Mutual influence mechanism of nitrate and sulfamethoxazole on their biotransformation in poly (3-hydroxybutyrate-3-hydroxyvalerate) supported denitrification biofilter for a long-term operation.

Nitrate and SMX both play a critical role in their biotransformation in biodegradable polymer-supported denitrification biofilters. However, the mutual influences of nitrate and SMX on their biotransformation for long-term operation remained obscure. Results showed SMX and nitrate had divergent effects on SMX removal. SMX removal rates was positively related with its loading rates, whereas they were negatively related to NLRs. The most abundant metabolite C10H14O3N3S (the reduced form of SMX moiety) from the N-O bond cleavage pathway by UHPLC-LTQ-Orbitrap-MS/MS and effluent TOC variations confirmed the presence of electron donor competition between nitrate and SMX. SMX less than 1000 µg/L had a negligible influence on denitrification performance. Denitrifiers such as Azospira and Denitratisoma were still enriched after chronic exposure, and nosZ/narG positively correlated with sul1/sul2 resistance genes, which were both responsible for the negligible influence of SMX. This work could guide the operational management of denitrification biofilters for simultaneous nitrate and antibiotics removal.

Human health risk assessment of heavy metals in a replaced urban industrial area of Qingdao, China.

The aim of this study was risk characterization of a replaced urban industrial land located north of Qingdao, in relation to heavy metals values. Soil concentrations of Cd, Pb, Cu, Ni, Cr, and Zn were analyzed. It was observed that the components of Cd, Pb, Cu, Ni, Cr, and Zn are about 2.22, 8.07, 4.70, 6.81, 2.65, and 3.0-folds, respectively, when compared with the local natural background values in Qingdao. The spatial distribution of heavy metals indicated that these hotspots for Cr and Zn located in the southwestern part, Ni and Cd in the middle of the south area, Pb in the northwest, and Cu in the middle of the east area. The values of pollution index and Nemerow integrated pollution index revealed that 100 % of soil samples were moderately or heavily contaminated by six heavy metals. From these results, human health risk assessment for sensitive population was performed according to two different land uses. For non-carcinogenic risk, the direct oral ingestion appeared to be the main exposure pathway followed by dermal and inhalation absorption. The HI values of Pb and Cr characterized for children were larger than 1, while HI values of each metal for adults in two scenarios were lower than 1. Besides, carcinogenic risk from inhalation exposure to Cr for children and adults in two scenarios all exceeded the safety limit.

Superior nitrate and chromium reduction synergistically driven by multiple electron donors: Performance and the related biochemical mechanism.

Nitrate and Cr(VI) are the typical and prevalent co-contaminants in the groundwater, how to synchronously and effectively diminish them has received growing attention. The most problem that currently limits the nitrate and Cr(VI) reduction technology for groundwater remediation is with emphasis on exploring the optimal electron donors. This study investigated the feasibility of utilizing the synergistical effect of inorganic electron donors (pyrite, sulfur) and inherently limited organics to promote synchronous nitrate and Cr(VI) removal, which meets the requirement of naturally low-carbon and eco-friendly technologies. The NO3--N and Cr(VI) removal efficiencies in the pyrite and sulfur involved mixotrophic biofilter (PS-BF: approximately 90.8 ± 0.6% and 99.1 ± 2.1%) were substantially higher than that in a volcanic rock supported biofilter (V-BF: about 49.6% ± 2.8% and 50.0% ± 9.3%), which was consistent with the spatial variations of their concentrations. Abiotic and biotic batch tests directly confirmed the decisive role of pyrite and sulfur for NO3--N and Cr(VI) removal via chemical and microbial pathways. A server decline in sulfate production correlated with decreasing COD consumption revealed that there was sulfur disproportionation induced by limited organics. Metagenomic analysis suggested that chemoautotrophic microbes like Sulfuritalea and Thiobacillus were key players responsible for sulfur oxidation, nitrate and Cr(VI) reduction. The metabolic pathway analysis suggested that genes encoding functional enzymes related to complete denitrification, S oxidation, and dissimilatory sulfate reduction were upregulated, however, genes encoding Cr(VI) reduction enzymes (e.g. chrA, chrR, nemA, and azoR) were downregulated in PS-BF, which further explained the synergistical effect of multiple electron donors. These findings provide insights into their potential cooperative interaction of multiple electron donors on greatly promoting nitrate and Cr(VI) removal and have implications for the remediation technology of nitrate and Cr(VI) co-contaminated groundwater.

