This study evaluated the
formation of hydrazine during the chloramination of water and wastewater.
The study began with the refinement of an existing hydrazine analytical method to allow for
low-level detection in water. The method was modified to allow for the reliable
quantification of hydrazine concentration in water down to 5 ng/L. Stability tests were then
conducted and they showed that hydrazine is stable in water up to 48 hours, especially with
decreasing temperature.
A detailed hydrazine formation model was developed based on information reported in the
literature. The model accounts for the effect of chloramine concentration, ammonia
concentration, pH, and contact time on the formation of hydrazine. The model suggested
that the maximum level of hydrazine formed is independent of the concentration of
chloramine present in the water. Hydrazine formation modeling suggested the following:
less than 5 ng/L hydrazine is expected to form in waters containing free
ammonia-nitrogen levels below 0.5 mg/L and a pH below 9.0;
hydrazine levels in chloraminated wastewaters containing more than 5 mg/L free
ammonia-nitrogen are expected to be greater than 40 ng/L at pH levels at or
above 9.0; and,
hydrazine formation increases dramatically with increased water pH. For
example, with 2 mg/L free ammonia, an increase in pH from 9.0 to 9.5 increases
hydrazine formation from 15 ng/L to 80 ng/L.
Limited hydrazine formation tests were conducted under varying chloramine and ammonia
conditions. The results showed that no quantifiable hydrazine level was formed under typical drinking water chloramination conditions. However, at elevated ammonia and pH
levels, hydrazine levels formed reached 584 ng/L. The model developed in this study seems
to under-predict the levels of hydrazine formed. However, this could be due to the high
sensitivity of hydrazine kinetics to the pH of the water. Includes 22 references, tables, figures.
| Edition : | Vol. - No. |
| Number of Pages : | 18 |
| Published : | 06/17/2005 |
