Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method.

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a-b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44-34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Effect of gradual increase of salt on performance and microbial community during granulation process.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.

Inhibition of denitrification and enhancement of microbial interactions in the AGS system by high concentrations of quinoline.

Quinoline represents a highly toxic and structurally stable nitrogen-containing heterocyclic compound in coking wastewater, posing a potential threat to human beings and the ecological environment. In this study, we investigated the impact of gradually elevating quinoline concentration on pollutant removal efficiency, sludge characteristics, microbial community and their interactions in the aerobic granular sludge (AGS) system. The results demonstrated that AGS was capable of effectively degrading quinoline, with a final removal rate of 90 mg/L quinoline reaching 98.54 ± 0.28%. Notably, the denitrification process was significantly impeded in the presence of 90 mg/L quinoline, with the Phase D effluent displaying a notably high NO3--N concentration of 37.09 ± 21.81 mg/L, primarily attributed to the reduced abundance of norank_f_A4b bacteria. As the quinoline concentration increased, the sludge particle size diminished from 3.46 to 2.60 mm, while the settling performance deteriorated significantly, escalating from 31.29 ± 1.63 mL/g to 62.32 ± 2.87 mL/g. Meanwhile, the protein (PN) content in EPS gradually increased (from 19.87 ± 0.88 mg/g MLVSS to 51.22 ± 3.21 mg/g MLVSS), while the polysaccharide (PS) content fluctuated. Quinoline profoundly modified microbial community composition and structure, with deterministic processes dominating community assembly. Network analysis indicated intensified and complex microbial interactions at 90 mg/L quinoline, characterized by significantly higher positive correlations. In addition, rare taxa (RT) dominated the network nodes, with 74 of 93 key species belonging to RT, highlighting their pivotal roles in sustaining system functions and strengthening microbial connections. This study provides new insights into the effects of quinoline on microbial community structure and interactions in AGS system.

Sludge size affects sorption of organic micropollutants in full-scale aerobic granular sludge systems.

Aerobic granular sludge (AGS) is gaining popularity as an alternative to activated sludge for wastewater treatment. However, little information is available on AGS regarding the removal of organic micropollutants (OMPs) through sorption. In this study, the sorption behavior of 24 OMPs at environmentally relevant concentrations (1 µg/L) was investigated in six sludge fractions of varying sizes (>4 mm, 2-4 mm, 1-2 mm, 0.6-1 mm, 0.2-0.6 mm, and <0.2 mm) from a full-scale AGS reactor using batch experiments. Sorption was significant (removal efficiency >40 %) for 10 OMPs, including 4 zwitterionic and 6 positively charged pharmaceuticals, indicating the importance of electrostatic interaction for OMP sorption in AGS systems. Larger granules exhibited a higher sorption coefficient and capacity than smaller AGS fractions, probably due to increased extracellular polymeric substance content for larger granules. Equilibrium OMP sorption was only reached after 72 h in granules larger than 2 mm, indicating an effect of longer diffusion distance for OMPs into larger granules. Additionally, compared to activated sludge, AGS demonstrates a similar or even slightly higher sorption capacity for 10 OMPs at 1 µg/L. Overall, this study is the first to investigate the sorption behavior of six AGS size fractions for OMPs at environmentally relevant concentrations (1 µg/L) and propose the possible roles of different-sized sludge in OMP sorption in the full-scale AGS reactor.

Enhancing Wastewater Treatment with Aerobic Granular Sludge: Impacts of Tetracycline Pressure on Microbial Dynamics and Structural Stability.

This study evaluated the efficiency of aerobic granular sludge (AGS) technology in treating wastewater contaminated with tetracycline (TC), a common antibiotic. AGS was cultivated under a TC pressure gradient ranging from 5 mg/L to 15 mg/L and compared with conventional wastewater conditions. The results demonstrated that AGS achieved high removal efficiencies and exhibited robust sedimentation performance, with significant differences in average particle sizes observed under both conditions (618.6 µm in TC conditions vs. 456.4 µm in conventional conditions). Importantly, exposure to TC was found to alter the composition and production of extracellular polymeric substances (EPSs), thereby enhancing the structural integrity and functional stability of the AGS. Additionally, the selective pressure of TC induced shifts in the microbial community composition; Rhodanobacter played a crucial role in EPS production and biological aggregation, enhancing the structural integrity and metabolic stability of AGS, while Candida tropicalis demonstrated remarkable resilience and efficiency in nutrient removal under stressful environmental conditions. These findings underscore the potential of AGS technology as a promising solution for advancing wastewater treatment methods, thus contributing to environmental protection and sustainability amid growing concerns over antibiotic contamination.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances.

