Succession of biofilm communities responsible for biofouling of membrane bio-reactors (MBRs)

Analysis of Microbial Communities in Membrane Biofilm Reactors Using a High-Density Microarray

Membrane biofilm reactors (MBfRs) have attracted more and more attention in the field of wastewater treatment due to their advantages of high mass transfer efficiency and low-carbon emissions. There are many factors affecting their nitrogen removal abilities, such as operation time, electron donor types, and operation modes. The operation time is directly related to the growth status of microorganisms, so it is very important to understand the effect of different operation times on microbial composition and community succession. In this study, two parallel H₂-based MBfRs were operated, and differences in microbial composition, community succession, and NO₃^--N removal efficiency were investigated on the 30th day and the 60th day of operation. The nitrogen removal efficiency of MBfRs with an operation time of 60 days was higher than that of MBfRs with an operation time of 30 days. Proteobacteria was the dominant phylum in both MBfRs; however, the composition of the microbial community was quite different. At the class level, the community composition of Proteobacteria was similar between the two MBfRs. Alphaproteobacteria was the dominant class in MBfR, and Betaproteobacteria and Gammaproteobacteria were also in high proportion. Combined with the analysis of microbial relative abundance and concentration, the similarity of microbial distribution in the MBfRs was very low on day 30 and day 60, and the phylogenetic relationships of the top 50 dominant universal bacteria and Proteobacteria were different. Although the microbial concentration decreased with the extension of the operation time, the microbial abundance and diversity of specific functional microorganisms increased further. Therefore, the operation time had a significant effect on microbial composition and community succession.

Carbon/nitrogen ratios determine biofilm formation and characteristics in model microbial cultures

The influence of growth medium water chemistry, specifically carbon/nitrogen (C/N) molar ratios, on the characteristics and development of biofilms of the model microorganism Pseudomonas aeruginosa was investigated. C/N = 9 had a unique effect on biofilm composition as well as quorum sensing (QS) pathways, with higher concentrations of carbohydrates and proteins in the biofilm and a significant upregulation of the QS gene lasI in planktonic cells. The effect of C/N ratio on total attached biomass was negligible. Principal component analysis revealed a different behavior of most outputs such as carbohydrates and QS chemicals at C/N = 9, and pointed to correlations between parameters of biofilm formation and steady state distribution of cells and extracellular components. C/N ratio was also shown to influence organic compound utilization by both planktonic and sessile organisms, with a maximum chemical oxygen demand (COD) removal of 83% achieved by biofilms at C/N = 21. Planktonic cells achieved higher COD removal rates, but greater overall rates after six days occurred in biofilms. The development of a dual-species biofilm of P. aeruginosa and Nitrobacter winogradskyi was also influenced by C/N, with increase in the relative abundance of the slower-growing N. winogradskyi above C/N = 9. These results indicate that altering operational parameters related to C/N would be relevant for mitigating or promoting biofilm formation and function depending on the desired industrial application or treatment configuration.

An increase in sludge loading rate induces gel fouling in membrane bioreactors treating real sewage

The main objective of this study was to investigate the cause of gel fouling in membrane bioreactors (MBRs) treating real sewage in terms of soluble microbial products (SMPs) and microbial aspects. Two anoxic/oxic-MBRs were operated as the control reactor (S1) and the sludge loading rate increased reactor (S2). The reactors were operated under low-temperature around 11 °C conditions. Membrane permeability substantially decreased in S2, and gel layer biofilm was formed on membrane surface. In contrast, the permeability of S1 gradually decreased and cake layer formed. When gel fouling occurred, the protein and polysaccharide of SMP in S2 were 47 and 23 mg L^-1, which were significantly lower than those recorded in S1 accounted for 118 and 68 mg L^-1, respectively. Furthermore, the total organic carbon concentration of SMPs was 24 mg L^-1, which was lower than the influent in S2, accounted for 62 mg L^-1. Finally, Campylobacteraceae which exists in sewage and uncultured OD1, dominated the gel layer biofilm in S2, unlike the cake layer biofilm in S1. These results indicated that the gel layer biofilm might be composed of influent substances, demonstrating the importance of influent decomposition in MBR for gel fouling mitigation.

