Aerobic Granular Sludge Technology Research Articles

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

IntroductionMicroplastics (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.MethodsThis 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 discussionsIt 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.

Rapid cultivation of aerobic granular sludge for shale gas flowback water treatment by bioaugmentation with inoculating multifunctional fungal pellets

Aerobic granular sludge (AGS) technology showed great potentials in treatment of hypersaline industrial wastewater such as shale gas flowback water (SGFW), while long start-up period was still a major bottleneck. To both strengthen its granulation and pollutant removal efficiency, herein, one multifunctional fungus Aspergillus sydowii NCSL-XY1 was first isolated with the capacities including formation of fungal pellets, salt tolerance, and efficient degradation of organics in SGFW. Subsequently, its appropriate fungal pellets were used to try to shorten the start-up period of AGS in SGFW. The results showed that inoculating fungal pellets evidently accelerated the formation of AGS from 41 to 16 days. Also, it could enhance the TOC removal from ∼30% to ∼45% in the initial start-up period (Day 2-Day 11). Mechanisms analysis showed that the inoculation of fungal pellets increased EPS secretion and microbial community diversity. When the reactor stabilized, both of the AGS in R1 and R2 had similar D50 (∼1200 μm), SVI30 (∼30 mL/g), and SVI30/SVI5 (∼0.95). Also, the TOC and PAM removal in R1 and R2 were also similar and maintained at ∼71% and ∼20%. Overall, the inoculated fungal pellets played significant roles of both biomass carrier and synergistic degrader in facilitation of AGS start-up, while it had limited functions after the granules maturation. This study provided a universally effective bioaugmentation mode (screening degrading fungus and inoculating its fungal pellets) for AGS cultivation in treatment of refractory industrial wastewater.

Emergence and spread patterns of antibiotic resistance genes during cultivating aerobic granular sludge under different feeding modes

Aerobic granular sludge (AGS) technology, which is a promising approach for wastewater treatment, encounters challenges associated with antibiotic resistance genes (ARGs) in biological treatment systems. This study investigates the dynamics of ARGs during AGS cultivation under anaerobic plug-flow (APM), anaerobic mixed-flow (AMM), and aerobic feeding mode (AFM). Significant differences (P < 0.05) are observed in the shifts of ARGs among these modes. The abundance of ARGs notably increases under all modes, with AMM exhibiting a lower average relative abundance (0.063 ± 0.025) compared to that of APM (0.148 ± 0.061) and AFM (0.147 ± 0.047). The observed variations in bacterial communities and the co-selection of ARGs among the feeding modes are likely influential factors contributing to the documented variations of ARGs. Furthermore, the study identifies tnpA and intl1 as key contributors to horizontal gene transfer (HGT) during APM and AFM operations. Additionally, a heightened level of HGT is observed in both APM and AFM, with a larger potential host range (12 hosts each) harboring ARGs, in contrast to AMM (4 hosts). The study highlights the pivotal role played by distinct bacterial communities and the co-selection of ARGs in ARG variations across feeding modes. AMM emerges as an effective strategy for mitigating ARG proliferation, thereby enhancing the safety and sustainability of AGS technology in wastewater treatment.

Treatment of hospital wastewater using aerobic granular sludge technology: Removal performance and microbial dynamics

Hospital wastewater contains several contaminants of emerging concern that cannot be removed by conventional treatment processes. Many of these emerging contaminants are pharmaceutical compounds, which are found in hospital wastewater at high loads. The presence of these toxics affects to the performance of biological processes in receiving wastewater treatment plants. This research evaluated the capability of the aerobic granular sludge technology to remove pharmaceutical compounds from hospital wastewater in a single chamber, which to date has not been investigated with real hospital wastewater. Despite the high non-biodegradable organic matter content, COD and BOD5 removal reached 75 % and 100 %, respectively. Nitrogen removal ranged from 70 %–90 %, and phosphate removal was maximum 50 %. The technology was able to efficiently remove antibiotics, antiepileptic and antidepressant drugs, whereas non-steroidal anti-inflammatory drugs were removed and released under oscillating patterns. The granular biomass increased in size, but it reduced the settling velocity. Bacterial and fungal communities were acclimated to pharmaceutical inlet, whereas the archaeal population had a progressive adaptation over time. The aerobic granular sludge technology is therefore a viable approach to enhance the disposal of real hospital wastewater prior to discharge into the urban wastewater network.

