Effect of settling time and organic loading rates on aerobic granulation processes treating high strength wastewater.

Despite its numerous advantages, the aerobic granular sludge (AGS) process faces several challenges that hinder its widespread implementation. One such challenge is the requirement for high organic load ratios (OLR), which significantly impacts AGS formation and stability, posing a barrier to commercialization. In response to these challenges, this study investigates the granulation and treatment efficacy of the AGS process for treating high-concentration wastewater under various OLR and settling time. Three sequential batch reactors (R1, R2, R3) were operated at OLRs of 0.167, 0.33, and 1 kg COD/m3·day. The study focuses on analyzing key parameters including sludge characteristics, extracellular polymeric substances (EPS) content, PN/PS ratio, and microbial clusters. Results demonstrate that reducing settling time from 90 to 30 min enhances sludge settleability, resulting in a maximum 50.8 % decrease in SVI30 (from 98.1 to 122.8 mL/g to 51.9-81.3 mL/g), thereby facilitating the selection of beneficial microorganisms during granulation. Particularly, at R2, the PN/PS ratio was 4.3, and EPS content increased by 1.52-fold, leading to a 1.41-fold increase in sludge attachment. This observation suggests a progressive maturation of AGS. Additionally, analysis of microbial diversity and cluster composition highlights the influence of OLR variations on the ratios of Proteobacteria and Bacteroidetes. These findings emphasize the significant impact of SBR operational strategies on AGS process performance and biological stability, offering valuable insights for the efficient operation of future high-concentration wastewater treatment processes.

Construction and application of a mCherry fluorescent labeling system for Stenotrophomonas AGS-1 from aerobic granular sludge.

To elucidate the specific mechanism by which high-attachment bacteria promote aerobic granular sludge (AGS) formation, a red fluorescent protein mCherry-based biomarker system was developed in the high-attachment strain Stenotrophomonas AGS-1 from AGS. The fluorescent labeling system used plasmid-mediated mCherry expression driven by a Ptac constitutive promoter. mCherry-labeled AGS-1 had normal unimpaired growth, strong fluorescent signals, and good fluorescence imaging. Also, the mCherry labeling system had no effect on the attachment ability of AGS-1. In addition, mCherry-labeled AGS-1 maintained high plasmid stability, even after more than 100 generations. Notably, after the addition of mCherry-labeled AGS-1 into the activated sludge system, the mCherry fluorescence of the sludge system can be used as a good reflection of the relative amount of AGS-1. Moreover, the spatial distribution of mCherry-labeled AGS-1 in the sludge system could be visualized and remained clear even after 5 days by fluorescence imaging. These results revealed that the mCherry-based biomarker system would provide a valuable tool for labeling AGS-1 to monitor the spatial distribution and fate of AGS-1 in AGS, which would help to better understand the mechanism of AGS formation and facilitate the development of AGS technology.

Bioaugmentation of intertidal sludge enhancing the development of salt-tolerant aerobic granular sludge.

Three parallel bioreactors were operated with different inoculation of activated sludge (R1), intertidal sludge (ItS) (R2), and ItS-added AS (R3), respectively, to explore the effects of ItS bioaugmentation on the formation of salt-tolerant aerobic granular sludge (SAGS) and the enhancement of COD removal performance. The results showed that compared to the control (R1-2), R3 promoted a more rapid development of SAGS with a cultivation time of 25 d. Following 110-day cultivation, R3 exhibited a higher granular diameter of 1.3 mm and a higher hydrophobic aromatic protein content than that in control. Compared to the control, the salt-tolerant performance in R3 was also enhanced with the COD removal efficiency of 96.4% due to the higher sludge specific activity of 14.4 g·gVSS-1·d-1 and the salinity inhibition constant of 49.3 gL-1. Read- and genome-resolved metagenomics together indicated that a higher level of tryptophan/tyrosine synthase gene (trpBD, tyrBC) and enrichment of the key gene hosts Rhodobacteraceae, Marinicella in R3, which was about 5.4-fold and 1.4-fold of that in control, could be the driving factors of rapid development of SAGS. Furthermore, the augmented salt-tolerant potential in R3 could result from that R1 was dominated by Rhodospirillaceae, Bacteroidales, which carried more trehalose synthase gene (otsB, treS), while the dominant members Rhodobacteraceae, Marinicella in R3 were main contributors to the glycine betaine synthase gene (ectC, betB, gbsA). This study could provide deeper insights into the rapid development and improved salt-tolerant potential of SAGS via bioaugmentation of intertidal sludge, which could promote the application of hypersaline wastewater treatment.

