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COD-BOD Ratio Anomaly: Explanations? Bangalore

We have a Bio-Gas Plant in Bangalore, which treats degradable Food waste & also organic Sludge from the STP. We have tested the samples of the Plant inlet & outlet.

Inlet Concentrations are, BOD - 3230.77 mg/l, COD - 10955.07 mg/l & TSS - 13325.38 mg/l

Outlet Concentrations are, BOD - 600 mg/l, COD - 150 mg/l & TSS - 432 mg/l

By seeing these we come to know that the Ratio between COD:BOD is 4. But as we have studied it should be between 1.6 to 2.

So kindly help me in this. How & what is the reason for this anomaly?

Sreesha T. G.




This is a query to Mr. Bhawalkar.

Mr. Bhawalkar, you have written “Raw sewage often breeds ordinary mosquitoes, nowadays(in the past when we were eating healthier food, it used to breed fish)."

Stated more clearly, what you are saying is - if people eat healthier food, the resulting raw sewage would breed fish; and if they eat non-healthy food, the raw sewage would breed ordinary mosquitoes.

This is most astonishing R&D. Please provide references of peer-reviewed papers for this.

[b]Author wishes to remain Anonymous[/b]


COD is a measure of total organic load. BOD is a measure of 'easy to crack organic load'. BOD, thus is a simple task and COD is the total task, so far as organic load is concerned.

(COD-BOD) or the ratio COD/BOD, thus can be used to assess toxicity of bio-medium. Higher amount implies that the medium has high toxicity and less food that can be used to remediate it. COD/BOD, thus, can be compared to Task/Remuneration ratio, this should be low, to keep people happy.

Similarly the ratio COD/BOD should be low(it cannot be a fraction because COD is always greater than BOD), to make a healthy bio-system. Treated waste water, thus, should have a reduced COD/BOD ratio, as compared to the input waste water. Only eco-technologies can do this.

In man-developed conventional treatment technologies, one can see that the ratio COD/BOD actually goes up, implying that an easy task has been completed and major challenge is still pending. After such a treatment, water appears to be 'cleaner' because there is no food left, to sound alarms(to eyes, ears or nose). The secondary treated water, is thus, actually more hazardous for ecology and man. It is like creating a situation by having no fire alarm, so as to get a good sleep. But this is achieved by removing the battery that powers the alarm system.

To illustrate this point, let us discuss the case of sewage treatment. Raw sewage often breeds ordinary mosquitoes, nowadays(in the past when we were eating healthier food, it used to breed fish). If conventional technology is used to treat the sewage, the treated sewage breeds malaria mosquitoes, implying that it is more hazardous. All pests(and pathogens, the microscopic pests) are the crisis managers of Nature.

Eco-technologies, however, produce water that is fish or soil friendly. Hence it is not let out, but used as far as possible, for irrigation at least. Discharge of 'treated' water implies that the treatment is not proper. This is why the Pollution Control Boards are now insisting a simple law of 'Zero Discharge'.

It should be clear now, that there is no fixed ratio of COD/BOD. It varies with each level of toxicity. For pesticide factory wastewater, this ratio will be very high and for sugar factory wastewater, it will be close to 1 because most of the molecules are sugar that are easy to crack.


Dr Uday Bhawalkar
Director R&D
Bhawalkar Ecological Research Institute (BERI), Pune


Dear Sreesha T. G.,

Firstly, I think you have made a mistake in mentioning BOD as 600 and COD as 150 ppm. It would be the other way around (based on the ratio mentioned by you and also BOD cannot be higher than COD).

The higher COD would simply mean that the entire Organic load is not bio degradable. The ratio of 1.6 to 2.0 is of no concern as it only indicates the content of biodegradable organic load.


Keshav Agarwal
Technical Consultant
Biotech Services
Noida, UP


Dear Sreesha T. G.,

BOD: COD ratio varies from waste to waste depending on the % of inorganic (non biodegradable) oxidisable portion in it. Consult any standard book (like Metcalfe and Eddy) for an elaboration on it.

It is confusing that the COD is 150 after treatment while BOD is 600!!! Logically this is not possible.


