Summarize several methods for treating high-salt wastewater
Published Time:
2025-03-21
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Under salinity conditions less than 2g/L, acclimation treatment of saline wastewater may be possible. However, the acclimation salinity concentration must be gradually increased, and the system must be acclimated to the required salinity level in stages. A sudden high-salinity environment can lead to acclimation failure and startup delays.
Since high salinity acts as an inhibitor and toxin for microorganisms, diluting the influent to a salinity below the toxic threshold will prevent inhibition of biological treatment. This method is simple and easy to operate and manage; however, its drawbacks include increased treatment scale, increased infrastructure investment, increased operating costs, and water waste.
When salinity is greater than 2g/L, evaporation concentration and desalination is the most economical and effective feasible method. Other methods, such as cultivating salt-tolerant bacteria, have practical difficulties in industrial applications.
Many studies have shown that biological methods can treat high-salinity wastewater. However, from low salinity to high salinity, microorganisms have an adaptation period. From freshwater to high-salinity environments, changes in salinity may cause changes in microbial metabolic pathways, resulting in fewer species adapted to high salinity. Only after microorganisms are cultured and acclimated can they produce species adapted to high salinity to tolerate a certain salt concentration.
Extended Information:
Biochemical Treatment of High-Salinity Wastewater:
Selection of Biological Treatment Processes for High-Salinity Wastewater The biological treatment process for high-salinity wastewater is basically the same as the ordinary biological treatment process, mainly including equalization tanks, aeration tanks, secondary sedimentation tanks, sludge return, excess sludge dewatering, and nutrient addition.
(1) Equalization Tank: The main factors to consider for the equalization tank of saline wastewater are the changes in wastewater salinity. In addition to production fluctuation cycles and impact factors, the changes in water salinity and how to adjust them should be considered, such as the reduction in low-salinity water volume or the impact of excessively high-salinity influent.
(2) Aeration Tank: Depending on the type of salt in the wastewater, the aeration tank selection should also vary. For biological treatment of wastewater with high CaCl2, traditional aeration methods should be used. Calcium ions can increase the floc strength of activated sludge, and high CaCl2 can increase the ash content in sludge to 40%~50%, increasing sludge density. The sludge concentration in the aeration tank can be above 5000mg/L. Therefore, aeration methods with high lifting force, such as traditional aeration, deep-well aeration, and fluidized bed aeration, should be used. Aerators with larger bubbles and stronger lifting force, such as diffused aerators, should also be selected.
(3) Secondary Sedimentation Tank: The surface load of the secondary sedimentation tank should have a certain margin, mainly considering the increased wastewater density, which is not conducive to sludge sedimentation, especially for NaCl wastewater. When the treatment water volume is large, especially for CaCl2 wastewater, it is best to use a peripheral drive scraper to adapt to the characteristics of high sludge concentration and density. When using the traditional activated sludge method to treat high CaCl2 wastewater, the sludge return flow rate should be appropriately increased to reduce the impact caused by wastewater fluctuations and improve system stability.
(4) Sludge Dewatering: Since the excess sludge from the biological treatment of CaCl2-containing wastewater contains a lot of calcium salts, it is conducive to dewatering and flocculants may not be needed. The concentration of the concentrated sludge 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.
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