Shu-Fang Yang

Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetowns model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.

A general model for biosorption of Cd2+, Cu2+ and Zn2+ by aerobic granules

Aerobic granules are microbial aggregates with a strong and compact structure. This study looked into the feasibility of aerobic granules as a novel type of biosorbent for the removal of individual Cd(2+), Cu(2+) and Zn(2+) from aqueous solution. Based on the thermodynamics of biosorption reaction, a general model was developed to describe the equilibrium biosorption of individual Cd(2+), Cu(2+) and Zn(2+) by aerobic granules. This model provides good insights into the thermodynamic mechanisms of biosorption of heavy metals. The model prediction was in good agreement with the experimental data obtained. It was further demonstrated that the Langmuir, Freundlich and Sips or Hill equations were particular cases of the proposed model. The biosorption capacity of individual Cd(2+), Cu(2+) and Zn(2+) on aerobic granules was 172.7, 59.6 and 164.5 mgg(-1), respectively. These values may imply that aerobic granules are effective biosorbent for the removal of Cd(2+), Cu(2+) and Zn(2+) from industrial wastewater.

Biosorption kinetics of cadmium(II) on aerobic granular sludge

Aerobic granules have excellent settle ability and high-porosity structure. This study investigated the feasibility of aerobic granules as a novel type of biosorbent, for cadmium removal from industrial wastewater. Batch tests were carried out at different initial Cd2+ and granule concentrations. Based on experimental data, a kinetic model was developed to describe Cd2+ biosorption by aerobic granules. Results showed that the Cd2+ biosorption on aerobic granule surface was closely related to both initial Cd2+ and granule concentrations. The maximum biosorption capacity of Cd2+ by aerobic granules was 566 mg/g. This study for the first time shows that aerobic granules have a high biosorption capacity to Cd2+ and can be used as an effective biosorbent for the removal of cadmium or other types of heavy metals from industrial 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.

Elemental compositions and characteristics of aerobic granules cultivated at different substrate N/C ratios

Abstract. The effects of the substrate N/C ratios on the formation, elemental compositions and characteristics of aerobic granules were investigated in four sequencing batch reactors. Results showed that aerobic granules could form at substrate N/C ratios ranging from 5/100 to 30/100 and the substrate N/C ratio had a direct and profound effect on the elemental compositions and characteristics of the aerobic granules. Nitrifying populations in aerobic granules were enriched significantly with the increase in the substrate N/C ratio, while the respective ratio of cell oxygen, nitrogen and calcium to cell carbon were also determined by the substrate N/C ratio. It was found that cell hydrophobicity of aerobic granules was inversely related to the ratio of cell oxygen normalized to cell carbon. Since the cell calcium content in aerobic granules developed at different substrate N/C ratios was even lower than that in the seed sludge, it is reasonable to conclude that the cell calcium would not contribute to aerobic granulation. This study probably for the first time demonstrates that the elemental composition, microbial distribution and characteristics of aerobic granules are related to the substrate N/C ratio applied.

Aerobic granules: a novel zinc biosorbent.

Aims: Aerobic granules are aggregates with a compact and porous microbial structure. In view of the potential use of aerobic granules as biosorbents for Zn(II) removal from industrial wastewater, this study investigated the effects of initial Zn(II) and aerobic granule concentrations on the kinetics of Zn(II) biosorption on the aerobic granule surface.

A balanced model for biofilms developed at different growth and detachment forces

Abstract In a steady state biofilm culture, dissolved organic carbon (DOC) distribution between catabolism and anabolism can be described by a ratio of the DOC channeled into carbon dioxide ( S CO2 ) to the DOC converted into biomass ( S g ). Based on a balanced oxidative reaction of DOC, a S CO2 / S g -dependent observed growth yield ( Y obs ) model was developed for biofilm culture and was verified with literature data. Growth and detachment forces are two decisive factors in biofilm process. The detachment force ( D f ) normalized with respect to the growth force ( G f ) was introduced to describe the interaction between the biofilm growth and detachment processes. Biofilm metabolism and structure were closely related to the D f / G f -ratio, and biofilm community could metabolically respond to changes in growth and detachment forces. A proper balance between growth and detachment forces is crucial for development of a compact and stable biofilm. The proposed D f / G f concept provides a theoretical basis for experimental data obtained at different growth and detachment forces to be interpreted in a unified sense. Biofilm structure may be manipulated by controlling the D f / G f ratio.

Respirometric activities of heterotrophic and nitrifying populations in aerobic granules developed at different substrate N/COD ratios.

Aerobic granules were successfully developed at substrate N/COD ratios ranging from 5/100 to 30/100 by weight. By measuring respective respirometric activities of heterotrophic, ammonia-oxidizing, and nitrite-oxidizing bacteria, it was found that the relative abundance of nitrifying bacteria over heterotrophs in aerobic granules was closely related to the substrate N/COD ratios. Results further showed that the populations of both ammonia and nitrite oxidizers were significantly enriched with the increase of the substrate N/COD ratio, while a decreasing trend of heterotrophic population was observed in the aerobic granules. These seem to indicate that high substrate N/COD ratio favors the selection of nitrifying bacteria in the aerobic granules, while the relative activity of nitrifying population against heterotrophic population evolved until a balance between two populations was reached in the aerobic granular sludge community. Moreover, cell elemental composition was correlated with the shift in microbial populations, e.g., the enriched nitrifying population in the aerobic granules resulted in a high cell nitrogen content normalized to cell carbon content. This study provides a good insight into microbial interaction in aerobic granules.

A thermodynamic interpretation of cell hydrophobicity in aerobic granulation

Abstract Aerobic granulation can be regarded as a microorganism-to-microorganism self-immobilization process, in which cell hydrophobicity could be a decisive parameter in determining the microorganism-to-microorganism interaction and structural compactness of aerobic granules. This study looked into the thermodynamic interpretation of cell hydrophobicity in aerobic granulation; and a model that correlates microbial interaction and relative cell hydrophobicity defined as the ratio of cell hydrophobicity over cell hydrophilicity was derived. This model describes how cell hydrophobic and hydrophilic interactions affect aerobic granulation and offers deep insights into the thermodynamic mechanisms of microbial aggregation. The model prediction was in good agreement with experimental data. Results showed that aerobic granulation was a function of cell hydrophobicity over cell hydrophilicity, i.e. a high cell hydrophobicity strongly favors microbial aggregation and results in a more compact structure.