Can Aggregate-Associated Organisms Influence the Fouling in a SWRO Desalination Plant?

This pilot study investigates the formation of aggregates within a desalination plant, before and after pre-treatment, as well as their potential impact on fouling. The objective is to provide an understanding of the biofouling potential of the feed water within a seawater reverse osmosis (SWRO) desalination plant, due to the limited removal of fouling precursors. The 16S and 18S rRNA was extracted from the water samples, and the aggregates and sequenced. Pre-treatment systems, within the plant remove < 5 µm precursors and organisms; however, smaller size particles progress through the plant, allowing for the formation of aggregates. These become hot spots for microbes, due to their nutrient gradients, facilitating the formation of niche environments, supporting the proliferation of those organisms. Aggregate-associated organisms are consistent with those identified on fouled SWRO membranes. This study examines, for the first time, the factors supporting the formation of aggregates within a desalination system, as well as their microbial communities and biofouling potential.

Innovative encapsulated self-forming dynamic bio-membrane bioreactor (ESFDMBR) for efficient wastewater treatment and fouling control

The concept of a novel living encapsulated self-forming dynamic bio-membranes (ESFDM) for an innovative wastewater treatment in membrane bioreactor (MBR) is presented in the current study. The active filtering membrane is encapsulated, and thus stabilized, between two support meshes with pore in micrometer size. The combination of activated sludge, the ESFDM and the cake layer formed external to the filtering module contributed to the treatment of municipal wastewater. COD concentration reductions (average value of 95.55 ± 1.44%) by ESFDM bioreactor (ESFDMBR) were comparable to those obtained with a previously reported membrane bioreactor (MBR), where a conventional membrane was studied under the same operating conditions. The ESFDMBR, compared to the conventional MBR, obtained higher reductions of NH₃-N, NO₃^-N and PO₄^3-P concentrations. Increased removals of nitrogen-containing nutrients were ascribed to anoxic conditions reached in the ESFDM layer protected from the aeration by the external cake layer. Rate of increase of transmembrane pressure (TMP) per day in the ESFDMBR (0.03 kPa/day) was lower than the value obtained in the previously reported conventional MBR (8.08 kPa/day). Lower concentrations of fouling precursors in combination with the effective filtration capacity of the porous living ESFDM resulted in the reduction of the fouling rate. Analysis of microbiological community revealed that the microbial community structures in the mixed liquor and ESFDM were different. The ESFDM layer promoted growth of bacteria as indicated by the higher total cell count and higher microbial diversity compared to those observed in the mixed liquor.

Polymer Surface Dissection for Correlated Microscopic and Compositional Analysis of Bacterial Aggregates during Membrane Biofouling

Multispecies biofilms are a common limitation in membrane bioreactors, causing membrane clogging, degradation, and failure. There is a poor understanding of biological fouling mechanisms in these systems due to the limited number of experimental techniques useful for probing microbial interactions at the membrane interface. Here, we develop a new experimental method, termed polymer surface dissection (PSD), to investigate multispecies assembly processes over membrane surfaces. The PSD method uses photodegradable polyethylene glycol hydrogels functionalized with bioaffinity ligands to bind and detach microscale, microbial aggregates from the membrane for microscopic observation. Subsequent exposure of the hydrogel to high resolution, patterned UV light allows for controlled release of any selected aggregate of desired size at high purity for DNA extraction. Follow-up 16S community analysis reveals aggregate composition, correlating microscopic images with the bacterial community structure. The optimized approach can isolate aggregates with microscale spatial precision and yields genomic DNA at sufficient quantity and quality for sequencing from aggregates with areas as low as 2000 μm², without the need of culturing for sample enrichment. To demonstrate the value of the approach, PSD was used to reveal the composition of microscale aggregates of different sizes during early-stage biofouling of aerobic wastewater communities over PVDF membranes. Larger aggregates exhibited lower diversity of bacterial communities, and a shift in the community structure was found as aggregate size increased to areas between 25,000 and 45,000 μm², below which aggregates were more enriched in Bacteroidetes and above which aggregates were more enriched with Proteobacteria. The findings demonstrate that community succession can be observed within microscale aggregates and that the PSD method is useful for identification and characterization of early colonizing bacteria that drive biofouling on membrane surfaces.