Sandeepan Choudhury


Dear Anonymous Well-wisher,

Thank you very much for raising this important point. In general, most of the creatures that have come earlier on this planet, food has higher nitrates/organics ratio, than the excreta. Man is probably one animal that has excreta that is more polluted than the food. Well, it may take some time to learn the laws of Nature.

Creatures that have learnt this, get their needs without going to the office. Nature has already given a task to them and they get food, etc. just by carrying out this task.

What is the task of animals? It is to eat food in a particular bandwidth of pollution, as defined by nitrates/organics ratio, distribute the seeds(not kill them in a garbage dump) so as to help clean the environment through better vegetation.

It is reported by one natural scientist who has spent a year in a forest that the tiger has excreta that attracts honeybees. This man may not publish this in a peer-reviewed journal. He may also get rejected because he is saying what is not convenient to know.

Each animal needs food as per the lifestyle. Or the lifestyle is decided by the food. Tiger in a forest chases the 'fast food' or food that can run away. On the other hand a tiger in a zoo, if fed with the same food, the excreta will not get honeybees. It will get green bottle flies, the cousins of houseflies.

Most of our urban population works with brain and physical activity is less. In such a case, consumption of low-nitrates vegetarian diet is desired. Otherwise person eating high-nitrate diet has to spend considerable time in the gim, to remove the nitrates.

How to know whether the food has low nitrates? Well, high nitrate food gets spoiled faster, as compared to the low nitrate food. This is one simple test.

Keep the fruits open outside the freeze. If it is consumed by insects or fungus, it is their food. Human food does not get spoiled, it may get dried up. Also if excreta is stinking in the toilet, we are consuming high nitrate food, than what we actually need.

Please see If people have understood ecology(it is new emerging science), this finding is obvious.

Asthma(and all other physical and mental ailments) are due to consumption of extra nitrates. Hookworm can remove that extra nitrates. But why consume more? Our body cannot through just the nitrates, the organic food also goes out and we then call it BOD and COD.

Please see to see the peer-reviewed papers that say that HIV is not the cause of AIDS. It is nitrates that can enter our body through polluted food, water or air. Air has NOx produced by burning of coal, petrol, diesel, LPG, CNG, biogas and hydrogen- all these are unholy fuels. Rain brings us nitrates by washing the air. Such high-nitrate rain refuses to enter the soil and gets accumulated or runs away. Only water that has nitrates can breed mosquitoes. And mosquitoes need nitrates for their growth. So they also bite nitrate-rich people.

Our food gets nitrates because farmers are scientifically taught to use N-rich fertilizers. Crops get pest attack only if they have unutilized residual nitrates. At higher nitrates, pests become microscopic and are called pathogens.

Animals get pests and diseases only because of extra nitrates. If these cleaning mechanisms are not allowed(by remaining clean), then extra nitrates cause 'madness'. We then get 'mad dogs', 'mad cows' and finally 'mad humans'. All the crime, violence and terrorism is due to nitrates.

All this knowledge has gone into my PhD thesis(1996) at Chemical Engineering Dept of IIT Bombay, it was evaluated by peers and granted a PhD. This work also has produced 2 Indian and 1 US patent.

I got all this knowledge by reading the books of ecology and ecological engineering and by analyzing how 'Nature is well designed'. Please see


Dr Uday Bhawalkar

Director R&D

Bhawalkar Ecological Research Institute (BERI), Pune


Dear Sreesha T. G.,

We are very appreciative to your effort of having a BGP with the STP and that you also treat food waste and others.

We wish to be advised whether your BGP is working well i.e pressurizing well to eject the slurry on a regular basis. Also the gas discharge is used for energy purposes, and the slurry when cured/ matured is used as manure for the greens. I would advise the type and the capacity of the BGP serving how many houses? What is the amount of daily loading STP, Vegetable waste etc?

If your BGP is healthy and working fine, don’t worry much on the COD: BOD ratios, some representative sampling is to be done to get exact inference. In our experience we have noted that when only STP sludge is fed, the fermentation in BGP would be less, but with food and bio-waste it improves. Horticulture and farm-yard wastes do not help much.

