Nitrate effects on perchlorate reduction in a H2/CO2-based biofilm

Biogenic Palladium Improved Perchlorate Reduction during Nitrate Co-Reduction by Diverting Electron Flow in a Hydrogenotrophic Biofilm

Microbial reduction of perchlorate (ClO4-) is emerging as a cost-effective strategy for groundwater remediation. However, the effectiveness of perchlorate reduction can be suppressed by the common co-contamination of nitrate (NO3-). We propose a means to overcome the limitation of ClO4- reduction: depositing palladium nanoparticles (Pd0NPs) within the matrix of a hydrogenotrophic biofilm. Two H2-based membrane biofilm reactors (MBfRs) were operated in parallel in long-term continuous and batch modes: one system had only a biofilm (bio-MBfR), while the other incorporated biogenic Pd0NPs in the biofilm matrix (bioPd-MBfR). For long-term co-reduction, bioPd-MBfR had a distinct advantage of oxyanion reduction fluxes, and it particularly alleviated the competitive advantage of NO3- reduction over ClO4- reduction. Batch tests also demonstrated that bioPd-MBfR gave more rapid reduction rates for ClO4- and ClO3- compared to those of bio-MBfR. Both biofilm communities were dominated by bacteria known to be perchlorate and nitrate reducers. Functional-gene abundances reflecting the intracellular electron flow from H2 to NADH to the reductases were supplanted by extracellular electron flow with the addition of Pd0NPs.

Impact of Nitrate on the Removal of Pollutants from Water in Reducing Gas-Based Membrane Biofilm Reactors: A Review

The membrane biofilm reactor (MBfR) is a novel wastewater treatment technology, garnering attention due to its high gas utilization rate and effective pollutant removal capability. This paper outlines the working mechanism, advantages, and disadvantages of MBfR, and the denitrification pathways, assessing the efficacy of MBfR in removing oxidized pollutants (sulfate (SO4-), perchlorate (ClO4-)), heavy metal ions (chromates (Cr(VI)), selenates (Se(VI))), and organic pollutants (tetracycline (TC), p-chloronitrobenzene (p-CNB)), and delves into the role of related microorganisms. Specifically, through the addition of nitrates (NO3-), this paper analyzes its impact on the removal efficiency of other pollutants and explores the changes in microbial communities. The results of the study show that NO3- inhibits the removal of other pollutants (oxidizing pollutants, heavy metal ions and organic pollutants), etc., in the simultaneous removal of multiple pollutants by MBfR.

Optimization of nitrogen removal and microbial mechanism of a hydrogen-based membrane biofilm reactor

The hydrogen-based membrane biofilm reactor (H2-MBfR) is an emerging biological nitrogen removal technology characterized by high efficiency, energy-saving capability, and environmental friendliness. The technology achieves denitrification and denitrogenation of microorganisms by passing hydrogen as an electron donor from inside to outside through the hollow fibre membrane module, and eventually the hydrogen reachs the biofilm attached to the surface of the fibre membrane. H2-MBfR has obtained favourable outcomes in the treatment of secondary biochemical effluent and low concentration nitrogen polluted water source. The experiment was optimized by s single-factor testing and response surface methodology-based optimization (RSM), and the optimal operational conditions were obtained as follows: an influent flow rate of 2 mL/min, hydrogen pressure of 0.04 MPa, and influent nitrate concentration of 24.29 mg/L. Under these conditions, a high nitrate removal rate of 98.25% was achieved. In addition, Proteobacteria and Bacteroidetes were the dominant bacteria in all stages, and the genus Hydrogenophaga was sufficiently enriched, occurring at 13.0%-49.0% throughout the reactor operation. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for nitrate reduction and inorganic carbon utilization by microorganisms in the H2-MBfR was explored through comparison with the KEGG database. The results provided a mechanistic explanation for the denitrification and carbon sequestration capacity of the H2-MBfR.

