The second-stage treatment is a continuation of the al-kali-chlorination process in which the cyanate is destroyed as follows:
The reaction occurs at a controlled pH level, usually between 8 and 9.5, for a reaction time of 30 min or less. Table 7.41.3 shows the retention time relationship to pH requirements for the second-stage reaction.
The retention time requirement should not be confused with the vessel hold time constant; the latter is the ratio of volume divided by flow (V/F). The V/F ratio gives a nominal time constant. To determine the variance about the nominal value, environmental engineers should use a statistical technique to insure that all of the material treated has spent the required amount of time in the reaction vessel.
This second-stage reaction can be treated in a manner similar to the first-stage treatment. The reduction potential is estimated as +0.4 V as follows:
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