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Reducing COD in final effluent wastewater


Q. We are currently experiencing high levels of COD in our wastewater stream. One of the methods I have researched in blowing air or oxygen into the effluent. I have carried this out on lab scale but there seems to be no effect on the COD content. Am I not performing the experiment correctly or is my method wrong? I am bubbling compressed air into a 25 liter drum of effluent and taking 20 ml samples every 1 hour these are then tested for COD. Do I need to stir the effluent before taking a sample? do I need to leave my aerated samples for a day or so before testing?
If anyone has any ideas or has performed this at lab scale and achieved good results please let me know.....

John Travis
metals - Leeds, England, UK


A. I have little experience in that treatment method or treating for high COD levels, but until a more experienced respondent checks in: if you have to ask about stirring, the air is certainly not agitating the wastewater sufficiently. If you had enough air you would have said something like "the solution is obviously thoroughly mixed" :-)

It is even possible that you are adding more COD via the oil in the compressed air than you are removing through oxygenation.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


A. It's not necessarily the case that the oxygen demand can be satisfied by making gaseous oxygen available to the liquid - the oxidisable constituents might not react with gaseous oxygen, but might need something like hydrogen peroxide or (dare I say it?) hex Cr or some other in-solution oxidiser.

Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia

We sadly relate the news that Bill passed away on Jan. 29, 2010.


A. Blowing air or oxygen into a wastewater sample will not reduce the COD on its own. You need to add the air/oxygen and allow microbes to degrade the organic materials in the wastewater. This is typically done in a tank that provides retention of several hours to several days.

You may be able to get an almost instant reduction in COD by adding hydrogen peroxide to the wastewater solution. The hydrogen peroxide will chemical attack the organics in the wastewater, degrading them and reduction the measured COD.

Roy Nuss
Trevose, Pennsylvania, USA


A. Evidently, your waste water requires something stronger than atmospheric oxygen to address the COD problem. Sometimes, suspended solids are a big part of the problem and can be settled or filtered out. If not, you will need to use a stronger oxidizer, like bleach or peroxide, etc.

Lyle Kirman
consultant - Cleveland, Ohio


A. The best way to reduce COD on wwtp is to have activated sludge on your treatment (propagation of bacterias in aeration tank, called biological treatment) using ammonium phosphate (fertilizer)can help propagate bacteria, a kilo of NH4OH a day for 100 cubic meter aeration tank.

Teody Delgado
- Manila, Philippines


A. Try ultra-filtration; it is very effective on waste streams.

John Neale
- Halesowen, West Midlands, UK


A. COD is a very broad parameter.
So the first step is to find out what substance is causing the high COD and only then to try a solution.

Two questions are crucial:
- which COD-rich substances are used in the plant ?
- taking samples of different rinsing waters and other waste water substreams : which are high in COD ?

Bubbling oxygen works fine if the cause is a large concentration of some inorganic reducing substance (e.g. Fe(II), sulphite, some of the reductors used in a chemical plating solution, ...)

Activated sludge (preferably the activated sludge of the local city waste water treatment station ; if not, your own installation which could be a serious investment) will do the job if biodegradable organic substances in solution are the main cause. Think of acetate and similar bath ingredients, most surfactants, ...

If most of the COD is coming from a water based degreasing operation, then try to separate the waste water from this operation and treat it physically (oil skimmer etc. or if you are using a degreaser with stable emulsions, ultrafiltration). (Find a lab to check the oil content of the sample with high COD).

Only if nothing else helps, switch to the very expensive aggressive chemicals like peroxide ... Even then, it is better to do this on the right substream which causes most of the COD load, before the final waste water treatment and not on the combined waste water stream.

Bert Gielen
- Gent, Belgium

March 13, 2008

Q. I have been engaged on a small organic food composting business. I have a problem COD level reduction in waste water from the composter. I had been tried to apply the aeration, peroxides, bleach and micorfiltration. They helped a little. But it is not satisfying level. Now I am trying COD reduction from 16000 to 700 at effluent of the Composter. If anyone know how to reduce COD level down to 700 level, please let me know it.

