Enhanced production of methane in anaerobic water treatment as mediated by the immobilized fungi

Recovery of Y(III) from wastewater by Pseudomonas psychrotolerans isolated from a mine soil

While microbial technologies, which are considered to be environmentally friendly, have great potential for the recovery of rare earth elements (REEs) from mining wastewater, their applications have been restricted due to a lack of efficient biosorbents. In this study, a strain of Pseudomonas psychrotolerans isolated from yttrium-enriched mine soil was used to recover yttrium (Y(III)) from rare-earth mining wastewater. At an initial Y(III) dose of 50 mg L-1, the amount of Y(III) adsorbed by P. psychrotolerans reached 99.9 % after 24 h. Various characterization techniques revealed that P. psychrotolerans adsorbed Y(III) mainly through complexation of oxygen-containing functional groups and electrostatic interactions. A high level of adsorption efficiency (>99.9 %) was maintained after five consecutive adsorption/desorption cycles, indicating that P. psychrotolerans was highly reusable. While the efficiency of adsorbing Y(III) by P. psychrotolerans decreased (34.4 %) in actual rare earth mining wastewater, selectivity toward other REEs (≤ 18.4 %) was still observed. Consequently, this study provides a promising green, environmentally friendly and sustainable microbial approach for the selective recovery of REEs from rare earth wastewater.

Mixotrophic aerobic denitrification facilitated by denitrifying bacterial-fungal communities assisted with iron in micro-polluted water: Performance, metabolic activity, functional genes abundance, and community co-occurrence

Low-dosage nitrate pollutants can contribute to eutrophication in surface water bodies, such as lakes and reservoirs. This study employed assembled denitrifying bacterial-fungal communities as bio-denitrifiers, in combination with zero-valent iron (ZVI), to treat micro-polluted water. Immobilized bacterial-fungal mixed communities (IBFMC) reactors demonstrated their ability to reduce nitrate and organic carbon by over 43.2 % and 53.7 %, respectively. Compared to IBFMC reactors, IBFMC combined with ZVI (IBFMC@ZVI) reactors exhibited enhanced removal efficiencies for nitrate and organic carbon, reaching the highest of 31.55 % and 17.66 %, respectively. The presence of ZVI in the IBFMC@ZVI reactors stimulated various aspects of microbial activity, including the metabolic processes, electron transfer system activities, abundance of functional genes and enzymes, and diversity and richness of microbial communities. The contents of adenosine triphosphate and electron transfer system activities enhanced more than 5.6 and 1.43 folds in the IBFMC@ZVI reactors compared with IBFMC reactors. Furthermore, significant improvement of crucial genes and enzyme denitrification chains was observed in the IBFMC@ZVI reactors. Iron played a central role in enhancing microbial diversity and activity, and promoting the supply, and transfer of inorganic electron donors. This study presents an innovative approach for applying denitrifying bacterial-fungal communities combined with iron enhancing efficient denitrification in micro-polluted water.

Fe-Mn binary oxides improve the methanogenic performance and reduce the environmental health risks associated with antibiotic resistance genes during anaerobic digestion

Increasing evidence indicates that metal oxides can improve the methanogenic performance during anaerobic digestion (AD) of piggery wastewater. However, the impacts of composite metal oxides on the methanogenic performance and risk of antibiotic resistance gene (ARG) transmission during AD are not fully understood. In this study, different concentrations of Fe-Mn binary oxides (FMBO at 0, 250, 500, and 1000 mg/L) were added to AD to explore the effects of FMBO on the process. The methane yield was 7825.1 mL under FMBO at 250 mg/L, 35.2% higher than that with FMBO at 0 mg/L. PICRUSt2 functional predictions showed that FMBO promoted the oxidation of acetate and propionate, and the production of methane from the substrate, as well as increasing the abundances of most methanogens and genes encoding related enzymes. Furthermore, under FMBO at 250 mg/L, the relative abundances of 14 ARGs (excluding tetC and sul2) and four mobile gene elements (MGEs) decreased by 24.7% and 55.8%, respectively. Most of the changes in the abundances of ARGs were explained by microorganisms, especially Bacteroidetes (51.20%), followed by MGEs (11.98%). Thus, the methanogenic performance of AD improved and the risk of horizontal ARG transfer decreased with FMBO, especially at 250 mg/L.

