Effect of biomass immobilization and reduced graphene oxide on the microbial community changes and nitrogen removal at low temperatures

The effects of graphene on low-temperature anammox process: The insights from short-term tests and long-term operation

Effluent quality deterioration caused by seasonal low temperature is a great challenge to the application of anammox technology. Here, the effects of different graphene materials on anammox process were investigated under both optimal temperature and low-temperature. The batch tests showed that at 30 °C, 300 mg/L of reduced graphene oxide‑sodium alginate gel (RGOSA) had the most significant promoting effect, reaching nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 95 % and 8.88 mgN/L/d, respectively. The changes of EPS secretion patterns and increasing of key enzymes activity might contribute to the enhanced anammox activity. During the long-term operation of anammox reactor, the NRE and NRR of the reactor decreased when the temperature dropped to 15 °C, showing an NRE of 50 %-57 % with the addition of 200 mg/L of reduced graphene oxide (RGO) and 40 %-45 % with the addition of 20 mg/L of RGO. Furthermore, specific anammox activity (SAA) of the RGO200 reactor at 15 °C increased by 57.1 % compared to the UASB reactor without graphene addition. Additionally, 16S rRNA and metagenomic analysis results revealed anammox bacteria Ca. Kuenenia was the dominant bacteria. Moreover, the RGO can significantly increase the relative abundance of N-converting functional genes. This study demonstrates the graphene materials can help anammox process adapting to low temperatures, providing a possible solution for the application of anammox technology.

Silver nanoparticles incorporated with superior silica nanoparticles-based rice straw to maximize biogas production from anaerobic digestion of landfill leachate

Treating hazardous landfill leachate poses significant environmental challenges due to its complex nature. In this study, we propose a novel approach for enhancing the anaerobic digestion of landfill leachate using silver nanoparticles (Ag NPs) conjugated with eco-friendly green silica nanoparticles (Si NPs). The synthesized Si NPs and Ag@Si NPs were characterized using various analytical techniques, including transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The anaerobic digestion performance of Si NPs and Ag@Si NPs was tested by treating landfill leachate samples with 50 mg/L of each NP. The results demonstrated an enhancement in the biogas production rate compared to the control phase without the nanocomposite, as the biogas production increased by 14% and 37% using Si NPs and Ag@Si NPs. Ag@Si NPs effectively promoted the degradation of organic pollutants in the leachate, regarding chemical oxygen demand (COD) and volatile solids (VS) by 58% and 65%. Furthermore, microbial analysis revealed that Ag@Si NPs enhanced the activity of microbial species responsible for the methanogenic process. Overall, incorporating AgNPs conjugated with eco-friendly green Si NPs represents a sustainable and efficient approach for enhancing the anaerobic digestion of landfill leachate.

Bibliometric analysis of research trends in biogranulation technology for wastewater treatment

Inadequate management and treatment of wastewater pose significant threats, including environmental pollution, degradation of water quality, depletion of global water resources, and detrimental effects on human well-being. Biogranulation technology has gained increasing traction for treating both domestic and industrial wastewater, garnering interest from researchers and industrial stakeholders alike. However, the literature lacks comprehensive bibliometric analyses that examine and illuminate research hotspots and trends in this field. This study aims to elucidate the global research trajectory of scientific output in biogranulation technology from 1992 to 2022. Utilizing data from the Scopus database, we conducted an extensive analysis, employing VOSviewer and the R-studio package to visualize and map connections and collaborations among authors, countries, and keywords. Our analysis revealed a total of 1703 journal articles published in English. Notably, China emerged as the leading country, Jin Rencun as the foremost author, Bioresource Technology as the dominant journal, and Environmental Science as the prominent subject area, with the Harbin Institute of Technology leading in institutional contributions. The most prominent author keyword identified through VOSviewer analysis was "aerobic granular sludge," with "sequencing batch reactor" emerging as the dominant research term. Furthermore, our examination using R Studio highlighted "wastewater treatment" and "sewage" as notable research terms within the field. These findings underscore a diverse research landscape encompassing fundamental aspects of granule formation, reactor design, and practical applications. This study offers valuable insights into biogranulation potential for efficient wastewater treatment and environmental remediation, contributing to a sustainable and cleaner future.

