Dr Bang Du

In parallel with novel process developments and experimental research in anaerobic digestion, considerable effort has been put into kinetic modelling. The use of mathematical models results in a better understanding of the system performance and process dynamics, including microbial growth and substrate degradation. Typically, various kinetic models, such as the Monod model, are employed to describe microbial growth dynamics. Substrate degradation within anaerobic digestion systems relies on the cooperation among multiple steps, with hydrolysis or methanogenesis often serving as the rate-limiting step. Additionally, the effluent substrate concentration (or the biogas production) can be estimated through models without detailed steps, such as the Chen and Hashimoto model. Ultimately, the accuracy and reliability of kinetic models depend on the goodness of fit to experimental data, ensuring robust evaluation of system performance based on the established kinetic models.

Iron sulfides-based autotrophic denitrification (IAD) is effective for treating nitrate-contaminated wastewater. However, the complex nitrate transformation pathways coupled with sulfur and iron cycles in IADs are still unclear. In this study, two columns (abiotic vs biotic) with iron sulfides (FeS) as the packing materials were constructed and operated continuously. In the abiotic column, FeS chemically reduced nitrate to ammonium under the ambient condition; this chemical reduction reaction pathway was spontaneous and has been over-looked in IAD reactors. In the biotic column (IAD biofilter), the complex nitrogen-transformation network was composed of chemical reduction, autotrophic denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and sulfate reducing ammonium oxidation (Sulfammox). Metagenomic analysis and XPS characterization of the IAD biofilter further validated the roles of functional microbial communities (e.g., Acidovorax, Diaphorobacter, Desulfuromonas) in nitrate reduction process coupled with iron and sulfur cycles. This study gives an in-depth insight into the nitrogen transformations in IAD system and provides fundamental evidence about the underlying microbial mechanism for its further application in biological nitrogen removal.

Anaerobic ethanol oxidation is thermodynamically unfavourable under standard conditions, while it can be exergonic with the participation of extracellular electron transfer (EET) through microbial redox-active proteins (RAP). In this study, effects of the fraction of substrate degraded through the EET pathway (EET fraction), product feedback, the distribution of produced electrons from the EET pathway between acetotrophic and hydrogenotrophic methanogenesis, and the redox potential of RAP on anaerobic ethanol oxidation were thermodynamically evaluated. Ethanol oxidation could occur when the redox potential was above -0.408 V with EET, or when the product concentration was below the threshold value. The appropriate redox potential ranges for active acetotrophic and hydrogenotrophic methanogens were below -0.214 V and -0.222 V, respectively. The EET fraction was a key factor in maintaining biomass yields, and the distribution of electrons produced from ethanol oxidation affected the biomass ratio of two types of methanogens. Finally, strategies for one-reactor and zone-separation systems were proposed to optimize system performance and bioenergy recovery from waste resources.

Bacterial surface attachment and subsequent biofilm expansion represent an essential adaptation to environmental signals and stresses, which are of great concern for many natural and engineered ecosystems. Yet the underlying mechanisms and driving forces of biofilm formation in a chlorinated and nutrient-restricted system remain sketchy. In this study, we coupled an experimental investigation and modeling simulation to understand how chlorination and nutrient limitation conspire to form biofilm using Pseudomonas aeruginosa as a model bacterium. Experimental results showed that moderate chlorination at 1.0 mg/L led to biofilm development amplified to 2.6 times of those without chlorine, while additional nutrient limitation (of 1/50-diluted or 0.4 g/L LB broth culture) achieved 4.6 times increment as compared to those of undiluted scenarios (of 20 g/L LB broth culture) with absence of chlorination after 24 h exposure. Meanwhile, intermediate chlorination stimulated instant flagellar motility and subsequently extracellular polymeric substances (EPS) secretion, particularly under limited nutrient condition (of 1/50-diluted or 0.4 g/L LB broth culture) that retarded chlorine consumption and provoked bacterial nutrient-limitation response. From our simulations, chlorine and resource levels along with associated spatio-temporal variations collectively drove bacterial cell movement and EPS excretion. Our results demonstrated that restraining nutrient intensified chlorination-excited cell movement and EPS production that reinforced biological and cell-surface interactions, thereby encouraging bacterial surface attachment and subsequent biofilm development. The findings provide the insights into the linkage of disinfectant and nutrient-regulated bacterial functional responses with consequent micro-habitats and biofilm dynamics. [Display omitted] •Moderate chlorination-enhanced chemotaxis contributes to initial surface attachment.•Chlorination stimulus-favored biofilm development is mainly linked to excited EPS.•Concurrently limiting resource retards chlorine decay and incites starvation response.•Cell motility and EPS excretion are tightly connected to instant local surroundings.