Acylase enzymes disrupting quorum sensing alter the transcriptome and phenotype of Pseudomonas aeruginosa, and the composition of bacterial biofilms from wastewater treatment plants

Biofilms represent an essential way of life and colonization of new environments for microorganisms. This feature is regulated by quorum sensing (QS), a microbial communication system based on autoinducer molecules, such as N-acyl-homoserine lactones (AHLs) in Gram negative bacteria. In artificial ecosystems, like Wastewater Treatment Plants (WWTPs), biofilm attachment in filtration membranes produces biofouling. In this environment, the microbial communities are mostly composed of Gram-negative phyla. Thus, we used two AHLs-degrading enzymes, obtained from Actinoplanes utahensis (namely AuAAC and AuAHLA) to determine the effects of degradation of QS signals in the biofilm formation, among other virulence factors, of a Pseudomonas aeruginosa strain isolated from a WWTP, assessing molecular mechanisms through transcriptomics. Besides, we studied the possible effects on community composition in biofilms from activated sludge samples. Although the studied enzymes only degraded the AHLs involved in one of the four QS systems of P. aeruginosa, these activities produced the deregulation of the complete QS network. In fact, AuAAC -the enzyme with higher catalytic efficiency- deregulated all the four QS systems. However, both enzymes reduced the biofilm formation and pyocyanin and protease production. The transcriptomic response of P. aeruginosa affected QS related genes, moreover, transcriptomic response to AuAAC affected mainly to QS related genes. Regarding community composition of biofilms, as expected, the abundance of Gram-negative phyla was significantly decreased after enzymatic treatment. These results support the potential use of such AHLs-degrading enzymes as a method to reduce biofilm formation in WWTP membranes and ameliorate bacterial virulence.

Assessing effects of Ca2+ addition on membrane bioreactor performance and macro-floc sludge characteristics

Calcium ions (Ca²⁺) can trigger coagulation-flocculation process to form macro-flocculated sludge (MFS). Thus, dosing Ca²⁺-containing reagents into membrane bioreactors (MBRs) is considered as a promising approach to mitigate membrane biofouling. However, a mechanistic understanding of Ca²⁺ addition to MBR performance remains elucidated, such as physicochemical characteristics of MFS and their functionality variations. Consequently, this study was sought to understand the interplays of Ca²⁺ addition and MBR performance with a focus on characterizing MFS in detail. Three parallel MBRs were amended with 82, 208 and 410 mg-Ca²⁺/L final concentrations. Particle size analyses revealed that MFS formation was overall enhanced by the Ca²⁺ addition and granular sludge with diameters of up to 900 μm was formed in the 410 mg-Ca²⁺/L scenario. We believed that cationic bridges facilitated by elevated Ca²⁺ concentrations in conjunction with coagulation-flocculation were primary mechanisms of the formation of large flocs. Moreover, significant portions of soluble proteins and polysaccharides were flocculated and precipitated by Ca²⁺, which demonstrated a negative correlation between extracellular polymeric substances (EPS) concentrations and the formation of MFS. Furthermore, the population abundancies of Thiotrichaceae, Sphingomonadales and Hyphomicrobiaceae decreased in the sludge with Ca²⁺ addition resulted in profound changes of the microbial communities in the MBRs. But MBR performance, such as chemical oxygen demand removal (over 90%), showed no variation during the MBR operation. On the contrary, total nitrogen removal was inhibited in the MBRs. It was because the enlarging MFS formed diffusion barriers to prevent organic component from entering into the sludge flocs to be consumed.

