Biological carbon capture from biogas streams: Insights into Cupriavidus necator autotrophic growth and transcriptional profile.

Recycling carbon-rich wastes into high-value platform chemicals through biological processes provides a sustainable alternative to petrochemicals. Cupriavidus necator, known for converting carbon dioxide (CO2) into polyhydroxyalkanoates (PHA) was studied for the first time using biogas streams as the sole carbon source. The bacterium efficiently consumed biogenic CO2 from raw biogas with methane at high concentrations (50%) proving non-toxic. Continuous addition of H2 and O2 enabled growth trends comparable to glucose-based heterotrophic growth. Transcriptomic analysis revealed CO2-adaptated cultures exhibited upregulation of hydrogenases and Calvin cycle enzymes, as well as genes related to electron transport, nutrient uptake, and glyoxylate cycle. Non-adapted samples displayed activation of stress response mechanisms, suggesting potential lags in large-scale processes. These findings showcase the setting of growth parameters for a pioneering biological biogas upgrading strategy, emphasizing the importance of inoculum adaptation for autotrophic growth and providing potential targets for genetic engineering to push PHA yields in future applications.

Heterotrophic and autotrophic production of L-isoleucine and L-valine by engineered Cupriavidus necator H16.

Advancement in commodity chemical production from carbon dioxide (CO2) offers a promising path towards sustainable development goal. Cupriavidus necator is an ideal host to convert CO2 into high-value chemicals, thereby achieving this target. Here, C. necator was engineered for heterotrophic and autotrophic production of L-isoleucine and L-valine. Citramalate synthase was introduced to simplify isoleucine synthesis pathway. Blocking poly-hydroxybutyrate biosynthesis resulted in significant accumulation of isoleucine and valine. Besides, strategies like key enzymes screening and overexpressing, reducing power balancing and feedback inhibition removing were applied in strain modification. Finally, the maximum isoleucine and valine titers of the best isoleucine-producing and valine-producing strains reached 857 and 972 mg/L, respectively, in fed-batch fermentation using glucose as substrate, and 105 and 319 mg/L, respectively, in autotrophic fermentation using CO2 as substrate. This study provides a feasible solution for developing C. necator as a microbial factory to produce amino acids from CO2.

The effect of reflux ratio on sulfur disproportionation tendency in anaerobic baffled reactor with the heterotrophic combining sulfur autotrophic processes under high concentration perchlorate stress.

In a laboratory scale, an anaerobic baffled reactor (ABR) consisting of eight compartments, the heterotrophic combining sulfur autotrophic processes under different reflux ratios were constructed to achieve effective perchlorate removal and alleviate sulfur disproportionation reaction. Perchlorate was efficiently removed with effluent perchlorate concentration below 0.5 µg/L when the influent perchlorate concentration was 1030 mg/L during stages I ~ V, indicating that heterotrophic combining sulfur autotrophic perchlorate reduction processes can effectively achieve high concentration perchlorate removal. Furthermore, the 100% reflux ratio could reduce the contact time between sulfur particles and water; thus, the sulfur disproportionation reaction was inhibited. However, the inhibition effect of reflux on sulfur disproportionation was attenuated due to dilute perchlorate concentration when a reflux ratio of 150% and 200% was implemented. Meanwhile, the content of extracellular polymeric substances (EPS) in the heterotrophic unit (36.79 ~ 45.71 mg/g VSS) was higher than that in the sulfur autotrophic unit (22.19 ~ 25.77 mg/g VSS), indicating that high concentration perchlorate stress in the heterotrophic unit promoted EPS secretion. Thereinto, the PN content of sulfur autotrophic unit decreased in stage III and stage V due to decreasing perchlorate concentration in the autotrophic unit. Meanwhile, the PS content increased with increasing reflux in the autotrophic unit, which was conducive to the formation of biofilm. Furthermore, the high-throughput sequencing result showed that Proteobacteria, Chloroflexi, Firmicutes, and Bacteroidetes were the dominant phyla and Longilinea, Diaphorobacter, Acinetobacter, and Nitrobacter were the dominant genus in ABR, which were associated with heterotrophic or autotrophic perchlorate reduction and beneficial for effective perchlorate removal. The study indicated that reflux was a reasonable strategy for alleviating sulfur disproportionation in heterotrophic combining sulfur autotrophic perchlorate removal processes.