Impact of food waste addition in energy efficient municipal wastewater treatment by aerobic granular sludge process

Recently, one of the main purposes of wastewater treatment plants is to achieve a neutral or positive energy balance while meeting the discharge criteria. Aerobic granular sludge (AGS) technology is a promising technology that has low energy and footprint requirements as well as high treatment performance. The effect of co-treatment of municipal wastewater and food waste (FW) on the treatment performance, granule morphology, and settling behavior of the granules was investigated in the study. A biochemical methane potential (BMP) test was also performed to assess the methane potential of mono- and co-digestion of the excess sludge from the AGS process. The addition of FW into wastewater enhanced the nutrient treatment efficiency in the AGS process. BMP of the excess sludge from the AGS process fed with the mixture of wastewater and FW (195 ± 17 mL CH4/g VS) was slightly higher than BMP of excess sludge from the AGS process fed with solely wastewater (173 ± 16 mL CH4/g VS). The highest methane yield was observed for co-digestion of excess sludge from the AGS process and FW, which was 312 ± 8 mL CH4/g VS. Integration of FW as a co-substrate in the AGS process would potentially enhance energy recovery and the quality of effluent in municipal wastewater treatment.Graphical abstract

Comparative evaluation of activated sludge and aerobic granular sludge for biological treatment of real domestic wastewater with oxytetracycline dosing

Aerobic granular sludge technology is an emerging choice for effective and sustainable wastewater treatment. The aim of this study was to determine the effect of antibiotics such as oxytetracycline on biological nutrient removal pathways in aerobic granular sludge and activated sludge sequencing batch reactors treating real domestic wastewater. The aerobic granular sludge and activated sludge reactors were operated in parallel for evaluating treatment of domestic wastewater and its response to 50–300 µg/L oxytetracycline dosing. The aerobic granular sludge and activated sludge sequencing batch reactors were dominated by compact granules (sludge volume index (SVI): 60 mL/g) and flocs (SVI: >100 mL/g), respectively, during treatment of real wastewater. Aerobic granular sludge has significantly outperformed activated sludge in achieving high phosphate removal of ∼99% against just 57%. This was corroborated with higher abundance of polyphosphate accumulating organisms and enhanced bio-P removal in the aerobic granular sludge system. In contrast, phosphate removal was achieved through normal bio-P removal in the activated sludge reactor. Oxytetracycline removals were distinct at 90% and 23%, respectively, in the aerobic granular sludge and activated sludge systems. High total nitrogen and phosphate removals of 97% and 96%, respectively, were maintained in the aerobic granular sludge system even during OTC dosing. In contrast, the total nitrogen and phosphate removals have dropped to 78% and 16%, respectively, in the activated sludge system due to oxytetracycline stress. Efficient biological nutrient removal and process stability along with environmental sustainability are critical for choosing aerobic granular sludge technology in wastewater treatment plants.

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.

Tire materials disturb transformations of nitrogen compounds and affect the structure of biomass in aerobic granular sludge reactors

Tire materials (TMs) present a notable hazard due to their potential to release harmful chemicals and microplastics into the environment. They can infiltrate wastewater treatment plants, where their effects remain inadequately understood, raising concerns regarding their influence on treatment procedures. Thus, this study investigated the impact of TMs in wastewater (10, 25, 50 mg/L) on wastewater treatment efficiency, biomass morphology, and microbial composition in aerobic granular sludge (AGS) reactors. TM dosage negatively correlated with nitrification and denitrification efficiencies, reducing overall nitrogen removal, but did not affect the efficiency of chemical-oxygen-demand removal. The presence of TMs increased the diameter of the granules due to TM incorporation into the biomass. The most frequently leached additives from TMs were N-(1,3-dimethylbutyl)-N′-phenyl-1,4-phenylenediamine, benzothiazole (BTH), and 2-hydroxybenzothiazole. In the treated wastewater, only BTH and aniline were detected in higher concentrations, which indicates that tire additives were biodegraded by AGS. The microbial community within the AGS adapted to TMs and their chemicals, highlighting the potential for efficient degradation of tire additives by bacteria belonging to the genera Rubrivivax, Ferruginibacter, and Xanthomonas. Additionally, our research underscores AGS's ability to incorporate TMs into biomass and effectively biodegrade tire additives, offering a promising solution for addressing environmental concerns related to TMs.

