Metagenomic insights into aniline effects on microbial community and biological sulfate reduction pathways during anaerobic treatment of high-sulfate wastewater

Exogenous additive ferric sulfate regulates sulfur-oxidizing bacteria in cow manure composting to promote carbon fixation

Enhancing carbon fixation in the composting process was of great significance in the era of massive generation of organic solid waste. In this study, the experimental results showed that the contents of dissolved organic matter (DOM) in the experimental group (CT) were 37.58% higher than those in the control group (CK). The CO2 emission peaked on day 5, and the value of CK was 1.34 times that of CT. Significant differences were observed between the contents of sulfur fractions in CT and CK. This phenomenon may be due to the suppression of sulfur-reducing gene expression in CT. On day 51 of composting, the abundance of sulfur-oxidizing bacteria (SOB) Rhodobacter (5.33%), Rhodovulum (14.76%), and Thioclava (23.83%) in CT was higher than that in CK. In summary, the composting fermentation regulated by Fe2(SO4)3 increased the sulfate content, enhanced the expression of sulfur-oxidizing genes and SOB, and ultimately promoted carbon sequestration during composting.

Exploring the synergistic interplay of sulfur metabolism and electron transfer in Cr(VI) and Cd(II) removal by Clostridium thiosulfatireducens: Genomic and mechanistic insights

In this study, a sulfate-reducing bacterium, Clostridium thiosulfatireducens (CT) was reported and the performance and removal mechanism of Cr(VI) and Cd(II) removal were investigated. It is noteworthy that the dsrAB gene is absent in this strain, but the strain is capable of producing sulfide. The conversion rate of Cr(VI) by CT was 84.24 % at a concentration of 25 mg/L, and the conversion rate of Cd(II) was 94.19 % at a concentration of 28 mg/L. The complete genome is 6,106,624 bp and the genome consisted of a single chromosome. The GC content of the chromosomes was 29.65 %. The mechanism of heavy metal removal by CT bacteria mainly includes biosorption, electron transfer and redox, with reduction combined with S2- precipitation as the main pathway. The product characterization results showed that the formation of mainly ionic crystals and precipitates (CdS, Cd(OH)2, Cr(OH)3, Cr2O3) after adsorption. Genome-wide techniques have shown that the clearance of Cr(VI) and Cd(II) by CT is largely dependent on sulfate transport, sulfur metabolism, and energy metabolism to some extent. In addition, genes related to ATP binding, electron carrier activity, transporter protein genes, and DNA repair are also important factors to improve the heavy metal resistance and transformation ability of CT strains. Both the Fe-S cycle and the ROS-resistant system can enhance the electron transfer activity and thus slow down the damage of heavy metals to microorganisms. This study fills the gap in the understanding of the basic properties and heavy metal transformation mechanism of CT.

Prospect of denitrifying anaerobic methane oxidation (DAMO) application on wastewater treatment and biogas recycling utilization

Old-fashioned wastewater treatments for nitrogen depend on heterotrophic denitrification process. It would utilize extra organic carbon source as electron donors when the C/N of domestic wastewater was too low to ensure heterotrophic denitrification process. It would lead to non-compliance with carbon reduction targets and impose an economic burden on wastewater treatment. Denitrifying anaerobic methane oxidation (DAMO), which could utilize methane serving as electron donors to replace traditional organic carbon (methanol or sodium acetate), supplies a novel approach for wastewater treatment. As the primary component of biogas, methane is an inexpensive carbon source. With anaerobic digestion becoming increasingly popular for sludge reduction in wastewater treatment plants (WWTPs), efficient biogas utilization through DAMO can offer an environmentally friendly option for in-situ biogas recycling. Here, we reviewed the metabolic principle and relevant research for DAMO and biogas recycling utilization, outlining the prospect of employing DAMO for wastewater treatment and biogas recycling utilization in WWTPs. The application of DAMO provides a new focal point for enhancing efficiency and sustainability in WWTPs.

