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ETP - solid overflow from final clarifier


We are having activated sludge process in our ETP (both industrial and sewage). Settling of biomass in jar is only upto 900ml even after 3-4 hours, will this indicate the presence of filamentous organisms. We are facing problem of solids overflow from final clarifier(floating problem). What would be remidial action for this situation? Our influent COD is around 1200-1400ppm, flow should be 4-5kl/hr, aeration tank volume 90kl, center feed clarifier volume 17kl. What is the general procedure for circulation of settled mass? Can anybody give details regarding this problem...

Seshagiri Rao




To begin with,if Mr.Seshagiri could send information on the source of waste water coming in to the STP,it would help a great deal in analyisng the problem.
If the clarifier is being de-sludged,some of the sludge should be pumped back into the aeration tank to bring the mlss content up.
Once information asked for comes,more suggestions would be possible.An analysis report of each of the inputs(effluents) would help.


Business Adviser, Ion Exchange Services Ltd Bangalore


I think that you mean you are mixing sewage and industrial effluent in the ETP. This is not a good idea unless the sewage is a very small percentage
(<10%) of the total effluent. Also, please tell us the nature of effluent (whether it is paintshop/electroplating/type of industry) to enable us to understand why the MLSS developed is low.

Whenever solids overflow from clarifier, it means floc size is small and certain solids are escaping from the clarifier. Also, you mention a high influent COD. Basically, it tells me that there is a high inorganic content in effluent.

The volume of aeration tank is about 18 hours which is good. The clarifier is also 3 hours detention time which is ok. It only lead me to believe that the bacterial culture is in a nascent stage. You may try adding fresh Gobar (not upla, which is dry) and then developing a bacterial culture. In the initial stage, go for 100% sludge recycle. then gradually add effluentstarting at 10% and take it up weekly to 30% then 50%, 70% and then full capacity.

It would be best to tell us the following:

a. Type of industry.
b. BOD as well as COD.
c. Aeration method and capacity of blower/aerator.

Taral Kumar.
Akar Impex Pvt.Ltd, New Delhi


Mr. Sheshagiri,

You do not mention B.O.D. values, without which it is difficult to judge the characteristic of your wastewater. A high C.O.D. does not necessarly mean a content of non degradable organics. It would appear that quite a high retention period has been provided in the aeration tank, which is not normal. This may be due to the high BOD that maybe present.

I would suggest your going in for Bioaugmentation, that is use of externally prepared and strengthened micro organisms, which have been found to be more effective, especially where the free cow dung has failed!

You may visit Tatva

Keshav Agarwal

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