Water Research最新文献

Periodic oxygen permeation is critical for pollutant removal within intertidal sediments. However, tidal effects on the vertical redox profile associated with cable bacterial activity is not well understood. In this study, we simulated and quantified the effects of tidal flooding, exposing, and their periodic alternation on vertical redox reactions and phenanthrene removal driven by cable bacteria in the riverbank sediment. Results show that electrogenic sulfur oxidation (e-SOx) mediated by cable bacteria during exposing process drove the vertical permeation of oxidation potential characterized by a decrease in Fe(II) and sulfide concentrations. The sulfate produced was observed in deep sediment (5–10 mm) and served as an electron acceptor for anaerobic oxidation, thereby triggering the functional succession of microbial community. About 78.2 % and 80.8 % of phenanthrene was degraded in deep sediment where cable bacteria grew well under exposing and tidal conditions. Anaerobic processes during tidal flood were also found to be important for the survival of cable bacteria. Higher cable bacteria abundance (up to 1.5 %) was observed under tidal conditions compared to that under continuous exposing conditions and flooding conditions. This might be attributed to lower oxidation stress and sulfide replenishment via sulfate reduction while flooding. Under tidal conditions, the cable bacteria interacted with sulfate reduction bacteria (e.g. Desulfobacca spp. and Desulfatiglans spp.) and maintained the dynamic balance of HS⁻ and SO₄²⁻ in sediment profiles. This HS⁻-SO₄²⁻ cycle could serve as a “redox connector” that continuously delivers oxidation potential to deep sediments, resulting in the removal of organic pollutants. The findings provide preliminary evidence of the self-purification mechanisms within intertidal sediments and suggest a potential strategy for sediment remediation.

Employing chemical pretreatment for waste activated sludge (WAS) fermentation is crucial to achieving sustainable sludge management. This study investigated the feasibility of metabisulfite (MS) pretreatment for enhancing volatile fatty acids (VFAs) production from WAS. The results show that after 24-h MS pretreatment, the content of soluble organic matter and loosely bound extracellular polymeric substances (LB-EPS), especially proteins, increased significantly. During the fermentation, MS pretreatment under alkaline conditions was more efficient, with VFA peaking on the fifth day, showing a 140 % increase compared to the alkaline control group. Correlation analysis suggests that the dosage of MS, rather than pH, is closely related to the levels of soluble protein, polysaccharides, LB-EPS, and subsequential VFAs production, while alkaline conditions facilitate the dissolution of total organic carbon. Furthermore, sulfite radicals (SO₃^•−) are attributed to cell inactivation and lysis, while alkaline conditions initially reduce the size of the flocs, further promoting MS for attacking flocs, thereby improving the performance of fermentation. The study also found that MS pretreatment reduced microbial community diversity, enriched hydrolytic and fermentation bacteria (Actinobacteriota and Firmicutes), and suppressed methanogens (Methanobacteriaceae and Methanosaetaceae), making it a safe, viable, and cost-effective chemical agent for sustainable sludge management.

The coupled process of anammox and reduced-sulfur driven autotrophic denitrification can simultaneously remove nitrogen and sulfur from wastewater, while minimizing energy consumption and sludge production. However, the research on the coupled process for removing naturally toxic thiocyanate (SCN^-) is limited. This work successfully established and operated a one-stage coupled system by co-cultivating mature anammox and SCN^--driven autotrophic denitrification sludge in a single reactor. In this one-stage coupled system, the average total nitrogen removal efficiency was 89.68±3.33 %, surpassing that of solo anammox (81.80±2.10 %) and SCN^--driven autotrophic denitrification (85.20±1.54 %). Moreover, the average removal efficiency of SCN^- reached 99.50±3.64 %, exceeding that of solo SCN^--driven autotrophic denitrification (98.80±0.65 %). The results of the ¹⁵N stable isotope tracer labeling experiment revealed the respective reaction rates of anammox and denitrification as 106.38±10.37 μmol/L/h and 69.07±8.07 μmol/L/h. By analyzing metagenomic sequencing data, Thiobacillus_denitrificans was identified as the primary contributor to SCN^- degradation in this coupled system. Furthermore, based on the comprehensive analysis of nitrogen and sulfur metabolic pathways, as well as the genes associated with SCN^- degradation, it can be inferred that the cyanate (CNO) pathway was responsible for SCN^- degradation. This work provided a deeper insight into coupling anammox with SCN^--driven autotrophic denitrification in a one-stage coupled system, thereby contributing to the development of an effective approach for wastewater treatment involving both SCN^- and nitrogen.

