The combined contamination of cadmium (Cd) and microplastics (MPs) in paddy soil always occurred, while its influence on Cd availability remained unclear. This study investigated the Cd availability ...in Cd-MPs co-contaminated paddy soil in consideration of both ferric minerals and sulfate reduction under flooding conditions. The presence of MPs resulted in a higher Cd releasing risk, as represented by the increase in the available Cd and decrease in Fe-Mn oxide-bound Cd contents, especially on the 7th and 14th days based on the sequential extraction results. MPs facilitated the formation of Fe-organic ligands, which accelerated the reductive dissolution of iron minerals but decreased the amounts of amorphous iron minerals due to the release of dissolved organic substances into pore water. Furthermore, MPs promoted the relative abundance of sulfate-reducing bacteria (such as Streptomyces and Desulfovibrio genera), thus increasing the contents of reductive S species, which was advantageous to the co-precipitation of Fe, S, and Cd on the surface of MPs based on our experimental and statistical results. Taken together, both iron and sulfate reduction under anaerobic conditions played a critical role in Cd mobilization in Cd-MPs co-contaminated paddy fields.
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•Microplastics (MPs) accelerated Cd availability in paddy soil.•MPs facilitated reduction of Fe(III) and sulfate simultaneously.•The reduction of Fe(III) promoted Cd releasing from iron minerals.•The sulfate reduction prohibited Cd passivation.
The biotic nitrate reduction rate in freshwater ecosystems is typically constrained by the scarcity of carbon sources. In this study, ‘two-chambers’ - ‘two-electrodes’ photoautotrophic biofilm-soil ...microbial fuel cells (P-SMFC) was developed to accelerate nitrate reduction by activating in situ electron donors that originated from the soil organic carbon (SOC). The nitrate reduction rate of P-SMFC (0.1341 d−1) improved by ∼ 1.6 times on the 28th day compared to the control photoautotrophic biofilm. The relative abundance of electroactive bacterium increased in the P-SMFC and this bacterium contributed to obtain electrons from SOC. Biochar amendment decreased the resistivity of P-SMFC, increased the electron transferring efficiency, and mitigated anodic acidification, which continuously facilitated the thriving of putative electroactive bacterium and promoted current generation. The results from physiological and ecological tests revealed that the cathodic photoautotrophic biofilm produced more extracellular protein, increased the relative abundance of Lachnospiraceae, Magnetospirillaceae, Pseudomonadaceae, and Sphingomonadaceae, and improved the activity of nitrate reductase and ATPase. Correspondingly, P-SMFC in the presence of biochar achieved the highest reaction rate constant for nitrate reduction (kobs) (0.2092 d−1) which was 2.4 times higher than the control photoautotrophic biofilm. This study provided a new strategy to vitalize in situ carbon sources in paddy soil for nitrate reduction by the construction of P-SMFC.
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•Photic biofilm-soil microbial fuel cells (PSMFC) were tested for nitrate removal.•Electroactive bacteria activated the in situ electron donor pools in soil.•Denitrifiers of the photic biofilm thrived in PSMFC, in the presence of biochar.•The denitrifiers made the main contribution to nitrate reduction among all the species.
•IAA less than 10 mg/L inhibits the growth of periphytic biofilm.•IAA more than 50 mg/L stimulates growth of periphytic biofilm.•The removal rate of IAA by periphytic biofilm is 95%–100%.•IAA more ...than 50 mg/L stimulates the capacity of periphytic biofilm to remove IAA.
Due to its extensive application in agriculture as a germinating agent and growth promoter, indole acetic acid (IAA) is present in a variety of aquatic ecosystems. To explore the response of microbial aggregates to exogenous IAA in aquatic ecosystems, periphytic biofilm, a typical microbial aggregate, was exposed to IAA at different concentrations. Results reveal an unexpected concentration-dependent effect of IAA on periphytic biofilm. Concentrations of IAA less than 10 mg/L inhibit periphytic growth, but stimulate growth when the IAA concentration exceeds 50 mg/L. Periphytic biofilm adapts to different IAA concentrations by antioxidant enzyme activation, community structure optimization and carbon-metabolism pattern change, and promotes bioremediation of IAA contaminated water in the process. The removal rates of IAA reached up to 95%–100%. This study reveals the capacity of periphytic biofilm for IAA removal in practice.
Adsorption is an effective and reliable method to recover phosphorus (P) from sewages. Extracellular polymeric substances (EPS) and agarose are common polysaccharides bioresources, and their ...carboxylic and phenolic hydroxyl groups can directly adsorb P via ion exchange and hydrogen bonding mechanisms. Here, we designed EPS-based and Fe-modified hydrogels (agarose (AG)- and agarose-humic (AH)- based hydrogels) for P recovery. The results showed that AG and AH hydrogels could adsorb 33.9 and 67.7 mg P g−1, respectively. Both as-developed hydrogels showed > 75% of the maximal adsorption capacity in the tested pH conditions (3−10). Coexisting anions (i.e., SO42-, NO3-, and CO32-) did not significantly affect the adsorption performance, except for CO32- which inhibited the process. Intraparticle diffusion controlled the adsorption process. After adsorption, large amounts of FePO4 and Fe2(HPO4)3 were generated in the hydrogels, confirming that ligand exchange was the major driving force.
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•EPS-based hydrogels are made from agarose and humic acid.•EPS-based hydrogel appeared to have excellent phosphorus adsorption performance.•Ligand exchange is the major driving force for hydrogels to trap phosphate.