Attenuation effects of ZVI/PDS pretreatment on propagation of antibiotic resistance genes in bioreactors: Driven by antibiotic residues and sulfate assimilation

Sulfate radical-based advanced oxidation processes (AOPs) combined biological system was a promising technology for treating antibiotic wastewater. However, how pretreatment influence antibiotic resistance genes (ARGs) propagation remains largely elusive, especially the produced by-products (antibiotic residues and sulfate) are often ignored. Herein, we investigated the effects of zero valent iron/persulfate pretreatment on ARGs in bioreactors treating sulfadiazine wastewater. Results showed absolute and relative abundance of ARGs reduced by 59.8%- 81.9% and 9.1%- 52.9% after pretreatments. The effect of 90-min pretreatment was better than that of the 30-min. The ARGs reduction was due to decreased antibiotic residues and stimulated sulfate assimilation. Reduced antibiotic residues was a major factor in ARGs attenuation, which could suppress oxidative stress, inhibit mobile genetic elements emergence and resistant strains proliferation. The presence of sulfate in influent supplemented microbial sulfur sources and facilitated the in-situ synthesis of antioxidant cysteine through sulfate assimilation, which drove ARGs attenuation by alleviating oxidative stress. This is the first detailed analysis about the regulatory mechanism of how sulfate radical-based AOPs mediate in ARGs attenuation, which is expected to provide theoretical basis for solving concerns about by-products and developing practical methods to hinder ARGs propagation.

Revealing impacts of operational modes on anaerobic digestion systems coupling with sulfate reduction

Anaerobic digestion (AD) is promising for treating high-strength wastewater. However, the effect of operational parameters on microbial communities of AD with sulfate is not yet fully understood. To explore this, four reactors were operated under rapid- and slow-filling modes with different organic carbons. Reactors in the rapid-filling mode generally exhibited a fast kinetic property. For example, the degradation of ethanol was 4.6 times faster in ASBR_ER than in ASBR_ES, and the degradation of acetate was 11.2 times faster in ASBR_AR than in ASBR_AS. Nevertheless, reactors in the slow-filling mode could mitigate propionate accumulation when using ethanol as organic carbon. Taxonomic and functional analysis further supported that rapid- and slow-filling modes were suitable for the growth of r-strategists (e.g., Desulfomicrobium) and K-strategists (e.g., Geobacter), respectively. Overall, this study provides valuable insights into microbial interactions of AD processes with sulfate through the application of the r/K selection theory.

Virus-Host Dynamics in Archaeal Groundwater Biofilms and the Associated Bacterial Community Composition

Spatial and temporal distribution of lytic viruses in deep groundwater remains unexplored so far. Here, we tackle this gap of knowledge by studying viral infections of Altivir_1_MSI in biofilms dominated by the uncultivated host Candidatus Altiarchaeum hamiconexum sampled from deep anoxic groundwater over a period of four years. Using virus-targeted direct-geneFISH (virusFISH) whose detection efficiency for individual viral particles was 15%, we show a significant and steady increase of virus infections from 2019 to 2022. Based on fluorescence micrographs of individual biofilm flocks, we determined different stages of viral infections in biofilms for single sampling events, demonstrating the progression of infection of biofilms in deep groundwater. Biofilms associated with many host cells undergoing lysis showed a substantial accumulation of filamentous microbes around infected cells probably feeding off host cell debris. Using 16S rRNA gene sequencing across ten individual biofilm flocks from one sampling event, we determined that the associated bacterial community remains relatively constant and was dominated by sulfate-reducing members affiliated with Desulfobacterota. Given the stability of the virus-host interaction in these deep groundwater samples, we postulate that the uncultivated virus-host system described herein represents a suitable model system for studying deep biosphere virus-host interactions in future research endeavors.

In-Situ Sludge Reduction Performance and Mechanism in Sulfidogenic Anoxic-Oxic-Anoxic Membrane Bioreactors

