Characteristics of chemical wastewater and principles of wastewater treatment
With the rapid development of economy, the environmental pollution caused by the production process of chemical products is increasing, and the harm to human health is becoming more and more common and serious. In particular, most of the organic substances discharged from the production process of fine chemical products (such as pharmaceuticals, dyes, daily chemicals, etc.) are complex, toxic, harmful and biodegradable substances. Therefore, it is difficult to treat chemical wastewater.
The basic characteristics of chemical wastewater are high COD, high salinity and toxicity to microorganisms. It is a typical refractory wastewater. It is the research focus and hotspot of water treatment technology at present. The characteristics of chemical wastewater are analyzed as follows:
(1) The composition of water quality is complex, there are many by-products, and the reaction raw materials are often solvents or compounds with ring structure, which increases the difficulty of wastewater treatment;
(2) The high content of pollutants in wastewater is caused by incomplete reaction of raw materials and a large number of solvent media used in raw materials or production entering the wastewater system;
(3) There are many toxic and harmful substances, and many organic pollutants in fine chemical wastewater are toxic and harmful to microorganisms, such as halogen compounds, nitro compounds, dispersants or surfactants with bactericidal effect, etc;
(4) There are many biodegradable substances, B is lower than C, and the biodegradability is poor;
(5) The color of wastewater is high.
Chemical wastewater treatment method
Wastewater treatment technology has been developed for more than 100 years. The types and amount of pollutants in wastewater are increasing with the development of social economy and the improvement of living standards. Wastewater treatment technology has changed with each passing day with the development of science and technology. At the same time, the old wastewater treatment technology is also being innovated and developed. In particular, the pollutants in chemical wastewater are diverse, and it is often impossible to remove all the pollutants in the wastewater by one process. It is very difficult to treat chemical wastewater to the discharge standard by physicochemical process, and the operation cost is high; Chemical wastewater contains more refractory organics, has poor biodegradability, and the water quantity and quality of chemical wastewater change greatly. Therefore, the effect of direct biochemical treatment of chemical wastewater is not very ideal.
In view of the characteristics of chemical wastewater treatment, we believe that appropriate pretreatment methods should be adopted according to the actual wastewater quality, such as flocculation, internal electrolysis, electrolysis, adsorption, photocatalytic oxidation and other processes, so as to destroy the refractory organic matter in the wastewater and improve the biodegradability of the wastewater; Then, biochemical methods, such as SBR, contact oxidation process and a / O process, are combined to carry out advanced treatment of chemical wastewater.
At present, the domestic research on the treatment of chemical wastewater also tends to adopt the combined process of multiple methods. For example, internal electric bait coagulation sedimentation anaerobic aerobic process is adopted to treat pharmaceutical wastewater, macroporous adsorption resin adsorption and anaerobic aerobic biological treatment flocculation sedimentation method are adopted to treat organic chemical wastewater, flocculation electric bait method is adopted to treat ephedrine wastewater, ozone biological activated carbon process is adopted to remove organic pollutants in water The combination of photocatalytic oxidation, internal electric bait and SBR has achieved good results in the treatment of high concentration chemical wastewater.
Chemical wastewater has complex components and large changes in water quality and quantity. With the increasingly strict requirements of the state for its treatment up to the standard, it is difficult for people to obtain a good treatment effect with one method. Various combined treatment technologies are adopted for the treatment of chemical wastewater according to the actual situation. To optimize the processing system.
Water pollution index
Water pollution index is a numerical indicator to measure the degree of water pollution, and it is also an important basis to control and detect the operation state of water treatment equipment. Among them, the most commonly used water pollution indicators are (8):
Biochemical oxygen demand (BOD): refers to the amount of free oxygen consumed by aerobic microorganisms to degrade organic matter per liter of water after a certain number of days at 20 ℃ under the condition of saturated oxygen. The common unit is mg / L. 5 days is often used as the standard time for BOD determination, and BOD5 is used.
Chemical oxygen demand (COD): refers to the amount of oxygen consumed by oxidizing organic matter to H2O and CO2 with strong oxidant. The commonly used oxidants are potassium dichromate or potassium permanganate, which are respectively expressed as CODcr or cod and CODMn (also known as oxygen consumption, OC), and the unit is mg / L.
Total oxygen demand (TOD): when organic matter is completely oxidized, the oxygen consumed when C, h, N and s are oxidized to CO2, H2O, no and SO2 respectively, unit: mg / L.
Total organic carbon (TOC): refers to the total carbon content of organic pollutants in water, expressed in carbon content, with the unit of mg / L.
Suspended solids (SS): substances left on the filter membrane or filter paper after water sample filtration, unit: mg / L.
PH: indicates the acidity and alkalinity of sewage.
Toxic substances: refers to the content of substances harmful to organisms contained in water, such as cyanide, arsenide, mercury, cadmium, chromium, lead, etc., in mg / L.
Number of Escherichia coli: refers to the number of Escherichia coli contained in each liter of water, unit: piece / L.
Classification of wastewater treatment methods
According to the characteristics of different pollutants, various wastewater treatment methods have been developed, especially the treatment of chemical wastewater. These treatment methods can be divided into four categories according to their working principles, namely physical treatment method, chemical treatment method, material chemical treatment method and biological treatment method.