Flocculants: Alum and Ferric Chloride Compared
Published on by Karl-Uwe Schmitz, President at Aqua Equip Technologies LLC (AET LLC) in Technology
Alum and ferric chloride are the most common used flocculants in wastewater treatment. But what are the pros and cons of both?
Pros of alum
- It’s inexpensive,
- Easy to use,
- Many vendors = good availability.
Cons of alum
- Alum has a demand for hydroxide and alkalinity and only works within a certain pH range,
- Large amounts are often required The dirtier the water, the more alum you need to feed,
- Doesn’t work in very dirty water,
- High sludge production,
- Sludge characteristics are very gelatinous = hard to dewater.
Pros of ferric chloride
- Works over a broad pH range,
- It’s fairly easy to use.
Cons of ferric chloride
- It’s very, very corrosive. Special piping, storage equipment, and pumping equipment are required because it’ll eat through things like the flow meter—and basically anything but 318 stainless steel.
- High price fluctuation.
There are alternatives to alum and ferric chloride. However they are not known by most plant operators because they aren’t promoted as much.
Learn more about all types of flocculants on the Water FAQ blog.
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