Effect of modified graphene oxide on Cu and phosphorus in eutrophic river sediments.

Ulansuhai nur is located in the cold and dry area of China, and the management of heavy metals in the sediments is related to water safety in the lower places of the Yellow River. Graphene oxide (GO) is modified to obtain magnetic graphene oxide (G-F) and chitosan grafted graphene oxide (G-N-C) materials, which are used to immobilize Cu in the sediments. The modified materials are characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometer (XRD). G-F respectively reduces the concentration of Cu in the overlying and interstitial water by 61.5-66.3% and 22.4-47.1%, which is more effective than GO and G-N-C. Experiments are designed to determine the effect of phosphates concentration on immobilizing Cu in the sediments by modified materials. The results show that a low concentration of phosphates solution is beneficial to the immobilization of Cu in the sediments, and the capability of G-F to immobilize Cu is higher than that of GO and G-N-C. G-F presents a lower increase in organic phosphorus in the sediments than GO and G-N-C. In summary, the modified materials can immobilize Cu in the sediments, potentially reduce the water body eutrophication, and improve the lake ecological environment.

Highly efficient enhancement of municipal sludge dewaterability using persulfate activation with nZVI/HA.

This study presents a sulfate radical-based oxidation method for improving municipal sludge dewaterability by combining persulfate and nanoscale zero-valent iron supported on humic acid (nZVI/HA-PS). Sludge dewaterability using persulfate activation with nZVI/HA was assessed for specific resistance to filterability (SRF), time to filter (TTF), settling volume percentage (SV30) and water content (Wc). The influencing factors, such as mass ratios of nZVI to HA, initial pH, PS dosage and nZVI/HA nanocomposite dosage, were investigated. Experimental results indicated that the SRF reduction efficiency of the sludge reached 86.47% using initial concentrations of 1.2 mmol/gVSS PS and 300 mg/L nZVI/HA. The soluble chemical oxygen demand (SCOD) of sludge supernatants increased from 79 mg/L to 710 mg/L under optimum conditioning, indicating that sludge flocs were effectively decomposed. Economic analysis demonstrated that the nZVI/HA-PS conditioning process is a potential method for improving sludge dewaterability.

Microbial community evolution and individual-based model validation of biofilms in single-stage partial nitrification/anammox system.

In this study, matrix degradation, microbial community development, and distribution using an individual-based model during biofilm formation on carriers at varying depths within a single-stage partial nitrification/anammox system were simulated. The findings from the application of individual-based model fitting, fluorescence in situ hybridization, and high-throughput sequencing reveal the presence of aerobic bacteria, specifically ammonia-oxidizing bacteria, as discrete particles within the outer layer of the carrier. Facultative anaerobic bacteria exemplified by anaerobic ammonia-oxidizing bacteria, are observed as aggregates within the middle layer. Conversely, anaerobic bacteria, represented by denitrifiers, are enveloped by extracellular polymeric substances within the inner layer. The present study extends the application of individual-based model to the formation of polyurethane-supported biofilms and presents valuable avenues for the design and advancement of pragmatic engineering carriers.

Critical role of extracellular DNA in the establishment and maintenance of anammox biofilms.

Anaerobic ammonium oxidation (anammox) has been widely used for the sustainable removal of nitrogen from wastewater. Extracellular DNA (exDNA), as one of the main components of biofilms, not only determines the initial formation process, but also allows the three-dimensional structure to be maintained. Since the effects of exDNA on anammox biofilm formation are still poorly understood, this study elucidated the effects of exDNA on different stages of anammox biofilm establishment and maintenance under static conditions and its mechanism. The results revealed that exDNA mainly affected the maintenance stage of anammox biofilm formation. Compared with the absence of exDNA, nitrogen removal efficiency in the presence of exDNA was 6.17 % higher; the number of bacteria cells attached to the carrier was 2.23 times that in the absence of exDNA. The spatiotemporal distribution of bacteria was revealed by fluorescence in situ hybridization. After 30 days, the relative abundances of anammox in biofilms were 6.19 % and 0.4 % in the presence and absence of exDNA, respectively, indicating its positive role in anammox bacteria (AnAOB) adhesion and biofilm formation. The presence of exDNA in extracellular polymeric substances (EPS) promotes the synthesis of proteins and soluble microbial products. According to the extended Derjaguin-Landau-Verwey-Overbeek (X - DLVO) theory, the presence of exDNA also reduced the Lewis acid-base interaction energy and created favorable thermodynamic conditions for AnAOB adhesion. These findings advance our understanding of the role of exDNA in anammox-mediated biofilm formation and offer insights into the mechanism of exDNA in the establishment and maintenance stages.

