Problem Of Wastewater Treatment Research Articles

Innovative synthesis of ternary heterojunction CuInS2/BiOI/Bi2MoO6 for 2,4-DCP degradation and its dechlorination performance

This study focuses on a novel ternary heterojunction catalyst for the removal of 2,4-dichlorophenol (2,4-DCP), an organic pollutant that is difficult to degrade. An efficient CuInS2/BiOI/Bi2MoO6 ternary heterojunction photocatalyst was formed by constructing a CuInS2/BiOI composite layer on a Bi2MoO6 substrate using an in-situ growth technique. The microstructure and photoelectric conversion properties of the catalysts were comprehensively resolved by systematic material characterization, including scanning electron microscopy (SEM) observation, X-ray photoelectron spectroscopy (XPS) analysis and photoelectrochemical testing. The experimental results showed that the optimized catalyst at a loading of 2.0 g/L exhibited excellent photocatalytic degradation efficiency against 20 mg/L concentration of 2,4-DCP at neutral pH, reaching 80.3 % degradation rate in 120 min. This high performance was mainly attributed to the enhanced charge-carrier separation mechanism at the heterojunction interface, which effectively enhanced the utilization and transfer rate of photogenerated electron-hole pairs and enhanced the photocatalytic activity of the catalyst. In addition, the study also deeply explored the conversion pathway of elemental chlorine in the photocatalytic system, elucidated the mechanism of 2,4-DCP degradation and dechlorination, and provided a theoretical basis for further improving the environmental adaptability and dechlorination efficiency of the catalyst. Overall, the CuInS2/BiOI/Bi2MoO6 ternary heterojunction photocatalysts proposed in this study demonstrate a broad application prospect in the purification of 2,4-DCP and other organic pollutants, and open up a new way to solve the problems of industrial wastewater treatment, which is of great environmental significance and scientific value.

Prediction of Biochar Adsorption of Uranium in Wastewater and Inversion of Key Influencing Parameters Based on Ensemble Learning.

With the rapid development of industrialization, the problem of heavy metal wastewater treatment has become increasingly serious, posing a serious threat to the environment and human health. Biochar shows great potential for application in the field of wastewater treatment; however, biochars prepared from different biomass sources and experimental conditions have different physicochemical properties, resulting in differences in their adsorption capacity for uranium, which limits their wide application in wastewater treatment. Therefore, there is an urgent need to deeply explore and optimize the key parameter settings of biochar to significantly improve its adsorption capacity. This paper combines the nonlinear mapping capability of SCN and the ensemble learning advantage of the Adaboost algorithm based on existing experimental data on wastewater treatment. The accuracy of the model is evaluated by metrics such as coefficient of determination (R2) and error rate. It was found that the Adaboost-SCN model showed significant advantages in terms of prediction accuracy, precision, model stability and generalization ability compared to the SCN model alone. In order to further improve the performance of the model, this paper combined Adaboost-SCN with maximum information coefficient (MIC), random forest (RF) and energy valley optimizer (EVO) feature selection methods to construct three models, namely, MIC-Adaboost-SCN, RF-Adaboost-SCN and EVO-Adaboost-SCN. The results show that the prediction model with added feature selection is significantly better than the Adaboost-SCN model without feature selection in each evaluation index, and EVO has the most significant effect on feature selection. Finally, the correlation between biochar adsorption properties and production parameters was discussed through the inversion study of key parameters, and optimal parameter intervals were proposed to improve the adsorption properties. Providing strong support for the wide application of biochar in the field of wastewater treatment helps to solve the urgent environmental problem of heavy metal wastewater treatment.

