Enhancing blackwater methane production by enriching hydrogenotrophic methanogens through hydrogen supplementation

Bisphenol A affects microbial interactions and metabolic responses in sludge anaerobic digestion

The widespread use of bisphenol A (BPA) has resulted in the emergence of new pollutants in various environments, particularly concentrated in sewage sludge. This study investigated the effects of BPA on sludge anaerobic digestion, focusing specifically on the interaction of microbial communities and their metabolic responses. While the influence of BPA on methane accumulation is not significant, BPA still enhanced the conversion of soluble COD, protein, and polysaccharides. BPA also positively influenced the hydrolysis-acidogenesis process, leading to 17% higher concentrations of volatile fatty acids (VFAs). Lower BPA levels (0.2-0.5 mg/kg dw) led to decreased hydrolysis and acidogenesis gene abundance, indicating metabolic inhibition; conversely, higher concentrations (1-5 mg/kg dw) increased gene abundance, signifying metabolic enhancement. Diverse methane metabolism was observed and exhibited alterations under BPA exposure. The presence of BPA impacted both the diversity and composition of microbial populations. Bacteroidetes, Proteobacteria, Firmicutes, and Chloroflexi dominated in BPA-treated groups and varied in abundance among different treatments. Changes of specific genera Sedimentibacter, Fervikobacterium, Blvii28, and Coprothermobacter in response to BPA, affecting hydrolysis and acetogenesis. Archaeal diversity declined while the hydrogenotrophic methanogen Methanospirillum thrived under BPA exposure. BPA exposure enabled microorganisms to form structured community interaction networks and boost their metabolic activities during anaerobic digestion. The study also observed the enrichment of BPA biodegradation pathways at high BPA concentrations, which could interact and overlap to ensure efficient BPA degradation. The study provides insights into the digestion performance and interactions of microbial communities to BPA stress and sheds light on the potential effect of BPA during anaerobic digestion.

Cleanup of Cr(VI)-polluted groundwater using immobilized bacterial consortia via bioreduction mechanisms

Cr(VI) bioreduction has become a remedial alternative for Cr(VI)-polluted site cleanup. However, lack of appropriate Cr(VI)-bioreducing bacteria limit the field application of the in situ bioremediation process. In this study, two different immobilized Cr(VI)-bioreducing bacterial consortia using novel immobilization agents have been developed for Cr(VI)-polluted groundwater remediation: (1) granular activated carbon (GAC) + silica gel + Cr(VI)-bioreducing bacterial consortia (GSIB), and (2) GAC + sodium alginate (SA) + polyvinyl alcohol (PVA) + Cr(VI)-bioreducing bacterial consortia (GSPB). Moreover, two unique substrates [carbon-based agent (CBA) and emulsified polycolloid substrate (EPS)] were developed and used as the carbon sources for Cr(VI) bioreduction enhancement. The microbial diversity, dominant Cr-bioreducing bacteria, and changes of Cr(VI)-reducing genes (nsfA, yieF, and chrR) were analyzed to assess the effectiveness of Cr(VI) bioreduction. Approximately 99% of Cr(VI) could be bioreduced in microcosms with GSIB and CBA addition after 70 days of operation, which caused increased populations of total bacteria, nsfA, yieF, and chrR from 2.9 × 10⁸ to 2.1 × 10¹², 4.2 × 10⁴ to 6.3 × 10¹¹, 4.8 × 10⁴ to 2 × 10¹¹, and 6.9 × 10⁴ to 3.7 × 10⁷ gene copies/L. In microcosms with CBA and suspended bacteria addition (without bacterial immobilization), the Cr(VI) reduction efficiency dropped to 60.3%, indicating that immobilized Cr-bioreducing bacteria supplement could enhance Cr(VI) bioreduction. Supplement of GSPB led to a declined bacterial growth due to the cracking of the materials. The addition of GSIB and CBA could establish a reduced condition, which favored the growth of Cr(VI)-reducing bacteria. The Cr(VI) bioreduction efficiency could be significantly improved through adsorption and bioreduction mechanisms, and production of Cr(OH)₃ precipitates confirmed the occurrence of Cr(VI) reduction. The main Cr-bioreducing bacteria included Trichococcus, Escherichia-Shigella, and Lactobacillus. Results suggest that the developed GSIB bioremedial system could be applied to cleanup Cr(VI)-polluted groundwater effectively.

