I was visiting a newly build wwtp and the first that I noticed that they constructed huge Imhoff tanks for the treatment of wastewater, though this technology nowadays is not used for a medium size community (20000 P.E.) wastewater treatment. I was curious why was this technology implemented but nobody there could give me an explanation. The question is that beside very high H2S odor at the plant (the taps were all black due to corrosion) the effluent wastewater had severe foaming. What is causing the foam?, probably of the ammonium generated from anaerobic processes? (The foam had white color). This phenomenon I also noticed at hyacinth wwtp where the water had white foam after the primary sedimentation process.
Foaming in wastewater treatment plants is very common which could arise due to any of the following reasons:
1) the wastewater contains surfactants that takes a long time to degrade;
2) the presence of excessive N2 or CH4 gases in the tank, these gases are produced during denitrification or in anoxic conditions and help to generate foams;
3) the sludge microorganisms might generate extra-cellular polymeric substances (EPS) uder extreme nutrient-deficient conditons, the development of EPS in imhoff tanks favors the generation of bubbles and foams.
However, there are control mechanisms for this which include operational pH, temperature, dissolved oxygen (DO) levels and etc. Many studies have been done on this.
It's a very nice question, thank you.
Probably the excessive methane is causing, but i am not sure about it because i never saw this kind of stable white foaming of the effluent. Low possibility of anoxic conditions, because the Imhoff is more anaerobic then anoxic reactor and also this kind of foam i observed at the effluent from covered circular classifiers, same with H2S smell ->probably in these settler the sludge take out occurred in rare occasions and turned into a quasi A.D.
I am attaching also pictures on the effluent, I forgot to tell that in the Imhoff tanks there is no foaming or any unusual behavior that i could notice.
protein materials not biodegraded due to excessively high F/M or, in a plant start-up situation, the optimum MLSS concentration not yet having been reached
I visited the treatment plant and according to the operator the circular settlers are cleaned yearly so there happens intense anaerobic process, the COD drops form 550 to approx 270 mg/L and the ammonium increases from 115 to 162 mg/L. I also think that because of the high F/M ratio the unbiodegraded protein materials are causing the foaming. Thanks for the answers and i think that optimizing the settled sludge removal from the settlers this foaming phenomena can be eliminated.
Partly degraded proteins are present in wastewater. These are surface active. When air is entrapped as in plunging water, surface active agents cause wet foam in the form of small spherical bubbles to last longer. The bubbles break when water drains from form, turning speherical air bubbles bounded by thick water films, to polyhedral bubbles bounded by a thin lamella film. The foam head builds up when the rate of breakage is less than the rate of formation of bubbles. The rate of breakage is reduced by the presence of surface active agents. Further, there could be be a biological stabilization of the bubbles by the growth of aerobic bacteria in the wet foam. The situation creates selective pressures that select bacteria that produce surfactants to stabilizes the foam, allowing greater access to oxygenic growth. With time, the bacteria run out of substrate or oxygen or moisture. In very long lived foams, it is possible that water has drained out of the lamella films of the foam cells, giving white colour. There are no studies that I know of, that address the production and possible biological stabilizaion of foams in wastewater discharges. It is a good topic for research and I encourage young researchers to take up the challenge. An extraordinary example of foaming from untreated sewage discharge is seen here https://www.theguardian.com/world/gallery/2015/oct/01/lake-toxic-foam-bangalore-india-in-pictures.
Informative answer Ajit Haridas .
I see something similar in many places. The attached photos are of however the downstream of grit chamber. The water looks pretty dark, almost black, and there is some heavy foaming at the free fall.
My question to you, what is the fate of surfactants in an conventional WWTP?
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