Juin-Yih Lai

Potential cause of aerobic granular sludge breakdown at high organic loading rates

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors operated under OLR of 9–21.3xa0kg chemical oxygen demand (COD) m−3 day−1. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5xa0kg COD m−3 day−1, and disintegrated at OLR of 21.3xa0kg COD m−3 day−1. Most tested isolates did not grow in the medium at >3,000xa0mg COD l−1; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of biological nature for aerobic granules breakdown.

Influence of Internal Biofilm Growth on Residual Permeability Loss in Aerobic Granular Membrane Bioreactors

Membrane fouling results in flux decline or transmembrane pressure drop increase during membrane bioreactor (MBR) operation. Physical and chemical cleanings are essential to keep an MBR operating at an appropriate membrane flux. Considerable residual membrane permeability loss that cannot be removed by conventional cleaning requires membrane replacement. This study demonstrates that an internal biofilm can develop inside a hollow-fiber membrane and can probably account for up to 58.9 and 81.3% of total membrane resistance for aerobic granular MBR operated in sequencing batch reactor (SBR) mode or continuous-fed mode, respectively. The Arthrobacter sp. (accession no. AM900505 in GenBank) corresponded to internal biofilm development by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis and the agar-plating technique. This study also identifies a single strain, Arthrobacter sp., generates the internal biofilm. The Arthrobacter sp. is a rod-shaped bacterium with a size close to that of membrane pores, and can secrete excess bound proteins, hence can penetrate and attach itself inside the membrane and grow. Internal biofilm growth could contribute significantly to membrane resistance during long-term MBR operation.

Aerobic granules with inhibitory strains and role of extracellular polymeric substances.

Microorganisms compete with other species by secreting antimicrobial compounds. The compact structure of aerobic granules was generally assumed to provide spatial isolation, resulting in the co-occurrence of diverse strains that have similar or dissimilar functions. No studies have investigated whether stable, mature aerobic granules can be formed with two mutually inhibitory strains. The strain Acinetobacter sp. I8 competes with Bacillus sphaericus I5 in a well-mixed environment, but can form stable and mature granules at 400 mg L(-1) phenol by repeatedly replenishing fresh medium in a sequencing batch reactor. The supernatants collected from the I8 medium in its exponential-growth phase or from the I5+I8 medium cultivated for 12 or 24h significantly inhibited I5 growth. Addition of tightly bound extracellular polymeric substances (TBEPS) or loosely bound extracellular polymeric substances (LBEPS) extracted from I5+I8 granules effectively suppressed the inhibitory effects of I8 on I5. The TBEPS or LBEPS physically separate strain I5 from I8 in the granule, and effectively adsorb the inhibitory substance(s) in the suspension.

Fouling with aerobic granule membrane bioreactor.

Aerobic granulation (AG) and membrane bioreactor (MBR) are two promising, novel environmental biotechnological processes that draw interest of researchers working in the area of biological wastewater treatment. Membrane fouling in the combined aerobic granular membrane bioreactor (AGMBR) process and the conventional MBR process was investigated in this work. The irreversible fouling on hollow-fibre membranes in both reactors were observed with the multiple staining and confocal laser scanning microscope technique. Following physical and chemical washing, the external fouling layers were mostly removed. However, the biofilms built up in the interior surface of membrane remained and contributed to the irreversible fouling resistance. AGMBR retained most cells with granules, thereby reducing their penetration through membrane and thus the chance to form internal fouling layer. The internal biofilm layer was principally composed of live cells embedded in a matrix of proteins and polysaccharides, with that on AGMBR denser and thicker than that on MBR. Prevention of development of internal biofilm is essential to reduce irreversible fouling of AGMBR and MBR membranes.

Biodiversity in aerobic granule membrane bioreactor at high organic loading rates.

The aerobic granular sludge process and the membrane bioreactor process are promising, novel environmental bioprocesses for the reclamation of industrial and municipal wastewaters. They are practical and have attracted much research interest. The combination of these two processes in the aerobic granular membrane bioreactor (AGMBR), yields reclaimed water of high quality in a compact reactor. Information on the microbial community in an AGMBR operated at a high organic loading rate is lacking. This study elucidates the microbial dynamics in acetate-fed AGMBR operated in sequencing batch reactor mode. The structure of the microbial community revealed by denaturing gradient gel electrophoresis, demonstrates the dominance of the denitrifying microbial community, which is affiliated with members of the families Comamonadaceae and Alcaligenaceae, of the class Betaproteobacteria. The role of the predominant strains in the AGMBR is discussed.

Pre-Treatment of Natural Organic Matters Containing Raw Water using Coagulation

Coagulation is a commonly adopted process as a pretreatment step for minimizing membrane fouling. Three coagulants, polyaluminum chloride (PACl), alum, and FeCl3 were tested under four mixing-settling schemes for turbidity and natural organic matters (NOM) removal. The organic matters in the raw waters were fractionated by high performance size exclusion chromatography (HP-SEC) system and were characterized using the excitation-emission matrix (EEM) fluorescence spectra. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit turbidity removal using PACl or FeCl3 under “electrostatic patch coagulation” (EPC) mechanism. The EPC mechanism is not efficient for alum coagulation. At higher coagulant doses, the NOM removal is not affected by mixing condition. Intensive rapid mixing alone benefits NOM removal using PACl or FeCl3. Alum is a poor coagulant for NOM removal under EPC mechanism.

Oxygen Diffusion in Single Sludge Floc

Sludge flocs are bioreactors that degrade organic matters with oxygen. The oxygen transfer rate from bulk solution to sludge floc presents an essential factor determining the efficiency of the adopted process. For the first time, this work quantitatively estimateds the oxygen inflow to a single sludge floc.

Visualizing Fouling Layer in Membrane Bioreactor

The membrane fouling layer in the combined aerobic granular membrane bioreactor (AGMBR) process and the conventional MBR process was probed in this study using the multiple staining and confocal laser scanning microscope (CLSM) technique. The fouling layer built up outside and inside the membrane was principally composed of live cells embedded in a matrix of proteins and polysaccharides. The fouling layer presented outside the membrane is noted denser in structure than that inside the membrane.