Effect of fish waste augmentation on anaerobic co-digestion of sludge with food waste

The effect of sudden augmentation with fish waste (FW) on an operating anaerobic digester was investigated. Fifteen repeated FW spikes (FWS) composed of 1% or 5% FW per working volume of digester were suddenly fed into semi-continuous operation of a mixture of sludge and food waste. Overall process efficiency was not inhibited by FW augmentation. The bacterial community were clustered differently in the 5% FWS treatment than in the control and 1% FWS. Protein-degrading bacteria (Porphyromonadacea, Family XI, and Family XII) were commonly found in the 5% FWS treatment. Their proportions positively correlated with numbers of other bacteria and dominant methanogens (Methanosaeta and Methanospirillum), showing their important role in FWS digestion. FWS caused a shift of bacteria community, but an increase in archaeal concentration. Therefore, sudden addition of an appropriate amount of FW to existing digesters did not provoke process failure. This result contributes an ecologically-benign method to process FW.

Role of interspecies electron transfer stimulation in enhancing anaerobic digestion under ammonia stress: Mechanisms, advances, and perspectives

Ammonia stress is a commonly encountered issue in anaerobic digestion (AD) process when treating proteinaceous substrates. The enhanced relationship between syntrophic bacteria and methanogens triggered by interspecies electron transfer (IET) stimulation is one of the potential mechanisms for an improved methane yield from the AD plant under ammonia-stressed condition. There is, however, lack of synthesized information on the mechanistic understanding of IET facilitation in the ammonia-stressed AD processes. This review critically discusses recovery of AD system from ammonia-stressed condition, focusing on H₂ transfer, redox compound-mediated IET, and conductive material-induced direct IET. The effects and the associated mechanisms of IET stimulation on mitigating ammonia stress and promoting methanogenesis were elucidated. Finally, prospects and challenges of IET stimulation were critically discussed. This review highlights, for the first time, the critical role of IET stimulation in enhancing AD process under ammonia-stressed condition.

Efficacy of a vermifilter at mitigating greenhouse gases and ammonia emissions from dairy wastewater

Dairy effluent is a potential source of gaseous pollutants associated with global warming and soil acidification. Mitigating such emissions during handling and storage requires substantial financial and labor input. This study evaluated a low-cost technology for mitigating gaseous emissions from dairy wastewater. For 9 mo, a pilot-scale vermifilter system installed on a commercial dairy farm was studied. Bimonthly samples of the dairy wastewater influent and effluent from the vermifilter system were collected. These samples' potential gas emissions (ammonia [NH₃ ], methane [CH₄ ], carbon dioxide [CO₂ ], and nitrous oxide [N₂ O]) were measured using a closed-loop dynamic flux chamber method. Results indicated the following reductions in emissions of these gases by the vermifilter system: 84-100% for NH₃ , 58-82% for CO₂ , and 95-100% for CH₄ . Nitrous oxide emissions were mainly below our instrument detection limits and were thus not reported. The vermifilter showed the potential of reducing the global warming potential from the dairy wastewater by up to 100%. This study further indicated that higher ambient temperatures led to higher emissions of CH₄ (R²  = .56) and NH₃ (R²  = .53) from untreated dairy wastewater. Overall, the vermifilter system has potential to mitigate gaseous emissions from dairy wastewater.

