Startup and long term operation of enhanced biological phosphorus removal in continuous-flow reactor with granules

Efficient nitrogen removal from municipal wastewater using an integrated fixed-film activated sludge process in a novel air-lifting loop reactor: A pilot-scale demonstration

A novel air-lifting loop reactor combines anoxic, oxic, and settling zones to achieve organic and nutrient removal, as well as solid-liquid separation. To address sludge settling ability and operation stability issues caused by low dissolved oxygen in aerobic zones, this study proposes using modified polypropylene carriers to establish a fixed-film activated sludge (IFAS) system. A pilot-scale demonstration of the IFAS-based air-lifting loop reactor is conducted, and the results show successful operation for approximately 300 days. The pilot-scale reactor achieves a maximum aerobic granulation ratio of 16% in the bulk liquid. The IFAS system contributes to efficient removal of organic matter (96%) and nitrogen (94%) by facilitating simultaneous nitrification and denitrification, as well as fast solid-liquid separation with a low sludge volume index of 34 mL/g. Microbial analysis reveals enrichment of functional bacteria involved in nitrification, denitrification, and flocculation throughout the operation process.

Response mechanism of non-biodegradable polyethylene terephthalate microplastics and biodegradable polylactic acid microplastics to nitrogen removal in activated sludge system

The issue of microplastics (MPs) has gained more attention among researchers and the public; however, there is still a lot to be studied about its impact on biological wastewater treatment. In this study, the effects of non-biodegradable polyethylene terephthalate (PET) and biodegradable polylactic acid (PLA) on wastewater treatment by sequencing batch reactor (SBR) were compared. The results showed that PET and PLA reduced the removal efficiency of NH4+-N by 1.7 % and 21.2 %, respectively. Structural equation functional model (SEM) analysis was used to infer the potential mechanism of PLA affecting ammonia oxidation. PLA primarily inhibits the activity of ammonia monooxygenase (AMO), while promoting an increase in reactive oxygen species (ROS) and antioxidant enzyme activity. Accordingly, the toxic effect of PLA further reduced the abundance of ammonia-oxidizing bacteria. This study showed that biodegradable MPs have a greater potential impact on wastewater treatment than non-biodegradable MPs, which warrants further investigation.

Microbial Ecology of Granular Biofilm Technologies for Wastewater Treatment: A Review

Nowadays, the discharge of wastewater is a global concern due to the damage caused to human and environmental health. Wastewater treatment has progressed to provide environmentally and economically sustainable technologies. The biological treatment of wastewater is one of the fundamental bases of this field, and the employment of new technologies based on granular biofilm systems is demonstrating success in tackling the environmental issues derived from the discharge of wastewater. The granular-conforming microorganisms must be evaluated as functional entities because their activities and functions for removing pollutants are interconnected with the surrounding microbiota. The deep knowledge of microbial communities allows for the improvement in system operation, as the proliferation of microorganisms in charge of metabolic roles could be modified by adjustments to operational conditions. This is why engineering must consider the intrinsic microbiological aspects of biological wastewater treatment systems to obtain the most effective performance. This review provides an extensive view of the microbial ecology of biological wastewater treatment technologies based on granular biofilms for mitigating water pollution.

Full-scale upgrade activated sludge to continuous-flow aerobic granular sludge: Implementing microaerobic-aerobic configuration with internal separators

Aerobic granular sludge (AGS) has been successfully used in sequencing batch reactors. However, their application to existing continuous-flow systems remains challenging. In this study, a novel microaerobic-aerobic configuration with internal separators was implemented in a full-scale municipal wastewater treatment facility with a nominal capacity of 2.5 × 104 m3 d-1. Sludge characteristics, pollutant removal and associated pathways, shifts in the microbial community, and underlying granulation mechanisms were investigated. Following a two-month operation period, the transition from flocculent-activated sludge to well-defined AGS with distinct boundaries and compact structures was successfully achieved. The average size of sludge increased from 31.9 to 138.5 μm, with granules larger than 200 μm constituting 28.9 % of the total sludge and SVI30 averaging 51.4 ± 8.2 mL g-1. The 95th percentile effluent COD, NH4+-N, and TN concentrations were 35.0, 1.2, and 13.3 mg L-1, respectively. The primary pathways for pollutant removal were identified as simultaneous nitrification, denitrification, and phosphorus removal within the microaerobic tanks. The enrichment of denitrifying phosphorus-accumulating organisms, including Hydrogenophaga, Accumulibacter, Azospira, Dechloromonas, and Pseudomonas, provides an essential microbial foundation. Furthermore, computational fluid dynamics modeling revealed that the incorporation of internal separators in aerobic tanks induced shifts in the flow pattern, transitioning from a single-circulation cell to multiple vortical cells. This alteration amplified the local velocity gradients, generating the required shear forces to drive granulation. Moreover, mass balance analysis revealed that the microaerobic and aerobic tanks operated under feast and famine conditions, respectively, creating a microbial selection pressure that favored granulation. This process eliminates the need for external clarifiers, resulting in a footprint reduction of 38.2 % and one-third energy savings for sludge reflux. This study offers valuable insights into the application of continuous-flow AGS to upgrade existing activated sludge systems with limited retrofitting requirements.