Characteristics of fungi formation in urban sewer at different flow conditions: Distribution, metabolism, and pathogenicity

Fungi are the significant components of the sewer ecology system which can consume substances and exhibit pathogenicity. However, the characteristics of fungi formation and metabolism in the complex sewer environment have not been revealed in depth. In this study, gradient flow conditions were conducted in a pilot sewer and the formation characteristics of fungi were synthetically investigated. The results showed that the low flow rate at 0.1-0.4 m/s led to the loose morphology of biofilms, while the overly loose environment did not allow fungi communities to thrive in sewer. The dense biofilms were found at the middle flow condition (0.4-0.6 m/s), and the fungal communities with degradation functions were exuberant at this condition (such as Tremellales with relative abundance of 6.18% and Talaromyces with relative abundance of 6.51%). In particular, eleven kinds of fungi with known pathogenicity of the sewer biofilm were found in this study, and it is worth noting that the abundance of pathogenic fungi at medium flow rates is significantly higher than that at other flow conditions (higher than 10 %). While, excessive flow shear force (0.8-1.2 m/s) led to biofilm shedding which caused hindering the proper generation of fungi. In summary, the pollutant transformation and pathogenic exposure conducted by fungi communities could affect the sewer management process significantly, and this study could provide research foundation for wastewater quality prediction and management of pathogenic risk in sewer systems.

Performance of aerobic denitrifying fungal community for promoting nitrogen reduction and its application in drinking water reservoirs

The effect of mix-cultured aerobic denitrifying microorganisms on the water remediation has been extensively explored, but little is known about the performance of mix-cultured low efficiency fungi on denitrification. In this study, two kinds of aerobic denitrifying fungi (Trichoderma afroharzianum H1 and Aspergillus niger C1) were isolated from reservoirs, improved the capacity by mix-cultured. The results showed a difference between northern and southern reservoirs, the dominants of genera were Cystobasidium and Acremonium. The removals of total nitrogen (TN) was 12.00%, 7.53% and 69.33% in Trichoderma afroharzianum H1, Aspergillus niger C1 and mix-cultured (C1 and H1) under the denitrification medium. The contents of ATP and electron transport system activity in mix-cultured amendment were increased by 42.54% and 67.52%, 1.72 and 2.91 times, respectively. Besides, the raw water experiment indicated that TN removals were 24.05%, 12.66% and 73.42% in Trichoderma afroharzianum H1, Aspergillus niger C1 and mix-cultured. The removals of dissolved organic carbon in mix-cultured were increased 35.02% and 50.46% compared to Trichoderma afroharzianum H1 and Aspergillus niger C1. Therefore, mix-cultured of two low efficiency aerobic denitrifying fungi has been considered as a novelty perspective for mitigation of drinking water source.

Anammox activity improved significantly by the cross-fed NO from ammonia-oxidizing bacteria and denitrifying bacteria to anammox bacteria

Nitric oxide (NO) has been suggested as an obligate intermediate in anaerobic ammonium oxidation (anammox), nitrification and denitrification. At the same time, ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB) are always existed in anammox flora, so what is the role of NO produced from AOB and DNB? Could it accelerate nitrogen removal via the anammox pathway with NO as an electron acceptor? To investigate this hypothesis, nitrogen transforming of an anammox biofilter was analyzed, functional gene expression of anammox bacteria (AnAOB), AOB and DNB were compared, and NO source was verified. For anammox biofilter, anammox contributed to 91.3 % nitrogen removal with only 14.4 % of AnAOB being enriched, while DNB was dominant. Meta-omics analysis and batch test results indicated that AOB could provide NO to AnAOB, and DNB also produced NO via up-regulating nirS/K and down-regulating nor. The activation of the anammox pathway of NH4++NO→N2 caused the downregulation of nirS and nxr in Ca. Kuenenia stuttgartiensis. Additionally, changes in nitrogen transforming pathways affected the electron generation and transport, limiting the carbon metabolism of AnAOB. This study provided new insights into improving nitrogen removal of the anammox system.

