Presence of anaerobic bacteroides in aerobically grown microbial granules

A comprehensive comparison of microbial communities between aerobic granular sludge and flocculent sludge for nutrient removal in full-scale wastewater treatment plants

Understanding the microbial community structure of sludge is crucial for improving the design, operation and optimisation of full-scale wastewater treatment plants (WWTPs). This study aimed to have a comprehensive comparison of microbial communities between aerobic granular sludge and flocculent sludge from two full-scale sequential batch reactors-based WWTPs with nutrient removal for the first time. To better understand key functional bacteria such as polyphosphate accumulating bacteria (PAOs), competitive bacteria such as glycogen accumulating bacteria (GAOs) and nitrifying bacteria for both nitrogen and phosphorus removal, another two full-scale WWTPs with only carbon (C) removal and C and nitrogen (N) removal were compared too. It was found that the richness and diversity of the microbial population in sludge increased with pollutant removal from only C, C and N, to C,N, P removal. For C, N P removal, granule structure led to a more diverse and rich microbial community structure than flocculent structure. Although more abundant nitrifying bacteria were enriched in granular sludge than flocculent sludge, the abundance of total putative PAOs was equivalent. However, the most typical putative PAOs such as Tetrasphaera and Candidatus Accumulibacter seemed to be more correlated with biological phosphorus removal performance, which might be more proper to be used as an indication for P removal potential. The higher abundance of GAOs in flocculent sludge with better phosphorus removal performance might suggest that further investigation is needed to understand the functions of GAOs. In addition, the equivalent abundances of PAOs in the WWTPs with only C removal and with C, N, and P removal, respectively, indicate that many newly reported putative PAOs might not contribute to P removal. This study provides insight into the microbial communities and functional bacteria in aerobic granular sludge and flocculent sludge in full-scale SBRs, which can provide microbes-informed optimisation of reactor operation for better nutrient removal.

Impact of nitrite and oxygen on nitrous oxide emissions from a granular sludge sequencing batch reactor

Maximizing nutrient removal and minimizing greenhouse gas (GHG) emissions is imperative for the future of wastewater treatment. As municipalities focus on minimizing their carbon footprints, future permits could regulate GHG emissions from wastewater treatment plants. This study investigates how nitrous oxide (N₂O) emissions are affected by dissolved oxygen and nitrite concentrations, providing potential strategies to meet possible gaseous emission permits. A lab-scale sequencing batch reactor (SBR) was enriched with aerobic granular sludge (AGS) capable of phosphate removal and simultaneous nitrification-denitrification (SND). N₂O emissions were tracked at varying dissolved oxygen (DO) and nitrite (NO₂^-) concentrations, with >99% SND efficiency and 93%-100% phosphate removal efficiency. Higher DO and NO₂^- concentrations were associated with higher N₂O emissions. Emissions were minimized at a DO concentration of 1 mg L^-1, with an average emission factor of 0.18% of oxidized NH₃-N emitted as N₂O-N, which is lower than factors from many full-scale treatment plants (Vasilaki et al., 2019) and similar to a Nereda® full-scale AGS SBR (van Dijk et al., 2021). This challenges assertions that AGS emits more N₂O than conventional activated sludge, although more research at full-scale with influent quality variations is required to confirm this trend. Molecular analyses revealed that the efficient SND was likely achieved with shortcut nitrogen removal facilitated by a low presence of nitrite oxidizing bacteria and a large population of denitrifying phosphate accumulating organisms, which far outnumbered denitrifying glycogen accumulating organisms.

Response of a Coastal Microbial Community to Olivine Addition in the Muping Marine Ranch, Yantai

Spreading olivine powder in seawater to enhance alkalinity through weathering reactions has been proposed as a potential solution to control atmospheric CO₂ concentration. Attention has usually been paid to the chemical properties of seawater after the addition of olivine within lab and modeling studies. However, both microbial acclimation and evolution in such manipulated natural environments are often overlooked, yet they are of great importance for understanding the biological consequences of whether olivine addition is a feasible approach to mitigating climate change. In this study, an olivine addition experiment was conducted to investigate variation in bacterial diversity and community composition in the surface and bottom seawater of a representative marine ranch area in the Muping, Yantai. The results show that the composition of the particle-attached microbial community was particularly affected by the application of olivine. The relative abundance of biofilm-forming microbes in particle-attached fraction increased after the addition of olivine, while no significant variation in the free-living bacterial community was observed. Our study suggests that olivine addition would reshape the bacterial community structure, especially in particle-attached microenvironments. Therefore, the risk evaluation of alkalinity enhancement should be further studied before its large-scale application as a potential ocean geoengineering plan.

