During filling (1 step), the liquor is pumped
to the reactor, where it is mixed with the residual
biomass from the previous cycle. The initial volume
assessment, that is the liquor volume present in the
vessel at the beginning of filling, depends on
different factors, among which sludge settling
sedimentation, biomass concentration and hydraulic
retention times. The initial liquor filled volume can
vary up to 40-50% of the total volume. Thus the liquor
is diluted or consists of an initial mixed liquor
volume accounting for at least 50-60% of the total
volume.
During filling, it is possible to forecast different
operations, alternating or in series. The filling can
be forecast under normal conditions or from simple
mixing to aeration at different rates.
When the scheduled maximum level is reached, the
mixing-aeration started during filled comes to an end
during the Reaction step (step 2). As during
filling, during reaction as well, there are different
anaerobic, anorexic and aerated steps, at the aeration
system level: two different degradation steps are
therefore possible, affecting microorganisms and
different enzymes, mutually interfering thus leading
to a more effective treatment, with no side effects
such as bulking, which generally often appear under
specific conditions in the traditional treatment
units.
The batch process leads to a constituent concentration
within the reactor, which on average is higher than in
the continuous stirred tank reactors (CSTR) and as a
consequence the average speed of the constituent
removal is higher.
In other words, the higher the constituent (pollutant)
concentration in the reactor, the higher the
constituent degradation speeds.
The decanting/settling starts (step 3), when
suspended solids are settled disabling the
aeration-mixing units, therefore the newly recovered
calm inside the oxidation vessel leads to the
activated sludge build-up on the vessel bottom,
leaving the surface cleaned.
After settling, the clarified liquor is removed (step 4).
The vessels are emptied through one of the
installation dedicated outlets, as it is necessary to
provide for the effluent good quality, thus avoiding
removing the biomass or the suspended solid
dragging.
The excess sludge is removed during settling, even
though sometimes the entire process is delayed during
the waiting period.
The system is entirely automated, through an
automation and control panel managing the different
treatment step durations according to the tank level
and the electro-mechanical unit operations
(compressors, mixers, feeding pumps, bleeding pumps of
the cleaned effluent).