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Carrera, P., Campo, R., Mendez, R., Di Bella, G., Campos, J. L., Mosquera-Corral, A., et al. (2019). Does the feeding strategy enhance the aerobic granular sludge stability treating saline effluents? Chemosphere, 226, 865–873.
Abstract: The development and stability of aerobic granular sludge (AGS) was studied in two Sequencing Batch Reactors (SBRs) treating fish canning wastewater. R1 cycle comprised a fully aerobic reaction phase, while R2 cycle included a plug-flow anaerobic feeding/reaction followed by an aerobic reaction phase. The performance of the AGS reactors was compared treating the same effluents with variable salt concentrations (4.97-13.45 g NaCl/L) and organic loading rates (OLR, 1.80-6.65 kg CODs/(m(3).d)). Granulation process was faster in R2 (day 34) than in R1 (day 90), however the granular biomass formed in the fully aerobic configuration was more stable to the variable feeding composition. Thus, in R1 solid retention times (SRT), up to 15.2 days, longer than in R2, up to 5.8 days, were achieved. These long SRT5 values helped the retention of nitrifying organisms and provoked the increase of the nitrogen removal efficiency to 80% in R1 while it was approximately of 40% in R2. However, the presence of an anaerobic feeding/reaction phase increased the organic matter removal efficiency in R2 (80-90%) which was higher than in R1 with a fully aerobic phase (75-85%). Furthermore, in R2 glycogen-accumulating organisms (GAOs) dominated inside the granules instead of phosphorous-accumulating organisms (PADS), suggesting that GAOs resist better the stressful conditions of a variable and high-saline influent. In terms of AGS properties an anaerobic feeding/reaction phase is not beneficial, however it enables the production of a better quality effluent. (C) 2019 Elsevier Ltd. All rights reserved.
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Carrera, P., Mosquera-Corral, A., Mendez, R., Campos, J. L., & del Rio, A. V. (2019). Pulsed aeration enhances aerobic granular biomass properties. Biochem. Eng. J., 149, 7 pp.
Abstract: The reduced footprint of Aerobic Granular Sludge (AGS) systems constitutes a good alternative to conventional treatments, despite their associated drawbacks (long start-up periods and high aeration requirements for granules formation and integrity). This study presents a pulsed aeration regime as a strategy to overcome these problems. Two AGS sequencing batch reactors (SBRs) were operated treating low-strength wastewater (190 mg COD/L) with pulses of 1 s ON/2 s OFF (R1) and continuous aeration (R2). Initially, different superficial gas velocities (SGV) of 3.6 cm/s (R1) and 1.2 cm/s (R2) were imposed for the same airflow (448 L/cycle). The granulation process was completed in 38 days for R1 whereas it took 48 days for R2. Denser and smaller granules were formed with pulsed regime and phosphate accumulating organisms were developed faster. The removal efficiencies were practically the same in both SBRs, being of 85% for COD, 95% for phosphorus and 30% for nitrogen. After granules formation the airflow in both reactors was reduced. For a SGV of 1.2 cm/s both systems behaved similarly. The minimum SGV required to maintain a uniform mixture of the biomass inside the reactor was 1.2 (R1) and 0.5 cm/s (R2), meaning less air consumption in the pulsed system (149 L/cycle) compared to the continuous one (179 L/min). Therefore, pulsed aeration successfully reduced granulation periods and aeration requirements in AGS systems.
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Franchi, O., Alvarez, M. I., Pavissich, J. P., Belmonte, M., Pedrouso, A., del Rio, A. V., et al. (2024). Operational variables and microbial community dynamics affect granulation stability in continuous flow aerobic granular sludge reactors. J. Water Process Eng., 59, 104951.
Abstract: Retrofitting wastewater treatment plants with continuous aerobic granular sludge reactors is a promising alternative to enhance treatment capacities and reduce footprint. This study investigates the main variables influencing granulation and microbial dynamics in two reactor configurations (25 L): stirred tanks in series (R1) and a plug-flow-like system (R2). Granule formation was achieved by increasing the organic loading rate (OLR) from 0.7 to 4.1 kg COD/(m3 & sdot;d) and the up-flow velocity in the biomass selector from 1.4 to 6.9 m/h. However, irreversible granule destabilization occurred at day 68 for R1 and day 108 for R2. Principal component analysis and examination of food-to-microorganisms (F/M) ratio medians identified the F/M ratio as the primary variable associated with instability. Microbial analysis revealed that a high F/M ratio induced significant increases in the abundance of specific genera such as Arcobacter, Cloacibacterium, Rikenella, Aquaspirillum and Sphaerotillus, whose overgrowth may negatively impact granule stability. Based on these findings, maximum F/M ratio thresholds were obtained to establish operational conditions allowing the maintenance of stable aerobic granules on continuous flow reactor configurations.
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Sepulveda-Mardones, M., Campos, J. L., Magri, A., & Vidal, G. (2019). Moving forward in the use of aerobic granular sludge for municipal wastewater treatment: an overview. Rev. Environ. Sci. Bio-Technol., 18(4), 741–769.
Abstract: Activated sludge is one of the most widely implemented technologies for municipal wastewater treatment. Yet, more restrictive environmental standards demand for more efficient technologies. Aerobic granular sludge (AGS) is a promising alternative in this context since this technology has shown potential for simultaneous organic matter and nutrient removal using smaller bioreactors and consuming less energy. However, despite such engaging claims, only ca. 40 full-scale AGS systems have been installed worldwide after 30 years of development. This reduced implementation suggests the existence of significant bottlenecks for this technology, which currently only have partially been overcome. This overview aims to analyze the recent progress in R&D concerning aerobic sludge granulation for municipal wastewater treatment via the analysis of research articles and invention patents as well as to elucidate exiting technological gaps and development opportunities. Culturing methods aiming at fast granulation, long-term stability and excellent process performance are of utmost interest for promoting massive implementation of full-scale AGS systems. Moreover, the recovery of biomaterials from waste sludge could contribute to the implementation of the biorefinery paradigm in wastewater treatment plants.
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