Bioaugmentation of activated sludge with elemental sulfur producing strain Thiopseudomonas denitrificans X2 against nitrate shock load

Efficient sulfur accumulation in biological desulfurisation and denitrification induced by microbial and chemical interactions

Efficient accumulation of sulfur from simultaneous desulfurisation denitrification process can achieve high economic and environmental benefits. This work aims to study the effect of product accumulation on elemental sulfur production and understand its potential mechanism. The addition of the intermediate product thiosulfate and the final product sulfate during the reaction led to an increase in the production of biological elemental sulfur (S bio 0 ). The effect is mainly reflected in the efficient accumulation effect of S bio 0 at high sulfide loads. When the sulfide feed water load was 300 mg/L, the S bio 0 production reached 65.94 mg/L in 24 h with the addition of 30 mg/L thiosulfate and 20 mg/L sulfate, which was 3.11 times higher than that of the control group. The addition of sulfate increased the content of aromatic protein I and aromatic protein II, and accelerated the propagation of Thiobacillus denitrificans, whose viable bacterial amount was 1.12-2.98 times higher than that of the control group. On the one hand, low-dose sulfate induced Thiobacillus denitrificans to participate in the sulfur-producing reaction (S 2 - →S bio 0 ) more quickly by accelerating the propagation of the strains in the pre-reaction stage. On the other hand, the addition of sulfate shifted the overall reaction equilibrium to the left and inhibited the formation of thiosulfate, thus accelerating the accumulation of S bio 0 in the whole reaction stage. This study would provide guidance for artificially promoting efficient sulfur accumulation in desulfurisation denitrification treatments.Highlights The S bio 0 production reached 65.94 mg/L in 24 h at high sulfide load.20 mg/L sulfate induced the rapid propagation of Thiobacillus denitrificans.Thiobacillus denitrificans were involved early in the sulfur-producing reaction.Inhibition of thiosulfate formation indirectly promoted sulfur accumulation.

Effects of inoculum temperature and characteristics on cellulose and sewage sludge biodegradability: A comparative study of three inocula

The role of inoculum in initiating anaerobic digestion (AD), and accelerating the start-up of anaerobic digesters has been well-documented. However, the effect of aligning the origin temperature of the inoculum with the operational temperature of the new digester remains underexplored. This study investigates how the origin temperature and characteristics of the inoculum affect the kinetics and biodegradability of sewage sludge (SS) and microcrystalline cellulose (MCC) under mesophilic and thermophilic conditions. Three inocula were used: one thermophilic (I1) and two mesophilic inocula (I2 and I3) in six Biomethane Potential tests (BMP) at 37 and 55 °C. Results indicated that inoculum temperature had no significant impact on the BMP values for MCC and SS, regardless of the experimental temperature. However, kinetic analyses revealed that I2 significantly outperformed I1 and I3 under both temperature conditions. This was attributed to I2's more diverse bacterial structure and lower inhibitor concentrations. High alkalinity, ammonia, and volatile fatty acids (VFA), as well as the presence of denitrifying bacteria (41.7 % of total communities in I1) contributed to poor kinetics of I1 and I3, which were unsuitable for mesophilic and thermophilic temperatures, respectively. Alkalinity (correlation with the Simpson index = -0.92, p < 0.05) and ammonia (correlations with Chao and ACE = -0.93 and -0.91, respectively, p < 0.05) were significantly linked to low bacterial diversity, while high VFA levels were strongly associated with poor inoculum kinetics (correlation with degradation kinetics = -0.90 to -0.99, p < 0.05). These findings offer insights into assessing the inoculum suitability based on its characteristics.

Microbial community dynamics in different floc size aggregates during nitrogen removal process upgrading in a full-scale landfill leachate treatment plant

Upgrading processes to reduce biodegradable organic substance addition is crucial for treating landfill leachate with high pollutant concentrations, aiding carbon emission reduction. Aggregate size in activated sludge processes impacts pollutant removal and sludge/water separation. This study investigated microbial community succession and driving mechanisms in different floc-size aggregates during nitrogen removal progress upgrade from conventional to partial nitrification-denitrification in a full-scale landfill leachate treatment plant (LLTP) using 16S rRNA gene sequencing. The upgrade and floc sizes significantly influenced microbial diversity and composition. After upgrading, ammonia-oxidizing bacteria were enriched while nitrite-oxidizing bacteria suppressed in small flocs with homogeneity and high mass transfer efficiency. Larger flocs enriched Defluviicoccus, Thauera, and Truepera, while smaller flocs enriched Nitrosomonas, suggesting their potential as biomarkers. Multi-network analyses revealed microbial interactions. A deep learning model with convolutional neural networks predicted nitrogen removal efficiency. These findings guide optimizing LLTP processes and understanding microbial community dynamics based on floc size.

