Industrial wastewater treatment: Current trends, bottlenecks, and best practices

Efficient activation of peroxymonosulfate for catalytic degradation of organic pollutants by simultaneously using low-level cobalt ions and calcium carbonate micro-particles

An efficient catalytic system was developed to remove various organic pollutants by simultaneously using low-level cobalt ions, calcium carbonate micro-particles and peroxymonosulfate (PMS). A simple base-induced precipitation was used to successfully loaded Co-centered reactive sites onto the surface of CaCO3 microparticles. Under optimal conditions at 25 °C, 10 mg/L methylene blue (MB) could be completely degraded within 10 min with 480 µg/L Co2+, 0.4 g/L CaCO3 microparticles (or 0.4 g/L Co@CaCO3) and 0.1 g/L PMS. The MB degradation followed the pseudo first order kinetics with a rate constant of 0.583 min-1, being 8.3, 11.5 and 53.0 times that by using Co-OH (0.07 min-1), Co2+ (0.044 min-1) and CaCO3 (0.011 min-1) as the catalyst, respectively. It was confirmed that there was a synergistic effect in the catalytic activity between Co species and the CaCO3 particles but the major contributor was the highly dispersed Co species. When Co2+-containing simulated electroplating wastewater was used as the Co2+ source, not only the added MB was also completely degraded within 5 min in this catalytic system, but also the coexisting heavy metal ions were substantially removed. The presently developed method was applied to simultaneously treat organic wastewater and heavy metals wastewater. The present method was also successfully used to efficiently degrade other organic pollutants including bisphenol A, sulfamethoxazole, rhodamine B, tetrabromobisphenol A, ofloxacin and benzoic acid. A catalytic mechanism was proposed for the PMS activation by Co@CaCO3. The surface of CaCO3 particles favors the adsorption of Co2+. More importantly, the surface of CaCO3 particles provides plentiful surface -OH and -CO32+, and these surface groups complex with Co2+ to produce more catalytically active species such as surface [CoOH]-, resulting in rapid Co2+/Co3+ cycling and electron transfer. These interactions cause the observed synergistic effect between Co species and CaCO3 particles in PMS activation. Due to good cycle stability, strong anti-interference ability and wide universality, the new method will have broad application prospects.

Recent advancements in the synthesis of anion exchange membranes and their potential applications in wastewater treatment

Water treatment procedures are increasingly utilized for resource recovery and wastewater disinfection, addressing the current challenges of clean water depletion and wastewater management. Various pollutants, including dyes, acids, pharmaceuticals, and toxic heavy metals have been released into the environment through industrial, domestic, and agricultural activities, posing serious environmental and public health risks. Addressing these issues requires the development of more effective waste treatment processes. Membrane-based treatment technologies offer significant advantages, including high efficiency, versatility, and cost-effectiveness, making them a promising solution for mitigating the impact of these pollutants. In view of this, the potential of ion exchange membranes (IEMs) is continuously increasing due to their advanced characteristics compared to conventional techniques. Anion exchange membranes (AEMs), a special class of IEMs, selectively allow anions to pass through their pores due to the positive charge on their surface. This selective passage aids in resource recovery and removing specific types of pollutants. This review covers preparation methods, modification techniques, and classification of AEMs. It offers a practical classification based on the method of synthesis and structural properties of AEMs. The water-based applications of AEMs including, electrodialysis, diffusion dialysis, and electro-electrodialysis for various wastewater treatments such as heavy metal recovery, dye removal, pharmaceutical removal, and acid separation, have been discussed in detail. Additionally, the effect of various operational parameters on the performance and SWOT (strengths, weaknesses, opportunities, and threats) analysis of AEMs in effluent treatment are presented. The review provides detailed insights into the current status, challenges, and future directions of AEM-based technologies, offering suggestions for future advancements.