Biological methane production coupled with sulfur oxidation in a microbial electrosynthesis system without organic substrates

Methane is produced in a microbial electrosynthesis system (MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions. In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS^- oxidized to SO₄^2- at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H₂ was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea, and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H₂ was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion, the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens, including Methanobacterium and Methanolinea, produced methane via H₂.

Effects of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS) on Soil Microbial Community

The extensive application of perfluoroalkyl and polyfluoroalkyl substances (PFASs) causes their frequent detection in various environments. In this work, two typical PFASs, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are selected to investigate their effects on soil microorganisms. Microbial community structure and microbe-microbe relationships were investigated by high-throughput sequencing and co-occurrence network analysis. Under 90 days of exposure, the alpha-diversity of soil microbial communities was increased with the PFOS treatment, followed by the PFOA treatment. The exposure of PFASs substantially changed the compositions of soil microbial communities, leading to the enrichment of more PFASs-tolerant bacteria, such as Proteobacteria, Burkholderiales, and Rhodocyclales. Comparative co-occurrence networks were constructed to investigate the microbe-microbe interactions under different PFASs treatments. The majority of nodes in the PFOA and PFOS networks were associated with the genus Azospirillum and Hydrogenophaga, respectively. The LEfSe analysis further identified a set of biomarkers in the soil microbial communities, such as Azospirillum, Methyloversatilis, Hydrogenophaga, Pseudoxanthomonas, and Fusibacter. The relative abundances of these biomarkers were also changed by different PFASs treatments. Functional gene prediction suggested that the microbial metabolism processes, such as nucleotide transport and metabolism, cell motility, carbohydrate transport and metabolism, energy production and conversion, and secondary metabolites biosynthesis transport and catabolism, might be inhibited under PFAS exposure, which may further affect soil ecological services.

Effect of low-thermal pretreatment on the methanogenic performance and microbiome population of continuous high-solid anaerobic digester treating dewatered sludge

Undigested and dewatered sludge at 10% total solids was pretreated at 60 °C for 3 h and fed to a lab-scale horizontal anaerobic bioreactor for 130 days with solids retention time (SRTs) from 25 to 16 d. The low-thermal pretreatment enabled higher net energy production, improved sludge treatment efficiency, and enhanced digestion stability. The highest average biomethane yield and production rate were 138.5 mL/g VS and 0.43 L/L.d, respectively, and the economic benefit was expected to be the maximum at SRT 16 d. Pretreatment did not increase the specific methanogenic activity per unit methanogen, but resulted in higher abundance of methanogenic archaea and hydrolytic bacteria. Methanogenic population shifted from hydrogenotrophic to acetoclastic, consistent with predicted gene expression at SRT equal or below 20 d. Anaerobic digestion along with low-thermal could be a feasible management strategy for undigested dewatered sludge from small WWTPs.

Methane Generation from Anthracite by Fungi and Methanogen Mixed Flora Enriched from Produced Water Associated with the Qinshui Basin in China

Biogenic coalbed methane (CBM) is generally believed to be formed by anaerobic bacteria and methanogens, while a few studies took fungi into account. Here, the microflora consisting of fungi and methanogens was enriched from the produced water associated with the Qinshui Basin using anthracite as the only carbon source. The maximum methane yield of 231 μmol/g coal was obtained after 22 days of cultivation under the optimum temperature of 35 °C, pH of 8, salinity of 0-2%, particle size of 0.075-0.150 mm, and the solid-liquid ratio of 1:30. It could remain active even after exposure to air for 24 h. Miseq results showed that the archaea were mainly composed of Methanocella, a hydrogenotrophic methanogen, followed by acetoclastic methanogen Methanosaeta and Methanosarcina, which could use various methanogenic substrates. The fungal communities mainly included Amorphotheca, Alternaria, Aspergillus, and Penicilium, which are all able to degrade complex organics such as aromatics and lignin. After cultivation, the crystal structure of anthracite became looser, as shown by XRD results, which might be due to the swelling effect caused by the destruction of the aromatic ring structure of coal under the function of fungi. The stretching vibration intensity of each functional group in coal decreased with cultivation, as revealed by FTIR. The GC-MS results showed that the concentration of alkanes and alcohols decreased significantly, which are the products of ring-opening of aromatics by fungi. These results suggested that fungi and methanogens in the coalbed also can syntrophically degrade coal effectively, especially for aromatics in coal.

