Acclimatizing waste activated sludge in a thermophilic anaerobic fixed-bed biofilm reactor to maximize biogas production for food waste treatment at high organic loading rates.

Thermophilic anaerobic digestion (TAD) provides a promising solution for sustainable high-strength waste treatment due to its enhanced methane-rich biogas recovery. However, high organic loading rates (OLR) exceeding 3.0 kgCOD/m3/day and short hydraulic retention times (HRT) below 10 days pose challenges in waste-to-energy conversion during TAD, stemming from volatile fatty acids (VFAs) accumulation and methanogenesis failure. In this study, we implemented a stepwise strategy for acclimatizing waste activated sludge (WAS) in a thermophilic anaerobic fixed-bed biofilm reactor (TA-FBBR) to optimize methanogen populations, thereby enhancing waste-to-energy efficiencies under elevated OLRs in food waste treatment. Results showed that following stepwise acclimatization, the TA-FBBR achieved stable methane production of approximately 5.8 L/L-reactor/day at an ultrahigh OLR of ∼20 kgCOD/m3/day and ∼15 kgVS/m3/day at 6-day HRT in food waste treatment. The average methane yield reached 0.45 m3/kgCODremoval, attaining the theoretical production in TAD. Moreover, VFA concentrations were stabilized below 1000 mg/L at the ultrahigh OLR under 6-day HRT, while maintaining an acetate/propionate ratio of > 1.8 and a VFA/TAK ratio of < 0.3 serving as effective indicators of system stability and methane yield potential. The microbial community analysis revealed that the WAS acclimatization strategy fostered the microbial diversity and abundance of Methanothermobacter and Methanosarcina. Methanosarcina in the biofilm were observed to be twice as abundant as Methanothermobacter, indicating a potential preference for biofilm existence among methanogens. The findings demonstrated an effective strategy, specifically the stepwise acclimatization of WAS in a thermophilic fixed-bed biofilm reactor, to enhance the food waste treatment performance at high OLRs, contributing valuable mechanistic and technical insights for future sustainable high-strength waste management.

3D spray-coated gradient profile ceramic membranes enables improved filtration performance in aerobic submerged membrane bioreactor.

Rational design of cross-sectional microstructure in ceramic membranes has shown to improve membrane filtration efficacy without affecting rejection performance. In this work, we adopted 3D spray-coating technique to generate multi-layered membrane layers on macro-porous flat-sheet ceramic supports. The thickness of each layer was controlled by spray-coating cycles, and a gradient membrane layer was rationalized by successively coating three ceramic slurries containing alumina powders of gradually refined particle sizes, followed by co-sintering. Gradient membrane layers on both sides of the various sized flat-sheet ceramic supports were fabricated. Compared to the non-gradient counterpart, the gradient membranes showed both higher pure water flux (at the same TMP) and lower membrane resistance, which clearly evidenced the benefits of gradient profile in the membrane layer. Further, their performance in aerobic membrane bioreactors (AeMBR) was comparably studied for the first time. The treatment performance was not significantly affected by the types of membranes used, while the gradient membrane showed better filtration performance (i.e., a slower rise in TMP). Although the fouling mechanisms were revealed to be similar, the fouling layer in the gradient membrane was composed of a higher percentage of smaller foulants compared to that of the non-gradient counterpart. The observed differences were closely correlated to the larger internal pore structure in the gradient membrane. The present work provides a feasible 3D spray-coating technique for the fabrication of gradient flat-sheet ceramic membranes, and clarifies the benefits in AeMBR for domestic wastewater treatment.

Feasibility of implementing quorum quenching technology to mitigate membrane fouling in MBRs treating phenol-rich pharmaceutical wastewater: Application of Rhodococcus sp. BH4 and quorum quenching consortium.

This study aimed to implement quorum quenching (QQ) to mitigate membrane fouling in membrane bioreactors (MBRs) treating phenol-rich pharmaceutical wastewater using Rhodococcus sp. BH4 and isolated QQ consortium (QQcs) from activated sludge. Neither BH4 nor QQcs impacted the removal efficiency of chemical oxygen demand (COD) (>94%), phenol (>99%), and ammonium (>99%), indicating that QQ did not have adverse impact on treatment performance. In addition, both BH4 and QQcs effectively retarded membrane fouling, which could be attributed to the reduction of soluble microbial products (SMP). Interestingly, the TMP increase was delayed 68.7% by Rhodococcus sp. BH4, while 31.3% was achieved by QQcs. This difference may be due to the relatively higher degradation for short- and medium-chain N-acyl-homoserine lactones (AHLs) by BH4 compared to the QQcs. Furthermore, the possible presence of quorum sensing (QS) bacteria within QQcs also could have contributed to the less effective fouling control than that of BH4.

