Characteristics Of Aerobic Granular Sludge Research Articles

Characterization of the dewaterability of excess aerobic granular sludge

Aerobic granular sludge technology has emerged as a promising wastewater treatment process. However, downstream granular sludge management framework is still challenging and lacks sufficient scientific coverage. This research aims to elucidate the dewatering characteristics of aerobic granular sludge compared to activated sludge. Several parameters, such as zeta potential, specific resistance to filtrate, capillary suction time, bound water content, and rheological behavior, were employed to obtain a comprehensive understanding of the dewatering capability of targeted sludge types. The results indicate that aerobic granular sludge has a higher demand for flocculant polymer than activated sludge (1.07 - 3.40 times). Additionally, aerobic granular sludge demonstrates higher resistance to filtrate (1.22 ± 0.09 - 6.59 ± 0.36 ×1011 m/kg) compared to activated sludge (2.93 ± 0.09 ×109 m/kg). The resistance to filtrate was shown to be positively associated with the average granules size. The usage of flocculant polymer significantly reduced the resistance to filtrate of all targeted samples. The bound water content of granular sludge (1.83 ± 0.37 - 4.31 ± 0.15 g/g TS) was higher than that of activated sludge (0.75 ± 0.13 g/g TS). According to the rheological data, aerobic granular sludge has a slightly higher apparent viscosity than activated sludge. The results of this study provide valuable insights into the potential implications of aerobic granular sludge dewatering at full-scale applications.

Performance and Bacterial Characteristics of Aerobic Granular Sludge in Treatment of Ultra-Hypersaline Mustard Tuber Wastewater

Mustard tuber wastewater (MTW) is an ultra-hypersaline high-strength acid organic wastewater. Aerobic granular sludge (AGS) has been demonstrated to have high tolerance to high organic loading rate (OLR), high salinity, and broad pH ranges. However, most studies were conducted under single stress, and the performance of AGS under multiple stresses (high salinity, high OLR, and low pH) was still unclear. Herein, mature AGS was used to try to treat the real MTW at 9% salinity, pH of 4.1–6.7, and OLR of 1.8–7.2 kg COD/m3·d. The OLR was increased, and the results showed that the upper OLR boundary of AGS was 5.4 kg COD/m3·d (pH of 4.2) with relatively compact structure and high removal of TOC (~93.1%), NH4+-N (~88.2%), and TP (~50.6%). Under 7.2 kg COD/m3·d (pH of 4.1), most of the AGS was fragmented, primarily due to the multiple stresses. 16S rRNA sequencing indicated that Halomonas dominated the reactor during the whole process with the presence of unclassified-f-Flavobacteriaceae, Aequorivita, Paracoccus, Bradymonas, and Cryomorpha, which played key roles in the removal of TOC, nitrogen, and phosphorus. This study investigated the performance of AGS under multiple stresses, and also brought a new route for highly-efficient simultaneous nitrification–denitrifying phosphorus removal of real MTW.

The formation and distinct characteristics of aerobic granular sludge with filamentous bacteria in low strength wastewater

In low strength wastewater, aerobic granular sludge (AGS) with filamentous bacteria is often found and regarded as unstable AGS. However, in this study, a new view is proposed that AGS with filamentous bacteria (FAGS) may be the result of low strength wastewater selection. FAGS was found when AGS was cultivated for 30 days. By increasing the settling time, FAGS could keep the mixed liquid suspension (MLSS) at 0.89 g/L. FAGS showed excellent ammonia nitrogen removal performance. The ammonia nitrogen oxidation rate and denitrification rate of FAGS were 1.72 and 1.20 times higher than that of AGS, respectively. FAGS have large specific surface area (15.99 m2/g), high extracellular polymeric substances (EPS) content (>200 mg/gVSS), and strong stability (integrity coefficient: 2 ∼ 8%). Furthermore, FAGS showed higher potential than AGS in many aspects such as carbon metabolism, nitrogen metabolism, and toxicant degradation.

Structural Characteristics of Aerobic Granular Sludge and Factors That Influence Its Stability: A Mini Review

Current extensive research on aerobic granular sludge (AGS) largely focuses on improving its microbial biodiversity, settlement behavior, nitrogen and phosphorus removal efficiency, and shock load resistance. Great challenges that have to be faced are the bottleneck of slow-speed granulation and easy disintegration after granulation, which are key to the extended application of AGS technology. In the present review, the typical morphological structures of AGS are firstly summarized as well as the granulation model hypotheses, and then, we analyze the dominant microflora and their spatial distribution features. The influencing factors on particle structure stability are discussed thereafter on a macro and micro scale. Prospects and future research trends are also discussed based on the current study results for AGS technology.