Biocomposite based on graphene oxide immobilized Pseudomonas psychrotolerans for the recovery of Y(III) in acid mine drainage

Rare earth elements (REEs) recovery is a critical issue concerning both resource recovery and wastewater utilization. In this study, a new bio-composite was fabricated using graphene oxide immobilized Pseudomonas psychrotolerans (PP@GO), which was isolated from the soil of REEs mine. Results showed that 99.6% Y(III) was removed in 48 h and various characterization confirmed that S-S, -NH2, HPO42-, -OH and -COOH from extracellular polymeric substances (EPS) secreted by microorganisms formed complexation with Y(III). As well, the Y(III) adsorption best followed Freundlich isotherm and non-linear pseudo-second-order kinetic model having R2 of 0.985 and 0.996, respectively, demonstrating that the adsorption was governed by multilayered chemisorption. Additionally, the effectiveness of PP@GO was not limited to Y(III), where 27.9% of this substance was removed in acid mine drainage (AMD), also exhibited great adsorption for other REEs, such as Er (45.0%) and Ho (43.8%). Furthermore, the adsorption efficiency of Y(III) remained high (70.0%) after a 5th cycle, emphasizing the consistent stability of PP@GO. Finally, REEs adsorbed could be greatly desorbed by KNO3, like Sm (80.1%) and La (80.0%), which revealed that PP@GO has great potential to recover REEs in AMD. Overall, this study offers a promising strategy for the green and sustainable REEs recovery and wastewater treatment.

Biomethane is produced by acetate cleavage, not direct interspecies electron transfer: genome-centric view and carbon isotope

Understanding the source of methane (CH4) is of great significance for improving the anaerobic fermentation efficiency in bioengineering, and for mitigating the emission potential of natural ecosystems. Microbes involved in the process named direct interspecies electron transfer coupling with CO2 reduction, i.e., electrons released from electroactive bacteria to reduce CO2 into CH4, have attracted considerable attention for wastewater treatment in the past decade. However, how the synergistic effect of microbiota contributes to this anaerobic carbon metabolism accompanied by CH4 production still remains poorly understood, especial for wastewater with antibiotic exposure. Results show that enhancing lower-abundant acetoclastic methanogens and acetogenic bacteria, rather than electroactive bacteria, contributed to CH4 production, based on a metagenome-assembled genomes network analysis. Natural and artificial isotope tracing of CH4 further confirmed that CH4 mainly originated from acetoclastic methanogenesis. These findings reveal the contribution of direct acetate cleavage (acetoclastic methanogenesis) and provide insightsfor further regulation of methanogenic strategies.

Co-culture of Acinetobacter sp. and Scedosporium sp. immobilized beads for optimized biosurfactant production and degradation of crude oil

The widespread exploration and exploitation of crude oil has increased the prevalence of petroleum hydrocarbon pollution in the marine and coastal environment. Bioremediation of petroleum hydrocarbons using cell immobilization techniques is gaining increasing attention. In this study, the crude oil degradation performance of bacterial and fungal co-culture was optimized by entrapping both cells in sodium-alginate and polyvinyl alcohol composite beads. Results indicate that fungal cells remained active after entrapment and throughout the experiment, while bacterial cells were non-viable at the end of the experimental period in treatments with the bacterial-fungal ratio of 1:2. A remarkable decrease in surface tension from 72 mN/m to 36.51 mN/m was achieved in treatments with the bacterial-fungal ratio of 3:1. This resulted in a significant (P < 0.05) total petroleum hydrocarbon (TPH) removal rate of 89.4%, and the highest degradation of n-alkanes fractions (from 2129.01 mg/L to 118.53 mg/L), compared to the other treatments. Whereas PAHs removal was highest in treatments with the most fungal abundance (from 980.96 μg/L to 177.3 μg/L). Furthermore, enzymes analysis test revealed that catalase had the most effect on microbial degradation of the target substrate, while protease had no significant impact on the degradation process. High expression of almA and PAH-RHDa genes was achieved in the co-culture treatments, which correlated significantly (P < 0.05) with n-alkanes and PAHs removal, respectively. These results indicate that the application of immobilized bacterial and fungal cells in defined co-culture systems is an effective strategy for enhanced biodegradation of petroleum hydrocarbons in aqueous systems.