Enhancement of nutrient removal in an activated sludge process using aerobic granular sludge augmentation strategy with ammonium-based aeration control

To enhance nutrient removal from low-strength municipal wastewater in a continuous-flow activated sludge (CFAS) process using aerobic granular sludge (AGS) augmentation strategy, a pilot-scale demonstration was configured with a mainstream reactor (anaerobic/aerobic process) and a sidestream sequencing batch reactor for AGS production. The aeration of the mainstream reactor was controlled based on dissolved oxygen (DO) and ammonium concentrations during Phases I and II-III, respectively. During Phase III, an anoxic zone was created in the mainstream aerobic tank. Throughout the demonstration period, excellent sludge settleability in the mainstream reactor (SVI30 ≤ 80 mL g-1) under long sludge retention time conditions (≥12 d) allowed the maintenance of a high mixed liquor suspended solids concentration (≥3000 mg L-1). The total nitrogen (TN) removal ratio improved significantly during Phases II and III (49.3 ± 4.1% and 50.1 ± 10.2%, respectively) compared to Phase I (43.2 ± 5.5%). Low DO concentration (< 0.5 mg L-1) by the ammonium-based aeration tended to increase the simultaneous nitrification and denitrification efficiency (> 40%), enhancing TN removal (> 50%). The reduction of DO and nitrate concentrations in the returning sludge liquor can stabilize phosphorus removal (approximately 80% of the 25th percentile). In addition, the aeration efficiency during Phase III decreased by 26-29% compared to Phase I. These results suggest that the introduction of ammonium-based aeration control to the CFAS using the AGS augmentation strategy could contribute to superior sewerage treatment, including nutrient removal and a low carbon footprint.

Changes in microbial community during hydrolyzed sludge reduction

In this study, the effects of different enzymes (lysozyme, α-amylase and neutral protease) on sludge hydrolysis efficiency and microbial community in sequencing batch reactor (SBR) were introduced. The results showed that the hydrolysis efficiencies of the three enzymes were 48.5, 22.5 and 31%, respectively, compared with the accumulated sludge discharge of the blank control group. However, it has varying degrees of impact on the effluent quality, and the denitrification and phosphorus removal effect of the system deteriorates. The lysozyme that achieves the optimal sludge hydrolysis effect of 48.5% has the greatest impact on the chemical oxygen demand (COD), total nitrogen (TN), and nitrate nitrogen (NO3--N) of the effluent. The sludge samples of the control group and the groups supplemented with different enzyme preparations were subjected to high-throughput sequencing. It was found that the number of OTUs (Operational Taxonomic Units) of the samples was lysozyme > α-amylase > blank control > neutral protease. Moreover, the abundance grade curve of the sludge samples supplemented with lysozyme and α-amylase was smoother, and the community richness and diversity were improved by lysozyme and α-amylase. The species diversity of the sludge supplemented with lysozyme and neutral protease was great, and the community succession was obvious. The introduction of enzymes did not change the main microbial communities of the sludge, which were mainly Proteobacteria, Actinobacteria and Bacteroidetes. The effects of three enzyme preparations on sludge reduction and microbial diversity during pilot operation were analyzed, the gap in microbial research was filled, which provided theoretical value for the practical operation of enzymatic sludge reduction.

