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Common Problems and Countermeasures of Anaerobic Process in Sewage Treatment

2023-02-07 16:40:42

  Question 1:

We have an anaerobic pond, which is being debugged. We haven’t added flour for five days, and now the sludge in the pond has turned black, and a lot of green algae has grown. What’s going on? How to solve it?


  There is no abnormality in the black sludge in the anaerobic tank. I wonder if the effluent index fluctuates abnormally. Algae can be seen in the clear liquid on the liquid surface, but should not exist in the mixed liquid.

  Question 2:

A very strange phenomenon, UASB effluent COD 4000, ammonia nitrogen 60, total nitrogen 120, PH6.5, after passing through the aerobic pool, COD500, almost no ammonia nitrogen, total nitrogen 40, but the pH reached 8.3. Why is this? How to explain it?


  1. It depends on whether it has been the case for a long time or recently. If it is the case for a long time, you should consider the water quality of your industrial wastewater. If it only happens occasionally recently, it is mostly caused by fluctuations in water intake. For example, if your total nitrogen has dropped, it means that denitrification has also occurred, and it has occurred relatively fully. When the nitrification reaction is not obvious, not only the denitrification alkalinity can make up for the nitrification process, but there is even a surplus, resulting in an increase in the pH of the effluent.

  2. In addition, you also need to consider whether the PH value you detected is reliable, that is, whether the PH value has been strictly corrected.

  Question 3:

Problem: Management of wastewater treatment plants in paper pulp mills. The pulping process of our company adopts the neutral sodium sulfate method. The middle section of water treatment adopts regulating tank, UASB, and combined biochemical and biological filter. Now the COD of the effluent in the anaerobic tank continues to be around 1200, but the combined biochemical tank does not drop at all. We continue to explode in 24 hours, but the oxygen content has been maintained between 0.2-0.6, and the water body is black. I don't know what the reason is, how should I solve it?


  1. 24-hour aeration does not mean that the aeration is sufficient, and it depends on whether the aeration capacity is satisfied.

  2. Reduce the return flow of the biochemical pool to see if it is effective.

  Question 4:

Due to the misoperation of the operator, all the sludge in the UASB was pumped into the aerobic tank. Now the aerobic tank is sampled for SV. The supernatant is very dark and turbid, and the sedimentation speed is slow. The sludge has become black. After I discovered this accident, I stopped the aeration, and after the aerobic tank settled for a period of time, I discharged the sludge in the aerobic tank into the UASB part. Should I return all the sludge that flows into the UASB at one time or slowly return the sludge to the UASB? What to do next in operation?


  Since UASB sludge has flowed into the aerobic zone, it needs to flow back into the UASB system as soon as possible. Due to the large proportion of anaerobic sludge particles, the aerobic part of the returned mixed solution will still flow out of UASB, while anaerobic sludge particles will continue to stay in UASB so that the impact on the system will not be too great. In the case of anaerobic pool, the recovery is much faster than UASB, so the focus is on your UASB.

  Question 5:

Our factory produces jelly wastewater with high sugar content. Generally, the effluent COD is 7,000 to 8,000, and sometimes it is more than 10,000. It is easy to acidify, and the PH is difficult to control manually. The self-adjusting PH circulation pump is broken and the PH can only be adjusted manually. Since then, the COD has started to rise, and it has not been able to drop until now. After stopping for a long time without water inflow, the sludge concentration is very low, but granular sludge can be seen. No methane was produced. Throw a truckload of sludge into it and recirculate it. After more than 2 weeks, there is still no effect, the water quality is more yellow, and there is a rust-like substance on the UASB liquid surface. But still no removal rate. I don't know why?


  The granular sludge you see now is impacted by pH, and the treatment efficiency is reduced. It is tangible, but not really, and the granular sludge takes a long time to cultivate, so the recovery is slow, and it needs to be recovered patiently, otherwise, more haste is wasteful.

  Question 6:

In the case of no water inflow, the air bubbles on the surface of the UASB pool are reduced, and the amount of biogas is very small. The COD has dropped from more than 700 to more than 200. It is obviously in the ground load operation. The sludge in the CASS pool is aging. The result is aeration without water. I don’t know why? Without aeration, I am afraid that the aerobic mud will lack oxygen. In this case, how should we deal with it?