Flow cytometry applications in water treatment, distribution, and reuse: A review

Ensuring safe and effective water treatment, distribution, and reuse requires robust methods for characterizing and monitoring waterborne microbes. Methods widely used today can be limited by low sensitivity, high labor and time requirements, susceptibility to interference from inhibitory compounds, and difficulties in distinguishing between viable and non-viable cells. Flow cytometry (FCM) has recently gained attention as an alternative approach that can overcome many of these challenges. This article critically and systematically reviews for the first time recent literature on applications of FCM in water treatment, distribution, and reuse. In the review, we identify and examine nearly 300 studies published from 2000 to 2018 that illustrate the benefits and challenges of using FCM for assessing source-water quality and impacts of treatment-plant discharge on receiving waters, wastewater treatment, drinking water treatment, and drinking water distribution. We then discuss options for combining FCM with other indicators of water quality and address several topics that cut across nearly all applications reviewed. Finally, we identify priority areas in which more work is needed to realize the full potential of this approach. These include optimizing protocols for FCM-based analysis of waterborne viruses, optimizing protocols for specifically detecting target pathogens, automating sample handling and preparation to enable real-time FCM, developing computational tools to assist data analysis, and improving standards for instrumentation, methods, and reporting requirements. We conclude that while more work is needed to realize the full potential of FCM in water treatment, distribution, and reuse, substantial progress has been made over the past two decades. There is now a sufficiently large body of research documenting successful applications of FCM that the approach could reasonably and realistically see widespread adoption as a routine method for water quality assessment.

Aerobic granular sludge and naphthenic acids treatment by varying initial concentrations and supplemental carbon concentrations

Aerobic granular sludge (AGS) has previously been utilized in the treatment of toxic compounds due to its diverse and dense microbial structure. The present study subjected mature AGS to model naphthenic acids (NAs) representative of the Canadian oil sands. To this effect, three NA concentrations (10, 50 and 100 mg/L) and three supplemental carbon source concentrations (600, 1200 and 2500 mg/L) were studied in batch reactors for 5 days. The responding variables were chemical oxygen demand (COD), NA concentrations and nutrients. Cyclohexane carboxylic acid (CHCA), cyclohexane acetic acid (CHAA) and 1-adamantane carboxylic acid (ACA) were chosen to study structure-based degradation kinetics. The optimal COD according to the runs was 1200 mg/L. CHCA was removed completely with biodegradation rate constants increasing with lower NA concentrations and lower COD concentrations. CHAA was also removed completely, however, an optimal rate constant of 1.9 d^-1 was achieved at NA and COD concentrations of 50 mg/L and 1200 mg/L, respectively. ACA removal trends did not follow statistically significant regressions; however, degradation and sorption helped remove ACA up to 19.9%. Pseudomonas, Acinetobacter, Hyphomonas and Brevundimonas spp. increased over time, indicating increased AGS adaptability to NAs.

Impact of food-to-microorganisms ratio on the stability of aerobic granular sludge treating high-strength organic wastewater

This work investigated the long-term stability of aerobic granular sludge treating high-strength organic wastewater in a semi-pilot scale sequential batch reactor (SBR). The reactor was operated for 316 days under different operational conditions. It was found that the F/M ratio is an important parameter affecting granules formation and stability. Three selection mechanisms were investigated: (1) cultivation and maturation at moderately high influent COD concentration (2500 mg/L) followed by increase in influent COD concentration to 7500 mg/L; (2) stressed cultivation and operation at high influent COD concentration of 4500 mg/L; and (3) alternate feed loading strategy (variable influent COD concentration across the daily schedule of cycles at 50%, 75%, and 100% of the peak concentration of 5000 mg/L). It was found that adopting high OLR at the reactor start-up accelerated the formation of granules. However, the overgrowth of biomass under high organics concentration negatively affected the stability of granules and led to disintegration due to the presence of methanogens in the granule core. Cultivation at high organics concentration resulted in a rapid loss of microbial diversity and reactor failure. Under alternate feed loading, adequate selection of microbial community was maintained and resulted in stable reactor performance. Moreover, a strong correlation between F/M ratio and the granules settling ability was observed. When F/M ratio exceeded 1.5 gCOD/gSS.d, granules showed poor settleability and under very high sludge loading rates (above 2.5), sludge bulking occurred and led to washout of sludge due to the strong selection pressure of short settling time. Operating the reactor at F/M ratio of 0.5-1.4 gCOD/gSS.d appears to favor stable long-term granule stability.