Urinary microbiota and metabolic signatures associated with inorganic arsenic-induced early bladder lesions

Inorganic arsenic (iAs) contamination in drinking water is a global public health problem, and exposure to iAs is a known risk factor for bladder cancer. Perturbation of urinary microbiome and metabolome induced by iAs exposure may have a more direct effect on the development of bladder cancer. The aim of this study was to determine the impact of iAs exposure on urinary microbiome and metabolome, and to identify microbiota and metabolic signatures that are associated with iAs-induced bladder lesions. We evaluated and quantified the pathological changes of bladder, and performed 16S rDNA sequencing and mass spectrometry-based metabolomics profiling on urine samples from rats exposed to low (30 mg/L NaAsO₂) or high (100 mg/L NaAsO₂) iAs from early life (in utero and childhood) to puberty. Our results showed that iAs induced pathological bladder lesions, and more severe effects were noticed in the high-iAs group and male rats. Furthermore, six and seven featured urinary bacteria genera were identified in female and male offspring rats, respectively. Several characteristic urinary metabolites, including Menadione, Pilocarpine, N-Acetylornithine, Prostaglandin B1, Deoxyinosine, Biopterin, and 1-Methyluric acid, were identified significantly higher in the high-iAs groups. In addition, the correlation analysis demonstrated that the differential bacteria genera were highly correlated with the featured urinary metabolites. Collectively, these results suggest that exposure to iAs in early life not only causes bladder lesions, but also perturbs urinary microbiome composition and associated metabolic profiles, which shows a strong correlation. Those differential urinary genera and metabolites may contribute to bladder lesions, suggesting a potential for development of urinary biomarkers for iAs-induced bladder cancer.

Generation, toxicity, and reduction of chlorinated byproducts: Overcome bottlenecks of electrochemical advanced oxidation technology to treat high chloride wastewater

Electrochemical advanced oxidation process (EAOP) is recommended for high-strength refractory organics wastewater treatment, but the accompanying chlorinated byproduct generation becomes a bottleneck that limits the application of this technology to actual wastewater. In this study, we applied EAOP (0.4-40 mA cm^-2) to treat ultrafiltration effluent of an actual landfill leachate, and quantitatively assessed the toxicities of the dominant chlorinated byproducts in EAOP-treated effluent. Considering both toxic effect and dose, it followed the order: active chlorine > chlorate > perchlorate > organochlorines. The toxic active chlorine could spontaneously decompose by settling. And secondary bioreactor originally serving for denitrification could be used to reduce perchlorate and chlorate. The effects of residual active chlorine and extra carbon addition on simultaneous denitrification, perchlorate, and chlorate reduction were investigated. It seemed that 20 mg of active chlorine was an acceptable level to bioactivity, and sufficient electron donors favored the removal of chlorate and perchlorate. Pseudomonas was identified as an active chlorine tolerant chlorate-reducing bacteria. And Thauera was responsible for perchlorate reduction under the conditions of sufficient carbon source supply. Our results confirmed that the perchlorate and chlorate concentrations in the effluent below their health advisory levels were achievable, solving the issue of toxic chlorinated byproduct generation during EAOP. This study provided a solution to realistic application of EAOP to treat high chloride wastewater.

Study on Degradation of 1,2,4-TrCB by Sugarcane Cellulose-TiO2 Carrier in an Intimate Coupling of Photocatalysis and Biodegradation System

1,2,4 trichlorobenzene (1,2,4-TrCB) is a persistent organic pollutant with chemical stability, biological toxicity, and durability, which has a significant adverse impact on the ecological environment and human health. In order to solve the pollution problem, bagasse cellulose is used as the basic framework and nano TiO₂ is used as the photocatalyst to prepare composite carriers with excellent performance. Based on this, an intimate coupling of photocatalysis and biodegradation (ICPB) system combining photocatalysis and microorganisms is constructed. We use the combined technology for the first time to deal with the pollution problem of 1,2,4-TrCB. The biofilm in the composite carrier can decompose the photocatalytic products so that the removal rate of 1,2,4-TrCB is 68.01%, which is 14.81% higher than those of biodegradation or photocatalysis alone, and the mineralization rate is 50.30%, which is 11.50% higher than that of photocatalysis alone. The degradation pathways and mechanisms of 1,2,4-TrCB are explored, which provide a theoretical basis and potential application for the efficient degradation of 1,2,4-TrCB and other refractory organics by the ICPB system.