Decolorization of Textile Dyes by Extracellular Enzymes Produced from Trametes sanguinea and Perenniporia taephropora Immobilized on Natural Media

The color of textile wastewater is still a main problem in wastewater treatment by biological processes. The colored effluents from textile factories usually exceed effluent standards. Therefore, various innovations were developed to treat textile wastewater for decolorization in the effluents. This research aims to decolorize textile wastewater by immobilizing white rot fungi degradation. At first, the 11 fungal stains were tested to find the decolorized efficiency then the high decolorized efficiency fungal stains were immobilized on four material media, namely water hyacinth stalks, coconut husk, corn cob, and loofah. After that, the immobilized fungi were cultivated in the culture media at 30, 60, and 120 C/N ratios, respectively. The results showed that Trametes sanguinea and Perenniporia tephropora were two stains with a high decolorized efficiency of 68.8% and 67.5% respectively, and the decolorized efficiency was increased when immobilized on loofahs and fed with 120 C/N ratio medium. In a comparison of two fungal stains, P. tephropora was found more suitable for the decolorization of textile wastewater than T. sanguinea because T. sanguinea could produce red-orange pigments that induced the colored enhancement in wastewater over time. Finally, immobilized P. tephropora was cultivated in a 120 C/N ratio medium within a 10 L continuous stirred tank reactor (8 L working volume) to investigate the decolorized efficiency, enzymatic activity, and repeated batch. It was found that three repeated cycles were carried out by reusing the immobilized P. tephropora and the highest decolorized efficiency was 63.4%. The enzymatic activity of laccase, manganese peroxidase, and lignin peroxidase was 15.5 U/L, 85.9 U/L, and 0 U/L, respectively

Role of nanocomposites and nano adsorbents for heavy metals removal and dyes. An overview

Water scarcity and wastewater treatment are major concerns due to increased urbanization, industrialization, and anthropogenic practices. Various toxic heavy metals, dyes, pollutants, and chemicals are a matter of concern as they have severe environmental and ecological damage and health effects. Various advancements are being introduced in the field of adsorption using nano adsorbents and composites to deal with wastewater treatment problems. Nanocomposites are intelligent to eliminate bacteria, viruses, and inorganic and organic pollutants from wastewater due to precise binding action (chelation, absorption, ion exchange). Nanocomposite materials, such as metal nanocomposite, metal oxide nanocomposite, carbon nanocomposite, polymer nanocomposite, and membrane nanocomposite, are active in water purification. Nanoparticles (N.P.s) are important for remediation because of their large surface area, size, reactivity, and active sites. For high adsorption of pollutants, N.P.s were treated by increasing the electron density and surface area and adding functional groups. They are more capable of eliminating hazardous organic-inorganic pollutants, pathogens, and heavy metals from wastewater. This nanotechnology treatment technique has no hazardous by-products; these techniques have various regenerative efficiencies. Among various treatment methods, the adsorption process is considered one of the most highly effective treatments of heavy metals, and the functionalization of adsorbents can fully enhance the adsorption process. Therefore, four adsorbent sources are highlighted: polymeric, natural mineral, industrial by-product, and carbon nanomaterial adsorbent. The major purpose of this review is to gather up-to-date information on research and development on various adsorbents in the treatment of heavy metal and dyes from water by emphasizing the adsorption capability, the effect of pH, isotherm and kinetic model, removal efficiency, and the contact of time of every adsorbent.

Constructing superhydrophilic/superhydrophobic Janus membrane assisted by dual-interface-confined strategy for on-demand oil-in-water and water-in-oil emulsions separation

Janus membranes with asymmetric wettability have attracted much attention because they can solve the problem that a single wettable material cannot effectively separate complex oil/water emulsions. Here, a dual-interface-confined strategy combining single-side interface-confined floating and single-side interface-confined spraying methods is provided to fabricate a robust Janus membrane with superwettability. The controllable single-side interface-confined floating method introduces a superior stable hydrophobic-superhydrophilic Janus interface, and the single-side interface-confined spraying method guarantees a robust superhydrophobic-superhydrophilic Janus interface. The Janus membrane featured both superhydrophilicity and superhydrophobicity with the outstanding stable interface and remarkable chemical stability could separate not only surfactant-stabilized water-in-oil emulsions by gravity alone, but also handle the surfactant-stabilized oil-in-water emulsions under low separation pressure through simple operation process. Moreover, this superwettable Janus membrane can achieve long-term on-demand oil/water emulsion separation with low flux decline and near 100% flux recovery. Overall, this work develops a new avenue for Janus membrane and provides a new application for a variety of oily wastewater treatment problems.

