Environmental Technologies and Eco-innovation in the Czech ...

The oxidation of ammonia nitrogen to
nitric nitrogen in activation is ensured by
nitrification bacteria. However, their share
in activated sludge ranges only from 1 to 3%.
Such low concentrations are given by the
lower growth rate of nitrification bacteria
compared to other bacteria. The most widespread
manner of compensating for their
low growth speed is increasing the sludge
age 13 , which, however, leads to reducing
the bacteria activity and to the need of
larger activation tanks. An alternative to
increase the nitrification bacteria share
in the activated sludge is the inclusion of
in situ nitrification bioaugmentation,
during which nitrification bacteria
cultivation takes place in a detached part of
the regeneration tank, into which a source
is lead containing substances with nitrogen
present, preferably the water from activated
sludge dewatering. The grown nitrification
bacteria are introduced back into the
system in order to increase the nitrification
bacteria concentration in the activation
tank to increase the nitrification efficiency.
This method was successfully applied in
Prague’s Central WWTP and in the Ústí
nad Labem WWTP. By introducing this
technology, a significant increase in the
efficiency of nitrogen removal was reached.
With the correct WWTP design with in situ
nitrification bioaugmentation in place, the
required activation tank sizes are reduced
by as much as 40% and, at the same time,
this brings an operating cost savings by as
much as 10%.
6.4 | New methods of activated sludge separation 13
One of the essential phases of biological waste water treatment is the separation of
activated sludge from treated waste water. Bad separation can lead to leakage of the
activated sludge into the discharge, which significantly increases the concentrations of
the discharge indicators and deteriorates the overall treatment. In the waste treatment
practice, the classical final settling tanks are being more and more often replaced
with membrane filters 14 that are either submerged directly into the activation tank
or outside the activation tank, or they are located in a separate tank. Air is supplied
into the system for biodegradation needs and for cleaning the membranes. The driving
power of the treated water discharge is the difference of hydrostatic pressures 15 in
front of and behind the membrane. The membrane modules eliminate the difficulties
connected with activated sludge separation in the final settling tanks; it is also possible
to operate the system at much higher activated sludge concentrations. Inasmuch as
the membrane technologies usually range from microfiltration to ultrafiltration areas,
the disposal of all undissolved substances, bacteria and viruses occurs during
13 sludge age – the average time that bacteria remain in the system
14 membrane filter – a filter made of plastic materials that serves as a sieve for separating the two phases
15 hydrostatic pressure – the pressure in a liquid that is caused by its weight