Hydrogen production in single-chamber microbial electrolysis cell under high applied voltages

The aim of this study was to investigate the performance of single-chamber MEC under applied voltages higher than that for water electrolysis. With different acetate concentrations (1.0-2.0 g/L), the MEC was tested under applied voltages from 0.8 to 2.2 V within 2600 h (54 cycles). Results showed that the MEC was stably operated for the first time within 20 cycles under 2.0 and 2.2 V, compared with the control MEC with significant water electrolysis. The maximum current density reached 27.8 ± 1.4 A/m² under 2.0 V, which was about three times as that under 0.8 V. The anode potential in the MEC could be kept at 0.832 ± 0.110 V (vs. Ag/AgCl) under 2.2 V, thus without water electrolysis in the MEC. High applied voltage of 1.6 V combined with alkaline solution (pH = 11.2) could result in high hydrogen production and high current density. The maximum current density of MEC at 1.6 V and pH = 11.2 reached 42.0 ± 10.0 A/m², which was 1.85 times as that at 1.6 V and pH = 7.0. The average hydrogen content reached 97.2% of the total biogas throughout all the cycles, indicating that the methanogenesis was successfully inhibited in the MEC at 1.6 V and pH = 11.2. With high hydrogen production rate and current density, the size and investment of MEC could be significantly reduced under high applied voltages. Our results should be useful for extending the range of applied voltages in the MEC.

Enhanced electrokinetic remediation for Cd-contaminated clay soil by addition of nitric acid, acetic acid, and EDTA: Effects on soil micro-ecology

Enhanced electrokinetic remediation (EKR) allows the rapid remediation of heavy metal-contaminated clay, but the impacts of this process on soil micro-ecology have rarely been evaluated. In this study, nitric acid, acetic acid, and EDTA were applied for enhancement of EKR and the effects on Cd removal, soil enzyme activity, and soil bacterial communities (SBCs) were determined. Nitric acid and acetic acid allowed 93.2% and 91.8% Cd removal, respectively, and EDTA treatment resulted in 40.4% removal due to the formation of negatively charged EDTA-Cd complexes, resulting in opposing directions of Cd electromigration and electroosmosis flow and slow electromigration rate caused by low voltage drop. Activities of soil beta-glucosidase, acid phosphatase, and urease, were all reduced by enhanced EKR treatment, especially nitric acid treatment, by 46.2%, 58.8% and 57.7%, respectively. The SBCs were analyzed by high-throughput sequencing and revealed significantly increased diversity for acetic acid treatment, no effect for EDTA treatment, and reduced diversity for nitric acid treatment. Compared with nitric acid and EDTA, acetic acid treatment enhanced EKR for higher Cd removal and improved biodiversity.

Effects of micro-aeration on microbial niches and antimicrobial resistances in blackwater anaerobic digesters

