Coking wastewater is a high-concentration organic wastewater produced in the process of coal-made coke, gas purification and coking product recovery. Its composition is complex, containing a large amount of organic pollutants such as Sanskrit, biphenyl, pyridine, indole and quinoline, as well as toxic and harmful substances such as cyanide, inorganic fluoride ion and ammonia nitrogen. Among them, the remaining ammonia produced during the ammonia distillation process is used as Main source. Distilled ammonia wastewater is the wastewater discharged after mixing the remaining ammonia water for distillation. The remaining ammonia water is the most important source of phenol cyanide wastewater in the coking plant. It is high-concentration phenol water containing ammonia, which is discharged by the circulating ammonia pump in the condensing blast section and sent to the remaining ammonia water storage tank. The remaining ammonia water is mainly composed of three parts: the wet stored water on the surface of the coal charged in the furnace, the combined water produced by the coal charged in the furnace and the oily process waste water added to the gas suction pipe and the circulating oxygen pump in the gas collecting pipe. 14% of furnace coal can be installed by multiplying the total amount of remaining ammonia. Polyacrylamide for coking wastewater, After the remaining ammonia water is mixed in the storage tank with the process wastewater sent from other production devices, it is called mixed remaining ammonia water. Where to mix the remaining ammonia water, some are directly distilled ammonia, some are first dephenol and then distilled ammonia, some are combined with ammonia-rich water to distill ammonia, and some are desulfurized rich liquid together with desulfurized rape ammonia, deacidification and degreasing before ammonia vaporization . The coking plant also contains some other wastewater, which accounts for a small proportion and has low pollution indicators.
The holding point of wastewater: Divided from the level of energy contained in substances, coking wastewater contains three types of substances. The first category is monocyclic and polycyclic organic compounds. There are many types of such substances, among which phenols are the most content, and the others are trace amounts. Such substances contain relatively high energy, most of which can be removed by chemical or physical chemical methods such as incineration, wet oxidation, ultrasound, ozone, liquid chlorine, chlorine dioxide, ion exchange, etc. However, the operation of these methods The cost is extremely expensive. Before the 1980s, phenols were extracted from wastewater by solvent dephenolization or steam dephenolization at home and abroad, and the remaining phenol and other organic substances in the wastewater after decoating were removed by biochemical methods. At that time, this was a relatively economical and effective way to control pollution. However, after the 1980s in the last century, due to the depression of the phenol market, all new coking projects, except for very few plants, eliminated wastewater solvent or steam dephenolization, and replaced them all with biochemical methods. It is important to note here that phenol is very easy to be used by microorganisms. Coking wastewater with a phenol content of 400~1000mg/L can reduce the concentration of phenol in wastewater with an aeration time of 2~6h. Below 1mg/L; With a high concentration of phenolic water with a wind concentration of 20000mg/L, microorganisms can reduce the wind concentration to about 1mg/L within three days and nights.
In recent years, pre-denitrification biological denitrification process has been widely adopted in China, so phenolic organic matter has become an indispensable source of energy and carbon source for microbial facultative oxygen denitrification. Although phenol is a scarce and important chemical and pharmaceutical resource, due to the need for biological denitrification of wastewater, phenol is not extracted from coking wastewater in newly built coking plants.
For the biological denitrification of coking wastewater, it is necessary to additionally add organic matter such as methanol to the wastewater. Obviously, this approach is uneconomical. It is biased to think that phenolic organics in coking wastewater are difficult to biodegrade. Especially in some coking wastewater treatment plans, some physical or chemical treatment measures are added before biochemical treatment, which is to remove phenols. However, I don’t know that such a process will not only increase a lot of capital investment and pay extremely expensive operating costs, but more importantly, its process has destroyed the foundation of the biological pre-denitrification of coking wastewater, making it impossible to realize coking wastewater. The biological denitrification. The production practice has proved that in the biological denitrification treatment of coking wastewater, most of the phenolic substances have been removed.
The second type of substances in coking wastewater are carbon-containing inorganic compounds, mainly cyanide and thiocyanide, especially the content of thiocyanide is extremely high.
The electrons in the N blue C" bond have lower energy, so the bond structure is relatively stable, and its breaking and
Reorganization needs to consume energy and be carried out under special environmental conditions. In fact, these substances are organic and inorganic amphoteric compounds, and their hydrolyzed products are formic acid, NH4+ and So42-, which contain lower energy than organic substances. Although these substances can be removed by many physical or chemical methods, they are very easy to cause secondary pollution of sulfur and nitrogen oxides.
The content of thiocyanide is relatively high in coking wastewater, which is ignored by many people engaged in coking wastewater. In fact, thiocyanide in coking wastewater is the second largest source of COD substances after phenol. Whether thiocyanide is completely removed is directly related to the COD content of the treated water. Thiocyanide is more difficult to be removed by microorganisms. Generally, only when the acyl concentration in coking wastewater is below 10mg/L, can thiocyanide be used by microorganisms, and a certain hydraulic retention time is required to ensure it. In the biological treatment of wastewater, thiocyanide is also a major source of NH3-N. Thiocyanide is a compound containing one carbon. When treating a single sulfur-containing cyanide wastewater, it is generally completed by a dedicated strain of desulfurizing cyanide, but in a phenol-thiocyanide combined biological treatment system , There is no need for such specific bacteria. In the biological treatment of coking wastewater, the removal of sulfur cyanide is a prerequisite for the biological oxidation of ammonia nitrogen. The coking wastewater treatment process that does not consider the removal of sulfur cyanide is an incomplete coking wastewater treatment process. For the biological denitrification treatment process, it may be a failed process.