Biomineralized manganese oxide mediated nitrogen-contained wastewater treatment.

In recent years, manganese (Mn) has emerged as an accelerator for nitrogen metabolism. However, the bioactivity of manganese is limited by the restricted contact between microbes and manganese minerals in the solid phase and by the toxicity of manganese to microbes. To enhance the bioactivity of solid-phase manganese, biomineralized manganese oxide (MnOx) modified by Lactobacillus was introduced. Nitrogen removal performance have confirmed the effective role of biomineralized MnOx in accelerating the removal of total inorganic nitrogen (TIN). Metagenomic analysis has confirmed the enhancement of the nitrogen metabolic pathway and microbial extracellular electron transfer (MEET) in biomineralized MnOx treatment group (BIOA group). Additionally, the enrichment of manganese oxidation and denitrification genus indicates a coupling between nitrogen metabolism and manganese metabolism. One point of views is that biomineralized MnOx-mediated nitrogen transformation processes could serve as a substitute for traditional nitrogen removal processes.

Characterization of phosphate solubilizing bacteria in the sediments of eutrophic lakes and their potential for cyanobacterial recruitment.

Microbes may induce endogenous phosphorus (P) migration from lacustrine sediment. This study focused on the role of phosphate-solubilizing bacteria (PSB) disturbance in affecting the sediment P release and further contributing to cyanobacterial recruitment in Meiliang Bay, Lake Taihu. Gluconic acid was the main mechanism of phosphate solubilizing by PSB. The dominant PSB (Burkholderia) isolated from eutrophic lake sediments was used as a representative to investigate the effects of disturbance on endogenous P release using diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper). The results show that soluble reactive phosphorus (SRP) and iron (Fe (II)) concentrations could reach 0.51 mg L-1 and 33.56 mg L-1 in pore water, respectively. And the sediment DGT-P and DGT-Fe were relatively reduced by PSB. Subsequent the chlorophyll a (Chl a) concentrations reached peaks of 344.8 µg L-1 in overlying water. The abundance of the dominant PSB (Burkholderia-Caballeronia-Paraburkholderia) were significantly associated with Chl a (P < 0.05) and algal effective state phosphorus (AAP) (P < 0.05), respectively. PSB mainly regulates AAP leaching to pore water and then diffusing across the sediment-water interface to the overlying water, producing the effect of cyanobacteria recruitment. The results provide new insights into early management of cyanobacterial resuscitation in a large eutrophic lake.

Simultaneous nitrification and denitrification in a PCL-supported constructed wetland with limited aeration.

Considerable advances have been made in the substrate design and operation strategies of constructed wetlands to facilitate nitrogen elimination. However, few studies examined the complicated interaction between solid organic substrates and limited aeration on nitrogen removal. A vertical flow constructed wetlands in gradient distribution of inorganic and solid organic substrates (polycaprolactone/PCL) (P-VFCW) and a controlled vertical flow constructed wetland without PCL (C-VFCW) were developed for the tertiary treatment of municipal tailwater. Results indicated that ammonia was nearly converted to nitrate, while the total nitrogen removal efficiencies (TNREs) in C-VFCW were negligible. In P-VFCW, however, optimal TNREs approached 95% with an aeration rate of 0.06 mL·min-1 and hydraulic retention time (HRT) of 24 h, and simultaneous nitrification and denitrification process (SND) in aerobic conditions was confirmed. As for the spatial microbial community structure evolution, Comamonas, which is associated with heterotrophic nitrification and anoxic/aerobic denitrification, was enriched along the vertical profiles of P-VFCW. Autotrophic nitrifier (Nitrospira), aerobic denitrifier (Bradyrhizobium and Azospira), and anoxic denitrifier (Ignavibacterium and Methyloversatilis) were dominated in different depths of P-VFCW, respectively. Besides, Canna indica biomass in P-VFCW was significantly larger than that in C-VFCW, which was attributed to the plant adaption response to diverse nitrogen. The P-VFCW in gradient distribution of inorganic and solid carbon sources under limited aeration is a promising technology for advanced nitrogen removal.

Simultaneous nitrate and chromium removal mechanism in a pyrite-involved mixotrophic biofilter.

