1, Purpose
This manual aims to provide detailed operational guidance for the domestication of activated sludge, enabling it to adapt to specific wastewater quality, efficiently degrade pollutants in wastewater, and ensure the stable operation of sewage treatment systems.
Scope of Application
Suitable for domestication of activated sludge in various sewage treatment plants (stations), especially for the treatment of industrial wastewater or wastewater containing difficult to degrade substances, toxic and harmful substances in activated sludge systems.
3, Preliminary preparation
Data collection: comprehensively understand the water quality, quantity, and composition of the wastewater to be treated, including chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia nitrogen, total phosphorus, pH, heavy metal content, types and concentrations of toxic and harmful substances, etc; Simultaneously collect design parameters, process flow, equipment operating parameters, and other data of sewage treatment plants (stations).
Equipment inspection: Conduct a comprehensive inspection and debugging of the aeration system, mixing equipment, water pumps, monitoring instruments (such as dissolved oxygen meters, pH meters, sludge concentration meters, etc.), sludge reflux system, drainage system, etc., to ensure that the equipment can operate normally and the instruments are accurate and reliable.
Preparation for inoculation of sludge: Priority should be given to selecting residual sludge from sewage treatment plants with similar or identical properties as inoculation sludge, which can improve the domestication effect and shorten the domestication time; If it is not possible to obtain such sludge, residual sludge from urban sewage treatment plants can also be used. The dosage of inoculated sludge is generally not less than 5% of the effective volume of the aeration tank. For difficult to treat wastewater, the dosage can be appropriately increased. Before adding sludge, pre-treatment is required. For example, dehydrated sludge can be mixed with water evenly to make it suspended; If the sludge contains large impurities, it needs to be filtered and removed.
Nutrient preparation: Based on the analysis of sewage quality, according to BOD ₅: N:P = 100: 5: Prepare nitrogen sources (such as ammonium chloride, urea, etc.), phosphorus sources (such as potassium dihydrogen phosphate, etc.), and other necessary trace elements in a ratio of 1 to meet the growth needs of microorganisms.
Safety protection measures: Operators should be equipped with necessary safety protection equipment, such as gloves, goggles, protective clothing, gas masks, etc. They should be familiar with the safety operating procedures of sewage treatment plants (stations), understand the possible toxic and harmful substances in sewage and emergency response methods.
4, Domestication method
Asynchronous domestication method
-Activated sludge cultivation: Inject an appropriate amount of clean water or domestic sewage into the aeration tank (if treating industrial wastewater, a small amount of easily degradable organic wastewater can be added first), add inoculated sludge, and start the aeration system for closed aeration (without inlet or outlet). During the period of exposure, the dissolved oxygen (DO) should be controlled at 1-2mg/L, the water temperature should be maintained at 15-35 ℃, and the pH value should be maintained at 6.5-8.5. Daily microscopic examination of the mixed liquid in the aeration tank is conducted to observe the growth of microorganisms, while also detecting indicators such as sludge settling ratio (SV) and sludge concentration (MLSS). After 2-3 days of aeration, stop aeration, let it settle for 1 hour, discharge some of the supernatant, add fresh sewage or nutrient solution, continue aeration, repeat the above operation, gradually increase the number and amount of water inflow. As microorganisms grow and reproduce, the sludge concentration gradually increases. When MLSS reaches over 1000mg/L and obvious flocculent sludge appears, the activated sludge cultivation stage ends.
-Activated sludge domestication: After the activated sludge is cultured and matured, the sewage to be treated is gradually added to the influent, with an initial addition amount of 10% -20% of the design flow rate. As the activated sludge adapts to the sewage, the proportion of sewage to be treated is gradually increased, with each increase being 10% -20% of the design flow rate. After each increase, stable operation is carried out for 2-3 days to observe the settling performance, microbial phase changes, and treatment effect of the activated sludge (such as COD, BOD, ammonia nitrogen removal rate, etc.). If the treatment effect is good, continue to increase the proportion of sewage to be treated; If the treatment effect deteriorates, the increase in water inflow should be paused and the current operating state should be maintained until the treatment effect returns to stability. Until the sewage to be treated reaches full capacity and the domestication of activated sludge is completed.
Synchronous domestication method: Combine the two stages of activated sludge cultivation and domestication. Add an appropriate amount of clean water or domestic sewage to the aeration tank, and immediately start adding a small amount of sewage to be treated after adding inoculated sludge. At the same time, start the aeration system for aeration. Control the quality and quantity of incoming water to ensure an appropriate concentration of organic matter in the mixture and avoid impacting microorganisms. As microorganisms grow and reproduce, gradually increase the proportion and inflow of wastewater to be treated, while adjusting the aeration intensity and other operating parameters to ensure that microorganisms can grow and metabolize normally while adapting to the new environment. During the synchronous domestication process, closely monitor the various indicators and treatment effects of activated sludge, adjust operating parameters in a timely manner until the activated sludge can adapt to the full load of wastewater to be treated.
Inoculation domestication method: If conditions permit, excess sludge is directly introduced from nearby sewage treatment plants as seed sludge for aeration cultivation domestication; If surplus sludge can be diverted from sewage treatment plants with similar properties, it can further improve the domestication effect and shorten the domestication time. The dosage and operation steps of inoculating sludge are similar to the cultivation stage of activated sludge in asynchronous domestication method, but since the inoculated sludge has already adapted to a similar sewage environment, the domestication process may be relatively fast. During the domestication process, it is also necessary to gradually increase the proportion of wastewater to be treated, observe the adaptability and treatment effect of activated sludge, and adjust operating parameters in a timely manner.