Anaerobic digestion (AD) of source-diverted blackwater (toilet flush) at ambient room temperature presents challenges for fast hydrolysis of particulate matters. This study investigated the effect of different micro-aeration dosages for blackwater AD. Sequencing batch reactors were operated at ambient room temperature (22 ± 1°C) with micro-aeration (0, 5, 10, 50, and 150 mg O₂ g^-1 COD_feed per cycle) and gradually reduced hydraulic retention times from 5 d to 2 d. The methanogenesis efficiencies were greater at low oxygen dosages (i.e., 0, 5, 10) while the volatile fatty acids (VFAs) accumulated more at high oxygen dosages (i.e., 50, 150). Microbial communities were significantly different under different oxygen dosages (p<0.05), with segregation of microbial ecological niches in low and high oxygen dosage communities. The low-oxygen-dosage niche (0, 5, and 10 mg g^-1 COD_feed) was inhabited by fermenting and syntrophic bacteria (e.g., Cytophaga, Syntrophomonas) and methanogens (e.g., Methanobacterium, Methanolinea, Methanosaeta). The high-oxygen-dosage niche (50 and 150 mg g^-1 COD_feed) had significantly (p<0.05) more facultative anaerobic bacteria (Ignavibacteriales and Cloacamonales), and aerobic bacteria (Rhodocyclales). Moreover, blackwater can be a source of antimicrobial resistance genes (ARGs), which are affected by different oxygen dosages. The ARG variation correlated with the microbial community composition (p<0.05). Low-oxygen-dosage communities contained a higher prevalence of mobile gene elements (intI1 and korB) and tetM, ermB, sul1, sul2, and blaCTX-M than the high-oxygen-dosage communities, indicating that oxygen dosage influenced the prevalence of populations carrying ARGs. These findings suggest that application of micro-aeration to AD can be used to control ARG profiles.

Effects of higher temperature on antibiotic resistance genes for in-situ biogas upgrading reactors with H2 addition

In-situ biogas upgrading by H₂ injection is a promising method for bio-natural gas production, yet the effect of H₂ addition on antibiotic resistance genes during the in-situ biogas upgrading process remains unknown. We analyzed mesophilic and thermophilic in-situ biogas upgrading digesters with intermittent or continuous mixing models using metagenomic and metatranscriptomic methods to evaluate the effects of H₂ addition on antibiotic resistance profiles. We found that H₂ addition had less impact in the mesophilic reactor. In the thermophilic reactor, the influenced antibiotic resistance ontology (AROs) was mostly bound to the integral membrane transporters of the ATP-binding cassette and major facilitator superfamily. The annotated gene numbers of four drug classes, including macrolide, glycopeptide, lincosamide, and fluoroquinolone, increased distinctly after H₂ addition. Acetate concentration is a vital indicator for distinguishing the abundance of different antibiotic efflux pumps. Most of the AROs influenced by Ruminiclostridium replaced the original dominant species Clostridium, and the versatile genus Methanosarcina was the sole methanogen correlated with the altered AROs of efflux pumps conferring antibiotic resistance. The introduced H₂ was synthesized to CH₄via the hydrogenotrophic pathway of Methanosarcina flavescens, and part of the consumed H₂ was used for cell growth.

Addition of nanoparticles increases the abundance of mobile genetic elements and changes microbial community in the sludge anaerobic digestion system

This study explored the fate of mobile genetic elements (MGEs) in anaerobic digestion (AD) system with four nanoparticles (NPs) added, including carbon NPs, Al₂O₃ NPs, ZnO NPs, and CuO NPs. 16S rRNA amplicon sequencing and quantitative PCR to investigate the microbial community, MGEs abundance and the potential host in the AD process. The results of high-throughput sequencing showed that ZnO NPs and CuO NPs significantly reduced the microbial diversity and significantly changed the microbial community structure. Simultaneously, the absolute abundance of MGEs increased by 145.01%, 159.67%, 354.70%, and 132.80% on the carbon NPs, Al₂O₃ NPs, ZnO NPs, and CuO NPs. The enrichment rate of tnpA-03 in ZnO NPs group was the highest, which could reach up to 2854.80%. Co-occurrence analysis revealed that Proteobacteria harbored the vast majority of MGEs followed by Firmicutes. Redundancy analysis and variation partitioning analysis showed that metabolites were the main factors that shifted the succession of bacterial communities. Moreover, there were significant positive correlations between metabolites and part MGEs (such as tnpA-01, tnpA-02, tnpA-03, tnpA-04, tnpA-05, tnpA-07 and ISCR1). This study provides a new perspective that NPs increase the risk of antibiotic resistance through MGEs during AD process.