Mechanistic insights into CO2 pressure regulating microbial competition in a hydrogen-based membrane biofilm reactor for denitrification

CO₂ is a proven pH regulator in hydrogen-based membrane biofilm reactor (H₂-MBfR) but how its pressure regulates microbial competition in this system remains unclear. This work evaluates the CO₂ pressure dependent system performance, CO₂ allocation, microbial structure and activity of CO₂ source H₂-MBfR. The optimum system performance was reached at the CO₂ pressure of 0.008 MPa, and this pressure enabled 0.18 g C/(m²·d) of dissolved inorganic carbon (DIC) allocated to denitrifying bacteria (DNB) for carbon source anabolism and denitrification-related proton compensation, while inducing a bulk liquid pH (pH 7.4) in favor of DNB activity by remaining 0.21 g C/(m²·d) of DIC as pH buffer. Increasing CO₂ pressure from 0.008 to 0.016 MPa caused the markedly changed DNB composition, and the diminished DNB population was accompanied by the enrichment of sulfate-reducing bacteria (SRB). A high CO₂ pressure of 0.016 MPa was estimated to induce the enhanced SRB activity and weakened DNB activity.

Model Evaluation of the Microbial Metabolic Processes in a Hydrogen-Based Membrane Biofilm Reactor for Simultaneous Bromate and Nitrate Reduction

The H₂-based membrane biofilm reactor (H₂-MBfR) has been acknowledged as a cost-effective microbial reduction technology for oxyanion removal from drinking water sources, but it remains unknown how the evolution of biofilm characteristics responds to the changing critical operating parameters of the H₂-MBfR for simultaneous bromate (BrO₃^-) and nitrate (NO₃^-) elimination. Therefore, an expanded multispecies model, applicable to mechanistically interpret the bromate-reducing bacteria (BRB)- and denitrifying bacteria (DNB)-dominated metabolic processes in the biofilm of the H₂-MBfR, was developed in this study. The model outputs indicate that (1) increased BrO₃^- loading facilitated the metabolism of BRB by increasing BRB fraction and BrO₃^- gradients in the biofilm, but had a marginal influence on NO₃^- reduction; (2) H₂ pressure of 0.04 MPa enabled the minimal loss of H₂ and the extension of the active region of BRB and DNB in the biofilm; (3) once the influent NO₃^- concentration was beyond 10 mg N/L, the fraction and activity of BRB significantly declined; (4) BRB was more tolerant than DNB for the acidic aquatic environment incurred by the CO₂ pressure over 0.02 MPa. The results corroborate that the degree of microbial competition for substrates and space in the biofilm was dependent on system operating parameters.

Nitrogen Removal From Nitrate-Containing Wastewaters in Hydrogen-Based Membrane Biofilm Reactors via Hydrogen Autotrophic Denitrification: Biofilm Structure, Microbial Community and Optimization Strategies

The hydrogen-based membrane biofilm reactor (MBfR) has been widely applied in nitrate removal from wastewater, while the erratic fluctuation of treatment efficiency is in consequence of unstable operation parameters. In this study, hydrogen pressure, pH, and biofilm thickness were optimized as the key controlling parameters to operate MBfR. The results of 653.31 μm in biofilm thickness, 0.05 MPa in hydrogen pressure and pH in 7.78 suggesting high-efficiency NO3−−N removal and the NO3−−N removal flux was 1.15 g·m⁻² d⁻¹. 16S rRNA gene analysis revealed that Pseudomonas, Methyloversatilis, Thauera, Nitrospira, and Hydrogenophaga were the five most abundant bacterial genera in MBfRs after optimization. Moreover, significant increases of Pseudomonas relative abundances from 0.36 to 9.77% suggested that optimization could effectively remove nitrogen from MBfRs. Membrane pores and surfaces exhibited varying degrees of calcification during stable operation, as evinced by Ca²⁺ precipitation adhering to MBfR membrane surfaces based on scanning electron microscopy (SEM), atomic force microscopy (AFM) analyses. Scanning electron microscopy–energy dispersive spectrometer (SEM–EDS) analyses also confirmed that the primary elemental composition of polyvinyl chloride (PVC) membrane surfaces after response surface methodology (RSM) optimization comprised Ca, O, C, P, and Fe. Further, X-ray diffraction (XRD) analyses indicated the formation of Ca₅F(PO₄)₃ geometry during the stable operation phase.