5, Operational parameter control
Dissolved oxygen (DO): In the early stages of domestication, DO is controlled at 1-2mg/L. At this time, the microbial floc has not yet formed a good flocculent structure. Excessive dissolved oxygen can lead to excessive microbial metabolic activity, insufficient nutrient supply, and oxidation of sludge itself, promoting sludge aging; With the growth and domestication of activated sludge, DO is gradually increased to 3-4mg/L to meet the oxygen demand of microorganisms, ensuring that the microorganisms inside the sludge flocs can also receive sufficient oxygen, and improving the settling performance and treatment effect of activated sludge. Control DO concentration by adjusting the air volume, aeration time, or aeration method of the aeration equipment.
Water temperature: The suitable temperature range for microbial growth is 10-40 ℃, with the optimal temperature being 20-30 ℃. During the domestication process of activated sludge, the water temperature should be kept within an appropriate range as much as possible to avoid adverse effects on microbial growth caused by excessively high or low water temperature. When the water temperature is below 10 ℃, the metabolic rate of microorganisms slows down, their growth and reproduction are inhibited, and the domestication time is prolonged; When the water temperature exceeds 40 ℃, some microorganisms may suffer thermal damage or even die. The water temperature can be controlled by taking insulation measures (such as covering the aeration tank with insulation) or adjusting the inlet water temperature (such as mixing with other water at a suitable temperature).
PH value: In the aeration system of wastewater treatment by activated sludge method, the suitable pH range for bacterial flocs and bacteria is 6.5-8.5. Under this pH condition, the life activities and material metabolism of microorganisms can proceed normally, and the bacteria in the microbial floc can produce a large amount of viscous substances, which is conducive to the formation of good flocs in activated sludge. If the pH value is below 6.5 or above 8.5, it will affect the enzyme activity of microorganisms and the stability of cell membranes, leading to inhibition or even death of microbial growth. When the pH value exceeds the appropriate range, it can be adjusted by adding acid (such as sulfuric acid, hydrochloric acid) or base (such as sodium hydroxide).
Sludge concentration (MLSS): Reasonably control the MLSS concentration in the aeration tank according to the sewage treatment process and water quality requirements. Generally speaking, when treating high concentration organic wastewater, it is necessary to maintain a high sludge concentration, usually between 3000-5000mg/L; When treating low concentration wastewater, the MLSS concentration can be appropriately reduced. During the domestication process of activated sludge, the MLSS concentration is gradually controlled to meet the design requirements by adjusting the sludge return ratio, residual sludge discharge, and other methods.
Sludge settling ratio (SV): SV is an important indicator for measuring the settling performance of activated sludge, generally controlled between 15% and 30%. During the domestication process, SV is regularly measured to observe changes in the settling performance of activated sludge. If the SV is too high, it may indicate that the sludge has expanded or the sludge settling performance has deteriorated. It is necessary to promptly identify the cause and take corresponding measures, such as increasing aeration, adjusting water quality, adding coagulants, etc; If the SV is too low, it may indicate insufficient sludge concentration or poor microbial growth. It is necessary to increase the amount of inoculated sludge or adjust operating parameters appropriately to promote microbial growth and reproduction.
Nutrient ratio: According to BOD ₅: N:P = 100: 5: The ratio of 1 ensures that the nutrients in the sewage are sufficient and balanced. Regularly detect indicators such as BOD, ammonia nitrogen, and total phosphorus in sewage, and supplement nitrogen sources, phosphorus sources, and other trace elements according to actual conditions. If the proportion of nutrients is imbalanced, it will affect the growth and metabolism of microorganisms, and reduce the treatment efficiency of activated sludge. For example, insufficient nitrogen source can lead to hindered protein synthesis in microorganisms, affecting their growth and reproduction; Insufficient phosphorus sources can affect the energy metabolism of microorganisms and the stability of cell structure.
6, Monitoring and recording
Water quality monitoring: Daily testing of the water quality of the inlet, mixed liquid in the aeration tank, and effluent from the secondary sedimentation tank, including COD BOD, Ammonia nitrogen, total phosphorus, pH value, suspended solids (SS), etc. Adjust operating parameters in a timely manner based on changes in water quality to ensure stable and compliant treatment effects.
Monitoring of activated sludge indicators: Regularly monitor the MLSS of the mixed liquid in the aeration tank SV, The sludge volume index (SVI), dissolved oxygen (DO) and other indicators should be examined by biological microscopy at least 1-2 times a week to observe the changes in microbial species, quantity, morphology and floc structure of activated sludge, and to determine the growth status and domestication effect of activated sludge.
Equipment operation parameter recording: Detailed records of the operation parameters of equipment such as aeration system, mixing equipment, water pump, sludge return system, etc., such as air volume, mixing speed, flow rate, head, operation time, as well as equipment maintenance and fault repair records. By analyzing the operating parameters of the equipment, problems can be identified in a timely manner to ensure the normal operation of the equipment.
Environmental parameter recording: Record daily environmental parameters such as temperature and water temperature, and analyze the impact of environmental factors on the domestication of activated sludge and the effectiveness of sewage treatment.