Kwansik Moon
Employee of the organic composter - Toronto, Ontario, Canada

May 2, 2011

Q. How to reduce COD load from effluent of dyes, only aeration or any other method -- kindly suggest to us

Industrialist - ANKLESHWAR, India

May 3, 2011

A. Hi, Chitrang.

You've seen H2O2 and biological treatment suggested as possibilities, plus Bert Gielen's explanation of when aeration alone might work and when it won't. You've also seen his recommendation of how to start choosing what to do. Please try to pose your question in terms of the discussion already on the table so we can keep moving forward instead of in circles :-)

It might help to tell us the wastewater volume, whether it is treated in batches or continuously, what COD you are starting at, and what COD you would like to achieve. Thanks!


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

June 13, 2011

Q. Hi
I am a chemical engineering student, currently doing my practical at a milk and cheese factory. We have a problem with the effluent waste water which is pumped to a farm and therefore the COD score must be below 400. At the moment it is at a average of 6000. I have read through the questions and responses on this page, but can't decide for myself which method to suggest to the management. The most economic method is also needed, since there isn't a lot of capital at hand. The tanks are continuous and I would guess the volume to be about 100 cubic meters. The surface contains a lot of fats and oils and therefore I am not sure if a simple filtration is going to do the job. Does someone have any advice?

Jacques Strydom
milk industry - Ladismith, Western Cape, South Africa

January 9, 2012

A. Dear Friend,

As the fat & oil content is high, Initially you have to add HCl; and if you go for agitation followed by oil skimmer, you will get better result. After Oil Skimmer if you add Demulsifier , then you will get best result.

Nelson Nirmal Raj
- Chennai

January 21, 2012

Q. In my vermi-filtration process, firstly COD decreased to 50 but after that, it is increasing ... why?
Please tell me the reason and solution.

Amandeep Singh
- Chandigrah, Punjab, INDIA

January 26, 2012

A. Try using a Microbubble Aerator together with Microbes from Roebic. (You can google for websites). Economical and effective in degrading BOD & COD.

Jay Lee
- L.A., California

February 28, 2012



Donwell Kodzwa
student - Gweru, Zimbabwe

May 20, 2012

Q. I'm working in a dry laundry plant preparing detergent, we need to reduce the COD of waste water including sanitary and cafeteria waste water only. Can anyone suggest the best economical process to reduce it apart from using peroxides.

Muhammad Farhan Qadri
- Karachi, Pakistan

August 10, 2012

Q. Dear Sir,

COD level in our fish processing plant is 5252 mg/l.

Please help us how to control and solutions.

Chandan S [last name deleted for privacy by Editor]
foods - KAMPALA,Uganda

August 28, 2012

A. Hi Mr. Chandan,
COD for fish processing effluent can be effectively reduced by membrane bioreactor.
We have successfully used biological effluent treatment solution in Kenya and Uganda.

Suresh Patel
- Nairobi, Kenya

September 19, 2012

Q. Hi. My company is using Terephatalic Acid (TPA) and Ethylene Glycol (EG) as the raw material. Our product is Poly Ethylene Terephatalate (PET). This undergoes Esterification and Polymerization process. Waste product contains water and e.g., base. So usually C.O.D. reading is 10,000 mg/L. Please advise how to reduce as low as 8000 mg/L.