State of the art of aerobic granulation in continuous flow bioreactors

In the wake of the success of aerobic granulation in sequential batch reactors (SBRs) for treating wastewater, attention is beginning to turn to continuous flow applications. This is a necessary step given the advantages of continuous flow treatment processes and the fact that the majority of full-scale wastewater treatment plants across the world are operated with aeration tanks and clarifiers in a continuous flow mode. As in SBRs, applying a selection pressure, based on differences in either settling velocity or the size of the biomass, is essential for successful granulation in continuous flow reactors (CFRs). CFRs employed for aerobic granulation come in multiple configurations, each with their own means of achieving such a selection pressure. Other factors, such as bioaugmentation and hydraulic shear force, also contribute to aerobic granulation to some extent. Besides the formation of aerobic granules, long-term stability of aerobic granules is also a critical issue to be addressed. Inorganic precipitation, special inocula, and various operational optimization strategies have been used to improve granule long-term structural integrity. Accumulated studies reviewed in this work demonstrate that aerobic granulation in CFRs is capable of removing a wide spectrum of contaminants and achieving properties generally comparable to those in SBRs. Despite the notable research progress made toward successful aerobic granulation in lab-scale CFRs, to the best of our knowledge, there are only three full-scale tests of the technique, two being seeded with anammox-supported aerobic granules and the other with conventional aerobic granules; two other process alternatives are currently in development. Application of settling- or size-based selection pressures and feast/famine conditions are especially difficult to implement to these and similar mainstream systems. Future research efforts needs to be focused on the optimization of the granule-to-floc ratio, enhancement of granule activity, improvement of long-term granule stability, and a better understanding of aerobic granulation mechanisms in CFRs, especially in full-scale applications.

Understanding azo dye anaerobic bio-decolorization with artificial redox mediator supplement: Considering the methane production

Artificial redox mediators (ARM) have been proven to accelerate the azo dye anaerobic bio-reduction (ADAB) but the mechanisms involved are still unclear. Previous studies do seldom focus on the production of methane during the ADAB, particularly if supplemented with ARM. Our studies revealed that the supplement of ARM could significantly accelerate the decolorization rate, recover the inhibited methanogenesis and decrease extracellular polymeric substance secretion in an ADAB system. Supplement of an ARM only enhanced the pre-existing metabolic pathway of the ADAB system. Significant differences in metabolic pathway and microbial community were found between traditional methanogenic system and ADAB system by high-throughput sequencing technique. The ADAB system performed an "over-requirement for electron donor" phenomenon and the requirement amount can be altered by regulating ARM dosage. Response surface methodology was then successfully employed to optimize the dosage of ARM and possible additional electron donor required for ADAB under different conditions.

Drying and recovery of aerobic granules

To dehydrate aerobic granules to bone-dry form was proposed as a promising option for long-term storage of aerobic granules. This study cultivated aerobic granules with high proteins/polysaccharide ratio and then dried these granules using seven protocols: drying at 37°C, 60°C, 4°C, under sunlight, in dark, in a flowing air stream or in concentrated acetone solutions. All dried granules experienced volume shrinkage of over 80% without major structural breakdown. After three recovery batches, although with loss of part of the volatile suspended solids, all dried granules were restored most of their original size and organic matter degradation capabilities. The strains that can survive over the drying and storage periods were also identified. Once the granules were dried, they can be stored over long period of time, with minimal impact yielded by the applied drying protocols.

Effects of Predation by Protists on Prokaryotic Community Function, Structure, and Diversity in Anaerobic Granular Sludge

Predation by protists is top-down pressure that regulates prokaryotic abundance, community function, structure, and diversity in natural and artificial ecosystems. Although the effects of predation by protists have been studied in aerobic ecosystems, they are poorly understood in anoxic environments. We herein studied the influence of predation by Metopus and Caenomorpha ciliates—ciliates frequently found in anoxic ecosystems—on prokaryotic community function, structure, and diversity. Metopus and Caenomorpha ciliates were cocultivated with prokaryotic assemblages (i.e., anaerobic granular sludge) in an up-flow anaerobic sludge blanket (UASB) reactor for 171 d. Predation by these ciliates increased the methanogenic activities of granular sludge, which constituted 155% of those found in a UASB reactor without the ciliates (i.e., control reactor). Sequencing of 16S rRNA gene amplicons using Illumina MiSeq revealed that the prokaryotic community in the UASB reactor with the ciliates was more diverse than that in the control reactor; 2,885–3,190 and 2,387–2,426 operational taxonomic units (>97% sequence similarities), respectively. The effects of predation by protists in anaerobic engineered systems have mostly been overlooked, and our results show that the influence of predation by protists needs to be examined and considered in the future for a better understanding of prokaryotic community structure and function.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

Rheological and fractal hydrodynamics of aerobic granules

The structural and hydrodynamic features for granules were characterized using settling experiments, predefined mathematical simulations and ImageJ-particle analyses. This study describes the rheological characterization of these biologically immobilized aggregates under non-Newtonian flows. The second order dimensional analysis defined as D2=1.795 for native clusters and D2=1.099 for dewatered clusters and a characteristic three-dimensional fractal dimension of 2.46 depicts that these relatively porous and differentially permeable fractals had a structural configuration in close proximity with that described for a compact sphere formed via cluster-cluster aggregation. The three-dimensional fractal dimension calculated via settling-fractal correlation, U∝l(D) to characterize immobilized granules validates the quantitative measurements used for describing its structural integrity and aggregate complexity. These results suggest that scaling relationships based on fractal geometry are vital for quantifying the effects of different laminar conditions on the aggregates' morphology and characteristics such as density, porosity, and projected surface area.

