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Will.B.

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poor settling sludge..then rising sludge
Mar 26^th, 2012, 10:14pm

The WWTP is for a dairy manufacturing plant. Uses upfront tank then SBRs. No DAF. Normally has settling problem due to high filamentous population. This gets controlled by Hypo. However 6 weeks ago the filamentous started to reduce. Settling was good. No Cl use.
3 weeks ago nearly all the filamentous had gone. Settling started to get very poor. Settling normally less than 3 hours. Then went to 10 hours. Now sludge rising after long settle. Production say they have not changed any procedures or sanitisers. Only difference is COD from plant has dropped. Also reduced labor so the SBR's didnt discharge for long periods (did this stuff the biology). Most likely denitrification in long settle period. Normally have great numbers of filaments, protzoa and metazoa but all gone. Why? Please help. desperate

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grrun

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Re: poor settling sludge..then rising sludge
Reply #1 - Mar 26^th, 2012, 11:48pm

How is the SBR controlled? Are the cycles timed; actuated on levels; or manually controlled? Having trouble understanding settling times from 3-10 hours.

Has the flow to the SBRs changed. Rising sludge indicates denitrification, but 10 hours is too long for settling.

What was the SRT when settling was good?

describing the operational cycles of the SBR (including DO) would be helpful.

grrun

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Will.B.

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Re: poor settling sludge..then rising sludge
Reply #2 - Mar 30^th, 2012, 2:04am

Hi Grrun,
SBR cycle:
Starts at idle 65% level, no DO.
Fills 8% at 8L/sec and aerates, no DO. Waits for DO 2. Then waits 30 min at DO 2.
Fills another 8% and aerates, no DO. Waits for DO 2. Then waits 30min
Fills another 8% and aerates ect ect.
Fills 6% waits DO 2. then DO of 2 for another 30 min. 95% level. Then settle.
In a cyclce normally 170 kL of waste at 2800 mg/L (varies 1500 to 4000mg/L). Cycle 24 hours on average. Intermitant fills due to varing COD of influent. Normal take 3 hours to settle.
COD of factory dropped and then higher DO levels were achieve alot faster. Then filaments disappeared. Then protozoa and metazoa disappeared then settling went to 6 hours then weeks later 10 hours. The denitrification and rising sludge. Settling was based on a clear sample tube being lowered into the SBR which collects layers in SBR. Shows clear water on top and interface b/w sludge. When below mark on stick the operators discharge. Dont know why bacteria and larger life forms disappeared. LACK OF FOOD?? or TOXIC KILL?? I am at a loss.

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The sludge judge

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Re: poor settling sludge..then rising sludge
Reply #3 - Mar 30^th, 2012, 11:09am

I think getting a microscopic examination by a professional is a good place to start to get to the root of the settling problems.

Toxicity isn't a factor if the floating sludge is due to nitrification (the nitrifiers are pretty sensitive). Do you have the ability to test soluble COD in your MLSS (filter this) prior to the settling cycle? This number is very useful. Also run an ammonia, nitrate, and orthophoshate on the filtered MLSS as this is worth checking out. What is the rise time in your settleability test?

How many lbs of COD are you treating per day and how many lbs of MLSS are in your system? (what's your F/M ratio?) How do you waste?

best regards,

Ryan

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grrun

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Re: poor settling sludge..then rising sludge
Reply #4 - Mar 30^th, 2012, 11:45am

Are you sure that the COD from the plant decreased because the aeration times shortened or could it have been because the MLSSs had increased? Since the higher life forms have disappeared; this indicates that a shift in the population distribution of organisms has occurred. Sludgefather's question about sludge wasting is significant. Have you changed wasting quantities during this period? What is the current sludge age? I've experienced slowly settling sludge from both very young sludge and very old sludge so that sludge age may be an important consideration (I tend to lean toward the young sludge because of the disappearence of filaments and higher life forms). Anyway, what is the WAS procedure?

grrun

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Will.B.

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Re: poor settling sludge..then rising sludge
Reply #5 - Apr 3^rd, 2012, 8:58pm

1) The MLSS is normally around 4500mg/L. The MLSS is taken at the end of the cycle just before settling. The MLSS is calculated daily. When MLSS hits >4500 mg/L approximately 7% is wasted giving a MLSS of approx 3900 - 4000 mg/L. Then MLSS climbs over two cycles to give 4500 mg/L then another 7% is wastes.
2) I dont know the C:N:P ratio but there normally is alot of Carbon in milk waste:CIP chemicals is nitric acid:P is normally 20 mg/L.
3) Dont have the ability to test soluble COD. But COD going into SBRs is apprx 3000 mg/L and coming out is 150 mg/L. Out of this discharge COD 40 mg/L is soluble.
4) Nitates would be 0 and NH3 is 150 - 300 mg/L (if memory serves me well)
5) Settling has improved at little should be 3 hours went to 10, now 7 hours. Sludge still looks the same under the microscope. No large life forms or filaments (some filaments but very very little amounts) .
6) Temp is 30 degs C.
7) Production say they are not using ant new chemicals or sanitisers.
8) Still a complete unknown. Having trouble finding a professional to do microscopic analysis

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grrun

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Re: poor settling sludge..then rising sludge
Reply #6 - Apr 4^th, 2012, 12:18am

"Nitates would be 0 and NH3 is 150 - 300 mg/L (if memory serves me well)

The lack of nitrification is a clue that makes me think that the filling cycles may have something to do with the poor settling. The 1/2 hour aeration at theshould should produce some nitrates and reduce the concentration of NH₃-N.