Potential of aerobic granular sludge technology for domestic wastewater treatment of high ammonia from urea fertilizer industry

Fertilizer is the main element that has an essential role in the sector of agriculture. Urea fertilizer has a source of Nitrogen with 46.04%. Ammonia is a chemical complex that is used and produced from the processing of urea fertilizer. A specific domestic wastewater quality standard for industry explains that the maximum level of ammonia allowed in effluent water was 10 mg/l. In the urea fertilizer industry wastewater treatment results were found to be in the range of 19.49 - 42.4 mg/l. Activated sludge technology is considered fairly effective in wastewater treatment but requires a large amount of energy and additional land for handling excess sludge. From the disadvantages, it is necessary to conduct research related to the effectiveness of high ammonia wastewater treatment that is environmentally friendly. Aerobic granule is characterized by a compact and dense structure, high biomass residence time, resistance to shock loading and toxic compounds, and a high settling speed so that it can produce a compact reactor design. Aerobic granule allows ammonia removal to reach more than 97%. This article aims to review the potential of implementing the use of aerobic granular sludge technology for ammonia removal in the wastewater of the urea fertilizer industry.

Application of full-scale aerobic granular sludge technology for removing nitrate from groundwater intended for human consumption

The dependence on groundwater for human consumption has increased worldwide in the last decades. Nitrate (NO3−) often reaches groundwater and causes significant degradation in groundwater quality. In an effort to address this issue, a full-scale water treatment plant using aerobic granular sludge (AGS) technology was built to remove NO3− from nitrate-polluted groundwater intended for human consumption in a rural village. The impact of changes in the operational conditions of hydraulic retention time (HRT) and organic matter loading (OML) rate on NO3− removal, overall system performance, and the granule microbiome were studied. Regardless of the HRT, the AGS technology was successful in removing NO3− with removal rates >50 % with an optimal OML rate of 75 mg L−1. No significant variations in the total abundance of any of the denitrification genes were observed. The composition of prokaryotic and eukaryotic communities was affected by changes in the HRT and OML rate. Specific prokaryotic taxa were identified as responsive to changes in operational parameters and their abundances were linked to the removal of NO3−, confirming that the microbes are critical to the NO3− removal process. This study demonstrates that the AGS technology can be successfully implemented to treat nitrate-polluted groundwater in rural villages to produce water of drinking quality. In addition, the reported hydraulic retention times and organic matter loading rate can be used to further improve the system performance to remove nitrate from groundwater.

Aerobic granular sludge phosphate removal using glucose

Enhanced biological phosphate removal and aerobic sludge granulation are commonly studied with fatty acids as substrate. Fermentative substrates such as glucose have received limited attention. In this work, glucose conversion by aerobic granular sludge and its impact on phosphate removal was studied. Long-term stable phosphate removal and successful granulation were achieved. Glucose was rapidly taken up (273 mg/gVSS/h) at the start of the anaerobic phase, while phosphate was released during the full anaerobic phase. Some lactate was produced during glucose consumption, which was anaerobically consumed once glucose was depleted. The phosphate release appeared to be directly proportional to the uptake of lactate. The ratio of phosphorus released to glucose carbon taken up over the full anaerobic phase was 0.25 Pmol/Cmol. Along with glucose and lactate uptake in the anaerobic phase, poly‑hydroxy-alkanoates and glycogen storage were observed. There was a linear correlation between glucose consumption and lactate formation. While lactate accounted for approximately 89 % of the observed products in the bulk liquid, minor quantities of formate (5 %), propionate (4 %), and acetate (3 %) were also detected (mass fraction). Formate was not consumed anaerobically. Quantitative fluorescence in-situ hybridization (qFISH) revealed that polyphosphate accumulating organisms (PAO) accounted for 61 ± 15 % of the total biovolume. Metagenome evaluation of the biomass indicated a high abundance of Micropruina and Ca. Accumulibacter in the system, which was in accordance with the microscopic observations and the protein mass fraction from metaproteome analysis. Anaerobic conversions were evaluated based on theoretical ATP balances to provide the substrate distribution amongst the dominant genera. This research shows that aerobic granular sludge technology can be applied to glucose-containing effluents and that glucose is a suitable substrate for achieving phosphate removal. The results also show that for fermentable substrates a microbial community consisting of fermentative organisms and PAO develop.