Impact of aeration rate on the transfer range of antibiotic-resistant plasmids during manure composting

Conjugative plasmids are important vectors of mobile antibiotic resvistance genes (ARGs), facilitating their horizontal transfer within the environment. While composting is recognized as an effective method to reduce antibiotics and ARGs in animal manure, its impact on the bacterial host communities containing antibiotic-resistant plasmids remains unclear. In this study, we investigated the permissiveness of bacterial community during composting when challenged with multidrug-resistant conjugative RP4 plasmids, employing Pseudomonas putida as the donor strain. Ultimately, this represents the first exploration of the effects of aeration rates on the range of RP4 plasmid transfer hosts. Transconjugants were analyzed through fluorescent reporter gene-based fluorescence-activated cell sorting and Illumina sequencing. Overall, aeration rates were found to influence various physicochemical parameters of compost, including temperature, pH, total organic matter, total nitrogen, and potassium. Regarding RP4 plasmid host bacteria, the dominant phylum was determined to shift from Bacteroidetes in the raw material to Proteobacteria in the compost. Notably, a moderate-intensity aeration rate (0.05 L/min/L) was found to be more effective in reducing the diversity and richness of the RP4 plasmid host bacterial community. Following composting, the total percentage of dominant transconjugant-related genera decreased by 66.15-76.62%. Ultimately, this study determined that the aeration rate negatively impacts RP4 plasmid host abundance primarily through alterations to the environmental factors during composting. In summary, these findings enhance our understanding of plasmid host bacterial communities under varying composting aeration rates and offer novel insights into preventing the dissemination of ARGs from animal manure to farmland.

Increasing urine nitrification performance with sequential membrane aerated biofilm reactors

This study aimed to investigate whether separating organics depletion from nitrification increases the overall performance of urine nitrification. Separate organics depletion was facilitated with membrane aerated biofilm reactors (MABRs). The high pH and ammonia concentration in stored urine inhibited nitrification in the first stage and therewith allowed the separation of organics depletion from nitrification. An organics removal of 70 % was achieved at organic loading rates in the influent of 3.7 gCOD d-1 m-2. Organics depletion in a continuous flow stirred tank reactor (CSTR) for organics depletion led to ammonia stripping through diffused aeration of up to 13 %. Using an MABR, diffusion into the lumen amounted for 4 % ammonia loss only. In the MABR, headspace volume and therefore ammonia loss through the headspace was negligible. By aerating the downstream MABR for nitrification with the off-gas of the MABR for organics depletion, 96 % of the ammonia stripped in the first stage could be recovered in the second stage, so that the overall ammonia loss was negligibly low. Nitrification of the organics-depleted urine was studied in MABRs, CSTRs, and sequencing batch reactors in fed batch mode (FBRs), the latter two operated with suspended biomass. The experiments demonstrated that upstream organics depletion can double the nitrification rate. In a laboratory-scale MABR, nitrification rates were recorded of up to 830 mgNL-1 d-1 (3.1 gN m-2 d-1) with ambient air and over 1500 mgNL-1 d-1 (6.7 gN m-2 d-1) with oxygen-enriched air. Experiments with a laboratory-scale MABR showed that increasing operational parameters such as pH, recirculation flow, scouring frequency, and oxygen content increased the nitrification rate. The nitrification in the MABR was robust even at high pH setpoints of 6.9 and was robust against process failures arising from operational mistakes. The hydraulic retention time (HRT) required for nitrification was only 1 to 2 days. With the preceding organics depletion, the HRT for our system requires 2 to 3 days in total, whereas a combined activated sludge system requires 4 to 8 days. The N2O concentration in the off-gas increases with increasing nitrification rates; however, the N2O emission factor was 2.8 % on average and independent of nitrification rates. These results indicate that the MABR technology has a high potential for efficient and robust production of ammonium nitrate from source-separated urine.

Power to biogas upgrading: Effects of different H2/CO2 ratios on products and microbial communities in anaerobic fermentation system

