Technical sharing: Cultivation and acclimatization of activated sludge

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This post was last edited by hesonchang214 on 2012-6-24 21:59. There are various methods for cultivating activated sludge, but different methods require different amounts of time, as well as human and material resources. The cultivation method should be selected based on factors such as the quality of the wastewater, climate, and the conditions specified in the permits. 1. Preparatory work before construction: (1) All structures are built, construction waste is removed through cleaning, static compaction is carried out to ensure there are no leaks or settlement issues, and finally they are inspected and approved in accordance with relevant regulations. (2) All equipment such as electrical appliances, motors, and pipelines have been installed, and single-unit tests as well as joint tests have been completed successfully. Finally, it passes the acceptance inspection in accordance with the relevant regulations (instructions). (3) Depending on future operational needs, sewage treatment plants that meet the requirements should carry out basic routine testing, such as pH, water temperature, COD, DO, and biological oxygen demand, to guide the cultivation of activated sludge and daily operations. (4) Investigation of basic data, including the diurnal variations in sewage flow, water quality (pH, water temperature, COD, BOD5, nitrogen content, phosphorus content, toxic substances, etc.) and their changes, as well as the technical parameters of various facilities and equipment. (5) Provide sufficient essential nutrients (carbon source, nitrogen source, phosphorus source) based on the quality of the water to be treated, so that any deficiencies can be addressed. When using the inoculation culture method, it is also necessary to have an adequate supply of dry (or concentrated) sludge from other wastewater treatment plants with similar wastewater characteristics, to serve as the microbial strain for culturing the activated sludge biomass. (6) Operators should be familiar with the piping layout and utility systems of the entire system, as well as understand the basic process of sludge cultivation and the associated control requirements. (7) Once the personnel are in place, the system should generally operate continuously after training and acclimatization; no one should be removed from it. (8) Prepare the necessary original records and reports for testing and operation, as well as establish preliminary rules and regulations. Starting from the culture cultivation phase, a more standardized organizational and management framework is gradually established to ensure a smooth start-up and subsequent operation. 2. Natural fermentation: Natural fermentation is also known as the direct fermentation method. It is a cultivation process that makes use of the small amount of microorganisms already present in wastewater to allow them to multiply gradually. For urban sewage and some industrial wastewater with a relatively complete range of nutrients and low toxicity, such as that from food factories and meat processing plants, this cultivation method can be considered; however, the cultivation time is relatively long. Natural fermentation can be further divided into batch fermentation and continuous fermentation. (1) Batch fermentation. Fill the aeration tank with wastewater and carry out anoxic aeration (that is, only aeration without adding wastewater). After a few days, stop aeration, let the mixture settle for 1 hour, then remove about 1/5 of the upper layer of wastewater from the tank and add an equal amount of fresh sewage. These processes of aeration, settling, and water addition are repeated in this manner, with the amount of water added each time being greater than before, and the aeration time being shorter than before. During spring and autumn, sludge can be initially cultivated in about two to three weeks. When the sludge concentration in the aeration tank mixture reaches around 1 gram per liter, continuous water feeding and aeration can proceed. Since the sludge concentration is low in the early stages of cultivation, less sludge accumulates in the sedimentation tank, and thus the amount of sludge returned is also lower. As the amount of sludge increases, the quantity of sludge returned also increases accordingly. Once the sludge concentration reaches the level required by the process, normal operation can begin, with control carried out in accordance with the process requirements. (2) Continuous culture. First, fill the aeration tank with wastewater, then stop the inflow of water. After allowing aeration for half a day to a day, water can be supplied continuously again. With continuous aeration and the inflow rate being increased gradually from low to high, and after operating continuously for a period of time (similar to the batch method), activated sludge will appear and gradually increase in quantity. When the sludge volume in the aeration tank reaches the concentration required by the process, it is controlled in accordance with the process requirements. Since the natural microbial cultivation method involves directly culturing activated sludge using wastewater, the cultivation process is also one in which microorganisms gradually adapt to the properties of the wastewater and become acclimated. 