Application of cold-adapted microbial agents in soil contaminate remediation: biodegradation mechanisms, case studies, and safety assessments

The microbial agent technology has made significant progress in remediating nitro-aromatic compounds (NACs), such as p-nitrophenol, 2,4-dinitrophenol, and 2,4,6-Trinitrotoluene, in farmland soil over the past decade. However, there are still gaps in our understanding of the bioavailability and degradation mechanisms of these compounds in low-temperature environments. In this review, we provide a comprehensive summary of the strategies employed by cold-adapted microorganisms and elucidate the degradation pathways of NACs pollutants. To further analyze their metabolic mechanisms, we propose using mass balance to improve our understanding of biochemical processes and refine the degradation pathways through stoichiometry analysis. Additionally, we suggest employing 13C-metabolic flux analysis to track enzyme activity and intermediate products during bio-degradation processes with the aim of accelerating the remediation of nitro-aromatic compounds, particularly in cold regions. Through a comprehensive analysis of pollutant metabolic activities and a commitment to the 'One Health' approach, with an emphasis on selecting non-pathogenic strains, the environmental management strategies for soil remediation could be positioned to develop and implement safe and effective measure.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7 ± 2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9 mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ± 2 and 16 ± 2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ± 2 and 7 ± 2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Novel insights into carbon nanomaterials enhancing anammox for nitrogen removal: Effects and mechanisms

Carbon nanomaterials (CNMs) possess the properties including large specific surface area, high porosity, and stable chemical structures, presenting significant application advantages in wastewater treatment. Indeed, CNMs are considered to be added to anammox systems to strengthen anammox function, especially to resolve the challenge of anammox technology, i.e., the slow growth rate of anammox bacteria, as well as its high environmental sensitivity. This paper systematically reviews the promotion effects and mechanisms of CNMs on the nitrogen removal performance of anammox system. Among the zero-, one-, and two-dimensional CNMs, two-dimensional CNMs have best promoting effect on the nitrogen removal performance of anammox system due to its excellent conductivity and abundant functional groups. Then, the promotion effects of CNMs on anammox process are summarized from the perspective of anammox activity and bacteria abundance. Furthermore, CNMs not only enhance the anammox process, but also stimulate the coupling of denitrification pathways with anammox, as well as the improvement of system operational stability (alleviating the inhibitions of low temperature and pH fluctuation), thus contributing to the promoted nitrogen removal performance. Essentially, CNMs are capable of facilitating microbial immobilization and electron transfer, which favor to improve the efficiency and stability of anammox process. Finally, this review highlights the gap in knowledge and future work, aiming to provide a deeper understanding of how CNMs can strengthen the anammox system and provide a novel perspective for the engineering of the anammox process.

Adsorption characteristics of nickel (II) from aqueous solutions by Zeolite Scony Mobile-5 (ZSM-5) incorporated in sodium alginate beads

Nickel, a prevalent metal in the ecosystem, is released into the environment through various anthropogenic activities, leading to adverse effects. This research explored utilizing zeolite scony mobile-5 (ZSM-5) nanoparticles encapsulated in sodium alginate (SA) for nickel (II) removal from aqueous solutions. The adsorption characteristics of SA/ZSM-5 were examined concerning contact duration, initial metal ion concentration, pH level, temperature, and sorbent dosage. The findings revealed that a rising pH reduced Ni (II) uptake by the sorbent while increasing the Ni (II) concentration from 25 to 100 mg L-1 led to a decrease in removal percentage from 91 to 80% under optimal conditions. Furthermore, as sorbent dosage increased from 4 to 16 g L-1, uptake capacity declined from 9.972 to 1.55 mg g-1. Concurrently, SA/ZSM-5 beads' Ni (II) sorption capacity decreased from 96.12 to 59.14% with a temperature increase ranging from 25 to 55 °C. The Ni (II) sorption data on SA/ZSM-5 beads are aptly represented by Langmuir and Freundlich equilibrium isotherm models. Moreover, a second-order kinetic model characterizes the adsorption kinetics of Ni (II) on the SA/ZSM-5 beads. A negative free energy change (ΔG°) demonstrates that the process is both viable and spontaneous. The negative enthalpy values indicate an exothermic nature at the solid-liquid interface while negative entropy values suggest a decrease in randomness. In conclusion, this novel adsorbent exhibits promise for removing nickel from aqueous solutions and could potentially be employed in small-scale industries under similar conditions.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

Enhanced removal of fluoride, nitrate, and calcium using self-assembled fungus-flexible fiber composite microspheres combined with microbially induced calcium precipitation

Self-assembled fungus-flexible fiber composite microspheres (SFFMs) were firstly combined with microbially induced calcium precipitation (MICP) in a continuous-flow bioreactor and achieved the efficient removal of fluoride (F^-), nitrate (NO₃^-), and calcium (Ca²⁺). Under the influent F^- of 3.0 mg L^-1, pH of 7.0, and HRT of 8 h, the average removal efficiencies reached 77.54%, 99.39%, and 67.25% (0.29, 2.03, and 8.34 mg L^-1 h^-1), respectively. Fluorescence spectrum and flow cytometry analyses indicated that F^- content significantly affected the metabolism and viability of bacteria. SEM images showed that flexible fibers and intertwined hyphae provided effective locations for bacterial colonization in SFFMs. The precipitated products were characterized by XRD and FTIR, which revealed that F^- was mainly removed in the form of calcium fluoride and calcium fluorophosphate (CaF₂ and Ca₅(PO₄)₃F). High-throughput analysis at different levels demonstrated that Pseudomonas sp. WZ39 acted as the core strain, which played a crucial role in the bioreactor. The mechanism of enhanced denitrification was attributed to minor F^- stress and bioaugmentation technology. This study highlighted the superiorities of SFFMs and MICP combined remediation and documented a promising option for F^-, NO₃^-, and Ca²⁺ removal.

