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RE: Poor Settling (but not filamentous)

Wiff P — Thu, 15 May 2008 10:49:42 GMT

Nadia, I'm checking in on this discussion 8 days after it started and 6 days after last post. Assume you're building MLSS per your give and take in the discussion. You never did mention whether you are treating industrial or municipal waste in response to another questioner and you only gave what I take to be a DO concentration at the end of the aeration tank, not at earlier points. Low DO concentrations can contribute to bulking if experienced outside a controlled anoxic zone, although I would normally expect that to be filimentous bulking. It is important to first assure you have a good environment (consistently aerobic DO levels, say 1.5 to 3.0 mg/L) and consistent pH levels (say 6.5 to 7.5).

To my experience zoogleal (non-filimentious) bulking can be caused by nutrient deficiencies, and or toxic chemical influences. I believe the earlier questions re. industrial waste was to see if you are limited in any nutrients (which might cause bulking, possibly P since it would appear you have plenty of N if you have significant levels of ammonia in the effluent) or other issues such as varying pH below say 6 or above say 9, highly varying influent, etc. If low nutrients or the presence of toxics are effecting you, then increasing MLSS may or may not help (likely not) and the better approach is to address the root cause of the problem (adding nutrient or removing toxics).

I assume you're calculating F/M based on influent BOD load to the aeration tank ratio'd to the weight of MLSS under aeration (not including clarifiers). The sludge age and F/M you cite are typical of extended aeration and while 1,600 mg/l is a bit low presumably it is low because your influent BOD is also low, presumably lower than design levels, and I'm not sure that changing your MLSS through reduced wasting will help in this instance.

Your recycle (assume you mean return sludge) should be set based on what is happening in your final clarifiers primarily and if blanket levels are low you are probably returning enough but if high you may want to increase the return rate. With poor settling however, you may reach a point at which higher return rates hurt rather than help (solids loading limited) so you will want to experiment carefully with return rates taking your cues for proper return rate from the sludge blanket levels in your clarifier(s). I don't know where those are currently or if you've had solids washout problems.

The more process info you share on line the better various folks who check in can help you so would encourage you to keep feeding information in.

RE: Poor Settling (but not filamentous)

nadiae — Fri, 09 May 2008 10:16:23 GMT

Dear Mr. Koch,

I send you a PM, anyways.

Before you said it would be good to put down the waste line and the return sludge. But now you mention somthing about putting the return line up. I didn't get that very clear.

Thank you

RE: Poor Settling (but not filamentous)

J.W.Koch — Fri, 09 May 2008 09:26:44 GMT

You need to increase your mlss this will help you achieve some degree of nitrification. With the mlss that low it is likely you over wasted and are now over aerating which would explain the high ammonia. So try building the mlss and increasing the return sludge rate. keep us posted

RE: Poor Settling (but not filamentous)

nadiae — Fri, 09 May 2008 09:05:05 GMT

It would be great if we can get some nitrification going. We can change the velocity of the first and second agitator.

What about the recicle line that you told me before?

RE: Poor Settling (but not filamentous)

J.W.Koch — Fri, 09 May 2008 08:23:32 GMT

Are you required to nitrify? Is the high ammonia in your effluent? Is there any speed control on the mixers?

RE: Poor Settling (but not filamentous)

nadiae — Thu, 08 May 2008 15:45:29 GMT

Another thing,

We are having high levels of Amonia and low of Nitrite and Nitrate at this moment.

We can put down the recicle line, in which way would taht help?

RE: Poor Settling (but not filamentous)

nadiae — Thu, 08 May 2008 15:37:08 GMT

Thanks for the answer.

The Mholman Index is the SVI index. When you put the sludge in a tube you see like smooth.

I am not really sure if it works at extended aireation. The F/M and sludge age goes with it, but not the LVR, which is aproximately around 1.0.

The lay out of the aireation tank is six surface aireator Actirotor and it works as a piston flow. The first 3 aireator give more oxignen than the other 3. The OD in the last 3 is about 3ppm.

Does it help?

RE: Poor Settling (but not filamentous)

J.W.Koch — Thu, 08 May 2008 13:33:33 GMT

Your F/M is in the range of extended aeration and I guess it safe to say that this is an extended aeration plant you are operating? Your MLSS # is very low specially for extended air typically anyways. Sounds like you may be over wasting and over aerating. Decrease your wasting and let your MLSS build up. You may want to try and reducing the return sludge rate if this is possible. This depends on how much you are returning compared to your influent "raw sewage" flow. If your plant is extended air I would try not wasting for awhile.

When observing the settability test how does the MLSS look in the cylinder is it smooth or granny in appearance? And what does Moholman mean ?

RE: Poor Settling (but not filamentous)

nadiae — Thu, 08 May 2008 13:03:35 GMT

Ok, I have done a few numbers... The sludge age is set to 30 days (taking into account the TSS of aireation tank and sedimentation tank), and it's done by wasting an amout of effluent, but the recicle is set at a constant rate (could this be one thing???).

I get an F/M of about 0.02/0.03, HRT is 35 hours (only the aireation tank), the MLSS is at about 1600mg/l (which I think is low) and in the recicle line in about 3000mg/l and with that we are getting an Moholman Index of more than 400.

We don't have a filamentous problem... What can you say about it?

Thank you

RE: Poor Settling (but not filamentous)

J.W.Koch — Thu, 08 May 2008 11:04:50 GMT

There are lots of things you can check. mixed liquor suspended solids in your aeration basin, pH, Dissolved oxygen and you could be over or under wasting. Look at these and let us know.

RE: Poor Settling (but not filamentous)

Victor — Wed, 07 May 2008 12:55:59 GMT

Nadia:

You say you have settling problems but do not describe the type of plant, domestic/industrial, flow, nutrient removal, whether you have bulking issues. You can still get bulking problems without filaments such as viscous/zoogleal bulking. Need more information about your plant before any help can be given as well as a microscopic examination of your mixed liquor.

Poor Settling (but not filamentous)

nadiae — Wed, 07 May 2008 11:20:02 GMT

Hi, in the plant we have a poor settling in the clarifier. We are working with not many filamentous m.o. but the settling is very poor.

we have a constant RAS flow. Do you think that could be the problem? What parameters should I check?

Thank you