Qi-Shan Liu

Microscopic observation of aerobic granulation in sequential aerobic sludge blanket reactor

Aims: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors.

The role of cellular polysaccharides in the formation and stability of aerobic granules

Aims: This paper attempts to investigate the role of cellular polysaccharides in the formation and stability of aerobic granules.

Characteristics of aerobic granules grown on glucose and acetate in sequential aerobic sludge blanket reactors.

Aerobic granules were cultivated in two column-type sequential aerobic sludge blanket reactors fed with glucose and acetate, respectively. The characteristics of aerobic granules were investigated. Results indicated that the glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density, hydrophobicity, physical strength, microbial activity and storage stability. Substrate component does not seem to be a key factor on the formation of aerobic granules. However, microbial diversity of the granules is closely associated with the carbon sources supplied to the reactors. Compared with the conventional activated sludge flocs, aerobic granules exhibit excellent physical characteristics that would be essential for industrial application. This research provides a complete set of characteristics data of aerobic granules grown on glucose and acetate, which would be useful for further development of aerobic granules-based compact bioreactor for handling high strength organic wastewater.

Substrate concentration‐independent aerobic granulation in sequential aerobic sludge blanket reactor

Abstract 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.

The Role of Cell Hydrophobicity in the Formation of Aerobic Granules

Cell hydrophobicity is an important affinity force in cell self-immobilization and attachment processes. The role of cell hydrophobicity in the formation of aerobic granules has not been clear. Therefore, two series of experiments were conducted to investigate the role of cell hydrophobicity in the formation of aerobic heterotrophic and nitrifying granules in sequencing batch reactors, while the effects of shear strength, hydraulic selection pressure, and organic loading rate on the cell hydrophobicity were also studied. Results showed that the formations of heterotrophic and nitrifying granules were associated very closely with the cell hydrophobicity. The hydrophobicity of granular sludge was nearly twofold higher than that of conventional bioflocs. A high shear force or hydraulic selection pressure imposed on microorganisms resulted in a significant increase in the cell hydrophobicity, while the cell hydrophobicity seemed not to be sensitive to the changes in the organic loading rates in the range studied. In conclusion, the cell hydrophobicity could induce and further strengthen cell–cell interaction, and might be a main triggering force to initiate the granulation of heterotrophic and nitrifying bacteria.

Growth kinetics of aerobic granules developed in sequencing batch reactors

Aims:  This paper attempts to develop a kinetic model to describe the growth of aerobic granules developed under different operation conditions.

Biomass and porosity profiles in microbial granules used for aerobic wastewater treatment.

Aims: To obtain biomass and porosity profiles for aerobically grown granules of different diameters and to determine a suitable range of granule diameters for application in wastewater treatment.

Startup of Pilot-Scale Aerobic Granular Sludge Reactor by Stored Granules

The startup of a pilot-scale aerobic granular sludge reactor was investigated by seeding with 4-month stored aerobic granules. Two liters of granules were inoculated into the reactor (5.9% of reactor volume), which gave a biomass concentration of 1.03 g l−1. Experimental results showed that seeding granules could be successfully maintained in the reactor. The microbial activity of seeding granules could be fully recovered to that of fresh granules after 2 days of operation, and new granules started to grow after day 5. Newly developed aerobic granules at stable period had similar size and morphology as seeding granules, and a biomass concentration of 6.0 g l−1 was achieved in the reactor. The experiment demonstrated for the first time that stored aerobic granules could be used for easy and quick startup of aerobic granular sludge reactor.