of a large number of algae in the water will show different colors due to the type of algae, such as chlorella to make the water is green, diatoms are brown green, dinoflagellates are dark brown, blue-green algae are emerald; Water polluted by industrial wastewater may take on the characteristic color of the industrial wastewater.

Water has color, it marks the water is polluted, colored water, affect people's psychology, so that the drinker has an unpleasant feeling; It also reduces the transparency of water, affects industrial water use, and reduces the quality of some light industrial products such as papermaking and textile.Chroma is one of the main pollution indicators, water quality standards in some countries, the requirements of chroma between 5 ~ 20 degrees. The sanitary standard of water quality in China stipulates that the color of drinking water does not exceed 15 degrees.

From the current application of wastewater treatment technology, the effective removal of wastewater chroma methods include adsorption method, coagulation method, biological method, membrane separation method, chemical oxidation method and electric flocculation method. Adsorption and decolorization: adsorption and decolorization technology depends on the adsorption of adsorbent to remove the chroma. Commonly used adsorbents include renewable adsorbents such as activated carbon and ion-exchange fibers, and non-renewable adsorbents such as various natural minerals (bentonite, diatomite), industrial wastes (coal cinder, fly ash) and natural wastes (charcoal, sawdust), etc.

At present, adsorbents used for adsorption and decolorization mainly rely on physical adsorption, but ion-exchange fibers and modified bentonite also have chemical adsorption. Flocculation and decolorization: Flocculation and decolorization are carried out by using flocculant to flocculate the precipitation of the colored material in the wastewater. Flocculation and decolorization technology is a widely used decolorization technology with low investment cost, less equipment and large processing capacity.

Inorganic coagulants include metal salts and inorganic polymer flocculants. Widely used metal salts are aluminum salts and iron salts; Inorganic polymer flocculant is a new type of water treatment agent developed on the basis of the traditional metal salt flocculant. It has the advantages of strong adaptability, non-toxicity, double efficiency and relatively low price, and has been rapidly developed and widely used.

Organic polymer flocculant, polyacrylamide (PAM) is the most used, it has non-ionic, cationic and anionic types of three. Oxidation decolorization: including chemical oxidation, photocatalytic oxidation and ultrasonic oxidation. Although the specific process is different, but the decolorization mechanism is the same.

Chemical oxidation is a mature method in research at present. The oxidizer generally uses Fenton reagent (Fe2+-H2O2), ozone, chlorine gas, sodium hypochlorite and so on. Decolorization by chemical oxidation means that the oxidation of chlorine, ClO2, O3, H2O2, HClO4 and hypochlorite can break or change the chemical structure of chromaticity groups in wastewater under certain conditions, so as to achieve the purpose of wastewater decolorization.