Coupling of photocatalysis and biological treatment for elemental chlorine free bleaching wastewater: Application of factorial design methodology

In this study, the visible-light-induced intimately coupled photocatalysis and biodegradation (ICPB) technology was fabricated using the TiO₂/bagasse cellulose composite as the carrier and Phanerochaete mixed activated sludge as the biological source. The ICPB degradation effect of elemental chlorine free (ECF) bleaching wastewater was evaluated via the response surface design. Then, the wastewater was characterized, including absorbable organic halogen (AOX), dissolved organic carbon (DOC), chemical oxygen demand (COD), chroma, pH, suspended solids, and the organic compound changes in wastewater were analyzed by fourier transform infrared spectroscopy (FT-IR). Under the optimal conditions of pH 7, carrier filling rate of 5%, aeration rate of 2 L/min, and reaction time of 7 h, the degradation efficiencies of AOX, COD, and DOC were 95%, 91%, and 82%, respectively. The X-ray photoelectron spectroscopy (XPS) results of the ICPB carrier after the reaction were almost identical to those before the reaction. The biomass and its activity on the ICPB system were analyzed by the dominant bacteria during degradation (Curaneotrichosporon, Paenibacillus, Cellulonas, Phanerochaete, Dechlorobacter, Rhodotorula, Sphingobacterium, and Ruminiclostridium), which had a good degradation effect on wastewater. This study affords a novel method for the degradation of ECF bleaching wastewater and a new idea for ICPB technology optimization.

Simultaneous reduction of perchlorate and nitrate using fast-settling anoxic sludge

Fast-settling, anoxic sludge (FAS) was cultivated and utilized in this study to simultaneously reduce elevated levels of perchlorate and nitrate in an anaerobic sequencing batch reactor (AnSBR). Average perchlorate and nitrate removal efficiencies of 96.5 ± 8.44 % and 99.8 ± 0.32 %, respectively, were achieved from an average perchlorate and nitrate loading rate of 159 ± 101 g ClO₄^-/m³·d and 10.8 ± 7.25 g NO₃^--N/m³·d, respectively, throughout long-term operation (>500-d). Batch activity tests revealed a preferential utilization of nitrate over perchlorate, where significant perchlorate reduction inhibition occurred when nitrate was present as a competing electron acceptor under carbon-limiting conditions. Specific perchlorate and nitrate reduction rates were shown to increase as the hydraulic retention time (HRT) of the AnSBR was step-wise decreased and subsequently the perchlorate and nitrate loading rates were step-wise increased. Functional, mRNA-based expression of the nitrite reductase (nirS and nirK), nitrous oxide reductase (nosZ), perchlorate reductase subunit A (pcrA), and the chlorite dismutase (cld) genes illustrated the simultaneous activity of heterotrophic denitrification and perchlorate reduction occurring throughout a complete standard reactor operational cycle, and allowed for expression trends to be documented as the HRT of the AnSBR was reduced from 5-d to 1.25-d. Nitrous oxide (N₂O) production was detected as a result of incomplete denitrification, where the largest N₂O production occurred at the highest nitrate loading rates investigated in this study. Thauera species were heavily enriched at a longer HRT of 5-d, but were out-competed by Dechloromonas species as the HRT of the AnSBR was step-wise reduced to 1.25-d.