Dynamic response of aerobic granular sludge to feast and famine conditions in plug flow reactors fed with real domestic wastewater

Plug flow reactors (PFRs) approximated by the connection of multiple completely stirred tank reactors (CSTRs) in series were used to achieve continuous flow aerobic granulation in real domestic wastewater. This study revealed, possibly for the first time, that the morphology and characteristics of aerobic granular sludge transformed in the course of a mixed liquor flow through a PFR. The feast zone, located at the front end of the PFR, can quickly develop filamentous structure on the surface of aerobic granular sludge which later disappeared in the famine zone at the back end of the PFR. Detention time from the front to the back end of the PFR was only 6.5 h. During this period the observed sludge morphological change led to sludge settleability fluctuation as much as 66% in zone settling velocity, 16% in specific gravity, and 40% in settled sludge volume. Further analysis revealed these types of sludge morphologies and characteristics were closely related to the specific substrate removal rate profiles of the PFR, i.e., the feast zone might have encouraged filamentous bacteria to extend outward into the bulk solution for soluble substrate, and the famine zone appeared to play an essential role in solidifying the structure of granular sludge structure prior to subjecting it to the gravity selection pressure. It can be inferred from this study that the lack of a famine zone in aerobic granulation reactors can loosen the granule structure and in turn deteriorate granule settleability. For a PFR, a famine zone following the feast zone is essential for maintaining the structural integrity of aerobic granular sludge in a continuous flow wastewater treatment system.

Nitrogen and Phosphorus Removal from Domestic Sewage Aerobic Granular Sludge Under Intermittent Gradient Aeration

In this study, three SBR reactors R1, R2, and R3 were set up and operated using (A/O)3-SBR gradient aeration, (A/O)3-SBR constant aeration, and the conventional (A/O)-SBR mode, respectively. The nutrient removal performance and aerobic granular sludge characteristics under these aeration modes were explored using real municipal wastewater as the influent matrix. The experimental results revealed that for the R1, R2, and R3 particles during the stable period, the average removal rate of COD was 88.68%, 89.05%, and 88.96%, respectively, the average removal rate of TN was 76.97%, 71.99%, and 64.92%, respectively, the average removal rate of TP was 96.28%, 85.05%, and 78.97%, respectively, and the proportion of denitrifying phosphorus accumulating bacteria to phosphorus accumulating bacteria was 25.52%, 19.60%, and 12.77%, respectively. The results showed that the operation mode of anaerobic, aerobic, and anoxic was more conducive to the enrichment of denitrifying phosphorus accumulating bacteria (DPAOs), and that the gradient aeration was more enriched than the constant aeration mode, which is of great significance to low-intensity municipal domestic sewage treatment with an insufficient carbon source. At the same time, the dissolved oxygen in the aeration section of R1 was reduced step-by-step, which improved the simultaneous nitrification and denitrification rates of particles and the utilization rate of the internal carbon source, which was beneficial for the efficient removal of TN. The particle size of the three groups of reactors was 727.368, 815.072, and 895.041 μm respectively. As the transfer rate of the matrix decreased with particle size, the microorganisms in R2 and R3 may have caused anaerobic respiration to release harmful gas, thus damaging the particle structure, such that the particles in R2 and R3 were less dense than those in R1. In addition, the PN/PS values of R1, R2, and R3 were 6.31, 5.63, and 4.83, respectively, and the EPS content (in terms of VSS) was 103.97, 92.22, and 76.98 mg·g-1, respectively, at the time of particle stabilization, which revealed that the mode of intermittent gradient aeration was beneficial to stimulate the secretion of EPS. This was especially the case for the secretion of PN, which increased the PN/PS value, enhanced the cell hydrophobicity, and made the particles dense and stable.