Improved efficiency and stability using a novel elemental sulfur-based moving-bed denitrification process.

Elemental sulfur-based denitrification (ESDeN) technology is known as a cost-saving alternative to its heterotrophic counterpart for nutrient removal from organic-deficient water. However, the traditional fixed-bed reactor (FixBR), as an extensively used process, suffers from a low denitrification rate and even performance deterioration during long-term operation. Herein, we proposed a novel elemental sulfur-based denitrifying moving-bed reactor (ESDeN-MovBR), in which a screw rotator was employed to drive the filled sulfur particles to be microfluidized vertically (a state of vertical-loop movement). Our results showed that the ESDeN-MovBR realized much superior and more stable denitrification performance compared to the ESDeN-FixBR, as indicated by 3.09-fold higher denitrification rate and over one order of magnitude lower intermediates (NO2- and N2O) yield, which could last for over 100 days. Further research revealed that the microfluidization of sulfur particles facilitated the expelling of nitrogen bubbles and excessive biomass, resulting in the prolongation of actual hydraulic retention time by over 80 % and could partially explain the higher denitrification rate in ESDeN-MovBR. The remaining contribution to the improvement of denitrification rate was suggested to be result from changes in biofilm properties, in which the biofilm thickness of ESDeN-MovBR was found to be 3.29 times thinner yet enriched with 2.52 times more autotrophic denitrifiers. This study offered a completely new solution to boost up the denitrification performance of ESDeN technology and provided in-depth evidence for the necessity of biofilm thickness control in such technology.

Autotrophic growth of Escherichia coli is achieved by a small number of genetic changes.

Synthetic autotrophy is a promising avenue to sustainable bioproduction from CO2. Here, we use iterative laboratory evolution to generate several distinct autotrophic strains. Utilising this genetic diversity, we identify that just three mutations are sufficient for Escherichia coli to grow autotrophically, when introduced alongside non-native energy (formate dehydrogenase) and carbon-fixing (RuBisCO, phosphoribulokinase, carbonic anhydrase) modules. The mutated genes are involved in glycolysis (pgi), central-carbon regulation (crp), and RNA transcription (rpoB). The pgi mutation reduces the enzyme's activity, thereby stabilising the carbon-fixing cycle by capping a major branching flux. For the other two mutations, we observe down-regulation of several metabolic pathways and increased expression of native genes associated with the carbon-fixing module (rpiB) and the energy module (fdoGH), as well as an increased ratio of NADH/NAD+ - the cycle's electron-donor. This study demonstrates the malleability of metabolism and its capacity to switch trophic modes using only a small number of genetic changes and could facilitate transforming other heterotrophic organisms into autotrophs.

Cooperation between autotrophic and heterotrophic denitrifiers under low C/N ratios revealed by individual-based modelling.

Denitrifying biofilms, in which autotrophic denitrifiers (AD) and heterotrophic denitrifiers (HD) coexist, play a crucial role in removing nitrate from water or wastewater. However, it is difficult to elucidate the interactions between HD and AD through sequencing-based experimental methods. Here, we developed an individual-based model to describe the interspecies dynamics and priority effects between sulfur-based AD (Thiobacillus denitrificans) and HD (Thauera phenylcarboxya) under different C/N ratios. In test I (coexistence simulation), AD and HD were initially inoculated at a ratio of 1:1. The simulation results showed excellent denitrification performance and a coaggregation pattern of denitrifiers, indicating that cooperation was the predominant interaction at a C/N ratio of 0.25 to 1.5. In test II (invasion simulation), in which only one type of denitrifier was initially inoculated and the other was added at the invasion time, denitrifiers exhibited a stratification pattern in biofilms. When HD invaded AD, the final HD abundance decreased with increasing invasion time, indicating an enhanced priority effect. When AD invaded HD, insufficient organic carbon sources weakened the priority effect by limiting the growth of HD populations. This study reveals the interaction between autotrophic and heterotrophic denitrifiers, providing guidance for optimizing wastewater treatment process.