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Effects of iron-carbon on nitrogen metabolism of floc and aerobic granular sludge.

The aerobic granular sludge (AGS) process had been extensively studied for its simultaneous nitrification and denitrification (SND) capabilities. Iron-carbon (IC) had enhanced AGS nitrogen removal efficiency, but the mechanism remained unclear. In this study, four reactors had been added with 50, 30, 10, and 0 g/L of IC. Total nitrogen removal efficiency increased with IC dosage under the same operation mode. IC enhanced sludge ammonia oxidation rate, denitrification rate, and specific oxygen uptake rate, allowing SND to complete 60 min earlier, potentially reducing wastewater treatment costs. Notably, IC eliminated nitrite accumulation in conventional AGS effluent. IC decreased the abundance of genes and enzyme activities related to NOR expression, while increasing those related to NOS, which may mitigate the potential for nitrous oxide formation by microorganisms. In this study, IC acted as an enzymatic reaction activator, affecting granules more than flocs, with the activity gap gradually decreasing with the IC dosage.

Enhanced aerobic granular sludge by thermally-treated dredged sediment in wastewater treatment under low superficial gas velocity.

The positive contributions of carriers to aerobic granulation have been wildly appreciated. In this study, as a way resource utilization, the dredged sediment was thermally-treated to prepared as carriers to promote aerobic granular sludge (AGS) formation and stability. The system was started under low superficial gas velocity (SGV, 0.6 cm/s)for a lower energy consumption. Two sequencing batch reactors (SBR) labeled R1 (no added carriers) and R2 (carriers added), were used in the experiment. R2 had excellent performance of granulation time (shortened nearly 43%). The maximum mean particle size at the maturity stage of AGS in R2 (0.545 mm) was larger compared to R1 (0.296 mm). The sludge settling performance in R2 was better. The reactors exhibited high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal rates. The total phosphorus (TP) removal rate in R2 was higher than R1 (almost 15% higher) on stage II (93-175d). R2 had a higher microbial abundance and dominant bacteria content. The relative abundance of dominant species was mainly affected by the carrier. However, the enrichment of dominant microorganisms and the evolution of subdominant species were more influenced by the increase of SGV. The results indicated that the addition of carriers induced the secretion of extracellular polymeric substances (EPS) by microorganisms and accelerated the rapid formation of initial microbial aggregates. This work provided a low-cost method and condition to enhance aerobic granulation, which may be helpful in optimizing wastewater treatment processes.

In-situ rapid cultivation of aerobic granular sludge in A/O bioreactor by using Ca(ClO)2 pretreating sludge.

The efficient utilization of residual sludge and the rapid cultivation of aerobic granular sludge in continuous-flow engineering applications present significant challenges. In this study, aerobic granular cultivation was fostered in a continuous-flow system using Ca(ClO)2-sludge carbon (Ca-SC). Ca-SC retained the original sludge properties, contributing to granular growth in an A/O bioreactor. By day 40, the granule diameters increased to 0.8 mm with the SVI30 decreased by 2.7 times. Moreover, Ca-SC facilitated protein secretion, reaching 98.06 mg/g VSS and enhanced the hydrophobicity to 68.4 %. The continuous-flow aerobic granular sludge exhibited a nutrient removal rate above 90 %. Furthermore, Tessaracoccus and Nitrospira were enriched to promote granular formation and nitrogen removal. The residual sludge was carbonized and reused in the traditional wastewater treatment process to culture granular sludge in situ, aiming to achieve "self-production and self-consumption" of sludge and promote the innovative model of "treating waste with waste" in urban sewage environmental restoration.

Two-way role of iron-carbon in biochemical reactions: Microelectrolysis and enhanced activity of aerobic granular sludge for efficient refractory wastewater treatment.

Industrial wastewater contained a large amount of refractory organics, and single treatment processes had limitations. This study investigated the mechanism of refractory organics removal using iron-carbon built-in coupled activated sludge (ICAS) and explored the role and function of iron-carbon (IC) within the ICAS system. The aerobic granular sludge (AGS) cultivated with IC exhibited a loose surface and a tight interior structure. Iron in the AGS concentrated near the outer layer to form a crust, which protected the inner microorganisms. IC promoted EPS secretion and regulated the abundance of positive and negative signaling molecules to maintain AGS stability. Experiments using quinoline as a model refractory organic showed that both physical adsorption by IC and biological adsorption by sludge rapidly fixed a large amount of pollutants, providing a buffer capacity for the system. The iron mineral crust on the AGS surface enhanced quinoline adsorption. Hydroxylation was the first step in quinoline degradation, with IC upregulating the genes iorA/B, qorB, and wrbA involved in this process, and the relative abundances of quinoline-degrading bacteria. Both pyridine ring opening and benzene ring cleavage occurred in the single IC system, and the microelectrolysis process produced •OH and [H], which made degradation pathway for quinoline through IC more complex than microbial degradation. Although the IC-mediated pathway accounted for only a small part of overall quinoline removal in the ICAS system, the ICAS system not only preserved the microelectrolysis process but also enhanced microbial metabolic activity. This work provided insights into the synergistic removal of pollutants and maintenance of AGS stability by the ICAS process, ensuring efficient treatment of refractory organic wastewater.