Study of methylene blue removal and photocatalytic degradation on zirconia thin films modified with Mn-Anderson polyoxometalates

Recalcitrant pollutants are challenging to degrade during water treatment processes. Methylene blue (MB), a cationic dye, is particularly resistant to degradation and is environmentally persistent. Heterogeneous photocatalysis has emerged as a suitable strategy for removing such pollutants from water. In this work, ZrO2 thin films were modified with Anderson-type Mn-polyoxometalate (MnPOM) ((NH4)3[MnMo6O24H6]), and the efficiency of MB removal from water was studied. ZrO2 was synthesized by a sol-gel method, with thin films deposited using the doctor blade method, and ZrO2 thin films were modified using chemisorption method. The synthesized materials were characterized using SEM, EDX, UV-Vis diffuse reflectance spectroscopy and FTIR. The adsorption kinetics and isotherms for MB were studied for both bare ZrO2 and ZrO2/MnPOM composites. Optical characterization showed a band gap energy of 4.02 eV for bare ZrO2, while the ZrO2/MnPOM composite exhibited a band gap of 3.7 eV. Furthermore, ZrO2 showed lower MB removal capacity (∼8%) than ZrO2/MnPOM thin films (∼29%). The isothermal adsorption studies indicated that MB adsorption onto both bare ZrO2 and ZrO2/MnPOM followed the Langmuir adsorption model (qm = 20.6 mg g-1 for ZrO2 and qm = 62.9 mg g-1 for ZrO2/MnPOM). Furthermore, the adsorption kinetics of MB were well described by a pseudo-second-order model. Photocatalytic testing under UV irradiation showed an apparent rate constant (kap) of 2 × 10-3 min-1 for bare ZrO2 and a value of kap 5.4 × 10-3 min-1 for ZrO2/MnPOM after 100 minutes. TD-DFT calculations revealed an LMCT interaction between the ZrO2 nanoparticle and the MnPOM, which likely contributes to the enhanced photocatalytic activity of the ZrO2/MnPOM composite.

Comparative analysis of heavy metals toxicity in drinking water of selected industrial zones in Gujranwala, Pakistan

Heavy metal contamination of drinking water, primarily driven by industrial activities, represents a critical challenge, with implications for human health and environmental safety. Gujranwala is an industrial and thickly populated city. The current study aimed to assess and compare heavy metal contamination levels in drinking water from five industrial areas and evaluate their potential impacts on human health. Total 100 water samples were collected and analysed for physicochemical parameters and heavy metals. Zonal variations in heavy metal concentrations revealed that Zone 2 had the highest mean levels of cadmium (0.331 mg/L), lead (0.573 mg/L), chromium (0.164 mg/L), arsenic (0.042 mg/L), and aluminium (0.484 mg/L), while Zone 4 showed elevated mean levels of iron (1.88 mg/L) and mercury (0.259 mg/L). Spearman correlation analysis among heavy metals revealed positive relationships among several heavy metals with As notably showing a strong correlation with Hg (0.701**). Kruskal-Wallis test revealed significant spatial variation (p < 0.05) in parameters like pH, EC, TDS, and heavy metals (Cd, Pb, Fe, Cu, Mn, Al), indicating spatial heterogeneity across zones. Spatial distribution maps also depicted heavy metal elevated concentrations of Cd, Pb, Fe, Cr, As, and Hg exceeding in Zone 2 (Engineering industries zone) and 4 (Iron and steel industries zone). The findings revealed a strong link between elevated heavy metal levels and health risks, including dermatological, respiratory, gastrointestinal, and neurological disorders. This study highlights the need for stricter wastewater management, regular monitoring of drinking water, and policies to address water toxicity in industrial premises and to protect public health.

The impact of wastewater treatment plants on the composition and toxicity of pollutants in urban rivers in Nanjing, China

Widespread wastewater pollution is one of the biggest challenges threatening the ecological health of rivers. It is crucial to identify the toxic changes of effluents after entering urban rivers as well as the toxic substances in the complex chemical mixtures found in these urban rivers. This study used HepG2 cell line for cytotoxicity test to evaluate the ecological impact of effluents on urban rivers. Water samples were collected from the Xingwu River and Yunliang River in Nanjing, China. The bacterial communities in the lower reaches of urban rivers were altered due to the differences in total nitrogen and nitrate nitrogen. The complex chemical mixtures collected in the urban rivers were divided into 10 fractions, >100 chemicals were screened in each fraction. The substances with LC50 < 1000 mg/L were listed as toxic substances, and the number of toxic substances dominated the toxicity of urban rivers. Our study highlights toxicity as a comprehensive indicator for assessing river pollutants and reveals relationship between the number of toxic substance and river toxicity. These findings have direct implications for the monitoring and management of environmental stressors and the protection of aquatic organisms and human health.

