Abstract Aerobic Granular Sludge Research Articles

Mechanistic study on the ferric chloride-based rapid cultivation and enhancement of aerobic granular sludge

ABSTRACT Aerobic granular sludge (AGS) can achieve simultaneous carbon, nitrogen and phosphorus removal owing to its three-dimensional oxygen gradient structure. However, long start-up period and poor operational stability restrict its application and promotion. A novel rapid granulation strategy, viz., the short-term (7 days) addition of ferric chloride at the commissioning stage, was developed and verified in this study. The granulation period was shortened by 9 days, and the formed granules were compact and dense with an Fe3+ concentration of 250 mg L−1. The addition of flocculant not only maintained a high sludge concentration during the initial stages of granulation (5.3 g L−1), but also stimulated the secretion of TB-EPS and increased protein and polysaccharide contents, thereby expediting granule formation. Additionally, ferric chloride induced a diverse microbial community in granules, resulting in the emergence of new genera, such as Thaurea, Brevundimonas and Kinneretia, which improved pollutant removal performance and flocculent aggregation. The removal efficiencies of COD, PO4 3--P, and NH4 +-N stabilized at 94.2, 62.4, and 71.3%, respectively. Therefore, it has been demonstrated that short-term ferric chloride dosing has a synergistic effect on aerobic granulation.

Developing Aerobic Granular Sludge With Sesame Like Biodegradable Support

Aerobic granular sludge (granules) is an innovative wastewater treatment, where dense biomass is in granular form. The problem of applying this technology at full scale is the granulation process time, which takes several months. In this paper, in an attempt to quicken this process, a biofilm was tested using several candidates as biodegradable support (BDS) for granulation. In this study, it was found that not only the granulation process was accelerated using sesame seeds as BDS (10, 15 and 21 days, compared to 2 months proposed by other studies), but also a new phenomenon was observed where new granules were generated from mature granules, enhancing the granulation process. This paper offers an enhanced option for granulation process.

Rapid aerobic granulation using biochar for the treatment of petroleum refinery wastewater

Aerobic granular sludge technology has great potential for the treatment of petroleum refinery wastewater. However, strategies to shorten the granulation time and improvement the stability still need to be developed. In this work, biochar was prepared from waste petroleum activated sludge (biochar-WPS) and used in a sequencing batch reactor for the treatment of petroleum refinery wastewater. Biochar-WPS presented the surface area of 229.77 m2/g, pore volume of 0.28 cm3/g, H/C and O/C atomic ratios of 0.42 and 0.21, respectively. The porous structure and a high degree of hydrophilicity were found to facilitate microbial colonization and adhesion as well as particle aggregation. Application of biochar-WPS resulted in the formation of more substantial and stable aerobic granules (~ 66% of granules > 0.46 mm diameter) 15 days earlier compared with the control. The addition of biochar-WPS enhanced the average removal efficiency of chemical organic demand (~ 3%), oil (~ 4%) and total nitrogen (~ 10%) over the control. Increased microbial richness and diversity were observed within the formed granules and had an increased (~ 4%) proportion of denitrifying bacteria. These results indicate that an aerobic granulation mechanism using biochar-WPS is a feasible option for the treatment of petroleum refinery wastewater.

Formation and characteristics of filamentous granular sludge.

Aerobic granular sludge process as a promising biotechnology has been one of the research hotspots in the area of wastewater treatment during the last two decades. In our study, after around 60 days' operation, filamentous granular sludge (FGS) was formed under low aeration (SAV = 0.085 cm/s) and multi-feeding conditions. The characteristics of FGS and the performance of the FGS system for organic matter and nutrients removal were investigated. The results showed that chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies were relatively stable, while COD removal efficiency increased from 82% to 94% in the presence of sulfamethoxazole (SMZ) at low concentration (1 mg/L). At the same time, the TP removal efficiency could be improved and maintained at around 75%, while TN removal efficiency was flocculated at around 50%. The analysis of microbial diversity showed that Thiothrix and Trichococcus as typical filamentous species were detected and dominant in the FGS system. The abundance of Thiothrix increased from 15% to 34%, while Trichococcus decreased from 23% to 3% in the presence of SMZ.

Cultivation of aerobic granular sludge in a microbial fuel cell

Aerobic granular sludge(AGS) is a special biofilm formed by the self-aggregation of sludge material. In this study, AGS was cultivated in the biocathode of a continuous flow microbial fuel cell (MFC). During the formation of AGS, changes in sludge concentration, extracellular polymers (EPS), pollutants removal and power generation were examined. The results showed that, MLVSS kept above 5 g/L, the PS, PN and PN/PS of TB-EPS showed a gradually increasing trend, the removal efficiency of COD and ammonia nitrogen was 94.46% and 93.03%, respectively. A maximum voltage output of 350 mV was achieved.