Current progress of continuous-flow aerobic granular sludge: A critical review

Aerobic granular sludge (AGS) is promising for water resource recovery. Despite the mature granulation strategies in sequencing batch reactor (SBR), the application of AGS-SBR in wastewater treatment is usually costly as it requires extensive infrastructure conversion (e.g., from continuous-flow reactor to SBR). In contrast, continuous-flow AGS (CAGS) that does not require such infrastructure conversion is a more cost-effective strategy to retrofit existing wastewater treatment plants (WWTPs). Formation of aerobic granules in both batch and continuous-flow mode depends on many factors, including selection pressure, feast/famine conditions, extracellular polymeric substances (EPS), and environmental conditions. Compared with AGS in SBR, creating proper conditions to facilitate granulation in continuous-flow mode is challenging. Researchers have been seeking to tackle this bottleneck by studying the impacts of selection pressure, feast/famine conditions, and operating parameters on granulation and granule stability in CAGS. This review paper summarizes the state-of-the-art knowledge regarding CAGS for wastewater treatment. Firstly, we discuss the CAGS granulation process and effective parameters (i.e., selection pressure, feast/famine conditions, hydrodynamic shear force, reactor configuration, the role of EPS, and other operating factors). Then, we evaluate CAGS performance in removing COD, nitrogen, phosphorus, emerging pollutants, and heavy metals from wastewater. Finally, the applicability of the hybrid CAGS systems is presented. At last, we suggest that integrating CAGS with other treatment methods such as membrane bioreactor (MBR) or advanced oxidation processes (AOP) can benefit the performance and stability of granules. However, future research should address unknowns including the relationship between feast/famine ratio and stability of the granules, the effectiveness of applying particle size-based selection pressure, and the CAGS performance at low temperatures.

Formation, application, and storage-reactivation of aerobic granular sludge: A review

It was an important discovery in wastewater treatment that the microorganisms in the traditional activated sludge can form aerobic granular sludge (AGS) by self-aggregation under appropriate water quality and operation conditions. With a typical three-dimensional spherical structure, AGS has high sludge-water separation efficiency, great treatment capacity, and strong tolerance to toxic and harmful substances, so it has been considered to be one of the most promising wastewater treatment technologies. This paper comprehensively reviewed AGS from multiple perspectives over the past two decades, including the culture conditions, granulation mechanisms, metabolic and structural stability, storage, and its diverse applications. Some important issues, such as the reproducibility of culture conditions and the structural and functional stability during application and storage, were also summarized, and the research prospects were put forward. The aggregation behavior of microorganisms in AGS was explained from the perspectives of physiology and ecology of complex populations. The storage of AGS is considered to have large commercial potential value with the increase of large-scale applications. The purpose of this paper is to provide a reference for the systematic and in-depth study on the sludge aerobic granulation process.

Research on rapid cultivation of aerobic granular sludge (AGS) with different feast-famine strategies in continuous flow reactor and achieving high-level denitrification via utilization of soluble microbial product (SMP)

The mixture of partial AGS and flocculent sludge in continuous flow reactors were operated with periodic famine (PF) strategy and continuous feast (CF) strategy to reveal the impact of the feast-famine strategies on cultivation of AGS and the dynamics of microbial communities. The experimental results showed that the mature AGS were cultivated with PF and CF strategy on the 31st and the 71st days respectively, which was the result of good extracellular polymeric substance (EPS) secretion with PF strategy. It could accelerate the formation of microbial aggregates due to the conditions of periodic famine. High-level denitrification with PF strategy via utilization of SMP was examined by EEM-PARAFAC on cycle test. The high-throughput pyrosequencing showed that the dominant bacteria with PF strategy involved functional bacteria of nutrient removal and EPS secreting bacteria, while the dominant bacteria were fast-growing heterotrophic organisms with CF strategy.

Operational mode affects the role of organic matter in granular anammox process

In the presence of organic matter, the granular anammox system under sequencing batch mode showed more robust anammox performance than that under completely mixed mode, which was attributed to the better biomass retention with high settling ability and stability of granular sludge. Based on the specific anammox activity test, stratified and mixed distribution of heterotrophic bacteria was found under completely mixed and sequencing batch mode, respectively. The stratified microbial distribution resulted in low enzyme activity of anammox bacteria and sludge disintegration by hindering substrate transfer with a large accumulation of EPS on the granular surface. Whereas the heterotrophic bacteria mixed in granules (mixed microbial distribution) act as a "skeleton", which increased the particle size, density, and stability of granular sludge. Compared with biokinetic-based selection, diffusion-based selection with high substrate penetration depth more likely resulted in the mixed granular structure and strong resistance to organic inhibition under sequencing batch mode.

