We all know that the aeration tank is crucial in sewage treatment, and pH value is an important indicator of the operation status of the aeration tank. If there is a problem, the treatment effect of the aeration tank will be greatly reduced. Today, let's talk about the factors that affect the pH changes in the aeration tank and the corresponding solutions.
Let's talk about the factors related to water quality first. The composition of sewage is complex, and if there are a large amount of acidic or alkaline substances inside, the pH value will definitely be affected. For example, in the production process of some industrial wastewater, various acid-base drugs are used, and the pH value of the discharged wastewater fluctuates greatly. Wastewater from electroplating factories may be highly acidic due to the use of strong acids in the electroplating process; The wastewater from the paper mill is also highly alkaline due to some chemical treatments during the papermaking process. If this goes directly into the aeration tank, can the pH value not 'rebel'!
The ammonia nitrogen content in sewage is also closely related to the pH value. During aeration, ammonia nitrogen undergoes nitrification reaction, which consumes alkalinity and releases hydrogen ions, thereby reducing the pH value. If the ammonia nitrogen content in the sewage is too high, the pH value in the aeration tank will decrease significantly. For example, if domestic sewage contains a large amount of nitrogen-containing organic matter, during the microbial decomposition process, ammonia nitrogen is continuously produced, nitrification reaction continues, and the pH value is easily lowered.
Next, let's talk about the impact of microbial metabolism on pH value. The microorganisms in the aeration tank are a group of diligent "little workers". When they decompose organic matter and carry out respiration, they produce various metabolic products, some of which are acidic and some are alkaline. When microorganisms multiply in large numbers, the rate of decomposition of organic matter accelerates, and acidic metabolites increase, the pH value will decrease; If microbial growth is inhibited, metabolic activity is weakened, alkaline substances are relatively increased, and pH may rise again. For example, when treating high concentration organic wastewater, microorganisms decompose organic matter to produce a large amount of organic acids, such as acetic acid and propionic acid, which will significantly lower the pH value in the aeration tank.
The conditions of aeration also have a significant impact on the pH value. If the aeration rate is too high, it will lead to two results: first, excessive nitrification reaction, exceeding the buffering capacity of the original alkalinity in the sewage, and the pH value will continue to decrease; Secondly, excessive aeration can exacerbate the oxidation of sludge itself, affect microbial activity, alter metabolic processes, and may also cause pH fluctuations. On the contrary, if the aeration rate is insufficient, the aerobic respiration of microorganisms is inhibited, and the decomposition of organic matter is incomplete, which will cause an increase in pH value. For example, in some small-scale sewage treatment plants, due to aging aeration equipment, the aeration rate may not be stable enough, sometimes too high and sometimes too low, which can cause the pH value of the aeration tank to fluctuate like riding a roller coaster.
Temperature is also an undeniable factor. The activity of microorganisms is sensitive to temperature. Generally speaking, when the temperature is between 20-30 ℃, the microbial activity is strongest, metabolism is normal, and the pH value is relatively stable. If the temperature is too low, the metabolic rate of microorganisms slows down, the transportation of nutrients is hindered, and a large amount of viscous sugars gather together, which will cause sludge disintegration and affect the pH value; When the temperature is too high, bacteria find it difficult to withstand the high temperature, leading to a large number of deaths, disrupted metabolic processes, and changes in pH values. In winter in the north, the temperature is very low. If the sewage treatment plant does not take good insulation measures, the water temperature in the aeration tank will decrease, the microbial activity will decrease, and the pH value may be abnormal.
After discussing the influencing factors, let's talk about how to solve these problems.
To address water quality issues, the first step is to strengthen monitoring of the incoming water quality. Once acidic or alkaline wastewater is detected flowing in, it should be immediately directed into a regulating tank for separate treatment. In the regulating tank, acid-base agents can be added for neutralization pretreatment to reach the appropriate pH range before entering the aeration tank. For wastewater containing toxic and harmful substances, physical and chemical methods should be used to remove or reduce the concentration of toxic and harmful substances before entering the biological treatment unit. It is also possible to set up regulating tanks in the sewage treatment plant to balance the quality and quantity of incoming water, buffer abnormal impacts of incoming water, monitor the quality of incoming water in real time, and adjust process parameters in a timely manner when the concentration is too high. If the exceedance is particularly severe, the emergency pool will be urgently called upon.
If the pH value drops due to high ammonia nitrogen content, on the one hand, the influent ammonia nitrogen load can be appropriately reduced, such as strengthening source control and reducing the emission of nitrogen-containing organic matter; On the other hand, the consumed alkalinity can be supplemented by adding alkalinity, commonly used alkalis include sodium hydroxide, sodium carbonate, etc. However, when adding, it is important to control the amount to avoid adding too much and causing new problems.
If the pH value changes caused by microbial metabolism, the growth environment of microorganisms needs to be adjusted. For example, controlling the appropriate sludge load, adjusting the inflow flow rate and sludge concentration reasonably according to the inflow water quality, and keeping the sludge load within an appropriate range. When the sludge load is too high, increase the sludge concentration appropriately or reduce the inflow rate. Regularly calculate the age of sludge, and when it is found that the sludge age is too long, increase the discharge volume appropriately, discharge aged sludge, supplement fresh sludge, and restore microbial activity. When using the general activated sludge method to treat wastewater, the sludge concentration should be controlled between 2000-6500mg/L.
In terms of aeration conditions, it is necessary to check the aeration equipment to ensure uniform aeration, adjust the aeration rate to an appropriate range, ensure that microorganisms can carry out sufficient and moderate aerobic respiration, and maintain the acid-base balance in the system. The dissolved oxygen (DO) of the nitration process mixture should be controlled at around 2.0mg/L, generally between 2.0-4.0mg/L. During the investigation, it is recommended to use a handheld dissolved oxygen monitor to avoid any malfunctions in online monitoring.
In the face of temperature issues, if the temperature is too low, insulation measures can be added to the aeration tank, such as covering with insulation materials; If the temperature is too high, cooling towers and other equipment can be used to cool the incoming water, ensuring that microorganisms work in a suitable temperature environment.
In short, the stability of pH value in the aeration tank is crucial for the effectiveness of sewage treatment. We should always pay attention to various influencing factors and take effective solutions in a timely manner, so that the aeration tank, as the "hero" of sewage treatment, can work stably and efficiently.
