Recently, aerobic granular sludge technology has been scaled-up and implemented for industrial and municipal wastewater treatment under the trade name Nereda®. With full-scale references for ...industrial treatment application since 2006 and domestic sewage since 2009 only limited operating data have been presented in scientific literature so far. In this study performance, granulation and design considerations of an aerobic granular sludge plant on domestic wastewater at the WWTP Garmerwolde, the Netherlands were analysed. After a start-up period of approximately 5 months, a robust and stable granule bed (>8 g L−1) was formed and could be maintained thereafter, with a sludge volume index after 5 min settling of 45 mL g−1. The granular sludge consisted for more than 80% of granules larger than 0.2 mm and more than 60% larger than 1 mm. Effluent requirements (7 mg N L−1 and 1 mg P L−1) were easily met during summer and winter. Maximum volumetric conversion rates for nitrogen and phosphorus were respectively 0.17 and 0.24 kg (m3 d)−1. The energy usage was 13.9 kWh (PE150·year)−1 which is 58–63 % lower than the average conventional activated sludge treatment plant in the Netherlands. Finally, this study demonstrated that aerobic granular sludge technology can effectively be implemented for the treatment of domestic wastewater.
•A robust and stable granule bed of more than 8 g L−1 was formed and maintained with an SVI5 of 45 mL g−1.•The energy usage was 13.9 kWh (PE150, removed year)−1.•The volume needed for the AGS plant was 33% lower than the existing CAS plant.•Maximum volumetric conversion rates for N and P were 0.17 and 0.24 kg (m3 d)−1 respectively.
Anammox related technologies are currently widely applied for nitrogen removal from sewage sludge digester rejection water. Nevertheless, many aspects of the anammox process like the kinetic ...characteristics and the reaction stoichiometry are still subject of debate. Parameter values reported in literature are often hampered by mass transfer limitation or by the presence of a significant side population. In this study a membrane bioreactor (MBR) based method for growing a highly enriched anammox microbial community is described. The almost pure free-cells suspension of highly active anammox bacteria was used for detailed kinetic and stoichiometric analysis of the anammox process. The anammox culture enriched during this study had a biomass specific maximum growth rate of 0.21 d(-)(1) which is higher than ever reported before in literature. Using an experimental methodology based on imposing dynamic process conditions combined with process modeling and parameter estimation, the intrinsic nitrite half saturation constant was identified to be as low as 35 μg-N L(-)(1). This was confirmed to be an accurate estimation in the pH range of 6.8-7.5.
The negative effect of nitrite on anammox activity has been reported widely during the past decade. Although the adverse effect is clear, conflicting reports exist on the level at which it occurs and ...its reversible/irreversible nature. An in depth study on nitrite inhibition therefore was performed in which the influence of environmental factors was evaluated. Anammox activity was measured in anammox granules by continuously monitored standardized manometric batch tests extending the interpretation by evaluation of lag times, maximum conversion rates during the tests and substrates/product conversion ratios. The granules where obtained from a one-stage anammox reactor, the dominant anammox organisms belonged to the Brocadia type. The observed 50% activity inhibition for nitrite (IC50) was 0.4 g N L−1. The activity recovered fully after removal of the nitrite. Conversion in fresh medium after exposure to up to 6 g NO2−–N L−1 for 24 h showed less then 60% loss of activity. Presence of ammonium during nitrite (2 g N L−1) exposure resulted in a stronger loss of activity after nitrite exposure (50% and 30% in presence and absence of ammonium respectively). Presence of oxygen during nitrite incubation led to a maximum activity reduction of 32%. The recovery after exposure indicates that the adverse effect of nitrite is reversible and thus inhibitory rather than toxic in nature. Similarities between exposure at three different pH-values indicate that nitrite rather than nitrous acid is the actual inhibiting compound.
Autotrophic nitrogen removal in the mainstream wastewater treatment process is suggested to be a prerequisite of energy autarkic wastewater treatment plants (WWTP). Whilst the application of ...anammox-related technologies in the side-stream is at present state of the art, the feasibility of this energy-efficient process at mainstream conditions is still under development. Lower operating temperature and ammonium concentration, together with required high nitrogen removal efficiency, represent the main challenges to face in order to reach this appealing new frontier of the wastewater treatment field. In this study, we report the evaluation of the process in a plug-flow granular sludge-based pilot-scale reactor (4 m ³) continuously fed with the actual effluent of the A-stage of the WWTP of Dokhaven, Rotterdam. The one-stage partial nitritation–anammox system was operated for more than 10 months at 19 ± 1°C. Observed average N-removal and ammonium conversion rates were comparable or higher than those of conventional N-removal systems, with 182 ± 46 and 315 ± 33 mg-N L ⁻¹ d ⁻¹, respectively. Biochemical oxygen demand was also oxidized in the system with an average removal efficiency of 90%. Heterotrophic biomass grew preferentially in flocs and was efficiently washed out of the system. Throughout the experimentation, the main bottleneck was the nitritation process that resulted in nitrite-limiting conditions for the anammox conversion. Anammox bacteria were able to grow under mainstream WWTP conditions and new granules were formed and efficiently retained in the system.