Managing stability of aerobic granules by coordinating diameter and denitrification

Aerobic Granular Sludge (AGS) technology is a promising solution for wastewater treatment due to its structure and high biomass retention capacity. However, the stability of AGS is still a challenge for widespread use. This study investigated the relationships among granule stability, granule diameter, biomass retention capacity, and denitrification efficiency. The results showed that granule diameter did not necessarily indicate granule stability, nor was it associated with biomass retention capacity. For mature granules, promoting simultaneous nitrification and denitrification rather than anoxic denitrification was found to improve granule stability. The deterioration of clarification capacity caused by increased anoxic denitrification at high nitrate concentration was not indicated by diameters or the commonly used SVI5/SVI30. Therefore, ensuring coordination between diameter and denitrification control is crucial for the stability of AGS. These results provide a basis for further research and development of efficient and user-friendly methods for monitoring granular stability.

REVIEW OF AEROBIC GRANULAR SLUDGE TECHNOLOGY AND APPLICATION IN WASTEWATER TREATMENT

This paper focuses on introducing an overview of aerobic granular sludge technology, granulation, removal efficiency and application of aerobic granules in wastewater treatment. Aerobic granular sludge has a bacterial layered structure including anaerobic, anoxic and aerobic bacteria in order from inside to outside layer, so it is capable of simultaneous chemical oxygen demand, nitrogen and phosphorus removal. Granular sludge also has capacity to remove persistent organic substances and adsorb heavy metals. As a result, aerobic granular sludge technology can be effectively applied for municipal and industrial wastewater treatment. Many wastewater treatment plants applying aerobic granular sludge technology have been deployed, most commonly in Europe and especially in the Netherlands, which is the first place to apply this technology in practical wastewater treatment with Nereda® trademark. However, aerobic granular sludge is stable on batch reactors and takes months to form stable granular sludge. Therefore, it is necessary to have further researches on the granulation mechanism and affective factors to shorten the time of aerobic granular sludge formation as well as maintain the long-term stability of the granular sludge and develop continuous reactors to maintain the stability of the aerobic granular sludge to meet the requirement of wastewater treatment plants in practice.

A systemic evaluation of aerobic granular sludge among granulation, operation, storage, and reactivation processes in an SBR

As a biological promising wastewater treatment technology, aerobic granular sludge (AGS) technology had been widely studied in sequencing batch reactors (SBRs) for the decades. Presently, the whole processes of its granulation, long-term operation, storage, and reactivation have not been thoroughly evaluated, and also the relationships among microbial diversity, granular size, and characteristics were still not that clear. Hence, they were systematically evaluated in an AGS-SBR in this work. The results demonstrated that Proteobacteria and Bacteroidetes were the dominant phyla, Flavobacterium, Acinetobacter, Azoarcus, and Chryseobacterium were the core genera with discrepant abundances in diverse stages or granular size. Microbial immigration was significant in various stages due to microbial diversity had a line relationship with COD/MLVSS ratio (R2 = 0.367). However, microbial diversity had no line relationship with granular size (R2 = 0.001), indicating the microbial diversity in different-sized AGS was similar, although granular size had a line relationship with settleability (R2 = 0.978). Overall, compared to sludge traits (e.g., sludge size, settleability), COD/MLVSS played a key role on microbial evolution. This study revealed the relationships between granule characteristics and microbial community, and contributed to the future AGS-related studies.

Evaluation of leachate impact on domestic sewage co-treatment in aerobic granular sludge systems

