Hardness removal processes, especially
for removing magnesium (Mg) and
silica (Si), are very pH-dependent. A
study was undertaken to determine the
extent to which aeration could replace chemical
addition as a means of calcium (Ca)
removal. Bench-scale tests were conducted
with a groundwater supersaturated with
carbon dioxide (CO2) and containing Ca,
Mg, and Si.
Optimal dosing of lime and soda ash
(OLSA) resulted in 79% removal of Ca and
Mg hardness and 23% Si removal. Addition
of iron salts during OLSA improved turbidity
removal, had minimal effect on Ca or Si
removal, and decreased Mg removal unless
pH was readjusted. Sodium aluminate addition
during OLSA improved turbidity
removal and increased settled sludge viscosity
but did not affect Ca, Mg, or Si removal. The
authors found that removing Ca from water
depends on the presence of "seed" particles
onto which calcite minerals precipitate; the
addition of a nuclei seed increased dissolved
Ca removal from 60 to > 80%. Addition of
polymers affects the density of the sludges
that are produced.
On the basis of these experiments, aeration
stripping would appear most appropriate
for waters supersaturated with CO2 and
containing predominating calcium carbonate
hardness. For utilities using these source
waters, the article offers a better understanding
of the effects of calcite chemistry
on aeration and softening processes that
should help them improve Ca removal while
minimizing chemical addition and sludge
production. Includes 20 references, tables, figures.
| Edition : | Vol. 94 - No. 3 |
| File Size : | 1
file
, 450 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 03/01/2002 |