Enriched autoinducer-2 (AI-2)-based quorum quenching consortium in a ceramic anaerobic membrane bioreactor (AnMBR) for biofouling retardation.

This study is the first to enrich a facultative QQ consortium for AI-2-based quorum sensing (QS) disruption (FQQ2) and discover its quorum quenching (QQ) performance in an anaerobic membrane bioreactor (AnMBR) for membrane fouling retardation. Herein, FQQ2 was enriched by the enrichment culture using 4,5-dihydroxy-2,3-pentanedione (DPD) followed by anaerobic screening. FQQ2 was composed of various facultative AI-2-based QQ microorganisms including Acinetobacter, Comamonas, Stenotrophomonas, and FQQ2 was capable to degrade 96.96% of DPD in 9 h. More importantly, FQQ2 prolonged membrane filtration operation by an average of 3.72 times via reduction of DPD in the AnMBR treating domestic wastewater (p ≤ 0.05). QQ was implicated to reduce the content of proteins and carbohydrates of the extracellular polymeric substances (EPS) of suspended biomass by 24.16% and 10.39%, respectively, and concentration of proteins of the soluble microbial products (SMP) by 18.77%. Parallel factor (PARAFAC) modelling of excitation-emission matrix (EEM) demonstrated that QQ could reduce the content of fulvic acid-like and humic acid-like substances, aromatic proteins and soluble-microbial-by-product-like proteins of the EPS (p ≤ 0.05) and abate the content of soluble-microbial-by-product-like proteins in the SMP (p ≤ 0.05). The lower EPS content of suspended biomass could be rendered with the reduced relative abundance of AI-2-regulated Christensenellaceae;g-, Hyphomicrobium, Leucobacter and Microbacterium by 48.48%, 76.56%, 64.78% and 59.26%, respectively, and QQ led to the reduction of the relative abundance of Christensenellaceae;g- and Leucobacter in the cake layer by 31.07% and 51.43%, respectively. Moreover, quantity of organics as well as planktonic microorganisms in the supernatant decreased in presence of FQQ2 (p ≤ 0.05). Of note, markedly lower relative abundance of AI-2-regulated Sulfurovum in supernatant by 97.74% resulted in its lower abundance of cake layer. Intriguingly, in the presence of QQ, methane production was statistically enhanced by 62.5% (p ≤ 0.05). It was closely linked to the decrease of sulfate reduction (p ≤ 0.05), which resulted from 37.93% lower abundance of sulfate-reduction Desulfomonile in the suspended biomass (p ≤ 0.05). Collectively, this study sheds lights on the development of AI-2-based QQ for biofouling control in AnMBRs.

Insights on fouling development and characteristics during different fouling stages between a novel vibrating MBR and an air-sparging MBR for domestic wastewater treatment.

Membrane fouling remains a major hindrance to a prevalent application of membrane bioreactor (MBR) for wastewater treatment. Vibrating membrane technology has recently attracted increasing attention in energy-efficient fouling control in MBR compared to air sparging. However, little is known about its fundamental fouling control mechanism and whether the vibrating MBR (VMBR) is a highly effective strategy to control fouling constitutions and fouling sources compared to the conventional air-sparging MBR (ASMBR). This study operated two parallel MBRs with vibrating or air-sparging membrane modules for long-term (215 d) real domestic wastewater treatment. Effects of air sparging and vibration rates on fouling control, fouling development and fouling sources across three fouling stages were comprehensively evaluated. Results showed that the VMBR achieved 70% lower fouling rates compared to the ASMBR due to a remarkable retardation in each fouling stage by membrane vibration. The VMBR significantly reduced over 62.7% of colloidCL and SMPCL within the cake layer (CL) to simultaneously alleviate the reversible and irreversible fouling compared to the ASMBR. The comparatively lower dissolved organic matter (DOM) and biopolymer contents in the cake layer of the VMBR resulted in a slower TMP rise. The main DOMs in the foulants of both MBRs were found in the following order: aromatic protein > soluble microbial by-products > other organics. EPSML from mixed liquor (ML) contributed more DOMs to form membrane foulant than the SMPML in both MBRs. Aromatic proteins and soluble microbial products in the EPSML were markedly reduced in the VMBR but increased in the ASMBR in high-shear phase, demonstrating higher effectiveness in fouling control by membrane vibration. This study provided insights into understanding fouling control, fouling development characteristics and fouling mechanisms between the VMBR and ASMBR, which might guide the researchers and engineers to apply novel vibrating MBRs to better control membrane fouling for holistic wastewater treatment in full scale.