Phosphorus (P) recovered from sludge-incinerated ash (SIA) could be applied to synthesize highly added-value products (FePO₄ and LiFePO₄) with in situ Fe in SIA. Indeed, LiFePO₄ is a future of rechargeable batteries, which makes lithium (Li) highly needed. Alternatively, Li could also be extracted from concentrated brines to face a potential crisis of Li depletion on lands. Based on H₃PO₄ and Fe³⁺ co-extracted from the acidic leachate of SIA by tributyl phosphate (TBP), FePO₄ (31.2 wt% Fe, 17.6 wt% P and the molar ratio of Fe/P = 0.98) was easily formed only adjusting pH of the stripping solution to 1.6. Interestingly, the organic phase from the first-stage co-extraction process of Fe³⁺ and H₃PO₄ could be utilized for Li-extraction from salt-lake brine, based on the TBP-FeCl₃-kerosene system, and a good performance (78.7%) of Li-extraction and separation factors (β) (186.0–217.4) were obtained. Furthermore, the compounds with Li-extraction are complex, possibly LiFeCl₄∙2TBP, in which Li⁺ could be stripped to form Li₂CO₃ by 4.0 M HCl (with a stripping rate up to 83%). Besides, Li₂CO₃ could also be obtained from desalinated brine by adsorption with manganese oxide ion sieve (HMO) and desorption with HCl. In the two cases, almost pure Li₂CO₃ products were obtained, up to 99.7 and 99.5 wt% Li₂CO₃ respectively, after further purification and concentration. Finally, recovered FePO₄ and extracted Li₂CO₃ were synthesized for producing LiFePO₄ that had a similar electrochemical property (69.5 and 77.8 mAh/g of the initial discharge capacity) to those synthesized from commercial raw materials.

Microalgae-based biotechnology is one of the most promising alternatives to conventional methods for the removal of antibiotic contaminants from diverse water matrices. However, current knowledge regarding the biochemical mechanisms and catabolic enzymes involved in microalgal biodegradation of antibiotics is scant, which limits the development of enhancement strategies to increase their engineering feasibility. In this study, we investigated the removal dynamics of amphenicols (chloramphenicol, thiamphenicol, and florfenicol), which are widely used in aquaculture, by Chlamydomonas reinhardtii under different growth modes (autotrophy, heterotrophy, and mixotrophy). We found C. reinhardtii removed >92 % chloramphenicol (CLP) in mixotrophic conditions. Intriguingly, gamma-glutamyl hydrolase (GGH) in C. reinhardtii was most significantly upregulated according to the comparative proteomics, and we demonstrated that GGH can directly bind to CLP at the Pro77 site to induce acetylation of the hydroxyl group at C3 position, which generated CLP 3-acetate. This identified role of microalgal GGH is mechanistically distinct from that of animal counterparts. Our results provide a valuable enzyme toolbox for biocatalysis and reveal a new enzymatic function of microalgal GGH. As proof of concept, we also analyzed the occurrence of these three amphenicols and their degradation intermediate worldwide, which showed a frequent distribution of the investigated chemicals at a global scale. This study describes a novel catalytic enzyme to improve the engineering feasibility of microalgae-based biotechnologies. It also raises issues regarding the different microalgal enzymatic transformations of emerging contaminants because these enzymes might function differently from their counterparts in animals.

Global warming and eutrophication contribute to frequent occurrences of toxic algal blooms in freshwater systems globally, while there is a limited understanding of their combined impacts on toxin-producing algal species under interspecific competitions. This study investigated the influences of elevated temperatures, lights, nutrient enrichments and interspecific interactions on growth and microcystin (MC) productions of Microcystis aeruginosa in laboratory condition. Our results indicated that elevated temperatures and higher nutrient levels significantly boosted biomass and specific growth rates of Microcystis aeruginosa, which maintained a competitive edge over Chlorella sp. Specifically, with phosphorus levels between 0.10 and 0.70 mg P L⁻¹, the growth rate of Microcystis aeruginosa in mixed cultures increased by 23 %–52 % compared to mono-cultures, while the growth rate of Chlorella sp. shifted from positive in mono-cultures to negative in mixed cultures. Redundancy and variance partition analyses suggested that Chlorella sp. stimulate MC production in Microcystis aeruginosa and nutrient levels outshine temperature for toxin productions during competition. Lotka‒Volterra model revealed a positive correlation between the intensities of competitions and MC concentration. Our findings indicate that future algal bloom mitigation strategies should consider combined influence of temperature, nutrients, and interspecific competition due to their synergistic effects on MC productions.

Enriching microorganisms using a 0.22-μm pore size is a general pretreatment procedure in river microbiome research. However, it remains unclear the extent to which this method loses microbiome information. Here, we conducted a comparative metagenomics-based study on microbiomes with sizes over 0.22 μm (large-sized) and between 0.22 μm and 0.1 μm (small-sized) in a subtropical river. Although the absolute concentration of small-sized microbiome was about two orders of magnitude lower than that of large-sized microbiome, sequencing only large-sized microbiome resulted in a significant loss of microbiome diversity. Specifically, the microbial community was different between two sizes, and 347 genera were only detected in small-sized microbiome. Small-sized microbiome had much more diverse viral community than large-sized fraction. The viruses had abundant ecological functions and were hosted by 825 species of 169 families, including pathogen-related families. Small-sized microbiome had distinct antimicrobial resistance risks from large-sized microbiome, showing an enrichment of eight antibiotic resistance gene (ARG) types as well as the detection of 140 unique ARG subtypes and five enriched risk rank I ARGs. Draft genomes of five major resistant pathogens having diverse ecological and pollutant-degrading functions were only assembled in small-sized microbiome. These findings provide novel insights into river ecosystems, and highlight the overlooked small-sized microbiome in the environment.