3. Incubation for inoculation: This method requires a shorter incubation time; it is a commonly used approach for culturing activated sludge and is suitable for most industrial wastewater treatment plants. There is a type of mud found near urban sewage treatment plants, which can also be used to shorten the cultivation time. The two commonly used methods for inoculation culture are as follows: (1) Inoculation culture with concentrated sludge. Concentrated sludge from a nearby wastewater treatment plant is used as a strain (seed sludge) for cultivation. For the cultivation of activated sludge in systems for treating urban wastewater and industrially wastewater that is rich in nutrients and low in toxicity, seed sludge can be added directly to the wastewater to be treated and aeration can be carried out; once the sludge turns brownish-yellow, the wastewater can be fed in continuously (with the flow rate gradually increased). At this point, the sedimentation tank is also put into operation to allow the sludge to circulate within the system. To accelerate the cultivation process, unfermented manure water or other nutrients can be added during the cultivation. The microbial cultivation process is complete once the activated sludge concentration reaches the required value for the process. Economically speaking, the amount of sludge used should be as low as possible; under ideal conditions, the sludge concentration of the mixed solution after dilution should be maintained at above 0.5 g/L. When culturing toxic industrial wastewater, river water can be introduced into the aeration tank first, or tap water can be used (which needs to be aerated for some time to remove any residual chlorine). After that, seed sludge and untreated manure wastewater are added and aerated until the sludge turns brownish-yellow; at this point, aeration is stopped, the sludge is allowed to settle and part of the supernatant liquid is removed. An additional amount of manure wastewater is then added and aeration continues. Once the amount of sludge increases significantly, the flow rate of the wastewater is gradually increased. In the later stages of cultivation, the microorganisms in the sludge have been able to adapt well to the quality of industrial wastewater. (2) Inoculation and cultivation of dry sludge. ““Dried sludge” generally refers to the sludge cake obtained after dehydration using a dehydrator, with a moisture content of 70–80%. This law applies to remote areas and situations where the distance for transporting the sludge used for seed production is long. The process of inoculating dry sludge is basically the same as the method of enriching concentrated sludge with microorganisms. For sludge inoculation, use fresh sludge cakes that have just been dewatered; before adding them to the aeration tank, a small amount of water should be added and the mixture should be turned into a slurry. The amount of dry sludge added is generally 2 to 5% of the tank volume. Dry sludge may contain a certain concentration of chemical agents (used for sludge conditioning); if the concentration of these agents is too high or their toxicity is significant, it is not suitable to be used as seed sludge for culturing bacteria. To determine whether sludge can be used for inoculation, a small amount of the sludge can be crushed and placed in a small container such as a beaker or plastic bucket; water is added and aeration is provided. If the color of the sludge changes to yellow after some time, it can then be used for inoculation. Precautions for sludge microbial cultivation: (1) During the cultivation of activated sludge, it is necessary to regularly measure parameters such as the pH, COD, ammonia nitrogen of the influent water, the dissolved oxygen in the aeration tank, and the sludge sedimentation properties. After the activated sludge is initially formed, no observation of the biological community should be carried out; instead, the cultivation status of the sludge should be assessed based on the observations, and the fermentation process should be adjusted dynamically. (2) The cultivation of activated sludge should be carried out as much as possible during the season with suitable temperatures. Because the temperature is suitable, microorganisms grow rapidly, resulting in a short cultivation time. If culturing can only be carried out in winter, the inoculation method should be used, and more seed sludge is required than in spring and autumn. (3) During the culture process, especially after the sludge begins to form, care should be taken to prevent excessive auto-oxidation of the sludge, particularly in summer. Many factories have experienced such situations. This not only increases the culture time and costs, but may even result in the wastewater treatment system failing to be put into operation on schedule. To prevent the sludge from oxidizing on its own, it is crucial to control the aeration volume and duration; the dissolved oxygen level in the tank should be monitored regularly, and water should be added as needed to meet the nutritional requirements of the microorganisms. If the influent concentration is too low, manure and similar substances must be added to supply nutrients; intermittent aeration can be used when such conditions are not available. (4) In the later stage of activated sludge cultivation, appropriately removing some aged sludge facilitates further growth and reproduction of microorganisms. (5) Industrial wastewater treatment plants usually have no wastewater inflow before the production units come online, but once the production units start operating, the wastewater generated must be treated promptly. At this time, the culture time should be determined reasonably based on actual conditions, and seed sludge as well as nutrients should be prepared in advance. (6) If the sludge in the aeration tank has matured but no wastewater is flowing in, aeration should be stopped to put the sludge into a dormant state, or intermittent aeration should be used (by increasing the aeration interval and reducing the amount of air supplied), in order to minimize the rate of self-oxidation of the sludge. When possible, nutrients such as manure and non-toxic organic waste (such as kitchen scraps) should be added. (7) Most wastewater treatment plants have two or more aeration tanks. In this case, activated sludge can first be cultivated in one aeration tank, and then transferred to adjacent aeration tanks for multi-stage expanded cultivation. This law applies to large-scale wastewater treatment plants.