Comparison and Optimization of Continuous Flow Reactors for Aerobic Granule Sludge Cultivation from the Perspective of Hydrodynamic Behavior.

Improving treatment efficiency and reducing investment and operating costs make aerobic granular sludge technology (AGS) a promising technology for treating aquaculture wastewater. The development of continuous flow reactors (CFRs) has become a new direction in the research of AGS. This study clarifies the granulation effect, hydrodynamic behavior and particle separation of three different CFRs (R1 to R3). The established CFD model was able to explain the hydrodynamic behavior in all three CFRs; in particular, R3 performed the best from the perspective of hydrodynamic behavior due to its abundant turbulence. In addition, the optimal baffle distance and baffle angle of R3 were simulated to be 40 mm and 60°, respectively, due to them providing the best turbulent flow and particle separation effect. However, an overlarge baffle angle could weaken the turbulent pattern in the reactor. The retention time distribution further confirmed the reasonability of these optimal parameters with the highest effective volume ratio of 0.82. In short, this study gives an instruction for exploring the rapid formation mechanism of AGS in a CFR to promote its engineering application.

Distribution characteristics of phosphorus-containing substances in a long running aerobic granular sludge-membrane bioreactor with no sludge discharge.

This work aimed at revealing the distribution characteristics of phosphorus (P) containing substances in an aerobic granular sludge-membrane bioreactor (AGS-MBR). During the long running period (180 days) with no sludge discharge, AGS was successfully cultivated on day 20, and the system performed well in removing organic pollutants and total nitrogen (TN). However, the removal of total P (TP) showed a fluctuant tendency, and P was found to distribute in all the phases of the system. In the intracellular phase, it occupied the largest ratio all through the period. In AGS, inorganic P (IP) was measured to be about 74.4-77.8% of TP, with non-apatite IP (NAIP) composing 57.5-69.6%, while in organic P (OP), the ratio of monoester and diester phosphate was in the range of 19-26.9% and 12-13.5%, respectively. The presence of highly releasable and bioavailable P (NAIP + OP) in AGS implied that it might be a potential P resource for utilization.

Alternating nitrogen feeding strategy induced aerobic granulation: Influencing conditions and mechanism.

Effective cultivation of stable aerobic granular sludge (AGS) is a crucial step in the successful application of this technology, and the formation of AGS could be facilitated by some environmental stress conditions. Four identical sequencing batch reactors (SBRs) were established to investigate the aerobic granulation process under the same alternating ammonia nitrogen feeding strategy superimposed with different environmental conditions (inorganic carbon source, temperature, N/COD). Although various superimposed conditions induced a significant difference in the size, settling velocity, mechanic strength of AGS, mature aerobic granules could be successfully obtained in all four reactors after 70 days' operation, indicating the alternating ammonia nitrogen feeding strategy was the most critical factor for AGS formation. Based on the results of redundancy analysis, the presence of an inorganic carbon source could facilitate the cultivation of AGS with nitrification function, while the moderate temperature and fluctuant N/COD might benefit the cultivation of more stable AGS. In addition, superimposed stress conditions could result in the difference in the microbial population between four reactors, but the population diversity and abundance of microorganisms were not the determinants of AGS formation. This study provided an effective method for the cultivation of AGS by using alternating ammonia nitrogen feeding strategy.

Phase equilibria, physical and rheological properties of extracellular polymeric substances in the aqueous urea solutions at different temperatures and concentrations.

Extracellular polymeric substances (EPS) were extracted from aerobic granule sludge (AGS) using 8 M aqueous urea solution. It seems that the knowledge of these multi-component systems properties and the ability to predict their phase behavior is necessary for the extraction units design as well as process optimization. In this regard, water activity using the Dynamic Vapor Sorption (DVS) method, viscosity and shear stress, pH, and conductivity were measured at 283.15-343.15 K and 0.0108 to 0.0375 wt fraction of EPS. The salting effects in ternary systems assessed and the results were interpreted in terms of solute-water and solute-solute interactions. It was found these systems were not semi-ideal and except at 283.15 K, had a positive deviation from ideal solution behavior and only at this temperature as the optimum extraction temperature, the salting-in effect was observed for each concentration of EPS. The ternary solutions behave like pseudo-plastic fluids while aqueous urea solution is a Newtonian fluid. Increasing the temperature causes a decrease and increase in pH and conductivity of ternary solutions, respectively and the presence of EPS increases those of 8 M urea solution significantly.