Enhanced Photodegradation of Methylene Blue Using Reusable Cobalt Ferrite Nanocomposites

Growing industrialization is contributing to the worsening shortage of potable water in society. Consequently, wastewater treatment and dye degradation become the foremost aim to overcome this problem. Magnetic nanoparticles (MNPs) emerged as an efficient tool to overcome the problem of wastewater treatment. Easy recovery of the MNPs reduces the operational cost of the reaction. Therefore, in the current study simple, cheap, green, and highly proficient synthesis methodology for the magnetically recoverable cobalt ferrite is reported. The X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR) confirm the crystalline structure and functional group on the synthesized nanoparticles. The elemental composition, surface morphology, and surface area were investigated by Energy-dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FESEM), and Brunauer-Emmett-Teller (BET) analysis. The Photo-Fenton process was used to check the catalytic activity of the prepared CoFe2O4 nanoparticles (NPs). The effect of the various experimental parameters like pH (3–9), catalyst dosage (50–200 mg/L), H2O2 dosage (5–20 mM), and varied dye (methylene blue) concentration (0.05–0.2 mM) on catalytic performance were studied. According to this investigation, 90% degradation of the methylene blue was achieved in just 90 minutes using the assynthesized catalyst. The catalyst showed 76.91% of the dye degradation even after 4 consecutive cycles; it suggests the admirable stability of the catalyst during the reaction. The robustness of the CoFe2O4 NPs makes it potential candidate for the waste water treatment.

Sustainable sewage water treatment based on natural plant coagulant: Moringa oleifera

In response to global water scarcity and environmental degradation, one promising technique in natural plant coagulation that has gained attention in recent years is the use of Moringa oleifera a plant native to the Indian subcontinent. This study investigates the potential of Moringa oleifera as a sustainable solution for sewage water treatment. The problem of effective wastewater treatment was addressed by employing Moringa oleifera as a natural plant coagulant (NPC). The methodology involved the use of a jar test as a qualitative technique in coagulation and flocculation to assess the plant’s effectiveness in reducing turbidity and impurities in sewage water. The physical and chemical parameters of raw and treated water were analyzed, revealing that an optimum dose of 0.4 g/1000 mL resulted in significant reductions in various water quality parameters: turbidity by 92%, COD by 88%, total solids by 96%, chloride by 75%, total hardness by 74%, and inorganic phosphorous by 68%. The specific reduction in BOD was not provided, indicating a need for further investigation. The results suggest that Moringa oleifera could offer significant improvements in water quality and societal health while promoting sustainability and environmental harmony. The study concludes that Moringa oleifera presents a promising green technique for sustainable sewage water treatment, with implications for future research focusing on the scalability of this method and its effectiveness in treating different types of wastewater.

Study on the preparation and performance of PVDF/SMA/CdS Fenton-like membrane with both separation and dye degradation functions

Nowadays, the discharge of wastewater causes serious environmental pollution, affecting the living environment and the health of human beings. So the problem of wastewater treatment is imminent. In this context, the PVDF/SMA/CdS membranes had oil-water separation and dye degradation effects were prepared by using non-solvent phase transition and in-situ deposition methods. Its separation efficiency reached more than 98%, and the oil-water removal rate was at more than 90% after 5 times of recycling. Under visible light irradiation, it could completely degrade methylene blue solution (MB, 10 mg·L-1, pH=3) within 20 min, cochineal solution (Ponceau 4R) within 12 min, and chromium blue-black R (EBR) solution within 6 min, and the degradation rate was at more than 95% after 5 cycles. Therefore, the PVDF/SMA/CdS membrane can effectively treat wastewater. This study opens up a promising avenue for wastewater treatment technology with high potential for application.

Optimal control for both forward and backward discrete-time systems

Forward discrete-time systems use past information to update the current state, while backward discrete-time systems use future information to update the current state. This study focuses on optimal control problems within the context of forward and backward discrete-time systems. We begin by investigating a general optimal control problem for both forward and backward discrete-time systems. Leveraging the inherent properties of these systems and the Bellman optimality principle, we derive recursive equations as a means to solve such optimal control problems. Using these recursive equations, we obtain analytical expressions for both the optimal controls and optimal values of bang–bang and linear quadratic optimal control problems. Finally, we present a numerical example and an industrial wastewater treatment problem to illustrate and demonstrate our findings.