Performance of Aerobic Granular Sludge in Treating Soy Sauce Wastewater at Different Hydraulic Retention Time

Aerobic granular sludge had shown its capability in treating soy sauce wastewater, but its reactor performance, granules properties and biokinetics in different hydraulic retention times (HRT) is still unknown. To ensure the reactor is performed in optimum condition, a judicially selection of HRT is important. The study was conducted in a high and slender column operated according to a sequential batch reactor (SBR) with a sequence of aerobic and anaerobic/anoxic reaction phases. Three different HRTs (8, 16, 24 h) and different anaerobic and aerobic reaction time were evaluated. In the study demonstrated the increase in HRT could reduce the organic loading rate (OLR) as well as biomass yield (Yobs, Y), endogenous decay rate (kd) and overall specific biomass growth rate (µoverall). It was observed a slight increase in the mixed liquor suspended solid (MLSS) and the granules mean size as the OLR decreased. Meanwhile, in the lowest HRT reactor, a narrow diameter range of aerobic granule from 3 to 100 µm was observed due to the development of small and dense granules. The HRT of 24h with aerobic and anaerobic/anoxic reaction time of 3.88 and 7.77h respectively is the SBR’s best performances due to the improvement of the aerobic granular physical properties.

Three-dimensional multi-species mathematical model of the aerobic granulation process based on cellular automata theory.

Aerobic granular sludge is a kind of microbial polymer formed by self-immobilization under aerobic conditions. It has been widely studied because of its promising application in wastewater treatment. However, the granulation process of aerobic sludge is still a key factor affecting its practical application. In this paper, a three-dimensional (3D) multi-species mathematical model of aerobic granular sludge was constructed using the cellular automata (CA) theory. The growth process of aerobic granular sludge and its spatial distribution of microorganisms were studied under different conditions. The simulation results show that the aerobic granules were smaller under high shear stress and that the autotrophic bacterial content of the granular sludge interior was higher. However, the higher the dissolved oxygen concentration, the larger the size of granular sludge and the higher the content of autotrophic bacteria in the interior of the granular sludge. In addition, inhibition of toxic substances made the aerobic granule size increase more slowly, and the spatial distribution of the autotrophic bacteria and the toxic-substance-degrading bacteria were mainly located in the outer layer, with the heterotrophic bacteria mainly existing in the interior of the granular sludge.

Performance of aerobic granular sludge at variable circulation rate in anaerobic-aerobic conditions.

Aerobic granular sludge (AGS) has been applied to treat a broad range of industrial and municipal wastewater. AGS can be developed in a sequencing batch reactor (SBR) with alternating anaerobic-aerobic conditions. To provide anaerobic conditions, the mixed liquor is allowed to circulate in the reactor without air supply. The circulation flow rate of mixed liquor in anaerobic condition is the most important parameter of operation in the anaerobic-AGS processes. Therefore, this study investigates the effect of circulation rate on the performance of the SBR with AGS. Two identical reactors namely R1 and R2 were operated using fermented soy sauce wastewater at circulation rate of 14.4 and 36.0 l/h, respectively. During the anaerobic conditions, the wastewater was pumped out from the upper part of the reactor and circulated back into the bottom of the reactor for 230 min. A compact and dense AGS was observed in both reactors with a similar diameter of 2.0 mm in average, although different circulation rates were adopted. The best reactor performance was achieved in R2 with chemical oxygen demand removal rate of 89%, 90% total phosphorus removal, 79% ammonia removal, 10.1 g/l of mixed liquor suspended solids and a sludge volume index of 25 ml/g.

Performance and Microbial Community of Aerobic Granular Sludge Bioreactor

Aerobic granular sludge was cultivated from activated-sludge in sequencing batch reactor. The change of physical properties and the effect of treatment of organic substance and microbial community were studied in the process of the different influent organic loading rate. The results showed that the formation process of aerobic granulation was rapid but the granular sludge was not stable and existed a disintegration-reunion dynamic balance system. The value of MLSS descended from 5.12g/L to 1.03g/L. The removal efficiency of NH4+-N decreased to 74.17% and total phosphorous (TP) removal efficiency maintained beyond 90% all the while. The CODCr removal was over 85% which higher than that of after adding in methanol, then reduced but had trend of rise to 31.89% at last. Microbial species in granulation were speculated by detecting polyhydroxyalkan- oates between granular sludge and activated sludge in the reactor. The results showed that microbial species of activated sludge are more diverse.

Study on aerobic granular sludge formation in sequencing batch reactors for tapioca wastewater treatment

Aerobic granular sludge has attracted extensive interest of researchers since the 90s due to the advantages of aerobic granules such as good settling ability, high biomass accumulation, being resistant to high loads and being less affected by toxic substances. Studies, however, which have mainly been carried out on synthetic wastewater, cannot fully evaluate the actual ability of aerobic granules. Study on aerobic granular sludge was performed in sequencing batch reactors, using seeding sludge taken from anaerobic sludge and tapioca wastewater as a substrates. After 11 weeks of operation, the granules reached the stable diameter of 2- 3 mm at 3.7 kgCOD/m3.day organic loading rate. At high organic loads, in range of 1.6 - 5 kgCOD/m3.day, granules could treat effectively COD, N, P with performance of 93 – 97%; 65 – 79% and 80 – 95%, respectively.

