Possible mechanism of efficient mainstream partial nitritation/anammox (PN/A) in hybrid bioreactors (IFAS).

An explanation of possible mechanism of efficient PN/A in hybrid bioreactors was presented. The bottleneck process is nitritation. Surplus nitrite production by ammonium oxidizing bacteria (AOB) is required for assuring the activity of anammox bacteria and eliminating nitrite oxidizing bacteria (NOB). It will be possible if nitrogen removal rate by AOB (rN_AOB) is higher than NOB (rN_NOB). It was shown that in biofilm AnAOB bacteria should out-compete NOB, whereas nitrogen transformation rates by AOB are usually lower than NOB. However, the growth of r-AOB in activated sludge allows out-selecting NOB. Impact of ammonium-, nitrite-nitrogen and suspended biomass concentration in hybrid PN/A systems on nitrogen removal rates in the temperature ranges from 10°C to 25°C was presented and discussed. Because bulk liquid ammonium nitrogen concentration can be higher in SBR bioreactors (after certain period of time after aeration starts) or in the initial zones of plug-flow systems than in fully mixed systems, conditions for running efficient PN/A are more favourable in intermittently aerated 'IFAS-SBR' or 'IFAS-plug flow' bioreactors.

Performance of partial nitritation-anammox processes at mainstream conditions in an IFAS system.

The partial nitritation-anammox processes implementation in the main line of wastewater treatment plants would lead them closer to the energy autarky. With this purpose, an integrated fixed film activated sludge (IFAS) reactor was operated at pilot scale. Efficient nitrogen removal (72 ±â€¯11%) was achieved for anaerobically pre-treated municipal wastewater at low temperature (21 - 15 °C), with a nitrogen removal rate of 37 ±â€¯3 g N/(m3·d) at 15 °C. The ammonium oxidizing bacteria were more abundant in the activated sludge, while anammox bacteria were primarily located in biofilm attached onto the carriers surface. Nitrite oxidizing bacteria (NOB) activity was similar between both fractions and its specific activity decreased more than that of other populations when the operating temperature was reduced. Furthermore, the IFAS operational strategy (aerobic/anoxic periods) allowed an efficient NOB activity suppression inside the reactor, which accounted only for the 10 - 20% of the maximum potential activity.

Nitrous oxide emissions from one-step partial nitritation/anammox processes.

Measurements of nitrous oxide were made at pilot- and full-scale plants to evaluate greenhouse gas emissions from one-step partial nitritation/anammox processes applied in moving bed biofilm reactors treating reject water. It was found that 0.51-1.29% and 0.35-1.33% of the total nitrogen loads in the pilot- and full-scale reactor, respectively, were emitted as nitrous oxide. Between 80 and 90% of nitrous oxide emissions were in gaseous form and the rest amount was found in the reactor effluent; over 90% of nitrous oxide emissions occurred in the aerated period and less than 8% in the non-aerated period in the full-scale study. Nitrous oxide productions/consumptions were closely related to aeration and the nitrogen loads applied in the system.

Pilot scale studies on nitritation-anammox process for mainstream wastewater at low temperature.

Process of partial nitritation-anammox for mainstream wastewater at low temperature was run in a pilot scale moving bed biofilm reactor (MBBR) system for about 300 days. The biofilm history in the reactor was about 3 years of growth at low temperature (down to 10 °C). The goal of the studies presented in this paper was to achieve effective partial nitritation-anammox process. Influence of nitrogen loading rate, hydraulic retention time, aeration strategy (continuous versus intermittent) and sludge recirculation (integrated fixed-film activated sludge (IFAS) mode) on deammonification process' efficiency and microbial activity in the examined system was tested. It was found that the sole intermittent aeration strategy is not a sufficient method for successful suppression of nitrite oxidizing bacteria in MBBR. The best performance of the process was achieved in IFAS mode. The highest recorded capacity of ammonia oxidizing bacteria and anammox bacteria in biofilm was 1.4 gN/m(2)d and 0.5 gN/m(2)d, respectively, reaching 51% in nitrogen removal efficiency.

Mainstream wastewater treatment in integrated fixed film activated sludge (IFAS) reactor by partial nitritation/anammox process.

In this study the system based on the combination of biofilm and activated sludge (IFAS - integrated fixed film activated sludge) was tested and compared with a system that relies only on biofilm (MBBR - moving bed biofilm reactor) for nitrogen removal from municipal wastewater by deammonification process. By introduction of suspended biomass into MBBR the nitrogen removal efficiency increased from 36 ± 3% to 70 ± 4% with simultaneous 3-fold increase of nitrogen removal rate. Results of batch tests and continuous reactor operation showed that organotrophic nitrate reduction to nitrite, followed by anammox reaction contributed to this high removal efficiency. After sCOD/NH4-N ratio decreased from 1.8 ± 0.2 to 1.3 ± 0.1 removal efficiency decreased to 52 ± 4%, while still maintaining 150% higher removal rate, comparing to MBBR. Activity tests revealed that affinity of NOB to oxygen is higher than affinity of AOB with half-saturation constants of 0.05 and 0.41 mg/L, respectively.