Meta-analyzing the mechanism of pyrogenic biochar strengthens nitrogen removal performance in sulfur-driven autotrophic denitrification system: Evidence from metatranscriptomics.

Sulfur-driven autotrophic denitrification (SAD) exhibits significant benefits in treating low carbon/nitrogen wastewater. This study presents an eco-friendly, cost-effective, and highly efficient method for enhancing nitrogen removal performance. The addition of biochar prepared at 300 °C (BC300) notably increased nitrogen removal efficiency by 31.60 %. BC300 concurrently enhanced electron production, the activities of the electron transfer system, and electron acceptors. With BC300, the ratio of NADH/NAD+ rose 2.00±0.11 times compared to without biochar, and the expression of NAD(P)H dehydrogenase genes was markedly up-regulated. In the electron transfer system, BC300 improved the electroactivity of extracellular polymeric substances and the activities of NADH dehydrogenase and complex III in intracellular electron transfer. Subsequently, electrons were directed into denitrification enzymes, where the nar, nir, nor, and nos related genes were highly expressed with BC300 addition. Significantly, BC300 activated the Clp and quorum sensing systems, positively influencing numerous gene expressions and microbial communication. Furthermore, the O%, H%, molar O/C, and aromaticity index in biochar were identified as crucial bioavailable parameters for enhancing nitrogen removal in the SAD process. This study not only confirms the application potential of biochar in SAD, but also advances our comprehension of its underlying mechanisms.

Widespread dissolved inorganic carbon-modifying toolkits in genomes of autotrophic Bacteria and Archaea and how they are likely to bridge supply from the environment to demand by autotrophic pathways.

Using dissolved inorganic carbon (DIC) as a major carbon source, as autotrophs do, is complicated by the bedeviling nature of this substance. Autotrophs using the Calvin-Benson-Bassham cycle (CBB) are known to make use of a toolkit comprised of DIC transporters and carbonic anhydrase enzymes (CA) to facilitate DIC fixation. This minireview provides a brief overview of the current understanding of how toolkit function facilitates DIC fixation in Cyanobacteria and some Proteobacteria using the CBB and continues with a survey of the DIC toolkit gene presence in organisms using different versions of the CBB and other autotrophic pathways (reductive citric acid cycle, Wood-Ljungdahl pathway, hydroxypropionate bicycle, hydroxypropionate-hydroxybutyrate cycle, and dicarboxylate-hydroxybutyrate cycle). The potential function of toolkit gene products in these organisms is discussed in terms of CO2 and HCO3- supply from the environment and demand by the autotrophic pathway. The presence of DIC toolkit genes in autotrophic organisms beyond those using the CBB suggests the relevance of DIC metabolism to these organisms and provides a basis for better engineering of these organisms for industrial and agricultural purposes.

Thermodynamic Inhibition of Microbial Sulfur Disproportionation in a Multisubunit Designed Sulfur-Siderite Packed Bioreactor.