Two anaerobic reactors with and without Ca²⁺ were operated at 35 °C to investigate the effects of different H₂/CO₂ ratios on products and microbial communities. Through the investigation of various parameters, it was shown that the change of pH triggered by the variations of H₂/CO₂ is the decisive factor affecting the product selection in anaerobic fermentation system. During the biosynthesis of ATP for cell growth and reproduction, protons (H⁺) were pumped from extracellular to intracellular by proton pump, which caused an increase of intrinsic pH of fermentative system. When the pH below 9.5, the methanogenic pathway was more prevalent. While the pH above 10.0 was conducive to the homoacetogenesis. Microbial community analysis showed that with the changes of H₂/CO₂ ratio, a turnover had occurred. When the ratio of H₂/CO₂ was 4, the main methanogen was Methanobacterium with the dominant interspecies electron transfer bacteria (IETB) of Thermovirga and DMER64. The turnover of microbial community occurred when the H₂/CO₂ ratio was 4.5 and 4.25. The dominant acetogenic microorganisms were norank_o_Clostridia_UCG-014 (homoacetogen) and Natronincola (obligately alkaliphilic acetogen). When the H₂/CO₂ ratio returned to 4, the dominant methanogens were hydrotropic Methanobacterium and Methanobrevibacter with four interspecies electron transfer bacteria including DMER64, Thermovirga, Dechlorobacter and Achromobacter.

Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage

Leachate leakage poses a serious environmental risk to the safety of surrounding soils and groundwater. A much faster approach to reflect landfill leakage is the premise to mitigate the ecological risk of landfills. In this study, two landfills (BJ and WZ) were selected to investigate the leaching characteristics of various pollutants along the vadose soil depths. The physiochemical properties of underlying soils including NO₃^--N, NO₂^--N, NH₄⁺-N, OM, TN, EC and Cl^- exhibited a typical leaching dynamic along the depths. Among them, TN, NH₄⁺-N, OM, NO₃^--N, and EC might be used as characteristic pollutants to evaluate the leachate leakage issues in landfilled sites. The genera Thiopseudomonas, Acinetobacter, Pseudomonas, and Hydrogenispora dominated in underlying soils. Compared to BJ samples, a more diverse and active microbiome capable of carbon and nitrogen cycles was observed in WZ samples, which was mainly ascribed to nutrients and elements contained in different types of soils. Among the environmental factors, nitrogenous compounds, SO₄^2-, pH and EC had significant effects on the microbial community structures in the underlying soils. The relative abundances of Hydrogenispora and Caldicoprobacter might be used as characteristic microorganisms to evaluate the leachate leakage issues in landfilled sites. These results provided a deep insight into effects of leachate leakage in underlying soils, especially the pollutants vertical distribution and the corresponding microbial community structures.

Partial nitrification in free nitrous acid-treated sediment planting Myriophyllum aquaticum constructed wetland strengthens the treatment of black-odor water

Black-odor water pollution in rural areas, especially swine wastewater, can lead to the deterioration of water quality and thus seriously affect the daily life of people in the area. However, there is a lack of effective treatment measures with simultaneous attention to carbon, nitrogen and sulfur pollution in rural black-odor water bodies. This study evaluated the feasibility of an in-situ pilot-scale constructed wetland (CW) for the synchronous removal of COD, ammonium, and sulfur compounds in the swine wastewater. In this study, the operation strategy of CW sediment pretreated with free nitrous acid (FNA) and Myriophyllum aquaticum plantation was established. Throughout the 114-day operation, the total removal efficiencies of COD and ammonium nitrogen in experimental groups were 81.2 ± 4.2 % and 72.8 ± 1.8 %, respectively, which were significantly higher than CW without any treatment. Removal efficiencies of Sulfur compounds, i.e. sulfide, sulfate, thiosulfate, and sulfite, were 92.3 ± 1.9 % (61.2 % higher than the no-treatment group), 42.1 ± 3.8 %, 97.9 ± 1.7 %, and 42.7 ± 4.5 % respectively. High-throughput sequencing and qPCR revealed that experimental group significantly increased denitrification genes (nirK, nosZ) and sulfur oxidation genes (soxB, fccAB) and enriched the corresponding microbial taxa (Bacillus, Conexibacter and Clostridium sensu stricto). Moreover, metabolic pathways related to nitrogen and sulfur and the degradation of organic matter were up-regulated. These results indicated that partial nitrification in CW planted with M. aquaticum promoted sulfur oxidation denitrification and heterotrophic denitrification. Overall, the in-situ pilot-scale study revealed that the cultivation of M. aquaticum in FNA-treated CW can be a sustainable approach to treat black-odor water bodies.

The mixed/mixotrophic nitrogen removal for the effective and sustainable treatment of wastewater: From treatment process to microbial mechanism

Biological nitrogen removal (BNR) is one of the most important environmental concerns in the field of wastewater treatment. The conventional BNR process based on heterotrophic nitrogen removal (HeNR) is suffering from several limitations, including external carbon source dependence, excessive sludge production, and greenhouse gas emissions. Through the mediation of autotrophic nitrogen removal (AuNR), mixed/mixotrophic nitrogen removal (MixNR) offers a viable solution to the optimization of the BNR process. Here, the recent advance and characteristics of MixNR process guided by sulfur-driven autotrophic denitrification (SDAD) and anammox are summarized in this review. Additionally, we discuss the functional microorganisms in different MixNR systems, shedding light on metabolic mechanisms and microbial interactions. The significance of MixNR for carbon reduction in the BNR process has also been noted. The knowledge gaps and the future research directions that may facilitate the practical application of the MixNR process are highlighted. Overall, the prospect of the MixNR process is attractive, and this review will provide guidance for the future implementation of MixNR process as well as deciphering the microbially metabolic mechanisms.