Effects of organic loading rate and temperature fluctuation on the microbial community and performance of anaerobic digestion of food waste

Semi-continuous anaerobic fermentation of food waste was carried out using a solar-assisted heat reactor to explore effects of temperature fluctuation and organic loading rate (OLR: 2.0, 4.0, 6.0, 7.0 kg/(m³ day)VS on the reactor performance and microbial community structure. The results showed that the best methane production was achieved when OLR was 6.0 kg/(m³ day)VS because the reactors did not operate stably at 7.0 kg/(m³ day)VS. Compared with fluctuation of fermentation temperature, methane production at stable fermentation temperature increased by 21.72%, but higher power consumption occured. The results of high-throughput sequencing showed that OLR played a decisive role in succession of microbial community structure, while temperature fluctuation was more likely to affect microbial activity. When OLR was lower than 4.0 kg/(m³ day)VS, aceticlastic methanogens Methanosaeta were the dominant bacteria, while at 6.0 kg/(m³ day)VS, relative abundance of hydrogenotrophic methanogens Methanoregula and Methanospirillum increased.

Robust operation through effluent recycling for hydrogen production from the organic fraction of municipal solid waste

The stability of fermentative hydrogen production from the organic fraction of municipal solid waste (OFMSW) was evaluated in this work using a strategy of effluent recycling. Three pretreatment conditions were applied on the recycled effluent: a) no heat shock treatment, b) one initial heat shock treatment (90 °C, 30 min) and c) systematic heat shock treatment at the beginning of each fermentation. When a systematic heat shock was applied, a maximal hydrogen yield of 17.2 ± 3.8 mLH₂/gVS was attained. The hydrogen productivity was improved by 331% reaching a stable value of 1.51 ± 0.29 mLH₂/gVS/h, after 8 cycles of effluent recycling. This strategy caused a sharp decrease of diversity with stable co-dominance of hydrogen- and lactate-producing bacteria, ie. Clostridiales and Lactobacillales, respectively. For the other conditions, a sharp decrease of the hydrogen yields was observed showing the importance of applying a heat shock treatment for optimal hydrogen production with effluent recycling.

Combined process of bio-contact oxidation-constructed wetland for blackwater treatment

In this study, a combined process of bio-contact oxidation and constructed wetland for blackwater treatment was assessed. The effects of hydraulic retention time and particle size on treatment performance were systematically studied. Additionally, microbial communities in the combined process were characterized. The results show that the removal efficiency of COD, TN, NH₄⁺-N, and TP under optimum conditions in this study were 81.6%, 56.1%, 42.2%, and 73.7%, respectively. The maximum nitrogen removal rate reached 16.5 g m^-2 d^-1 (3 d). N and P removed via direct plant absorption accounted for only 19.7% and 16.1% of the total system, respectively. Plants play a crucial role in the microbial community of constructed wetlands and influence the overall performance of the system. The biofilm on roots favored aerobic and heterotrophic bacteria such as the aerobic denitrification microorganisms of Pelagibacterium, Halomonas, and Zoogloea. Overall, the combined process is a suitable technique for the treatment of blackwater.

Direct and Indirect Effects of Increased CO2 Partial Pressure on the Bioenergetics of Syntrophic Propionate and Butyrate Conversion

Simultaneous digestion and in situ biogas upgrading in high-pressure bioreactors will result in elevated CO₂ partial pressure (pCO₂). With the concomitant increase in dissolved CO₂, microbial conversion processes may be affected beyond the impact of increased acidity. Elevated pCO₂ was reported to affect the kinetics and thermodynamics of biochemical conversions because CO₂ is an intermediate and end-product of the digestion process and modifies the carbonate equilibrium. Our results showed that increasing pCO₂ from 0.3 to 8 bar in lab-scale batch reactors decreased the maximum substrate utilization rate (r_smax) for both syntrophic propionate and butyrate oxidation. These kinetic limitations are linked to an increased overall Gibbs free energy change (ΔG_Overall) and a potential biochemical energy redistribution among syntrophic partners, which showed interdependence with hydrogen partial pressure (pH₂). The bioenergetics analysis identified a moderate, direct impact of elevated pCO₂ on propionate oxidation and a pH-mediated effect on butyrate oxidation. These constraints, combined with physiological limitations on growth exerted by increased acidity and inhibition due to higher concentrations of undissociated volatile fatty acids, help to explain the observed phenomena. Overall, this investigation sheds light on the role of elevated pCO₂ in delicate biochemical syntrophic conversions by connecting kinetic, bioenergetic, and physiological effects.

