1. The phenomenon of sludge poisoning is roughly divided into the following four situations after sludge poisoning, with slight differences depending on the reasons. The activated sludge flocs are finely refined, with abnormal color and deteriorated settling performance. The supernatant is turbid and contains many small feather like sludge fragments. Microscopic examination can reveal a significant decrease in the number of protozoa, such as rotifers, bell worms, and branchiopods, and even a few have died or lost their activity. Under the microscope, the volume of sludge flocs is smaller and more scattered than usual. The sludge in the secondary sedimentation tank floats up in a cloud like pattern and gradually spreads throughout the tank, causing serious sludge leakage in the effluent. The final effluent water quality is turbid, and its COD value is much higher than the normal fluctuation range.
2. Cause of poisoning: pH shock
When the pH value of the environment in which the activated sludge is located is less than 6 or greater than 9, in most cases, the activity of the microorganisms in the activated sludge is inhibited or loses its activity, and even dies. At this time, sludge loosening and floating phenomena occur. Toxic manifestations: Activated sludge flocs become finer in size, with a lighter color and poorer settling performance. The supernatant is turbid and contains a large number of small particles that are difficult to settle. Microscopic examination can still detect a certain amount of protozoa (such as nematodes and nematodes) and post protozoa (such as rotifers), but their activity is insufficient. The dissolved oxygen in the mixed liquid of the aeration tank gradually increases under constant aeration rate, and some dead bacterial colonies become liquid surface scum under the action of aeration. The color of the scum is dull, thin and loose. After the biological system was impacted, the suspended solids in the secondary sedimentation tank floated up in a cloud like manner and gradually spread throughout the entire tank, resulting in severe sludge discharge from the effluent. Solution: As illegal discharge by enterprises is only a short-term behavior, a certain number of microorganisms can still be detected through microscopic examination after the biological system is impacted by pH values, but their activity is inhibited or partially dead. Therefore, restoring the activity of inhibited microorganisms and accelerating the reproduction of residual microorganisms are key to restoring biological systems. Main measures taken: Add waste alkali solution at the inlet of the biological tank to increase the pH value of the mixed solution in the aeration tank as much as possible. Increase the external reflux rate, maintain a relatively high sludge concentration in the biochemical unit, and improve the system's ability to withstand shock loads. Continuously adding nutrients (industrial glucose) to the biological pool to supplement the nutrients in the influent and accelerate the recovery and reproduction of microbial activity. When the salt content increases and the chloride ion concentration in the wastewater exceeds 2000 mg/L, the activity of microorganisms will be inhibited, and the COD removal rate will significantly decrease; When the concentration of chloride ion in the wastewater is more than 8000 mg/L, the sludge volume will expand, a lot of foam will appear on the water surface, and microorganisms will die one after another. Due to the fact that chloride ion content is not a routine indicator for inflow monitoring, it is difficult to detect during operation. When making judgments based on certain indicators of the biological system, it is often accompanied by the paralysis of the biological system. Toxic manifestations: Activated sludge is loose and fine, with a light color and poor settling performance. The supernatant is turbid and contains a large number of difficult to settle small particles. Microscopic examination will reveal a significant reduction in microorganisms and complete death. The dissolved oxygen value of the aeration tank will rise suddenly when the aeration rate is constant, and a large number of small bubbles will appear on the surface of the activated sludge mixture, and a large number of foam will emerge. ④ The suspended solids in the secondary sedimentation tank float up in a cloud like manner and gradually spread throughout the entire tank. Solution: When the biological system is impacted by high salt wastewater, it is often accompanied by the complete death of activated sludge microorganisms, making it difficult for the system to recover. Due to the chloride ion content in enterprise drainage not being within the monitoring range of environmental protection departments, blocking the further inflow of high salt wastewater is the primary task before restoring the system. The main measures taken during the recovery process are to increase the external return flow and dilute the incoming water. Re feed the dehydrated sludge from our factory into the biological tank as inoculum sludge for microbial cultivation. To shorten the cultivation time and accelerate the reproduction of microorganisms, some nutrients (industrial glucose) are added to the biological pool.
When the inflow contains a large amount of oil and fat, it will affect the stability and permeability of the sludge cell membrane, causing the loss of certain essential components of the cells and leading to microbial growth arrest and death. In addition, when the oil content in the incoming water is too high, after aeration and mixing, the oil will adhere to the surface of the bacterial micelle, causing the bacteria to float up after hypoxia. Toxic manifestations: Activated sludge is loose and fine, with a black color and poor settling performance. The supernatant contains a large number of small particles that are not easy to settle. Microscopic examination still shows a certain amount of microorganisms, but their activity is insufficient. The oxygen demand in the aeration tank increases and a large amount of liquid surface scum appears, which turns black in color and has viscosity. The overall color of the water in the secondary sedimentation tank is black, and the effluent contains a large amount of suspended solids. Solution: When the oil content in the incoming water is too high, after aeration and mixing, the oil will adhere to the surface of the bacterial gel cluster, causing a decrease in density and floating up, and the bacteria will be in a state of hypoxia, resulting in the entire aeration tank turning black in color and a large amount of floating slag appearing on the liquid surface. Due to the fact that most of the incoming oil is emulsified oil, the more it enters the aeration tank, the tighter the oil wraps around the sludge particles and the looser the sludge becomes. Therefore, how to remove the oil and grease in the aeration tank as soon as possible is the key to system recovery. During the recovery process, the main measures taken are to stop water inflow, stop aeration, perform static settling on the aeration tank, and then open water inflow to push out the supernatant in the aeration tank, in order to minimize the oil content in the aeration tank. After restoring aeration, the dissolved oxygen should be controlled at a relatively high level (4 mg/L). Add some nutrients appropriately to accelerate the proliferation of sludge. Increase the amount of sludge discharge to promote the replacement of new and old sludge. Although a large amount of oil and fat entered the aeration tank, the biological system was not completely destroyed, so after taking the above measures, the biological system recovered quickly.