However these veg. wastes should be fed in a well-mixed pulpy form. And to homogenize the loading, you may local gobar-cow dung from a healthy dairy (avoid road-side cattle!!) around 25% daily load once in 2-weeks. This would improve your C:N ratios. And also socially loading cow-dung gets more acceptability in communities.

We desire that you should make efforts to promote these green practices in your neighborhood, to improve the environment, and be in touch with us.
There is more to gain from these practices, and that there exists a mechanism to earn Carbon-credits from these initiatives.

With well wishes from VigyanVijay,

Er. Ajit Seshadri
Head-Environmental Wing (NGO)
The Vigyan Vijay Foundation
New Delhi-110 045


There is considerable knowledge that is outside the peer reviewed journals. We have to learn how to read the 'books of Nature' that have the real knowledge.

Please see

Sewage quality is a combined effect of food and water quality. Of this, water quality is more important because we use water for cleaning our food. This cleaning is with respect to nitrates. Cooking is also a 'nitrate cleansing' act.

But water can do this cleansing, only to the extent it is clean. If nitrates are high, the cleansing stops at this level.

Because of nitrates, bacteria grow in our digestion system and we then have to consume higher carbohydrates and proteins for the bacteria. Sewage also get more polluted because of this. Then it breeds frogs and mosquitoes at still higher nitrates.

Ganga water has, even today, interesting 'nitrate-locking' properties that are not understood by the scientists(hence these are also not admitted). This is why Kolkata sewage feeds the aquaculture ponds and sewage from Bangalore, Chennai and other cities gets wasted.

It is also interesting to know how the fish near LA beaches is undergoing sexual changes by sex hormones that do not get 'treated' in the sewage treatment units there. Please see

It is better to learn from Nature that has sustained for 5 billion years, than the US knowledge that keeps on changing back and forth.


Dr Uday Bhawalkar
Director R&D
Bhawalkar Ecological Research Institute (BERI), Pune


Dear Sreesha T. G.,

What is biodegradable by micro-organisms is BOD. What is chemically oxidisable by Chemicals in acid medium at high temperature close to boiling is COD. Usually what all is biodegradable can be done away by COD. But what all can be done away by COD cannot be biodegraded by bacteria. This is why BOD is lesser than COD. IN this case food waste and STP sludge are biodegradable. Thus COD must be higher than BOD. I feel the tests have to be repeated. We can await the retesting.

Thanks & Regards

Dr. S. Sundaramoorthy
Technical Advisor (ex-Engineering Director of Chennai Metropolitan Water Supply and Sewerage Board)
Creative Environmental Consultants
Chennai, Madras


Dear Sreesha T. G.,

Normally the sewage from domestic origin will have COD/ BOD ratio of 1.5 to 2.0. But in the case of Food waste & organic Sludge from the STP, the rate of degradation is comparatively high. Hence the COD/BOD ratio is 4 in this case. It shows that rate of degradation of the feed waste like food and STP sludge is very high.

With regards

Scientist (Water Lab)
Central Pollution Control Board
New Delhi


Dear Sreesha T. G.,

Let me assure you first that the BOD to COD ratio is not necessarily 1.6 to 2. Besides, you have incorrectly mentioned COD as 150 mg/l. I suppose you may have 1500 mg/l at the outlet. In any case, the COD shall be lesser than the BOD. Thus, the BOD to COD ratio at inlet and outlet is substantially different. Unless of course, you have BOD 150 mg/l and COD 600 mg/l.

Kindly verify to enable us to answer your query.


Taral Kumar
Executive Director
Akar Impex Pvt. Ltd.
Noida, Uttar Pradesh


Dear Sreesha T. G.,

Following are may be the reasons.

• From the values it seems that you are using diluted waste. It means more water is being added during 'prepetition' of slurry.
• Cellulosic or other difficult to biodegrade organic matter may be more in the waste.
• STP sludge if biological then it must be stabilized organic matter where COD/BOD ratio is higher.

As soon as it is producing the gas and giving the reduction in BOD you can neglect the ratio.

With regards,

Prof. R. V Saraf
Viraj Envirozing India Pvt. Ltd.
Pune, Maharashtra

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