Effect of prolonged sludge retention times on the performance of membrane bioreactor and microbial community for leachate treatment under restricted aeration

Leachate treatment is challenging owing to the complex composition of pollutants. This study investigated the treatment performance of a membrane bioreactor (MBR) and the microbial community structure corresponding to the effect of prolonged sludge retention times (SRTs) under restricted aeration. In the present study, a pilot-scale MBR was designed to treat leachate after being pretreated with an anaerobic filter for continuous operation for 240 days. The experimental results showed that removal performance of over 90% was achieved for biochemical oxygen demand, total Kjeldahl nitrogen, ammonia-nitrogen, and suspended solids when the MBR was operated at SRTs of 150-300 days. The results on microbial communities revealed that Proteobacteria, Bacteroidetes, Firmicutes, Planctomycetes, Chloroflexi, and Actinobacteria were the major phyla. Furthermore, ammonia-oxidizing bacteria belonging to Nitrosomonadaceae were considered to play a vital role in the ammonia-nitrogen removal. A high abundance of Rhizobiales was detected on the biofilm of the membrane, which could be the key driver of bio-fouling. The dynamic changes in the microbial community indicate steady performance of MBR and can act as an indicator of membrane bio-fouling. The results of our study highlight that MBR can be viably operated in long SRTs under restricted aeration for leachate treatment with technical, economic, and environmental feasibility for resource recovery.

Relative Importance of Stochastic Assembly Process of Membrane Biofilm Increased as Biofilm Aged

The relative importance of different ecological processes controlling biofilm community assembly over time on membranes with different surface characteristics has never been investigated in membrane bioreactors (MBRs). In this study, five ultrafiltration hollow-fiber membranes - having identical nominal pore size (0.1μm) but different hydrophobic or hydrophilic surface characteristics - were operated simultaneously in the same MBR tank with a constant flux of 10 liters per square meter per hour (LMH). In parallel, membrane modules operated without permeate flux (0 LMH) were submerged in the same MBR tank, to investigate the passive microbial adsorption onto different hydrophobic or hydrophilic membranes. Samples from the membrane biofilm were collected after 1, 10, 20, and 30days of continuous filtration. The membrane biofilm microbiome were investigated using 16S rRNA gene amplicon sequencing from DNA and cDNA samples. Similar beta diversity trends were observed for both DNA- and cDNA-based analyses. Beta diversity analyses revealed that the nature of the membrane surface (i.e., hydrophobic vs. hydrophilic) did not seem to have an effect in shaping the bacterial community, and a similar biofilm microbiome evolved for all types of membranes. Similarly, membrane modules operated with and without permeate flux did not significantly influence alpha and beta diversity of the membrane biofilm. Nevertheless, different-aged membrane biofilm samples exhibited significant differences. Proteobacteria was the most dominant phylum in early-stage membrane biofilm after 1 and 10days of filtration. Subsequently, the relative reads abundance of the phyla Bacteroidetes and Firmicutes increased within the membrane biofilm communities after 20 and 30days of filtration, possibly due to successional steps that lead to the formation of a relatively aged biofilm. Our findings indicate distinct membrane biofilm assembly patterns with different-aged biofilm. Ecological null model analyses revealed that the assembly of early-stage biofilm community developed after 1 and 10days of filtration was mainly governed by homogenous selection. As the biofilm aged (days 20 and 30), stochastic processes (e.g., ecological drift) started to become important in shaping the assembly of biofilm community.

Shotgun metagenomics assessment of the resistome, mobilome, pathogen dynamics and their ecological control modes in full-scale urban wastewater treatment plants

The conventional activated sludge (CAS) process has limited capacity to remove pathogenic microorganisms and antibiotic resistance genes (ARGs), compared to membrane bioreactors (MBRs). However, the full extent of pathogenic microbial fraction, resistome (antibiotic and biocide resistance genes, ARGs and BRGs) and mobilome (mobile genetic elements, MGE) of urban wastewater treatment plant (UWTP) influents and effluents remains unknown. Thus, the fate of putative pathogenic bacteria, ARGs and potential co-occurrence patterns with BRGs, MGEs and bacterial-predatory microorganisms was determined in two full-scale UWTPs, a MBR and a CAS system, using shotgun metagenomics. Both UWTPs significantly reduced the BOD₅ (99.4-99.9%), COD (97.6-99.4%) and TSS (98.9-99.9%). MBR was more effective in reducing the abundance and diversity of pathogen-containing taxa, with 4 and 30 taxa enriched in MBR and CAS effluents, respectively. MBR treatment favored resistance genes associated with triclosan, whereas CAS effluents contained ARGs associated with antibiotics of clinical importance. Correlations between putative pathogenic bacteria, ARG/BRGs/MGEs and bacterial-predatory microorganisms suggested that: (i) opportunistic pathogens (Clostridia, Nocardia) may acquire ARGs against first-line treatments and (ii) bacteriophages may act as a biogenic mechanism of pathogen removal. These findings reinforce the MBR capacity to retain pathogenic components, hence reducing potential health risks associated with treated wastewater reuse.

