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Emilio

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Nitrification in a biofilm reactor
Feb 20^th, 2005, 6:05am

I am doing a study in the wastewater treatment plant of a pharmaceutical factory wich is running in problems in its Nitrification process.

Its wastewater treatment is a fixed biofilm reactor (4 serial reactors), in which I have not very much experience.

Influent data:
COD: 40000 mg/l
BOD: 2000 mg/l
N-NH4: 1500 mg/l.
Influent: 2 m3/h
Reactor volume: 2000 m3
DO: 3 ppm
pH: 8
Temperature: ? - lower than normal (< 10ºC)

Effluent N-NH4: 230 mg/l

I have already made some respirometry tests:
I have found there is not acute toxicity, but since its AUR (Ammonium Uptake Rate) is very low ( 0,6 mg NH4-N/gVSS.h) I could guess there is a possible nitrification inhibition.

My pre-diagnosis is that it could be an important inhibition level due to very high Ammnium concentration together with an abnormal low temperature.

Perhaps it could be more factors that could create some inhibition effect (such as conductivity and antibiotics presence) but, for the moment, I have not more data.

My questions are:

With the current data, do you have any other diagnosis ?

Since the company has got budget for some possible treatment plant improvements, do you know any alternative Nitrification system that could be adapted to the current fixed biofilm reactor ? - I have already noticed about systems such as Annamox that perhaps are not very much experimented and also very expensive -

Thank you for your help.

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grrun

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Re: Nitrification in a biofilm reactor
Reply #1 - Feb 20^th, 2005, 7:18pm

Emilio,

I also do not have experience with fixed film systems and I think that you have been very systematic in your approach to this problem so my suggestions may seem too simple.

1. Have you checked for a nutrient ( P, or possible micro nutrient) deficiency? An addition to your respirometer tests may provide this information. This occurred to me because of the low AUR.

2. What are the other effluent parameters. Could more time under aeration (perhaps another reactor in series) help? Have you determined the NH3 up take for each of the individual cell in series?

3. You might run a series of grab samples to determine if variability in inputs might have any impact on the process.

4. Finally, because uptake rates can sometimes vary with DO, you might also investigate this possibility with the respirometer.

grrun Undecided

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judo

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Re: Nitrification in a biofilm reactor
Reply #2 - Feb 21^st, 2005, 11:11am

There are two major problems in your situation:

1.COD is too high
Perhaps the observed NH4-N reduction(1500 -> 230 mg/L) is due to assimilation into biomass. Why don't you check out NO2-N plus NO3-N concentrations to verify the nitrification activity.

Besides too much COD (or BOD) is usually the major problem for nitrifiers. Vigorously growing heterotrophic biomass helps nitrifiers to be washed out by shortening biomass retention time.

2.Temperature is too low
Personally I think you should be so thankful for that the NH4-N removal efficiency is not bad at all, considering the given temperature. It is like you are doing academic research on cryogenic nitrification activities....

First thing to do is to heat up your wastewater at least more than 15 C. Your COD/N ratio is still too high, but under the given (not too high) volumetric loading, it would not be impossible to achieve good nitrification.

Second thing, if necessary, would be to separate the reactor into two stages in series, with the first one for COD reduction with the following nitrification stage.

Seriously, forget about all diagnoses thing or alternative anything. Everything starts after you raise the temperature.

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Emilio

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Re: Nitrification in a biofilm reactor
Reply #3 - Feb 21^st, 2005, 6:29pm

Thank you Grrun and Judo.

Today we have made a 20ºC respirometry assay with endogeous sludge (*) and nutrients by starting with half normal NH4-N concentration (by making use of ClNH4 standard) and progresively increasing the concentration. The result was that the AUR at 20ºC - equivalent to a specific nitrification activity - did not change practically and continues being very low - I do not know if it is possible that a biomass could create a low nitrification rate habit ???, even if the temperature incrases -

(*) Since we can not use the attached biomass, we are making use of the suspended liquor from the reactor (MLSS = 2000 mg/l)

Even if the relation COD/N is very high, we have to take into account that the biodegradability relation BOD/COD is very low and perhaps is better to consider BOD instead of COD. According to the historical data I have just received: BOD/N/P could be about 2 ~ 3 /1/1

There are already four serial stages.

