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

decompose the mentioned specific substances, are being carried out in the Czech
Republic. The main obstacle for their successful application in normal operation are
completely different cultivation conditions, where, contrary to the activated sludge
microorganisms, they work at pH levels lower than 5 and the temperatures higher than
26 °C. Activated sludge microorganisms work at pH levels of 6–7.
Municipal waste water mainly contains organic substances and compounds
of nitrogen and phosphorus. Higher nitrogen and phosphorus concentrations in
water leads to the eutrophication 12 of water with all accompanying negative effects
(increased costs for treating this surface water into drinking water, hygienic problems
for bathing, and fluctuations in the concentration of oxygen dissolved in the water,
etc.). Also for this reason, the limits of total nitrogen and phosphorus at the discharge
point from waste water treatment plants are constantly being reduced. Therefore, it
was necessary to adapt WWTP technologies for nitrogen and phosphorus removal (the
original biological treatment was designed mainly for organic substance removal).
It has been determined that the most important factor for the eutrophication
of water is phosphorus concentration. During biological treatment, its removal
with excessive sludge occurs because it is possible to select processes that force
microorganisms to accumulate more phosphorus in their bodies. Based on today’s
legislative requirements on the discharge from WWTPs, this biological phosphorus
removal is insufficient and not too efficient. Today, phosphorus removal from waste
water occurs through chemical precipitation, namely by dosing iron and aluminium
salts into the sludge and waste water mixture in the activation tank.
On the contrary, nitrogen removal occurs through new biological treatment
methods, where the legal limits are achieved by correct sequencing of the parts
of a WWTP line with different concentrations of oxygen dissolved in water. The
way of sequencing oxic (with oxygen present) and anoxic zones (with lower oxygen
concentrations) in a technological line may be generally described as follows:
the waste water being brought in enters the anoxic zone, into which the thickened
activated sludge is lead and the activation mixture from the end of the oxic zone with
high nitrate concentrations. In the anoxic zone, the development of denitrification
bacteria occurs that reduce the nitric nitrogen to nitrogen gas, and for this process
they use the organic substances from the waste water being brought in. The activation
mixture flows off into the oxic zone where the remaining organic pollution is removed
and the ammonia nitrogen is oxidised into nitrates.
12 eutrophication – excessive growth of algae and cyanobacteria, the cause of which is a high concentration of nutrients in
water; this mainly includes nitrogen and phosphorus compounds
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