Towards planetary boundary sustainability of food processing wastewater, by resource recovery & emission reduction: A process system engineering perspective

Meeting the needs of a growing population calls for a change from linear production systems that exacerbate the depletion of finite natural resources and the emission of environmental pollutants. These linear production systems have resulted in the human-driven perturbation of the Earth's natural biogeochemical cycles and the transgression of environmentally safe operating limits. One solution that can help alleviate the environmental issues associated both with resource stress and harmful emissions is resource recovery from waste. In this review, we address the recovery of resources from food and beverage processing wastewater (FPWW), which offers a synergistic solution to some of the environmental issues with traditional food production. Research on resource recovery from FPWW typically focuses on technologies to recover specific resources without considering integrative process systems to recover multiple resources while simultaneously satisfying regulations on final effluent quality. Process Systems Engineering (PSE) offers methodologies able to address this holistic process design problem, including modelling the trade-offs between competing objectives. Optimisation of FPWW treatment and resource recovery has significant scope to reduce the environmental impacts of food production systems. There is significant potential to recover carbon, nitrogen, and phosphorus resources while respecting effluent quality limits, even when the significant uncertainties inherent to wastewater systems are considered. This review article gives an overview of the environmental challenges we face, discussed within the framework of the planetary boundary, and highlights the impacts caused by the agri-food sector. This paper also presents a comprehensive review of the characteristics of FPWW and available technologies to recover carbon and nutrient resources from wastewater streams with a particular focus on bioprocesses. PSE research and modelling advances are discussed in this review. Based on this discussion, we conclude the article with future research directions.

Effect of inorganic component of biochar on lead adsorption performance and the enhancement by MgO modification

Biomass-derived biochar has enormous potential for sustainable and low-cost treatment of lead-contained wastewater. In this study, corncob and cow dung-derived biochar were prepared. The increase in pyrolysis temperature could improve the porous structures, surface area, functional groups and alkalinity, and further provide a higher Pb2+ capacity in both biochars. Cow dung biochar performed better than corncob for its higher inorganic mineral content and more alkaline surface. Among them, CDB-600 performed the Langmuir maximum capacity of 357.1 mg/g, with a high surface area of 144.3 m2/g; ion exchange and precipitate were the main adsorption mechanisms. After further MgO modification, the M-CDB displayed a high surface area of 166 m2/g, and ion exchangeability and precipitate-promoting effects were improved. M-CDB performed a Langmuir maximum capacity of 833.3 mg/g. The pHpzc was found to be 10 and the adsorbents portray a very good Pb2+ adsorption selectivity among coexisting ions in the solution. The adsorption process was found to be endothermic, feasible, spontaneous and chemisorption. The fixed lead on CDB-600 was stable in water. The immobilized lead could be desorbed by acid wash. CDB-600 performed better in terms of sustainability in use, which could support its continuous application ability.

Associative analysis of sludge microbiota and wastewater degradation efficacy within swine farm sludge systems

Industrial wastewater management is a significant global challenge. Sludge microbiota from swine farms may play a crucial role in enhancing wastewater treatment processes, thereby reducing water pollution from industrial activities. A deeper understanding of this complex community could lead to innovative approaches for improving wastewater treatment methods. Sludge samples were collected from the anaerobic, sedimentation, and thickening tanks of ten swine farms. The microbiota communities were analyzed using 16S rRNA full-length sequencing on the PacBio platform, with subsequent data analysis conducted on the QIIME2 platform utilizing the SILVA database. Compared to anaerobic and thickening tanks, the sedimentation tanks exhibited a unique profile of sludge microbiota, with higher abundances of the phyla Proteobacteria, Bacteroidota, and Caldatribacteriota. Additionally, sludges from farms already utilized in processing industrial water-specifically farms B, G, and J-contained higher concentrations of bacteria (>20 ng/μL), indicating the robustness of the bacterial load for practical industrial use. Furthermore, sludge from farms with higher alpha diversity, such as E, G, I, and J, exhibited enriched degradation profiles, including the degradation of aromatic compounds, polymers, industrial compounds, toluene, and vanillin. The farms were categorized based on wastewater ammonia nitrogen degradation levels, revealing a clustering effect of the microbiota from the sedimentation tanks in the Principal Coordinates Analysis (PCoA) plot. A higher relative abundance of the families Rhodocyclaceae, AKYH767, and Comamonadaceae, and a lower abundance of the families Anaerolineaceae and Christensenellaceae, were found in groups with high ammonia nitrogen reduction, suggesting potential targets for bioaugmentation strategies. In conclusion, this study underscores the critical role of microbial abundance, composition, and biodiversity in optimizing wastewater treatment and advocates for comprehensive microbiota analysis to identify suitable sludge for industrial applications.

