Pharmaceutical and API plants often produce effluent with high COD and compounds that biological treatment cannot break down. Fenton oxidation is one of the most widely used chemical pre-treatments for these streams: it uses hydrogen peroxide and an iron catalyst to break stubborn organics into simpler compounds that the biological stage, or the next treatment step, can handle.
The chemistry in one paragraph
When ferrous iron (Fe2+) meets hydrogen peroxide (H2O2) in acidic conditions, it produces hydroxyl radicals, among the strongest oxidising agents used in water treatment. These radicals attack organic molecules and break them down. Fenton treatment is often used to improve biodegradability rather than to remove all the COD.
Typical steps
- Acidify: bring the effluent to an acidic pH. Around pH 3 is the most commonly reported optimum.
- Add iron: dose ferrous sulphate as the catalyst.
- Add peroxide: dose hydrogen peroxide gradually and allow reaction time with mixing.
- Neutralise: raise the pH with lime or caustic soda, which also precipitates the iron as sludge.
- Flocculate and settle: a polyelectrolyte helps the iron sludge settle before the water moves on.
Getting the doses right
The right ratio of peroxide to iron, and the total dose, depend on the effluent and must be found in lab trials. Too little peroxide leaves COD behind; too much wastes an expensive chemical and the leftover peroxide can upset the biological stage downstream. Too much iron simply makes more sludge.
Run trials on fresh effluent from each major product campaign, because pharma effluent changes with what the plant is making.
Sludge and safety
Fenton produces iron hydroxide sludge that has to be dewatered and disposed of as hazardous waste in most cases, so include sludge handling in your cost comparison.
Hydrogen peroxide is a strong oxidiser. Store it away from organics, metals and reducing agents, in vented containers, and follow the SDS. Our guide Safe Storage of Oxidizers covers the basics.
Chemicals for a Fenton system
We supply hydrogen peroxide, ferrous sulphate, lime, caustic and polyelectrolytes, and the rest of the pharma ETP range on our Pharmaceutical ETP & ZLD Chemicals page. We dispatch to pharma clusters in Hyderabad and Vizag.