The excess sludge generated from the activated sludge process remains a big issue. Sustainable approaches that achieve in situ sludge reduction with satisfactory effluent quality deserve attention. This study explored the sludge reduction performance of sulfidogenic anoxic-oxic-anoxic (AOA) membrane bioreactors. The dynamics of the microbial community and metabolic pathways were further analyzed to elucidate the internal mechanism of sludge reduction. Compared with the conventional anoxic-oxic-oxic membrane bioreactor (MBR_control), AOA_S150 (150 mg/L SO₄^2- in the membrane tank) and AOA_S300 (300 mg/L SO₄^2- in the membrane tank) reduced biomass production by 40.39% and 47.45%, respectively. The sulfide reduced from sulfate could enhance the sludge decay rate and decrease sludge production. Extracellular polymeric substances (EPSs) destruction and aerobic lysis contributed to sludge reduction in AOA bioreactors. The relative abundance of Bacteroidetes (phylum), sulfate-reducing bacteria (SRB, genus), and Ignavibacterium (genus) increased in AOA bioreactors compared with MBR_control. Our metagenomic analysis indicated that the total enzyme-encoding genes involved in glycolysis, denitrification, and sulfate-reduction processes decreased over time in AOA_S300 and were lower in AOA_S300 than AOA_S150 at the final stage of operation. The excess accumulation of sulfide in AOA_S300 may inactive the functional bacteria, and sulfide inhibition induced sludge reduction.

Roles of Fe-C amendment on sulfate-containing pharmaceutical wastewater anaerobic treatment: Microbial community and sulfur metabolism

The effects of multiple two-phase anaerobic treatment involving acidification coupling Fe-C on sulfate-containing chemical synthesis-based pharmaceutical wastewater treatment were investigated. Fe-C was added as a filler with 25% vol. to acidogenic reactors for semi-continuous operation. The results suggested that Fe-C amendment promoted sulfate removal efficiency by 47.5% and shortened the reaction time by 50% in the acidogenic phase. With mitigation of sulfate inhibition, SCOD removal efficiency and methane production were further increased by 24.6% and 398% compared to direct raw wastewater anaerobic digestion, respectively, in methanogenic phase. The results of sulfate removal kinetics confirmed a 150% increase of removal rate in acidogenic phase. However, the apparent kinetic microbial sulfate removal constant without Fe-C amendment was maintained at approximately 0.06 h^-1. The Fe-C amendment not only increased the relative abundance of Methanothrix and Desulfovibrio for sulfate reduction but also enriched unclassified_p__Chloroflexi and unclassified_c__Deltaproteobacteria for acidification. Metagenomic results indicated that Fe-C enhanced dissimilatory sulfate reduction and PAPS synthesis of assimilatory step. The hydrogen sulfide production through the 3-mercaptopyruvate to pyruvate pathways was also enhanced. Butyrate-oxidizing genes were increased synchronously to convert butyrate to acetate.

Core carbon fixation pathways associated with cake layer development in an anoxic-oxic biofilm-membrane bioreactor treating textile wastewater

Microbial carbon fixation pathways have not yet been adequately understood for their role in membrane case layer formation processes. Carbon fixation bacteria can play critical roles in either causing or enhancing cake layer formation in some autotrophic-prone anoxic conditions, such as sulfur-cycling conditions. Understanding the microbes capable of carbon fixation can potentially guide the design of membrane biofouling mitigation strategies in scientific ways. Thus, we used meta-omics methods to query carbon fixation pathways in the cake layers of a full-scale anoxic-oxic biofilm-MBR system treating textile wastewater in this study. Based on the wastewater constituents and other properties, such as anoxic conditions, sulfide-reducing and sulfur-oxidizing bacteria could co-exist in the membrane unit. In addition, low-light radiation conditions could also happen to the membrane unit. However, we could not quantify the light intensity or total energy input accurately because the whole experimental setup was a full-scale system. Potentially complete carbon fixation pathways in the cake layer included the Calvin-Benson-Bassham cycle, Wood-Ljungdahl pathway, and the 3-hydroxypropionate bicycle. We discovered that using aeration could effectively inhibit carbon fixation, which resulted in mitigating membrane cake layer development. However, the aeration resulted in the 3-hydroxypropionate bicycle pathway, presumably used by aerobic sulfur-oxidizing prokaryotes, to become a more abundant carbon fixation pathway in the cake layer under aerobic conditions.

