Adverse Effect of Sludge Aeration

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I'm working with a client that is about to install a sludge mixing system in a retention tank. 

One of the mixing options that we are looking at is the use coarse air diffuser. We like this approach because the maximum sludge height is only 1.5 m. 

We also looked at submersible mixers but submergence allowed is 1 m (hence, useful height is only 0.5 m...).

My questions for you is: is there an adverse effect of aerating the sludge?

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10 Answers

  1. If you need to keep the sludge from going septic then using coarse bubble diffusers is a good way to go. The only disadvantage would be if the sludge is going from retention to anaerobic digestion, where the residual DO may be a slight problem.  Another option would be to use a pump and recirculate the sludge - I think Red Valve markets systems like that. Pumping is less energy intensive than aeration.

  2. Efficency will depend on:

    Dry solids concentration (Viscosity)

    Tank design (circular, rectangular).

    The whole ground floor has to be equipped with a grid of diffusors, which can become quite expensive.

    Anyway, mixing shallow tanks has low efficiency, no matter if you use mechanical mixers or gas mixing.

     

  3. No problem at all : coarse bubbles mixing is an advisable solution, however the air or gaz blower has to be energetic engouh to mix the sludge in case it has been turned off for a long period of time.

  6. The sludge you are trying to dispose is probably a good source of energy if properly used in a biomass gasification system.  Why try to reduce the fuel from this source? Use it. 

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  8. Hello mud is the transformation of a living organic matter into an inert, dead organic matter. It's an irreversible process. The transformation of a living organic matter into mud is carried out by the effect of rot activated by a strong anaerobic digestion of the environment.
    The aeration arm has the advantage of killing the action of the anaerobic digestion. But the organic matter turned into mud, the rest of the mud.
    Of course there is no oxygen-free medium in any tray of a step because for this state to settle it would require at least 1000 years which is far from the case in an effluent that remains on the step no more than 5 days and often transferred from a BAC  to another.
    Even less in the aeration tray since the medium is on oxygenated by the rotating arm.
    I do not see the point of mixing mud with mud: the whole thing will always be mud. 
    The height does not matter also except to say that the more this mud will remain in retention in the BAC and the more it will be exposed to a strong anaerobic digestion of the environment. 

    1 Comment

    1. Hi All,

      Tank is a retention/collection tank that received septic tank sludge before dewatering (the main goal of the facility, which is also equipped with sludge press). 

      From that tank, sludge is pumped toward the press for dewatering.

       

  9. I would be concerned on thickness of the sludge. Above about 2.2% the O2 transfer is very poor. A hyperbolic mixer(Invent) should fit lower in the tank and they are low HP. Aeration would help keep odor away. Over aeration can break apart the floc and make dewatering more expensive.

     

    I think Patrick R. is on the right track. What kind of sludge and what do you want to do with the sludge.

  10. Dear Mathieu,

    What kind of sludge are we talking of ? Primary, secondary (stabilised/unstabilised), digested, dewatered, thickened ?

    In the end it depends what you are doing with the sludge afterwards. If you do anaerobic digestion, you will lose some biogas since your sludge gets (slightly) digested aerobically.

    Otherwise they are not many drawbacks, except that your diffusers might clog with a crust if you do not aerate enough. People like that solution since there is no rotary equipment inside the tank, and in your case a mixer doesn't seem to make much sense because of water level depth.

    Best regards,

    Patrick

     

    1 Comment

    1. Hi All,

      Tank is a ​retention/​collection tank ​that received ​septic tank ​sludge before ​dewatering (the ​main goal of ​the facility, ​which is also ​equipped with ​sludge press).​  ​

      From that ​tank, sludge is ​pumped toward ​the press for ​dewatering. ​

      1 Comment reply