Sulfur disproportionation (S0DP) poses a challenge to the robust application of sulfur autotrophic denitrification due to unpredictable sulfide production, which risks the safety of downstream ecosystems. This study explored the S0DP occurrence boundaries with nitrate loading and temperature effects. The boundary values increased with the increase in temperature, exhibiting below 0.15 and 0.53 kg-N/m3/d of nitrate loading at 20 and 30 °C, respectively. A pilot-scale sulfur-siderite packed bioreactor (150 m3/d treatment capacity) was optimally designed with multiple subunits to dynamically distribute the loading of sulfur-heterologous electron acceptors. Operating two active and one standby subunit achieved an effective denitrification rate of 0.31 kg-N/m3/d at 20 °C. For the standby subunit, involving oxygen by aeration effectively transformed the facultative S0DP functional community from S0DP metabolism to aerobic respiration, but with enormous sulfur consumption resulting in ongoing sulfate production of over 3000 mg/L. Meanwhile, acidification by the sulfur oxidation process could reduce the pH to as low as 2.5, which evaluated the Gibbs free energy (ΔG) of the S0DP reaction to +2.56 kJ, thermodynamically suppressing the S0DP occurrence. Therefore, a multisubunit design along with S0DP inhibition strategies of short-term aeration and long-term acidification is suggested for managing S0DP in various practical sulfur-packed bioreactors.

Dominance of net autotrophy in arid landscape low relief polar lakes, Nunavut, Canada.

The Arctic is the fastest warming biome on the planet, and environmental changes are having striking effects on freshwater ecosystems that may impact the regional carbon cycle. The metabolic state of Arctic lakes is often considered net heterotrophic, due to an assumed supply of allochthonous organic matter that supports ecosystem respiration and carbon mineralization in excess of rates of primary production. However, lake metabolic patterns vary according to regional climatic characteristics, hydrological connectivity, organic matter sources and intrinsic lake properties, and the metabolism of most Arctic lakes is unknown. We sampled 35 waterbodies along a connectivity gradient from headwater to downstream lakes, on southern Victoria Island, Nunavut, in an area characterized by low precipitation, organic-poor soils, and high evaporation rates. We evaluated whether lakes were net autotrophic or heterotrophic during the open water period using an oxygen isotopic mass balance approach. Most of the waterbodies were autotrophic and sites of net organic matter production or close to metabolic equilibrium. Autotrophy was associated with higher benthic primary production, as compared to its pelagic counterpart, due to the high irradiance reaching the bottom and efficient internal carbon and nutrient cycling. Highly connected midstream and downstream lakes showed efficient organic matter cycling, as evidenced by the strong coupling between gross primary production (GPP) and ecosystem respiration, while decoupling was observed in some headwater lakes with significantly higher GPP. The shallow nature of lakes in the flat, arid region of southern Victoria Island supports net autotrophy in most lakes during the open water season. Ongoing climate changes that lengthen the ice-free irradiance period and increase rates of nutrient evapoconcentration may further promote net autotrophy, with uncertain long-term effects for lake functioning.

Mesophotic corals in Hawai'i maintain autotrophy to survive low-light conditions.

In mesophotic coral ecosystems, reef-building corals and their photosynthetic symbionts can survive with less than 1% of surface irradiance. How depth-specialist corals rely upon autotrophically and heterotrophically derived energy sources across the mesophotic zone remains unclear. We analysed the stable carbon (δ13C) and nitrogen (δ15N) isotope values of a Leptoseris community from the 'Au'au Channel, Maui, Hawai'i (65-125 m) including four coral host species living symbiotically with three algal haplotypes. We characterized the isotope values of hosts and symbionts across species and depth to compare trophic strategies. Symbiont δ13C was consistently 0.5‰ higher than host δ13C at all depths. Mean colony host and symbiont δ15N differed by up to 3.7‰ at shallow depths and converged at deeper depths. These results suggest that both heterotrophy and autotrophy remained integral to colony survival across depth. The increasing similarity between host and symbiont δ15N at deeper depths suggests that nitrogen is more efficiently shared between mesophotic coral hosts and their algal symbionts to sustain autotrophy. Isotopic trends across depth did not generally vary by host species or algal haplotype, suggesting that photosynthesis remains essential to Leptoseris survival and growth despite low light availability in the mesophotic zone.

Sulfur-manganese carbonate composite autotrophic denitrification: nitrogen removal performance and biochemistry mechanism.

