Aerobic Granular Sludge Research Articles

Novel insights into the biological state in algal-bacterial granular sludge granulation: Armor-like protection provided by the algal barrier

Algal-bacterial granular sludge (ABGS) composed of microalgae and aerobic granular sludge, is a sustainable and promising technology for wastewater treatment. However, the formation mechanism of ABGS has not been clearly defined, and the direct formation of ABGS in saline wastewater has rarely been investigated. This study proposed novel insights into the granulation process of ABGS by assembling the algal barrier, which was successfully cultivated directly in saline wastewater. The results concluded that ABGS with the algal barrier maintained a higher biomass (MLSS of 7046 ± 61 mg/L), larger particle sizes (1.21 ± 0.06 mm), and better settleability (SVI30 of 46 ± 1 mL/g), enabling efficient pollutants removal. Soluble microbial products (SMP) were found to be closely related to the emergence of the algal barrier. In addition, under salinity stress, the high production of extracellular polymeric substances (EPS, 133.70 ± 1.40 mg/g VSS), specifically TB-EPS (90.29 ± 1.12 mg/g VSS), maintained a crucial role in the formation of ABGS. Further analysis indicated that biofilm producing bacteria Pseudofulvimonas and filamentous eukaryote Streptophyta were the key players in ABGS formation with the algal barrier. Furthermore, the enhancement of key genes and enzymes involved in nitrogen metabolism, TCA cycle, and polysaccharide metabolism suggested a more robust protective effect provided by the algal barrier. This study is expected to advance the application of simultaneous ABGS formation and pollutant removal in wastewater.

Phosphorous speciation in EPS extracted from Aerobic Granular Sludge

Wastewater treatment technologies opened the door for recovery of extracellular polymeric substances (EPS), presenting novel opportunities for use across diverse industrial sectors. Earlier studies showed that a significant amount of phosphorus (P) is recovered within extracted EPS. P recovered within the extracted EPS is an intrinsic part of the recovered material that potentially influences its properties. Understanding the P speciation in extracted EPS lays the foundation for leveraging the incorporated P in EPS to manipulate its properties and industrial applications. This study evaluated P speciation in EPS extracted from aerobic granular sludge (AGS). A fractionation lab protocol was established to consistently distinguish P species in extracted EPS liquid phase and polymer chains. 31P nuclear magnetic resonance (NMR) spectroscopy was used as a complementary technique to provide additional information on P speciation and track changes in P species during the EPS extraction process. Findings showed the dominance of organic phosphorus and orthophosphates within EPS, besides other minor fractions. On average, 25% orthophosphates in the polymer liquid phase, 52% organic phosphorus (equal ratio of mono and diesters) covalently bound to the polymer chains, 16% non-apatite inorganic phosphorus (NAIP) precipitates mainly FeP and AlP, and 7% pyrophosphates (6% in the liquid phase and 1% attached to the polymer chains) were identified. Polyphosphates were detected in initial AGS but hydrolyzed to orthophosphates, pyrophosphates, and possibly organic P (forming new esters) during the EPS extraction process. The knowledge created in this study is a step towards the goal of EPS engineering, manipulating P chemistry along the extraction process and enriching certain P species in EPS based on target properties and industrial applications.

Successful operation of nitrifying granules at low pH in a continuous-flow reactor: Nitrification performance, granule stability, and microbial community

Acidic nitrification, as a novel process for treating wastewater without sufficient alkalinity, has received increasing attention over the years. In this study, a continuous-flow reactor with aerobic granular sludge was successful operated at low pH (<6.5) performing high-rate acidic nitrification. Volumetric ammonium oxidation rate of 0.4–1.2 kg/(m3·d) were achieved with the specific biomass activities of 5.8–13.9 mg N/(gVSS·h). Stable partial nitritation with nitrite accumulation efficiency over 85% could be maintained at pH above 6 with the aid of residual ammonium, whereas the nitrite accumulation disappeared when pH was below 6. Interestingly, the granule morphology significantly improved during the acidic operation. The increased secretion of extracellular polymeric substances (especially polysaccharides) suggested a self-protective behavior of microbes in the aerobic granules against acidic stress. 16S rRNA gene sequencing analyses indicated that Candidatus Nitrospira defluvii was always the dominant nitrite-oxidizing bacteria, while the dominant ammonia-oxidizing bacteria shifted from Nitrosomonas europaea to Nitrosomonas mobilis. This study, for the first time, demonstrated the improved stability of aerobic granules under acidic conditions, and also highlighted aerobic granules as a useful solution to achieve high-rate acidic nitrification.