Pre-treatment of composite industrial wastewater by Fenton and electro-Fenton oxidation processes

The present study aims to characterize three industrial wastewater samples collected from petrochemical, food and beet sugar industries to determine the pollution potential and select the appropriate pre-treatment approach. According to the biodegradability profile of the multi-sourced mixed (composite) sample, the advanced oxidation process (AOPs) namely, Fenton (F) and Electro-Fenton (EF) were adopted as pre-treatment techniques and the operating parameters such as time, type of electrodes, pH, voltage, iron and H2O2 concentrations were critically examined. Analysis of Variance (ANOVA) was conducted to compare the performance efficiency of F& EF AOPs for treating the composite samples and the total operating costs for both approaches were assessed. The results revealed that, the initial values of the composite sample were 7.11, 19.2, 32.6, 19.3, 937, 1512, 860, 3.9, 2110 and 2.34 for pH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), Salinity, BOD, COD, Oil and grease (O&G), Total Phosphorous (TP), Total Suspended Solids (TSS) and Total Kjeldahl Nitrogen (TKN), respectively. In addition, EF process achieved more removal efficiency for COD, O&G, BOD, TSS, and TKN (84.3%, 69%, 85%, 72% and 71.27%) compared to Fenton which displayed 78.43%, 66%, 69%, 70.1%, and 61%, respectively. Moreover, there are statistically significant differences (p < 0.05) between the initial and final (pretreated) values of the composite industrial wastewater for the addressed parameters and EF was significantly (p < 0.05) more effective than F process. The total operating costs were 3.117 and 2.063$ for F and EF, respectively, which confirmed that EF is more efficient and cost effective than F process. It was concluded that electro-Fenton process is favorable, eco-friendly and cost-effective option for pretreating real complicated multi-sourced industrial wastewater. The present study demonstrated a new avenue for achieving efficient management of industrial wastewater generated from similar industries.

Progress and challenges in the use of electrochemical oxidation and reduction processes for heavy metals removal and recovery from wastewaters

Heavy metals-laden industrial wastewater represents both a threat to ecosystems and human health and, in some instances, a potential source of valuable metals however the presence of organic ligands that bind the metals in heavy metal complexes (HMCs) renders metal removal (and, where appropriate, recovery) difficult. Electrochemical-based oxidation and reduction processes represent a potentially promising means of degrading the organic ligands and reducing their ability to retain the metals in solution. In this state-of-the-art review, we provide a comprehensive overview of the current status on use of electrochemical redox technologies for organic ligand degradation and subsequent heavy metal removal and recovery from industrial wastewaters. The principles and degradation mechanism of common organic ligands by various types of electrochemical redox technologies are discussed in this review and consideration given to recent progress in electrode materials synthesis, cell architecture, and operation of electrochemical redox systems. Furthermore, we highlight the current challenges in application of electrochemical redox technologies for treatment of HMC-containing wastewaters including (i) limited understanding of the chemical composition of industrial wastewaters, (ii) constrained mass transfer process affecting the direct/indirect electron transfer, (iii) absence of approaches to convert recovered metal into high-value-added products, and (iv) restricted semi-or full-industrial-scale application of these technologies. Potential strategies for improvement are accordingly provided to guide efforts in addressing these challenges in future research.

