how to design an anoxic tank? 1

[chela21]

Our wastewater, 1.5 m3/hr constant flow rate, has high nitrate levels of 6-8 mg/L.
We have an existing tank we are not using and we are planning to convert it to an anoxic tank. how do we actually do it? most articles in the internet describes the process but i cannot find the actual design or construction of one. can anyone help?

 

[FiltrationEngineer]

If you already have a tank you are going to use, the design isn't much of an issue because you won't be able to design the volume required.

Anoxic tanks are just tanks with mixers. Thats it, assuming you have an activated sludge process, you would recycle your water from your aeration zone to your anoxic zone. If you don't have an activated sludge process, there are some other options including denitrifying sand filters.

There are 4 things necessary to achieve denitrification:
1. Bacteria
2. Food for the bacteria to eat (BOD)
3. Nitrates
4. Anoxic conditions. This is why you have an anoxic tank. You want a place for the bacteria to spend time where they don't have access to dissolved oxygen. The bacteria then use nitrate (NO3) as an oxygen source and the BOD as food. Anoxic conditions are best measured using an ORP probe. You want the ORP to be between -50 and 50 milivolts for good denitrification.

For specific design equations, you can get this book:
Biological and Chemical Systems for Nutrient Removal, published by WEF.

 

[chela21]

Thanks, Filtration Engineer, for the info and for the book.