New Advances in Aerobic Granular Sludge Technology Using Continuous Flow Reactors: Engineering and Microbiological Aspects

Aerobic granular sludge (AGS) comprises an aggregation of microbial cells in a tridimensional matrix, which is able to remove carbon, nitrogen and phosphorous as well as other pollutants in a single bioreactor under the same operational conditions. During the past decades, the feasibility of implementing AGS in wastewater treatment plants (WWTPs) for treating sewage using fundamentally sequential batch reactors (SBRs) has been studied. However, granular sludge technology using SBRs has several disadvantages. For instance, it can present certain drawbacks for the treatment of high flow rates; furthermore, the quantity of retained biomass is limited by volume exchange. Therefore, the development of continuous flow reactors (CFRs) has come to be regarded as a more competitive option. This is why numerous investigations have been undertaken in recent years in search of different designs of CFR systems that would enable the effective treatment of urban and industrial wastewater, keeping the stability of granular biomass. However, despite these efforts, satisfactory results have yet to be achieved. Consequently, it remains necessary to carry out new technical approaches that would provide more effective and efficient AGS-CFR systems. In particular, it is imperative to develop continuous flow granular systems that can both retain granular biomass and efficiently treat wastewater, obviously with low construction, maintenance and exploitation cost. In this review, we collect the most recent information on different technological approaches aimed at establishing AGS-CFR systems, making possible their upscaling to real plant conditions. We discuss the advantages and disadvantages of these proposals and suggest future trends in the application of aerobic granular systems. Accordingly, we analyze the most significant technical and biological implications of this innovative 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.

Feast/famine ratio determined continuous flow aerobic granulation

Plug flow reactors (PFRs) made of multiple completely stirred tank reactors (CSTRs) in series were used to cultivate aerobic granules in real domestic wastewater. Theoretically, changing the number of CSTR chambers in series will change the nature of plug flow, and thus alter the pattern of the feast/famine condition and impact the aerobic granulation progress. Therefore, PFRs were operated in 4-, 6-, and 8-chamber mode under the same gravity selection pressure (a critical settling velocity of 9.75 m h^-1) and hydraulic retention time (6.5 h) until steady states were reached to evaluate the effect of the feast/famine condition on continuous flow aerobic granulation. The sludge particle size, circularity, settleability, specific gravity, zone settling velocity, and extracellular polymeric substance contents were analyzed to evaluate the role that a feast/famine regime plays in aerobic granulation. It was found that aerobic granulation failed whenever the feast/famine ratio was greater than 0.5. The results support a conclusion that the feast/famine condition is likely a prerequisite for continuous flow aerobic granulation.

Effect of different operational modes on the performance of granular sludge in continuous-flow systems and the successions of microbial communities

Continuous flow reactors with time intermittent operational (TIO) mode and spatial intermittent operational (SIO) mode were operated to evaluate the effects of operational modes on the removal performances, the characteristics of granules and the dynamics of microbial communities in simultaneous nitrification, denitrification and phosphorus removal (SNDPR) granular system. The results showed that the removal efficiency of TP, TN were 81.3%, 86.7% under TIO mode, and 70.6%, 77.4% under SIO mode, respectively. Meanwhile, the PN and value of PN/PS in SIO were higher than those in TIO. Besides, results of high-throughput pyrosequencing illustrated that the combination of filamentous archaea (Methanothrix) and filamentous bacteria (Thiothrix) had resulted in the increase of EPS and SVI under SIO mode. Finally, functional bacterial and archaeal species, involving HMA, AMA, AOA, DPAOs etc., were identified to reveal the effects of operational modes on the mechanism of nutrients removal in granular SNDPR continuous-flow system.

Startup and stable operation of advanced continuous flow reactor and the changes of microbial communities in aerobic granular sludge

In this study, the granular sludge was operated under low aeration condition in sequencing batch reactor (SBR) and advanced continuous flow reactor (ACFR), respectively. Through increasing the sludge retention time (SRT) from 22 days to 33 days, the ACFR was successful startup in 30 days and achieved long term stable operation. Under SBR operation condition, the aerobic granular sludge (AGS) showed good nitrogen (60%), phosphorus (96%) and COD removal performance. During stable operation of continuous-flow, the nitrogen removal efficiency was increasing to 70%, however, the phosphorus removal efficiency could only be restored to 65%. Meanwhile, the sludge discharge volume from ACFR was about half of that in SBR. Results of high-throughput pyrosequencing illustrated that methanogenic archaea (MA), ammonia oxidizing archaea (AOA), denitrifying bacteria (DNB), denitrifying polyphosphate-accumulating organisms (DPAOs) played an important role in the removal of nutrients in ACFR. This study could have positive effect on the practical application of AGS continuous flow process for simultaneous biological nutrient removal (SBNR).