Deciphering the role of micro/nano-hydroxyapatite in aerobic granular sludge system: Effects on treatment performance and enhancement mechanism.

Hydroxyapatite (HAP), a mineral nucleus identified within aerobic granular sludge (AGS), plays a vital role in enhancing the AGS systems. However, the microscopic mechanism underlying their roles remains largely unexplored. Herein, a systematic investigation was carried out to elucidate the impact and enhanced mechanisms associated with HAP of different sizes, i.e. micro-HAP (mHAP) and nano-HAP (nHAP), on the aerobic granulation, nutrient removal and microbial diversity of AGS. Results showed that the presence of nHAP and mHAP significantly shortened the granulation process to 15 and 20 days, respectively. This might be ascribed to the fact that the large specific surface area of nHAP aggregates was conducive to microbial adhesion, biomass accumulation and sludge granulation. Compared with mHAP, the granules with nHAP showed better settlement performance, mechanical strength and larger diameter. The X-ray diffraction (XRD) and Raman spectrometer analysis confirmed the presence of HAP within the granules, which was found to stimulate the secretion of extracellular polymeric substance, improve the compactness of granule structure and suppress the growth of filamentous bacteria, thereby contributing to a stable AGS system. The presence of HAP, especially nHAP, effectively enriched the functional microorganisms, such as nitrifying and denitrifying bacteria (e.g. Candidatus_Competibacter) and phosphorus accumulating organisms (e.g. Flavobacterium), leading to the improved nutrient removal efficiencies (COD > 96%, TN > 76%, and TP > 74%). Further analysis revealed the up-regulation of functional enzymes (e.g. nitrite oxidoreductase and polyphosphate kinase) involved in nutrient metabolism, underlying the inherent mechanisms for the excellent nutrient removal. This study deepens the understanding of granulation mechanisms from the perspective of mineral cores, and proposes an economically feasible strategy for rapid initiation and stabilization of AGS reactors.

Effects of carrier surface hydrophilic modification on sludge granulation: From sludge characteristics, extracellular polymeric substances, and microbial community.

Aerobic granular sludge (AGS) is a powerful biotechnological tool capable of treating multiple pollutants simultaneously. However, the granulation process and pollutant removal efficiency still need to be further improved. In this study, Fe2O3- and MnO2-surface-modified straw foam-based AGS (Fe2O3@SF-AGS and MnO2@SF-AGS), with an average particle size of 3 mm, were developed and evaluated. The results showed that surface modification reduced the hydrophobic groups of carriers, facilitating the attachment and proliferation of microorganisms. Notably, MnO2@SF-AGS showed excellent granulation performance, reaching a stable state about one week earlier than the unmodified SF-AGS. The polymeric substance content of MnO2@SF-AGS was found to be 1.28 times higher than that of the control group. Furthermore, the removal rates for NH4+-N, TN, and TP were enhanced by 27.28%, 12.8%, and 32.14%, respectively. The bacterial communities exhibited significant variations in response to different surface modifications of AGS, with genera such as Saprospiraceae, Terrimonas, and Ferruginibacter playing a crucial role in the formation of AGS and the removal of pollutants specifically in MnO2@SF-AGS. The charge transfer of metal ions of MnO2@SF promotes the granulation process and pollutant removal. These results highlight that MnO2@SF-AGS is an effective strategy for improving nitrogen and phosphorus removal efficiency from wastewater.

Archaea communities in aerobic granular sludge: A mini-review.

Recent research on the archaea community in aerobic granular sludge (AGS) has attracted considerable attention. This review summarizes the existing literature on composition, distribution, and related functions of archaea community in AGS. Furthermore, the effects of granulation, substrate, temperature, process types, and aeration models on the archaea community were discussed. Significantly, the layered structure of AGS facilitates the enrichment of archaea, including methanogenic archaea and ammonia-oxidizing archaea. Archaea engage in metabolic interactions with other microorganisms, enhancing the ecological functionalities of AGS and its tolerance to adverse conditions. Future investigations should focus on minimizing greenhouse gas emissions and exploring the roles and interactive mechanisms of archaea and other microorganisms within AGS.