Microbially mediated NO3--N and Cr(VI) reduction is being recognized as an eco-friendly and cost-effective remediation strategy. Iron sulfide mineral, as a natural inorganic electron donor, has a strong influence on NO3--N and Cr(VI) transformation, respectively. However, little is known about the simultaneous nitrate and chromium removal performance and underlying mechanism in an iron sulfide mineral-involved mixotrophic biofilter. This study demonstrated that the NO3--N and Cr(VI) removal efficiencies were stable at 62 ± 8% and 56 ± 10%, and most of them were eliminated in the 0-100-mm region of the biofilter. Cr(VI) was reduced to insoluble Cr(III) via microbial and chemical pathways, which was confirmed by the SEM-EDS morphology and the XPS spectra of biofilm and pyrite particles. SO42- was as a main byproduct of pyrite oxidation; however, the bacterial SO42- reduction synchronously occurred, evidenced by the variations of TOC and SO42- concentrations. These results suggested that there were complicated and intertwined biochemical relations between NO3--N/Cr(VI)/SO42-/DO (electron acceptors) and pyrite/organics (electron donors). Further investigation indicated that both the maximal biomass and greatest denitrifiers' relative abundances in microbial sample S1 well explained why the pollutants were removed in the 0-100-mm region. A variety of denitrifiers such as Pseudoxanthomona, Acidovorax, and Simplicispira were enriched, which probably were responsible for both NO3--N and Cr(VI) removal. Our findings advance the understanding of simultaneous nitrate and chromium removal in pyrite-involved mixotrophic systems and facilitate the new strategy development for nitrate and chromium remediation.

Manganese oxide-loaded activated carbon for ammonium removal from wastewater: the roles of adsorption and oxidation.

The urgent need to address the severe issue of nitrogen pollution has prompted the search for a functional and easy recycling material. In this study, manganese oxides (MnOx) were loaded on activated carbon (AC), resulting in a composite known as AC-MnOx, for efficient ammonium removal from aqueous solutions. The results indicated a remarkable 15.6-fold increase in ammonium removal efficiency and a fivefold enhancement in removal capacity for AC-MnOx (3.20 mg/g) compared to AC. Under specific conditions (initial NH4+-N concentration of 15 mg/L, adsorbent dose of 2.5 g, pH of 6.5, and temperature of 35 ℃), the highest achieved ammonium removal efficiency reached 94.6%. Furthermore, the study distinguishes the contributions of catalytic oxidation and adsorption in the removal process. The adsorption process was effectively modeled using pseudo-second-order kinetics and Langmuir isotherm models. Interestingly, the amount of oxidation conversion (Ntur) exhibited a linear relationship with the dosage when the initial ammonium concentration was sufficiently high, while the relationship between initial ammonium concentration and the ratio of Ntur to adsorption capacity (Nsur) followed a negative exponential trend. The removal mechanisms involved electrostatic interaction between ammonium and the negatively charged dehydrogenated hydroxyl groups (- OHsur) or cation tunnel in crystal structures of MnOx, ion exchange adsorption, and the oxidation impact of MnOx. This research provides valuable insights into the application of immobilized MnOx media for ammonium removal. Moreover, filling AC-MnOx into constructed wetlands (CW) proved to be an effective method for reducing ammonium pollution, demonstrating its potential in the field of engineering wastewater treatment.

New insights on simultaneous nitrate and phosphorus removal in pyrite-involved mixotrophic denitrification biofilter for a long-term operation: Performance change and its underlying mechanism.

Simultaneous nitrate and phosphorus removal can be completed by pyrite- and influent organics-involved mixotrophic denitrification and chemical phosphorus removal via iron precipitation. However, so far, how their removal performances change with iron precipitation accumulation remains unclear. In this study, the differences in nitrate and phosphorus removal from municipal tailwater between volcanic and pyrite supported biofilters (V-BF, P-BF) for a long-term operation were investigated, as well as the underlying mechanism for these differences. The nitrate removal efficiencies (NREs) in P-BF were greater than those in V-BF due to the synergistic effect of influent organic and pyrite, as evidenced by comparable TOC consumption and Fe2+/SO42- production. The NREs in P-BF were gradually lower than in V-BF as a result of bacterial cell-iron encrustation observed in TEM images, which would deteriorate microbial activity. However, the phosphorus removal efficiencies (PREs) in P-BF remained consistently higher than in V-BF, resulting from chemical phosphorus removal which was confirmed that P, Fe and O elements dominated on the pyrite surface after use by SEM-EDS. The dominant denitrifying bacteria differed significantly, autotrophic and heterotrophic denitrifying microorganisms coexisted in P-BF. The relative abundances of the narG coding gene in P-BF were higher than that in V-BF, which was consistent with the total relative abundances of identified denitrifying bacteria. Besides, the mechanism of simultaneous nitrogen and phosphorus removal in the pyrite-involved mixotrophic denitrification process has been deduced. This work has significant implications for the practical application of a pyrite-involved mixotrophic denitrification process for low C/N wastewater treatment.

