Stephen Tiong-Lee Tay

High organic loading influences the physical characteristics of aerobic sludge granules

Aims: The effect of high organic loading rate (OLR) on the physical characteristics of aerobic granules was studied.

Aggregation of immobilized activated sludge cells into aerobically grown microbial granules for the aerobic biodegradation of phenol

Aims: The aim of this study is to evaluate the utility of aerobically grown microbial granules for the biological treatment of phenol‐containing wastewater.

Presence of Anaerobic Bacteroides in Aerobically Grown Microbial Granules

Microbial granules were grown in a column-type sequential aerobic sludge blanket reactor inoculated with activated sludge flocs taken from a wastewater treatment plant and containing a medium with glucose as the main carbon source. The reactor selected for granules that could settle rapidly by employing a short settling time of 2 min. Matured granules with diameters between 2 and 3 mm were examined for anaerobic bacteria as their presence can signal the onset of diffusion limitation problems that can potentially diminish granule stability due to the bacterial production of fermentation gases and organic acids under anaerobic conditions. To detect the anaerobes in the granules, clones were constructed from 16S rRNA PCR amplicons. Two sequence types associated with a strict anaerobe Bacteroides spp. were identified from these clones. Fluorescence in situ hybridization (FISH) followed by confocal laser scanning microscopy (CLSM) demonstrated that cells of Bacteroides spp. were concentrated at a depth of approximately 800 mm below the surface of the granule. Cell enumeration using flow cytometry showed that the percentage of labeled cells of Bacteroides spp. compared to total bacterial cells in the granules was 0.56%. This is the first study to use a suite of culture-independent techniques to report the presence of a defined species of anaerobic bacteria in aerobically grown microbial granules.

Bacterial Diversity and Function of Aerobic Granules Engineered in a Sequencing Batch Reactor for Phenol Degradation

ABSTRACT Aerobic granules are self-immobilized aggregates of microorganisms and represent a relatively new form of cell immobilization developed for biological wastewater treatment. In this study, both culture-based and culture-independent techniques were used to investigate the bacterial diversity and function in aerobic phenol- degrading granules cultivated in a sequencing batch reactor. Denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rRNA genes demonstrated a major shift in the microbial community as the seed sludge developed into granules. Culture isolation and DGGE assays confirmed the dominance of β-Proteobacteria and high-G+C gram-positive bacteria in the phenol-degrading aerobic granules. Of the 10 phenol-degrading bacterial strains isolated from the granules, strains PG-01, PG-02, and PG-08 possessed 16S rRNA gene sequences that matched the partial sequences of dominant bands in the DGGE fingerprint belonging to the aerobic granules. The numerical dominance of strain PG-01 was confirmed by isolation, DGGE, and in situ hybridization with a strain-specific probe, and key physiological traits possessed by PG-01 that allowed it to outcompete and dominate other microorganisms within the granules were then identified. This strain could be regarded as a functionally dominant strain and may have contributed significantly to phenol degradation in the granules. On the other hand, strain PG-08 had low specific growth rate and low phenol degradation ability but showed a high propensity to autoaggregate. By analyzing the roles played by these two isolates within the aerobic granules, a functional model of the microbial community within the aerobic granules was proposed. This model has important implications for rationalizing the engineering of ecological systems.

Specific layers in aerobically grown microbial granules

Aims: To determine the optimal size of aerobically grown granules for wastewater treatment by measuring specific layers within the granules.

Importance of Gram-positive naphthalene-degrading bacteria in oil-contaminated tropical marine sediments

Aims: The aim of this study was to isolate, characterize and evaluate the importance of naphthalene‐degrading bacterial strains from oil‐contaminated tropical marine sediments.

Comparing activated sludge and aerobic granules as microbial inocula for phenol biodegradation

Activated sludge and acetate-fed granules were used as microbial inocula to start up two sequencing batch reactors (R1, R2) for phenol biodegradation. The reactors were operated in 4-h cycles at a phenol loading of 1.8 kg m−3 day−1. The biomass in R1 failed to remove phenol and completely washed out after 4 days. R2 experienced initial difficulty in removing phenol, but the biomass acclimated quickly and effluent phenol concentrations declined to 0.3 mg l−1 from day 3. The acetate-fed granules were covered with bacterial rods, but filamentous bacteria with sheaths, presumably to shield against toxicity, quickly emerged as the dominant morphotype upon phenol exposure. Bacterial adaptation to phenol also took the form of modifications in enzyme activity and increased production of extracellular polymers. 16S rRNA gene fingerprints revealed a slight decrease in bacterial diversity from day 0 to day 3 in R1, prior to process failure. In R2, a clear shift in community structure was observed as the seed evolved into phenol-degrading granules without losing species-richness. The results highlight the effectiveness of granules over activated sludge as seed for reactors treating toxic wastewaters.

Phosphate removal from the returned liquor of municipal wastewater treatment plant using iron‐reducing bacteria

Aim:  The application of iron‐reducing bacteria (IRB) to phosphate removal from returned liquor (liquid fraction after activated sludge digestion and anaerobic sludge dewatering) of municipal wastewater treatment plant (WWTP) was studied.

The effect of hydraulic retention time on the stability of aerobically grown microbial granules

Aims:  The aim of this study is to evaluate the effect of hydraulic retention time (HRT) on the development of aerobically grown microbial granules.

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.