Promoted aerobic denitrification through denitrifying fungal communities: Co-occurrence patterns and treatment of low C/N micro-polluted water

Despite the growing interest in using mixed-culture aerobic denitrifying fungal flora (mixed-CADFF) for water remediation, there is limited research on their nitrogen removal performance in low C/N polluted water bodies. To address this knowledge gap, we isolated three mixed-CADFFs from overlying water in urban lakes to evaluate their removal performance. The total nitrogen (TN) removal efficiencies were 93.60 %, 94.64 %, and 95.18 %, while the dissolved organic carbon removal efficiencies were 96.64 %, 95.12 %, and 96.70 % for mixed-CADFF LN3, LN7, and LN15, respectively in the denitrification medium under aerobic conditions at 48 h cultivation. The three mixed-CADFFs could utilize diverse types of low molecular weight carbon sources to drive the aerobic denitrification processes efficiently. The optimal C/N ratio for the mixed-CADFFs were C/N = 10, and then C/N = 15, 7, 5, and 2. The high-throughput sequencing analysis of three mixed-CADFFs indicated that Eurotiomycetes, Cystobasidiomycetes, and Sordariomycetes were the dominant class in the communities at class level. The network analysis showed that the rare fungal species, such as Scedosporium dehoogii Saitozyma, and Candida intermedia presented positively co-occurred with the TN removal and organic matter reduction capacity. Immobilization mixed-CADFFs treatment raw water experiments indicated that three mixed-CADFFs could reduce nearly 62.73 % of TN in the low C/N micro-polluted raw water treatment. Moreover, the cell density and cell metabolism indexes were also increased during the raw water treatment. This study will provides new insight into resource utilization of the mixed-culture aerobic denitrifying fungal community in field of environment restoration.

Towards sustainability: Threat of water quality degradation and eutrophication in Usangu agro-ecosystem Tanzania

The agrochemicals and nutrient losses from farming areas such as paddy farming significantly dictate quality and eutrophication of the freshwater resource. However, how farming and land use pattern affect water qualities and eutrophication remain poorly understood in most African agro-ecosystems. The present study characterized how paddy farming influences water qualities and eutrophication in 10 irrigation schemes in Usangu agro-ecosystem (UA). About 42 water samples were sampled from intakes, channels, paddy fields, and drainages and analyzed for EC, Cl, P, NH₄-N, NO₃-N, TN, Zn, Cu, Ca, and Mg. We observed water pH ranging from 4.89 to 6.76, which was generally below the acceptable range (6.5-8.4) for irrigation water. NH₄-N concentration was in a range of 10.6-70.0 mg/L, NO₃-N (8.4-33.9 mg/L), and TN (19.1-21,104 mg/L). NH₄-N increased along sampling transect (sampling points) from intakes (5.7-29.1 mg/L), channels (19-20 mg/L), fields (12.9-35.8 mg/L), and outflow (10.6-70.0 mg/L), the same trend were found for NO₃-N and TN. The TP determined in water samples were in the range of 0.01 to 1.65 mg/L; where some sites had P > 0.1 mg/L exceeding the allowable P concentration in freshwater resource, thus indicating P enrichment and eutrophication status. The P concentration was observed to increase from intake through paddy fields to drainages, where high P was determined in drainages (0.02-1.65 mg/L) and fields (0.0-0.54 mg/L) compared to channels (0.01-0.13 mg/L) and intakes (0.01-0.04 mg/L). Furthermore, we determined appreciable amount of potentially toxic elements (PTEs) such as Cu, Pb, Cd and Cr in studied water samples. The high N, P, and PTEs in drainages indicate enrichment from agricultural fields leading to water quality degradation and contaminations (eutrophication). The study demonstrates that water quality in UA is degrading potentially due to paddy rice farming and other associated activities in the landscape. Thus, the current study recommends starting initiatives to monitor irrigation water quality in UA for better crop productivity, and improved quality of drainage re-entering downstream through the introduction of mandatory riparian buffer, revising irrigation practices, to include good agronomic practices (GAP) to ensure water quality and sustainability.

