Wastewater treatment technology: analysis of high salt wastewater treatment methods
High-salt wastewater refers to wastewater with a total salt content of at least 1%, which mainly comes from chemical plants, oil and natural gas collection and processing, etc. This wastewater contains a variety of substances (including salt, oil, organic heavy metals and radioactive substances). Salt wastewater is produced in a wide range of ways, and the amount of water is increasing year by year. The environmental impact of removing organic pollutants in saline wastewater is crucial. How to deal with high-salt wastewater, first we make a simple analysis of its different situations.
1. Under the condition that the salinity is less than 2g/L, it is possible to treat saline sewage through domestication. However, the acclimation salinity concentration must be gradually increased, and the system must be acclimatized to the required salinity level in stages. Sudden high salinity conditions can cause failure of acclimatization and delays in initiation.
2. Dilute the influent salinity. Since high salinity becomes the inhibitory and toxic agent of microorganisms, the influent water will be diluted so that the salinity is lower than the toxic threshold value, and the biological treatment will not be inhibited. This method is simple, easy to operate and manage; its disadvantage is to increase the scale of treatment, increase infrastructure investment, increase operating costs, and waste water resources.
3. When the salinity is greater than 2g/L, evaporation and concentration desalination is the most economical and most effective feasible method. Other methods, such as cultivating halobacteria, etc., have the problem that industrial practice is difficult to operate.
How to treat high-salt wastewater can achieve better results, we need to have a detailed understanding and understanding of the biological process of its treatment:
(1) Regulating pool. The main factor to be considered in the saline wastewater regulating pool is the change of the salt concentration of the wastewater. In addition to the production fluctuation cycle and impact factors, the change of the salt concentration in the water and how to adjust it should be considered, such as the reduction of low salt water content or excessive salt content The impact of incoming water.
(2) Aeration tank. Depending on the type of salt in the wastewater, the selection of the aeration tank should also be different. Biological treatment of wastewater with high CaCl2 content should use traditional aeration methods. Calcium ions can increase the floc strength of activated sludge. High CaCl2 can make the ash content in the sludge reach 40% to 50%, increase the sludge density, and the sludge concentration in the aeration tank can be above 5000mg/L. Therefore, aeration methods such as traditional aeration, deep well aeration, and fluidized bed aeration with large lifting power should be used. For aeration, aeration methods such as diffuse aerators with larger bubbles and stronger lifting power should also be used. Do not use microporous aerators and variable pore aerators with small bubbles to prevent the aeration holes from being blocked by inorganic salts, which is not conducive to the agitation of the aeration tank. Jet aeration can also be used when the water volume is less than 1000m3. Jet aeration has high oxygen transfer efficiency and is not easy to block the aeration equipment. The aeration intensity should also be greater than that of ordinary biological treatment, about 10m3/(m2?h), or use a central tube to increase the lifting and stirring capacity. In the case of high salt content, the increase of oxygen transfer rate is beneficial to high sludge concentration. As long as the bacterial micelles do not disintegrate, even if filamentous bacteria are produced, the sludge will not float up and be lost. Phosphorus-containing nutrient salts should pay attention to the dosing position, so as to avoid the precipitation of calcium phosphate salt not only affecting the use effect, but also causing scaling and easily blocking the pipeline.
When using the SBR process to treat high-salt wastewater, since SBR is a waterfall gas and precipitation, it is necessary to fully consider the precipitation time when designing, especially when dealing with wastewater containing high concentrations of sodium salts. The effect is poor, so the settling time should be extended accordingly, and in order to reduce the interference of the decanter on the settled sludge, the depth of the decanted water should also be reduced accordingly. When dealing with wastewater with large fluctuations in salinity, it is still necessary to set up a regulating tank. Units that need to treat high-concentration saline wastewater can also consult companies with similar sewage treatment experience on the service platform of the Sewage Bao project.
Biofilm technology is an ideal process for treating high-salinity wastewater, such as waterfall biofilter technology, contact oxidation process aeration, etc. When treating wastewater with high calcium salt content, attention should be paid to the selection of fillers or filter materials. Larger backwashing intensity and time should be designed in the biological filter. The packing of the contact oxidation tank should also adopt the type with high porosity, and the installation of the packing should take into account that it is easy to disassemble and wash, so as to prevent the calcium carbonate formed in the process of wastewater treatment from blocking the packing. During the biological treatment of wastewater with a high NaCl content, the ash content of the sludge is lower than that of the wastewater containing CaCl2, while the wastewater containing saline has a high density. Therefore, the biological treatment of wastewater with high NaCl content is best to use the biofilm method.
(3) Secondary sedimentation tank. The surface load of the secondary sedimentation tank should have a certain margin, mainly because the increase in the density of wastewater is not conducive to sludge sedimentation, especially wastewater containing NaCl. When the amount of water to be treated is large, especially the wastewater containing CaCl2, it is best to use a peripheral transmission type mud scraper to adapt to the characteristics of high sludge concentration and high density. When using the traditional activated sludge method to treat high CaCl2 wastewater, the sludge return flow should be appropriately increased to reduce the impact caused by wastewater fluctuations and improve system stability.
(4) Sludge dehydration. Since the remaining sludge from the biological treatment of CaCl2-containing wastewater contains more calcium salts, which is beneficial to dehydration, no flocculant is required. The concentrated sludge concentration can be greater than 50g/L. The amount of excess sludge is similar to that of ordinary wastewater treatment, and the design parameters can refer to ordinary sludge dewatering.
When treating wastewater with a high concentration of calcium ions, due to the high inorganic components in the activated sludge, the removal capacity of organic matter is low, and the removal rate of pollutants is higher than that under high load conditions, but the time delay Aeration is not suitable for treating high-salt wastewater, because the sludge age is long, the hydraulic retention time is long, the activated sludge is easy to age, and the flocculation performance becomes poor, which ultimately affects the water outlet effect.
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