3.Characteristics of oily wastewater and its treatment methods

Oily wastewater mainly comes from petroleum, petrochemical, iron and steel, coking, gas generating station, machining and other industrial sectors. Except for the relative density of heavy tar above 1.1, the relative density of oil pollutants in wastewater is less than 1. Oil usually exists in three states in wastewater. (1) Oil slick, oil droplet size greater than 100 um, easy to separate from wastewater ;(2) dispersed oil, oil droplet size between 10~100 um, suspended in water ;(3) emulsified oil, oil droplet size less than 10 um, not easy to separate from wastewater. Waste due to different industrial sectors  The concentration of oil in water varies greatly, such as wastewater produced in refining process, oil content is 150~1000 mg\L, tar content in coking wastewater is about 500~800. Therefore, the treatment of oily wastewater should first use cadmium oil tank, recovery oil slick or heavy oil, treatment efficiency is 60~80, oil content in effluent is about 100~200 mg\L; emulsified oil and dispersed oil in wastewater are difficult to treat, Therefore, to prevent or reduce the phenomenon of emulsification. One of the methods is to reduce waste during production  The emulsification of oil in water; second, in the treatment process, as far as possible to reduce the number of pumps to lift the wastewater, so as not to increase the degree of emulsification. The treatment methods are usually air floatation and demulsification.

4.Characteristics of cyanide-containing wastewater and its treatment methods

Cyanide wastewater mainly comes from electroplating, gas, coking, metallurgy, metal processing, chemical fiber, plastics, pesticides, chemical industry and other departments. Cyanide wastewater is a kind of industrial wastewater with great toxicity, which is unstable in water and easy to decompose. Inorganic cyanide and organic cyanide are local toxic substances, and human ingestion can cause acute poisoning. The lethal dose of cyanide to human body is 0.18 g, potassium cyanide is 0.12 g, the mass concentration of cyanide to fish is 0.04~0.1 mg\L. in water The main treatment measures of cyanide-containing wastewater are as follows :(1) reforming the process to reduce or eliminate the effluents of cyanide-containing wastewater, such as using cyanide-free electroplating method to eliminate electroplating Workshop industrial wastewater. (2) Wastewater with high cyanide content should be recycled, and wastewater with low cyanide content should be purified and treated before discharge. The recovery methods include acidified aeration and lye absorption, steam desorption and so on. The treatment methods include alkaline chlorination, electrooxidation, pressurized hydrolysis, biochemistry, biological iron, ferrous sulfate, air blowing hair loss and so on. The alkaline chlorination method is widely used, the ferrous sulfate method is not thorough and stable, and the air blowing method not only pollutes the atmosphere, but also fails to meet the discharge standard.