Effect of TiO2 nanoparticles on aerobic granulation of algal-bacterial symbiosis system and nutrients removal from synthetic wastewater

The influence of TiO2 nanoparticles (TiO2-NPs) (10-50mg/L) on aerobic granulation of algal-bacterial symbiosis system was investigated by using two identical sequencing batch reactors (SBRs). Although little adverse effect was observed on their nitritation efficiency (98-100% in both reactors), algal-bacterial granules in the control SBR (Rc) gradually lost stability mainly brought about by algae growth. TiO2-NPs addition to RT was found to enhance the granulation process achieving stable and compact algal-bacterial granules with remarkably improved nitratation thus little nitrite accumulation in RT when influent TiO2-NPs⩾30mg/L. Despite almost similar organics and phosphorus removals obtained in both reactors, the stably high nitratation efficiency in addition to much stable granular structure in RT suggests that TiO2-NPs addition might be a promising remedy for the long-term operation of algal-bacterial granular system, most probably attributable to the stimulated excretion of extracellular polymeric substances and less filamentous TM7.

Characterization of the bacterial communities of aerobic granules in a 2-fluorophenol degrading process

Aerobic granular sludge constitutes a novel technology for wastewater treatment. This study focused on the effect of 2-fluorophenol (2-FP) shock loadings on the microbial community diversity present in aerobic granules before and after inoculation with a bacterial strain able to degrade 2-FP, Rhodococcus sp. strain FP1. After bioaugmentation, apart from strain FP1, five culturable bacteria were isolated from the 2-FP degrading granules, belonging to the following genera: Serratia, Chryseobacterium, Xanthomonas, Pimelobacter and Rhodococcus. The latter two isolates are able to degrade 2-FP. Changes in the aerobic granules' bacterial communities related to 2-FP shock loadings were examined using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene pool. Numerical analysis of the DGGE profiles showed high diversity with an even distribution of species. Based on cluster analysis of the DGGE profiles, the bacterial communities present in the aerobic granules changes were related to the sampling time and the 2-FP concentration fed.

Treatment of domestic wastewater with an anaerobic ceramic membrane bioreactor (AnCMBR)

In this study, a ceramic membrane with a pore size of 80 nm was incorporated into an anaerobic membrane bioreactor for excellent stability and integrity. Chemical oxygen demand (COD) removal efficiencies by biodegradation reached 78.6 ± 6.0% with mixed liquor suspended solids (MLSS) of 12.8 ± 1.2 g/L. Even though the total methane generated was 0.3 ± 0.03 L/g CODutilized, around 67.4% of it dissolved in permeate and was lost beyond collection. As a result, dissolved methane was 2.7 times of the theoretical saturating concentration calculated from Henry's law. When transmembrane pressure (TMP) of the ceramic membrane reached 30 kPa after 25.3 d, 95.2% of the total resistance was attributed to the cake layer, which made it the major contributor to membrane fouling. Compared to the mixed liquor, cake layer was rich in colloids and soluble products that could bind the solids to form a dense cake layer. The Methanosarcinaceae family preferred to attach to the ceramic membranes.

Aerobic sludge granulation in a full-scale sequencing batch reactor

Aerobic granulation of activated sludge was successfully achieved in a full-scale sequencing batch reactor (SBR) with 50,000 m(3) d(-1) for treating a town's wastewater. After operation for 337 days, in this full-scale SBR, aerobic granules with an average SVI30 of 47.1 mL g(-1), diameter of 0.5 mm, and settling velocity of 42 m h(-1) were obtained. Compared to an anaerobic/oxic plug flow (A/O) reactor and an oxidation ditch (OD) being operated in this wastewater treatment plant, the sludge from full-scale SBR has more compact structure and excellent settling ability. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that Flavobacterium sp., uncultured beta proteobacterium, uncultured Aquabacterium sp., and uncultured Leptothrix sp. were just dominant in SBR, whereas uncultured bacteroidetes were only found in A/O and OD. Three kinds of sludge had a high content of protein in extracellular polymeric substances (EPS). X-ray fluorescence (XRF) analysis revealed that metal ions and some inorganics from raw wastewater precipitated in sludge acted as core to enhance granulation. Raw wastewater characteristics had a positive effect on the granule formation, but the SBR mode operating with periodic feast-famine, shorter settling time, and no return sludge pump played a crucial role in aerobic sludge granulation.