Anaerobic ethanol oxidation relies on syntrophic interactions among functional microorganisms to become thermodynamically feasible. Different operational modes (sequencing batch reactors, SBRs, and continuous flow reactors, CFRs) and solids retention times (SRT, 25 days and 10 days) were employed in four ethanol-fed reactors, named as SBR , SBR , CFR , and CFR , respectively. System performance, syntrophic relationships, microbial communities, and metabolic pathways were examined. During the long-term operation, 2002.7 ± 56.0 mg COD/L acetate was accumulated in CFR due to the washout of acetotrophic methanogens. Microorganisms with high half-saturation constants were enriched in reactors of 25-day SRT. Moreover, ethanol oxidizing bacteria and acetotrophic methanogens with high half-saturation constants could be acclimated in SBRs. In SBRs, Syner-01 and Methanothrix dominated, and the low SRT of 10 days increased the relative abundance of Geobacter to 38.0%. In CFRs, the low SRT of 10 days resulted in an increase of Desulfovibrio among syntrophic bacteria, and CFR could be employed in enriching hydrogenotrophic methanogens like Methanobrevibacter.

•Tolerance of HMs to FAN and NH4+ was near 11 times and 3 times that of AMs•AMs were more impacted by FAN while HMs were more impacted by NH4+•A low TAN concentration (1.0-4.0 g N/L) caused irreversible inhibition of AMs•HMs were fully or over recovered from severe ammonia stress (TAN≤10.0 g N/L) A shift from the acetoclastic to the hydrogenotrophic pathway in methanogenesis under ammonia inhibition is a common observation in anaerobic digestion. However, there are still considerable knowledge gaps concerning the differential ammonia tolerance of acetoclastic and hydrogenotrophic methanogens (AMs and HMs), their responses to different ammonia species (NH4+, NH3), and their recoverability after ammonia inhibition. With the successful enrichment of mesophilic AMs and HMs cultures, this study aimed at addressing the above knowledge gaps through batch inhibition/recovery tests and kinetic modeling under varying total ammonia (TAN, 0.2-10 g N/L) and pH (7.0-8.5) conditions. The results showed that the tolerance level of HMs to free ammonia (FAN, IC50=1345 mg N/L) and NH4+ (IC50=6050 mg N/L) was nearly 11 times and 3 times those of AMs (NH3, IC50=123 mg N/L; NH4+, IC50=2133 mg N/L), respectively. Consistent with general belief, the AMs were more impacted by FAN. However, the HMs were more adversely affected by NH4+ when the pH was ≤8.0. A low TAN (1.0-4.0 g N/L) could cause irreversible inhibition of the AMs due to significant cell death, whereas the activity of HMs could be fully or even over recovered from severe ammonia stress (FAN≤ 0.9 g N/L or TAN≤10 g N/L; pH ≤8.0). The different tolerance responses of AMs and HMs might be associated with the cell morphology, multiple energy-converting systems, and Gibbs free energy from substrate-level phosphorylation. [Display omitted]

Q935; 为揭示外界环境中营养物质对细菌运动和附着行为特征的影响,以给水管网中常见的铜绿假单胞菌(Pseudomonas aeruginosa)野生株(WT PAO1)和变异株(无运动能力,PAO1ΔfliC)为研究对象,采用基于个体的数学模型方法,使用MATLAB平台模拟微尺度下营养条件胁迫与细菌初期表面附着、个体运动、生长的定量关系,研究其在不同营养环境中的附着与运动行为.结果表明:营养条件显著影响着环境中细菌的运动速度和附着量(P

