I have been using Ferric chloride as coagulant on a lab (1Litre Jar), on a pilot scale (treating 1000L of influent) and on one of my sumps treating 9000L of influent. I have a lot aluminium sulphate flakes and I wanted to try it out using it as coagulant. But i'm concerned that it might affect the sulphates concentration which I'm trying to precipitate out of the influent.
Thank you
Optimum use of Aluminum Sulphate will depend on your dissolved solids in the water you are testing. Calculate your bivalent and trivalent radicals and match them with trivalent Aluminum ion. Then 1.5 times excess Aluminum Sulphate will be helpful to reduce your sulphate load.
This depends on pollution of wastewater. You should carry out Jar Test with different additions of Al-sulphate. Normally we started with 10-500 mg/L of Al-sulphate. Regards, Milenko Ros.
In practice they are used solutions containing about 4% of aluminium. Sulphates in wastewater pose a danger of creating hydrogen sulphide. Ferric chloride can oxidize sulphides and precipitate them.
Aluminum sulphate (Al2 (SO4)3,18 H2O) is a best coagulant, used for higher water temperature to 12 ° C.
The dose of AL3+ (mg / l) which may be used for the treatment of wastewater is varied between 50 to 200 mg / l.
it depends on pollution of wastewater. you should apply jar test using different dosage. Suspanded solid material in wastewater should be determined. after coagulation experiments suspended solid material sould be determined also. Waste water pH is important . Al2SO4 will be hydrolised . pH decreases . Al(OH)3 is soluble at low Ph .So treatment is not effective at low pH using this coagulant.
The stock solution should be 10% (solution of Aluminium sulphates)according to different levels of water turbidity and chemical conditions(TDS,pH,Tu...) it specifies and defines the Jar test.
For preparing the alum solution, you can take 5-20% by weight. Start with the lower end.
It’s true that you can get high concentration, but it depends on addition. Try to carry out jar test and analyse sulphate in the effluent. If the concentration of the sulphate exceed limit value than try to combine addition of Al-sulphate and Ferric chloride.
It all depends on the type, strenght and the composition/particle size distribution of the wastewater.
Although that information is not provided, I presume the wastewater in question is sewage. In that case we may assume total COD of 500 mg/L with 60 to 70% particulate COD. Our experiments indicated that with 250 mg/L alum, we were able to remove around 30% COD and 80% SS from sewage.
pH of sewage is also an important factor for selecting the coagulant. Note that ferric chloride is effective at high pH ranges and it is best used with lime, which increases the amount of sludge generated.
Why not using synthetic coagulants as such PAC, etc.
Try to determine in the influent the dose of coagulant and the pH range that suits you and after measures the sulfates. In case of increasing sulphates concentration try a combination with other coagulants.
You can optimize the dosage depending on the expected parameter or result you want to achieve. A jar test with different concentrations using the RSM technique should give you an optimal dosage.
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