A novel composite sulfur-manganese carbonate autotrophic denitrification (SMAD) system was developed to reduce sulfate production and provide pH buffer function while improving denitrification efficiency without external organics. The average removal efficiency of total nitrogen (TN) was 98.09% and 96.29%, and that of NO3--N was 99.53% and 97.77%, respectively, in the SMAD system with a hydraulic retention time (HRT) of 6 h and 3 h. They were significantly higher than that in the controls (quartz sand, manganese carbonate ore, and sulfur systems). The H+ produced by the sulfur autotrophic denitrification (SAD) process promoted the release of Mn2+ in the SMAD system. And this system had a stable pH with no accumulation of NO2--N. The decrease of sulfate and formation of Mn oxides through Mn2+ electron donation confirmed the presence of the manganese autotrophic denitrification (MAD) process in the SMAD system. Dominant functional bacteria in the SMAD system were Thiobacillus, Chlorobium, and Sulfurimonas, which were linked to nitrogen, sulfur, and manganese conversion and promoted denitrification. Meanwhile, Flavobacterium participating in Mn2+ oxidation was found only in the SMAD system. The SMAD system provided a new strategy for advanced tailwater treatment.

Simultaneous removal of NOM and sulfate in a bioelectrochemical integrated biofilter treating reclaimed water.

Biofiltration is an environmentally 'green' technology that is compatible with the recently proposed sustainable development goals, and which has an increasingly important future in the field of water treatment. Here, we explored the impacts of bioelectrochemical integration on a bench-scale slow rate biofiltration system regarding its performance in reclaimed water treatment. Results showed that the short-term (<3 months) integration improved the removal of natural organic matter (NOM) (approximately 8.8%). After long-term (5 months and thereafter) integration, the cathodic charge transfer resistance was found to have a significant reduction from 2662 to 1350 Ω. Meanwhile, bioelectrochemical autotrophic sulfate (SO42-) reduction (over 27.6% reduction) through the syntrophic metabolism between hydrogen oxidation strains (genus Hydrogenophaga) and sulfate-reducing microbes (genera Dethiobacter, Desulfovibrio, and Desulfomicrobium) at the cathodic region was observed. More significantly, the microbial-derived chromophoric humic substances were found to act as electron shuttles at the cathodic region, which might facilitate the process of bioelectrochemical SO42- reduction. Overall, this study provided valuable insights into the potential application of bioelectrochemical-integrated biofilter for simultaneous reduction of NOM and SO42- treating reclaimed water.

Deciphering the influencing mechanism of hydraulic retention time on purification performance of a mixotrophic system from the perspective of reaction kinetics.

At present, eutrophication is increasingly serious, so it is necessary to effectively reduce nitrogen and phosphorus in water bodies. In this study, a pyrite/polycaprolactone-based mixotrophic denitrification (PPMD) system using pyrite and polycaprolactone (PCL) as electron donors was developed and compared with pyrite-based autotrophic denitrification (PAD) system and PCL-based heterotrophic denitrification (PHD) system through continuous flow experiment. The removal efficiency of NO3--N (NRE) and PO43--P (PRE) and the contribution proportion of PAD in the PPMD system were significantly increased by prolonging hydraulic retention time (HRT, from 1 to 48 h). When HRT was equal to 24 h, the PPMD system conformed to the zero-order kinetic model, so NRE and PRE were mainly limited by the PAD process. When HRT was equal to 48 h, the PPMD system met the first-order kinetic model with NRE and PRE reaching 98.9 ± 1.1% and 91.8 ± 4.5%, respectively. When HRT = 48 h, the NRE and PRE by PAD system were 82.7 ± 9.1% and 88.5 ± 4.7%, respectively, but the effluent SO42- concentration was as high as 152.1 ± 13.7 mg/L (the influent SO42- concentration was 49.2 ± 3.3 mg/L); the NRE by PHD system was 98.5 ± 1.7%, but the PO43--P could not be removed ideally. The concentrations of NO3--N, total nitrogen, PO43--P, and SO42- in the PPMD system also showed distinct changes along the reactor column. In addition, the microbial diversity analysis showed that prolonging HRT (from 24 to 48 h) increased the abundance of autotrophic denitrifying microorganisms in the PPMD system, ultimately increasing the contribution proportion of PAD.

