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Diluting Of Sulphuric Acid In Water Treatment Plant Industries

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Posted 15 January 2023 - 10:55 PM

Hi Everyone, 


I am currently designing on a Sulphuric Acid Dosing Plant for a water treatment plant. This is a new experience for my company and I have went through a lot of literatures. 


I have a lot of queries as I understand that to do this plant is not that easy due to a lot of safety circumstances in the storage and dosing system. 


The client is asking to use 98% of sulphuric acid as initial concentration and dilute to a concentration before dosing into the process line. In this case, the process line is the raw water from a river. The purpose is to reduce the pH to the optimum pH for the coagulant optimum performance. 


Firstly, in terms of the dosage required. I did my calculations and  the required amount of Sulphuric acid. The result to lower down the pH from pH 8 to 6 is about 0.49ppm of 10% Sulphuric Acid. This is contradict with the lab result report that it claimed to dose 98% H2SO4 at 20-30ppm. I understand that it could because certain organic matters in the raw water will react with the acid ions, but would it make a such different? I have no idea on what is wrong with my calculations. 


Secondly, to calculate the heat of enthalpy of dilution. From my understanding, It is batter to do a higher ratio dilution due to the higher amount of water creates a larger heat dissipating medium to absorb the heat of dilution due to the addition of acid to the water. I get the temperature rising from diluting 98% to 3% is about 30 degree C from my calculation. However, in reality, obviously, the temperature would go up to 180 degree C (boiling), and dilution shall be done by stages 98-60-30-20-10%, with heat removal system after each stages of dilution.


There is a lot of contradict when we look at literature and the reality in the industry in actual. I have no idea on it and hope anyone could answer my queries. 


Thank you very much in advanced. 










#2 breizh


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Posted 16 January 2023 - 12:02 AM

Hi Yumi,

Consider the doc attached to support your work. #7 in particular.

Note: To get the quantity of acid you need to neutralize the effluent, forget about calculation.

Take a sample of your water and perform a titration in the lab, you will get the right number of cm3 of Acid you need per g or kg of water. 100% accurate.

Yes, you are right about safety concern using sulfuric acid and water. More info in the doc attached. Always add Acid in water, not reverse.

Note: you may consider having a specific unit to prepare diluted acid solution.


Good luck.




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Posted 17 January 2023 - 12:27 AM

Hi Breizh, 


Many thanks for the info. 


Have a great day ahead and Happy New Year!

#4 breizh


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Posted 17 January 2023 - 12:42 AM


Welcome and happy new year!


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