Evaluating the effect of antibiotics on aerobic granular sludge treatment of pharmaceutical wastewater.

Aerobic granular sludge (AGS) has been widely applied in pharmaceutical wastewater treatment due to its advantages such as high biomass and excellent settling performance. However, the influence of commonly found antibiotics in pharmaceutical wastewater on the operational efficiency of AGS has been poorly explored. This study investigated the effects of tetracycline (TE) on AGS treating pharmaceutical wastewater at room temperature and analyzed the related mechanisms. The results demonstrate a dose-dependent relationship between TE's effects on AGS. At concentrations below the threshold of 0.1 mg/L, the effects are considered trivial. In contrast, TE with more than 2.0 mg/L reduces the performance of AGS. In the 6.0 mg/L TE group, COD, TN, and TP removal efficiencies decreased to 72.6-75.5, 54.6-58.9, and 71.6-75.8%, respectively. High concentrations of TE reduced sludge concentration and the proportion of organic matter in AGS, leading to a decline in sludge settling performance. Elevated TE concentrations stimulated extracellular polymeric substance secretion, increasing polymeric nitrogen and polymeric phosphorus content. Intracellular polymer analysis revealed that high TE concentrations reduced polyhydroxyalkanoates but enhanced glycogen metabolism. Enzyme activity analysis disclosed that high TE concentrations decreased the activity of key enzymes associated with nutrient removal.

Impact of biochemical properties on the gelation of EPS extracted from aerobic granules

Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge are a promising source of gel-forming biopolymers. Gaining insights on the charge distribution of these polymers was performed through a fractionation using anionic chromatography. A gelling factor (GF) based on the apparent gel volume and the reactivity of polymers to calcium was attributed to each eluted fraction. The GF values of the eluted anionic EPS correlated with their negative charge. A GF of 0.04 ± 0.03 is measured for molecules eluted at NaCl 0.25 M and a GF of 0.32 ± 0.02 for the molecules eluted at NaCl 0.75 M. However, upon reaching a very high negative charge (elution at NaCl 1 M), the gelation capacity decreases. The size distribution of gelling molecules was analyzed by Size Exclusion Chromatography. High Molecular Weight (MW) molecules are predominantly involved in gelation (between 65 % and 100 % of the high molecular weight fraction from each sample) while low MW molecules participation is relatively limited (lower than 40 % of the low molecular weight fraction from each sample). Moreover, infra-red spectroscopy analysis of the molecules before and after calcium addition showed that mostly proteins and polysaccharides contribute to the hydrogel formation. Colorimetric methods showed that around 60 % of the uronic acids present in the samples could form hydrogels whereas proteins’ participation varied between 0 % and 100 % depending on the fraction.Thus, modulating EPS extraction and purification methods to ensure the preservation of their molecular weight and the selection of appropriate negative charge could be a strategy for EPS valorization.

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.

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.