Promotion of anammox process by different graphene-based materials: Roles of particle size and oxidation degree

Graphene oxide (GO) and reduced graphene oxide (RGO) have been applied in the anaerobic ammonium oxidation (anammox) process for nitrogen removal as electron shuttles. However, there is still controversy about their efficacy. In this study, nine graphene-based materials with a gradient of three particle sizes (large (l), medium (m) and small (s) sizes) and oxidation degrees, were used to compare their effects on the anammox process efficiency. The graphene-based materials include GO and its reduced products (RGO250 and RGO800) obtained at temperatures of 250 °C and 800 °C respectively. It was observed that their enhancements on the anammox process were in the order of GO > RGO800 > RGO250. In detail, at the dose of 100 mg/L, specific anammox activities (SAA) were promoted by 6.7% (l-GO), 4.9% (l-RGO800), 11.5% (m-GO), 7.3% (m-RGO800), 13.2% (s-GO) and 8.3% (s-RGO800) compared to the control respectively; while RGO250 with the same dose inhibited the process. In addition, the enhancement of the anammox process was increasing with the decreasing size of GO and RGO800. The nitrite reductase (NIR) activity was greatly increased by up to 24.9% with the presence of GO, which might be attributed to organized and specific electron transport with oxygen functional groups. The finding of hydroxyl on RGO and increasing content of oxygen determined after reaction detected by Fourier transform infrared spectroscopy and energy dispersive spectrometer respectively, indicated the essential condition for RGO's function on transferring electrons for key enzymes in annamox bacteria. Most importantly, O/C (Oxygen/Carbon) ratios of graphene-based materials had greater effects on the promotion of the anammox process than the particle size and electrical conductivity.

Waterborne Polyurethane Acrylates Preparation towards 3D Printing for Sewage Treatment

Conventional immobilized nitrifying bacteria technologies are limited to fixed beds with regular shapes such as spheres and cubes. To achieve a higher mass transfer capacity, a complex-structured cultivate bed with larger specific surface areas is usually expected. Direct ink writing (DIW) 3D printing technology is capable of preparing fixed beds where nitrifying bacteria are embedded in without geometry limitations. Nevertheless, conventional bacterial carrier materials for sewage treatment tend to easily collapse during printing procedures. Here, we developed a novel biocompatible waterborne polyurethane acrylate (WPUA) with favorable mechanical properties synthesized by introducing amino acids. End-capped by hydroxyethyl acrylate and mixed with sodium alginate (SA), a dual stimuli-responsive ink for DIW 3D printers was prepared. A robust and insoluble crosslinking network was formed by UV-curing and ion-exchange curing. This dual-cured network with a higher crosslinking density provides better recyclability and protection for cryogenic preservation. The corresponding results show that the nitrification efficiency for printed bioreactors reached 99.9% in 72 h, which is faster than unprinted samples and unmodified WPUA samples. This work provides an innovative immobilization method for 3D printing bacterial active structures and has high potential for future sewage treatment.

Preparation and Characterization of Temperature/pH Dual-Responsive Gel Spheres for Immobilizing Nitro Bacteria

The temperature/pH dual-responsive gel spheres were prepared by orthogonal experiments and response surface methodology, and finally, the optimal synthesis conditions were obtained by a composite score, including swelling, mechanical properties, mass transfer properties, and so forth. The results showed that a sodium alginate concentration of 3% (w/v), CaCl₂ concentration of 2% (w/v), gelling time of 40 h, drop height of 14 cm, NaCl concentration of 0.6% (w/v), N-isopropylacrylamide concentration of 0.03% (w/v), and acrylic acid concentration of 4.06% (w/v) were optimal synthesis conditions. The environmental change tolerance experiments showed that the nitrogen removal of the dual-response nitrifying gel spheres was better than the domesticated sludge at low temperatures (4 °C) and in alkaline (pH 9 and 10) conditions. The as-obtained gel spheres can respond intelligently to the changes in ambient temperature and pH. It is hoped that this study will provide technical parameters for the development and application of microbial immobilization carriers.