Dear Concern,
I'm facing a problem in using acid to neutralize the raw wastewater using Sulfuric acid. Here is my question.
In a Industrial Wastewater Treatment Plant, During lab testing, less amount of 18M sulfuric acid is required to get a pH 0f 7 in the raw wastewater, but to achieve the same neutralization, the plant uses more acid, though. Why?
I think you may need to provide more information here. For example, are you testing identical samples? Are you using the same bottle of H2SO4? How much more? 5%, 150%? Where are the water sources coming from? If your lab water source is deionized water or distilled, it may have no CO2 dissolved in it. CO2 forms carbonic acid in water (H2CO3). If the raw water has carbonic acid in it it is already somewhat more acidic (less basic) and would therefore require less sulfuric to neutralize it. Best guess with info you have provided...
Total dissolved solids is certainly a possibility. A lot depends on differences of her lab sample and the raw sample.
Use flash mixing to reduce the sulphuric acid dosage. Means, raise pH to 8-9 by addition of Lime. Lime is much cheaper. This would also promote better coagulation/flocculation of the impurities present in real wastewater.
When dealing with raw wastewaters, neutralizing with an acid in the laboratory to adjust the pH is not a good idea. Because, in the lab, the acid consumed may be in mL, but in ground reality, the acid consumption can be in cubic metres, which goes impractical for field application.
Also the reason could be in biological reduction of sulfuric acid during wastewater treatment.
If acid added in upcoming wastewater to the station - it has very low redox potential and all oxidizers could be reduced pretty quickly.
So i should take in consideration the time distance between adding acid and measuring pH points.
Thank you all of you for the answers. I'll try to work out with them. If I need your help, I'll get back to you in future.