Treatment of high ammonia anaerobically digested molasses wastewater using aerobic granular sludge reactor

This study addressed the treatment of high ammonia, low biodegradable chemical oxygen demand (bCOD) anaerobically digested molasses wastewater, utilizing an aerobic granular sludge (AGS) reactor. The AGS achieved 99 % ammonia removal regardless of the bCOD supplementation. By adding low ammonia (<60 mg/L), high bCOD raw molasses wastewater (before anaerobic digestion) as a carbon source, enhanced nitrogen removal, increasing from 10 % to 97 %, and improved sludge settleability via bio-induced calcite precipitation were observed. Functional genes prediction suggested two potential denitrification pathways, including heterotrophic denitrification by Paracoccus and Thauera, and autotrophic denitrification, specifically sulfide-oxidizing autotrophic denitrification by Thiobacillus. An increase in the relative abundance of microorganisms involved in heterotrophic denitrification was observed with the addition of high bCOD raw molasses wastewater. Consequently, incorporating raw molasses wastewater into the AGS presents a sustainable approach to achieve mixotrophic denitrification, maintain stable granular sludge and ensure stable treatment performance when treating anaerobically digested molasses wastewater.

Characteristics and performance of aerobic granular sludge technology in the treatment of real batik textile wastewater

Characteristics and performance of aerobic granular sludge technology in the treatment of real batik textile wastewater

Impact of truncated modified basalt fibers on aerobic granular sludge stability and pollutant removal in piggery wastewater treatment

Modified basalt fibers (MBF) and carbon fibers (CF) are effective bio-carrier materials that enhance wastewater treatment performance. This study explored the use of two lengths of truncated MBF and CF (0.1 and 0.4 mm) in a sequencing batch reactor to support activated sludge treatment, facilitating the formation of aerobic granular sludge (AGS). This approach aimed to enhance the stability and pollutant removal efficiency of AGS, particularly for treating piggery wastewater (PWW). The study further assessed the impact of adding truncated fibers on AGS formation, stability, and its chemical oxygen demand (COD) and total nitrogen (TN) removal capabilities. Results indicate that truncated MBF notably enhanced sludge activity, promoting the secretion of extracellular polymeric substances (EPS) within AGS. This process further increased the protein/polysaccharide ratio and bolstered AGS stability. Specifically, the addition of 0.1 mm MBF boosted PWW treatment efficiency. Fluorescence in situ hybridization (FISH) revealed that the addition of fibers had a minimal impact on the distribution of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) within AGS, although truncated MBF enriched the population of AOB. Microbial community analysis showed that the addition of MBF favored the enrichment of bacteria associated with nitrogen removal, upregulating the tricarboxylic acid cycle, nitrogen and amino acid metabolism. Overall, truncated MBF significantly improved AGS stability and its effectiveness in PWW treatment.

Resistance to salt stresses by aerobic granular sludge: sludge property and microbial community

Resistance to salt stresses by aerobic granular sludge: sludge property and microbial community

Aerobic granular sludge sequencing batch reactor for high strength domestic wastewater treatment: Assessing kinetic models and microbial community dynamics

The study aims to treat high strength domestic wastewater (HSDW) and cultivate microbial granular sludge in a sequencing batch reactor (SBR). A bench-scale bioreactor was used for startup. Response surface methodology (RSM) was used to determine the ideal parameters for removing organic materials from HSDW. Organic loading rate (OLR) and cycle time were the independent variables taken into consideration, while the response variable was COD removal. Results from RSM revealed that the optimal conditions for achieving > 98 % COD and TP (>80) removal were a cycle length of 6 h and an OLR of 1.5 kgCOD/m3d. The Modified-Kincannon and the Grau second-order kinetic models were compared to the COD removal rate for the SBR system. The saturation rate constant (Ni) and maximal substrate removal rate (Vc) were proposed to be 6.8 g L−1 d−1 and 0.83 g L−1 d−1, respectively, based on the modified Stover-Kincannon model. The modified Stover-Kincannon (R2 = 0.93673) and Grau second order (R2 = 0.99219) models high correlation coefficient values show that the experimental results and the prediction for the microbial aerobic granular based SBR system accord well. It was discovered that the modified Stover-Kincannon model was less suitable than the Grau second order model. The system microbial community changed because of the granulation process, as the reactor design operation had a big impact on the community structure. Decreased filamentous bacteria favoured several taxa that have been found to exist in granular biomass that is appropriate for treating wastewater. This study sheds important light on the complex interactions that occur between microbial populations and operational variables all through the granulation process in SBR.