The fouling layer development on MD membrane for water treatments: An especial focus on the biofouling progress

This study evaluated the fouling development of membrane distillation (MD) when treating different feed waters were taken from three local water bodies: Xuanwu Lake, Nan Lake and Qinhuai River. Trends of flux decline could be divided into three phases including a similar rapid decline in first phase, a slow decline in phase II, while significant difference was observed in the last phase. It could be seen that inorganic matters in feed waters had some influences on the attachment of salt crystals to membrane, mainly in the form of CaCO3. Furthermore, the biovolume exhibited little difference but the amount of extracellular polymeric substances (EPS) was distinct in the three systems. 16S rRNA revealed that although the microbial communities in feed waters had different structures, they on-membrane microbes shared the same dominant communities in the early stage due to the same growth environment including Tepidimonas, Meiothermus, OLB14_norank, Env.OPS 17_norank and Schlegelella with a relatively stable proportion of 63.5%-68.0%. However, at the later operational phase, the bacteria composition was changed with community succession, and Armatimonadetes_norank, Hydrogenophilaceae_uncultured and Methyloversatilis respectively thrived on the three scaling membrane surfaces which was correlated with the concentration of feed water, resulting the influence of inorganic substances on microbial growth was enhanced. A result obviously suggested that bacteria had great influence on the degree of flux decline due to their structure and property, especially at the later operational phase. It would be helpful to explore the structure and potential function of dominant communities on membranes and provide basic theory for the treatment of microbial pollution.

Nitrate Removal and Dynamics of Microbial Community of A Hydrogen-Based Membrane Biofilm Reactor at Diverse Nitrate Loadings and Distances from Hydrogen Supply End

The back-diffusion of inactive gases severely inhibits the hydrogen (H2) delivery rate of the close-end operated hydrogen-based membrane biofilm reactor (H2-based MBfR). Nevertheless, less is known about the response of microbial communities in H2-based MBfR to the impact of the gases’ back-diffusion. In this research, the denitrification performance and microbial dynamics were studied in a H2-based MBfR operated at close-end mode with a fixed H2 pressure of 0.04 MPa and fed with nitrate (NO3−) containing influent. Results of single-factor and microsensor measurement experiments indicate that the H2 availability was the decisive factor that limits NO3− removal at the influent NO3− concentration of 30 mg N/L. High-throughput sequencing results revealed that (1) the increase of NO3− loading from 10 to 20–30 mg N/L resulted in the shift of dominant functional bacteria from Dechloromonas to Hydrogenophaga in the biofilm; (2) excessive NO3− loading led to the declined relative abundance of Hydrogenophaga and basic metabolic pathways as well as counts of most denitrifying enzyme genes; and (3) in most cases, the decreased quantity of N metabolism-related functional bacteria and genes with increasing distance from the H2 supply end corroborates that the microbial community structure in H2-based MBfR was significantly impacted by the gases’ back-diffusion.

A comparative analysis of drinking water employing metagenomics

The microbiological content of drinking water traditionally is determined by employing culture-dependent methods that are unable to detect all microorganisms, especially those that are not culturable. High-throughput sequencing now makes it possible to determine the microbiome of drinking water. Thus, the natural microbiota of water and water distribution systems can now be determined more accurately and analyzed in significantly greater detail, providing comprehensive understanding of the microbial community of drinking water applicable to public health. In this study, shotgun metagenomic analysis was performed to determine the microbiological content of drinking water and to provide a preliminary assessment of tap, drinking fountain, sparkling natural mineral, and non-mineral bottled water. Predominant bacterial species detected were members of the phyla Actinobacteria and Proteobacteria, notably the genera Alishewanella, Salmonella, and Propionibacterium in non-carbonated non-mineral bottled water, Methyloversatilis and Methylibium in sparkling natural mineral water, and Mycobacterium and Afipia in tap and drinking fountain water. Fecal indicator bacteria, i.e., Escherichia coli or enterococci, were not detected in any samples examined in this study. Bacteriophages and DNA encoding a few virulence-associated factors were detected but determined to be present only at low abundance. Antibiotic resistance markers were detected only at abundance values below our threshold of confidence. DNA of opportunistic plant and animal pathogens was identified in some samples and these included bacteria (Mycobacterium spp.), protozoa (Acanthamoeba mauritaniensis and Acanthamoeba palestinensis), and fungi (Melampsora pinitorqua and Chryosporium queenslandicum). Archaeal DNA (Candidatus Nitrosoarchaeum) was detected only in sparkling natural mineral water. This preliminary study reports the complete microbiome (bacteria, viruses, fungi, and protists) of selected types of drinking water employing whole-genome high-throughput sequencing and bioinformatics. Investigation into activity and function of the organisms detected is in progress.