Tannery wastewater is a kind of organic wastewater with complex composition and high concentration, which is difficult to treat. At the same time, most of the tanning processes are completed in water, so the tanning process consumes a lot of water, Polyacrylamide for leather wastewater.
The nature of leather wastewater The tanning industry is an industry that produces a lot of wastewater. The tanning wastewater is not only large, but also a complex and high-concentration organic wastewater containing a large amount of lime, dyes, proteins, salts, grease, ammonia, nitrogen, Sulfide, chromium salt and toxic and harmful substances such as wool, leather residue, mud and sand. CODCr, BOD5, sulfide, ammonia nitrogen.
In the treatment of tanning wastewater, the main role of the flocculant PAM. In the production of tanning, due to some differences in raw skins, different processing techniques, and different finished products, the quality of wastewater varies greatly, and the amount of wastewater from tanning is not only large. , And it is also a kind of complex, high-concentration organic wastewater, which contains a lot of toxic and harmful substances such as lime, dyes, salts, grease, ammonia nitrogen, sulfide, wool and leather residues, so what should leather wastewater be? To deal with it?
Tannery wastewater treatment is mainly biological treatment. Generally, oxidation ditch or SBR is used. Oxidation ditch treatment of this wastewater is a relatively mature process. First, we must carry out a series of pretreatments. Pretreatment is very important for leather wastewater. One of the treatment processes of the company, its main function is to remove as much SS, oil, chromium ion and sulfide as possible, reduce the concentration of organic and toxic substances, to ensure the stable operation of subsequent biological treatment.
Coagulation precipitation and air flotation are commonly used pretreatment methods for leather wastewater. Coagulation precipitation is mainly through the addition of chemicals to precipitate and remove sulfide and chromium ions in the water; while air flotation is mainly through the addition of demulsifiers and Flocculant, through the floating and adhesion of tiny bubbles, removes oily substances and SS in the water, so polyacrylamide flocculant is generally used, and the effect is better.
The tannery wastewater has better biodegradability, so biological treatment is the preferred process. But before that, chromium-containing wastewater, degreasing wastewater, and sulfur-containing wastewater must be collected separately for pretreatment.
According to the "Discharge Standard of Water Pollutants for Tanning and Fur Processing Industry" (GB30486-2013), chromium-containing wastewater should be collected separately, added with alkali and precipitated and then separated into mud and water. The supernatant will be discharged after reaching the standard in GB30486-2013 Comprehensive wastewater regulating tank. The sedimentation sludge in the sedimentation tank is discharged into the chromium-containing sludge thickening tank, and it is pressed and dried by a filter press, and then it is entrusted to a qualified unit for hazardous waste treatment.
The degreasing waste water is treated with acid to adjust the PH demulsification, and then the demulsified oil is treated by air flotation to achieve oil-water separation, and the sewage is discharged to the comprehensive waste water regulating tank. Sulfur-containing wastewater can be pretreated by iron salt sedimentation, chemical coagulation, catalytic oxidation, etc. Generally, catalytic oxidation is used for pretreatment.
The wastewater is pretreated and transported together with other wastewater to the wastewater treatment plant in the plant area for biological-chemical secondary treatment. The primary treatment of comprehensive sewage passes through the fine grid, aeration grit tank, adjustment tank and primary sedimentation tank to balance the water quality and quantity, and remove large-particle inorganic substances, part of COD and BOD. The secondary treatment is biological treatment, the traditional activated sludge method, the plug flow reactor, and the pollutants in the blast aerated sewage are degraded or removed to the greatest extent at this stage.
Finally, the sewage enters the chemical pond for chemical coagulation and precipitation, the coagulant is basic aluminum chloride and the inclined pipe is used for precipitation. SS and COD in the sewage are further reduced. The primary sludge, surplus sludge and chemical sludge produced in the sewage treatment process are concentrated and collected. After gravity concentration and sludge conditioning, they enter the plate and frame filter press for dewatering, the filtrate returns to the sewage treatment system, and the filter cake Centralized handling by the local environmental protection department.
Leather wastewater is generally unstable. The amount of tannery wastewater varies greatly over time, often intermittently. In the peak period of discharge, the discharge can account for 70% of the total discharge, and the difference in water quality is also large. During the time period, *we must adjust the model of water treatment agent PAM, so as to adapt to the changes caused by the environment.
So, in the leather wastewater treatment, what are the stages of the polyacrylamide flocculation process?
1. Added flocculant to wastewater
2. The flocculant diffuses in the liquid
3. Stirring in order to contact the flocculant and suspended particles
4. Stirring in order to make the contacted particles become large and heavy particles.
From the above process, polyacrylamide flocculation is a physical and chemical process, so there are many factors that affect it, except for the type of colloidal particles in the waste liquid, the size of the colloidal particles, the surface characteristics, and the size of the colloidal particles. In addition to factors such as the concentration and the type and characteristics of the flocculant, it also includes the pH value of the solution, the type and concentration of coexisting substances, the temperature and temperature changes of the reaction, the method of stirring, and the amount of flocculant.
In short, the flocculation of colloidal particles is a relatively complicated process, and the influencing factors are also various. Therefore, the best method is to conduct flocculation tests on actual wastewater, and select the best flocculants and their flocculation conditions, Polyacrylamide for leather wastewater.
From the influence of many factors, as long as the waste liquid and flocculant are certain, the most important influencing factor is the concentration of colloidal particles and the conditions of stirring. The denser the colloidal particles, the more uneven the particle size. The greater the chance of contact, the better the flocculation effect. In the process of flocculated particle growth, if the stirring is too violent, the particles will be destroyed or not grow. At this time, it should be stirred slowly. Therefore, in the process of flocculation, after adding flocculant, the stirring should be fast and then slow. The charge of ionized ions in the solution and the amount of flocculant are also greatly affected by adding flocculant. Generally, the higher the charge of ionized ions, the greater the concentration. Larger, the better the effect of flocculation.
In addition to chemical methods, the waste water treatment of leather factories can also adopt mechanical methods, sedimentation methods, filtration methods, centrifugal separation methods, biochemical methods, etc., and various methods have certain effects. Which method should be used to treat wastewater? It needs to be considered according to the composition and concentration of the substances contained therein, the degree of purification required, the discharge standard, the comprehensive utilization of recycled waste and other factors. In order to improve the efficiency of wastewater treatment, multiple methods can be combined.