The removal of arsenic (As(III)) from acidic wastewater using neutralization or sulfide precipitation generates substantial arsenic-containing hazardous solid waste, posing significant environmental challenges. This study proposed an advanced ultraviolet (UV)/dithionite reduction method to recover As(III) in the form of valuable elemental arsenic (As(0)) from acidic wastewater, thereby avoiding hazardous waste production. The results showed that more than 99.9 % of As(III) was reduced to As(0) with the residual concentration of arsenic below 25.0 μg L⁻¹ within several minutes when the dithionite/As(III) molar ratio exceeded 1.5:1 and the pH was below 4.0. The content of As(0) in precipitate reached 99.70 wt%, achieving the purity requirements for commercial As(0) products. Mechanistic investigations revealed that SO₂^·‒ and H· radicals generated by dithionite photolysis under UV irradiation are responsible for reducing As(III) to As(0). Dissolved O₂, Fe(III), Fe(II), Mn(II), dissolved organic matter (DOM), and turbidity slightly inhibited As(III) reduction via free radicals scavenging or light blocking effect, whereas other coexisting ions, such as Mg(II), Zn(II), Cd(II), Ni(II), F(−I), and Cl(−I), had limited influence on As(III) reduction. Moreover, the cost of treating real arsenic-containing (250.3 mg L⁻¹) acidic wastewater was estimated to be as low as $0.668 m⁻³, demonstrating the practical applicability of this method. This work provides a novel method for the reductive recovery of As(III) from acidic wastewater.

Methylisothiazolinone (MIT) and Benzisothiazolinone (BIT) are two widely used non-oxidizing biocides of isothiazolinones. Their production and usage volume have sharply increased since the pandemic of COVID-19, inevitably leading to more release into water environment. However, their photochemical behaviors in water environment are still unclear. Therefore, this study investigated photodegradation properties of MIT and BIT in natural water under simulated sunlight. The results demonstrated that direct photolysis was mainly responsible for their photodegradation which occurred through their excited singlet states rather than triplet states. The quantum yields of MIT and BIT photodegradation were 11 - 13.6 × 10⁻⁴ and 2.43 - 5.79 × 10⁻⁴, respectively. pH had almost no effect on the photodegradation of MIT, while the photodegradation of BIT was significantly promoted under alkaline condition due to abundance of BIT in its deprotonated form (BIT-N⁻). Cl⁻, NO₃⁻ and dissolved organic matter (DOM) in natural water inhibited the photodegradation of both MIT and BIT, with the light screening effect of DOM being the most significantly inhibitory factor. The addition of other isothiazolinones, which possibly coexisted with MIT and BIT in actual condition, slightly inhibited the photodegradation of MIT and BIT. The estimated half-life under natural sunlight at a 30°N latitude was estimated to be approximately 1.1 days. The photodegradation pathways of MIT and BIT are similar, primarily initiated from the ring-opening at the N-S bond, with Frontier electron densities (FED) calculations suggesting the likelihood of oxidation and ·OH addition reactions at the O, N, and S sites. While the photodegradation products exhibited significantly reduced acute toxicity compared to their parent compounds, they nonetheless posed substantial chronic toxicity. These insights are vital for assessing the ecological impacts of MIT and BIT in aquatic environments.

While air stripping combined with acid scrubbing remains a competitive technology for the removal and recovery of ammonia from wastewater streams, its use of strong acids is concerning. Organic acids offer promising alternatives to strong acids like sulphuric acid, but their application remains limited due to high cost. This study proposes an integration of air stripping and organic acid scrubbing with bipolar membrane electrodialysis (BPMED) to regenerate the organic acids. We compared the energy consumption and current efficiency of BPMED in recovering dissolved ammonia and regenerating sulphuric, citric, and maleic acids from synthetic scrubber effluents. Current efficiency was lower when regenerating sulphuric acid (22 %) compared to citric (47 %) and maleic acid (37 %), attributable to the competitive proton transport over ammonium across the cation exchange membrane. Organic salts functioned as buffers, reducing the concentration of free protons, resulting in higher ammonium removal efficiencies with citrate (75 %) and malate (68 %), compared to sulphate (29 %). Consequently, the energy consumption of the BPMED decreased by 54 % and 35 % while regenerating citric and maleic acids, respectively, compared to sulfuric acid. Membrane characterisation experiments showed that the electrical conductivity ranking, ammonium citrate > ammonium malate > ammonium sulphate, was mirrored by the energy consumption (kWh/kg-N recovered) ranking, ammonium sulphate (15.6) < ammonium malate (10.2) < ammonium citrate (7.2), while the permselectivity ranking, ammonium sulphate > ammonium citrate > ammonium malate, aligned with calculated charge densities. This work demonstrates the potential of combining organic acid scrubbers with BPMED for ammonium recovery from wastewater effluents with minimum chemical input.