Robustness of an aerobic granular sludge sequencing batch reactor for low strength and salinity wastewater treatment at ambient to winter temperatures

Acclimation performances and characteristics of aerobic granular sludge to salt and temperature were investigated in a sequencing batch reactor (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR). The aerobic granular SNDPR system was firstly subjected to low salinity (0.5%, w/v) at moderate temperature (> 15 ℃) and subsequent low temperature (< 15 ℃). The shock loading of salinity temporarily deteriorated biological phosphorus removal, while dual stresses of salinity and low temperature induced temporary inhibition on both nitrogen and phosphorus removal. Both salinity and low temperature stimulated the settleability of aerobic granules, accompanied with decreased ratios of protein to polysaccharide (PN/PS). Illumina MiSeq sequencing revealed that salinity rarely affected bacterial richness, but significantly decreased the diversity. Whereas low temperature strengthened both bacterial richness and diversity. Phyla Proteobacteria, Chloroflexi and their sub-groups acted as the main halophilic bacteria while Proteobacteria was also psychrophilic. The functional bacteria such as nitrifiers, denitrifiers, and phosphorus removal bacteria exhibited greater tolerance to salt and low temperature than glycogen accumulating organisms (GAOs). Overall, the present study demonstrated the resilience and robustness of aerobic granular sludge toward salinity and low temperature, which could aid the knowledge of saline wastewater treatment by aerobic granular sludge.

The effects of high salinity on nitrogen removal and the formation characteristics of aerobic granular sludge

This study investigated the biological treatment of high-salinity wastewater using aerobic granular sludge (AGS). The removal performance, AGS characteristics, and microbial community were examined under salinity conditions ranging from 0.5 to 3.0 wt.%. When the salinity was increased, the removal efficiency of the chemical oxygen demand did not change substantially. The mean removal efficiency of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;-N ranged from 43.7 to 72.6% during the operation period. As for the concentration of extracellular polymeric substances (EPS), the polysaccharide/protein (PS/PN) ratio increased from 0.37 to 0.57. The concentrations of the mixed liquor suspended solid (MLSS) and mixed liquor volatile suspended solid (MLVSS) were 4,560 and 3,170 mg/L, respectively, in the end phase, and the MLVSS/MLSS ratio decreased from 0.81 to 0.69. The sludge volume index (SVI&lt;sub&gt;30&lt;/sub&gt;) decreased linearly from 88 to 58 mL/g. In the microbial community analysis, &lt;i&gt;Nitrosomonas&lt;/i&gt; species accounted for 22.9% of the total bacteria in the initial phase, whereas &lt;i&gt;Halomonas&lt;/i&gt; accounted for 43.2% in the end phase. Hence, the gradually increased salinity appears to facilitate the dominance of halophilic microorganisms in the long-term operation of an AGS-based biological treatment system and the stable retention of AGS.

Proceso de granulación y mecanismo de lodo granular aeróbico bajo estrés salino en un reactor de secuenciación por lotes

The formation and characteristics of aerobic granular sludge (AGS) under different operational conditions in a sequencing batch reactor (SBR), designed to treat Mustard tuber wastewater (MTW, characterized as saline wastewater), had been investigated in this study. Morphology and structure during granulation were determined using a microscope with digital camera and scanning electron microscope (SEM). Granules formed in the reactors could be classified as zoogloea granules with a clear boundary outline and filamentous granules with mycelia bestrewing boundary. Zoogloea granules, cultivated in reactor R1 and R2, were with higher density than filamentous granules, cultivated in reactor R3, and consequently had a higher settling velocity. Results showed that divalent metal ions such as Ca2+ and Mg2+ with phosphate in inflow could transform into precipitates, serving as crystal nucleus and carriers for granulation. Moreover, appropriate organic loading, hydrodynamic

Performance and bacterial characteristics of aerobic granular sludge in response to alternating salinity

Salt concentration often fluctuates in influent industrial wastewater. The behavior of aerobic granular sludge (AGS) in response to the stress of alternating salt concentrations remains unclear. In this study, we ran six identical sequencing batch reactors to follow the performance and microbial characteristics of AGS under 1%, 2%, 4% salinity and corresponding alternating salinity, respectively. The results demonstrated that when compared with the control, alternating salinity not only increased the COD removal efficiency of the reactor significantly (p < 0.001) but also generated high concentration of granular biomass with good settling ability. Pearson correlation analysis indicated that the microorganism mostly used an intracellular second messenger molecule c-di-GMP to regulate extracellular polymer contents. Specifically, the increase of extracellular polysaccharide was conducive to the cohesive strength of the granules, resulting in higher biomass concentration and carbon removal efficiency. Additionally, microbial community analysis confirmed that the relative abundance of c-di-GMP pathway-dependent community, in particular Propionibacterium (24.4%–50.9%), was significantly more dominant under alternating salt conditions.

