Is volume of aeration basin enough and how much air, what difuzors and blower is needed?
asked 10 July 2017 asked by Lavica (450 points)
Hello Lavica, It may very well be that you do not have enough oxygen transferring to your mixture. However, this may be because the aeration basin was not designed to take the load. The aeration system may be under powered. Or as you mentioned, the system may need some cleaning. With the limited information you provided, it would be difficult to assess if you are simply overloading the aeration tank or if the problem is coming from somewhere else. How long does this aeration system has been running? Is this a one time occurrence? Did it happen before? How long have you had the aeration running since it was last maintenanced? Is the pressure reading on the blower within acceptable range? Thank you
Hello, thank You for the answer. Our plant should go under reconstruction but we have to work till then under these conditions. We had sewer cleaning and we have about 100-200 m3 septic water per day and inflow of about 7500 m3 per day, but on this line is coming about 6000 m3 per day. Aeration is running for about 6 years and as I know basins haven't been emptied since. As been told pressure is ok. We had periods without enough oxygen but not for such a long period. If we close valves for air for two of four basins (it is one line for four basins) we can get our oxygen. So what could be the problem?
Lavica, The information you provided is limited, but I will try to give you some ideas to check on. 1st, as Floating Cover Expert noted, you have insufficient detention time in the aeration basin. You have 6 hrs. detention. The BOD loading is extremely high. On the maximum level, the loading is 3000 to 3100 ppd BOD/1000cf. If you haven't cleaned your diffusors in 6 yrs., they are probably clogged to some extent. You can recognize this as some sections of the aeration basins will not have many bubbles near the surface while other spots maybe roiling at the surface. I would definitely get in there and begin cleaning them out. Some of the other things you did not mention would help us to help you. What kind of diffusors do you have, coarse or fine bubble? How deep are your aeration basins. What is the rating capacity of your blowers, scfm at psig? How many blowers do you operate at once? What is blower motors horsepower? For the present, can you series the flow through the aeration basins? Another words have one basin flow into another before discharging to the clarifiers. This sometimes can help when you are overloaded like this. What are your MLSS and MLVSS concentrations? Have you performed a microscopic examination of your mixed liquor or return sludge. I suspect with your overloading you do not have a lot of rotifers which are indicative of a highly polished effluent. What are your effluent SS and BOD concentrations from the clarifiers? Do you have a problem with filamentous bacteria in your clarifiers? If you do, I would suggest temporarily stopping the sewer cleaning. Septic water is a good source of filamentous and when they hit air in the aeration basins they usually flourish. Finally, what is your DO concentration in the aeration basins?
Thank You for the answer! We have problems with filamentous bacteria and we have problematic clarifiers and high SVI. At the moment I don't see filaments out of floculas but I don't stain them. Our problem is that we have lately oxygen about 0.7-0.9 mg/L and blower (we have one) is constantly working. Today we reached 1.5-1.8 but than it drops. My question is also if I can't reach enough oxygen should I waste more sludge because there will be more filamentous bacteria and if I waste more sludge than water is not cleaned and there is white foam and still not enough oxygen. Sorry for my English, I didn't check translation so I hope You understand.
How high is your SVI? Your plant is definitely overloaded. Is there any time of the year when the flows and loadings are less than what you reported earlier? If there is, I would clean your diffusors then, but not now during these high loadings. You are in a very vulnerable position with only 1 blower. The DO should be consistently between 1 and 2 ppm. The low readings are occurring during your high hourly loadings and when the low hourly readings occur when loads are low. What is your sludge age or what is your MLSS? If you increase wasting, do not increase by more than 10% week. The white foam indicates you either do not have enough sludge or your loading is so high you are constantly producing more microorganisms. You are not in a good predicament, but get back to me with your SVI, MLSS concentration and clarifier volume(s). Hopefully, I can provide you some more information that will temporarily help you. You are really overloaded. I really would advise stopping the dumping of sewer cleanings to the plant until you get the filamentous and SVI under control.
Thank you. I will give you information tommorow. Good night