Recovery of stored aerobic granular sludge and its contaminants removal efficiency under different operation conditions

The quick recovery process of contaminants removal of aerobic granular sludge (AGS) is complex, and the influencing factors are still not clear. The effects of dissolved oxygen (DO, air intensive aeration rate), organic loading rate (OLR), and C/N on contaminants removal characteristics of AGS and subsequently long-term operation of AGS bioreactor were investigated in this study. DO had a major impact on the recovery of AGS. The granules reactivated at air intensive aeration rate of 100 L/h achieved better settling property and contaminants removal efficiency. Moreover, protein content in extracellular polymeric substance (EPS) was almost unchanged, which demonstrated that an aeration rate of 100 L/h was more suitable for maintaining the biomass and the structure of AGS. Higher OLR caused polysaccharides content increase in EPS, and unstable C/N resulted in the overgrowth of filamentous bacteria, which presented worse NH₄⁺-N and PO₄³⁻-P removal. Correspondingly, quick recovery of contaminants removal was accomplished in 12 days at the optimized operation conditions of aeration rate 100 L/h, OLR 4 g/L·d, and C/N 100 : 10, with COD, NH₄⁺-N, and PO₄³⁻-P removal efficiencies of 87.2%, 86.9%, and 86.5%, respectively. The renovation of AGS could be successfully utilized as the seed sludge for the rapid start-up of AGS bioreactor.

Drying and re-cultivation of aerobic granules

Aerobic granules stored in liquid medium can lose structural integrity during storage. This study demonstrated that the aerobic granules cultivated by seeding activated sludge into column-type sequential batch reactors and fed with synthetic wastewater at organic loading rate of 1.5 kg/m3-d can be dried by acetone gradient method to moisture content less than 1%. Then, the dried granules can be reactivated through a re-cultivation process to recover their organic degradation capacity in 12 h, or their appearance in 5 d. During the drying and recovery, the granules experienced volume and weight losses by >80% and >85%, respectively, with minimal loss in structural integrity. The microbial communities of the dried and re-cultivated granules were probed using polymerase chain reaction-denaturing gradient gel electrophoresis technique. The family Xanthomonadaceae and the family Comamonas can survive in dried granules and could contribute to maintain structural integrity in re-cultivation stage.

Nitrous oxide emission and nutrient removal in aerobic granular sludge sequencing batch reactors

Application of aerobic granular sludge into wastewater treatment is promising due to its excellent settling ability and high microbial concentrations. However, its spatial structure could induce incomplete denitrification, leading to generation of nitrous oxide (N(2)O) - a potent greenhouse gas. Under the temperature of 14 ± 4 °C, three identical laboratory-scale aerobic granular sludge sequencing batch reactors (SBRs) were established to treat synthetic wastewater simulating a mixture of liquid pig manure digestate and municipal wastewater at three aeration rates (0.2, 0.6 and 1.0 L air/min) and three COD:N ratios (1:0.22, 1:0.15 and 1:0.11). The studies show the proportions of N(2)O emission to the influent nitrogen loading rate at the aeration rates of 0.2, 0.6 and 1.0 L air/min were 8.2%, 6.1% and 3.8% at a COD:N ratio of 1:0.22; 7.0%, 5.1% and 3.5% at a COD:N ratio of 1:0.15; and 4.4%, 2.9% and 2.2% at a COD:N ratio of 1:0.11, respectively. With NO(2)(-) as the only nitrogen source in the liquid phase, the specific N(2)O generation rates via denitrification were 1.7, 1.6 and 1.3 μg N(2)O/(g SS· min) at the aeration rates of 0.2, 0.6 and 1.0 L air/min, respectively, which were 40.9%, 44.8%, 39.9% higher than those with NO(3)(-) as the only nitrogen source, respectively. N(2)O generation by aerobic granular sludge due to NH(4)(+)-N nitrification was not sensitive to the aeration rate, and the average specific N(2)O generation rate was 0.8 ± 0.02 μg N(2)O/(g SS· min).

Variations of both bacterial community and extracellular polymers: the inducements of increase of cell hydrophobicity from biofloc to aerobic granule sludge

To investigate the inducements of increase of cell hydrophobicity from aerobic biofloc (ABF) and granular sludge (AGS), in this study, as the first time the hydrophilic and hydrophobic bacterial communities were analyzed independently. Meanwhile, the effect of extracellular polymers (EPS) on the cell hydrophobicity is also studied. Few Bacteroidetes were detected (1.35% in ABF and 3.84% in AGS) in hydrophilic bacteria, whereas they are abundant in the hydrophobic cells (47.8% and 43% for ABF and AGS, respectively). The main species of Bacteroidetes changed from class Sphingobacteria to Flavobacteria in AGS. On the other hand, EPS is directly responsible to cell hydrophobicity. For AGS, cell hydrophobicity was sharply decreased after EPS extraction. Both quantity and property of the extracellular protein are related to hydrophobicity. Our results showed the variation of cell hydrophobicity was resulted from variations of both bacterial population and EPS.