Removal performance and mechanism of phosphorus by different Fe-based layered double hydroxides.

Phosphorus pollution has the potential to cause both aquatic eutrophication and global phosphorus scarcity. Fe-based layered double hydroxides (LDHs) have received much attention due to their high phosphorus adsorption and recovery. The composition of Fe-based LDHs is an important factor in determining their adsorption performance. However, the mechanism by which single component regulation of Fe-based LDHs affects phosphorus adsorption performance remains unknown. In this study, two typical types of Fe-based LDHs were prepared: Mg/Fe LDH and Zn/Fe LDH. Results showed that the equilibrium adsorption capacity of Zn/Fe LDH was much greater than that of Mg/Fe LDH, reaching 65.85 mg/g with a phosphorus concentration of 150 mg/L. Calcination facilitated a substantial increase of adsorption capacity for Mg/Fe LDH rather than Zn/Fe LDH. Meanwhile, the phosphorus removal efficiency of Fe-based LDHs both exceeded 90% with an initial pH of 3.0, but it decreased as pH increased, and pH inhibition was relatively weaker for Zn/Fe LDH than Mg/Fe LDH. The common coexisting anions caused a phosphorus adsorption loss, with SO42- possessing the most competition with phosphorus. Combined with FTIR, XRD, XPS, and BET analyses, a superior adsorption performance of Zn/Fe-LDH over Mg/Fe-LDH was probably attributed to a higher surface complexation and larger specific surface area. It was also concluded that Fe-based LDHs are a promising method for removing phosphorus from recirculating aquaculture wastewater.

Intensifying anoxic ammonium removal by manganese ores and granular active carbon fillings in constructed wetland-microbial fuel cells: Metagenomics reveals functional genes and microbial mechanisms.

The conventional biological ammonium removal process is challenged for lack of electron acceptors. A lab-scale integrated constructed wetland coupled with microbial fuel cells (CW-MFC) filling manganese ores (MO) and granular active charcoal (GAC) has been developed, named CW-CM. It enhanced the nitrogen removal two times over the control. A metagenomic-based study illustrated the functional genes and taxonomic groups related to N transformations, explored metabolic mechanisms of nitrogen and carbon sources, and then revealed some characteristics of the extracellular electron transfer (EET). Many nitrifying bacteria and autotrophic and heterotrophic denitrifiers were enriched in CW-CM. Furthermore, most nitrification and denitrification reactions except for the conversion of ammonium to hydroxylamine were significantly enhanced in CW-CM. Glycolysis and the TCA cycle were also improved. Overall, a novel anoxic ammonia removal process was achieved in the experimental group with no need of anammox functional bacteria and anammox key genes.

Pathways regulating the enhanced nitrogen removal in a pyrite based vertical-flow constructed wetland.

In this study, two vertical constructed wetland using natural pyrite (P-VFCW) and quartz sand (C-VFCW) as substrate were constructed, and the enhanced nitrate removal mechanism by pyrite was further investigated. Results showed that the nitrate removal efficiency (NRE) of P-VFCW was 4% higher than that of C-VFCW with a C/N of 0. Interestingly, the difference on NRE between CWs markedly enlarged with C/N and hydraulic retention time (HRT) simultaneously increasing. At a COD/N of 6 and HRT of 24 h, the effluent average NO3--N and NO2--N concentrations in P-VFCW and C-VFCW were 2.36 ±â€¯2.64 mg/L/1.34 ±â€¯1.28 mg/L, 9.20 ±â€¯6.91 mg/L/5.57 ±â€¯3.68 mg/L, respectively, revealing pyrite could promote heterotrophic denitrification and avoid nitrite accumulation. After the whole operation, a better growth of Canna indica occurred in P-VFCW. High-throughput sequencing implied that denitrifying bacteria (Comamonas), iron oxidation and reduction microorganism (Thiobacillus) and the rhizosphere microorganism differed in CWs.