Effects of ammonia nitrogen and organic carbon availability on microbial community structure and ecological interactions in a full-scale partial nitritation and anammox (PN/A) system.

Nutrient availability significantly impacts microbial biosynthesis, cell growth, and cell cycle progression. In this study, a full-scale plug-flow partial nitritation/anammox (PN/A) system was used to investigate variations in the microbial community structure in both immobilized carriers and flocs, as well as a gradual decrease in nutrient availability from upstream to downstream. We found that reduced ammonia nitrogen (from 150.4 to 30.6 mg/L) and organic carbon (from 415.7 to 342.8 mg/L) availability significantly lowered microbial diversity and altered microbial communities in biofilms other than flocs from upstream to downstream. The abundance of all anammox bacteria increased by 1.97 times, from 3.25 × 1010 to 6.40 × 1010 copies per gram of wet sludge, in the biofilm core microbiome. Furthermore, from upstream to downstream, taxa with lower ribosomal RNA operon copy numbers were consistently enriched in both biofilm and floc communities, indicating that slow-growing microorganisms are more likely to be enriched in low-nutrient environments. Rare taxa with a relative abundance of less than 0.1% exhibited unique metabolic functions, including amino acid, carbohydrate, cofactor, and vitamin metabolisms, which was inferred by PICRUST2 and persisted across the nutrient gradient in both the biofilm and floc communities. Despite their low abundance, they may play important roles in mediating the stability and function of the PN/A system. Overall, the results demonstrate the impact of a naturally formed ammonia nitrogen and organic carbon gradient in a full-scale plug-flow PN/A installation on nutrient availability and its effects on microbial diversity, community composition, and microbial interactions, which expands our fundamental understanding of this energy-efficient and promising biotechnology for treating high-strength ammonium wastewater.

Digested extracellular DNA shortens the anodic startup of microbial electrolysis cell.

While the multiple functions of extracellular DNA (exDNA) in biofilm formation and electron transfer have been extensively studied in pure culture, its role in mixed anodic biofilm was still unknown. In this study, we employed DNase I enzyme to digest exDNA, thereby investigating its role in anodic biofilm formation based on the performance of four microbial electrolysis cells (MECs) groups with different DNase I enzyme concentration (0, 0.05, 0.1, 0.5 mg/mL). The responding time to reach 60 % maximum current of treatment group with DNase I enzyme has been significantly reduced to 83 %-86 % of the blank group (t-test, p < 0.01), indicating the exDNA digestion could promote the biofilm formation at the early stage. The anodic coulombic efficiency was enhanced by 10.74- 54.42 % in treatment group (t-test, p < 0.05), which could be ascribed to the higher absolute abundance of exoelectrogens. The lower relative abundance of exoelectrogens indicated the DNase I enzyme addition was beneficial for the enrichment of extensive species rather than exoelectrogens. As the DNase I enzyme augments the fluorescence signal of exDNA distribution in the small molecular weight region, implying the short chain exDNA could contribute to the biomass enhancement via boosting the most species enrichment. Furthermore, the exDNA alteration improved the complexity of microbial network. Our findings provide a new insight into the role of exDNA in the extracellular matrix of anodic biofilms.

Immobilization of Cd and phosphorus utilization in eutrophic river sediments by biochar-supported nanoscale zero-valent iron.

The Ulansuhai River is polluted by heavy metals and faces a serious problem of eutrophication. According to a previous study, biochar-supported nanoscale zero-valent iron composite (BC-nZVI) can be used to effectively immobilize heavy metals, converting Cd from labile to a stable fraction. The present study aimed to evaluate the immobilization of Cd in sediments of eutrophic rivers by BC-nZVI and investigate the effects of phosphorus on Cd immobilization in BC-nZVI immobilized sediments. The immobilization of Cd with BC-nZVI as a stabilizer at different KH2PO4 solution concentrations, the available phosphorus in the sediments, the total phosphorus in the overlying water, and the changes in the pH of the sediments were investigated. The changes of available phosphorus in sediments after the addition of BC, nZVI and BC-nZVI stabilizers were also studied. Results showed that the presence of phosphorus could promote the immobilization of Cd in sediments. The content of total phosphorus in overlying water was reduced, precipitates of phosphate and Cd were produced, and the available phosphorus in sediments was increased after the addition of BC-nZVI. The pH of sediments increased along with the increase in incubation time, which is beneficial for Cd immobilization. This study proved that (1) BC-nZVI can effectively immobilize Cd in eutrophic river sediments, (2) the presence of phosphorous in overlying water is conductive to the conversion of Cd from labile fractions to stable fraction in the sediment, and (3) adsorption and precipitation may be the main mechanisms in Cd immobilization.