In-situ hydrothermal synthesis of MoS2 /TiO2 nanocomposites for enhanced and stable photocatalytic performance: Methylene blue degradation pathway and mechanism

BackgroundIn recent years, nanocomposite photocatalytic has become more and more attractive and important since it has a great potential to contribute to such wastewater treatment and environmental problems. Pollutant dyes such as methylene blue (MB) have utilizations in manufacturing, paper, medicine and textiles. In addition, creating a Z-scheme nanocomposite illustrates a fitting approach for improving the photocatalytic performance of photocatalysts. Mott-Schottky curves demonstrate that MoS2 and TiO2 are combined to form Z-scheme nanocomposite. MethodsNovel MoS2/TiO2 nanocomposite photocatalysts were well synthesized by a simple hydrothermal process. The photodegradation intermediate products of MB dye are also identified by liquid chromatography-mass spectrometry (LC-MS) and the possible degradation pathway is proposed. Ultimately, the potential photocatalytic pathway mechanism of nanocomposites was verified according to the LC-MS analysis and trapping experiments. Significant findingsThe construction of a Z-scheme nanocomposite is a crucial factor in improving the photocatalytic activity of heterojunction photocatalysts. MoS2/TiO2 nanocomposites had photocatalytic activity within 120 min irradiation to visible light and achieved 98.5 % of MB. A stable heterostructure has been effort designed using MoS2/TiO2 with improved electron and hole migration. The photodegradation performance for MoS2/TiO2 is 3.8 folds that the bare photocatalysts. This nano-heterojunction significantly suppresses the recombination rate of photoexcited charge carriers and enhances the operation of solar energy. The Z-scheme nano-heterojunctions offer a potential strategy for promoting the utilization of photocatalysts in waste environmental purification and clean water.

G-C3N4 modified with non-precious metal Al with LSPR as an efficient visible light catalyst.

The issue of water pollution has emerged as a formidable challenge, prompting a pressing need for solutions. The utilization of metal nanoparticles with surface plasmon resonance and semiconductor composite photocatalysts is regarded as a highly effective approach to solve this problem. g-C3N4 is an effective catalyst for the degradation of organic pollutants. Its photocatalytic performance is usually enhanced by the use of the noble metal Au Ag. However, the high cost of these materials limits their application. In this study, we present the synthesis of Al NPs/g-C3N4 nanocomposites using the bridging effect of ligands. The characterized of transmission electron microscopy (TEM), X-ray diffractometer (XRD) and ultraviolet-visible spectroscopy (UV-Vis) proved that Al NPs/g-C3N4 with a wider light absorption range were successfully synthesized. The effects of ligands, (glutathione (GSH), glutamic acid (GAG), and cysteine (CYS)), Al diameter (40 to 200 nm) and the ratio of Al to g-C3N4 (1:1 to 5:1) on the photocatalytic degradation of methylene blue (MB) by Al NPs/g-C3N4 were also evaluated. The results showed that the optimum degradation efficiency of Al NPs/g-C3N4 for MB at 5 mg/L reached 100% within 60 min, which was 11 times higher than that of pure g-C3N4. The principal analysis of Al enhancing the photocatalytic performance of g-C3N4 was studied through transient photocurrent spectroscopy (TPC), electrochemical impedance spectroscopy (EIS), and steady-state transient fluorescence spectroscopy (PL). The results confirmed that hot carriers generated by localized surface plasmon resonance (LSPR) of Al nanoparticles increase the carrier concentration. In addition, the Schottky barrier generated by Al and g-C3N4 could also improve the carrier separation rate and increase the carrier lifetime. This work is expected to solve the problem of organic wastewater treatment and lay the foundation for subsequent research on photocatalysis.