Perhaps, as Judo says, the key factor, is to consider heating up the waste water as a first thing to do.

From the last information I have got: the tempereture is lower than 15ºC, but perhaps not below 10ºC

By other side, as you know, also a key factor for nitrification is the MCRT, but I have no idea how to calculate this parameter in a fixed biomass system ???

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C. Gillen

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Re: Nitrification in a biofilm reactor
Reply #4 - Feb 23^rd, 2005, 8:05am

Emilio,
Would tend to agree with Judo that the main problem is low temperatures. I would suggest checking the alkalinity as well. You will need a lot of alkalinity to oxidise that level of ammonia (7.1 parts alkalinity for every part of ammonia). What is your final effluent COD and BOD? Check NO2 and NO3 levels to make sure you are nitrifying. Have a look at nitrification inhibition using a source of pure nitrifiers. I can provide details on this if required.
If there is no inhibition the addition of nitrifiers will help to complete the oxidation of ammonia.

Best regards,
Cgillen
cgillen@biofuture.ie

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grrun

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Re: Nitrification in a biofilm reactor
Reply #5 - Feb 23^rd, 2005, 3:21pm

Emilio.

The flow rate indicates a detention time of approximately 20 days under plug flow conditions. While you have 5 day BOD results, the COD results indicate that the 20 day BOD would be significantly higher so your nutrient ratios may be lower than indicated.

I too have been struggling to figure out how to control the MCRT in this type of process. If this is an upflow reactor, air bubbles impinging on the fixed support media might affect the rate that sludge sloughs off or the wastewater upflow rate might also affect the rate that the biofilm sloughs off. This could change wasting rates which would affect the MCRT. Many Trickling Filters have recycle circuits which can also be varied to change the MCRT. Does your FBR have recycling capabilities?

It seems to me that the detention time and air flow rate (and DO concentration) are the principal control variables in this type of process and that is why I suggested sampling the discharge from each cell. As Judo suggested, simply raising the temperature may increase reaction rate in the cells.

I think that running a respirometer with the sludge in the discharge should provide you with an estimate of the additional reaction time needed under existing conditions, but I'm not sure that this is the type of solution you are seeking or that it is indicative of reaction rates in the preceding cells.

Keep us posted on your progress, grrun Embarrassed

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sobisch

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Re: Nitrification in a biofilm reactor
Reply #6 - Feb 24^th, 2005, 5:40am

Dear Emilio,

maybe the supporting media of the biofilm might be not the best choice. So you might look for alternative media. A key might be the accessibility and the presence of oxic and anoxic zones insight the support media.
Somewhere I read about a company claiming that there support media have these superior properties.

Kind regards
T. Sobisch

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T. Sobisch
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sobisch God Member Offline Posts: 1372 Gender: Company or Organization: L.U.M. GmbH	Re: Nitrification in a biofilm reactor Reply #7 - Feb 24^th, 2005, 12:15pm Dear Emilio, I just bumped into an article at water online about 'Bioaugmentation Treats Cold Weather Problems' which is related to nitrification enhancement during cold weather: http://www.wateronline.com/content/news/article.asp?docid=2c859101-3cde-4da6-869...
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Emilio

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Re: Nitrification in a biofilm reactor
Reply #8 - Feb 25^th, 2005, 7:14am

Thank you to all.

This job has stoped for the moment and will resume in short perhaps within a global project not only to solve the nitrification problem but also all the critical points of the process.

Here there are several variables, and from your comments and my own job I can see the following:

. The process is nitrifying, but with very low nitrification rate capacity.

. Temperature is a critical factor. This comes from the abnormal winter we are getting in Spain. That means: it could be an acassionally problem of about 2 months. Even, like that, the problem should be solved because it could continue when the temperature raises due to the fact that nitrifying biomass were seriously affected.

. A possible inmediate solution could be to add a nitrifying bacteria culture preparation together with improving alcalinity level.

Grrun, the process has a recycling capability. I was thinking about how to take advantage of it. Perhaps to improve the dark MCRT, ... ???

In the next step we have to be not only approached to nitrification but also for the rest of the biological process.

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