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The dilemma of biological treatment of textile effluent-I want to learn the magic

The textile industry in Bangladesh is going for biological effluent treatment plant extensively assuming that this is the low cost safest solution for wastewater treatment. And my collea Kazy Mohammad Iqbal Hossaingues in the industries are certifying those ETP as “GREEN ETP”. Let’s see what is the relationship between two major parameters of wastewater is and how it affects the design consideration of an ETP.

Biological treatment of textile effluent
Figure: A biological ETP in a textile factory.

BOD= Biochemical Oxygen Demand indicate the amount of oxygen required to degrade the degradable organic matter present in the wastewater. So, the main objective of this measurement is to know the amount of biodegradable organic carbon.

COD= Chemical Oxygen Demand indicate the amount of oxygen required to oxidize (Carbon to Carbon Di Oxide) the organic matter present in the wastewater. This includes both biodegradable and non-biodegradable organic matter. The relation is given below-

COD= bCOD+nbCOD

NbCOD= COD-bCOD

In general, we call bCOD as BOD. For testing purpose, we only measure BOD5, which actually measures the amount of biodegradable organic carbon that will degrade naturally in 5 days in normal temperature.

Now I have a wastewater test report from 1 of my supplier factories, it shows the inlet wastewater contain:

BOD=210 ppm, and COD=720 ppm

So, the amount of non-biodegradable hydrocarbon present in the ETP =

NbCOD= 720-210=510 ppm, i.e. 510 ppm is biologically non-biodegradable.

BOD/COD ratio =0.29

That clearly means the amount of non-biodegradable Organic carbon present in the wastewater is 510ppm (mg/l). And biological treatment is not possible for such wastewater. But my factory installed a biological effluent treatment plant and it is certified as ‘GREEN’ by my colleagues and friends.

I have reviewed several scientific research paper on this and found this conclusion in almost all papers-

“If BOD/ COD is > 0.6 then the waste is fairly biodegradable and can be effectively treated biologically. If BOD/COD ratio is between 0.3 and 0.6, then seeding is required to treat it biologically, because the process will be relatively slow, as the acclimatization of the microorganisms that help in the degradation process takes time. If BOD/COD < 0.3, biodegradation will not proceed, thus it cannot be treated biologically, because the wastewater generated from these activities inhibits the metabolic activity of bacterial seed due to their toxicity or refractory properties.”

You will obviously ask me what is the outlet wastewater test result, it shows outlet BOD= 03 ppm and COD= 10 ppm.

I do not know how it is possible. How non-biodegradable organic matter will degrade here. The factory doesn’t have any type of oxidation process or don’t use any sophisticated filtration technology like UF/ NF, etc. so where this carbon goes? Maybe there are something magical in between which I don’t know, so can you please help me to understand the reason, I like to learn this magical reason, I am ready to accept any type of criticism, would be grateful if any of you became able to help me to understand this situation. Please explain in comments or write me on iqbalwrdbuet@gmail.com

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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