Refining habitat selection for sulfate-reducing bacteria: Evaluating suitability and adaptability for sulfate-metal wastewater treatment during anaerobic-to-aerobic transitions

Inoculating sulfate-reducing bacteria (SRB) habitats offers an eco-friendly method for treating sulfate-metal laden wastewater, characterized by high sulfate levels, low pH, and elevated heavy metals. This study optimizes source habitat selection of SRB by evaluating groundwater, sewage sludge, and lake sediment, focusing on their suitability and adaptability to aerobic-anaerobic transitions in industrial settings. Sewage sludge, with its slightly acidic pH, reducing environment, and high nutrient levels (Total organic carbon: 207.53 g kg-1, Total nitrogen: 47.12 g kg-1), provides robust SRB potential, as supported by its highest diversity index. However, heavy metals and polycyclic aromatic hydrocarbons pose application challenges. All habitats effectively reduced metal concentrations anaerobically, with Cu removal reaching 95%-99%, and groundwater achieved the highest chemical oxygen demand reduction (63.6%) aerobically. Sludge and sediment showed high biomass and extracellular polymeric substances (EPS) accumulation, while groundwater's nucleic acid-rich EPS enhanced metal immobilization, resulting in stable residual metal forms but with potential remobilization under oxidative conditions. Microbial analysis revealed that Proteobacteria and Firmicutes were key players during transitions, with the highest SRB abundance in groundwater. SRB composition varied across habitats, with Sedimentibacter (13.04%), Desulfovibrio (6.33%), and Desulfomonile (8.1%) dominating in groundwater, sludge, and sediment, respectively, during the anaerobic stage. Functional analysis highlighted sludge's persistence in sulfate reduction under aerobic conditions, while groundwater's limited nitrogen cycle involvement indicated broader biogeochemical limitations. Collectively, these findings highlight strengths and limitations of each habitat as SRB inoculum source, emphasizing the importance of tailored anaerobic-to-aerobic strategies for effective wastewater management.

Environmental effects and spatial inequalities of paddy field utilization are increasing in China

Understanding the spatiotemporal dynamics of the environmental effects associated with paddy field utilization (PFU) is imperative for safeguarding the availability of food while preserving the environment. While thorough investigations have been carried out on the individual environmental effects of PFU, study on comprehensive environmental effects of PFU and the spatial inequity issues stemming from the transfer of these effects are scarce. This study aims to quantify the greenhouse gas emissions (GHGE), nitrogen emissions (NE), and water consumption (WC) linked to PFU in China from 2000 to 2020. Additionally, it evaluates the transference of environmental effects through the inter-provincial rice flow and examines the resultant spatial inequity issues. The intensity of GHGE has demonstrated a consistent increase, while the intensity of NE has shown a fluctuating yet generally decreasing trend. Provinces with high water footprints are predominantly located in the northern regions. Specifically, GHGE increased by 3.54 Mt, primarily due to intensified agricultural inputs. NE decreased by 0.08 Mt, largely influenced by the enforcement of sustainable agricultural practices. WC escalated by 3.49 billion m3, chiefly as a result of heightened groundwater dependence. Significant increases in environmental effects were observed in Northeast China Plain (NECP) and Middle-lower Yangtze Plain (MLYP), whereas Yunnan-Guizhou Plateau (YGP), Southern China (SC), and Sichuan Basin and surrounding regions (SBSR) experienced reductions. The volume of inter-provincial rice flow initially surged before witnessing a decline, with a net increase of 15.59 Mt in rice outflow from NECP. The transferred volumes of GHGE, NE, and WC within China surged by 123.87%, 105.26%, and 119.05%, respectively. Huang-Huai-Hai Plain (HHHP) and SC emerged as principal outflows of environmental effects, while MLYP and NECP became the main inflows, exacerbating regional environmental disparities. Lorenz curves for GHGE, NE, and WC indicate a growing deviation from the line of absolute equality, highlighting a substantial increase in spatial inequality regarding the environmental effects of PFU in China. Moving forward, it is crucial to optimize PFU and rice flow patterns to mitigate the specific regional environmental effects, enhance the spatial efficiency of rice production, and promote spatial equity in environmental effects.