Quorum quenching affects biofilm development in an anaerobic membrane bioreactor (AnMBR): from macro to micro perspective.

The first experimental study on the influence of acyl homoserine lactones (AHLs) degrading quorum quenching (QQ) consortium on the dynamics of biofilm bio-communities (i.e., from suspended biomass to initial biofilm and mature biofilm) in an anaerobic membrane bioreactor (AnMBR) at a microscopic scale (denoted as QQAnMBR) was reported. QQ did not change the overall bacterial community of the suspended biomass, inclusive of the key functional bacteria. Moreover, the retarded initial biofilm formation was attributed to not only the lower extracellular polymeric substance content of suspended biomass, but also the decelerated colonization of the AHL-regulated low-abundance in suspended biomass but pioneering keystone taxa Rhodocyclaceae;g- on membrane surface. However, pioneering fouling-related taxa such as Sulfurovum and Rhodocyclaceae;g- still played paramount roles in the delayed initial biofilm formation in the QQAnMBR. Furthermore, the microbial assemblies of the mature biofilm were changed in the QQAnMBR, probably attributable to the abiotic microbial floc attachment.

Comparison between novel vibrating ceramic MBR and conventional air-sparging MBR for domestic wastewater treatment: Performance, fouling control and energy consumption.

Two crucial themes emerge from the growing application of MBRs treating domestic wastewater so far: fouling control and energy demand. The significance of in-situ shear-enhanced methods for fouling control in MBRs has been widely acknowledged with air sparging over decades. However, it is still a challenge to develop energy-efficient ways to replace energy-intensive air sparging for effective fouling control during long-term real domestic wastewater treatment. A novel vibrating flat-sheet ceramic MBR (VMBR) was established for investigating the effects of different shear rates on treatment performance, fouling control and specific energy demand compared with air-sparging MBR (ASMBR). Three levels of shear rates with vibration speed of 120, 80, and 40 RPM in the VMBR, versus specific aeration rate of 1.5, 1.0 and 0.5 LPM in the ASMBR were examined as high-, middle- and low-shear phases. Results showed that the VMBR removed over 78.35% TOC, 89.89% COD and 99.9% NH4-N over three phases, and retarded initial increases in transmembrane pressure to control membrane fouling effectively with average fouling rate around 2.31 kPa/d, 3.59 kPa/d and 10.15 kPa/d, almost 70% lower than the ASMBR in Phase 1, 2 and 3, respectively. Particle size distribution of mixed liquor revealed that colloids and biopolymer clusters were significantly reduced in the VMBR showing less propensity for foulant formation. DOM characteristics further indicated that lower production of polysaccharides and protein (by approximately half in Phases 1 and 2) of SMP and EPS in the VMBR generated lower biopolymer content, promoting better fouling mitigation and enhanced dewaterability compared to the ASMBR. Moreover, the VMBR showed superior energy efficiency for fouling control and could save 51.7% to 78.5% energy of the ASMBR under similar-shear condition. The combination of excellent treatment performance, fouling control and energy efficiency from the VMBR makes this an attractive strategy for future improvement of MBR designs in full-scale application with the potential to replace conventional ASMBR.

Overcoming the Trade-off between Water Permeation and Mechanical Strength of Ceramic Membrane Supports by Interfacial Engineering.

Porous ceramic membrane supports with high mechanical strength and permeation are required for highly permeable ceramic membranes. The water permeation of a ceramic membrane support is largely dependent on its level of open porosity, which can be however generally detrimental to the mechanical strength. In this work, low-cost kaolin nanoflakes were rationally composited with coarse alumina particles, and multichannel flat-sheet ceramic supports were successfully fabricated by extrusion and subsequent partial sintering. The macroscopic properties, microstructure characteristics, permeability, and mechanical strength of the ceramic membrane supports were systematically established and comprehensively studied. The incorporation of kaolin nanoflakes effectively reduced the sintering temperature to about 1200 °C. An interesting evolution of the pore structure was evidenced with the increase in sintering temperature. Interestingly, the porous ceramic supports prepared at 1400 °C with a nominal pore size of 1.47 µm showed the highest water permeability of 9911.9 ± 357.5 LMHB, and at the same time the flexural strength reached 109.6 ± 4.6 MPa. The much improved permeability was attributed to the unique multilevel pore structures, and the enhanced flexural strength mainly originated from the strongly interfacial bonding, as evidenced by the trans-granular fracture behavior. Also, the ceramic membrane supports exhibited excellent chemical resistance and good removal efficiency for oily wastewater. This work highlights the significant role of interfacial engineering in simultaneously improving the water permeation and mechanical strength, thereby overcoming their trade-off in porous ceramic membrane supports.