Propagation of anaerobic bacteria within an aerobic multi-species chronic wound biofilm model

OBJECTIVE

Most chronic wound biofilms have been shown to have significant populations of anaerobes. In order to better screen antimicrobial and antibiofilm therapeutics, we evaluated the ability of key anaerobes to incorporate and propagate within our aerobic chronic wound biofilm.

METHOD

We had previously developed a rapid model to simulate polymicrobial chronic wound biofilms. This model incorporated meticillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE) and Pseudomonas aeruginosa. The model was used along with a variety of anaerobes to determine whether this biofilm model would support propagation of anaerobes similar to that we have identified in chronic wounds.

RESULTS

Using our previously defined Lubbock Chronic Wound Biofilm (LCWB) model combined with quantitative PCR, anaerobic bacteria were shown to proliferate through integration into the biofilm under aerobic conditions. Using electron microscopy we show close association between aerobes and anaerobes within the biofilm suggesting a synergistic relationship.

CONCLUSION

We have expanded the utility of the LCBW to show the ability of clinically significant anaerobic bacteria to thrive in aerobic conditions. The expansion of this model can further simulate the functional characteristics of chronic wound pathogenic biofilms and the species that dwell within them allowing improved ability to evaluate therapeutics that target anaerobes.

The application of molecular techniques to the study of wastewater treatment systems

Wastewater treatment systems tend to be engineered to select for a few functional microbial groups that may be organized in various spatial structures such as activated sludge flocs, biofilm or granules and represented by single coherent phylogenic groups such as ammonia-oxidizing bacteria (AOB) and polyphosphate-accumulating organisms (PAO). In order to monitor and control engineered microbial structure in wastewater treatment systems, it is necessary to understand the relationships between the microbial community structure and the process performance. This review focuses on bacterial communities in wastewater treatment processes, the quantity of microorganisms and structure of microbial consortia in wastewater treatment bioreactors. The review shows that the application of molecular techniques in studies of engineered environmental systems has increased our insight into the vast diversity and interaction of microorganisms present in wastewater treatment systems.

Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge

Changes in organic matter degradation and microbial communities during thermophilic composting were compared using two different types of anaerobic sludge, one from mesophilic methane fermentation, containing a high concentration of proteins (S-sludge), and the other from thermophilic methane fermentation, containing high concentrations of lipids and fibers (K-sludge). The difference in the organic matter degradation rate corresponded to the difference in the organic matter constituents; the CO(2) evolution rate was greater in the composting of S-sludge than of K-sludge; moreover, the NH(3) evolution resulting from the protein degradation was especially higher in the composting of S-sludge. Then the differences in the microbial communities that contributed to each composting were determined by the PCR-DGGE method. Ureibacillus sp., which is known as a degrader with high organic matter degradation activity, was observed during the composting of S-sludge, whereas Thermobifida fusca, which is a well known thermophilic actinomycete that produces enzymes for lignocellulose degradation, were observed during the composting of K-sludge.

Proteolytic activity in stored aerobic granular sludge and structural integrity

Aerobic granules lose stability during storage. The goal of this work was to highlight the main cause of stability loss for stored granules as intracellular protein hydrolysis. The quantity of extracellular proteins was noted to be significantly lower during granule storage, and protease enzyme activities were correspondingly higher in the cores of stored granules. The proteolytic bacteria, which secrete highly active protease enzymes, were for the first time isolated and characterized by analyzing 16S rDNA sequences. The proteolytic bacteria belonged to the genera Pseudomonas, Raoultella, Acinetobacter, Pandoraea, Klebsiella, Bacillus and uncultured bacterium, and were grouped into Proteobacteria, Enterobacteria and Firmicutes. The PB1 (Pseudomonas aeruginosa) strain, which exhibited very high proteolytic activity during the skim milk agar test, was located at the core regime with active protease enzymes, and was close to the obligate anaerobic strain Bacteroides sp. Hence, the extracellular proteins in stored granules were proposed to be hydrolyzed by enzymes secreted by proteolytic bacteria with the hydrolyzed products ultimately being used by nearby anaerobic strains. This process gradually digests the protein core, and eventually consumes the entire granule.