Wild Heterotrophic Nitrifying Strain Pseudomonas BT1 Isolated from Kitchen Waste Sludge Restores Ammonia Nitrogen Removal in a Sewage Treatment Plant Shocked by Thiourea

Thiourea is used in agriculture and industry as a metal scavenger, synthetic intermediate, and nitrification inhibitor. However, in wastewater, it can inhibit the nitrification process and induce the collapse of the nitrification system. In such a case, ammonia-oxidizing bacteria (AOB) lose their ability to remove ammonia. We investigated the nitrification system of a 60,000-t/d municipal sewage treatment plant in Nanjing, which collapsed after receiving 5–15 ppm (5–15 mg/L) thiourea. Ammonia nitrogen removal quickly recovered to more than 95% after inoculation with 10 t high-efficiency nitrification sludge, which was collected from a kitchen waste treatment plant. A heterotrophic nitrification strain was isolated from the inoculated sludge and identified as wild Pseudomonas by 16S rDNA sequencing and named “BT1.” Based on thiourea tolerance tests, BT1 can tolerate a thiourea content of more than 500 ppm. For comparison, the in situ process was imitated by the simulation system, and the wastewater shocked by 10 ppm thiourea could still meet the emission standard after adding 1% (V/V) BT1. High-throughput sequencing analysis was applied to study microbial succession during thiourea shock loading. The results showed that Hydrogenophaga and Thiobacillus grew with the growth of BT1. Pseudomonas BT1 was used for a 6,000-t/d printed circuit board (PCB) wastewater treatment system, the nitrification system returned to normal in 15 days, and the degradation rate stabilized at more than 95%.

Behavior of nitrogen and sulfur compounds in the rice husk pellet bioscrubber and its circulation water

In this study, pellet-type biofilter media was developed with rice husk and applied in a wet scrubber system for odor removal. The lab-scale bioscrubber system was operated for 200 days to evaluate odorous gas removal (i.e., NH₃, H₂S, methyl mercaptan, and dimethyl sulfide), and the removal mechanism of odor gases was studied by analyzing the behavior of nitrogen and sulfur compounds in circulation water of bioscrubber system. The rice husk pellets supplied the organic carbon source and phosphoric acid necessary for microbial growth, allowing the system to continue successfully for 200 days without any maintenance technology. By analyzing the behavior of the nitrogen and sulfur compounds in the circulation water, we confirmed that the odor gas removal resulted from various mechanisms, including adsorption and biodegradation. Ammonia gas was absorbed by the rice husk pellets and accumulated in the circulation water as nitrite under conditions of sufficient alkalinity and above pH 7. Conversely, when the alkalinity and pH decreased, nitrite was rapidly converted to nitrate. However, H₂S gas was oxidized to sulfate and continuously accumulated in the circulation water regardless of the pH and alkalinity. In addition, it was confirmed that the decrease in nitrate in the bioscrubber system was due to heterotrophic denitrification by the organic carbon source supply and autotrophic denitrification by sulfur gas. During the operation of the rice husk pellet bioscrubber for 8 months, under low solubility condition, more than 99% of NH₃ and H₂S were removed and about 85% of methyl mercaptan (MM) and dimethyl sulfide (DMS) were removed.

The interaction between Pseudomonas C27 and Thiobacillus denitrificans in the integrated autotrophic and heterotrophic denitrification process

Compared to autotrophic and heterotrophic denitrification process, the integrated autotrophic and heterotrophic denitrification (IAHD) shows wider foreground of applications in the actual wastewaters with organic carbon, nitrogen and sulfur co-existing. The efficient co-removal of sulfur, nitrogen, and carbon in the IAHD system is guaranteed by the interaction between heterotrophic and autotrophic denitrificans. In order to further explore the interaction between functional bacteria, Pseudomonas C27 and Thiobacillus denitrifcans were selected as typical heterotrophic and autotrophic bacteria, and their characteristics metabolic responses to different sulfide concentrations were studied. Pseudomonas C27 had higher metabolic activity than T. denitrificans in the IAHD medium with sulfide concentration of 3.12-15.62 mmol/L. Moreover, the fastest sulfide removal rate (0.35 mmol/L·h) was achieved with a single inoculation of Pseudomonas C27. Meanwhile, in mixed inoculant conditions, the interaction between Pseudomonas C27 and T. denitrificans (P:T = 3:1, P:T = 1:1 and P:T = 1:3) yielded the highest sulfide removal efficiency (more than 85%) when sulfide concentration was 6.25-12.5 mmol/L. Additionally, the sulfide removal rate increased with the inoculation proportion of Pseudomonas C27. Thus, this apparent interaction provided a theoretical basis for further understanding and guidance on the efficient operation of IAHD system.