Efficient Elimination of Inorganic/Organic Pollutants by Fe3O4/biochar@sodium Alginate Gel Beads

The magnetic composite gel bead (Fe3O4-C@SA GB) adsorbent was prepared by sodium alginate (SA) crosslinking with pitaya peel-derived porous carbons (PPDPCs) and magnetic iron oxide nanoparticles (Fe3O4 NPs). The adsorption effects of Fe3O4-C@SA GBs on heavy metal ions (HMIs) and 17 β-estradiol (E2) in water are evaluated by classical kinetic models and isotherm models. The pseudo-second-order kinetic model shows that Fe3O4-C@SA GBs have maximum adsorption capacities of 9.62, 7.50, and 13.61 mg/g for Cu (II), Cd (II), and Pb (II), respectively. Meanwhile, the highest adsorption performance of the synthesized gel beads to E2 is of ca. 276.3 mg/g. In addition, the Fe3O4-C@SA GBs can still maintain a high level of adsorption efficiency after five adsorption cycles, displaying economic efficiency and reusability. Hence, this work provides useful insights into the efficient adsorption elimination of pollutants in sewage and the corresponding adsorption mechanisms.

Effectiveness of constructed wetland technology-treated industrial wastewater on the spinach (Spinacia oleracea) health risks and biochar efficiency

In peri-urban areas, use of industrial wastewater for irrigation is a common practice. Industrial wastewater contains cadmium, chromium, lead, nickel, and other elements that deteriorate food quality and affect human health. Biochar has been proven to remediate heavy metal contaminated soil by reducing their mobility and bioavailability. A pot experiment was conducted to evaluate the efficiency of different levels of biochar on spinach growth with low heavy metal concentration and to minimize associated health issues. The experiment lasted two months and the treatments: Control (tap water), untreated and treated industrial wastewater and both in combination with biochar (0.5% and 1%) were applied in completely randomized design. Findings suggested that treated industrial wastewater with 1% biochar resulted in maximum plant height, shoot weight, chlorophyll contents (SPAD value), photosynthetic and transpiration rate. Biochar significantly reduced heavy metal mobility in soil due to its porous structure, high pH, higher CEC, and variety of surface functional groups. The cumulative hazard index (HI), hazard quotient, cancer risk, and total cancer risk (TCR) were calculated using method provided by US-EPA for each metal. All treatments had HI values of < 1, however applying 1% biochar significantly reduced the HI values to 2.00E-01 and 2.88E-01 in adults and children, respectively. TCR for all treatments was < 1, while treated industrial wastewater and biochar (1%) has significantly reduced to 1.55E-02 and 1.91E-03 for adults and children, respectively. Thus, it was determined that irrigation with industrial effluents caused toxicity in vegetables, which had a negative impact on human health. Biochar effectively mitigated metal toxicity in both soil and spinach plants that resulted in reduced health/cancer risk.

Development of inorganic and mixed matrix membranes for application in toxic dyes-contaminated industrial effluents with in-situ treatments

Dyes are the most ubiquitous organic pollutants in industrial effluents. They are highly toxic to both plants and animals; thus, their removal is paramount to the sustainability of ecosystem. However, they have shown resistance to photolysis and various biological, physical, and chemical wastewater remediation processes. Membrane removal technology has been vital for the filtration/separation of the dyes. In comparison to polymeric membranes, inorganic and mixed matrix (MM) membranes have shown potentials to the removal of dyes. The inorganic and MM membranes are particularly effective due to their high porosity, enhanced stability, improved permeability, higher enhanced selectivity and good stability and resistance to harsh chemical and thermal conditions. They have shown prospects in filtration/separation, adsorption, and catalytic degradation of the dyes. This review highlighted the advantages of the inorganic and MM membranes for the various removal techniques for the treatments of the dyes. Methods for the membranes production have been reviewed. Their application for the filtration/separation and adsorption have been critically analyzed. Their application as support for advanced oxidation processes such as persulfate, photo-Fenton and photocatalytic degradations have been highlighted. The mechanisms underscoring the efficiency of the processes have been cited. Lastly, comments were given on the prospects and challenges of both inorganic and MM membranes towards removal of the dyes from industrial effluents.

UV LED wastewater disinfection: The future is upon us

The world's first full-scale, 280 nm UV LED reactor for wastewater disinfection was tested at flows of 545 and 817 m3 day-1. The system achieved a > 3 average log reduction of total coliform at 545 m3 day-1 and the 817 m3 day-1 flow rate achieved over a > 2.5 average log reduction for all operational conditions. The delivered fluence of the full-scale system ranged from 28 to 148 mJ cm-2 and aligns with a UV auditing study that was conducted prior to the installation of the wastewater reactor. These results benchmark the performance that can be achieved by UV LED disinfection and further connect bench-scale disinfection results with full-scale performance. The approach established in this manuscript provides a novel tool for utilities when considering emerging UV disinfection technologies. In summary, this study establishes that UV LEDs are an effective wastewater disinfectant at-scale and are comparable to conventional low-pressure UV systems. This is the first instance where the efficacy of UV LEDs for municipal wastewater disinfection has been demonstrated using a large-scale installation at a functioning wastewater facility.