Effects of Cu2+ on morphological structure, functional groups, and elemental composition of aerobic granular sludge

Aerobic granular sludge (AGS) is shaped by the self-immobilization of microorganisms. In this study, AGS was cultivated successively in a column sequencing batch reactor (SBR) with glucose and sodium acetate as the carbon sources. The shock-loading effects of varying the Cu2+ concentration (0.0, 1.0, 3.0, 5.0, or 10.0 mg/L) on the characteristics of aerobic granules were studied. The results show that Cu2+ has a toxic effect on the aerobic granules. Although the aerobic granules became increasingly loose as the Cu2+ concentration increased from 1.0 to 5.0 mg/L, their structural integrity was largely maintained. However, the aerobic granules disintegrated and their skeletons consisting of internal filamentous bacteria were exposed at the Cu2+ concentration of 10.0 mg/L. The functional groups ‒NH2, ‒OH, ‒COOH, and C‒N reacted with Cu2+. Ca, Fe, and P were the major trace elements observed in the AGS. With an increase in the Cu2+ concentration from 0.0 to 10.0 mg/L, the weight percentages of the essential elements Fe, Ca, Na, and K in the granules decreased from 23.98%, 24.64%, 3.86%, and 3.87% to 14.90%, 13.93%, 0%, and 0%, respectively, whereas the weight percentage of copper increased correspondingly from 0% to 35.43%. Cu2+ was exchanged with the essential metals and chelated by the nitrogen-containing functional groups (–NH2 or C‒N) of the protein. These effects influenced the structural stability of the sludge.

Aerobic granulation in a mechanical stirred SBR: treatment of low organic loads

Aerobic granular sludge was produced in a sequencing batch reactor (SBR) characterized by a height to diameter ratio of 2.5 and the use of mechanical stirring. Compact and regular aerobic granules of up to 1.75 mm of average diameter were formed in the reactor with an organic loading rate of 1.75 kg COD/(m3 d). Settling properties of the obtained aggregates were: sludge volumetric index of 30-40 mL/g VSS and settling velocity higher than 8 m/h. The effects of different carbon to nitrogen ratios (TOC/N) in the feeding on the organic matter oxidation and nitrification process were studied. The concentration of organic matter in the feeding was stepwise reduced (from 190.0 to 37.5 mg TOC/L) and ammonium increased (from 25 to 50 mg NH4+ -N/L). TOC/N ratios of 7.50, 3.00, 1.50 and 0.75 g/g in the feeding were tested. The TOC removal percentage was around 80-95% during the whole operational period and the N removal percentages obtained in the reactor were up to 40%, however, physical properties of the granules were not maintained.

Toxicity effect of phenol on aerobic granules

Aerobic granular sludge cultivated in a pilot‐scale sequencing batch reactor, through mechanical separation using metal sieves, was categorized into five size categories of 0.09 (flocs), 0.35, 0.82, 1.65 and 2.54 mm in mean diameter. Granule microbial activity of each size category and the activity of the sludge flocs were determined after exposure to phenol (0–3000 mg L−1) at various exposure times of 4, 12, and 24 hours. The microbial activity reduction follows a linear relationship with the increase in phenol concentration for both granules and sludge flocs. The C50 value, i.e. the phenol concentration causing 50% inhibition of the microbial activity, decreased significantly with the exposure time, but it increased with granule size. The C50 increased by 18% from 1273 mg L−1 for sludge flocs to 1497 mg L−1 for granules of size 2.54 mm at an exposure time of 24 hours. The results indicated that the granular structure could protect the microbial cells from phenol toxicity. The application of aerobic granules in wastewater treatment could provide an improved ability to tolerate toxic chemical shock, particularly at longer exposure times.

Cultivation of Aerobic Granules in A Sequential Batch Shaking Reactor

Aerobic granular sludge is a promising biotechnology for wastewater treatment system. In this report, aerobic granular sludge was successfully cultivated in a sequential batch shaking reactor in which horizontal circular flow could be formed by shaking. In this way, granulation and aeration could be simultaneously achieved. In comparison with sequential batch airlift reactor, more homogeneous circular flow was formed in the sequential batch shaking reactor. The aerobic granules obtained in the reactor were smooth, 1.2 mm in average diameter, and had a settling velocity of 50-52 m h-1. In addition, an increase in the hydrophobicity of the cell surface of granules indicated that granulation could be related to the change in cell hydrophobicity. Finally, microbial observation showed that rod-shape and coccoid bacteria were the dominant species in mature granules. Results of this study have important implications on the mechanism of the granulation process and further practical application.