Biological nitrogen removal from wastewater of the chemical industry
by an activated sludge-biofilm system
Vince BAKOS
Supervisor: Dr. Andrea JOBBÁGY
Department of Applied Biotechnology and Food Sciences
Budapest University of Technology and Economics
H-1521 Budapest, Hungary
e-mail: bvince@freemail.hu
As compared to the municipal wastewater treatment the appropriate biological nitrogen
removal of pharmaceutical wastewater is achievable only at a higher sludge retention time
(SRT) due to the toxic and recalcitrant material content and the seasonal variation of the
production [1,2].
The comparative pilot-scale experiment was carried out by using two model systems,
operating simultanously on the site at the wastewater treatment plant of Novartis AG. (Basel,
Switzerland) with the direct and continous usage of the incoming wastewater.
The aim of this study was the determination of the optimal total bioreactor volume (and
accordingly the optimal biomass retention time) which can assure the efficient nitrification
and denitrification in contempt of the variable load and wastewater quality. The experimental
work also examined whether the incoming wastewater contains enough soluble carbon source
for efficient denitrification. Moreover, the on-site pilot-scale experiment studied the
upgrading influence of the fixed-bed reactors, namely whether the nitrification and the
organic carbon elimination efficiency increases and the effluent suspended solid concentration
decreases in the combined system. Finally, the excess biomass formed in the biofilm unit was
removed through the activated sludge system and this study tried to find out whether the
recirculated nitrifying biomass backseeds the activated sludge, resulting in efficient
nitrification.
Nitrate recirculation (100%)
Recirculation of the backwashed biomass
Internal nitrate recirculation (100%)
Anoxic reactors
Aerated reactors
Incoming
wastewater
Secondary
clarifier
V = 54 l
Treated
wastewater
x = 6-8 g/l; Total volume = 54 l
Sludge recirculation (250%)
Fixed-bed
reactors
V = 5+5 l
The bioreactor arrangement of the pilot-scale system
Backwashing water
The results of the on-site pilot-scale experiment showed, that an SRT value of 28-30 days
is necessary for the stable nitrification of the activated sludge (at an average wastewater
temperature of 27 ºC), which is by about one magnitude higher than it would be in a domestic
treatment plant, and can be attributed to the inhibitory effect of the toxic organics. In case of
low nitrification rate in the activated sludge, the effluent ammonia was efficiently oxydized in
the fixed-bed reactors. The incoming wastewater proved to be a suitable substrate to the
denitrification. The denitrification rate increased and favourable sludge sedimentation was
achieved through the nitrate recirculation. In the biofilm system an important additional
organic carbon elimination was observed, however, the fixed-bed reactors operated also as
efficient biofilters resulted low suspended solid concentration in the treated effluent.
References
[1] Juliastuti, S. R., Baeyens, J., Creemers, C., Bixio, D., Lodewyckx, E. (2003): The
inhibitory effects of heavy metals and organic compounds on the net maximum specific
growth rate of the autotrophic biomass in activated sludge. Journal of Hasardous
Materials, B100, 271-283.
[2] Pagga, U., Bachner, J., Strotmann, U. (2006): Inhibition of nitrification in laboratory tests
and model wastewater treatment plants. Chemosphere. 65, 1-8.