Sustainable Water Management: An Integrated Approach to Solving the Problems of Wastewater Treatment

The relevance of the study of this problem today lies in the fact that the awareness of the lack of water resources and the threat of environmental pollution forces us to focus on the development of sustainable water management solutions. In the context of population growth, water pollution and climate change, it is necessary to respond quickly and improve wastewater treatment methods, assess their impact on the environment and improve water supply systems to ensure stable and environmentally safe access to water resources for future generations. The purpose of this article is to consider an integrated approach to solving the problems of wastewater treatment, assessing their impact on the environment, and improving the water supply system to build a sustainable water economy. Among the methods used, it should be noted the analytical method, the classification method, the functional method, the statistical method, the synthesis method, and others. Water management and environmental protection research included analysis of wastewater treatment technologies, environmental impact assessment, development of water supply systems, municipal waste management, hydrological processes, environmental pollution, use of renewable energy, risk assessment and soil erosion. The effectiveness of wastewater treatment systems, the need for technology improvement, the impact of some types of industry and agricultural activity on the environment, the need to modernize water supply systems, effective management of urban waste, conservation of water resources and prevention of soil erosion were revealed. Research results indicate the need to develop strategies and policies to preserve water resources and improve the state of the environment. This research makes a significant contribution to science, contributing to the development of sustainable water management by developing an integrated approach to solving the problems of wastewater treatment, assessing their impact on the environment, and improving the water supply system.

Flocculants as a means of environmental safety in the process of wastewater treatment from cutting fluids

In the modern conditions of steady industrial growth, the problem of wastewater treatment is becoming extremely urgent. For this purpose, special attention is paid to those substances that significantly enhance the processes of separation of impurities and precipitating substances. The article examines the efficiency of flocculants in the treatment of contaminated wastewater with liquid cutting fluids. The authors directly consider the mechanisms of action of flocculants and their influence on the physical and mechanical properties of wastewater, as well as the possibility of returning purified water to the production process. The article also provides an environmental analysis of the advantages of using flocculants, including reducing the toxicity of wastewater and minimizing the negative impact on the environment. The conclusions of the article can become the basis for improving and optimizing technological processes, as well as the introduction of safer and more effective methods of wastewater treatment in the context of modern environmental challenges.

Wastewater Management in Africa: Challenges and Recommendations.

In Africa, the growing population and industrial growth have resulted in a notable increase in wastewater generation, affecting the quality of water in the region. Wastewater treatment plays a crucial role in safeguarding the environment, public health, aquatic organisms, and water resources, reducing environmental impact, and adhering to regulations. However, the current methods for treating wastewater in Africa fall short of these goals, resulting in substantially poor environmental and health outcomes and inadequate provision of safe water and essential sanitation. Poor wastewater management in several African countries has led to severe health risks for humans, animals, and aquatic ecosystems. This poses a particular threat to vulnerable groups like children, women, and the disabled residing in rural and remote areas with limited access to healthcare. Hence, this article aims to shine a spotlight on the difficulties in managing wastewater in Africa and to recommend several plausible strategies to tackle this issue. A literature search to find the most recent and relevant research papers from various databases, such as Scopus, Web of Science, PubMed, and Google Scholar, along with resources from the World Health Organization, was conducted. The selection criteria focused on including the most recent and relevant publications published in English to facilitate comprehension, analysis, and interpretation of the secondary data. Essentially, addressing the challenge of wastewater management in Africa requires developing indigenous innovative technologies, transitioning to a sustainable economy, establishing wastewater treatment infrastructures in rural and remote areas, enhancing operation and maintenance practices, training treatment facility workers, improving electricity supply, strengthening government participation and support, encouraging public involvement, setting local water quality benchmarks, and international financial and technical support. By tackling the problem of insufficient wastewater treatment in Africa, it is possible to achieve Sustainable Development Goal 6, which centers on ensuring clean water and sanitation for all.

Sterilization and Long-Term Stability of Cobalt Intercalated MnO₂ Catalyst in the Cathode of Separator-Free Microbial Fuel Cells

Microbial Fuel Cells (MFCs) are a promising technology that can simultaneously address recent energy shortages and wastewater treatment problems for freshwater production. Recently, inexpensive Pt-free catalysts have been investigated to improve the cathode performance of MFCs. In this study, birnessite manganese oxide intercalated a cobalt (Co-MnO₂) catalyst to make the cathode sterilizable. The use of a bactericidal cathode is expected to improve output by suppressing electron transfer from microorganisms to the cathode, which is the cause of MFC performance degradation, and by eliminating the separator that limits proton transfer. The MFC with Co-MnO₂ catalyst on the cathode achieved a maximum power density of 110 μW/cm². In addition, the function of the Co-MnO₂ catalyst did not degrade for at least 158 days.