Rapid start of high-concentration denitrification and desulfurization reactors by heterotrophic denitrification sulphur-oxidising bacteria

High sulphide concentrations can be toxic to denitrifying and desulphurising microorganisms. In this study, bioaugmentation was used to solve this problem. Pseudomonas sp. gs1 can tolerate 400 mg/L sulphide and converts most of the sulphide into elemental sulphur after 4 h. A solid inoculum of Pseudomonas sp. h1 was prepared. Two reactors, that is, one with and one without inoculum, were simultaneously run for 60 days. Bioreactor II to which bacterial inoculum was added reached a good treatment performance on day 3. The elemental sulphur concentration of the effluent was 342.6 mg/L. It was maintained at 245.3-333.8 mg/L during the subsequent operation. In contrast, reactor I without inoculants achieved the same performance on day 50. High-throughput sequencing shows that Pseudomonas and Azoarcus are the dominant genera. The abundance of the genus Pseudomonas and related denitrifying sulphur-oxidising bacteria in reactor I increases with the operation time. This phenomenon was confirmed by testing the sqr and gltA genes. The quantitative fluorescence PCR test also proves that the addition of bacteria leads to a rapid increase in the sulphur oxidation and carbon metabolism of the activated sludge in the reactor.

Regulating intermediates to realize the coupled hydrion with biology polysulfide in wastewater treatment

The purpose of this study is to clarify the mechanism of the coupled hydrion with biology polysulfide in the simultaneous denitrification and desulfurization process. The coupled hydrion with biology polysulfide, uncoupled hydrion with biology polysulfide and no polysulfide experiments were performed in wastewater with two kinds of sulfide loads (100 and 200 mg/L). When the concentration of thiosulfate was suitable, the free H⁺ concentration (74.2 and 91.0 mg/L) and the proportion of Thiobacillus denitrificans (85.4% and 59.7%) were both higher under the two kinds of sulfide loading conditions (100 and 200 mg/L), and coupled hydrion with biology polysulfide was realized (the production of elemental sulfur is as high as 33 and 101 mg/L). Further analysis shown that the way of coupled hydrion with biology polysulfide were both: 2.0S2-+6.4NO3-+30.1H++21.7e-→1.0S2-+1.0SO42-+3.2N2+15.0H2O. In addition, for the coupled hydrion with biology polysulfide, more nitrates could be utilized to produce elemental sulfur S⁰, and the lower ratio of H⁺/S⁰ and SO42-/S0 were observed (S^2- = 100 mg/L: 2.3 and 0.9; S^2- = 200 mg/L: 0.9 and 0.03), which could promote the growth of Thiobacillus denitrificans and increase the proportion of Thiobacillus denitrificans. This maybe one of the reasons why coupled hydrion with biology polysulfide could be achieved.

Application oriented bioaugmentation processes: Mechanism, performance improvement and scale-up

Bioaugmentation is an optimization method with great potential to improve the treatment effect by introducing specific strains into the biological treatment system. In this study, a comprehensive review of the mechanism of bioaugmentation from the aspect of microbial community structure, the optimization methods facilitating application as well as feasible approaches of scale-up application has been provided. The different contribution of indigenous and exogenous strains was critically analyzed, the relationship between microbial community variation and system performance was clarified. Operation regulation and immobilization technologies are effective methods to deal with the possible failure of bioaugmentation. The gradual expansion from lab-scale, pilot scale to full-scale, the transformation and upgrading of wastewater treatment plants through the combination of direct dosing and biofilm, and the application of side-stream reactors are feasible ways to realize the full-scale application. The future challenges and prospects in this field were also proposed.

Effect of biochar combined with a biotrickling filter on deodorization, nitrogen retention, and microbial community succession during chicken manure composting

The high-nitrogen content and dense structure of poultry manure compost cause volatilization of N to ammonia (NH₃). This study evaluated the combined application of biochar and biotrickling filtration (BTF) to remove of odor in chicken manure mixed straw compost (w/w, 2.5:1). Adding of 10% biochar reduced NH₃, hydrogen sulfide (H₂S), and total volatile organic compounds (TVOCs) contents by 20.04%, 16.18%, and 17.55% respectively, and decreased the N loss rate by 8.27%, compared with those observed in control. The organic matter content decreased by 28.11% and germination index reached 97.36% in the experimental group. Meanwhile, the N-cycling microorganisms such as Pusillimonas and Pseudomonas became more active, and the relative abundance of sulfur-cycling microorganisms Hydrogenispora decreased in the experimental group. Following BTF application, the NH₃, H₂S, and TVOCs removal rates reached 95%, 97%, and 53%, respectively.

