Nitrogen removal from sludge digester liquids by nitrification/denitrification or partial nitritation/anammox: environmental and economical considerations

Abstract

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this "achievement" turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.

Effect of Nitric Oxide on Anammox Bacteria

“…that are used to detoxify NO to the less-reactive and more-stable nitrous oxide (N 2 O) (24). Still, N 2 O is a very effective greenhouse gas and an unfavorable constituent in the off-gases from nitrification/denitrification nitrogen removal systems (4). The presence of gene(s) encoding cytochrome cd 1 nitrite reductase (EMBL accession no.…”

Biological nitrogen removal over nitritation/denitritation using phenol as carbon source

“…Although the free ammonia concentrations in the aerobic stages of the treatment cycles were within the range determined by Anthonisen et al (1976) as inhibiting for nitrite oxidizing bacteria (0.1 to 1.0 mg NH 3 .L -1 ), this was not the only factor in establishing a stable nitritation. Due to the long-term reactor operation, NOB could adapt to an inhibitory free ammonia concentration, as suggested by other researchers Fux and Siegrist, 2004;Ruiz et al, 2003). In fact, stable nitritation was achieved with the maintenance of a maximum DO concentration of 1.0 mgO 2 /L, a pH value of 8.3 and the adjustment of the aeration time required for ammonia oxidation.…”

“…Other advantages of this process are a biological nitrogen reduction rate 63% higher than the conventional one, less biomass production and 40% reduction of the heterotrophic carbon demand (Phillips et al, 2002;Fux and Siegrist, 2004;Fux et al, 2006).…”

Recovery of N and P from Urine by Struvite Precipitation Followed by Combined Stripping with Digester Sludge Liquid at Full Scale

“…With the current price of the fertilizer, chemical cost was higher than fertilizer incomes. However, indirectly extra costs can be compensated by the reduction in the cost of aeration for nitrification and in the carbon source for denitrification in the biological reactors of the WWTP [44,45].…”