Effect of quorum quenching on EPS and size-fractioned particles and organics in anaerobic membrane bioreactor for domestic wastewater treatment.

Quorum quenching (QQ) has been applied as a promising membrane fouling control strategy for anaerobic membrane bioreactors (AnMBRs). Nevertheless, long-term operation of AnMBRs for real domestic wastewater (DWW) treatment needs to be systematically studied to evaluate comprehensive membrane fouling mechanisms and bioprocess performance. In this study, the impact of QQ on membrane fouling was investigated using a quorum quenching AnMBR (QQAnMBR) deploying a bead-entrapped facultative quorum quenching consortium (FQQ) to treat DWW. FQQ was shown to prolong membrane filtration operation by an average of 75%. Reduced proteins (p < 0.005) and carbohydrates (p < 0.005) in the extracellular polymeric substances (EPS) of mixed liquor (ML) were key differentiators that led to lower cake layer (CL) formation. Additionally, reduced biopolymers production (p < 0.05) in EPS improved sludge dewaterability. The findings suggested that QQ could alter fluorescent microbial metabolites of both EPS and CL as unveiled by excitation-emission matrix spectra pattern. Furthermore, colloidal particles (i.e., particles with size larger than 0.45 µm in ML supernatants) production was retarded by QQ, thereafter, also contributed to the reduced CL formation. Pore blockage was slightly increased by QQ, which might be attributed to pore blockage by large (∼230 nm) and small organic compounds (∼51 nm) in soluble microbial products (SMP). However, QQ had no significant impact on organic concentration of SMP, and QQ was not associated with particle size distribution of biomass. QQ performance was further affirmed through suppressed production of C4-HSL, 3-OXO-C6-HSL, and C6-HSL. The overall AHLs degradability of FQQ was well-maintained even after five membrane service cycles (total operation of 70 d). Moreover, QQ had no compromised impact on treatment performance (i.e., chemical oxygen demand (COD) removal and methane yield). Collectively, this study bridged the knowledge gap to bring forward QQ technology in AnMBR for widespread domestic wastewater treatment application.

Characterisation of initial fouling in aerobic submerged membrane bioreactors in relation to physico-chemical characteristics under different flux conditions.

The initial fouling characteristics of aerobic submerged membrane bioreactors (MBRs) were analysed under different flux conditions. Physico-chemical analyses of the mixed liquor hinted that carbohydrates were more important to membrane fouling than proteins. However, this contrasted with the characterisation of foulants on the membrane surfaces. Micro-structural analyses of the foulants on the membrane surfaces showed that the dominant foulants were different under different flux conditions. Membrane fouling occurred through a biofilm-dominated process under lower flux conditions, but the mechanism shifted towards a non-biofilm, organic fouling process as the flux was increased. In spite of the differences in fouling mechanisms, it was found that the protein fraction on the membrane surfaces, in the initial stages of MBR operations, had the greatest impact in the rise of transmembrane pressure.

Rapid lab-on-a-chip profiling of human gut bacteria.

The human gut microbiota has a substantial impact on human health. Different factors such as disease, diet and drug use can have significant impacts on the gut microbiota. Therefore, it is of interest to have simple, rapid methods for analysis of the composition of the gut microbiota for clinical diagnostic purposes. Since only a minor fraction of the gastrointestinal bacterial community is presently possible to cultivate, molecular approaches are currently the best suited to investigate its composition. However, most of these molecular approaches require technical expertise and expensive equipment to run and they are not routinely available. Ideally, the analyses should be point-of-care options that can be run on a chip. In this study, an existing lab-on-chip (LOC) system for sizing/quantifying DNA was combined with length heterogeneity PCR (LH-PCR), a PCR-based profiling method targeting bacterial 16S rRNA gene sequences, to develop a fast, straightforward, reproducible, and economical method for profiling bacterial communities. The LOC LH-PCR method was first evaluated using a standardized gut cocktail containing genomic DNA from eight different bacterial species representing different genera of relevance for human health. The method was also tested on DNA that was directly extracted from human faecal samples and it was consistently capable of detecting alterations in the bacterial samples before and after antibiotic treatment. Although the resolution of the method needs improvement, this study represents the first step towards development of a diagnostic LOC for profiling gut bacterial communities.