Sunny Boy
- Malaysia

November 2, 2012

Q. dear Sir,we have primary fruit processing plant(aseptic),juice production (jam & cordial), tomato sauce.
we had old ETP, but it is not working in to CEA requirement in our country.All process water (CIP-use quaternary ammonia as a antibacterial agent),kitchen waste,toilets & bathing water in to ETP.
Influent -BOD5=2510mg/l ,COD=3750mg/l,TSS=250mg/l
Qavg=7.2m3/hr , aeration tank capacity=323m3
we want to meet treated water quality as follows,
BOD5<30mg/l ,COD <250mg/l ,TSS <50mg/l
we faced PH reduction in aeration tank in several time & we partially sort out it increasing influent PH near 10 & try to keep PH near 6-7 range in aeration tank.But the final water quality meet BOD=850mg/l ,COD=1013mg/l yet.we also chemically treat after aeration.
we want to know cost effective way to reduce these values.
please advice us to go ahead with this.

Your cooperation will be highly appreciated.
Thanks and best regards

Dhanushka Wijesooriya
- Colombo, Sri Lanka

November 15, 2012

Q. I have conducted 6-month bio-treatment trial in a condominium septic tank. I was able to lower down the BOD, but the COD exceeds the 1:2 ratio. We must comply to BOD 50:COD 100 here. How come I can't lower down the COD with my bio-treatment?

Gigi Montano
- Manila, Philippines

February 5, 2013

Q. Dear Sir,
My company produces pharmaceutical products. Our waste water treatment operates 100 m3/day continuously. Currently, we are facing bubble and high COD issues despite having biological treatment in plant. Do you have any idea how to solve both issues? I already checked our plant activities and found that no new chemicals or materials were introduced or used when the issue occurred. This totally gives me a dead end. Is there any solution that won't require me to use peroxide?

Nurul Abdul Multalib
Pharmaceutical - Bandar Baru Bangi, Selangor, Malaysia

March 20, 2013

Q. Hi
I'm currently employed in the petro-chemical industry. I'm working on ways to improve our current operation. We have, a bio-treatment facility utilising MBR technology, our COD levels are below the stipulated limits, however, I am looking at ways to improve the current levels as part of my final thesis.

Thielshad Karriem
- Cape Town, Western Cape, South Africa

August 22, 2013

Q. Dear sir,

We have a chemical plant and are having trouble to treat effluent water of high COD. Daily we have approx. 9000 liters.
Please let us help to reduce COD below 200 mg/l.


Mr Parthiv Parikh
- Ahmedabad, Gujarat, India

August 29, 2013

A. Hello Mr Parthiv,

As Bert said above, "COD is a very broad parameter", please read his post, identify your flow source of COD, your main component that has high COD, and we might help you in choosing the best way to lower your COD value.


Daniel Montanes
- Canuelas, Buenos Aires, Argentina

September 26, 2013

A. You can reduce COD by adding hydrogen peroxide.

jeffrey holmes
Jeffrey Holmes, CEF
      South Carolina

June 6, 2014

Q. Dear All

We are a biotech plant with standard Effluent treatment plant (USABR followed by Aeration & clarifier then ACF filter). General sewage and caustic washing we are able to handle, and get the treated water COD less than 200 -- but there is a shock load (killed cell mass) of effluent from the manufacturing of 6.0 KL QTY once in 10 days which has COD around 30 million which is disturbing the entire stream.

Please let me know how I can instantly reduce COD in this biomass at least bring it down by 10 times so that my ETP should be able to handle it. I have read peroxide helps in instant reduction. Please confirm as I will take a trial of the same.


shaik sayeed
- bangalore, karnataka, india

September 12, 2014

Hypochlorite and anthracite only reduce COD to 110 ppm

Q. We are having high COD as 160 ppm, mainly cellulosic material.
We are dosing Hypo and reducing it to 130 ppm and with anthracite to 110 ppm.
This stream we are running in RO plant and further reduction of COD is needed.
Please suggest any dosing/pretreatment to reduce COD of this stream.