Bioconversion of food and lignocellulosic wastes employing sugar platform: A review of enzymatic hydrolysis and kinetics

Bioenergy and biochemicals can be sustainably produced through fermentation and anaerobic digestion (AD). However, this bioconversion processes could be more economical if the hydrolysis rates of substrates in bioreactors can be accelerated. In this review, the feasibilities of including enzymatic hydrolysis (EH) in various bioconversion systems were studied to facilitate the biological synergy. The reaction kinetics of EH in bioconversion systems comparing pretreated lignocellulosic biomass (LCB) and food waste (FW) substrates were reviewed. Possible strategies to improve the hydrolysis efficiency were explored, including co-cultivation during enzyme production and replacement of pure enzyme with on-site produced fungal mash during EH. Key insights into improvement of current AD and fermentation technologies were summarized and further formed into suggestions of future directions in techno-economic feasibility of biorefinery using mixture of the first-generation food crop feedstock with FW; and/or co-digestion of FW with LCB.

Anaerobic digestion of wood vinegar wastewater using domesticated sludge: Focusing on the relationship between organic degradation and microbial communities (archaea, bacteria, and fungi)

Thermochemical process of biomass is one of the promising renewable energy technologies; however, the by-product (wood vinegar wastewater) is rich in refractory organics, which is harmful to the environment and inhibits the conversion efficiency of microorganisms. Consequently, the dominant functional microbial communities corresponding to the various substrate were obtained through the continuous domestication, and the relationship between the dominant functional communities and the degradation of organic compounds was comprehensively analyzed. The bacterial community was absolutely dominant (approximately 85%), while archaea and fungi had similar relative abundance. The diversity showed that glucose was not conducive to the development of microbial diversity, while the substrate containing wood vinegar wastewater showed the opposite trend. The functional analysis revealed that the enrichment of bacteria associated with the hydrolysis and acidification of organics increased in the domestication process. Glucose facilitated hydrogen-trophic methanogenesis as the main methanogenic pathway in the methanogenic stage.

Promoting anaerobic co-digestion of sewage sludge and food waste with different types of conductive materials: Performance, stability, and underlying mechanism

In this research, we investigated and compared the effects of three widely used conductive materials, e.g., zero-valent iron (Fe⁰), magnetite (Fe₃O₄), and biochar on the performance, stability, and in-depth mechanism during the anaerobic co-digestion process of sewage sludge and food waste. Among the three conductive materials, Fe⁰ could achieve the highest cumulative methane production of 394.0 mL/g volatile solids (VS) _added, which was 1.24-fold and 1.17-fold higher than that receiving Fe₃O₄ and biochar. The mechanistic studies indicated that compared to the Fe₃O₄ and biochar groups, Fe⁰ could significantly enhance the release of soluble protein, polysaccharide, and dissolved organic matters, the degradation of volatile fatty acids and VS, and the activities of key enzymes and direct interspecies electron transfer (DIET). Consequently, the methane yield and digestate dewaterability were notably improved. Collectively, these findings will offer suggestions of the preferable conductive materials in the anaerobic co-digestion process for decision makers.

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.

Genomic driven factors enhance biocatalyst-related cellulolysis potential in anaerobic digestion

Anaerobic digestion (AD) is a promising technology to recover bioenergy from biodegradable biomass, including cellulosic wastes. Through a few fractionation/separation techniques, cellulose has demonstrated its potential in AD, but the performance of the process is rather substrate-specific, as cellulolysis bacteria are sensitive to the enzyme-substrate interactions. Cellulosome is a self-assembled enzyme complex with many functionalized modules in the bacteria which has been gradually studied, however the genomic fingerprints of the culture-specific cellulosome in AD are relatively unclear especially under processing conditions. To clarify the key factors affecting the cellulosome induced cellulolysis, this review summarized the most recent publications of AD regarding the fates of cellulose, sources and functional genes of cellulosome, and omics methods for functional analyses. Different processes for organic treatment including applying food grinds in sewer, biomass valorization, cellulose fractionation, microaeration, and enzymatic hydrolysis enhanced fermentation, were highlighted to support the sustainable development of AD technology.