Aerobic granular sludge (AGS) technology has been consolidated for sewage treatment. However, studies about the co-treatment of landfill leachate in municipal wastewater treatment plants (MWWTPs) with AGS systems are still incipient. The engineering and microbiological aspects of leachate co-treatment with sewage in step-feeding (R1) and conventional (R2) AGS systems were evaluated. Initially, synthetic sewage with a gradual increase in the organic load for granule formation was used (Periods I and II). Subsequently, co-treatment with leachate pre-treated by coagulation-flocculation was carried out with 5% (Period III) and 10% (Period IV) concentrations. Finally, methanol supplementation was conducted as an attempt to improve nutrients removal performance (Period V). Based on the results obtained, the co-treatment in granular reactors was feasible. The best conditions were obtained in R1 during Period V with methanol supplementation. Step-feeding produced a more compact and resistant aerobic granular biomass, resulting in better operational stability. Moreover, this strategy favored denitrification, especially during methanol supplementation, minimizing one of the main problems reported regarding leachate co-treatment in AGS systems. As a result, higher total nitrogen (TN) removals were obtained. At the end of the last period, in R1, Chemical Oxygen Dissolved (COD), TN, and Dissolved Organic Carbon (DOC) removals were 93%, and phosphorus removal was 54%, reaching values higher or similar to other AGS investigations with sewage, leachate, or co-treatment. Therefore, the strategies investigated unprecedentedly contribute to consolidating the domestic sewage co-treatment with leachate in AGS systems and providing a good perspective for other industrial wastewaters.

Anaerobic digestibility of aerobic granular sludge from continuous flow reactors: the role of granule size distribution.

There is an increasing interest in integrating aerobic granular sludge (AGS) technology into wastewater industries. Several projects are being performed to cultivate the aerobic granules for continuous flow reactors (AGS-CFR), while there is a scarcity of those projects that investigate the bio-energy recovery from AGS-CFR. This research was designed to examine the digestibility of AGS-CFR. Beyond that, it aimed at defining the role of the granule size on their digestibility. For this purpose, a series of bio-methane potential (BMP) tests have been run at mesophilic conditions. The results showed that AGS-CFR has a lower methane potential (107.43 ± 4.30 NmL/g VS) compared to activated sludge. This may be the result of the high sludge age (30 days) of AGS-CFR. Additionally, the results revealed that the average size of granules is among the main factors that reduce their digestibility, but it does not inhibit it. It was noticed that granules of size >250 μm have a significantly lower methane yield than the smaller ones. Kinetically, it was noticed that the kinetic models with two hydrolysis rates fit well with the methane curve of AGS-CFR. Overall, this work showed that the average size of AGS-CFR characterizes its biodegradability, which in turn defines its methane yield.

Potential of direct granulation and organic loading rate tolerance of aerobic granular sludge in ultra-hypersaline environment

Salt-tolerant aerobic granular sludge (SAGS) technology has shown potentials in the treatment of ultra-hypersaline high-strength organic wastewater. However, the long granulation period and salt-tolerance acclimation period are still bottlenecks that hinder SAGS applications. In this study, “one-step” development strategy was used to try to directly cultivate SAGS under 9% salinity, and the fastest cultivation process was obtained under such high salinity compared to the previous papers with the inoculum of municipal activated sludge without bioaugmentation. Briefly, the inoculated municipal activated sludge was almost discharged on Day 1–10, then fungal pellets appeared and it gradually transitioned to mature SAGS (particle size of ∼4156 μm and SVI30 of 57.8 mL/g) from Day 11 to Day 47 without fragmentation. Metagenomic revealed that fungus Fusarium played key roles in the transition process probably because it functioned as structural backbone. RRNPP and AHL-mediated systems might be the main QS regulation systems of bacteria. TOC and NH4+-N removal efficiencies maintained at ∼93.9% (after Day 11) and ∼68.5% (after Day 33), respectively. Subsequently, the influent organic loading rate (OLR) was stepwise increased from 1.8 to 11.7 kg COD/m3·d. It was found that SAGS could maintain intact structure and low SVI30 (< 55 mL/g) under 9% salinity and the OLR of 1.8–9.9 kg COD/m3·d with adjustment of air velocity. TOC and NH4+-N (TN) removal efficiencies could maintain at ∼95.4% (below OLR of 8.1 kg COD/m3·d) and ∼84.1% (below nitrogen loading rate of 0.40 kg N/m3·d) in ultra-hypersaline environment. Halomonas dominated the SAGS under 9% salinity and varied OLR. This study confirmed the feasibility of direct aerobic granulation in ultra-hypersaline environment and verified the upper OLR boundary of SAGS in ultra-hypersaline high-strength organic wastewater treatment.