Zn2SnO4/SnO2/g-C3N4 heterojunction: High efficiency photocatalytic degradation of Rhodamine B in simulated visible light

Photocatalysis is an effective solution to wastewater treatment problems, and semiconductor heterojunctions for photocatalysis can effectively separate photogenerated carriers to improve the performance of photocatalytic degradation of pollutants. In this paper, a ternary composite photocatalyst with a heterojunction structure (Zn2SnO4/SnO2/g-C3N4) was prepared to photodegradeRhodamine B in simulated visible light. The experimental findings demonstrate that the Zn2SnO4/SnO2/g-C3N4 photodegradation rates and efficiencies for RhB are much higher than those for SnO2, g-C3N4, SnO2/g-C3N4, and Zn2SnO4/SnO2. We obtained a 3:1 mass ratio of Zn2SnO4/SnO2 to g-C3N4 by optimization, with a maximum degradation rate of 99.5 % and a maximum kinetic constant k of 0.692 min-1·g−1 for the photocatalytic removal of RhB by Zn2SnO4/SnO2/g-C3N4. The radical trapping experiments suggest the primary role of ·O2– for the photocatalytic removal of RhB. The ternary composite photocatalyst Zn2SnO4/SnO2/g-C3N4 shows promise for potential applications in RhB degradation owing to its exceptionally.

UV‐initiated preparation and absorption properties of pseudo‐polyrotaxane cyclodextrin‐based PVA/poly (acrylamide‐co‐acrylic acid) hydrogel

AbstractThe recycling of dyes from dye wastewater is one of the most challenging problems in wastewater treatment. In this study, a pseudo‐polyrotaxane cyclodextrin based PVA/poly (acrylamide‐co‐acrylic acid) hydrogel was prepared by UV‐initiated polymerization. The network structure of the hydrogel and the performance on the dye absorption were adjusted by controlling the content of cyclodextrin. The study was mainly focused on the absorption of methylene blue (MB) in different environments, selectivity of absorption in mixed solutions and the cyclic absorption behavior. At room temperature, the absorption efficiency of this hydrogel for MB and methylene green reached 91.37% and 94.23%, respectively. In addition, the hydrogel exhibited highly selective absorption towards MB in mixed dye solutions. In the absorption‐desorption cyclic experiments, a more cost‐effective and environmental friendly solvent, a mixture of ethanol and water, was used, and after ten cycles, the highest absorption efficiency was basically maintained. Hence, the hydrogel is expected to be a candidate for more efficient and economical absorbent material in dye wastewater treatment.

Study on sewage characteristics in rural China and pollutants removal performance of biologically enhanced internal circulation treatment system

With rapid economic development and urbanization in China, rural wastewater treatment has become an important issue. This study investigated 63 rural sewage treatment stations in northern, central and southern Shaanxi, China for a 1-year period, 2021 to 2022. The main purpose of the research was to investigate the quality and discharge characteristics of rural sewage, along with current problems in rural wastewater treatment, in order to provide evidence for the optimal construction and operation of rural sewage treatment stations. We found that the biodegradability of rural wastewater is adequate, and BOD5/COD ratio in sewage was 0.4, which is suitable for biological treatment. It has obvious intermittent flow cut-off characteristics, and the range of cut-off duration of sewage was 6–16 h/d, which leads to poor pollutant removal efficiency (COD: 50.0 ± 29.2%, NH4+-N: 46.0 ± 26.1%, TN: 38.5 ± 24.9% and TP: 38.3 ± 23.8%) in sewage treatment stations. In response to the above characteristics, the rural sewage biologically enhanced internal circulation treatment (BEICT) system was constructed. After 97 days of operation, the system has a stable removal effect on TN and TP with an average removal rate of 77.42% and 89.69%, respectively, under the condition of influent interruption for 12 h per day. The activated sludge of system maintained good activity and stable sedimentation performance during the whole experiment, with MLVSS/MLSS and SVI of 0.72 and 128 mL/g, respectively. This study can provide the basis and technical support for the accurate design of rural sewage treatment facilities, and has important significance for guiding the treatment of rural domestic sewage in China.