Continuous-flow aerobic granulation in plug-flow bioreactors fed with real domestic wastewater

This pilot study was designed to explore the feasibility of achieving successful aerobic granulation in continuous flow infrastructure like that existing in modern wastewater treatment plants (WWTPs). Results demonstrated that aerobic granulation of activated sludge can be achieved in plug-flow reactors (PFRs) fed with primary effluent from a domestic WWTP with seasonal temperature variation between 10 and 22.5 °C. It took about 90 days during the reactor startup to reach a state of sustained aerobic granulation. The characteristics of aerobic granules formed were comparable to those measured in sequential batch reactors (SBRs). The feast-to-famine concentration profiles measured in the plug-flow pilot reactors were found to be in line with those present in the full-scale treatment trains, lending support to the feasibility of converting existing infrastructure to continuous flow aerobic granulation systems. A selection pressure based on settling velocity (V_s) was applied in a V_s selector to retain bioparticles with V_s greater than ~9-9.75 m h^-1. It was theorized that an external V_s selection pressure would be necessary but would not be the sole condition sufficient to drive aerobic granulation. The alternating feast-to-famine internal selection provided by the PFRs is also believed to be a required condition to transform biomass from flocs toward dense and compact aerobic granules. While the pilot-scale Plug-flow Aerobic Granulation (PAG) reactor achieved similar COD and NH₃ removal efficiencies as the full-scale WWTP treatment train, its effluent from V_s selector contained an average of 138 mg L^-1 total suspended solids (TSS) as a result of the biomass 'wash-out" by the V_s selection pressure. Pilot results suggest a second clarifier for polishing, in addition to the V_s selector, may be needed in a full-scale application of the technique unless other downstream processes (flocculation, sedimentation, filtration) are provided to reach final water quality goals.

Phosphate adsorption from aqueous solution by lanthanum-iron hydroxide loaded with expanded graphite

In this study, a novel adsorbent of expanded graphite loaded with lanthanum (III)-iron (III) hydroxide (EG-LaFe) was prepared for phosphate removal. The single factor of oscillating time, La/Fe molar ratio and total concentration of EG-LaFe were studied for optimization of preparation conditions. Effects of contact time, initial phosphate concentration, adsorption temperature and coexisting ions on the phosphate removal performance of EG-LaFe were investigated in detail. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-second-order and the Langmuir model fitted the experimental data quite well. Thermodynamic analysis showed that the phosphate adsorption of EG-LaFe was spontaneous and endothermic. In addition, EG-LaFe exhibit high sorption selectivity toward phosphate over other coexisting ions. The phosphate adsorption mechanism was investigated by means of pH study, scanning electron microscopy and Fourier transform infrared spectroscopy. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaFe were the replacement of surface hydroxyl groups (M-OH), electrostatic interaction and Lewis acid-base interaction.

State of the art of aerobic granulation in continuous flow bioreactors

In the wake of the success of aerobic granulation in sequential batch reactors (SBRs) for treating wastewater, attention is beginning to turn to continuous flow applications. This is a necessary step given the advantages of continuous flow treatment processes and the fact that the majority of full-scale wastewater treatment plants across the world are operated with aeration tanks and clarifiers in a continuous flow mode. As in SBRs, applying a selection pressure, based on differences in either settling velocity or the size of the biomass, is essential for successful granulation in continuous flow reactors (CFRs). CFRs employed for aerobic granulation come in multiple configurations, each with their own means of achieving such a selection pressure. Other factors, such as bioaugmentation and hydraulic shear force, also contribute to aerobic granulation to some extent. Besides the formation of aerobic granules, long-term stability of aerobic granules is also a critical issue to be addressed. Inorganic precipitation, special inocula, and various operational optimization strategies have been used to improve granule long-term structural integrity. Accumulated studies reviewed in this work demonstrate that aerobic granulation in CFRs is capable of removing a wide spectrum of contaminants and achieving properties generally comparable to those in SBRs. Despite the notable research progress made toward successful aerobic granulation in lab-scale CFRs, to the best of our knowledge, there are only three full-scale tests of the technique, two being seeded with anammox-supported aerobic granules and the other with conventional aerobic granules; two other process alternatives are currently in development. Application of settling- or size-based selection pressures and feast/famine conditions are especially difficult to implement to these and similar mainstream systems. Future research efforts needs to be focused on the optimization of the granule-to-floc ratio, enhancement of granule activity, improvement of long-term granule stability, and a better understanding of aerobic granulation mechanisms in CFRs, especially in full-scale applications.