High performance B2O3/MWCNTs and TiB/MWCNTs nano-adsorbents for the co-sorption of cyanide and phenol from refinery wastewater

The refinery industry has witnessed tremendous activity aimed at producing petrochemicals for the benefit of the teeming populace. These activities are accompanied by the discharge of wastewater containing chemical substances and elements that have negative impacts on the ecosystem. The presence of phenol and cyanide contaminants in refinery wastewater poses serious health hazards to humans, necessitating their removal. In this study, boron oxide-doped multi-walled carbon nanotubes (B2O3/MWCNTs) and titanium boride-doped MWCNT (TiB/MWCNTs) nanoadsorbents were prepared via a wet impregnation method and characterized using High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS). HR-TEM images depict the nanostructure of the nanoadsorbent, the presence of doped materials, and the internal, external, and wall thickness of B2O3/MWCNTs and TiB/MWCNTs nanoadsorbents. XRD results indicate that the nanomaterials were monocrystalline with average crystallite sizes of 22.75 nm and 16.79 nm for B2O3/MWCNTs and TiB/MWCNTs, respectively. The formation of B2O3 and TiB was observable in the results obtained from the XPS at the binding energy of 192 and 193.1 eV, respectively. The application of the produced B2O3/MWCNTs and TiB/MWCNTs nanoadsorbents for the removal of phenol and cyanide from refinery wastewater was explored in a batch adsorption system. The effects of contact time, adsorbent dosage, and adsorption temperature were investigated. To the best of our knowledge, the incorporation of B2O3 and TiB in MWCNTs resulted in the highest adsorption capacities for phenol and cyanide from aqueous solutions. The highest percentage removal of 100% for phenol and 99.06% for cyanide was observed for the TiB/MWCNTs nanoadsorbent at a residence time of 70 minutes, a temperature of 60 °C, and 0.3 g of adsorbent. The isotherm models show that cyanide and phenol removal obeyed the Langmuir isotherm, indicating monolayer adsorption over B2O3/MWCNTs nanoadsorbent. Furthermore, cyanide and phenol removal depict multilayer adsorption on the TiB/MWCNT nanoadsorbent. The research shows that B2O3/MWCNTs are proficient in cyanide sorption, while TiB/MWCNT favors phenol sorption due to their respective adsorption capacities.

Functional Bio-Based Polymeric Hydrogels for Wastewater Treatment: From Remediation to Sensing Applications

In recent years, many researchers have focused on designing hydrogels with specific functional groups that exhibit high affinity for various contaminants, such as heavy metals, organic pollutants, pathogens, or nutrients, or environmental parameters. Novel approaches, including cross-linking strategies and the use of nanomaterials, have been employed to enhance the structural integrity and performance of the desired hydrogels. The evolution of these hydrogels is further highlighted, with an emphasis on fine-tuning features, including water absorption capacity, environmental pollutant/factor sensing and selectivity, and recyclability. Furthermore, this review investigates the emerging topic of stimuli-responsive smart hydrogels, underscoring their potential in both sorption and detection of water pollutants. By critically assessing a wide range of studies, this review not only synthesizes existing knowledge, but also identifies advantages and limitations, and describes future research directions in the field of chemically engineered hydrogels for water purification and monitoring with a low environmental impact as an important resource for chemists and multidisciplinary researchers, leading to improvements in sustainable water management technology.