Microbial adaptation in vertical soil profiles contaminated by an antimony smelting plant

Antimony mining has resulted in considerable pollution to the soil environment. Although studies on antinomy contamination have been conducted, its effects on vertical soil profiles and depth-resolved microbial communities remain unknown. The current study selected three vertical soil profiles (0–2 m) from the world's largest antimony mining area to characterize the depth-resolved soil microbiota and investigate the effects of mining contamination on microbial adaptation. Results demonstrated that contaminated soil profiles showed distinct depth-resolved effects when compared to uncontaminated soil profiles. As soil depth increased, the concentrations of antimony and arsenic gradually declined in the contaminated soil profiles. Acidobacteria, Chloroflexi, Proteobacteria and Thaumarchaeota were the most variable phyla from surface to deep soil. The co-occurrence networks were loosely connected in surface soil, but obviously recovered and were well-connected in deep soil. The metagenomic results indicated that microbial metabolic potential also changed with soil depth. Genes encoding C metabolism pathways were negatively correlated with antimony and arsenic concentrations. Abundances of arsenic-related genes were enriched by severe contamination, but reduced with soil depth. Overall, soil depth-resolved characteristics are often many meters deep and such effects affected the indigenous microbial communities, as well as their metabolic potential due to different contaminants along vertical depths.

Anaerobic Co-Digestion of Kitchen Waste and Blackwater for Different Practical Application Scenarios in Decentralized Scale: From Wastes to Energy Recovery

This study was performed to investigate the anaerobic digestion feasibility of kitchen waste and blackwater under different scenarios in laboratory tests. According to biochemical methane potential tests, when the kitchen waste to blackwater solid ratio was 1:1, the cumulative methane production reached the highest amount at 313.2 mL/g volatile solids (VSs), which was 26.4% and 29.4% higher than the anaerobic monodigestion of kitchen waste and blackwater, respectively, indicating that the anaerobic codigestion of kitchen waste and blackwater had a synergetic effect. Furthermore, the effect of different initial total ammonia nitrogen concentrations in blackwater on anaerobic digestion was determined based on the above experimental results, thereby proving that reducing the total ammonia nitrogen concentration in blackwater can appropriately improve the efficiency of methane production. Therefore, anaerobic digestion is a suitable method for the biogas production of kitchen waste and blackwater. It is of great significance for the organic waste stream treatment of households in a decentralized scale, especially in rural areas.

The role of magnetic MOFs nanoparticles in enhanced iron coagulation of aquatic dissolved organic matter

Dissolved organic matter (DOM) is not only a vector for the migration of aquatic environmental pollutants, but is also key to the control of water pollution. Economic and effective DOM removal through coagulation is essential in water treatment processes. This work investigated the role of carboxylated magnetic metal organic frameworks (MMOFs) nanoparticles in polymeric iron-based coagulation for the removal of aquatic DOM using a MMOFs-doped polyferric iron-based coagulant (MMOF-PIC). Analytical methodologies and tools used in this research included scanning electron microscopy (SEM), zeta potential, molecular weight cut off (MWCO), vibrating sample magnetometer (VSM) measurement, excitation emission matrix spectroscopy (EEMs), and X-ray photoelectron spectroscopy (XPS). The results showed that MMOF-PIC had the potential to change the structure of the polyferric iron-based coagulant (PIC) and charge, as determined by a porous surface morphology, a higher medium polymeric species distribution, and a more positive zeta potential. The MMOFs consequently enhanced PIC action on the removal of UV254 exposed DOM species with molecular weight <30 kDa, including aromatic CC based compounds, org-N as primary amines and amide/peptide bound species, water containing microbial metabolites and protein-like materials. The coagulation of DOM was enhanced by improving charge neutralization, adsorption-bridging and sweep-flocculation in the presence of MMOFs nanoparticles. This was due to hydrogen bonds, π-π bonds and covalent bonds resulting from actions of nanoparticles and pollutants. These results indicate that magnetic MOF nanoparticles can improve PIC coagulation for DOM, enhancing future removal of target pollutants.