Addition of Trichocladium canadense to an anaerobic membrane bioreactor: evaluation of the microbial composition and reactor performance

Membrane bioreactors are powerful systems for wastewater treatment and the removal of toxic compounds. However, membrane biofouling stands in the way of their widespread usage. In this study, the saprophytic fungus Trichocladium canadense was used as the bioaugmentor in an anaerobic membrane bioreactor (AnMBR) and its impact on membrane biofouling, biogas production, the microbial communities of the reactor and removal of the common antibiotics erythromycin (ERY), sulfamethoxazole (SMX) and tetracycline (TET) from synthetic wastewater was investigated. The results indicated that through bioaugmentation with 20% T. canadense, membrane biofouling was slowed by 25%, the chemical oxygen demand removal increased by 16% and a higher efficiency removal of ERY and SMX was achieved. The presence of T. canadense significantly increased the abundance and diversity of the biofilm archaeal community and the bacterial phylum Firmicutes, a known bio-foulant.

Role of live cell colonization in the biofilm formation process in membrane bioreactors treating actual sewage under low organic loading rate conditions

Biofilm development on the membrane surface is one of the main reasons for membrane fouling in membrane bioreactors (MBRs) and it is a big problem for their stable operation. Precise information on the microbial community composition of the biofilm is needed for a better understanding of biofilm development. However, there have been limited investigations of the relationship between the biofilm formation process and the microbial community of activated sludge and biofilm in MBRs treating real sewage. In this study, relationships between the microbial community structure of biofilm and activated sludge at each biofilm formation stage were investigated and biofilm growth was elucidated by nondestructive observations. Two anoxic/oxic MBRs were operated and membrane fouling was induced. Permeability rapidly decreased in both reactors and live cell microcolonies were formed on dead cell conditioning film on the membrane surface. Principal component analysis based on 16S rRNA gene sequences showed that the biofilm microbial community changed significantly from middle stage to mature biofilm when compared with that of activated sludge. The abundance of specific bacteria, such as unclassified Neisseriaceae, increased in middle-stage biofilm and the diversity indexes of middle-stage biofilm were lower than those of mature biofilm and activated sludge. These results suggested that the presence of specific bacteria with colonization ability played a crucial role in biofilm formation. Strategies are needed to target membrane fouling mitigation during early- and middle-stage biofilm formation to reduce MBR membrane fouling. KEY POINTS: • Microbial community of mature biofilm was approached to that of activated sludge. • In the middle-stage biofilm, live cells colonized on a dead-cell-conditioning-film. • Microbial diversity was lower in live cell colonizing stage than in activated sludge.

Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater

The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h^-1) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h^-1 drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.

The Rhodamine Isothiocyanate Analogue as a Quorum Sensing Inhibitor Has the Potential to Control Microbially-Induced Biofouling

Quorum sensing inhibitors (QSIs) have been proven to be an innovative approach to interfering with biofilm formation, since this process is regulated by QS signals. However, most studies have focused on single-species biofilm formation, whereas studies of the effects of signal interference on the development of multispecies biofilm, especially in the natural environment, are still lacking. Here we develop and evaluate the anti-biofilm capability of a new QSI (rhodamine isothiocyanate analogue, RIA) in natural seawater. During the experiment, biofilm characteristics, microbial communities/functions and network interactions were monitored at 36, 80, and 180 h, respectively. The results showed that the biomass and 3D structure of the biofilm were significantly different in the presence of the QSI. The expression of genes involved in extracellular polysaccharide synthesis was also downregulated in the QSI-treated group. Dramatic differences in microbial composition, β-diversity and functions between the RIA-treated group and the control group were also observed, especially in the early stage of biofilm development. Furthermore, co-occurrence model analysis showed that RIA reduced the complexity of the microbial network. This study demonstrates that rhodamine isothiocyanate analogue is an efficient QS inhibitor and has potential applications in controlling biofouling caused by multispecies biofilm, especially in the early stage of biofouling formation.