Sludge wasting is puzzeling. A 28 day sludge age is indicated, but you may be operating (for some unknown reason) at a lower sludge age (which would explain the lack of nitrification). Do you include the TSSs lost in the discharge as "wasted"? Poor settling may distort the actual quantity of actual sludge wasted.

I would try raising the DO above 2 for the last cycle and see if that offers any improvement in settling (check for nitrates as well).

There are just some contradictory information that still needs to be understood, but we'll keep working on it.

grrun

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Will.B.

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Re: poor settling sludge..then rising sludge
Reply #7 - Apr 4^th, 2012, 5:57am

Yes about cycle times.
We have always struggled determining the best cycle times in our SBRs. We went to intermitant fills due to the high and varing COD of the influent. Originally the fill were 12 L/sec from level 65% to 95%. This ofteren resulted in 14 to 20 hours of aeration with no DO. Totally anoxic.
This situation also lead to bad odours at times.
Also the settling time was always 3 hours. If the SBRs had not settled in 3 hours it was discharged anyway. This lead to washout of TSS.
So with a system lacking DO for such long times we introduced the step fill/aerate cycle. This has stopped odours and the plant ran well for 8 months.
But know we have this very strange situation. Expecially not having filaments.
In the passed we had poor settling but that was due to two main courses. i) to many filaments, but their were always alot of ciliates and protozoa and metazo. ii) wash out of TSS lowering the MLSS, shorting the sludge age and an obvious amount of pin floc.
This is a strange case we have at the moment.
Our wasting has often been random. Sometimes SBRs would not get wasted because so much MLSS would get lost in the discharged. Now we dont lose our MLSS because we dont discharge until the interface between the supernanant and the sludge blanket is below the discharge pipe (which is at 64%). This was to introduce regular WAS and to have stead sludge age.
Do you have any suggestions for cycle times, DO levels and wasting rate. We often find things go wrong in our biological plant but if we feed it and wait for DO the system comes good after a week. But not know. Its not coming good now..

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grrun

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Re: poor settling sludge..then rising sludge
Reply #8 - Apr 4^th, 2012, 12:53pm

[b]Your last posting has helped to clarify the situation. I think that your sludge (due to losses in the discharge and intermittant operation) may be too young (lacking nitrifiers). I think that you may want to try to create some time limits on your fill cycles and perhaps extend the time on the final cycle to accomplish improved sludge settling and nitrification.

If the anoxic cycles are taking less time; I suspect that there is little to no concentration of nitrates in the SBR so that time required to raise the DO to 2.0 doesn't have anything to do with denitrification. I also think that you are wasting/(losing) sludge at a far greater rate than indicated by your wasting procedure (7% every two days or maintaining MLSSs @ 4,000 to 4,500 mg/L).

I would also consider manufacturing plant operations cycles and try to limit the fill cycles to some time limit (perhaps 18 hours to begin with) and see if that may help.

"Now we dont lose our MLSS because we don't discharge until the interface between the supernanant and the sludge blanket is below the discharge pipe (which is at 64%). This was to introduce regular WAS and to have stead sludge age."

I would be sure that the sludge was well below the discharge pipe opening because the sludge/water interface could be sucked into the discharge pipe thus reducing the quantity of sludge left in the SBR. Do you thourghly mix the sludge before wasting to insure uniform wasting? Which part of the cycles is the sludge wasted?

Anyway, don't make all of these changes at the same time, but consider the possibilities. My current focus is on the fact that there is little or no nitrification occurring which implies a young sludge. Therefore, excessive wasting is preventing nitrifer and other organism growth.

grrun

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The sludge judge

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Re: poor settling sludge..then rising sludge
Reply #9 - Apr 4^th, 2012, 8:21pm

It's best to determine the aeration period by measuring the OUR. (oxygen uptake rate). Determine by trial and testing. Once your OUR slows down to your desired rate you can begin the settling cycle.

It sounds like you have a very high strength influent (common in dairy- as well as the fluctuating CODs) A longer fill cycle is probably needed as you have a ton of soluble COD and it's taken up right away. (like candy for the bugs).

If you have denitrification in the clarifier you are nitrifying. My gut feeling if you're not seeing a lot of filaments and you have very poor slow settling sludge is you have a zooglea problem. Send me a pm if you want a free microscopic eval to be sure.

Zooglea are a very common problem in dairy due to the high organic acid content of the water. They grow at high F/M. Filling intermittently (to simulate step feed) probably worked because these organic acids are taken up very rapidly. It sounds like you lost a ton of solids to the effluent and your MLSS decreased (the M component of F/M- giving you all the ingredients for zooglea)

Any control strategy for wasting is good. Either a constant SRT (maybe start at 15-20 days) or a target MLSS based on your maximum loading rates. I've had success with both strategies.

best regards,

Ryan

best regards,

Ryan

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: poor settling sludge..then rising sludge Reply #10 - Apr 5^th, 2012, 11:15am For tips on denitrification problems you can type it into the search engine on the upper right hand corner fo the page.
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