Han, Z. Y., Chen, H., He, C. L., Dodbiba, G., Otsuki, A., Wei, Y. Z., et al. (2023). Nanobubble size distribution measurement by interactive force apparatus under an electric field. Sci. Rep., 13(1), 3663.
Abstract: Nanobubbles have been applied in many fields, such as environmental cleaning, material production, agriculture, and medicine. However, the measured nanobubble sizes differed among the measurement methods, such as dynamic light scattering, particle trajectory, and resonance mass methods. Additionally, the measurement methods were limited with respect to the bubble concentration, refractive index of liquid, and liquid color. Here, a novel interactive force measurement method for bulk nanobubble size measurement was developed by measuring the force between two electrodes filled with bulk nanobubble-containing liquid under an electric field when the electrode distance was changed in the nm scale with piezoelectric equipment. The nanobubble size was measured with a bubble gas diameter and also an effective water thin film layer covered with a gas bubble that was estimated to be approximately 10 nm based on the difference between the median diameter of the particle trajectory method and this method. This method could also be applied to the solid particle size distribution measurement in a solution.
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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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Pedrouso, A., Morales, N., Rodelas, B., Correa-Galeote, D., del Rio, A. V., Campos, J. L., et al. (2023). Rapid start-up and stable maintenance of the mainstream nitritation process based on the accumulation of free nitrous acid in a pilot-scale two-stage nitritation-anammox system. Sep. Purif. Technol., 317, 123851.
Abstract: Two-stage partial nitritation (PN) and anammox (AMX) systems showed promising results for applying auto-trophic nitrogen removal under mainstream conditions. In this study, a pilot-scale (600 L per reactor) two-stage PN/AMX system was installed in a municipal wastewater treatment plant (WWTP) provided with a high-rate activated sludge (HRAS) system for organic carbon removal. The PN/AMX system was operated without tem-perature control (ranging from 11 to 28 degrees C) and was subjected to the same variations in wastewater charac-teristics as the WWTP (22 to 63 mg NH4+- N/L). The developed strategy is simple, does not require the addition of chemicals and is characterised by short start-up periods. The PN process was established by applying a high hydraulic load and maintained by in situ accumulated free nitrous acid (FNA) of 0.015-0.2 mg HNO2-N/L. Based on pH value, a controlled aeration strategy was applied to achieve the target nitrite to ammonium ratio in the effluent (1.1 g NO2--N/g NH4+-N) to feed the AMX reactor. Although NOB were not fully washed out from the system, nitrite accumulation remained (>99 %) stable with no evidence of NOB activity. In the AMX reactor, an overall nitrogen removal efficiency of 80 % was achieved. Regarding effluent quality, 12 +/- 3 mg TN/L was obtained, but 5 mg NO3--N/L was already in the HRAS effluent. The relative abundance of NOB showed a strong negative correlation with the FNA concentration, providing a good strategy for establishing PN under main-stream conditions.
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Pichel, A., Moreno, R., Figueroa, M., Campos, J. L., Mendez, R., Mosquera-Corral, A., et al. (2019). How to cope with NOB activity and pig manure inhibition in a partial nitritation-anammox process? Sep. Purif. Technol., 212, 396–404.
Abstract: The treatment of pig manure can be performed by anaerobic digestion to diminish the organic matter content and produce biogas, and the resulting digestate has to be subsequently treated for the removal of nitrogenous compounds. The partial nitritation-anammox (PN-AMX) process constitutes an interesting alternative. In the present study, three different short experiments were initially performed to study the influence of nitrite oxidizing bacteria (NOB) present in the inoculum and the pig manure composition over the start-up of the PN-AMX process. The presence of NOB in the inoculum showed to be more crucial than the available anammox activity for a good performance of the PN-AMX process. Batch activity experiments showed a reduction of at least 44.4% in the maximum specific anammox activity due to the pig manure, probably owed to its conductivity (between 6 and 8 mS/cm). In the subsequent long-term operation of the PN-AMX process with non-diluted pre-treated pig manure, the NOB were successfully limited for DO concentrations of 0.1 mg O-2/L, and a nitrogen removal rate (NRR) of 0.1 g N/(L.d) was achieved despite the presence of significant NOB activity in the start-up. A strict control of the DO concentration, with an optimal range of 0.07-0.10 mg O-2/L, was fundamental to balance the removal of nitrogen by PN-AMX and prevent NOB activity. The presence of organic matter, with a ratio sCOD/N in the influent between 0.18 and 1.14 g/g, did not hinder the PN-AMX process, and the contribution of heterotrophic denitrification to the removal of nitrogen was less than 10%.
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Valenzuela-Heredia, D., Panatt, C.:, Belmonte, M., Franchi, O., Crutchik, D., Dumais, J., Vazquez-Padin, J. R., et al. (2022). Performance of a two-stage partial nitritation-anammox system treating the supernatant of a sludge anaerobic digester pretreated by a thermal hydrolysis process. Chem. Eng. J., 429, 131301.
Abstract: A two-stage system (partial nitritation (PN) and anammox processes) was used to remove nitrogen from the dewatering liquor originating from the thermal hydrolysis/anaerobic digestion (THP/AD) of municipal WWTP sludge. Two strategies were tested to start up the PN reactor: 1) maintaining a fixed hydraulic retention time (HRT) and increasing the ammonium loading rate (ALR) by decreasing the feeding dilution ratio and 2) feeding undiluted dewatering liquor and gradually decreasing the HRT. With diluted feeding, the reactor performance had destabilization episodes that were statistically correlated with the application of high specific ammonium (> 0.6 g NH4+-N/(g TSS.d)) and organic (> 0.7 g COD/(g TSS.d)) loading rates. The second strategy allowed stable PN reactor operation while treating ALR up to 4.8 g NH4+-N/(L.d) and demonstrating that dilution of THP/AD effluents is not required. The operating conditions promoted the presence of free nitrous acid levels (> 0.14 mg HNO2-N/L) inside the PN reactor that inhibited the proliferation of nitrite oxidizing bacteria.
Batch activity tests showed that the inhibitory effects of organic compounds present in the THP/AD dewatering liquor on the ammonia oxidizing bacteria activity can be removed in the PN reactor. Thus, aerobic pretreatment would not be necessary when two-stage systems are used. The PN reactor effluent was successfully treated by an anammox reactor.
An economic analysis showed that using two-stage systems is advantageous for treating THP/AD dewatering liquor. The implementation of an aerobic pre-treatment unit is recommended for WWTPs capacities higher than 5.10(5) inhabitants equivalent when one-stage systems are used.
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