Stability of algal-bacterial granules in continuous-flow reactors to treat varying strength domestic wastewater

Stability of algal-bacterial granules was investigated in two continuous-flow systems to treat synthetic domestic wastewater using single (R₁) and series (R₂=R_2-1+R_2-2 with automatically internal recirculation) reactors by seeding 50% (w/w) algal-bacterial granules. Almost similar organics and phosphorus removal efficiencies were obtained from the two systems, with no significant difference found for each between the designed two operation stages. However, R₂ exhibited superior performance on total nitrogen (TN) removal (76%). When double increased strength influent fed to R₁, R₁ achieved better denitrification with TN removal increased from 29% to 80%, possibly due to the increased influent organics concentration favored the denitrification process. Most importantly, the two systems well maintained their granular stability, and all granules became algal-bacterial ones with very little change detected in algae content in granules after 120days' operation. At last, the mechanisms were proposed regarding the formation and enhanced stability of new algal-bacterial granules in continuous-flow reactors.

Transformation of anaerobic granules into aerobic granules and the succession of bacterial community

In this study, we demonstrated that anaerobic granular sludge could be successfully transformed into aerobic granular sludge in a continuous up-flow reactor in 45 days. An aerobic microbial community successfully developed in the granules and high organic matter and nitrogen removal performance was achieved. Under an ammonia nitrogen loading rate of 0.8 kg N/(m³ day), ammonia nitrogen and the total nitrogen removal efficiency of the reactor reached up to 100 and 93%, respectively. An obvious bacterial community shift in granular sludge was observed during the transformation process. By comparing with the bacterial community in aerobic granules cultivated from floccular activated sludge, some bacteria (affiliated with Comamonadaceae, Xanthomonadaceae, Rhodocyclaceae, Moraxellaceae, and Nitrosomonadaceae) playing significant roles in maintaining the structures and functions of aerobic granules were identified. After the transformation, the granules could be clearly separated into the inner core and outer shell. 16S rRNA gene sequencing results indicated many bacterial species present in both the inner core and outer shell; however, their abundance differed significantly. Overall, this study confirms the feasibility of transforming anaerobic granules into aerobic granules and provides novel approaches and insights to understand the microbial ecology in granular sludge.

Effect of sludge retention time on continuous-flow system with enhanced biological phosphorus removal granules at different COD loading

The effect of sludge retention time (SRT) on the continuous-flow system with enhanced biological phosphorus removal (EBPR) granules at different COD loading was investigated during the operation of more than 220days. And the results showed that when the system operated at long SRT (30days) and low COD loading (200mg·L(-1)), it could maintain excellent performance. However, long SRT and high COD loading (300mg·L(-1)) deteriorated the settling ability of granules and the performance of system and resulted in the overgrowth of filamentous bacteria. Meanwhile, the transformation of poly-β-hydroxyalkanoates (PHAs) and glycogen in metabolism process was inhibited. Moreover, the results of pyrosequencing indicated that filamentous bacteria had a competitive advantage over polyphosphate-accumulating organisms (PAOs) at high COD loading and long SRT. The PAOs specious of Candidatus_Accumlibater and system performance increased obviously when the SRT was reduced to 20days at high COD loading.

Long term operation of continuous-flow system with enhanced biological phosphorus removal granules at different COD loading

In this study, a continuous-flow system with enhanced biological phosphorus removal (EBPR) granules was operated at different COD concentrations (200, 300 and 400mgL(-)(1)) to investigate the effect of COD loading on this system. The results showed that when the COD concentration in influent was increased to 400mgL(-)(1), the anaerobic COD removal efficiency and total phosphorus removal efficiency reduced obviously and the settling ability of granules deteriorated due to the proliferation of filamentous bacteria. Moreover, high COD loading inhibited the EPS secretion and destroyed the stability of granules. Results of high-through pyrosequencing indicated that filamentous bacteria had a competitive advantage over polyphosphate-accumulating organisms (PAOs) at high COD loading. The performance of system, settling ability of granules and proportion of PAOs gradually recovered to the initial level after the COD concentration was reduced to 200mgL(-)(1) on day 81.