The
separated microsand is concentrated, discharged
through the bottom of the hydrocyclone, and reinjected
into the ballasted flocculation process. Most of
the microsand is recycled in the ballasted flocculation
basins for further flocculation. The solids separated
by the hydrocyclone will flow by gravity back to
the head of the plant to the influent pumping station,
where they are treated by the main biological treatment
process.
Mechanical
Checkout and Performance Testing
After the ballasted flocculation basins were constructed,
each basin was checked mechanically and tested for
performance. The ideal time for process performance
testing is during wet weather events, but it is
difficult to predict when a storm event will occur.
So, the project team developed a plan to simulate
a storm event to test the system (see Table 2, p.
33). However, this plan proved to be unworkable
because the influent pumping was being modified.
Furthermore, during ballasted
flocculation basin testing, more than 50% of the
primary basin capacity was out of service due to
construction, so the primary basin effectiveness
was low. Total suspended solids in the primary basin
effluent were about 140 to 180 mg/L, which is in
the anticipated range of influent flow to the ballasted
flocculation basins, so primary basin effluent was
used during mechanical equipment checkout, process
optimization, and performance testing. The effluent
was stored in the holding basin for excess-flow
stormwater and pumped to the splitter—screening
facility by temporarily installed pumps.
During testing, separated solids
were pumped to the liquid process streams downstream
of the primary basins. If the chemically enhanced
solids had been recycled during the performance
test, the project team was concerned that they would
enhance the polymer and ferric chloride dosages
and skew the results.
After the ballasted flocculation
equipment was completely field-tested, mechanical
startup testing began. Because the ballasted flocculation
basin is discharged directly into the Kansas River
and this was the first sanitary sewer overflow facility
of its kind, the project team designed two testing
operations. In the first, the facilities were operated
with a blend of nonpotable (disinfected plant effluent)
and service water to alleviate any concerns about
direct discharge into the
