When starting the activated sludge system in a sewage treatment plant, the first step is often to inoculate the sludge. But you know what? Different types of sludge require specific methods of addition! Today we will break and crush it, and talk about the methods of adding activated sludge during inoculation.
1, Common types of sludge: first clarify what the "main force" looks like
The inoculated sludge we usually come into contact with is mainly divided into three categories: dehydrated sludge, concentrated sludge, and residual sludge, each with its own temperament.
1. Dehydrated sludge: This type of sludge is usually dehydrated by filter presses and centrifuges, with a moisture content that can be reduced to 75% -85%. It looks like "mud bricks" and is easy to transport and store. However, during the dewatering process, the microbial activity in the sludge will be "suppressed", and a way must be found to "awaken" them before use.
2. Concentrated sludge: it is directly discharged from the secondary sedimentation tank. The sludge after thickening treatment has a moisture content of 95% -98%. It is a bit like thick Congee and has good fluidity. Microbial activity is relatively high, but it is prone to "spoilage" during transportation, so it is best to use it as soon as possible.
3. Excess sludge: Fresh goods that have just been discharged from the biochemical tank have a moisture content of about 99%, almost in liquid form, and have the strongest microbial activity. However, the problem is that they are too large in volume, have high transportation costs, and are easily prone to losing their temper due to lack of oxygen during transportation, resulting in a large number of microbial deaths.
2, Big competition of adding methods: different sludge needs different "services"
(1) The "resurrection" addition method for dehydrated sludge
Because the dehydrated sludge is too dry, it is definitely not feasible to directly put it into the aeration tank. It needs to be soaked first!
1. Dissolution pretreatment: Find a large tank, put the dehydrated sludge into it, and mix it with water in a ratio of 1:5-1:10 (sludge and water). Slowly stir with a blender, like soaking dry goods, allowing the sludge to fully absorb water and soften. This process may take 2-4 hours until the sludge becomes a uniform paste.
2. Secondary activation: Add nutrients such as glucose and urea to the dissolved sludge, and then aerate with air for 6-8 hours to "charge" the microorganisms and restore their activity.
3. Batch addition: Do not pour all of it into the aeration tank at once, add it 3-5 times, with an interval of half a day to a day between each time. This can allow the microorganisms in the aeration tank to adapt and not "strike" due to sudden "environmental changes".
(3) The 'race against time' method of adding surplus sludge
The residual sludge has strong activity but a short shelf life, and must be quickly resolved:
1. Direct on-site transfer: If the remaining sludge comes from a nearby sewage treatment plant, it should be transported directly by pipeline or tanker and immediately connected to the aeration tank. It is best to control the time from sludge discharge to feeding into the aeration tank within 3-4 hours, and the shorter the time, the better.
2. Anti hypoxia measures: During transportation, the tank truck should be sealed and filled with nitrogen or compressed air to prevent sludge from lacking oxygen. If the transportation time exceeds 2 hours, it is recommended to add a small mixing device to the tanker to prevent the sludge from settling and maintain its activity.
3. One time addition: Due to the dilute state and high activity of the remaining sludge, a sufficient amount can be added at once. The dosage is calculated based on the volume of the aeration tank and the designed sludge concentration. Generally, the initial sludge concentration in the aeration tank should reach 1500-2000mg/L. After adding, immediately start aeration and stirring to quickly integrate the sludge into the system.
3, Guidelines for Avoiding Pitfalls during the Investment Process
Regardless of which sludge or addition method is used, attention must be paid to these details:
1. Temperature control: When adding sludge, the water temperature in the aeration tank should ideally be between 20-30 ℃. The temperature is too low, and microorganisms are "frozen" and do not like to work; The temperature is too high and it is easy to suffer from heatstroke. If the water temperature is not suitable, it can be adjusted through heating or cooling equipment.
2. Monitoring water quality: Before and after adding, the water quality indicators of the aeration tank should be tested, such as pH value, dissolved oxygen, COD, etc. The pH value should be maintained between 6.5-8.5, and the dissolved oxygen should be controlled at 2-4mg/L. Any abnormalities should be adjusted promptly.
Step by step: Don't try to increase the sludge concentration to the design value all at once, add it in stages. For example, adding 30% of the planned amount on the first day, adding another 40% on the second day, and filling it up on the third day. Providing microorganisms with a process to adapt to new environments also facilitates our observation of system reactions.
The method of adding activated sludge inoculation may seem simple, but it actually contains hidden mysteries. Only by selecting the right method based on the type of sludge and paying attention to various details can our sewage treatment system start smoothly, and microorganisms can also "happily" decompose pollutants! Next time you encounter sludge inoculation, don't forget to try these methods!
