What would be the best way of reducing COD levels prior to a Bioreactor?



We run an AMBR system at our site. The COD levels have risen substantially lately and the blowers are struggling to reach D.O.(Dissolved Oxygen) set points. All process water is collected in a sump, transferred to a balance tank which undergoes DAF before going into the Aerobic - bio tank.

Please suggest some methods for reducing COD levels prior to a Bioreactor.




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Bruno Peeters
Hi Gary,
A DAF removes FOG (fat, oil, grease) and particulate COD including colloids after coagulation-flocculation. Hence if turbidity at the DAF outlet = MBR inlet has increased along with the COD, then the DAF needs to optimized as recommended by Ciaran and Stephanus. However if the turbidity did not increase with the COD, then the additional COD is soluble and apparently readily biodegradable.
In that case (electro-)chemical pretreatment would probably not be very efficient.
An efficient and low cost alternative would be to add biosorption upstream of the DAF (in existing coagulation tank) using some waste activated sludge (WAS) from the MBR after regeneration. The WAS with adsorbed COD will be removed in the DAF. We remove up to 80% COD in 15 minutes via biosorption on regenerated activated sludge.
Bruno Peeters
Hi Gary,
The media for biosorption (= adsorption on + absorption by biomass) is just the regenerated biosludge (flocs) in the WAS. Hence perfectly biodegradable.
Gary O. Shaw MIET MCIM
Hi Bruno.
This is very interesting. What is the media you use for biosorption and is it biodegradable?
Thank you .
Shikha Srivastava
Please check TSS & turbidity before and after DAF, this will estimate performance efficiency of Daf and try optimise the coagulant and flocculent dose then. You might use some sieve tubes as well. If there is a sudden change in characteristic of effluent water please analyse that also. This may help to eradicate the COD problem
Randy  De Luca
Hello Gary

Our dual stage EC-AO electro chemical reactor process will provide multiple pretreatment constituent reductions including COD. Www.boydel.ca . The WaterMiner effluent delivered to your bioreactor will be clean clear and very stable meaning your bioreactor will be stable removing the smal dissolved fraction for digestion.
Gary O. Shaw MIET MCIM
Hi Randy.
Thank you for your comments.
Do you have a UK partner I can contact?
Morgan Mc Millan
Have you characterized the wastewater? Do you know what fraction of the COD is particulate, soluble, biodegradable and unbiodegradable? If some of the COD is particulate biodegradable then you could consider primary sedimentation. Patrick's proposal of fine sieves is also not a bad idea. Bu ultimately you would have to know in what form the COD is and how much. Do your perhaps have a process flow diagram of the current installation ?

Ciaran Gillen
Hi Gary,
If the influent has changed it is likely that the polymers used for the DAF also need to change so get some jar tests done and see if this can be optimised. This might be enough for your requirements. If not you will have to look at other options. Need more details on the plant to offer advice on this.
Nikhilesh Mukherjee
Have those compounds causing high COD been identified? Are those compounds biodegradable?

Please ref to this link. It may help. Best regards

Stephanus Victor
Start by optimisation of the DAF.
1. Coagulant selection + concentration
2. pH control (probe maintenance, ...))
3. Ensure mechanical system is working( aeration, nozzles)
Patrick Rambosson
Hi Gary,

as it is process water, May be you could reduce COD by reducing particular matter in the inlet (using a fine sieve). This can reduce COD about 10% in municipal wastewater, and is easier to install than a primary clarifier. But again, this depends if you have a relevant amount of suspended matter in your wastewater.

Best regards.
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