Microbes drive changes in arsenic species distribution during the landfill process

Landfills are considered an anthropogenic source of arsenic (As). The As species mediated by microbes in landfills vary significantly in toxicity. Based on random matrix theory, 16S rRNA genes were used to construct four microbial networks associated with different stages over 12 years of landfill ages. The results indicated that network size and microbial structure varied with landfill age. According to the network scores, about 208 taxa were identified as putative keystones for the whole landfill; the majority of them were Firmicutes, which accounted for 66.8% of all specialists. Random Forest analysis was performed to predict the keystone taxa most responsible for As species distribution under different landfill conditions; 17, 10 and 14 keystone taxa were identified as drivers affecting As species distribution at early, middle, and later landfill stages, respectively.

Ozone direct oxidation pretreatment and catalytic oxidation post-treatment coupled with ABMBR for landfill leachate treatment

In order to treat the high concentration landfill leachate, ozone direct oxidation pretreatment and catalytic oxidation post-treatment coupled with anaerobic baffled membrane bioreactor (ABMBR) system was proposed in this study. For pretreatment, ozone direct oxidation could remarkably reduce UV₂₅₄, 3D fluorescence peak value and fluorescence regional integration (FRI) of organic pollutants. For ABMBR treatment, the removal efficiencies of COD and ammonia nitrogen were 80.38% and 21.56%, respectively. Post-treatment included struvite precipitation, ozone catalytic oxidation and membrane bioreactor (MBR) treatment. Finally, the total removal efficiencies of COD and ammonia nitrogen were 91.2% and 99.4%, respectively. The chroma was remarkably decreased from 1250 times to 40 times after a series of treatments. The acids in ABMBR could be degraded by microorganisms of Proteobacteria and Chloroflexi. The cellulose and polysaccharides could be decomposed by Bacteroidetes and ketones could be decomposed by Brevundimonas in ABMBR. Electron paramagnetic resonance (EPR) analysis indicated that the hydroxyl radicals were the main reactive oxygen species during the direct ozone oxidation process, while the superoxide radicals played an important role in the ozone catalytic oxidation process.

Zeolitic imidazolate framework-derived porous carbon enhances methanogenesis by facilitating interspecies electron transfer: Understanding fluorimetric and electrochemical responses of multi-layered extracellular polymeric substances

Modulating microbial electron transfer during anaerobic digestion can significantly improve syntrophic interactions for enhanced biogas production. As a carbonaceous conductive material, zeolite imidazolate framework-67 (ZIF-67)-derived porous carbon (PC) was hypothesized to act as a microbial electron transfer highway and assessed with respect to understanding the fluorimetric and electrochemical responses of multilayered extracellular polymeric substances (EPS). The highest biomethane yield (614.0 mL/g) from ethanol was achieved in the presence of 100 mg/L PC prepared at a carbonization temperature of 800 °C (PC-800), which was 28.2% higher than that without PC addition. Electrochemical analysis revealed that both the redox peak currents and conductivity of the methanogenic sludge increased, while the free charge transfer resistance decreased with PC-800 addition. The conductive PC-800 potentially functioned as an abiotic electron conduit to promote direct interspecies electron transfer, thereby resulting in decreased expression of functional genes associated with electrically conductive pili (e-pili) and hemeproteins. Additionally, PC-800 stimulated the secretion of redox-active humic substances (HSs), and excitation emission matrix spectra analysis indicated that the largest increase in percent fluorescence response of HSs occurred in the tightly bound EPS (TB-EPS) with addition of PC-800. This was attributed to the strong complexation ability of PC-800 particles to hydroxyl/carboxylic/phenolic moieties of HSs contained in the TB-EPS. Microbial analysis revealed that syntrophic/exoelectrogenic bacteria such as Pelotomaculum and Syntrophomonas, as well as hydrogenotrophic/electrotrophic methanogens such as Methanoculleus and Methanobacterium, were enriched in methanogenic sludge with adding PC-800. This study provided comprehensive insights for understanding the interactions among ZIF-derived PC, methanogenic microorganisms and their multilayered EPS.

