Ozone removal - technical issues

[cikiste]

Dear group,

I need member's opininon regarding Ozone removal procedure in civil waterplant.

Namely, in the last stage of production process, H2O2 solution is injected in water stream in order to eliminate Ozone rez. and to lower it in accepteable level. The main question is how to inject or to apply relatively small quantity of H2O2 solution (about 0,1% of 500lit/h) in to 6 meters width water stream?

Is the H2O2 solution good choice for this particular application?

Sincerely,
Ivan Lazarevic.

 

[ChemOxGuy]

Though totally miscible with water, 50% H2O2 is 20% heavier than water. Diluting the H2O2 'inline' with carrier water (to e.g., 1-2% or less) will help its mixing, as will using one or more pressure injectors to shoot the diluted solution into the center of the flow (as opposed to letting 50% H2O2 scoot along with the water perimeter as a substream). Since the half-life of H2O2 in potable water is hours, inefficiency due to H2O2 decomposition is not likely to be the problem, but rather O3 removal efficacy within the time constraints. Also, residual H2O2 into filter beds can shorten backwash cycle times, and residual H2O2 into final disinfection will consume active chlorine.

Another potential problem is that many water plants that use H2O2 for O3 destruction derive benefit from the resultant hydroxyl radicals (AOP). Since this reaction has an optimal ratio of H2O2:O3 (typically ca. 0.3 w/w), poor mixing will reduce hydroxyl radical production efficiency.

Of the alternatives to H2O2, calcium thiosulfate is one I've encountered, though it doesn't generate hydroxyl radicals when neutralizing O3.

 

[bimr]

You can use the same type of diffusers as used to inject chlorine. Metcalf & Eddy Wastewater Engineering 3rd edition, page 503 shows some typical diffuser setups.

As ChemOxGuy suggests, diluting the chemical first with a bypass stream (also commonly included with chlorination) will improve the efficiency.

 

[cikiste]

Hello!

First of all, thank you for reply.

The initial idea was like the one you proposed: diluting the 35% solution of H202 into water in order to get some 0,1% solution, and then by means of diffuser (I wanted to use perforated tube), apply it into 6 meter wide water stream with O3 of 0,4mg/l rez. inside.

As my colleagues calculated, the 1,25kg/h of H2O2 will be enough to eliminate O3 rez. for water flow of 3600m3/h.

I have some issues regarding diluting system, i.e. what kind of pump I should use for bypass stream and construction of diffusor?

Regards,
I Lazarevic