Cultivation and Characteristics of Aerobic Granular Sludge in SBAR

By cultivating and observing the formation process of granular sludge and the characteristics of mature aerobic granular sludge, the formation mechanism of aerobic granular sludge and the structure of the granular sludge are studied. After 60 days, the removal rate of COD and NH3-N of aerobic granular sludge is much higher than that of traditional flocculation sludge, and both of them can be stabilized up to 90%. The removal rate of COD is about 90% and the removal rate of NH3-N at 45d is 95% in final reactor, which enhances the effect of wastewater purification greatly. Due to the compact structure of aerobic granular sludge, the density is much larger than that of traditional activated sludge, and its high activity and the short sedimentation time contribute to much higher sedimentation rate than that of flocculation sludge.

Stability and Performance Characteristics of Aerobic Granular Sludge with Different COD Concentrations in Alternating Anaerobic/Aerobic Sequencing Batch Reactors

Stability and Performance Characteristics of Aerobic Granular Sludge with Different COD Concentrations in Alternating Anaerobic/Aerobic Sequencing Batch Reactors

Performance and Characteristics of Aerobic Granular Sludge Degrading 2,4,6‐Trichlorophenol at Different Volumetric Organic Loading Rates

Aerobic granular sludge represents a promising option for the treatment of wastewater contaminated by 2,4,6‐trichlorophenol (2,4,6‐TCP). Nevertheless, the need for high volumetric organic loading rates (vOLR) still constitutes a practical drawback, since the supply of an external carbon source for the treatment of low‐strength industrial wastewater would imply significant costs at full‐scale. This study investigates the possibility to sustain 2,4,6‐TCP degrading aerobic granules with low vOLR, preserving long‐term process performance. Sodium acetate was used as external carbon source for aerobic granules degrading 2,4,6‐TCP (20 mg/L), and its concentration in the influent was progressively reduced from 1000 to 420 mg/L. The effects on process performance, granule properties and microbial population dynamics were investigated: complete 2,4,6‐TCP removal was maintained, specific removal rates increased from 2.2 ± 0.5 to 4.3 ± 0.4 mg 2,4,6‐TCP/g VSS per hour (mg2,4,6‐TCP/gVSS · h) and a shift of granule diameter toward smallest size fractions occurred. Moreover, the qualitative evaluation of polyhydroxyalkanoates (PHA) inclusions in microbial cells suggested their active role in 2,4,6‐TCP degradation. The results showed that for low‐strength wastewater containing toxic substances like 2,4,6‐TCP, high concentrations of the external carbon source are required during the process start‐up, but not in the long‐term operation, thus reducing the operating costs significantly without compromising process performance: this represents an important step toward process scale‐up.

Influence of carbon source on nutrient removal performance and physical–chemical characteristics of aerobic granular sludge

The impact of carbon source variation on the physical and chemical characteristics of aerobic granular sludge and its biological nutrient (nitrogen and phosphorus) removal performance was investigated. Two identical sequencing batch reactors, R1 and R2, were set up. Granular biomass was cultivated to maturity using acetate-based synthetic wastewater. After mature granules in both reactors with simultaneous chemical oxygen demand (COD), ammonium and phosphorus removal capability were achieved, the feed of R2 was changed to municipal wastewater and R1 was continued on synthetic feed as control. Biological phosphorus removal was completely inhibited in R2 due to lack of readily biodegradable COD; however, the biomass maintained high ammonium and COD removal efficiencies. The disintegration of the granules in R2 occurred during the first two weeks after the change of feed, but it did not have significant impacts on settling properties of the sludge. Re-granulation of the biomass in R2 was then observed within 30 d after granules’ disintegration when the biomass acclimated to the new substrate. The granular biomass in R1 and R2 maintained a Sludge Volume Index close to 60 and 47 mL g−1, respectively, during the experimental period. It was concluded that changing the carbon source from readily biodegradable acetate to the more complex ones present in municipal wastewater did not have significant impacts on aerobic granular sludge characteristics; it particularly did not affect its settling properties. However, sufficient readily biodegradable carbon would have to be provided to maintain simultaneous biological nitrate and phosphorus removal.

Performance of aerobic granular sludge in a sequencing batch bioreactor for slaughterhouse wastewater treatment

Lab-scale experiment was conducted to investigate the formation and characteristics of aerobic granular sludge for biological nutrient removal of slaughterhouse wastewater. Experimental results showed that removal performances of chemical oxygen demand (COD), ammonia and phosphate were enhanced with sludge granulation, and their removal efficiencies reached 95.1%, 99.3% and 83.5%, respectively. The aerobic granular sludge was matured after 90days cultivation, and protein-like substances were the main components. Simultaneously, the mass ratio of proteins and polysaccharides (PN/PS) was enhanced to 2.5 from 1.7. The granules with particle sizes of 0.6–1.2 and 1.2–1.8mm, accounting for 69.6%, were benefit for the growth of ammonia oxidizing bacteria (AOB) and nitrate oxidizing bacteria (NOB), and corresponding specific oxygen demand rates (SOUR) of AOB and NOB were 31.4 and 23.3mgO2/gMLSSh, respectively.