Ethanol plays a key role in advancing the sustainable technology of anaerobic digestion. A comprehensive understanding of ethanol metabolism is essential for optimizing the enhanced recovery of renewable energy from waste feedstocks via anaerobic digestion. This review aims to summarize key findings on ethanol metabolism, focusing on metabolic pathways, kinetics and ecological applications, as well as functional microorganisms and their enrichment strategies. Three ethanol metabolic pathways are discussed: (i) the conventional pathway yielding acetate and hydrogen, (ii) the direct interspecies electron transfer (DIET) pathway, and (iii) the propionate-producing pathway. A comprehensive summary of the kinetics involved in ethanol degradation, microbial growth, and inhibition can enhance reactor design and facilitate the application of the r/K selection theory to enrich functional microorganisms. Operational parameters informed by the r/K selection theory can be used to enrich functional ethanol-oxidizing bacteria, such as Geobacter, thereby influencing ethanol metabolic pathways. These insights offer valuable guidance for further exploration of ethanol degradation toward desired products in the anaerobic treatment of waste feedstocks. Future research should aim to develop a unified ecological framework to explain the coexistence of multiple ethanol metabolic pathways, potentially through concepts such as division of labour or overflow metabolism. Additionally, integrating extracellular electron transfer into thermodynamic models may yield new insights into ethanol metabolism. Finally, DIET-based anaerobic digestion technologies utilizing ethanol should be explored for the degradation of complex substrates.

Efficient anaerobic digestion requires the syntrophic cooperation among diverse microorganisms with various metabolic pathways. In this study, two operational modes, i.e., the sequencing batch reactor (SBR) and the continuous-flow reactor (CFR), were adopted in ethanol-fed systems with or without the supplement of powdered activated carbon (PAC) to examine their effects on ethanol metabolic pathways. Notably, the operational mode of SBR and the presence of CO facilitated ethanol metabolism towards propionate production. This was further evidenced by the dominance of Desulfobulbus, and the increased relative abundances of enzymes (EC: 1.2.7.1 and 1.2.7.11) involved in CO metabolism in SBRs. Moreover, SBRs exhibited superior biomass-based rates of ethanol degradation and methanogenesis, surpassing those in CFRs by 53.1% and 22.3%, respectively. Remarkably, CFRs with the extended solids retention time enriched high relative abundances of Geobacter of 71.7% and 70.4% under conditions with and without the addition of PAC, respectively. Although both long-term and short-term PAC additions led to the increased sludge conductivity and a reduced methanogenic lag phase, only the long-term PAC addition resulted in enhanced rates of ethanol degradation and propionate production/degradation. The strategies by adjusting operational mode and PAC addition could be adopted for modulating the anaerobic ethanol metabolic pathway and enriching Geobacter.

Operational mode and powdered activated carbon (PAC) are key factors facilitating microbial syntrophy and interspecies electron transfer during anaerobic digestion, consequently benefiting process stability and efficient methanogenesis. In this study, continuous-flow reactor (CFR) and sequencing batch reactor (SBR), with and without the addition of PAC, respectively, were operated to examine their effects on system performance and methanogenic activity. Based on the cycle-test result, the PAC-amended CFR (CFR ) recorded both the highest methane yield (690.1 mL/L) and the maximum CH production rate (28.8 mL/(L·h)), while SBRs exhibited slow methanogenic rates. However, activity assays indicated that SBRs were beneficial for organics removal in batch experiments fed with peptone. Taxonomic and functional analysis confirmed that CFRs were optimal for proliferating oligotrophs (e.g., Geobacter) and SBRs were more suitable for copiotrophs (e.g., Desulfobulbus). Metagenomic analysis revealed that CFRs had efficient acetate metabolic pathways from propionate and ethanol, whereas SBRs did not, resulting in the buildup of propionate. Furthermore, Methanobacterium and Methanothrix were acclimated to the different operational conditions, while acetoclastic Methanosarcina and hydrogenotrophic Methanolinea were acclimated in SBRs (5.1-13.4%) and CFRs (0.3-1.7%), respectively. This study confirmed the enhancement of microbial syntrophy by the addition of PAC as well as the acclimation of electroactive bacteria (e.g., Geobacter) with complex organic substances.

