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del Rio, A. V., Campos, J. L., Da Silva, C., Pedrouso, A., & Mosquera-Corral, A. (2019). Determination of the intrinsic kinetic parameters of ammonia-oxidizing and nitrite-oxidizing bacteria in granular and flocculent sludge. Sep. Purif. Technol., 213, 571–577.
Abstract: The different oxygen affinities of ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) are often used to define the operational strategy to achieve partial nitritation (PN) required before the anammox (AMX) process. For this purpose, apparent kinetic parameters are mainly used in the case of granular sludge, which can lead to errors when defining the operational conditions to obtain only nitritation (avoiding nitratation). In the present study, a mathematical methodology is proposed to determine the intrinsic kinetic parameters of AOB and NOB in granular sludge based on data obtained by respirometric assays. Additionally, the oxygen affinity constant (K-O2) and maximum specific rate (r(max)) of flocculent and granular sludge sample, produced under mainstream and sidestream conditions were determined at various temperatures (15, 20 and 30 degrees C). The results show that for granules, the intrinsic K-O2 and r(max) values were lower and higher, respectively, than the apparent values. Furthermore, the K-O2 values for flocs and granules at all of the tested temperatures were lower for NOB than for AOB. The values obtained for the kinetic parameters indicated that it is impossible to maintain partial nitritation by only controlling the dissolved oxygen concentration.
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del Rio, A. V., da Silva, T., Martins, T. H., Foresti, E., Campos, J. L., Mendez, R., et al. (2017). Partial Nitritation-Anammox Granules: Short-Term Inhibitory Effects of Seven Metals on Anammox Activity. Water Air Soil Pollut., 228(11), 9 pp.
Abstract: The inhibitory effect of seven different metals on the specific anammox activity of granular biomass, collected from a single stage partial nitritation/anammox reactor, was evaluated. The concentration of each metal that led to a 50% inhibition concentration (IC50) was 19.3 mg Cu+2/L, 26.9 mg Cr+2/L, 45.6 mg Pb+2/L, 59.1 mg Zn+2/L, 69.2 mg Ni+2/L, 174.6 mg Cd+2/L, and 175.8 mg Mn+2/L. In experiments performed with granules mechanically disintegrated (flocculent-like sludge), the IC50 for Cd+2 corresponded to a concentration of 93.1 mg Cd+2/L. These results indicate that the granular structure might act as a physical barrier to protect anammox bacteria from toxics. Furthermore, the presence of an external layer of ammonia oxidizing bacteria seems to mitigate the inhibitory effect of the metals, as the values of IC50 obtained in this study for anammox activity were higher than those previously reported for anammox granules. Additionally, the results obtained confirmed that copper is one of the most inhibitory metals for anammox activity and revealed that chromium, scarcely studied yet, has a similar potential inhibitory effect.
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Jungles, M. K., Val del Rio, A., Mosquera-Corral, A., Campos, J. L., Mendez, R., & Costa, R. H. R. (2017). Effects of Inoculum Type and Aeration Flowrate on the Performance of Aerobic Granular SBRs. Processes, 5(3), 10 pp.
Abstract: Aerobic granular sequencing batch reactors (SBRs) are usually inoculated with activated sludge which implies sometimes long start-up periods and high solids concentrations in the effluent due to the initial wash-out of the inoculum. In this work, the use of aerobic mature granules as inoculum in order to improve the start-up period was tested, but no clear differences were observed compared to a reactor inoculated with activated sludge. The effect of the aeration rate on both physical properties of granules and reactor performance was also studied in a stable aerobic granular SBR. The increase of the aeration flow rate caused the decrease of the average diameter of the granules. This fact enhanced the COD and ammonia consumption rates due to the increase of the DO level and the aerobic fraction of the biomass. However, it provoked a loss of the nitrogen removal efficiency due to the worsening of the denitrification capacity as a consequence of a higher aerobic fraction.
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Morales, N., del Rio, A. V., Vazquez-Padin, J. R., Mendez, R., Campos, J. L., & Mosquera-Corral, A. (2016). The granular biomass properties and the acclimation period affect the partial nitritation/anammox process stability at a low temperature and ammonium concentration. Process Biochem., 51(12), 2134–2142.
Abstract: Extensive research on the anammox-based processes under mainstream conditions is currently in progress. Most studies have used a long acclimation period for the partial nitritation-anammox (PN-An) sludge at a low temperature and ammonium concentration. However, in this study, the results demonstrated that PN-An granular biomass produced under sidestream conditions (30 degrees C and 1000 mg NH4+-N/L) can operate at 15 degrees C and 50 mg NH4+-N/L without acclimation. The nitrogen removal efficiency was 70% and was stable for 60 days. The long-termoperation of the system with progressive adaptation provided important information for process optimization. Control of the dissolved oxygen (DO) concentration was crucial to maintain the balance between ammonia oxidizing bacteria (AOB) and anammox bacteria activities. A calculation of the oxygen penetration depth inside the granules is proposed to estimate an adequate DO level, which allows for the definition of the aerobic and anoxic zones that depend on the temperature, the size distribution and the granule density. However, the development of NOB was difficult to avoid with DO control alone. The selective washing-out of the floccular biomass, which contains mainly NOB, is proposed, leaving the granular fraction with the AOB and anammox bacteria in the system. (C) 2016 Published by Elsevier Ltd.
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Pedrouso, A., del Rio, A. V., Campos, J. L., Mendez, R., & Mosquera-Corral, A. (2017). Biomass aggregation influences NaN3 short-term effects on anammox bacteria activity. Water Sci. Technol., 75(5), 1007–1013.
Abstract: The main bottleneck to maintain the long-term stability of the partial nitritation-anammox processes, especially those operated at low temperatures and nitrogen concentrations, is the undesirable development of nitrite oxidizing bacteria (NOB). When this occurs, the punctual addition of compounds with the capacity to specifically inhibit NOB without affecting the process efficiency might be of interest. Sodium azide (NaN3) is an already known NOB inhibitor which at low concentrations does not significantly affect the ammonia oxidizing bacteria (AOB) activity. However, studies about its influence on anammox bacteria are unavailable. For this reason, the objective of the present study was to evaluate the effect of NaN3 on the anammox activity. Three different types of anammox biomass were used: granular biomass comprising AOB and anammox bacteria (G1), anammox enriched granules (G2) and previous anammox granules disaggregated (F1). No inhibitory effect of NaN3 was measured on G1 sludge. However, the anammox activity decreased in the case of G2 and F1. Granular biomass activity was less affected (IC50 90 mg/L, G2) than flocculent one (IC50 5 mg/L, F1). Summing up, not only does the granular structure protect the anammox bacteria from the NaN3 inhibitory effect, but also the AOB act as a barrier decreasing the inhibition.
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