Combination of upflow anaerobic sludge blanket (UASB) reactor and partial nitritation/anammox moving bed biofilm reactor (MBBR) for municipal wastewater treatment.

In this study the combination of an upflow anaerobic sludge blanket (UASB) reactor and a deammonification moving bed biofilm reactor (MBBR) for mainstream wastewater treatment was tested. The competition between aerobic ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) was studied during a 5months period of transition from reject water to mainstream wastewater followed by a 16months period of mainstream wastewater treatment. The decrease of influent ammonium concentration led to a wash-out of suspended biomass which had a major contribution to nitrite production. Influence of a dissolved oxygen concentration and a transient anoxia mechanism of NOB suppression were studied. It was shown that anoxic phase duration has no effect on NOB metabolism recovery and oxygen diffusion rather than affinities of AOB and NOB to oxygen determine the rate of nitrogen conversion in a biofilm system. Anammox activity remained on the level comparable to reject water treatment systems.

Ammonium removal by partial nitritation and Anammox processes from wastewater with increased salinity.

This work is dedicated to the biological treatment of wastewater with increased salinity using a combination of partial nitritation and Anammox processes. Two one-stage deammonification moving bed biofilm reactors were operated with the increase in NaCl concentration every two weeks by 5 and 2.5 g/L. The strategy with a step of 5 g/L of salinity increase led to complete inhibition of the process at the salinity level of 15 g/L. The strategy with a step of 2.5 g/L gave possibility to adapt bacteria to the elevated salinity. After reaching the salinity level of 10 g NaCl/L, the reactor was operated during 92 days with a nitrogen removal rate of 0.39±0.19 g N/(m2·day) (0.078±0.038 kg N/m3·day) and an average nitrogen removal efficiency of 59%. It was shown that conductivity cannot be used for monitoring the process when a reactor is treating wastewater with increased salinity, whereas pH can be correlated to effluent ammonium concentration regardless of wastewater salinity.

Combination of ion exchange and partial nitritation/Anammox process for ammonium removal from mainstream municipal wastewater.

In this study, a new technology of nitrogen removal from mainstream municipal wastewater is proposed. It is based on ammonium removal by ion exchange and regeneration of ion exchange material with 10-30 g/L NaCl solution with further nitrogen removal from spent regenerant by partial nitritation/Anammox process. Influence of regenerant strength on performance of ion exchange and biological parts of the proposed technology was evaluated. Moreover, the technology was tested in batch mode using pretreated municipal wastewater, strong acid cation (SAC) resin and partial nitritation/Anammox biomass. It was shown that with ion exchange it is possible to remove 99.9% of ammonium from wastewater while increasing the concentration of ammonium in spent regenerant by 18 times. Up to 95% of nitrogen from spent regenerant, produced by regeneration of SAC resin with 10 g/L NaCl solution, was removed biologically by partial nitritation/Anammox biomass. Moreover, the possibilities of integration of the technology into municipal wastewater treatment technology, and the challenges and advantages are discussed.

N2O emissions from a one stage partial nitrification/anammox process in moving bed biofilm reactors.

Nitrous oxide (N2O) emissions from wastewater treatment are getting increased attention because their global warming potential is around 300 times that of carbon dioxide. The aim of the study was to measure nitrous oxide emissions from one stage partial nitrification/anammox (Anaerobic Ammonium Oxidation) reactors, where nitrogen is removed in a biological way. The first part of the experimental study was focused on the measurements of nitrous oxide emissions from two pilot scale reactors in the long term; one reactor with intermittent aeration at 25 °C and the other reactor with continuous aeration at 22-23 °C. The second part of the experiment was done to evaluate the influence of different nitrogen loads and aeration strategies, described by the ratio between the non-aerated and aerated phase and the dissolved oxygen concentrations, on nitrous oxide emissions from the process. The study showed that 0.4-2% of the nitrogen load was converted into nitrous oxide from two reactors. With higher nitrogen load, the amount of nitrous oxide emission was also higher. A larger fraction of nitrous oxide was emitted to the gas phase while less was emitted with the liquid effluent. It was also found that nitrous oxide emissions were similar under intermittent and continuous aeration.

Nitrate reduction by organotrophic Anammox bacteria in a nitritation/anammox granular sludge and a moving bed biofilm reactor.

The effects of volatile fatty acids (VFAs) on nitrogen removal and microbial community structure in nitritation/anammox process were compared within a granular sludge reactor and a moving bed biofilm reactor. Nitrate productions in both systems were lower by 40-68% in comparison with expected nitrate production. Expected sludge production on VFAs was estimated to be 67-77% higher if heterotrophs were the main acetate degraders suggesting that Anammox bacteria used its organotrophic capability and successfully competed with general heterotrophs for organic carbon, which led to a reduced sludge production. FISH measurements showed a population consisting of mainly Anammox and AOB in both reactors and oxygen uptake rate (OUR) tests also confirmed that flocculent biomass consisted of a minor proportion of heterotrophs with a large proportion of AOBs. The dominant Anammox bacterium was Candidatus "Brocadia fulgida" with a minor fraction of Candidatus "Anammoxoglobus propionicus", both known to be capable of oxidizing VFAs.