  Half a day without aeration is fine, but it is not better without aeration for more than one day, especially when the sludge concentration is high. The best way is to maintain the minimum amount. Generally, it can be stopped for 4 hours and turned on for 10 minutes to maintain aeration.

  Question 7:

A UASB system is running in a starch factory, and an acidification tank is installed in front of the anaerobic reactor. Generally, the COD of the influent water is 16000mg/L, and the VFA is 4500~5000mg/L; the COD of the effluent water is 900mg/L, and the VFA is 120mg/L L; but recently the COD of influent water has risen to 20,000mg/L, while VFA has gradually increased from 5,000 mg/L to 8,000mg/L (COD is still around 20,000mg/L), and the effluent COD is currently at 1,500mg/L, and VFA is around 200mg/L Fluctuation. I would like to ask the reason for the continuous increase of VFA under the condition of stable COD. Is it caused by incomplete acidification and too much macromolecular acid? Will it have adverse effects on the UASB system?


  It can’t be called high, mainly because your influent water concentration is high. Naturally, if the system does not keep up (adapt to the increased pollutant concentration and passively increase the microbial biomass), your effluent pollutant concentration will rise. Judging from the increased ratio, it is normal. The system should be corrected automatically, and the removal rate will increase subsequently.

  Question 8:

What I debug is a wood processing factory wastewater, the process is UASB+SBBR process. Now the COD of the water in UASB is about 5000, and the pH is about 7.5--8. The effluent COD2500--3000, PH around 6.5. The water temperature in the pool is 16--20 degrees. At this stage, the hydraulic load in the pool is 0.24m3/(m2.h), the volumetric load is 0.083KgCOD/(m3.d), the sludge load value cannot be done, and the water has been fully loaded. In the follow-up SBBR tank, PH7.5 and SV25% were tested unconditionally by MLSS. The COD of the effluent in the biochemical tank was about 350, and the F/M value must be high. However, the specific value of F/M is unclear because MLVSS cannot detect it. The effluent index is COD≤100mg/L. Please tell me the key to this problem. Is it because the temperature in the UASB pool is low and VFA is accumulated? In addition, what should be done in the SBBR pool?


  The temperature affects the UASB treatment effect. For the SBBR system, if the influent water is 2500-3000 and the outgoing water is 350, the removal rate is close to 90%, which should not be low.

  Question 9:

Production wastewater treatment, the production process is adjusted according to the raw material formula, the influent COD4000-6000, the combination process of adjustment-UASB-sinking-SBR is adopted, and a submersible return pump from the middle sinking to the UASB is installed, which has been adjusted for more than half a year. After adjusting well, it is easy to acidify. The PH of the adjustment pool is adjusted to 9. The PH in the UASB has been around 5, and the SBR is around 6.5. The COD of the UASB effluent is also not stable, ranging from 1500-3000, so it is difficult for the SBR to effluent It has reached the standard; the sedimentation ratio observation shows that the sludge properties are not good, and the separation is not obvious, the chroma is higher than that of the influent, and it is obviously yellowish, and it has not been treated. Is there any inhibitory component in the wastewater? Please ask if you are familiar with this type of wastewater What's the best way to do it?


  Is it possible to adjust the pH (dosing sodium hydroxide) after the UASB is out of the water, otherwise the pH of 6.5 is still difficult to control for the SBR. In addition, according to the sludge concentration of your effluent SBR? If the sludge concentration is low or high, it will also affect your effluent color and removal rate.

Common Problems and Countermeasures of Anaerobic Process in Sewage Treatment

  Question 10:

The recently debugged anaerobic reactor has a lot of mud in the effluent, and the measured settlement ratio is as high as 20%~30%, most of them float up, and the surface sludge is sticky. The measuring cylinder is taken from the sampling port of each layer of the anaerobic tank. It is also 30%~40% that floats up, and less than 10% that settles down. The anaerobic effluent goes to the first settling tank, and the surface of the first settling tank is also a thick layer of viscous foam, which cannot settle down. As a result, it goes to the aerobic tank, resulting in a large amount of aerobic sludge, the highest SV is 70%, and the dissolved oxygen is also consumed. , the aerobic sludge discharge can't be discharged. This situation has continued for more than a week.


  It should be that the anaerobic effect is good, more gas is produced and the sludge floats up, right? This is related to weather, water intake, etc. If the floating objects in the first sedimentation tank are broken and can sink, it is estimated that the flow into the biochemical tank in the latter stage can be reduced.