Rapid start-up sulfur-driven autotrophic denitrification granular process: Extracellular electron transfer pathways and microbial community evolution.

Sulfur-driven autotrophic denitrification (SAD) granular process has significant advantages in treating low-carbon/nitrogen wastewater; however, the slow growth rate of sulfur-oxidizing bacteria (SOB) results in a prolonged start-up duration. In this study, the thiosulfate-driven autotrophic denitrification (TAD) was successfully initiated by inoculating anaerobic granular sludge on Day 7. Additionally, the electron donor was successfully transferred to the cheaper elemental sulfur from Day 32 to Day 54 at the nitrogen loading rate of 176.2 g N m-3 d-1. During long term experiment, the granules maintained compact structures with the α-helix/(ß-sheet + random coil) of 29.5-40.1 %. Extracellular electron transfer (EET) pathway shifted from indirect to direct when electron donors were switched thiosulfate to elemental sulfur. Microbial analysis suggested that thiosulfate improved EET involving enzymes activity. Thiobacillus and Sulfurimonas were dominant in TAD, whereas Longilinea was enriched in elemental sulfur-driven autotrophic denitrification. Overall, this strategy achieved in-situ enrichment of SOB in granules, thereby shortening start-up process.

Seafloor incubation experiments at deep-sea hydrothermal vents reveal distinct biogeographic signatures of autotrophic communities.

The discharge of hydrothermal vents on the seafloor provides energy sources for dynamic and productive ecosystems, which are supported by chemosynthetic microbial populations. These populations use the energy gained by oxidizing the reduced chemicals contained within the vent fluids to fix carbon and support multiple trophic levels. Hydrothermal discharge is ephemeral and chemical composition of such fluids varies over space and time, which can result in geographically distinct microbial communities. To investigate the foundational members of the community, microbial growth chambers were placed within the hydrothermal discharge at Axial Seamount (Juan de Fuca Ridge), Magic Mountain Seamount (Explorer Ridge), and Kama'ehuakanaloa Seamount (Hawai'i hotspot). Campylobacteria were identified within the nascent communities, but different amplicon sequence variants were present at Axial and Kama'ehuakanaloa Seamounts, indicating that geography in addition to the composition of the vent effluent influences microbial community development. Across these vent locations, dissolved iron concentration was the strongest driver of community structure. These results provide insights into nascent microbial community structure and shed light on the development of diverse lithotrophic communities at hydrothermal vents.

Response of sulfide autotrophic denitrification process and microbial community to oxytetracycline stress.

The coexistence of antibiotics with sulfide and nitrate is common in sewage. Thus, this study explored the removal performance of nitrate and sulfide, and the response of extracellular polymer substances (EPS) and the microbial community to the sulfide autotrophic denitrification (SAD) process under oxytetracycline (OTC) stress. In Phase Ⅰ, the SAD system showed favouranle performance (nitrate removal rate ＞ 92.57%, sulfide removal rate ＞ 97.75%). However, in Phase Ⅳ, at OTC concentrations of 10, 15, and 20 mg/L, the NRE decreased to 76.13%, 40.71%, 11.37%, respectively, and the SRE decreased to 97.58%, 97.09%, 92.84%, respectively. At OTC concentrations of 0, 10, 15, and 20 mg/L, the EPS content were 1.62, 1.75, 2.03, and 1.42 mg/gVSS, respectively. The results showed that SAD performance gradually deteriorated under OTC stress. In particular, when the OTC concentration was 20 mg/L, the EPS content was lower than that of the control test, which could be attributed to the occurrence of microbial death. Finally, high-throughput sequencing results showed that OTC exposure led to gradual domination by heterotrophic denitrifying bacteria.

The Arabidopsis katamari2 Mutant Exhibits a Hypersensitive Seedling Arrest Response at the Phase Transition from Heterotrophic to Autotrophic Growth.