Autotrophic nitrogen removal in the main stream appears as a prerequisite for the implementation of energy autarchic wastewater treatment plants. To investigate autotrophic nitrogen removal a ...lab-scale gas-lift sequencing batch reactor with granular sludge was operated for more than 500 days. The reactor was operated at temperatures between 20 and 10 °C on autotrophic medium with ammonium (60 and 160 mg-N L−1) as only nitrogen compound at an HRT of 0.23–0.3 d. The dissolved oxygen (DO) concentration was shown to be an effective control parameter for the suppression of the undesired nitratation process. DO control guaranteed the effective suppression of the nitratation both at 20 and 15 °C, allowing nitrogen removal rates of 0.4 g-NTot L−1 d−1 at nitrogen removal efficiencies of 85-75%. Prolonged operation at 10 °C caused a slow but unrestrainable decrease in anammox activity and process efficiency. This study represents a proof of concept for the application of the autotrophic nitrogen removal in a single reactor with granular sludge at main stream conditions.
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•Proof of concept: autotrophic N-removal with granules at main stream conditions.•Effective suppression of nitratation at DO up to 2.5 mg-O2 L−1 with NOB presence.•Nitrogen removal rates of 0.4 g-NTot L−1 d−1 with high removal efficiencies.•Decreased anammox activity and process efficiency after prolonged operation at 10 °C.
In the present study, the factors influencing density of granular sludge particles were evaluated. Granules consist of microbes, precipitates and of extracellular polymeric substance. The volume ...fractions of the bacterial layers were experimentally estimated by fluorescent in situ hybridisation staining. The volume fraction occupied by precipitates was determined by computed tomography scanning. PHREEQC was used to estimate potential formation of precipitates to determine a density of the inorganic fraction. Densities of bacteria were investigated by Percoll density centrifugation. The volume fractions were then coupled with the corresponding densities and the total density of a granule was calculated. The sensitivity of the density of the entire granule on the corresponding settling velocity was evaluated by changing the volume fractions of precipitates or bacteria in a settling model. Results from granules originating from a Nereda reactor for simultaneous phosphate COD and nitrogen removal revealed that phosphate-accumulating organisms (PAOs) had a higher density than glycogen-accumulating organisms leading to significantly higher settling velocities for PAO-dominated granules explaining earlier observations of the segregation of the granular sludge bed inside reactors. The model showed that a small increase in the volume fraction of precipitates (1–5 %) strongly increased the granular density and thereby the settling velocity. For nitritation–anammox granular sludge, mainly granular diameter and not density differences are causing a segregation of the biomass in the bed.
Anaerobic ammonium oxidizing (anammox) bacteria based technologies are widely applied for nitrogen removal from warm (25–40 °C) wastewater with high ammonium concentrations (∼1 gNH4–N L−1). Extension ...of the operational window of this energy and resource efficient process is restricted by the “supposed” low growth rate of the responsible microorganisms. Here we demonstrate that the maximum specific growth rate (μmax) of anammox bacteria can be increased to a μmax value of 0.33 d−1 by applying a novel selection strategy based on the maximization of the electron transfer capacity in a membrane bioreactor. This value is four times higher than the highest previously reported value. The microbial community was strongly dominated by anammox bacteria closely related (99%) to Candidatus Brocadia sp.40 throughout the experiment. The results described here demonstrate the remarkable capacity of a phylogenetically stable anammox community to adjust its growth rate in response to a change in the cultivation conditions imposed.
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•Novel selection strategy based on maximization of the electron transfer capacity.•Three times increase in specific ammonium uptake rate during cultivation.•Highest (four times higher) directly estimated growth rate of 0.334 d−1 (at 30 °C).•No shift in dominant anammox strain nor major mutations in the dominant strain.•Demonstration that maximum growth rate is not an intrinsic process property.
Salinity can adversely affect the performance of most biological processes involved in wastewater treatment. The effect of salt on the main conversion processes in an aerobic granular sludge (AGS) ...process accomplishing simultaneous organic matter, nitrogen, and phosphate removal was evaluated in this work. Hereto, an AGS sequencing batch reactor was subjected to different salt concentrations (0.2 to 20 g Cl⁻ l⁻¹). Granular structure was stable throughout the whole experimental period, although granule size decreased and a significant effluent turbidity was observed at the highest salinity tested. A weaker gel structure at higher salt concentrations was hypothesised to be the cause of such turbidity. Ammonium oxidation was not affected at any of the salt concentrations applied. However, nitrite oxidation was severely affected, especially at 20 g Cl⁻ l⁻¹, in which a complete inhibition was observed. Consequently, high nitrite accumulation occurred. Phosphate removal was also found to be inhibited at the highest salt concentration tested. Complementary experiments have shown that a cascade inhibition effect took place: first, the deterioration of nitrite oxidation resulted in high nitrite concentrations and this in turn resulted in a detrimental effect to polyphosphate-accumulating organisms. By preventing the occurrence of the nitrification process and therefore avoiding the nitrite accumulation, the effect of salt concentrations on the bio-P removal process was shown to be negligible up to 13 g Cl⁻ l⁻¹. Salt concentrations equal to 20 g Cl⁻ l⁻¹ or higher in absence of nitrite also significantly reduced phosphate removal efficiency in the system.
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