Dry goods/comprehensive analysis of high salt wastewater treatment

Salt tolerant microorganisms: capable of withstanding a certain concentration of salt solution, but growing under salt free conditions does not require a large amount of inorganic salts. Halophilic microorganisms refer to bacteria that can grow under high salt conditions, and their growth cannot be separated from high salt environments. According to the range of good growth salinity, it can be divided into three categories. Marine bacteria: Good growth salinity 1-3% Moderate halophilic bacteria: Good growth salinity 3-15% Extreme halophilic bacteria: Good growth salinity 15-30%

Poor adaptation to salinity

　　The traditional activated sludge method is used to domesticate and treat wastewater with salinity below 2%. When the salinity environment changes to a freshwater environment, the adaptability of sludge will quickly disappear.

Salinity changes have a significant impact

Salinity changes of 0.5-2% usually cause serious interference to the treatment system.

Sudden changes in salinity have a greater impact on the system than gradual changes in salinity. The impact of transitioning from high salinity to no salinity is greater than that of transitioning from low salinity to high salinity environments

Slow degradation rate

　　As the salinity increases, the degradation rate of organic matter decreases, making low F/M more suitable for the treatment of saline wastewater. Figure 3.5 shows the treatment effect of SBR method at different salinities.

Serious sludge loss

　　Salinity changes the composition of microorganisms in sludge, altering its sedimentation and effluent SS, resulting in severe sludge loss.

Microorganisms adapted to live in freshwater biological treatment facilities will balance the intracellular osmotic pressure or protect the cytoplasm through their own osmotic pressure regulation mechanism when entering a certain concentration of saline environment. These regulation mechanisms include aggregating low molecular weight substances to form a new extracellular protective layer, regulating their own metabolic pathways, changing gene composition, etc. Therefore, normal activated sludge can be domesticated to treat saline wastewater within a certain salinity range for a certain period of time. Although domestication of sludge can improve the salt tolerance range and treatment efficiency of the system, the microorganisms in domesticated sludge have limited tolerance to salinity and are sensitive to environmental changes. When the salinity environment changes, the adaptability of microorganisms will immediately disappear. Domestication is only a temporary physiological adjustment of microorganisms to adapt to the environment and does not have genetic characteristics. This adaptability sensitivity is very detrimental to the implementation of sewage treatment projects. Research suggests that under conditions of salinity less than 20g/L, saline wastewater can be treated through salinity acclimation. However, the domestication of salinity concentration must be gradually increased, and the system must be domesticated to the required salinity level in stages. Sudden high salt environments can cause domestication failure and delayed initiation.

Since high salt becomes an inhibitory and toxic agent for microorganisms, diluting the influent to lower the salinity below the toxicity threshold will not inhibit biological treatment. This method is simple, easy to operate and manage; Its disadvantages are increasing processing scale, increasing infrastructure investment, increasing operating costs, and wasting water resources.

Inoculation or gene immobilization of salt tolerant microorganisms is an effective treatment method for high salt wastewater. This method can treat over 3% of high salt wastewater, which cannot be achieved by different domestication methods. Some of the selected salt tolerant bacteria with specific pollutant removal capabilities can have high specific degradation ability, greatly improving treatment efficiency. Screening of inoculants from marine or estuarine sediments, substrates from salt fields, and other active substances in high salt environments. Screening often involves certain procedures and genetic measures. The disadvantage of this method is that it has a long start-up time and high initial start-up costs. But for the biological treatment of high salt wastewater, it is a feasible method.

Antagonistic effect refers to the situation where the toxic effect of a toxin is reduced due to the presence or increase of another substance.

It can be seen from the figure that the toxic effect of one toxin decreases with the increase of low concentration of another substance, and after reaching a good state, the reaction rate decreases with further increase of antagonist concentration.

At present, research has found that K has an antagonistic effect on Na, reducing the toxic effects of Na salts on microorganisms. Potassium absorption and sodium excretion function

The main principle may be the Na+/K+reverse transport function. Although bacterial growth requires a high sodium environment, the concentration of Na inside the cell is not high. For example, the H+proton pump mediated by halophilic bacteria has the function of Na+/K+reverse transport, which has the ability to absorb and concentrate K+and discharge Na+to the outside of the cell K+, as a compatible solute, can regulate osmotic pressure to achieve intracellular and extracellular balance, with a concentration of up to 7mol/L, to maintain the same water activity inside and outside the cell For example, halophilic anaerobic bacteria, halophilic sulfur reducing bacteria, and halophilic archaea use intracellular accumulation of high concentrations of K+to counteract the high osmotic environment outside the cell The Na+/K+reverse carrier in yeast can eliminate excess salt from the body and improve the salt tolerance of yeast.

To prevent and control environmental pollution, improve the quality of the ecological environment, and standardize the construction and operation management of ceramic industry wastewater treatment projects, this standard is formulated. This standard specifies the technical requirements for the design, construction, acceptance, operation, and maintenance of ceramic industry wastewater treatment projects. Appendix A of this standard is an informative appendix. This standard is being released for the first time. This standard will be implemented from May 1, 2023.

Different processing techniques affect the salt tolerance range of microorganisms. The following are the limits of NaCl concentration in several reported biological treatment methods.

It is generally believed that the salt tolerance of biofilm process is greater than that of suspended activated sludge process. In addition, adding a salt tolerant segment can greatly improve the salt tolerance range of subsequent aerobic segments.

Salinity changes have a significant impact on stable systems, manifested as a sharp decrease in treatment efficiency and significant loss of sludge. A regulating tank should be established during design to ensure relative stability of salinity. Conductivity monitoring devices can be installed at the inlet and outlet of the regulating pool to enhance online control and feedback of salinity, preventing salt shock from causing processing system failure.

　Salinity reduces the rate of biodegradation, therefore the design load should be relatively reduced. Many studies have shown that the sludge index decreases in high salt environments, so there is no need to worry about sludge expansion caused by low loads.

The high salt treated sludge has poor coagulation and severe sludge loss. Therefore, high sludge concentration should be ensured in the design. This is also a means to improve processing efficiency. When designing sludge concentration tanks, additional sludge storage can be ensured to quickly replenish sludge when it is lost.

High salt content affects the coagulation properties, therefore an extended residence time is beneficial for the sedimentation of sludge.

Microorganisms adapt to high salt environments by increasing aerobic respiration rates, resulting in additional oxygen consumption during respiration. Increasing the concentration of dissolved oxygen in water is beneficial for the metabolism of microorganisms. Provide physiological requirements for adapting to high salt environments.