Factors affecting aerobic granule sludge formation in leachate treatment - a systematic review.

The biological treatment of landfill leachate due to high concentration of Chemical Oxygen Demand (COD), ammonia, and other toxic compounds is so difficult. One of the leachate treatment technology is the sludge biogranulation, that containing the two aerobic and anaerobic process. The aim of this study was conducted for determining the main factors affecting aerobic granule sludge formation in leachate treatment. In this study, all related papers in international databases were evaluated including Google Scholar, Science Direct, and PubMed, Also Open Access Journal Directory from 1990 until 2020 were investigated. The keywords used included Aerobic Granule Sludge (AGS), leachate treatment, Wastewater treatment, Granular Sequential Batch Reactors (GSBR), Formation Extracellular polymeric substance (EPS). Overall, 2,658 articles were retrieved of which 71 were selected after revising the titles and abstracts. Aerobic granulation has been only lately studied and a limited number of studies have been devoted to identification aspects of the process such as the organic source, and other factor affecting on formation granules. Some factors as shear stress, settling time, and the effluent discharge site have direct effect on the efficiency of aerobic granules reactor and other factors such as divalent metal ions, dissolved oxygen concentration, the ratio of height to diameter of the reactor, temperature affecting on the granulation process. If suitable conditions provide, the aerobic granule sludge process can be useful for leachate treatment.

Enhancing robustness of aerobic granule sludge under low C/N ratios with addition of kitchen wastewater.

Aerobic granular sludge (AGS) is one of the most promising biotechnologies for wastewater treatment. However, the instability of AGS at low carbon to nitrogen (C/N) ratios limited its application. In this study, kitchen wastewater addition in the influent was found to improve the morphology, characteristics, and treatment performance of AGS at low C/N ratios of 10, 5 and 2, which strongly reduced the negative impact of low C/N ratios on the biomass concentration, settleability, EPS secretion, stability and performance of AGS. At C/N ratio of 2, sludge disintegration was observed in RA with synthetic wastewater as influent, while the sludge in RB was able to keep a compact microbial structure with particle size of 1.0-1.5 mm. When C/N ratio decreased from 20 to 2 (phase 1 to 4), the MLSS, SVI and EPS secretion in RB were negatively affected at the beginning of each phase, but recovered to 4800 mg L-1, 60 mL g-1, and 86 mg/g SS at the end of phase 4 (C/N ratio of 2), which were 1.3, 0.6 and 1.3 times of those in RA, respectively. Meanwhile, the removal efficiencies of COD, TN, TP and NH4+-N in RB were 90%, 73%, 53%, and 99% at the end of phase 4, which were 1.1, 1.2, 2.2 and 2.4 times of those in RA, respectively. Thus, high-performance AGS with enhanced robustness and high abundance of HN-AD functional bacteria Paracoccus was obtained. These findings provided a promising and cost-effective method to improve the long-term stability and performance of AGS dealing with wastewater of low C/N ratio.

Organic loading rate (OLR) regulation for enhancement of aerobic sludge granulation: Role of key microorganism and their function.

According to unique growth characteristics of various environmental microorganism specially with different substrates and their levels, aerobic sludge granulation are studied under different operation mode of influent organic loading rate (OLR), and the EPS component, sludge surface characters and functional microbes are analyzed to achieve a novel process for stable sludge granulation. Results showed that activated sludge cultivated under gradient influent OLR decreasing from 5.5 to 3.5 kgCOD m-3 d-1 achieved complete granulation with average size of 438 µm and exopolysaccharide (PS) to protein (PN) ratio over 2.0. Meanwhile, these granules had excellent flocculability and hydrophobicity with Zeta potential and contact angle of -15 mV and 110°, respectively. Principal component analysis (PCA) illustrated that microbes with function of EPS secretion enriched with decreased OLR regulation for their suitable specific growth characteristics, then promoted other microbes aggregation and sludge granulation along with the improvement of cellular surface characters and microbial niche.