The toxic effects of nanoparticles on individual organisms have been widely investigated, while few studies have investigated the effects of nanoparticles on ubiquitous multicommunity microbial ...aggregates. Here, periphyton as a model of microbial aggregates, was employed to investigate the responses of microbial aggregates exposed continuously to Fe2O3 nanoparticles (5.0 mg L–1) for 30 days. The exposure to Fe2O3 nanoparticles results in the chlorophyll (a, b, and c) contents of periphyton increasing and the total antioxidant capacity decreasing. The composition of the periphyton markedly changes in the presence of Fe2O3 nanoparticles and the species diversity significantly increases. The changes in the periphyton composition and diversity were due to allelochemicals, such as 3-methylpentane, released by members of the periphyton which inhibit their competitors. The functions of the periphyton represented by metabolic capability and contaminant (organic matter, nitrogen, phosphorus and copper) removal were able to acclimate to the Fe2O3 nanoparticles exposure via self-regulation of morphology, species composition and diversity. These findings highlight the importance of both physiological and ecological factors in evaluating the long-term responses of microbial aggregates exposed to nanoparticles.
To explore whether and how anthropogenic activities related to surface water regulation (i.e., dam construction) disturb soil ecosystems in the surrounding uplands, a long-term monitoring program was ...conducted from 1998 to 2017 in the Three Gorges Reservoir Region, China. The Three Gorges Dam (TGD) is the largest hydraulic engineering project in the world. We present a direct, ecosystem-scale demonstration of changes in the soil organic carbon (SOC) content in the TGD watershed before and after the surface water was reshaped. The average SOC content decreased from 12.9 to 9.5 g/kg between 2004 and 2012 and then recovered to 13.8 g/kg in 2017. Dynamics of SOC were partly attributed to shifts in the composition of soil microbial communities responsible for carbon biogeochemistry. The shifts in microbial taxa were associated with the changed microclimate affected by the TGD as well as global and regional climate variability. The microclimate, soil microorganisms, and plant organic carbon input explained 40.2% of the variation in the SOC content. This study revealed that dam construction was an important and indirect driver for the SOC turnover, and the subsequent effects on the upland soil ecosystem must be considered when large-scale disturbance activities (such as dam construction) are conducted in the future.
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•Pr-Li stimulated periphytic biofilm changed microbial community structure.•Pr-Li stimulated periphytic biofilm enhanced carbon utilization and metabolic capacity.•Synergic action of ...algae, bacteria biomasses and AWCD contributed to P and Cu2+ removal.
Upconversion phosphors (UCPs) can convert visible light into luminescence, such as UV, which can regulate the growth of microbes. Based on these fundamentals, the community composition of periphytic biofilms stimulated by UCPs doped with Pr3+-Li+ was proposed to augment the removal of phosphorus (P) and copper (Cu). Results showed that the biofilms with community composition optimized by UCPs doped with Pr3+-Li+ had high P and Cu2+ removal rates. This was partly due to overall bacterial and algal abundance and biomass increases. The synergistic actions of algal, bacterial biomass and carbon metabolic capacity in the Pr-Li stimulated biofilms facilitated the removal of P and Cu2+. The results show that the stimulation of periphytic biofilms by lanthanide-doped UCPs is a promising approach for augmenting P and Cu2+ removal.
Lubrication is one of the key factors to improve metal-forming quality. In the process of deep drawing, seizing tumors easily occur on the contact surfaces between the tantalum metal and the mold, ...which greatly affects the forming quality of the deep-drawn parts. Quality-forming quality problems that occur during the deep drawing of tantalum metal are studied from the perspective of lubrication in this paper. Three lubrication media, caster oil, PE (polyethylene) film, and DLC (Diamond Like Carbon) film, were adopted in the deep drawing of tantalum cylindrical cups. A universal testing machine and microscope were used to investigate the effect of lubrication media on the limit-drawing ratio, maximum forming force, and surface topography quality during the deep drawing process of the tantalum sheet. The results reveal that the lubrication of the PE film and DLC film can greatly improve the forming quality of the tantalum metal sheet, in which the DLC film has higher wear resistance and lower friction coefficient and can be used as the lubricating medium in the industrial forming process of tantalum deep-drawn parts.
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•UCPs were first used to stimulate nitrogen removal of periphytic biofilms.•UCPs optimized the microbial community structure of periphytic biofilms.•Periphytic biofilms simulated by ...UCPs could adapt to nitrogen fluctuation.
The application of periphytic biofilm in removing nitrogen from water is limited by the fluctuating nitrogen concentration. Here, we delineate a novel approach to enhance periphytic biofilm performance in nitrogen removal via upconversion luminescence of upconversion phosphors (UCPs). Nitrogen removal rates (14 d) in high nitrogen wastewater (26 mg/L) were significantly improved to 58.6% and 61.4% by UCPs doped with Pr3+ and Li+ and UCPs doped with Pr3+, respectively, and to 95.1% and 95.9% in low nitrogen surface water (2 mg/L), respectively. The stimulation of UCPs optimized the microbial community structure in the periphytic biofilms, and also resulted in good acclimation to use different carbon sources. The enhanced synergic action of cyanobacterial biomass, ratio of Gram +ve to Gram −ve bacteria and carbon source metabolic capacity contributed to the improved nitrogen removal. This novel approach is promising in nitrogen removal from wastewater and surface water with fluctuating initial nitrogen concentration.
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