Effect of temperature on tertiary nitrogen removal from municipal wastewater in a PHBV/PLA-supported denitrification system.

In this study, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(lactic acid) (PHBV/PLA)-supported denitrification system was built to remove nitrogen from municipal wastewater treatment plant secondary effluent, and the influence of operating temperature on nitrogen removal was further investigated. Results indicated that a PHBV/PLA-supported denitrification system could effectively fulfill the tertiary nitrogen removal. The nitrogen removal efficiency gradually declined with the operating temperature decreasing, and the denitrification rate at 30 °C was 5 times higher than that at 10 °C. Meanwhile, it was found that a slight TOC accumulation only occurred at 30 °C (with an average of 2.03 mg/L) and was avoided at 10~20 °C. The reason for effluent TOC variation was further explained through the consumption and generation pathways of TOC in this system. Furthermore, the temperature coefficient was about 0.02919, indicating that the PHBV/PLA-supported denitrification system was a little sensitive to temperature. A better knowledge of the effect of operating temperature will be significant for the practical application of the solid-phase denitrification system.

Effect of different carbon sources on denitrification performance, microbial community structure and denitrification genes.

Solid and liquid organic substances as carbon sources for denitrification process were deeply explored. In this study, the effect of three carbon sources, referred to as poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/poly (lactic acid) (PHBV/PLA) polymer, glucose and CH3COONa, on denitrification performance, microbial community and functional genes were investigated. It was found that maximum denitrification rates of 0.37, 0.46 and 0.39gN/(L·d) were achieved in PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Meanwhile, Illumina MiSeq sequencing revealed that three carbon sources led to different microbial community structures. It can be seen that Brevinema/Thauera/Dechloromonas, Tolumonas/Thauera/Dechloromonas, Thauera dominated in the PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Transcriptome-based analysis further indicated that the glucose supported denitrification system showed the highest FPKM values (the fragments per kilobase per million mapped reads) of the genes participating in the dissimilatory nitrate reduction process, corresponding to the greatest effluent NH4+-N concentration. A better knowledge of effect of different carbon sources on denitrification process will be significant for nitrate removal in practice.

PHBV polymer supported denitrification system efficiently treated high nitrate concentration wastewater: Denitrification performance, microbial community structure evolution and key denitrifying bacteria.

Biodegradable polymer supported denitrification (BPD) system shows good denitrification performance for the wastewater with low nitrate concentrations. In this study, a BPD system using Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) polymer as carbon source was developed to treat the wastewater with high nitrate concentrations. The denitrification performance, utilization ratio of PHBV polymers, and microbial community structure evolution and key denitrifying bacteria were comprehensively studied. Results indicated that an average nitrate removal efficiency of 99% could be achieved with an influent NO3--N concentration of 100 mg L-1 and a hydraulic retention time (HRT) of 7.25 h. Mass balance model predicted that 80% of the PHBV polymers were consumed by denitrifying bacteria, close to 72% consumption in real condition, suggesting the model might be useful for PHBV polymers management in BPD system. Further, the bacterial community structures varied along the bioreactor profile, which closely linked to the concentration profiles of nitrate and ammonia. Metatranscriptomic analysis identified the key denitrifying bacteria as Comamonas, Acidovorax and Dechloromonas. The PHBV supported denitrification system developed in this study shows potential for removal of high concentration of nitrate from wastewater.

Ecosystem activation system (EAS) technology for remediation of eutrophic freshwater.

Ecosystem activation system (EAS) was developed to create beneficial conditions for microbiome recovery and then restore and maintain the ecological integrity (microbial community, phytoplankton, zooplankton) for eutrophic freshwater rehabilitation. A 30 day's filed test of EAS indicated that over 50% of contaminant was removed and the algae visibly disappeared. EAS treatment 2.5-fold increased the diversity of microbial community and changed the microbial community structure (e.g., two and three-fold decrease in the amount of Flavobacterium and Pseudomonas, typical abundant species of eutrophic freshwater, respectively). Further, the diversity of phytoplankton and zooplankton of treated water suggested that these species were diverse. Representative phytoplankton of eutrophic freshwater, Chlorella and Chlamydomonas were undetectable. The possible mechanism of EAS is restoring the trophic levels of the water body via bottom-up approach by microbial community.