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Locating A Suitable Antifoaming Agent
Q: We are having an Effluent Treatment Plant of 300 KLD capacity which receives effluents from our Biscuit, Shampoo,Soap and Printing plants and Domestic sewage also gets added to it. The process is of Extended Aeration type. The foam that gets generated at times affects the ETP operations and hence the treated water quality. We have not been able to locate suitable antifoaming agent which could kill the source of the foam itself. The defoamers dont give any results. Could you pls provide some solution to this problem?
A:
A couple of things come to mind.
First, I'm almost willing to bet that somewhere in the plant you are using Alkyl Benzyl Sulfonates or their derivatives. The problem may be that the ABS or similar surfactant does not degrade within the residence time the wastewater is in the system. That's my best guess.
Look at and do some sampling in the soap and shampoo plants. Then when you have identified the problem with GC analyses, or have queried the formulation chemists (if you can get them to talk about formulation chemistry and ingredients). If that is the case, and you can get them to change, it probably will solve your problem.
If you can isolate the problem to one area within the plant, attempt to implement spill and ingredients control measures. Personally, I found that systems which required the operators to rework and reformulate rather than waste off specification batches always helped reduce sewer and wastewater problems. You might also want to see if you can help them take away their hoses and substitute high pressure cleaning guns and remove the sewers and substitute collection sumps which are not connected to your sewers. In one instance I went so far as to plug the plant sewers in the offending operation with quick set concrete. [Note: You need to have plant management buy in before you try this because it is an ultimate and radical solution-- but it works!]
It would be far better to convince the formulation people to switch to a biodegradable Linear Sulfonate form, and there are many of them available.
Finally, there is another solution, not pretty, but it is a solution. The addition of powdered activated carbon to the aeration tank, or the installation of an activated carbon treatment system in the wastewater coming from the offending plant, before it is combined with sanitary wastes, will probably do the trick. Both solutions have good and bad points, but both should work.
The short description of the negatives include higher operating costs, and higher maintenance costs. I believe that I've seen some data indicating that the efficiency of carbon is about 0.05- 0.1 lb of material absorbed per lb of carbon used. At about $1.75 per lb, that means that each lb of material absorbed will cost between $17.50- $35.00 additional in carbon, plus the disposal costs.
The problem with adding powdered activated carbon to the wastewater treatment plant is that you have to carry a fairly large additional amount of energy in the form of aeration or mixing just to keep the additional solids in suspension. The same general cost figures apply with regard to carbon absorption efficiency.
The positive thing is that they should be able to reduce your foaming problem.
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