Novel separate aeration self-circulating technology for continuous aerobic granular sludge process: Performance evaluation, hydrodynamic simulation and control strategy.

The continuous aerobic granular sludge (AGS) process is promising for upgrading existing wastewater treatment facilities. However, this approach is still challenging because of its complicated structure and operation. To address this issue, a novel separate aeration self-circulating technology (abbreviated as Zier) was proposed, which is promising for cultivating AGS by its outstanding upflow velocity and circulation multiplier (more than 30 m/h and 200, respectively). This study elaborated on the Zier reactor's feasibility, optimization, and control strategy through computational fluid dynamics simulations, theoretical calculations, and experiments. An appropriate flow regime for efficient removal of pollutant and granulation of sludge was attained at a superficial gas velocity of 1.3 cm/s. Moreover, optimizing the aeration column diameter to half of the reaction column and increasing the height/diameter ratio to 20 dramatically boosted the nitrogen removal capacity over 1.6 kg N/m3/d. Utilizing a smaller circulation pipe diameter ensured granulation under a consistent flow regime. By judiciously regulating, multiple CSTRs and PFRs seamlessly integrated within the Zier reactor across a broad spectrum of particle sludge. The validity of these findings was further substantiated through experimental and theoretical validations. Drawing from these findings, a multi-scenario control strategy was proposed as Zier's map. With all the superiorities shown by the Zier reactor, this study could offer new insights into an efficient continuous AGS process.

Dewatering performance of aerobic granular sludge under centrifugal with different sludge conditioning agent.

The aerobic granular sludge(AGS) technology draw scientific researchers attention, and more and more scientific research focuses on it, due to its superior advantages, such as good settling performance, high biological phase, high toxicity resistance and multiple biological effects. With the rapid development of AGS technology, a considerable amount of residual AGS will be produced, and dehydration is the biggest bottleneck of sludge reduction. This study investigated the dewatering process and method of residual AGS cultured by continuous flow experiment. Experiments were conducted using centrifugal dewatering technology with a dosing scheme to analyze the granular sludge dewatering process, and investigate the release process of EPS component in AGS dewatering. Our results implied the specific resistance of AGS has a very low value ((1.82 ± 0.03) × 109 m/kg) and it was not obvious for the conditioning effect of chemical conditioner on AGS dewatering. However, the moisture content can be reduced to 63.5% after dewatering with the presence of inorganic substances. The addition of drinking water treatment plant sludge (Alum sludge) can improve the efficiency of the dewatering of AGS. A possible dewatering process of AGS dewatering was proposed which was divided into two stages: First, a considerable amount of free water in the sludge was quickly removed under the action of gravity without pressure filtration. Second, the bound water release required cooperation between applying centrifugal or pressing force to grind granular cells and separate protein-like substances with the inorganic matter inside the granular sludge. The possible mechanism of AGS dewatering and hypothesis dewatering process are useful to optimize the AGS dewatering process.

Microbial response to the chronic toxicity effect of graphene and graphene oxide nanomaterials within aerobic granular sludge systems.

Nanomaterials present in wastewater can pose a significant threat to aerobic granular sludge (AGS) systems. Herein, we found that compared to graphene nanomaterials (G-NMs), the long-term presence (95 days) of graphene oxide nanomaterials (GO-NMs) resulted in an increased proliferation of filamentous bacteria, poorer sedimentation performance (SVI30 of 74.1 mL/g) and smaller average particle size (1224.4 µm) of the AGS. In particular, the GO-NMs posed a more significant inhibitory effect to the total nitrogen removal efficiency of AGS (decreased by 14.3 %), especially for the denitrification process. The substantial accumulation of GO-NMs within the sludge matrix resulted in a higher level of reactive oxygen species in AGS compared to G-NMs, thereby inducing lactate dehydrogenase release, and enhancing superoxide oxidase and catalase activities. Such excessive oxidative stress could potentially result in a significant reduction in the activity of nitrogen metabolism enzymes (e.g., nitrate reductase and nitrite reductase) and the expression of key functional genes (e.g., nirS and nirK). Altogether, compared to G-NMs, prolonged exposure to GO-NMs had a more significant chronic toxicity effect on AGS systems. These findings implied that the presence of G-NMs and GO-NMs is a hidden danger to biological nitrogen removal and should receive more attention.