Hydrogen sulfide (H2S), a product of sulfate reduction in anaerobic digestion (AD) systems, poses severe challenges by reducing methane production and destabilizing system performance. Despite extensive studies on H2S toxicity, the specific responses and adaptation mechanisms to H2S stress of key functional microorganisms in AD systems remain insufficiently elucidated. Four reactors were operated with sequencing batch reactor (SBR) and continuous flow reactor (CFR) configurations under varying COD/sulfate ratios (2 and 1) to investigate microbial response to H2S inhibition. Long-term experiments demonstrated that CFRs combined with a COD/sulfate ratio of 1 achieved superior sulfate reduction and ethanol degradation rates under H2S stress, while SBRs with a COD/ sulfate ratio of 2 facilitated methanogenic activity. Batch inhibition experiments revealed that ethanol-oxidizing bacteria (EOB) and incomplete oxidizing sulfate-reducing bacteria (IO-SRB) exhibited greater H2S tolerance in CFRs, with EOB (IC50 = 51.2-185.1 mg/L) generally outperforming IO-SRB (IC50 = 47.4-97.7 mg/L). While acetoclastic methanogens (AM) and complete oxidizing sulfate-reducing bacteria showed enhanced H2S tolerance in SBRs compared to CFRs, particularly AM in SBR with the COD/sulfate ratio of 2 (IC50 = 113.2 mg/L). Microbial adaptation analysis demonstrated that SBRs promoted Methanothrix enrichment, enhancing detoxification capacity by specifically increasing the relative abundance of genes encoding thiosulfate sulfurtransferase to mitigate H2S toxicity. Desulfomicrobium and Geobacter were significantly enriched in CFRs, and they mitigated H2S inhibition through increased cytochrome bd oxidase and cysteine synthase genes, respectively. Furthermore, thioredoxin and cysteine desulfurase protein repair genes sustained microbial metabolism under H2S stress. This study provides critical insights into microbial tolerance and adaptive strategies to H2S under different reactor configurations, offering guidance for optimizing AD processes in sulfate-rich wastewater treatment.

Tetracycline exerts an inhibitory effect on anaerobic digestion, inducing stressed microbial activities and even system failure. Continuous -flow reactors (CFRs) and sequencing batch reactors (SBRs) were employed along with the dosage of powdered activated carbon (PAC) to enhance tetracycline removal during anaerobic digestion of complex organic compounds. PAC increased the maximum methane production rate by 15.6% (CFRs) and 13.8% (SBRs), and tetracycline biodegradation by 24.4% (CFRs) and 19.2% (SBRs). CFRs showed higher tetracycline removal and methane production rates than SBRs. Geobacter was enriched in CFRs, where Methanothrix was enriched with the addition of PAC. Desulfomicrobium harbored abundant propionate degradation -related genes, significantly correlating with tetracycline removal. The genes encoding carbon dioxide reduction in Methanothrix along with the detection of Geobacter might indicate direct interspecies electron transfer for methanogenesis in CFRs and PAC -added reactors. The study offers new insights into anaerobic digestion under tetracycline -stressed conditions and strategies for optimizing tetracycline removal.

Mechanistic understanding of acetoclastic methanogenesis is pivotal for optimizing anaerobic digestion for efficient methane production. In this study, two different operational modes, continuous flow reactor (CFR) and sequencing batch reactor (SBR), accompanied with solids retention times (SRT) of 10 days (SBR10d and CFR10d) and 25 days (SBR25d and CFR25d) were implemented to elucidate their impacts on microbial communities and energy metabolism of methanogens in acetate-fed systems. Microbial community analysis revealed that the relative abundance of Methanosarcina (16.0%–46.0%) surpassed Methanothrix (3.7%–22.9%) in each reactor. SBRs had the potential to enrich both Methanothrix and Methanosarcina. Compared to SBRs, CFRs had lower total relative abundance of methanogens. Methanosarcina exhibited a superior enrichment in reactors with 10-day SRT, while Methanothrix preferred to be acclimated in reactors with 25-day SRT. The operational mode and SRT were also observed to affect the distribution of acetate-utilizing bacteria, including Pseudomonas, Desulfocurvus, Mesotoga, and Thauera. Regarding enzymes involved in energy metabolism, Ech and Vho/Vht demonstrated higher relative abundances at 10-day SRT compared to 25-day SRT, whereas Fpo and MtrA-H showed higher relative abundances in SBRs than those in CFRs. The relative abundance of genes encoding ATPase harbored by Methanothrix was higher than Methanosarcina at 25-day SRT. Additionally, the relative abundance of V/A-type ATPase (typically for methanogens) was observed higher in SBRs compared to CFRs, while the F-type ATPase (typically for bacteria) exhibited higher relative abundance in CFRs than that in SBRs. [Display omitted] •Reduction in SMR shortened the lag phase in acetoclastic methanogenesis.•SBRs with 25-day SRT tend to enrich both Methanosarcina and Methanothrix.•SRT of 10 days benefited the enrichment of Methanosarcina, particularly in SBR.•The V/A-type and F-type ATPase were mainly affected by operational modes.