Young seedlings use nutrients stored in the seeds to grow and acquire photosynthetic potential. This process, called seedling establishment, involves a developmental phase transition from heterotrophic to autotrophic growth. Some membrane-trafficking mutants of Arabidopsis (Arabidopsis thaliana), such as the katamari2 (kam2) mutant, exhibit growth arrest during seedling development, with a portion of individuals failing to develop true leaves on sucrose-free solid medium. However, the reason for this seedling arrest is unclear. In this study, we show that seedling arrest is a temporal growth arrest response that occurs not only in kam2 but also in wild-type (WT) Arabidopsis; however, the threshold for this response is lower in kam2 than in the WT. A subset of the arrested kam2 seedlings resumed growth after transfer to fresh sucrose-free medium. Growth arrest in kam2 on sucrose-free medium was restored by increasing the gel concentration of the medium or covering the surface of the medium with a perforated plastic sheet. WT Arabidopsis seedlings were also arrested when the gel concentration of sucrose-free medium was reduced. RNA sequencing revealed that transcriptomic changes associated with the rate of seedling establishment were observed as early as 4 d after sowing. Our results suggest that the growth arrest of both kam2 and WT seedlings is an adaptive stress response and is not simply caused by the lack of a carbon source in the medium. This study provides a new perspective on an environmental stress response under unfavorable conditions during the phase transition from heterotrophic to autotrophic growth in Arabidopsis.

Effect of copper, arsenic and nickel on pyrite-based autotrophic denitrification.

Pyritic minerals generally occur in nature together with other trace metals as impurities, that can be released during the ore oxidation. To investigate the role of such impurities, the presence of copper (Cu(II)), arsenic (As(III)) and nickel (Ni(II)) during pyrite mediated autotrophic denitrification has been explored in this study at 30 °C with a specialized microbial community of denitrifiers as inoculum. The three metal(loid)s were supplemented at an initial concentration of 2, 5, and 7.5 ppm and only Cu(II) had an inhibitory effect on the autotrophic denitrification. The presence of As(III) and Ni(II) enhanced the nitrate removal efficiency with autotrophic denitrification rates between 3.3 [7.5 ppm As(III)] and 1.6 [7.5 ppm Ni(II)] times faster than the experiment without any metal(loid) supplementation. The Cu(II) batches, instead, decreased the denitrification kinetics with 16, 40 and 28% compared to the no-metal(loid) control for the 2, 5 and 7.5 ppm incubations, respectively. The kinetic study revealed that autotrophic denitrification with pyrite as electron donor, also with Cu(II) and Ni(II) additions, fits better a zero-order model, while the As(III) incubation followed first-order kinetic. The investigation of the extracellular polymeric substances content and composition showed more abundance of proteins, fulvic and humic acids in the metal(loid) exposed biomass.

Establishment and optimization of sulfur-based autotrophic-heterotrophic denitrification biofilters for advanced post-anaerobic treatment of effluent from kitchen wastewater and landfill leachate under low temperature.

Landfill leachate treatment is a major challenge in wastewater treatment. In this study, two sulfur-based autotrophic-heterotrophic denitrification biofilters (Ra biofilter with room-temperature molded filler and Rb biofilter with melt molded filler) were used to treat kitchen-landfill leachate at low temperatures. The effects of reflux ratio, concentrations of NaHCO3, and Na2S2O3 on the total nitrogen removal efficiency were analyzed, and based on response surface methodology, the optimum parameters were determined. After optimization, the total nitrogen removal efficiency for the Ra and Rb biofilters increased by 83% and 81%, respectively. Moreover, sulfur-based autotrophic denitrification accounted for more than 70% of the nitrogen removal in both biofilters. Based on high-throughput sequencing results, the functional bacteria exhibited high abundance in the Ra biofilter, indicating that the room-temperature molded filler favored the enrichment of functional bacteria. These findings were important for optimizing the operation of sulfur autotrophic-heterotrophic denitrification biofilters at low temperatures.