Sunil Ajmera
cellulosics - Kharach, Bharuch, Gujarat, India

COD is 9000 ppm and peroxide doesn't help

September 14, 2014

Q. I've been experimenting with the use of H2O2 with one of my effluent samples and the result seems to go nowhere. Current reading of COD from the effluent is around 9000 mg/L. I've tried manipulating the H202's ratios and also pH of the effluent.
Is there any other solution to reduce the COD on site as I've been holding the effluent for about a week in a skidded tank?

M.Syahrizan Mahmood
- Johor, Malaysia

September 16, 2014

A. Hydrogen peroxide is a powerful oxidant, but unless it is used in conjunction with a catalyst, and/or UV light, it can be very slow to react.

Try adjusting the pH to 5 or so, and dosing with 200 - 500 mg/l of ferrous sulfate. Then add the peroxide. This is called Fentons reaction. It generates hydroxyl radicals, very powerful and rapid oxidizers. Other catalysts that have been used include vanadium pentoxide and copper sulfate.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

September 22, 2014

Q. Sir we are experiencing COD levels around 150000-200000 ppm. Is there any method that can bring this COD levels to 10000-20000 ppm?

k.vinay kumar reddy
- hyderabad,telagana,india
  ^- Privately contact this inquirer -^

October 7, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

We are designing a effluent treatment plant - 1000 GPD, to reduce COD from 150,000 ppm to 1000 ppm

Mohammed kaleem
process engineer - chennai city tamilnadu india
  ^- Privately contact this inquirer -^


A. Hi K.Vinay. Surely there are such methods, but I doubt that anyone can offer practical advice without more info to go on. Sorry. Please give us some ideas on the volume, source of the waste, what other treatments (if any) have been done, etc.
Also, please remember forum netiquette: it's your problem not theirs, so most readers consider it rude if you ask them to spend more time on their answer than you spent on the question :-)

Was that a question or an answer, Muhammed? If it's a question, 2 GPM is a small plant, but what industry is it serving (or is it sanitary waste), and what treatments have been done to it? Thanks.

Thanks and Regards,

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

October 9, 2014

Q. Dear sir,

This is a question, we need to reduce the COD to 1000 ppm; yes it for 1000 GPD small plant, but we need to have a treatment plant due to environmental restrictions.

Best regards,

Mohammed kaleem [returning]
- chennai tamilnadu india

November 14, 2014

Q. How can I reduce COD (chemical oxygen demand) in the waste water?
My waste water COD :- 9000 ppm and TDS :- 28000

ketan shah
- vadodara,Gujarat,India

December 22, 2014

Q. Dear friend,
I am vikram lad, working in Inorganic API industry. I want to reduce COD in wastewater. Generally our COD is about 1600 mg/l in water. Can you help me to reduce COD? Please suggest whether I should use hydrogen peroxide or FeSO4 or both.

- mahad maharashtra, india.

August 7, 2015

A. Yes, what Mr. Mooney so wisely said.

Without giving details about what process is generating the COD, it is impossible to say what the best solution is. If you have a waste with lots of carbohydrates, cellulosic materials, that sort of thing, chemical treatment is a loser - you would be better off with some kind of bio-reactor, let the bacteria do the work.

We are happy to help here but we're not mind readers, eh?

dave wichern
Dave Wichern
Consultant - The Bronx, New York

July 31, 2015

Q. 1. If using hydrogen peroxide is a solution for removing COD of waste water, then what is the daily requirement of the hydrogen peroxide, if we have to treat 450 KL water every day?

2. If using hydrogen peroxide is not economic for such large volumes then what are other options available. At present we are using a condensate polishing unit having Bio-Towers, Aeration & Clarifier Tanks, but COD is still 5500...???

deepak sharma
ENA Distillation Plant - Karnal, Haryana, India

Ed. note -- Readers: This is a public forum with readers helping each other. This particular thread now has too many unanswered questions! If you know enough about this subject to be able to post an answerable question, you know enough to at least try to answer one of the open questions :-)
Please don't post a question or start a new thread until you have attempted to answer at least one of the open questions. Thanks!

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