The major competitors of Ferric Chloride are mainly
PAC (Poly Aluminium Chloride)
Alum
Ferric Alum
It is a well-established fact that PAC offers superior performance than Alum and Ferric Alum. Ferric Chloride on the other hand offers even better performance than PAC over wide range of applications. To compare a few:
1. Turbidity Removal
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and water quality.
Ferric Chloride offers higher levels of Turbidity Removal than PAC and Alum and at much lower dosage levels. As per NEERI only 15 ppm Ferric Chloride is required to bring down the Turbidity of water from 100 NTU to 4 NTU, whereas to do the same 30 ppm PAC is required and 40 ppm Alum is required.
Dose in PPM to bring down 100 NTU to 4 NTU
Coagulant Used
2. DOC Removal
DOC is the measure of the dissolved organic matter in water that can pass through standard filter paper. Hence it requires chemical treatment to be removed.
DOC Removal Comparison
Dosage in PPM
3. Sludge Settlement Rate
Ferric Chloride forms much heavier flocs than PAC, Alum and Ferric Alum. The heavier floc leads to faster settlement of the sludge. Hence it effectively cleans the water faster. Comparison of the sludge settlement velocity of the coagulants is given below
Sludge Settlement Rate Comparison
Coagulant Used
4. Colour Removal
Most waters have some colour; this may or may not be visible to the naked eye. The cause for this colour is algae / organic matter / other impurities.
Colour Removal Comparison
Coagulant Used
5. Trialomethane Removal
The use of chlorine in water treatment is very common. Its usage leads to the formation of Trialomethanes. Ferric Chloride can remove Trialomethanes whereas PAC, Alum and Ferric Alum do not.
Trialomethane Removal Comparison
Coagulant Used
6. Heavy Metal Removal
Ferric Chloride can remove heavy metals like arsenic from water whereas PAC cannot.
7. Odor / Hydrogen Sulfide Removal
Ferric Chloride removes odor causing hydrogen sulfide from water whereas PAC does not. Hence sometimes for wastewater treatment Ferric Chloride is even preferred over PAC.
8. Phosphates Removal
Phosphates are the reason for foaming in rivers and lakes. Hence its removal is very important. Ferric Chloride can remove phosphates whereas PAC cannot.
9. Ammonia Removal
Excess ammonia in water can cause blue baby disease. Hence its removal is important. Ferric Chloride can remove ammonia whereas PAC cannot.