June 14, 2021, 05:39:01 AM
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Topic: Recirculating Oxidant (NaClO/ClO2) During a Pilot Test - Will it break down?  (Read 453 times)

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Offline erkvos

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I am planning a set of experiments where two oxidants (NaClO and ClO2) will be evaluation for the disinfection of water. The process flow rate is 850 gpm - passing water through two air stripping units before a small portion of this flow is diverted to a 15 gpm side-stream for testing.

Three pilot test process lines (5 gpm each) will be used for the evaluation of ClO2 and sodium hypochlorite. One 5 gpm process stream will be untreated (control), but the other two will have doses of ClO2 from .15 - 1 mg/l, and `.5 - 2.5 mg/l of NaClO. For each dose, a sample will be collected and testing for ClO2, Chlorite, Total Chlorine, Free Chlorine, and disinfection by products (DPB's), such as THM's, HAA5's, and Bromate. Microbial plate counts will also be measured for treated and untreated process water collected from the side-stream.

Naturally, I do not want recirculated oxidant to interfere with tests. But because each test run may take an hour, I have two options:

1. Position ~ 1000 gal of storage outside of the process room, diverting the 15 gpm flow to IBC totes for intermediate storage. This volume will be exposed to sunglight, degrading any residual Chlorite ion, ClO2, NaClO, HOCl, OCl', monochloramine, etc...

2. Use a 55 gallon drum as intermediate storage (~3.5 min retention time), before water is subsequently pumped into a clearwell, and recirculated to the process. Before any recirculated water would potentially become reintroduced to my 15 gpm test side-stream, it will pass through a air stripper, with a vacuum of approximately 3 iwc (inches of water column).

While option one will prevent cross contamination with near certainty, it may be complete overkill. THe highest doses of ClO2 and NaClO will be 1 and 2.5 mg/l, respectively at 5 gpm. This would be reintroduced to a clear-well with more than 2000 gallons of capacity before any cross contamination would occur.

Am I OK to reciruclate? I'm not sure how easily Chlorite would break down in an air stripper.

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