[Zurück]

V. Parravicini, K. Svardal, R. Hornek, H. Kroiss:
"Aeration of anaerobically digested sewage sludge for COD and nitrogen removal: optimization at large-scale";
Water Science and Technology, 57 (2008), 2; S. 257 - 264.

The paper will report about the experiences at an Austrian large wastewater treatment plant of
720,000 population equivalents, where anaerobically digested sewage sludge is further stabilised
under aerobic conditions. Enhanced stabilisation of the anaerobically digested sludge was
required at the plant in order to get a permit for landfill disposal of the dewatered stabilized
sludge. By implementing a post-aeration treatment (SRT , 6d; 36 8C) after anaerobic digestion
the organic content of the anaerobically well digested sludge can be decreased by 16%.
Investigations on site showed that during digested sludge post-aeration anoxic phases for
denitrification are needed to provide stable process conditions. In this way the pH value can be
kept in a more favourable range for micro-organisms and concrete structures. Additionally,
inhibition of the biological process due to nitrite accumulation can be avoided. By optimising the
aeration/pause ratio , 45% of total nitrogen in digested sludge can be removed. This significantly
improves nitrogen removal efficiency at the wastewater treatment plant. NH4-removal occurs
mainly through nitritation and denitritation with an efficiency of 98%. The costs/benefit analysis
shows that post-aeration of digested sludge results in an increase of total annual costs for
wastewater treatment of only 0.84%, corresponding to 0.19 Euro/pe/a. Result of molecular
biological analyses (DGGE) indicate that all four ammonium-oxidizing bacteria species present in
activated sludge can survive anaerobic digestion, but only two of them can adapt in the digested
sludge post-aeration tanks. Additionally, in the post-aerated digested sludge a further ammoniumoxidizing
bacteria species was identified.

digested sludge aeration, enhanced sewage sludge stabilisation, nitritation and denitritation, ammonia-oxidizing bacteria, nitrogen removal in reject water

http://dx.doi.org/10.2166/wst.2008.020