Insights into the stabilization of landfill by assessing the diversity and dynamic succession of bacterial community and its associated bio-metabolic process

The distribution of bacterial community in an actual landfill was analyzed and the bioprocess involved in refuse degradation was clarified. The results showed that the degradation degree of refuse showed great differences with the landfill age, in which the contents of organic matter (OM) and total Kjeldahl nitrogen (TKN) in refuse as well as the chemical oxygen demand (COD) in leachate presented decreasing trends with increasing landfill age. The diversity of bacterial community increased first and then decreased with increasing landfill age. The main bacterial phyla involved in refuse degradation were Proteobacteria, Firmicutes and Bacteroidetes, among which, Proteobacteria had an absolute advantage with a relative abundance ranging of 66-78%. With increasing landfill age, the abundance of Firmicutes decreased gradually, while that of Bacteroidetes increased. Pseudomonas, Thiopseudomonas, Psychrobacter and Desemzia were the main genera. The distribution of bacterial community in samples with landfill ages of 0-1 and 1-3 years were greatly influenced by TKN and pH, respectively. Amino acid and carbohydrate metabolism were the main biological pathways according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and the biodegradation of xenobiotics as well as terpenoids and polyketides also accounted relatively high frequencies in the landfill. These results provide a better understanding of landfill microbiology and bioprocesses for landfill stabilization.

Biological denitrification potential as an indicator for measuring digestate stability

Biological stability is an essential parameter for assessing the environmental impact from the land application of digestate as organic amendment. In this paper, a new indicator, biological denitrification potential (BDP), was developed for evaluating the biological stability of digestate. Digestate samples collected along the digestion process from a mesophilic anaerobic batch digester fed with food waste were investigated under different solid retention time. The value of BDP based on nitrate removal ranged from 176.3 to 48.3 mg-N/g-VS_digestate, corresponding well to the digestion time, and strongly correlated with total organic carbon content. Evolution trends similar to respiration index (RI) and biochemical methane potential (BMP) can be also observed for BDP, indicating that values presented of these stability indices decreased with the degree of digestate stabilization. The mass balance of the BDP process indicated that nitrate was mainly converted into N₂ gas with mineralizing organic carbon from digestate, implying that biostability evaluated by BDP depends on carbon source and denitrification activity in digestate. The denitrifying bacteria Thiopseudomonas and Pseudomonas accounted for the majority of microorganisms. These findings of this study concluded that BDP can be an efficient indicator to assess the bio-stability of digestate planned for agricultural or land use. Compared with the existing biostability index, BDP has the additional advantage of no exogenous inoculum addition, homogenous test condition and possibility of shortening incubation time.

Simultaneous energy harvest and nitrogen removal using a supercapacitor microbial fuel cell

The insufficient removal of pollutants and bioelectricity production have become a bottleneck for high-concentration saline wastewater treatment through microbial fuel cell (MFC) technology. Herein, a novel supercapacitor MFC (SC-MFC) was constructed with carbon nanofibers composite electrodes to investigate pollutant removal ability, power generation, and electrochemical properties using real landfill leachate. The possible extracellular electron transfer and nitrogen element conversion pathways in the bioanode were also analyzed. Results showed that the SC-MFC had higher pollutant removal rates (COD: 59.4 ± 1.2%; NH₄⁺-N: 78.2 ± 1.6%; and TN: 77.8 ± 1.2%), smaller internal impedance R_t (∼6 Ω), higher exchange current density i₀ (2.1 × 10^-4 A cm^-2), and a larger catalytic current j₀ (704 μA cm^-2) with 60% leachate than those with 10% and 20% leachate, resulting in a power output of 298 ± 22 mW m^-2. Ammonium could be incorporated by chemoautotrophic bacteria to produce organic compounds that could be further utilized by heterotrophs to generate power when biodegradable organic matters are depleted. Three conversion pathways of nitrogen might be involved, including NH₄⁺ diffusion from anode to cathode chamber, nitrification, and the denitrification process. Additionally, cyclic voltammetry tests showed that both the direct electron transfer (DET) and the mediator electron transfer in bioanode were involved and dominated by DET. The microbial analysis revealed that the bioanode was dominated by salt-tolerant denitrifying bacteria (38.5%), which was deduced to be the key functional microorganism. The electrochemically active bacteria decreased significantly from 61.7% to 4% over three stages of leachate treatment. Overall, the SC-MFC has demonstrated the potential for wastewater treatment along with energy harvesting and provides a new avenue toward sustainable leachate management.