Simultaneous biological nutrients removal from wastewater with high ammonium and phosphorus loading using aerobic granular sludge

In this study, two SBRs were inoculated with biomass from a flocculant biological nutrient removal facility and operated for the biological treatment of synthetic wastewater to explore the impact of low influent COD/TN/TP ratio on the start-up, performance, and development of stable, matured AGS. AGS maturation and simultaneous nutrient removals were investigated for 422 days under applying limited DO (1.5–2.0 mg L−1); after that, an optimization period was performed till day 558 to study the influence of applying high DO levels (5.0–8.5 mg L−1). Initial observations at day 118 indicated high settling velocities for granules with a size ≥1.5 mm, with 90 % COD removal achieved since day 35, while exhibiting moderate levels of ammonium (68–71 %) and phosphorus removal (42–44 %). By day 422, the maturation of granules continued, reaching sizes exceeding 3 mm, with a 70 % increase in biomass growth (14.3 g L−1). P-release and P-uptake rates of 52 and 12 mg-P/g-MLVSS·h, respectively, resulted in reduced effluent PO4−3-P (1.5 ± 0.2 mg-P L−1). TN removal performance reached 82 % (NH4-N removal of 88 %), and SND of 99 % was achieved by matured granules maintaining effluent nitrite/nitrate concentrations ≤0.5 ± 0.3 mg-N L−1 (days 330–422). The optimization period was conducted by enhancing biomass mixing conditions and increasing DO, resulting in improved nitrification, with oxidation rate reaching 19.2 mg-NH4/g-MLVSS·h at DO 6 mg L−1. However, DO > 6.5 mg L−1 adversely affected EPS secretion, and granules exhibited poor settleability.

RSM and ANN Comparative Modelling with a Granulation Treatment in Mixed Waters

AbstractA Box‐Behnken design was used for the analysis using a gray wolf optimizer (GWO)‐coupled artificial neural network (ANN) model and response surface methodology (RSM) to analyze the effect of three operating parameters (volumetric exchange ratio [VER], aeration rate [AR], and cycle time [CT]) manipulated during an aerobic granular sludge process (AGS) sequencing batch reactor on modeling the removal of chemical oxygen demand (COD) in mixed wastewater. The most efficient architecture for COD showed the highest efficiency for modeling the AGS. The RSM model and plot results indicate that the CT and AR were the most influential on COD removal efficiency. When compared with models with statistical indices, GWO‐ANN demonstrated higher performance compared to RSM.

A comprehensive comparison of microbial communities between aerobic granular sludge and flocculent sludge for nutrient removal in full-scale wastewater treatment plants

Understanding the microbial community structure of sludge is crucial for improving the design, operation and optimisation of full-scale wastewater treatment plants (WWTPs). This study aimed to have a comprehensive comparison of microbial communities between aerobic granular sludge and flocculent sludge from two full-scale sequential batch reactors-based WWTPs with nutrient removal for the first time. To better understand key functional bacteria such as polyphosphate accumulating bacteria (PAOs), competitive bacteria such as glycogen accumulating bacteria (GAOs) and nitrifying bacteria for both nitrogen and phosphorus removal, another two full-scale WWTPs with only carbon (C) removal and C and nitrogen (N) removal were compared too. It was found that the richness and diversity of the microbial population in sludge increased with pollutant removal from only C, C and N, to C,N, P removal. For C, N P removal, granule structure led to a more diverse and rich microbial community structure than flocculent structure. Although more abundant nitrifying bacteria were enriched in granular sludge than flocculent sludge, the abundance of total putative PAOs was equivalent. However, the most typical putative PAOs such as Tetrasphaera and Candidatus Accumulibacter seemed to be more correlated with biological phosphorus removal performance, which might be more proper to be used as an indication for P removal potential. The higher abundance of GAOs in flocculent sludge with better phosphorus removal performance might suggest that further investigation is needed to understand the functions of GAOs. In addition, the equivalent abundances of PAOs in the WWTPs with only C removal and with C, N, and P removal, respectively, indicate that many newly reported putative PAOs might not contribute to P removal. This study provides insight into the microbial communities and functional bacteria in aerobic granular sludge and flocculent sludge in full-scale SBRs, which can provide microbes-informed optimisation of reactor operation for better nutrient removal.