The Best-Practice Organism for Single-Species Studies of Antimicrobial Efficacy against Biofilms Is Pseudomonas aeruginosa

As potable water scarcity increases across the globe; it is imperative to identify energy and cost-effective processes for producing drinking-water from non-traditional sources. One established method is desalination of brackish and seawater via reverse osmosis (RO). However, the buildup of microorganisms at the water-membrane interface, known as biofouling, clogs RO membranes over time, increasing energy requirements and cost. To investigate biofouling mitigation methods, studies tend to focus on single-species biofilms; choice of organism is crucial to producing useful results. To determine a best-practice organism for studying antimicrobial treatment of biofilms, with specific interest in biofouling of RO membranes, we answered the following two questions, each via its own semi-systematic review: 1. Which organisms are commonly used to test antimicrobial efficacy against biofilms on RO membranes? 2. Which organisms are commonly identified via genetic analysis in biofilms on RO membranes? We then critically review the results of two semi-systematic reviews to identify pioneer organisms from the listed species. We focus on pioneer organisms because they initiate biofilm formation, therefore, inhibiting these organisms specifically may limit biofilm formation in the first place. Based on the analysis of the results, we recommend utilizing Pseudomonas aeruginosa for future single-species studies focused on biofilm treatment including, but not limited to, biofouling of RO membranes.

LDPE microplastics significantly alter the temporal turnover of soil microbial communities

Although the ubiquitous presence of microplastics in various environments is increasingly well studied, knowledge of the effects of microplastics on ambient microbial communities is still insufficient. To estimate the response of soil bacterial community succession and temporal turnover to microplastic amendment, a soil microcosm experiment was carried out with polyethylene microplastics. The soil samples under control and microplastic amendment conditions were collected for sequencing analysis using Illumina MiSeq technology. Microplastic amendment was found to significantly alter soil bacterial community structure, and the community differences were increased linearly with the incubation time. Compared with the turnover rate of bacterial community in the control samples (0.0103, p < .05, based on Bray-Curtis similarity), the succession rate was significantly (p < .001) higher in the soil with microplastic amendment (0.0309, p < .001). In addition, the effects of microplastic amendment on the time-decay relationships (TDRs) on taxonomic divisions revealed considerable variations of TDRs values, indicating the effects were lineage dependent. Our results propose that the presence of microbial in soil ecosystem may lead to a faster succession rate of soil bacterial community, which provides new insights into the evolutionary consequences of microplastics in terrestrial environment.

Quorum quenching bacteria bioaugmented GO/PPy modified membrane in EMBR for membrane antifouling

A novel integrated system with quorum quenching (QQ) bacterium Burkholderia sp. ssn-2 bioaugmented graphene oxide/polypyrrole (GO/PPy) conductive polymercomposite membrane (CPM) in MBR with electric field (EMBR) was established. The integrated system exhibited the highest degradation efficiency for phenol (100%) and COD (93.2%-99.9%) during the 120 days operation. Membrane fouling in the integrated system was notably mitigated by the coupling effect of CPM + voltage and QQ bacterium ssn-2. The hydrophilicity and antibacterial activity of CPM inhibited the hydrophobic protein foulants adsorption, bacteria colonization and attachment on the CPM surface. Extracellular polymeric substances (EPS) content was positively correlated with N-acyl-homoserine lactones (AHLs) concentration, and decreased with AHLs degradation by QQ bacterium ssn-2. The increased negative charge of EPS on the CPM surface augmented the electrostatic repulsion between the EPS and cathode CPM in the integrated system. Moreover, the coupling effect altered the microbial communities. A decreased AHLs concentration had a significantly negative correlation with QQ bacterium ssn-2 enrichment, which exhibited the dual effects of degrading phenol and AHLs, and enriching biopolymer-degrading genera Clostridium sensu strict and Acidovorax in the integrated system and on the CPM surface. This can lead to a decrease in the EPS content.