A bibliometric analysis of research progress in sulfate-rich wastewater pollution control technology

Sustainable industrial development requires research on pollution control in industrial wastewater, particularly sulfate-rich wastewater, which poses a threat to the environment. This article differs from the previous sulfate wastewater treatment process and equipment review. Based on the quantitative analysis, this paper has determined some characteristics of the related literature on the pollution control technology of high-concentration sulfate wastewater to help researchers establish future research directions. From 1991-2020, the WoS database published 9473 articles related to high-concentration sulfate wastewater treatment technology. We used bibliometric analysis combined with social network analysis and s-curve technical analysis in this research. The United States was the first to start this type of research, Australia has insightful and instructive research articles in this area, and China is the most active in international cooperation. The keywords that appear most frequently in the dataset are degradation, adsorption, oxidation, reduction, and recovery. By S-curve fitting, it is known that biological treatment methods are closer to the maturity stage than physical and chemical treatment methods.

Dissimilatory sulfate reduction in the cake layer of a full-scale anaerobic dynamic membrane bioreactor for hotel laundry wastewater treatment: Bacterial community and functional genes

Dissimilatory sulfate reduction (DSR) in cake layer of full-scale anaerobic dynamic membrane bioreactor for treating hotel laundry wastewater was studied. Change (Δ) of sulfate concentration (ΔSO₄^2-) was positively correlated to dynamic cake layer (DCL) development, while ΔS^2- was negatively correlated. ΔSO₃^2- and ΔS_{organic sulfur} remained around 1.5-2.5 and 1.2-2.3 mg-S/L, respectively. Thus, DSR was the predominant sulfate reduction process in DCL. 33 binned genomes from DCL microbiome samples possessed one or more DSR functional genes. But only four binned genomes possess all functional genes, and thus can achieve complete DSR. However, no significant variations of these DSR bacteria was obseared during DCL development. Metagenomic analysis predicted that sulfate reduction in DCL was mainly carried out by collaborations between bacteria with incomplete DSR pathways. Among which, sulfite → sulfide by dissimilatory-sulfite-reductase expression bacteria was the key process. Overall results suggested that controlling dissimilatory-sulfite-reductase activities could prevent sulfide buildup in the effluent.

Can a compact biological system be used for real hydraulic fracturing wastewater treatment?

Hydraulic fracturing wastewater (HFW), a byproduct of hydraulic fracturing oil extraction, contains a complex mixture of oil, aldehydes, and benzene compounds. Efficient and eco-friendly HFW treatment means are critical for the oil extraction industry, particularly in developing countries. In this study, two biological processes namely an anaerobic/anoxic/moving bed biofilm reactor (A²-MBBR) and an A²-MBBR with a microfiltration membrane (A²-MFMBBR) were established, and assessed for the real HFW treatment. Removal efficiencies of chemical oxygen demand (COD) and NH₄⁺-N were over 92% and 95%, respectively, in both processes with a hydraulic retention time of 72 h. The majority of organic compounds in both systems identified by GC-MS were degraded in the anaerobic units. In comparison, A²-MFMBBR demonstrated higher removal efficiencies for oil, total suspended solids, and complex compounds. The average relative abundances of refractory compound degrading bacteria were 43.4% and 51.6% in the A²-MBBR and A²-MFMBBR, respectively, which was consistent with the COD and oil removal, and suggested that the MBR could maintain a high diversity of microorganisms and contribute to deep recalcitrant organics degradation. This study sheds light on the potential of using a compact biological process for the real HFW treatment.

Direct-determination of high-concentration sulfate by serial differential spectrophotometry with multiple optical pathlengths

Direct-determination is a fast and free of contamination method for analysis of substances in water samples. However, direct-determination of SO₄^2- with high concentration in environmental systems is still challenging due to deviation from Beer-Lambert law is generally observed when a substance with high concentration is directly determined, resulting in poor accuracy, sensitivity, and narrow linear range. In this study, a simple and rapid method for the direct-determination of SO₄^2- with high concentration was proposed. Serial high-absorbance differential spectrophotometry was applied to incrementally widen the determination range under different optical pathlengths. In this process, the effects of optical pathlength and reference concentration on sensitivity were further investigated. The results showed that SO₄^2- could be accurately quantified within a concentration range of 0-4.10 g/L, and the determination range by this method was 10-fold and 19.5-fold wider than those by conventional differential spectrophotometry and conventional spectrophotometry, respectively. And the applicable ranges of sensitivity were obtained at various optical pathlengths by adjusting the reference solution concentration. This approach exhibited several advantages over conventional methods, including high accuracy, excellent precision, low cost, less time consumption, and easy operation. This method is promising and can provide accurate and reliable data support for environmental monitoring and pollution control.