Non-filamentous sludge bulking induced by exopolysaccharide variation in structure and properties during aerobic granulation

The forming mechanism of non-filamentous sludge bulking during aerobic granulation were investigated basing on three feeding strategies (R1 direct aeration after fast feeding, R2 anaerobic stirring after fast feeding and R3 anaerobic plug-flow slow feeding). Results showed that strong selection stress (shortening settling time) led to a sharp flocs washout and the subsequent increase of food to microorganisms (F/M) in R1 and R3 reactors, but not found in R2 due to the different strategies of feeding modes. With the increase of F/M, zeta potential and hydrophobicity of sludge surfaces significantly decreased and thus leading to an enhanced repulsive force and energy barriers for sludge aggregation. Particularly, when F/M exceeded 1.2 kgCOD/(kgMLSS·d), non-filamentous sludge bulking was ultimately triggered in R1 and R3. Further analysis showed that massive extracellular exopolysaccharide (PS) accumulated on the surfaces of non-filamentous bulking sludge due to the increased abundance of the microorganisms related to PS secretion during sludge bulking. In addition, significantly increased intracellular second messenger (c-di-GMP), a key substance regulating PS biosynthesis, was confirmed via its concentration determination as well as microbial function prediction analysis, which played a critical role in sludge bulking. Combing with the systematic detection from surface plasmon resonance system, rheometer and size-exclusion chromatography-multiangle laser light detection-refractive index system, higher molecular weight, compact conformation, higher viscosity and higher hydrophilicity was determined in sludge bulking PS relative to PS extracted from non-filamentous bulking sludge. Clearly, the changes of PS (content, structures and properties) driven by c-di-GMP are the dominant mechanism for the formation of non-filamentous sludge bulking during aerobic granulation. This work could provide theoretical support for successful start-up and application of aerobic granular sludge technology.

De novo granulation of sewage-borne microorganisms: A proof of concept on cultivating aerobic granular sludge without activated sludge and effective enhanced biological phosphorus removal

Long start-up periods for granulating activated sludge and concerns on granular stability are the bottlenecks reported during implementation of novel aerobic granular sludge (AGS) technology in municipal wastewater treatment plants. Here, de novo granulation of sewage-borne microorganisms without using activated sludge (AS) inoculum was investigated in bench-scale sequencing batch reactors (SBR). Data showed that formation of AGS from sewage-borne microorganisms was rapid and first granules appeared within one week. Granulation was indicated by appearance of biomass particles (size >0.12 mm), high biomass levels (∼8 g/L) and superior settling properties (SVI30 min: 30 mL/g). Granulation process involved distinct stages like formation of aggregates, retention of aggregates, and growth of millimetre sized granules. Simultaneous COD, nitrogen and phosphorous removal was established within 10 days of start-up in the SBR without using AS inoculum. However, phosphorus removal became stable after 50 days of start-up. Total nitrogen (TN) and total phosphorus (TP) removals of 92% and 70%, respectively, were achieved from real domestic wastewater. Furthermore, addition of granular activated carbon (GAC) had improved both granulation and biological nutrient removals. Interestingly, phosphorus removal became quite stable within 10 days of start-up in the SBR operated with GAC particles. TN and TP removals were found to be higher at >98% and >94%, respectively, in GAC-augmented SBR. Removal of ammonia and phosphorus were mediated by nitritation-denitritation and enhanced biological phosphorus removal (EBPR) pathways, respectively. The bacterial diversity of AGS was lower than that of sewage. Quantitative PCR indicated enrichment of ammonia oxidizing bacteria, denitrifying bacteria and polyphosphate accumulating organisms during granulation. De novo granulation of sewage-borne microorganisms is a promising approach for rapidly cultivating AGS and establishing biological nutrient removal in sewage treatment plants.

Review on Digestibility of Aerobic Granular Sludge

Full-scale wastewater treatment plants utilizing aerobic granular sludge technology are being built in many countries worldwide. As with all biological wastewater treatment plants, the produced waste biomass must be stabilized to protect the population, wildlife, and the environment. Digestion is usually used to break down the complex organics in the waste sludge; however, the digestibility of aerobic granular sludge still needs to be fully understood compared to the conventional activated sludge. This paper reviews the studies published on the digestibility of waste aerobic granular sludge to date. Studies comparing aerobic granular sludge and activated sludge in terms of composition, properties, and digestibility are highlighted. The impact of biological composition and physical properties on the digestibility of sludge is reviewed in terms of biomethane production and biodegradability. The effect of pre-treatment is also covered. Areas for future research are presented.