  Question 11:

This is the treatment of beer wastewater. The process is primary sedimentation tank-regulating tank-UASB-aerobic tank-secondary sedimentation tank. The UASB anaerobic tank has a capacity of 3200 cubic meters and is divided into two groups for water inflow. The design The rising flow rate is 0.9 m/h, but now the problem is that our anaerobic removal rate will always fluctuate, sometimes it can be stable above 80%, but sometimes it will go down again, and the COD value of the influent is normally 1500 Left or right, sometimes it may be lower. The influent flow rate is changing according to the production situation. Our anaerobic system has an internal circulation pump. Every time the amount of sewage is not enough, I will add internal circulation. How can the anaerobic system run stably? ? In addition, the sludge concentration we added to the anaerobic tank at the beginning was about 30,000, and now the sludge concentration in the east and west groups has decreased. I wonder if there is any impact?


  It is still necessary to count and analyze the data to see the status of other indicators when the removal rate is low, so as to establish a correlation so that the reason for the fluctuation of the removal rate can be verified.

  Question 12:

For the anaerobic biochemical system, which is better to use hydrochloric acid or sulfuric acid to adjust the pH?


  The excessive addition of both will inhibit the system, but the inhibition of sulfuric acid is more obvious than that of hydrochloric acid. Therefore, as you said, hydrochloric acid is mainly used, but if the dosage is not large, hydrochloric acid can also be added.

  Question 13:

Regarding beer wastewater, because beer production is generally divided into off-season and peak season, in the off-season, it is mainly used for bottle washing and car washing in the production workshop, most of which are waste lye, so when it comes to our sewage station, the pH is always on the high side, when entering the water collection well, the PH can reach above 11, and the regulating tank is about 8.3, so the acid has been added, and the dosage is quite large, and the anaerobic system is generally controlled at 7-8, so now I want to solve the off-season use Aiming at the problem of high acidity, I thought about it for a while, and decided whether it is possible to use pipes to introduce anaerobic effluent into the adjustment tank, because normally the pH of the adjustment tank is significantly higher than the pH of the anaerobic effluent, and I also press 1: 1 Sampling was done to measure the mixed pH, and it was found that the pH had dropped significantly, but I was thinking about it. Generally, the COD value in the anaerobic effluent is still around 300-400. These should be difficult to degrade. In case of adjustment Will it affect the anaerobic system if it is mixed with raw water after the pool? After mixing in this way, will the COD of the mixture increase or decrease? The COD of the adjustment pool is generally around 1500. Is this advisable? I don't know whether the COD of the mixture is rising or falling.


  The focus is on whether the increase in water volume after backflow will exceed the hydraulic load of the anaerobic system. As for whether the concentration of the mixed solution will increase, I think that if you enter the water at 1500 and the return liquid is only 400, the cod will be reduced after natural mixing. As for the difficulty of degrading, whether you reflow or not, it is the same in the system, so there is no need to worry about it.

  Question 14:

USAB has sludge in the water outlet. After sampling for a period of time, all the sludge can settle and the supernatant is relatively clear. Pour the settled sludge into your hand and see that the sludge is flocculent with rough edges. There is no Granular sludge exists. Personally, I don't think this kind of mud phenomenon is important, I don't know if it is correct. The COD of the UASB influent is around 2000. Today, the distribution of the UASB effluent was taken to test the supernatant and muddy water mixture. The COD of the supernatant was 354mg/l, and the COD of the muddy water mixture was 1330mg/l. The system only operates during the day and does not receive water at night.


  It takes time to form granular sludge, I don't know how long you have cultivated it. If you are in the process, then continue to observe.

  Question 15:

Our factory used an improved IC before aerobic treatment, but after several months of debugging, it was still not good, and it went back and forth. Now in the monitoring, we found a problem with dissolved oxygen. In order to reduce the COD of the influent water, a small amount of water inflow + a large amount of circulation is adopted, but the circulation process causes oxygen to be mixed in. The measured DO of the circulating water is about 2.5 PPM, and the DO of the IC effluent is about 0.7 PPM. Became 1.27 PPM, is this system normal? Will DO be the fatal factor?


  The IC reactor is dominated by anaerobic bacteria, and if the dissolved oxygen control is not good, it must be badly debugged. In addition, the flow rate should be well controlled to avoid sludge loss.

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