Here is a common story. The ETP was built for the wastewater the factory had five years ago. Since then the products have changed and the pollution has doubled. The tanks foam, the sludge beds overflow, and the outlet keeps failing the pollution board test. Adding more chemicals only makes more sludge.
What COD and BOD tell you
COD is the total pollution in the water. BOD is the part that bacteria can eat. If BOD is less than about one third of COD, most of the pollution is too tough for bacteria. More air in the tank will not fix that. You need a step that breaks the tough pollution down, or holds it long enough for bacteria to finish the job.
Carbon beds that do the hard work
Three proven methods use activated carbon to trap the pollution so it can be broken down.
- Carbon bed with bacteria. Bacteria live on carbon packed in a tank, and air is blown in. The carbon holds the pollution while the bacteria eat it, so very little sludge comes out. INR 8 to 10 per 1,000 litres.
- Moving carbon bed. Air and water keep carbon granules moving, and the pollution breaks down on them. Built up to 15 lakh litres a day, at about INR 8 per 1,000 litres.
- Carbon bed for very strong wastewater. For pesticide and dye wastewater that kills normal ETP bacteria. Hydrogen peroxide and iron-coated carbon break the pollution down, with no iron sludge. INR 12 to 15 per 1,000 litres.
Breaking tough pollution first
Bubble devices have no moving parts. Water spins through them, tiny bubbles burst, and big tough molecules break into small ones that bacteria can eat. Each unit handles up to 40,000 litres an hour. A strong oxidation stage does a similar job when STP or food factory water must be clean enough to reuse.
Match the fix to the problem
- Fat and oil clogging your biogas reactor: a biogas reactor built for oily water.
- Too much sludge at the first stage: a first-stage tank that needs no chemicals.
- Coloured water from dyeing: bacteria that remove dye colour.
- Foam from leftover detergent: an enzyme filter.
- Neighbours complaining about smell: a biofilter on the tank vents and sludge area.
- A tannery told to stop all wastewater discharge: separate lines with electric treatment.
Try it small before you build
Every factory's wastewater is different. Test the method on a small scale with your own water first. Measure COD, colour and sludge. This takes weeks, not months, and takes the guesswork out of spending money.
Is your ETP failing the COD test?
Send us a sample. Our lab tests it, and we try the best method from our technology showcase on your own water.
Request a consultationFrequently asked questions
Why does my ETP make so much sludge?
Usually because a lot of chemicals are added to make up for pollution the bacteria cannot handle. Breaking down that tough pollution first means fewer chemicals and less sludge.
Can these be added to my existing ETP?
Yes. Most are added as an extra step before or after your current tanks. You do not need to rebuild the plant.
How much does it cost to run?
It depends on how polluted the water is. The carbon-based methods used at full size cost about INR 8 to 15 per 1,000 litres.
Sources: Water Channel: what your BOD/COD ratio tells you, Central Pollution Control Board. The results above come from real use of each method. Your results depend on your water, so test it first.
More problem guides: Arsenic and Fluoride in Borewell Water: How to Remove Them Without Electricity · Yellow Water and Red Stains: How to Remove Iron from Hand Pump and Borewell Water · Why Village RO Plants Stop Working, and What Works Better · All proven technologies