Characteristics and performances of microalgal-bacterial consortia in a mixture of raw piggery digestate and anoxic aerated effluent

The piggery digestate of high ammonia was mixed with the anoxic aerated effluent of high nitrate and phosphorus, to cultivate a microalgal-bacterial consortium for simultaneous pollution removal and resource recovery. The highest removal of total inorganic nitrogen was achieved at 324.77 mg/L in 40% piggery digestate mixed with 60% anoxic aerated effluent, along with the most microalgae biomass production. The crude protein and fatty acids of C14-C20 in microalgae cells were 21.80% and 69.78%, indicating that this mixing strategy could produce abundant microalgal biomass suitable for biofuel generation and animal feed. High-throughput sequencing showed that microbial diversity increased and Paenibacillus, Thiopseudomonas and Pseudomonas were the dominant species promoting microalgal growth. Overall, these results provided a new insight of mixing two types of wastewaters for cultivating microalgal-bacterial consortia, to remove contamination and recover nutrients simultaneously.

Microbial community structures and functions of hypersaline heterotrophic denitrifying process: Lab-scale and pilot-scale studies

High-nitrate wastewaters are known pose substantial risks to human and environmental health, while their effective treatment remains difficult. The denitrification of saline, high-NO₃^- wastewaters was investigated at the laboratory- and pilot-scale experiment. Complete denitrification was achieved for three different realistic wastewaters, and the maximum influent [NO₃^-]₀ and salinity were as high as 20,500 mg/L and 7.8%, respectively. The results of microbial community structure analyses revealed that the sequences of denitrifying functional bacteria accounted for 96.2% of all sequences, and the functional genes for denitrification in bacteria were enriched with elevated salinity and [NO₃^-]₀. A significant difference was observed in the dominant bacterial genus between synthetic and realistic wastewaters. Thauera and Halomonas species evolved to be the most common dominant genera contributing to the processes of nitrate, nitrite, and nitrous oxide reductase. This study is practically valuable for the treatment of realistic, saline, high-NO₃^- wastewaters via denitrification by heterotrophic bacteria.

Bioaugmentation with Clostridium tyrobutyricum to improve butyric acid production through direct rice straw bioconversion

One-pot bioconversion is an economically attractive biorefinery strategy to reduce enzyme consumption. Direct conversion of lignocellulosic biomass for butyric acid production is still challenging because of competition among microorganisms. In a consolidated hydrolysis/fermentation bioprocessing (CBP) the microbial structure may eventually prefer the production of caproic acid rather than butyric acid production. This paper presents a new bioaugmentation approach for high butyric acid production from rice straw. By dosing 0.03 g/L of Clostridium tyrobutyricum ATCC 25755 in the CBP, an increase of 226% higher butyric acid was yielded. The selectivity and concentration also increased to 60.7% and 18.05 g/L, respectively. DNA-sequencing confirmed the shift of bacterial community in the augmented CBP. Butyric acid producer was enriched in the bioaugmented bacterial community and the bacteria related to long chain acids production was degenerated. The findings may be useful in future research and process design to enhance productivity of desired bio-products.

Influence of reflux ratio on two-stage anoxic/oxic with MBR for leachate treatment: Performance and microbial community structure

A lab-scale two-stage Anoxic/Oxic with MBR (AO/AO-MBR) system was operated for 81 days for leachate treatment with different reflux ratio (R). The best system performances were observed with a R value of 150%, and the average removal efficiencies of chemical oxygen demand, ammonia and total nitrogen were 85.6%, 99.1%, and 77.6%, respectively. The microbial community were monitored and evaluated using high-throughput sequencing. Proteobacteria were dominant in all process. Phylogenetic trees were described at species level, genus Thiopseudomonas, Amaricoccus, Nitrosomonas and Nitrobacter played significant roles in nitrogen removal. Co-occurrence analyzing top 20 genera showed that Nitrosomonas-Nitrobacter presented perfect positive relationship, as well as Paracoccus-Brevundimonas and Pusillimonas-Halobacteriovorax.

Metabolic divergence in simultaneous biological removal of nitrate and sulfide for elemental sulfur production under temperature stress

The simultaneous removal of NO₃^- and HS^- at temperature stress (25-10°C) is evaluated here. An expanded granular sludge bed (EGSB) reactor was run over 120days at N/S molar ratio of 0.35 (for S⁰ production) under constant sulfur loading rate of 0.4kgS/m³d. The simultaneous removal of NO₃^- and HS^-, was achieved at applied conditions. Average HS^--S removal varied from 98 (25°C) to 89.2% at 10°C, with almost complete NO₃^- removal. Average S⁰ yield ranged from 83.7 at 25°C to 67% at 10°C. The temperature drop caused a decrease in granular sludge accumulated S⁰ fraction by nearly 2.5 times. Decreased temperature caused metabolic pathway change observed as higher SO₄^2- production, apparently allowing the biomass to obtain more energy per HS^- consumed. It is hypothesized that the metabolic shift is a natural response to compensate for temperature-induced changes in energy requirements.