MICROBIAL BIOREMOVAL OF DIVALENT TOXIC METALS

The problems of polymetallic wastewater treatment from mining enterprises as well as the accumulation of organic waste are acute worldwide. The application of any existing methods of wastewater purification is ineffective and impossible due to the huge volumes and high concentrations of metals. Similarly, modern methods are ineffective for the treatment of huge amounts of organic waste. Therefore, there is a necessity to develop novel environmental biotechnologies providing the simultaneous degradation of organic waste and detoxification of toxic metals. The purpose of the work was to theoretically substantiate and experimentally confirm the possibility of toxic divalent cations removal using dissimilatory sulfate reduction via anaerobic fermentation of ecologically hazardous model organic waste. Colorimetric and potentiometric methods were used for pH and redox potential measurement; volumetric and chromatographic methods – to control volume and composition of synthesized gas; permanganate method – to determine the concentration of dissolved organic carbon (DOC); photocolorimetric method via the qualitative reaction with Nessler’s reagent was used to determine the concentration of ammonium ions. The Co2+ and Ni2+ content in medium was determined by a colorimetric method with 4-(2-pyridylazo)resorcinol (PAR). Fermentation parameters were calculated with the use of mathematical and statistical ones. Modified Postgate B medium with different sources of carbon and energy (potatoes, alanine, and meat) was used for cultivation of dissimilatory sulfate reducing bacteria. The anaerobic microbiome obtained from the sludge of methane tanks showed high efficiency to remove Co2+ and Ni2+ from the liquid medium. The highest efficiency (100% in 9 days) was observed when alanine was used as a source of carbon and energy. The slowest metal precipitation process occurred using meat (20 days). Also, the use of a protein substrate did not provide the expected alkalinization of the medium, which could significantly accelerate the process of metal precipitation. The precipitation of cobalt and nickel cations during the hydrogen fermentation of potato starch was complicated by acidification of the medium, but it was equally effective when the pH was adjusted. The proposed approach, the slow dissimilatory sulfate reduction, due to the sparingly soluble calcium sulfate as electron acceptor, can be used as a basis for the development of new biotechnologies for the treatment of wastewater contaminated with divalent heavy metals with the simultaneous treatment of ecologically hazardous compounds.

Green synthesis of graphene-oxide based nanocomposites for efficient removal of methylene blue dye from wastewater

Water-soluble dyes are a common problem in wastewater treatment, requiring highly efficient methods for removal. In this study, novel sustainable adsorbents made from graphene-oxide (GO) and other materials, such as eggshell-derived calcium oxide nanoparticles (CaONPs-ES), fish bone calcium oxide nanoparticles (CaONPs-FB), and durian shell activated carbon (DSAC) were synthesized, characterized, and demonstrated for soluble dye removal from wastewater. Fermented maize grain extract (MES) was used as a green cross-linker in the synthesis process. The resulting nanocomposites, GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC, showed promising adsorption capabilities for methylene blue (MB) dye removal from aqueous environments. The prepared nanocomposites (GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC) were characterize using state-of-art instrumental techniques. The BET measurement revealed that the nanocomposites surface areas were enhanced due to the cross-linking phenomenon, improving their adsorption capability towards MB dye treatment. The adsorption data of GO@CaONPs-FB/DSAC and GO@CaONPs-ES/DSAC was well fitted to the Harkins-Jura and Freundlich models, respectively. The maximum sorption capacities of GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC were 1274.5 and 689.7 mg/g, respectively. The MB dye removal mechanism was driven by π-π interaction, hydrogen bonding, electrostatic attraction and physical interactions and the adsorption process of the nanocomposites followed pseudo-second-order kinetics. The adsorptive performance of the nanocomposites was stable, showing ∼96.45 % and ∼85.18 % after 10 successive cycles for GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC respectively. Cost evaluation revealed that bulk synthesis of GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC nanocomposites is cost-effective for treating large quantities of MB contaminated water and other potential dyes as well. Finally, the independent and synergetic contributions between pH, adsorbent dosage and temperature on MB removal by GO@CaONPs-ES/DSAC and GO@CaONPs-FB/DSAC were studied and optimized by central composite design (CCD) an aspect of the response surface methodology (RSM). Finally, this study suggests that the novel green cross-linking approach has a significant impact in enhancing the adsorptive performances of the developed nanocomposites to effectively capture MB from aqueous environment.