Discrepant roles of a quorum quenching bacterium (Rhodococcus sp. BH4) in growing dual-species biofilms

Quorum quenching (QQ) is a promising alternative method for biofilm control. However, a largely unexplored issue is the mechanism through which QQ bacteria interact with biofilm-forming bacteria. Here, we explore inter-species interactions during biofilm development (using 96-well polystyrene plates in a static incubator) between the QQ bacterium Rhodococcus sp. BH4 and sludge bacteria. Experimental results revealed that strain BH4 provoked both competitive (76%) and cooperative (24%) interactions (P < 0.05) in dual-species biofilms after 24 h of incubation (mature biofilm), implying that signal destruction by strain BH4 was strain-dependent. Besides hike in the biofilm biomass (~21%), amount of extracellular polymeric substances (EPS) (25-30 times) and particle size (3.5 times) in the Serratia sp. JSB1 biofilm were increased by str. BH4. This suggests that strain BH4 may only have quenching effects against certain bacteria, and that such effects are overlooked at the community level. Taken together, present results imply that in a given biofilm community, not all QS-bacteria interact similarly with Rhodococcus sp. BH4, either because QS-bacteria are tolerant of strain BH4 or QS-bacteria have more than one mechanism for biofilm development. Overall, the QQ-strategy alone seems ineffective at controlling biofilm development, although it may be used in combination with other strategies.

Effects of Quorum Quenching on Biofilm Metacommunity in a Membrane Bioreactor

Quorum quenching (QQ) has received attention for the control of biofilms, e.g., biofilms that cause biofouling in membrane bioreactors (MBRs). Despite the efficacy of QQ on biofouling, it is elusive how QQ influences biofilm formation on membranes. A pilot-scale QQ-MBR and non-QQ-MBR were identically operated for 4 days and 8 days to destructively sample the membranes. QQ prolonged the membrane filterability by 43% with no harmful influence on MBR performance. qPCR showed no effect of QQ on microbial density during either of these time periods. Community comparisons revealed that QQ influenced the bacterial and fungal community structures, and the fungal structure corresponded with the bacterial structure. Metacommunity and spatial analyses showed that QQ induced structural variation rather than compositional variation of bacteria and fungi. Moreover, QQ considerably enhanced the bacterial dispersal across membrane during the early development. As the dispersal enhancement by QQ counteracted the ecological drift, it eliminated the distance-decay relationship, reflecting a neutral theory archetype of metacommunity. Network analyses showed that QQ substantially reduced the amount and magnitude of interactions, e.g., competition and cooperation, for bacteria and fungi, and weakened their network structures, irrespective of time. Additionally, QQ suppressed the growth of specific microbial species (e.g., Acinetobacter), abundant and widespread at the early stage. These findings suggest that QQ influenced the community dynamics at the regional and local levels, correspondingly the ecological selection and dispersal processes, during the biofilm development.

Diversity, Co-occurrence and Implications of Fungal Communities in Wastewater Treatment Plants

Three wastewater treatment plants (WWTPs) located in Gauteng province in South Africa were investigated to determine the diversity, co-occurrence and implications of their fungal communities using illumina sequencing platform and network analysis. Phylogenetic taxonomy revealed that members of the fungal communities were assigned to 6 phyla and 361 genera. Basidiomycota and Ascomycota were the most abundant phyla, dominated by the genera Naumovozyma, Pseudotomentella, Derxomyces, Ophiocordyceps, Pulchromyces and Paecilomyces. Phylogenetic analysis revealed the existence of fungal OTUs related to class lineages such as Agaricomycetes, Eurotiomycetes and Sordariomycetes indicating new fungal diversity in WWTPs. Dominant and rare fungal genera that can potentially be used in bioremediation such as Trichoderma, Acremonium, Talaromyces, Paecilomyces, cladophialophora and Saccharomyces were detected. Conversely, genera whose members are known to be pathogenic to human and plant such as Olpidium, Paecilomyces, Aspergillus, Rhodotorula, Penicillium, Candida, Synchytrium, Phyllosticta and Mucor were also detected in all WWTPs. Phylotype analysis confirmed that some fungal phylotypes were highly similar to the reported fungal pathogens of concern. Co-occurrence network analysis revealed that the fungal genera such as Minimedusa, Glomus, Circinella, Coltricia, Caloplaca, Phylosticta, Peziza, Candida, and Hydnobolites were the major networking hub in the WWTPs. The overall results in this study highlighted that WWTPs represent a potential source of beneficial fungi for bioremediation of pollutants in the ecosystem and the need to consider human and plant fungal pathogens during safety evaluation of treated wastewater for reuse.