Higher load operation by adoption of ethanol fermentation pretreatment on methane fermentation of food waste

The study aims to examine whether ethanol fermentation pretreatment (EP) of food waste can contribute to high load operation on methane fermentation using an anaerobic membrane bioreactor (AnMBR). The hydraulic retention time was reduced stepwise from 20 to 5 days to increase the load by increasing the feeding volume. The corresponding organic loading rate (OLR) ranged from 6.6 to 26.5 g-COD/L/day. The control series (without pretreatment) was operable to an OLR of 8.8 g-COD/L/day versus 26.5 g-COD/L/day for the EP series. In the control series, the major volatile fatty acid (VFA) produced by acidogenesis in the reactor was propionic acid because based on Gibbs free energy variations for the methane conversion, acetic acid conversion was not as easy as from propionic acid as from ethanol in the EP series. EP proved effective in avoiding VFA accumulation and subsequent decreased pH. Therefore, EP significantly improves AnMBR performance.

Progress towards catalyzing electro-methanogenesis in anaerobic digestion process: Fundamentals, process optimization, design and scale-up considerations

Electro-methanogenesis represents an emerging bio-methane production pathway that can be achieved through integrating microbial electrolysis cell (MEC) with conventional anaerobic digester (AD). Since 2009, a significant number of publications have reported superior methane productivity and kinetics from MEC-AD integrated systems. The overall objective of this review is to communicate the recent advances towards promoting electro-methanogenesis in the anaerobic digestion process. Firstly, the electro-methanogenesis pathways and functional roles of key microbial members are summarized. Secondly, various extrinsic process parameters, such as applied voltage/potential, pH, and temperature are discussed with emphasis on process optimization. Moreover, available methods for the inoculation and start-up of MEC-AD process are critically reviewed. Finally, system design and scale-up considerations, such as the selection of electrode materials, surface area and surface chemistry of electrode materials, and electrode spacing are summarized.

Impact of zero valent iron on blackwater anaerobic digestion

The source diverted blackwater treatment is receiving growing attention as an alternative to conventional energy intensive wastewater management and treatment systems. Blackwater, containing concentrated organic materials, can be anaerobically digested to recovery bioenergy. However, the methane recovery from blackwater is often inhibited by the presence of high free ammonia (FA) in blackwater. In order to improve the methane production in blackwater, nano-scale zero valent iron (nZVI, 35 nm or 50 nm) or micro-scale zero valent iron (mZVI, 200 μm) at different dosages (i.e., 0.5, 1, and 10 g/L) were applied respectively in the anaerobic digestion (AD) reactor for blackwater treatment. The results demonstrated that low doses (0.5-1 g/L) of nZVI slightly improved methane (CH₄) production, possibly due to a reduced oxidation-reduction potential (ORP) and improved hydrolysis-acidification in the nZVI supplemented systems. However, a lower biochemical methane potential (BMP) of blackwater was observed with high doses (10 g/L) of nZVI which induced a pH increase (>8.5) in AD reactor leading to a higher FA inhibition of CH₄ production. In contrast, the effect of mZVI on blackwater AD system was not significant. The study demonstrated the successful application of nZVI for improving AD of blackwater, however, which requires dosage control.