Hydrogen sulphide management in anaerobic digestion: A critical review on input control, process regulation, and post-treatment

Hydrogen sulphide (H₂S) in biogas is a problematic impurity that can inhibit methanogenesis and cause equipment corrosion. This review discusses technologies to remove H₂S during anaerobic digestion (AD) via: input control, process regulation, and post-treatment. Post-treatment technologies (e.g. biotrickling filters and scrubbers) are mature with >95% removal efficiency but they do not mitigate H₂S toxicity to methanogens within the AD. Input control (i.e. substrate pretreatment via chemical addition) reduces sulphur input into AD via sulphur precipitation. However, available results showed <75% of H₂S removal efficiency. Microaeration to regulate AD condition is a promising alternative for controlling H₂S formation. Microaeration, or the use of oxygen to regulate the redox potential at around -250 mV, has been demonstrated at pilot and full scale with >95% H₂S reduction, stable methane production, and low operational cost. Further adaptation of microaeration relies on a comprehensive design framework and exchange operational experience for eliminating the risk of over-aeration.

Metagenomic analysis reveals the linkages between bacteria and the functional enzymes responsible for potential ammonia and biogenic amine production in alfalfa silage

AIMS

To clarify the molecular mechanisms underlying ammonia (NH₃ ) and biogenic amines (BAEs) formation in alfalfa silage, whole metagenomic sequencing analysis was performed to identify the linkages between functional bacteria and their responsible enzymes in alfalfa silage prepared with and without sucrose addition.

METHODS AND RESULTS

Genes encoding nitrite reductase (nirB) resulting in NH₃ formation were the most abundant and were mostly assigned to Enterobacter cloacae and Klebsiella oxytoca. Putrescine-related genes, classified mainly to encode ornithine decarboxylase (odcA), were predominantly carried by Escherichia coli, Ent. cloacae and Citrobacter sp. Escherichia coli and Kl. oxytoca were the important species responsible for cadaverine and tyramine formation. Ent. cloacae, E. coli, and Kl. oxytoca dominated the bacterial community in naturally fermented alfalfa silage, whilst sucrose-treated silages greatly inhibited the growth of these species by promoting the dominance of Lactobacillus plantarum, thus decreasing the concentrations of NH₃ , cadaverine, putrescine and tyramine.

CONCLUSIONS

Enterobacteriaceae bacteria are mainly responsible for the NH₃ , putrescine, cadaverine and tyramine formations in alfalfa silage.

SIGNIFICANCE AND IMPACT OF THE STUDY

Whole metagenomic sequencing analysis served as a useful tool to identify the linkages between functional bacteria and associated enzymes responsible for NH₃ and BAEs formation.

Hydraulic flow direction alters nutrients removal performance and microbial mechanisms in electrolysis-assisted constructed wetlands

In this study, an electrolysis-assisted down-flow constructed wetland (E-DFCW) was successfully established, and achieved simultaneously efficient removal of PO₄^3--P (93.6% ± 3.2%), NO₃^--N (97.1% ± 2.0%) and TN (80.6% ± 5.4%). When compared with electrolysis-assisted up-flow constructed wetland (E-UFCW), E-DFCW allowed significantly lower concentrations of PO₄^3--P, NO₃^--N, total Fe and SO₄^2--S in effluents. In addition, microbial community and functional genes prediction results indicated that hydraulic flow direction significantly altered microbial nitrogen, sulfur and carbon metabolisms in electrolysis-assisted constructed wetlands (E-CWs). Specifically, multi-path denitrification facilitated NO₃^--N reduction in cathodic chamber of E-DFCW, whereas autohydrogenotrophic denitrification might dominate NO₃^--N reduction in cathodic chamber of E-UFCW. More abundant and diverse denitrifiers in cathodic chamber of E-DFCW contributed to enhanced denitrification performance. Overall, this work provides microbial insights into multi-path nitrogen metabolisms in electrolysis-assisted denitrification systems in response to hydraulic flow direction.