The third type of substance in coking wastewater is carbon-free ammonia-nitrogen inorganic compounds. The energy contained in this type of substance is much lower than that of organic matter and carbon-containing inorganic matter. Therefore, it is difficult to be oxidized by wet oxidation and liquid chlorine And many other physical and chemical methods to remove. Only by creating conditions suitable for the survival and growth of bacteria that oxidize ammonia and nitrogen, and cultivating various required bacterial species, can it be possible to achieve aerobic biological oxidation of ammonia.
Due to the high concentration of ammonia nitrogen contained in coking wastewater, physical and biochemical methods are generally used for combined treatment.
The reason is that high-concentration coking wastewater is generally first removed by adding alkali and ammonia distillation to remove most of the volatile ammonia and fixed ammonia. The residual ammonia nitrogen in the ammonia wastewater after ammonia distillation is then removed by biochemical methods. The concentration of ammonia nitrogen in the ammonia wastewater after ammonia distillation is related to the desulfurization and decyanation process of gas purification, and is also related to the comprehensive operating costs of ammonia distillation and biochemistry. Under normal circumstances, it is best to control the comprehensive operating cost of ammonia distillation and biochemistry as the lowest.
In summary, the diversity of chemical substances contained in coking wastewater and the obvious level differences in the energy levels of different types of substances determine that coking wastewater cannot be completely treated with a single method. The biological treatment of coking wastewater is a combined treatment of multiple flora, and each biological flora lives in a complex ecological environment that is both interdependent and restrictive, and full of contradictions everywhere, and the living habits of each biological flora Different, and there are nearly half of the vulnerable groups. If a certain biological flora cannot be cultivated, biological denitrification will not be successful. If a certain bacterial flora in the system fails, the entire system will be paralyzed, many of which Phenomenon, in the wastewater biological treatment system dominated by single-bacteria, it does not exist at all. This is why the biological denitrification treatment of coking wastewater is different from other biological wastewater treatment processes, and this difference is caused by coking Determined by the characteristics of wastewater quality.
In general, coking wastewater has the characteristics of complex composition, toxic and difficult to degrade, high organic content, high ammonia nitrogen concentration, and large changes in water quality and quantity. Therefore, the removal efficiency of ordinary physicochemical and biochemical methods is low, and the effluent does not meet the standard. Therefore, it should be treated properly. The key to wastewater is to choose effective treatment methods.
The harm of coking wastewater Coking wastewater contains a large number of cyclic organic compounds, inorganic nitrogen compounds and ammonia nitrogen, etc., whether these substances enter the water body (such as discharged into the ground water body or infiltrate into the ground water body), or some of them are released into the atmosphere. They will directly or indirectly cause serious harm to animals and plants.
People have directly consumed water containing this type of substance-a certain concentration, or inhaled air containing this type of substance for a long time.
Qi can get sick, and in severe cases it can cause cancer; especially some substances can be accumulated in animals or plants.
The concentration is concentrated many times, and it can be harmful to people through the food chain; carbon-containing species in coking wastewater
Most of the compounds are oxygen-consuming substances. After they enter the water body, they will consume the dissolved oxygen in the water body.
Heavy time can cause the corruption of water bodies; and the nitrogen-containing substances in coking wastewater can lead to eutrophication of water bodies, which can lead to the growth and reproduction of algae; ammonia nitrogen can also be converted into nitrate nitrogen in water bodies, which can be eaten by infants and young children. If the water contains a certain concentration of nitrate nitrogen, it can cause leukemia. Because the coking wastewater is extremely serious to the natural ecology and threatens human beings, it is necessary not only to treat it, but also to conduct a thorough treatment, and to prevent the transfer of pollution and secondary pollution.
Pollution control is neither an optional thing, nor is it a costly project that consumes no output.
Pollution control not only has obvious environmental and social benefits, but also according to the national "three simultaneous".
The principle of construction, whether pollution control is complete or not, is the prerequisite for whether a construction project can be put into production and operation, just like production has to use electricity and have to hire I-. If the ecology is severely damaged, it will not only bring disasters to humans, but the economic cost of restoring the ecology may be several times higher than the economic benefits now obtained, and the time required to restore the ecology often takes decades , And even hundreds of years.
Coking plant sewage contains a lot of organic substances in its composition, Polyacrylamide for coking wastewater, so it needs to use cationic polyacrylamide. The environment around the coking plant is harsh and pollutes water and air very seriously. It is difficult to deal with. The sewage treatment station of the industrial coking plant is primarily responsible for the treatment of ammonia wastewater, recovery and refining workshop wastewater, surface water, incident water, gas water seal condensate, etc. Coking wastewater is industrial wastewater containing evaporated phenols, polycyclic aromatic hydrocarbons and heterocyclic compounds such as oxygen, sulfur and nitrogen during the process of coking and coal gas retorting, purification and by-product recovery. It is a kind of high COD, high phenol value, high A type of industrial organic wastewater that is ammonia nitrogen and difficult to treat.
Generally, cationic flocculant, cationic polyacrylamide is commonly used to treat coking sewage because it has a variety of vivid groups, which can be affinity with many substances and form hydrogen bonds by adsorption. The first is to flocculate negatively charged colloids, which have the functions of turbidity removal, decolorization, adsorption and adhesion. Cationic pam is suitable for the treatment of wastewater with high organic colloid content such as dyeing, papermaking, food, construction, metallurgy, mineral processing, coal powder, oil field, aquatic processing and fermentation, etc. It is especially suitable for municipal sewage, municipal sludge, paper sludge and Dewatering treatment of other industrial sludge.