Cake layer bacterial communities during different biofouling stages in full-scale membrane bioreactors

A detailed understanding of the bacterial communities in the cake layers formed on the membrane surface is required to control biofouling in a membrane bioreactor (MBR). This study aimed to investigate the dynamics of the cake layer bacterial communities in full-scale MBRs operated in a wastewater treatment plant in Japan and to identify the key bacteria responsible for cake layer formation. The bacterial communities in the cake layer and the activated sludge were analyzed using 16S rRNA gene amplicon sequencing when biofouling occurred under different fouling conditions. The most dominant phyla in activated sludge were almost always Proteobacteria and Bacteroidetes. By contrast, when the cake layer had unique bacterial communities distinguishable from those in the activated sludge, members of Firmicutes were highly dominant in the cake layer, irrespective of the fouling conditions. This study reported for the first time that Firmicutes play an important role throughout the biofouling process.

Influence of fermentation liquid from waste activated sludge on anoxic/oxic- membrane bioreactor performance: Nitrogen removal, membrane fouling and microbial community

In order to investigate effects of waste activated sludge (WAS) fermentation liquid on anoxic/oxic- membrane bioreactor (A/O-MBR), two A/O-MBRs with and without WAS fermentation liquid addition were operated in parallel. Results show that addition of WAS fermentation liquid clearly improved denitrification efficiency without deterioration of nitrification, while severe membrane fouling occurred. WAS fermentation liquid resulted in an elevated production of proteins and humic acids in bound extracellular polymeric substance (EPS) and release of organic matter with high MW fractions in soluble microbial product (SMP) and loosely bound EPS (LB-EPS). Measurement of deposition rate and fluid structure confirmed increased fouling potential of SMP and LB-EPS. γ-Proteobacteria and Ferruginibacter, which can secrete and export EPS, were also found to be abundant in the MBR with WAS fermentation liquid. It is implied that when WAS fermentation liquid was applied, some operational steps to control membrane fouling should be employed.

Enhancement of operating flux in a membrane bio-reactor coupled with a mechanical sieve unit

Filtration flux is one of the key factors in regulating the performance of membrane bio-reactors (MBRs) for wastewater treatment. In this study, we explore the effectiveness of a mechanical sieve unit for effective flux enhancement through retardation of the fouling effect in a modified MBR system (SiMBR). In brief, the coarse sieve unit having 100 μm and 50 μm permits small size microorganism flocs to adjust the biomass concentration from the suspended basin to the membrane basin. As a result, the reduced biofouling effect due to the lowered biomass concentration from 7800 mg/L to 2400 mg/L, enables higher flux through the membrane. Biomass rejection rate of the sieve is identified to be the crucial design parameter for the flux enhancement through the incorporation of numerical simulations and operating critical-flux measurement in a batch reactor. Then, the sieve unit is prepared for 10 L lab-scale continuous SiMBR based on the correlation between sieve pore size and biomass rejection characteristics. During continuous operation of lab-scale SiMBR, biomass concentration is maintained with a higher biomass concentration in the aerobic basin (7400 mg/L) than that in the membrane basin (2400 mg/L). In addition, the SiMBR operations are conducted using three different commercial hollow fiber membranes to compare the permeability to that of conventional MBR operations. For all cases, the modified MBR having a sieve unit clearly results in enhanced permeability. These results successfully validate that SiMBR can effectively improve flux through direct reduction of biomass concentration.