Characterization, modeling and application of aerobic granular sludge for wastewater treatment

Recently extensive studies have been carried out to cultivate aerobic granular sludge worldwide, including in China. Aerobic granules, compared with conventional activated sludge flocs, are well known for their regular, dense, and strong microbial structure, good settling ability, high biomass retention, and great ability to withstand shock loadings. Studies have shown that the aerobic granules could be applied for the treatment of low- or high-strength wastewaters, simultaneous removal of organic carbon, nitrogen and phosphorus, and decomposition of toxic wastewaters. Thus, this new form of activate sludge, like anaerobic granular sludge, could be employed for the treatment of municipal and industrial wastewaters in near future. This chapter attempts to provide an up-to-date review on the definition, cultivation, characterization, modeling and application of aerobic granular sludge for biological wastewater treatment. This review outlines some important discoveries with regard to the factors affecting the formation of aerobic granular sludge, their physicochemical characteristics, as well as their microbial structure and diversity. It also summarizes the modeling of aerobic granule formation. Finally, this chapter highlights the applications of aerobic granulation technology in the biological wastewater treatment. It is concluded that the knowledge regarding aerobic granular sludge is far from complete. Although previous studies in this field have undoubtedly improved our understanding on aerobic granular sludge, it is clear that much remains to be learned about the process and that many unanswered questions still remain. One of the challenges appears to be the integration of the existing and growing scientific knowledge base with the observations and applications in practice, which this paper hopes to partially achieve.

The influence of storage on the morphology and physiology of phthalic acid-degrading aerobic granules

The precultured aerobic granules with special degradabilities could be used as a feasible bioseed for enhancement of aerobic granulation systems. In practice, the storage stability, physicochemical characteristics, and recovering efficiency of granules are crucial for a long-distance transportation and successful application. In this study, phthalic acid (PA)-degrading aerobic granules were cultivated and stored for 8 wk at 4 degrees C. The granular size, settling ability as well as structure integrity was found stable during the storage period. It was observed that the upper 1/3 part of granules stored in the reagent bottle turned to black color, while the lower 2/3 part granules did not significantly change color (brown-yellow) after the 8-wk storage. The black and brown-yellow color PA-degrading granules were manually separated and re-inoculated into two identical sequencing batch reactors for reviving the PA degradation capability. After a 7d operation, both black and yellow granules restored their activities to the levels before storage, in terms of total organic carbon removal efficiency (100%), specific oxygen uptake rate (59 mg g VSS(-1) h(-1)), and adenosine triphosphate content (0.016 mg g VSS(-1)). This study demonstrated that aerobic granules grown on a complex substrate could tolerate storage conditions and rapidly restored their bioactivities toward the target pollutant. The results also shed the light on the future application of precultured aerobic granules with unique functions for biodegradation and bioremediation purpose.

Oxygen diffusion and consumption in active aerobic granules of heterogeneous structure

The interior structure of aerobic granules is highly heterogeneous, hence, affecting the transport and reaction processes in the granules. The granule structure and the dissolved oxygen profiles were probed at the same granule in the current work for possible estimation of transport and kinetic parameters in the granule. With the tested granules fed by phenol or acetate as carbon source, most inflow oxygen was consumed by an active layer thickness of less than 125 microm on the granule surface. The confocal laser scanning microscopy scans also revealed a surface layer thickness of approximately 100 microm consisting of cells. The diffusivities of oxygen transport and the kinetic constant of oxygen consumption in the active layers only were evaluated. The theoretical models adopted in literature that ignored the contributions of the layered structure of aerobic granule could have overlooked the possible limitations on oxygen transport.

Flow cytometry and cell sorting

Flow cytometry and cell sorting are well-established technologies in clinical diagnostics and biomedical research. Heterogeneous mixtures of cells are placed in suspension and passed single file across one or more laser interrogation points. Light signals emitted from the particles are collected and correlated to entities such as cell morphology, surface and intracellular protein expression, gene expression, and cellular physiology. Based on user-defined parameters, individual cells can then be diverted from the fluid stream and collected into viable, homogeneous fractions at exceptionally high speeds and a purity that approaches 100%. As such, the cell sorter becomes the launching point for numerous downstream studies. Flow cytometry is a cornerstone in clinical diagnostics, and cheaper, more versatile machines are finding their way into widespread and varied uses. In addition, advances in computing and optics have led to a new generation of flow cytometers capable of processing cells at orders of magnitudes faster than their predecessors, and with staggering degrees of complexity, making the cytometer a powerful discovery tool in biotechnology. This chapter will begin with a discussion of basic principles of flow cytometry and cell sorting, including a technical description of factors that contribute to the performance of these instruments. The remaining sections will then be divided into clinical- and research-based applications of flow cytometry and cell sorting, highlighting salient studies that illustrate the versatility of this indispensable technology.

