Aims: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors. Methods and Results: A series of experiments were conducted in two column-type sequential aerobic sludge reactors fed with glucose and acetate as sole carbon source, respectively. The evolution of aerobic granulation was monitored using image analysis and optical and scanning electron microscopy. The results indicated that the formation of aerobic granules was a gradual process from seed sludge to compact aggregates, further to granular sludge and ®nally to mature granules with the sequential operation proceeding. Glucose-and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density and microbial activity. However, the microbial diversity of the granules was associated with the carbon source supplied. In this work, an important aerobic starvation phase was identi®ed during sequential operation cycles. It was found that periodical aerobic starvation was an effective trigger for microbial aggregation in the reactor and further strengthened cell±cell interaction to form dense aggregates, which was an essential step of granulation. The periodical starvation-induced aggregates would ®nally be shaped to granules by hydrodynamic shear and ow. Conclusions: Aerobic granules can be formed within 3 weeks in the systems. The periodical starvation and hydrodynamic conditions would play a crucial role in the granulation process. Signi®cance and Impact of the Study: Aerobic granules have excellent physical characteristics as compared with conventional activated sludge¯ocs. This research could be helpful for the development of an aerobic granule-based novel type of reactor for handling high strength organic wastewater.

Aims: This paper attempts to investigate the role of cellular polysaccharides in the formation and stability of aerobic granules. Methods and Results: Three column sequential aerobic sludge blanket reactors (R1, R2 and R3) were operated at a super®cial air up¯ow velocity of 0á3 cm s ±1 , 1á2 cm s ±1 and 2á4 cm s ±1 , respectively. Aerobic granules appeared at cycle 42 in R2 and R3 with a mean size of 0á37 mm in R2 and 0á35 mm in R3, however, aerobic granulation was not observed in R1. After the formation of aerobic granules, the sludge volume index (SVI) decreased to 55 ml g ±1 in R2 and 46 ml g ±1 in R3. Aerobic granulation was concurrent with a sharp increase of cellular polysaccharides normalized to cellular proteins, which increased from 5á7 to 13á0 mg per mg proteins in R2, and 7á5±13á9 mg per mg protein in R3. The content of polysaccharides in aerobic granules was 2±3 times higher than that in the bio¯occi cultivated in R1. The disappearance of aerobic granules in R2 was tightly coupled to a drop in cellular polysaccharides. After the reappearance of bio¯occi in R2, the content of cellular polysaccharides were found to be restored to the level observed in R1.Conclusions: It appears that the production of cellular polysaccharides could be stimulated by hydrodynamic shear force and contributes to the formation and stability of aerobic granules. Signi®cance and Impact of the Study: It is expected that this study would provide useful information for better understanding the mechanisms of aerobic granulation.

The development of aerobic granules was studied in four column-type sequential aerobic sludge blanket reactors fed with different substrate concentrations ranging from 500 to 3000 mg l(-1) COD. Results showed that aerobic granules successfully formed in all reactors fed with different substrate concentrations, indicating that the formation of aerobic granules is independent of the substrate concentration. The granule size, roundness, compactness, physical strength, as well as cell surface hydrophobicity and cell polysaccharides contents of the cultivated aerobic granules were investigated. It was shown that aerobic granules formed with different substrate concentrations had similar roundness and compactness. However, the size of aerobic granules slightly increased with an increase in substrate concentration, while granule strength decreased with substrate concentration. It was found that there was a significant increase in cell surface hydrophobicity and cell polysaccharides of the aerobic granules compared to that of seed sludge. The high cell surface hydrophobicity and high cell polysaccharides contents were believed to play an important role in the formation of aerobic granules. However, substrate concentration seems not to be a governing factor for the formation of aerobic granules. The results of this study would be useful for developing aerobic granules-based bioreactor and for better understanding of the mechanism of aerobic granulation. It was also clearly demonstrated that aerobic granules-based bioreactor would have great potential in the treatment of high-strength wastewater.

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Aerobic granulation was studied in a column-type of sequential sludge blanket reactor. Reactor was operated 4 hours per cycle under a chemical oxygen demand (COD) loading rate of 6.0 kg/m3/d by using acetate as substrate. Results showed that aerobic granules with a mean diameter of 0.35 mm were observed at cycle 42. With granulation proceeding, the sludge volume index (SVI) value gradually decreased, and to an average value of 50 mL/g at stable granulation period. Observation of granules' microstructure by scanning electron microscopy (SEM) showed that rod bacteria were dominant in granules with lots of cavities presented. An increase in cell hydrophobicity was observed after the appearance of aerobic granules. The cell hydrophobicity of sludge was found to be about 50% higher after granulation. It appears that high hydrophobicity could induce cell attachment and further strengthen cell-cell interaction; cell hydrophobicity might therefore play a major role in the formation of aerobic granules.

Aims: This paper attempts to develop a kinetic model to describe the growth of aerobic granules developed under different operation conditions. Methods and Results: A series of experiments were conducted by using four-column sequencing batch reactors to study the formation of aerobic granules under different conditions, e.g. organic loading rates, hydrodynamic shear forces and substrate N/COD ratios. A simple kinetic model based on the Linear Phenomenological Equation was successfully derived to describe the growth of aerobic granules. It was found that the growth of aerobic granules in terms of equilibrium size and size-dependent growth rate were inversely related to shear force imposed to microbial community, while a high organic loading favoured the growth of aerobic granules, leading to a large size granule. The effect of substrate N/COD ratio on the growth kinetics of aerobic granules was realized through change in microbial populations, and enriched nitrifying population in aerobic granules developed at high substrate N/COD ratio resulted in a low overall growth rate of aerobic granules. Conclusions: The proposed model can provide good prediction for the growth of aerobic granules indicated by the correlation coefficient >0AE95. Significance and Impact of the Study: The kinetic model proposed could offer a useful tool for studying the growth kinetics of cell-to-cell immobilization process. The study confirmed that the growth of aerobic granules and biofilms are subject to a similar kinetic pattern. This work would also be helpful for better understanding the mechanism of aerobic granulation.

Aims: To investigate the size effect of aerobic granules on mass transfer efficiency by introducing the effective factor and the modified Thiele modulus. Methods and Results: Batch experiments of aerobic granules with different sizes were conducted to study the size effect of granules on mass transfer resistance. Results showed that both specific substrate removal and biomass growth rates were size dependent, i.e. reduced rates were observed at big sizes. It was found that the diffusion resistance described by the effective factor and the Thiele modulus increased with the increase of the size of aerobic granules.Conclusions: The effective factor should be controlled at values higher than 0AE44 and the Thiele modulus lower than 1AE05 for efficient mass transfer in aerobic granules. Significance and Impact of the Study: Based on the coupled effective factor and Thiele modulus, an operation guidance including granule radius, kinetics of biomass and environmental conditions could be proposed for stable aerobic granulation.

Coke breeze and anthracite are the traditional heat suppliers to iron and steel industry while global warming issue has been a focus of concern. Using biomass for partial or complete replacement of coke breeze in the iron ore sintering process is an attractive technique for reducing emissions of greenhouse gas and gaseous pollutants. However, short supply of charred wood and low sinter quality for raw biomass are the biggest constraints for wide application in sinter production at present. In this paper, the commercial charcoal made from sawdust, nutshell and some other waste biomass (with extensive source and low cost) was employed as the alternative fuel in the sintering process. The primary fuel was coke breeze with 20%, 40%, 60%, 80% and 100% substitution of the fixed carbon input with