Deciphering relationships between sulfate-reducing bacteria (SRB) and other microorganisms is crucial for stable operation of anaerobic digestion systems when treating sulfate-containing wastewater. However, few studies have differentiated the incomplete oxidizing SRB (IO-SRB) and complete oxidizing SRB (CO-SRB) in anaerobic digestion ecosystems. Four ethanol-fed bioreactors were operated under two operational modes (sequencing batch reactor, SBR; and continuous-flow reactor, CFR) and two chemical oxygen demand (COD) to sulfate ratios (1 and 2) to systematically explore strategies for enriching IO-SRB and/or CO-SRB and their microbial interactions with other microorganisms. Compared to SBRs, CFRs could enhance sulfate removal and demonstrated higher microbial activities in sulfate and ethanol degradation. IO-SRB competed with ethanol oxidizing bacteria in all reactors, and IO-SRB's contribution to ethanol degradation increased from 62.9 %-67.1 % to 69.0 %-82.1 % as the COD/sulfate ratio decreased from 2 to 1. Moreover, CO-SRB competed acetotrophic methanogens exclusively in CFRs, as CO-SRB could not be efficiently enriched in SBRs. Low COD/sulfate ratios facilitated the enrichment of Desulfococcus (CO-SRB), and the CFR operational mode further strengthened its enrichment. Additionally, hydrogenotrophic SRB outperformed hydrogenotrophic methanogens in all four reactors. In general, IO-SRB and CO-SRB possessed distinct microbial interactions with methanogens, with potential syntrophic relationships between IO-SRB and acetotrophic methanogens while competitive relationships between CO-SRB and acetotrophic methanogens.

Flagellar motility enables resource acquisition and noxious substance evasion, underpinning imperative ecological processes in aquatic environments. Yet the underlying mechanism that links flagellar motility with surface attachment and thereby biofilm formation, especially in conditions of limited resource availability, remains elusive. Here, we present experimental and modeling evidence to unveil bacterial motility and biofilm formation under nutrient-limited stresses with Pseudomonas aeruginosa (WT) and its nonflagellated isogenic mutant (Delta fiiC) as model bacteria. Results revealed that boosted flagellar motility of WT strain promoted biofilm initialization to a peak value of 0.99 x 10(7) cells/cm(2) at 1/50 dilution after 20 min incubation. We hypothesized that bacteria can invoke instant motility acceleration for survival confronting nutrient-limited stress, accompanied by optimized chemotactic foraging through sensing ambient chemical gradients. Accordingly, accelerated cell motility in oligotrophic environment created increased cell-cell and cell-surface interactions and thereof facilitated biofilm initialization. It was confirmed by the consistence of modeling predictions and experimental results of cell velocity and surface attachment. With the development of biofilm, promotion effect of flagellar motility responding to nutrient deprivation-stress faded out. Instead, loss of motility profiting increased growth rates and extracellular protein excretion, associated with an enhancement of biofilm development for the mutant in oligotrophic aquatic environment. For both strains, nutrient limitation evidently reduced planktonic cell propagation as expected. Our results offer new insights into the mechanical understanding of biofilm formation shaped by environmental stresses and associating biological responses.