Talk:Activated sludge

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[edit] Purposes

concerning the edits of Velela/ 5th July added: "4 driving off entrained gases carbon dioxide, ammonia, nitrogen etc. 5 generating a biological floc that is easy to settle. 6 generating a liquor low in dissolved or suspended material"

we talk here about the main purposes of an activated sludge process, i.e. why the hell would i build an activated sludge plant ? I will not build it to create a floc and remove CO2, but to remove organic matter, which will incidentally create a floc and take out CO2. probably, these steps might be detailed elsewhere in the article, but they are not purposes.

4. carbon dioxide is a by-product of endogenous respiration, not a purpose of the process. There is even no specific need to remove CO2, as it helps keeping a buffered pH I don't think ammonia can exist in activated sludge process, because under 9.3 of pH, ammonium is prevalent. never seen so far process with pH values that high. nitrogen is removed from the system in the denitrification step of nitrogen removal, mentioned in 2

5. the biological floc is the mean to reach the purpose, not a purpose by itself

6. I don't see how we can consider that activated sludge allow reducing the DS content. But I agree that SS is aggregated in the flocs. Kekel 15:58, 9 July 2006 (UTC)

What the article actually says is :Activated Sludge process can be used for one or several of the following purpose: which I agree is a slightly strange way of approaching the subject. However, whilst this structure exists, my edits are only intended to demonstrate what reasonable outcomes any operator could expect of an activated sludge plant. All of them are relevant to nornal operations. Getting rid of CO2 and methane are critical considerations in a plant treating landfill leachate for example. The ability to create a floc is important if you have a waste stream poorly suited to filter bed treatment and having a settleable floc is essential in achieving the effluent standards. In extended aeraton plants managed to effect de-nitrification, the release of ammonia and nitrogen can both occur at near neutral pH - try sampling the atmosphere above an activated sludge tank receiving a high ammoniacal nitrogen load such a fish processing plant to demonstrate this. As for DS, which includes dissolved carbonaceous material etc, this is one of the principal purposes of sewage treatment - converting dissolved organics to floc using bacteria and protozoans (mostly) so that it can be settled out and removed. However , I do agree that this structure is less than helpful and a re-write would greatly assist understanding. Velela 18:03, 9 July 2006 (UTC)

Maybe we should limit this to "main purposes" or "guaranteed effluent vaues" ?

Found a reference:

As of Degremont's "Water Treatment Handbook" 6th English Edition, the applications of activated sludge are:

1- carbonaceous pollution removal

2- Nitrification and denitrification

3- biological phosphate removal

4- aerobic stabilization (which is actually aerobic digestion...)

My experience being principally in urban sewage treatment plants, main purposes are actually limited to the 4 above. With urban WT, DS and gases are not usually an issue - in fact I don't know any example.

As you seem to have experience in industrial water, maybe you could complete this with other industrial-specific references ?

Kekel 08:04, 10 July 2006 (UTC)

I would be happy with Degremont's definitions. I can make the other points in the more relevant articles such as Leachate. Thanks Velela 08:09, 10 July 2006 (UTC)

[edit] Bacteria & Co

Being a bit in a hurry, I have no time to edit this article further at the moment. but I'm embarrassed by an obvious flaw: only bacteria are mentioned, though other folks are involved in the process, such as protozoans. Could anyone there be kind enough to complete this and add the nice wikilinks to other organisms ? Kekel 08:49, 11 July 2006 (UTC)

I've added a few bits and peices but I need to find my reference books that have been sat on the shelves for the last 40 years to provide definitive context and references. Velela 09:34, 11 July 2006 (UTC)