| pH depression |
shifting HOBr/OBr– equilibrium,
decreasing Rct (increased
O3 stability) |
pH 8 to 6 in drinking water, 50–91%47,121
|
enhanced (stabilized ozone) |
potentially diminished for
O3 recalcitrant micropollutants (lower Rct) |
expensive,
requires storage
of caustic chemicals, not applicable for medium/high-alkalinity water |
| NH3 addition |
HOBr quenching
(NH2Br formation) |
42–73% (surface water,
pH 8, 100–900 μg of NH3-N/L)47,121,124,125
|
unaltered from conventional
ozonation |
unaltered
from conventional
ozonation |
•OH pathway
not affected, removal of excess ammonium in biological postfiltration |
| preformed NH2Cl |
decreasing Rct (radical scavenging), HOBr and Br• quenching |
68–87%
(wastewater, 1–5 mg of NH2Cl as Cl2/L)130
|
unaltered, although lower
levels of ozone exposures have been demonstrated |
potentially diminished for
O3 recalcitrant micropollutants (lower Rct) |
monochloramine
must be produced
on site, removal of excess ammonium in biological postfiltration |
| chlorine–ammonium |
bromide sequestration (NH2Br formation), HOBr quenching |
44–94% (surface water,
0.25–1.0 mg/L Cl2 and 100–500 μg of NH3-N/L)124−126
|
unaltered from ozone alone
or slightly enhanced |
unaltered from ozone alone |
formation of chlorinated/brominated
DBPs |
| H2O2
|
reduced lifetime of ozone,
reaction with HOBr |
–130% to 60% (surface
water, 0.5–1.5 mol of H2O2/mol of O3);135 −50% to 67% (wastewater,
0.14–4.2 mol of H2O2/mol of O3)96,136,137
|
diminished (low level of
or no O3 exposure) |
enhanced (increased level
of radical production) |
residual H2O2 removal in biological postfiltration |