The Effect of Setting Time to the Formation of Aerobic Granular Sludge in SBAR under Low Organic Loading

The setting time was regarded as the selection pressure to make the particles which were unable to get acclimatized to that cultivation circumstance so as to get the aerobic granular sludge which own excellent setting ability with screening and beneficiation. The internal-circulate sequencing batch airlift reactor (SBAR) process was adopted in this experiment to investigate the effect of setting time to the formation of aerobic granular sludge in SBAR under low organic loading. The results showed that aerobic granular sludge with an average particle diameter of 4.0 mm had a good settling ability with spherical or ellipsoidal, smooth and dense on surface, furthermore, the removal rates of NH3-N,TP and CODCr were 96%, 94% and 90% ,respectively. The setting time can be treated as the dominant element for the control of formation and characteristics of aerobic granular sludge to a certain degree in its forming process.

Advancements in the application of aerobic granular biomass technology for sustainable treatment of wastewater

Aerobic granular sludge technology can be regarded as the future standard for industrial and municipal wastewater treatment. As a consequence, a growing number of institutes and universities focus their scientific research on this new technology. Recently, after extensive Dutch research and development effort, an aerobic granular biomass technology has become available to the market. Full scale installations for both industrial and municipal applications are already on stream, under construction or in design. The technology is distinguished by the name ‘Nereda®’ and based on the specific characteristics of aerobic granular sludge. It can be considered as the first mature aerobic granular sludge technology applied at full scale. It improves on traditional activated sludge systems by a significantly lower use of energy and chemicals, its compactness and its favorable capital and operational costs.

Strength characteristics of aerobic granular sludge

Aerobic granular sludge has a number of advantages over conventional activated sludge flocs, such as cohesive and strong matrix, fast settling characteristic, high biomass retention and ability to withstand high organic loadings, all aspects leading towards a compact reactor system. Still there are very few studies on the strength of aerobic granules. A procedure that has been used previously for anaerobic granular sludge strength analysis was adapted and used in this study. A new coefficient was introduced, called a stability coefficient (S), to quantify the strength of the aerobic granules. Indicators were also developed based on the strength analysis results, in order to categorize aerobic granules into three levels of strength, i.e. very strong (very stable), strong (stable) and not strong (not stable). The results indicated that aerobic granules grown on acetate were stronger (high density: >150 g T SSL(-1) and low S value: 5%) than granules developed on sewage as influent. A lower value of S indicates a higher stability of the granules.

Formation and Characteristics of Aerobic Granular Sludge for Simultaneous Phosphorus and Nitrogen Removal in a SBR

With inoculum sludge from a conventional activated sludge wastewater treatment plant, formation of aerobic granular sludge for simultaneous phosphorus and nitrogen removal was realized in a sequencing batch reactor by the selective pressure as a driving force. Selective pressure created by means of decreasing sedimentation time and increasing substrate loading enhanced the formation of aerobic granular sludge, which followed four consecutive stages: acclimation, granulation, growth and maturation. Under the condition that the substrate loading were increased to 500mg COD/(L•d) and 48mg NH4 +-N/(L•d), the granules were the dominant sludge forms with most of diameter about 0.5–2.0 mm, a minimal settling velocity of 0.55 cm/s and a MLSS of 6800 mg/L after 120 days operation. The granules were composed of filamentous species with varying degrees of rod- and coccal-type bacteria. Microscopic examination revealed that granules microecosystem was more stable and should be less vulnerable to the changes of mixed liquor condition.

Dewaterability of Aerobic Granular Sludge

Dewatering characteristics of aerobic granular sludge, activated sludge and sludge which mixed flocculant was studied. It was shown that the specific resistance of aerobic granular sludge is lower than activated sludge and sludge with mixed flocculant was in the range of 1.07~1.80×109 S2/g, and it increased with the increase of diameters of the granules. The water ratio of aerobic granular sludge by pressure filtrate dehydration was decreased to 83.5~86.1%, activated sludge and sludge which mixed flocculant were 94.2% and 91.4%, respectively. The structural characteristics, distribution features of extracellular polymeric substances and PN/PS values of aerobic granular sludge were important factors of its excellent dewaterability. Aerobic granular sludge technology was regarded as one of the promising biotechnologies in sludge treatment.