The impacts of biodegradable and non-biodegradable microplastic on the performance and microbial community characterization of aerobic granular sludge.

Introduction: Microplastics (MPs), identified as emerging contaminants, have been detected across diverse environmental media. Their enduring presence and small size facilitate the adsorption of organic pollutants and heavy metals, leading to combined pollution effects. MPs also accumulate in the food chain thus pose risks to animals, plants, and human health, garnering significant scholarly attention in recent years. Aerobic granular sludge (AGS) technology emerges as an innovative approach to wastewater treatment. However, the impacts of MPs on the operational efficiency and microbial characteristics of AGS systems has been insufficiently explored. Methods: This study investigated the effects of varying concentration (10, 50, and 100 mg/L) of biodegradable MPs (Polylactic Acid, PLA) and non-biodegradable MPs (Polyethylene Terephthalate, PET) on the properties of AGS and explored the underlying mechanisms. Results and discussions: It was discovered that low and medium concentration of MPs (10 and 50 mg/L) showed no significant effects on COD removal by AGS, but high concentration (100 mg/L) of MPs markedly diminished the ability to remove COD of AGS, by blocking most of the nutrient transport channels of AGS. However, both PLA and PE promoted the nitrogen and phosphorus removal ability of AGS, and significantly increased the removal efficiency of total inorganic nitrogen (TIN) and total phosphorus (TP) at stages II and III (P < 0.05). High concentration of MPs inhibited the growth of sludge. PET noticeably deteriorate the sedimentation performance of AGS, while 50 mg/L PLA proved to be beneficial to sludge sedimentation at stage II. The addition of MPs promoted the abundance of Candidatus_Competibacter and Acinetobacter in AGS, thereby promoting the phosphorus removal capacity of AGS. Both 50 mg/L PET and 100 mg/L PLA caused large amount of white Thiothrix filamentous bacteria forming on the surface of AGS, leading to deterioration of the sludge settling performance and affecting the normal operation of the reactor. Comparing with PET, AGS proved to be more resistant to PLA, so more attention should be paid to the effect of non-biodegradable MPs on AGS in the future.

Characteristics, Performance and Microbial Response of Aerobic Granular Sludge for Treating Tetracycline Hypersaline Pharmaceutical Wastewater.

Salt-tolerant aerobic granular sludge(AGS) was successfully cultivated under the dual stress of tetracycline and 2.5% salinity, resulting in an average particle size of 435.0 ± 0.5 and exhibiting a chemical oxygen demand(COD) removal rate exceeding 80%, as well as excellent sedimentation performance. The analysis of metagenomics technology revealed a significant pattern of succession in the development of AGS. The proportion of Oleiagrimonas, a type of salt-tolerant bacteria, exhibited a gradual increase and reached 38.07% after 42 days, which indicated that an AGS system based on moderate halophilic bacteria was successfully constructed. The expression levels of targeted genes were found to be reduced across the entire AGS process and formation, as evidenced by qPCR analysis. The presence of int1 (7.67 log10 gene copies g-1 in 0 d sludge sample) enabled microbes to horizontally transfer ARGs genes along the AGS formation under the double pressure of TC and 2.5% salinity. These findings will enhance our understanding of ARG profiles and the development in AGS under tetracycline pressure, providing a foundation for guiding the use of AGS to treat hypersaline pharmaceutical wastewater.

Potential for curdlan recovery from aerobic granular sludge wastewater treatment systems - A review.

The aerobic granular sludge (AGS) biotechnology has been explored for wastewater treatment for over two decades. AGS is gaining increased interest due to its enhanced treatment performance ability and the potential for resource recovery from AGS-based wastewater treatment systems. Resource recovery from AGS is a promising approach to sustainable wastewater treatment and attaining a circular economy in the wastewater management industry. Currently, research is at an advanced stage on recovering value-added resources such as phosphorus, polyhydroxyalkanoates, alginate-like exopolysaccharides, and tryptophan from waste aerobic granules. Recently, other value-added resources, including curdlan, have been identified in the aerobic granule matrix, and this may increase the sustainability of biotechnology in the wastewater industry. This paper provides an overview of AGS resource recovery potential. In particular, the potential for enhanced curdlan biosynthesis in the granule matrix and its recovery from AGS wastewater treatment systems is outlined.

Innovation for continuous aerobic granular sludge process in actual municipal sewage treatment: Self-circulating up-flow fluidized bed process.

Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20-32 times and an up-flow velocity within the reactor of 7-16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1-0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300-1210 µm, the percentage of mass with particle size distribution < 200 µm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%-0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50-80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage.