6. Pesticide wastewater
The pollution caused by pesticide wastewater to the environment is extremely serious. The purpose of treating pesticide wastewater is to reduce the concentration of pollutants in the wastewater from pesticide production, increase the recovery rate, and strive to achieve harmless treatment. The treatment methods for pesticide wastewater include activated carbon adsorption method, wet oxidation method, solvent extraction method, distillation method and activated sludge method, etc.
However, developing new pesticides that are highly effective, low in toxicity and low in residue is the direction of pesticide development. Some countries have banned the production of organochlorine and organomercury pesticides such as hexachlorocyclohexane, and are actively researching and using microbial pesticides, which is a new way to fundamentally prevent pesticide wastewater from polluting the environment.
7. Metallurgical wastewater
The main characteristics of metallurgical wastewater are large volume, diverse types and complex and variable water quality. Classified according to the source and characteristics of the wastewater, it mainly includes cooling water, acid washing wastewater, washing wastewater (for dust removal, gas or smoke), slag flushing wastewater, coking wastewater, and wastewater resulting from condensation, separation or overflow during production.
The trend of development in the treatment of metallurgical wastewater is:
Develop and adopt new processes and technologies that do not use water or use less water, and are pollution-free or have less pollution, such as dry quenching of coke, preheating of coking coal, and direct desulfurization and decyanation from coke oven gas, etc.
Develop comprehensive utilization technologies, such as recovering useful substances and heat energy from wastewater and waste gas, and reducing the loss of raw materials and fuels;
According to different water quality requirements, through comprehensive balancing and integrated utilization, while improving water quality stabilization measures, continuously enhance the water recycling rate.
Develop new treatment processes and technologies suitable for the characteristics of metallurgical wastewater, such as using magnetic methods to treat steel wastewater. These methods are highly efficient and require less space.
8. Acid and alkali wastewater
Acidic wastewater mainly comes from steel mills, chemical plants, dye factories, electroplating plants and mines, etc. It contains various harmful substances or heavy metal salts. The quality fraction of acid varies greatly, with the lower ones being less than 1% and the higher ones exceeding 10%.
Alkaline wastewater mainly comes from dyeing factories, leather factories, paper mills, oil refineries, etc. Some of them contain organic bases or inorganic bases. The mass fraction of alkali in some of them is higher than 5%, while in others it is lower than 1%. In acidic and alkaline wastewater, in addition to acids and bases, there are often acid salts, base salts, as well as inorganic and organic substances.
Acid and alkali wastewater is highly corrosive and requires proper treatment before it can be discharged.
The principle for treating acidic and alkaline wastewater is:
High-concentration acid and alkali wastewater should be given priority for recycling and reuse. Based on the water quality, quantity and different process requirements, scheduling should be carried out within the factory or regionally, and reuse should be maximized. If reuse is difficult or the concentration is low while the water volume is large, the method of concentration can be adopted to recover the acid and alkali.
Low-concentration acid or alkali wastewater, such as the cleaning water from the acid washing tank or the rinsing water from the alkali washing tank, should undergo neutralization treatment.
For neutralization treatment, the principle of "reducing waste through waste" should be considered first. For example, acidic and alkaline wastewater can be neutralized with each other, or waste alkali (sludge) can be used to neutralize acidic wastewater, and waste acid can be used to neutralize alkaline wastewater. When these conditions are not available, neutralizing agents can be used for treatment.
9. Mineral processing wastewater
The beneficiation wastewater has the characteristics of large volume, high suspended solids content, and a wide variety of harmful substances. The harmful substances are heavy metal ions and beneficiation reagents. The heavy metal ions include copper, zinc, lead, nickel, barium, cadmium, as well as arsenic and rare elements, etc.
The flotation reagents added during the mineral processing include the following categories:
Capping agents. Such as Roxysme (RocssMe), Blackite [(RO)2PSSMe], and Whiteite [CS(NHC6H5)2];
Inhibitory poisons, such as cyanide salts (KCN, NaCN) and sodium silicate (Na2SiO3);
Foaming agents, such as turpentine and cresol (C6H4CH2OH);
Active poisons, such as copper sulfate (CuSO4) and heavy metal salts;
Sulfurizing agents, such as sodium sulfide;
Mineral flocculants, such as sulfuric acid, lime, etc.
The beneficiation wastewater can be effectively treated by the tailings dam to remove the suspended solids, heavy metals and the content of flotation reagents in the wastewater. If the discharge standards are not met, further treatment should be carried out. The commonly used treatment methods include:
Removal of heavy metals can be achieved through the lime neutralization method and the calcination of dolomite for adsorption.
The main flotation reagents can be prepared using the mineral adsorption method or the activated carbon adsorption method.
Wastewater containing cyanide can be treated by chemical oxidation method. The quality fractions of substances or metal salts vary greatly, ranging from less than 1% to more than 10%.
Alkaline wastewater mainly comes from dyeing factories, leather factories, paper mills, oil refineries, etc. Some of them contain organic bases or inorganic bases. The mass fraction of alkali in some of them is higher than 5%, while in others it is lower than 1%. In acid-base wastewater, in addition to acids and bases, there are often acid salts, base salts, as well as inorganic and organic substances.
Acid and alkali wastewater is highly corrosive and requires proper treatment before it can be discharged.
The principle for treating acidic and alkaline wastewater is:
High-concentration acid and alkali wastewater should be given priority for recycling and reuse. Based on the water quality, quantity and different process requirements, scheduling should be carried out within the factory or regionally, and reuse should be maximized. If reuse is difficult or the concentration is low while the water volume is large, the method of concentration can be adopted to recover the acid and alkali.
Low-concentration acid or alkali wastewater, such as the cleaning water from the acid washing tank or the rinsing water from the alkali washing tank, should undergo neutralization treatment.
For neutralization treatment, the principle of "reducing waste through waste" should be considered first. For example, acidic and alkaline wastewater can be neutralized with each other, or waste alkali (sludge) can be used to neutralize acidic wastewater, and waste acid can be used to neutralize alkaline wastewater. When these conditions are not available, neutralizing agents can be used for treatment.
10. Heavy metal wastewater
Heavy metal wastewater mainly comes from the effluents discharged by enterprises such as mines, smelters, electrolysis plants, electroplating plants, pesticide factories, pharmaceutical factories, paint factories, and pigment factories. The types, contents and forms of heavy metals in the wastewater vary depending on different production enterprises.
The principle for treating heavy metal wastewater is:
The most fundamental thing is to reform the production process and avoid or minimize the use of highly toxic heavy metals.
Secondly, by adopting reasonable process flows, scientific management and operation, the usage of heavy metals and the amount of waste water leakage can be reduced, and the amount of wastewater discharged outside should be minimized. Heavy metal wastewater should be treated on-site at the generation location and not mixed with other wastewater to avoid complicating the treatment process. Even more importantly, it should not be directly discharged into the urban sewer without treatment to prevent the expansion of heavy metal pollution.
The treatment of heavy metal wastewater can generally be divided into two categories:
One approach is to convert the dissolved heavy metals in the wastewater into insoluble metal compounds or elements, which can then be removed from the wastewater through precipitation and flotation. Applicable methods include neutralization precipitation, sulfide precipitation, flotation separation, electrolytic precipitation (or flotation) method, and membrane electrolysis method, etc.
Second, the heavy metals in the wastewater can be concentrated and separated without changing their chemical forms. The applicable methods include reverse osmosis, electrodialysis, evaporation, and ion exchange, etc. These methods should be used individually or in combination based on the quality and volume of the wastewater.