Persistence and growth of fecal Bacteroidales assessed by bromodeoxyuridine immunocapture

Extraintestinal growth of fecal bacteria can impair accurate assessment of watershed health. Anaerobic fecal bacteria belonging to the order Bacteroidales are attractive candidates for fecal source tracking because they have host-specific distributions and do not grow well in the presence of high oxygen concentrations. Growth of general and human-specific fecal Bacteroidales marker organisms in environmental samples (sewage) and persistence of the corresponding genetic markers were investigated using bromodeoxyuridine (BrdU) DNA labeling and immunocapture, followed by PCR detection. Background amplification of unlabeled controls occasionally occurred when a high number of PCR cycles was used. By using fluorescent detection of PCR products obtained after 15 cycles, which was determined to be quantitative, we enriched for BrdU-labeled DNA and did not detect unlabeled DNA. By using pure cultures of Bacteroides vulgatus, the ability of Bacteroidales bacteria to take up and incorporate BrdU into nascent DNA was confirmed. Fecal Bacteroidales organisms took up and incorporated BrdU into DNA during growth. In sewage incubated aerobically at the in situ temperature, Bacteroidales genetic marker sequences persisted for at least 24 h and Bacteroidales fecal bacteria grew for up to 24 h as well. Detection by PCR using a low, quantitative cycle number decreased the sensitivity of the assay such that we were unable to detect fecal Bacteroidales human-specific marker sequences in unlabeled or BrdU-labeled fractions, even when fluorescent detection was used. Using 30 PCR cycles with unlabeled fractions, human-specific Bacteroidales sequences were detected, and they persisted for up to 24 h in sewage. These data support the utility of BrdU labeling and immunocapture followed by length heterogeneity PCR or fluorescent detection using low numbers of PCR cycles. However, this method may not be sensitive enough to identify cells that are present at low densities in aquatic environments.

Formation and instability of aerobic granules under high organic loading conditions

The cultivation and instability of aerobic granular sludge in a sequencing batch reactor under high loading conditions were investigated. Compact bacteria-dominated aerobic granules with a mean diameter of 1 mm were formed at a chemical oxygen demand (COD) loading rate of 6.0 kg m(-3) d(-1) within 30 d. However, the compact bacteria-dominated aerobic granules were not stable and transited to large-sized filamentous ones gradually. With the formation of bacteria-dominated granules, the hydrophobicity and specific gravity of the sludge increased. When the granules were transited to filamentous ones, the hydrophobicity and specific gravity decreased. Both granules had a high COD removal efficiency, excellent settling ability and showed a clear, regular round-shaped outline. After the filamentous granules reached a diameter of 16 mm, due to the mass transfer limitation and the possible presence of anaerobes in the inner part of the granules, they began to disintegrate and be washed out of the reactor, follow by failure of the reactor.

Performances and microbial features of an aerobic packed-bed biofilm reactor developed to post-treat an olive mill effluent from an anaerobic GAC reactor

BACKGROUND

Olive mill wastewater (OMW) is the aqueous effluent of olive oil producing processes. Given its high COD and content of phenols, it has to be decontaminated before being discharged. Anaerobic digestion is one of the most promising treatment process for such an effluent, as it combines high decontamination efficiency with methane production. The large scale anaerobic digestion of OMWs is normally conducted in dispersed-growth reactors, where however are generally achieved unsatisfactory COD removal and methane production yields. The possibility of intensifying the performance of the process using a packed bed biofilm reactor, as anaerobic treatment alternative, was demonstrated. Even in this case, however, a post-treatment step is required to further reduce the COD. In this work, a biological post-treatment, consisting of an aerobic biological "Manville" silica bead-packed bed aerobic reactor, was developed, tested for its ability to complete COD removal from the anaerobic digestion effluents, and characterized biologically through molecular tools.

RESULTS

The aerobic post-treatment was assessed through a 2 month-continuous feeding with the digested effluent at 50.42 and 2.04 gl(-1)day(-1) of COD and phenol loading rates, respectively. It was found to be a stable process, able to remove 24 and 39% of such organic loads, respectively, and to account for 1/4 of the overall decontamination efficiency displayed by the anaerobic-aerobic integrated system when fed with an amended OMW at 31.74 and 1.70 gl(-1)day(-1) of COD and phenol loading rates, respectively. Analysis of 16S rRNA gene sequences of biomass samples from the aerobic reactor biofilm revealed that it was colonized by Rhodobacterales, Bacteroidales, Pseudomonadales, Enterobacteriales, Rhodocyclales and genera incertae sedis TM7. Some taxons occurring in the influent were not detected in the biofilm, whereas others, such as Paracoccus, Pseudomonas, Acinetobacter and Enterobacter, enriched significantly in the biofilter throughout the treatment.

CONCLUSION

The silica-bead packed bed biofilm reactor developed and characterized in this study was able to significantly decontaminate anaerobically digested OMWs. Therefore, the application of an integrated anaerobic-aerobic process resulted in an improved system for valorization and decontamination of OMWs.