3 replies to this topic

[terrahjeanette]

I'm attempting to design the neutralization system for a batch waste water neutralization process. The waste water will be recirculated through a 4" 250 gpm line. The line has a steam injector to heat-kill and organisms, a PHe to cool the water back down to acceptable temperature, and a series of injection quills to neutralize any pH inconsistencies.

The question I have is how much of each of the neutralizing chemicals (93% H2SO4 and 24% NaOH) I might need to neutralize the 6000 gal batch? If it's a small amount, then a small metering pump should be sufficient, but we might have to look other place if its turns out to be more like 5 to 10 gallons.

I really have no intuition for this.

Thanks for your help.

[ankur2061]

terrahjeanette,

Two books are recommended for Waste Water Neutralization system design guidelines:

Water and Waste Water Calculations Manual by Shun Dar Lin

This book provides detailed calculation methods with plenty of examples for different waste water treatment methods including primary, secondary and tertiary treatment of waste water. Neutralization system calculations are also included.

Another useful book resource including examples is:

Handbook of Water and Wastewater Treatment Technologies by Nicholas P. Cheremisinoff

This should help you in determining the quantity of the neutralizing chemicals.

Hope this helps.

Regards,
Ankur.

[Zauberberg]

Quantity of neutralizing chemicals can be easily calculated by following Acid-Base chemistry equations, and knowing total volume of the system. For example, if you have 6,000 gallons of solution with pH=3, calculation of required quantity of 24% NaOH is quite straightforward. For theory and some calculation examples see:

http://www.chem1.com...df/c1xacid2.pdf
http://www.ausetute....u/titrcalc.html

To implement an accurate and reliable neutralization control system in practice can be quite tricky, as you will have to depend on pH analyzer/controller to tell you how far are you from the desired solution. If the system has fouling tendencies, many pH analyzers will simply not work. In addition to that you want to avoid continuous addition of either Acid or Base, so there must be some sort of "dead band" (e.g. pH between 6.5 and 7.5) when you don't want to add any chemical - otherwise they will be continuously injected (acid, Base, Acid, Base etc.) trying to catch each other.

Fortunately it is a batch system, so you can design it with proper mixing device(s), a fouling-free analyzer system, and a metering pump to inject required quantities of each chemical.

[kkala]

Even though 23 m3 batch is not a big quantity, I believe complete waste water analysis is needed to estimate even approximate consumptions of H2SO4 or NaOH (why both, is composition varying?). Water can contain buffer solutions, needing much more acid or alkali for neutralization (to what pH?) than what pure water of same pH would require. I have seen that by trying to measure pH of soil, actually containing buffer solutions.
Precipitates can be also formed (e.g. in the form of MOH) as pH is increasing, contributing to increased NaOH consumption. Or increased acid consumption, if the reverse way has to be realized.
In case that detailed analysis is not (yet) known, probably some experts can make a reasonable range estimate by knowing source of waste water, some gross analysis, anything relevant. That is judging waste water nature by knowing the process which it has been come from. Probably someone with specific expertise could help, if you can give info as mentioned.
I am not expert to offer a more helpful opinion, yet waste water composition varies widely from case to case.

Edited by kkala, 18 November 2011 - 06:57 AM.