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.

Ultra-rapid development of ‘solid’ aerobic granular sludge by stable transition/filling of inoculated ‘hollow’ mycelial pellets in hypersaline wastewater

To overcome the long start-up period in cultivating aerobic granular sludge (AGS) under hypersaline environment, mycelial pellets (MPs) of halotolerant fungus Cladosporium tenuissimum NCSL-XY8 were inoculated to try to realize the ultra-rapid development of salt-tolerant AGS by stable transition of ‘hollow’ MPs into ‘solid’ AGS without apparent fragmentation. The granules directly met the standard of AGS after inoculating MPs (Day 0), and it basically satisfied relatively strict standards of AGS (SVI30 < 50 mL/g, D50 > 300 μm, D10 > 200 μm and SVI30/SVI5 > 0.9) under anaerobic/aerobic mode during whole cultivation processes. Microstructure of the granular cross section clarified that MPs with hollow/loose inner layer transitioned into solid/dense AGS under anaerobic/aerobic mode within 7 days, while formed skin-like floating pieces and unstable double-layer hollow granules under aerobic mode. Organics removal reached relatively stable within 13 days under anaerobic/aerobic mode, 6 days faster than aerobic mode. This study provided a strategy for ultra-rapid and stable development of AGS, which showed the shortest granulation period in various AGS-cultivation strategies.

Advances in aerobic granular sludge stabilization in wastewater

This study provides a comprehensive overview of the advancements made in the research concerning the stability of aerobic granular sludge, and succinctly outlines the development mechanisms of aerobic granular sludge, encompassing the "filamentous bacteria theory" and the "extracellular polymer theory", "selective pressure driven hypothesis", and "self coagulation hypothesis"; The primary elements influencing the stability of aerobic granular sludge include temperature, pH levels, the rate of organic loading, and concentrations of ammonia nitrogen, dissolved oxygen and particle size, satiety hunger period, hydraulic shear force, sludge age and toxic and harmful substances; It is discussed in detail that measures such as inhibiting filamentous bulking, promoting the secretion of extracellular polymers, enhancing the growth of slow-growing microorganisms and fortifying the central structure of granules can improve the stability of aerobic granular sludge. It is suggested that future studies should prioritize exploring the formation mechanisms and functional microbial communities associated with aerobic granular sludge. Such investigations will lay the groundwork for its broader industrial applications.

Synergistic role of powdered activated carbon (PAC) for aerobic granular sludge (AGS) formation and organic micropollutant (OMPs) removal

Aerobic granular sludge (AGS) is a spherical aggregate formed by the self-aggregation of activated sludge. AGS consists of diverse microbial groups, not only shortening the settling time but also enhancing treatment efficacy within a shorter reaction time. However, it necessitates a longer start-up time for granule formation. This study aims to investigate the synergistic effects of powdered activated carbon (PAC) on AGS formation in a sequencing batch reactor (SBR) and its potential for maintaining biodegradability in the presence of inhibitory organic micro-pollutants (OMPs). PAC substantially supported the formation of faster and more stable granule (PAC-AGS) with a very low sludge volume index (SVI < 50 mL/g). Morphological observation indicated that PAC-AGS is more compact than AGS without PAC addition, and PACs were broadly present inside and on the surface of PAC-AGS granules. Respirometric bioassay demonstrated that biodegradation of organic matter in the presence of OMP, e.g., diclofenac and isoproturon, was enhanced when PAC-AGS was used as seed instead of AGS due to the alleviated inhibition of those OMPs by PAC. The overall result illustrated that PAC has dual positive contributions to AGS reactor for wastewater treatment by accelerating the formation of AGS and enhancing removal performance even in the presence of inhibitory OMPs.

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.