A review on titanium oxide nanoparticles modified metal-organic frameworks for effective CO2 conversion and efficient wastewater remediation

Environmental pollution has been increasing since last decade due to increasing industrialisation and urbanisation. Various kinds ofenvironmental pollutants including carbon dioxide (CO2), dyes, pharmaceuticals, phenols, heavy metals along with many organic and inorganic species have been discovered in the various environmental compartments which possess harmful impacts tox human health, wildlife, and ecosystems. Thus, various efforts have been made through regulations, technological advancements, and public awareness campaigns to reduce the impact of the pollution. However, finding suitable alternatives to mitigate their impacts remained a challenge. Metal-organic frameworks (MOFs) are one of the advanced materials with unique features such as high porosity and stability which exhibit versatile applications in environmental remediation. Their composites with titanium oxide nanoparticles (TiO2) have been discovered to offer potential feature such as light harvesting capacity and catalytic activity. The composite integration and properties have been confirmed through characterization using surface area analysis, scanning electron/transmission electron microscopy, atomic force microscopy, fourier transformed infrared spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and others. Thus, this work rigorously discussed potential applications of the MOF@TiO2 nanomaterials for the CO2 capture and effective utilization in methanol, ethanol, acetone, acetaldehyde, and other useful products that served as fuel to various industrial processes. Additionally, the work highlights the effective performance of the materials towards photocatalytic degradation of both organic and inorganic pollutants with indepth mechanistic insights. The article will offer significant contribution for the development of sustainable and efficient technologies for the environmental monitoring and pollution mitigation.

Removal of contaminants present in water and wastewater by cyclodextrin-based adsorbents: A bibliometric review from 1993 to 2022

Cyclodextrin (CD), a cyclic oligosaccharide from enzymatic starch breakdown, plays a crucial role in pharmaceuticals, food, agriculture, textiles, biotechnology, chemicals, and environmental applications, including water and wastewater treatment. In this study, a statistical analysis was performed using VOSviewer and Citespace to scrutinize 2038 articles published from 1993 to 2022. The investigation unveiled a notable upsurge in pertinent articles and citation counts, with China and USA contributing the highest publication volumes. The prevailing research focus predominantly revolves around the application of CD-based materials used as adsorbents to remove conventional contaminants such as dyes and metals. The CD chemistry allows the construction of materials with various architectures, including cross-linked, grafted, hybrid or supported systems. The main adsorbents are cross-linked CD polymers, including nanosponges, fibres and hybrid composites. Additionally, research efforts are actually concentrated on the synthesis of CD-based membranes, CD@graphene oxide, and CD@TiO2. These materials are proposed as adsorbents to remove emerging pollutants. By employing bibliometric analysis, this study delivers a comprehensive retrospective review and synthesis of research concerning CD-based adsorbents for the removal of contaminants from wastewater, thereby offering valuable insights for future large-scale application of CD-based adsorption materials.

Reconciling and contextualising multi-dimensional aspects for consolidated water security index: A synthesis

The present paper aims to review and develop a Consolidated Water Security Index (CWSI) as a tool to evaluate water security status within river basins by considering five key dimensions, namely (i) water supply and sanitation, (ii) water demand and socio-economic, (iii) water ecosystem and environment, (iv) water-related disaster and (v) water governance. This index is a holistic assessment since it aims to capture the interconnected and complex nature of water-related issues by considering multiple dimensional aspects which helps stakeholders and policymakers to understand the overall status of water security. This framework uses the Analytic Hierarchy Process (AHP), involving pairwise comparison, normalisation and weighting. Then, a CWSI will be calculated using the Linear Aggregation method. The robustness of this consolidated index is validated using sensitivity analysis by modifying the weight in the linear aggregation formula. By following each step cautiously, a CWSI can be constructed and interpreted correctly, thus, becoming a powerful tool for conveying complex information to the different stakeholders and assessing the status of water security with river basins. The CWSI allows decision-makers to prioritise areas that are most at risk and facilitate sustainable planning and management of water resources.

Progressive Insights into Metal-Organic Frameworks and Metal-Organic Framework-Membrane Composite Systems for Wastewater Management

The sustainable management of wastewater through recycling and utilization stands as a pressing concern in the trajectory of societal advancement. Prioritizing the elimination of diverse organic contaminants is paramount in wastewater treatment, garnering significant attention from researchers worldwide. Emerging metal-organic framework materials (MOFs), bridging organic and inorganic attributes, have surfaced as novel adsorbents, showcasing pivotal potential in wastewater remediation. Nevertheless, challenges like limited water stability, elevated dissolution rates, and inadequate hydrophobicity persist in the context of wastewater treatment. To enhance the performance of MOFs, they can be modified through chemical or physical methods, and combined with membrane materials as additives to create membrane composite materials. These membrane composites, derived from MOFs, exhibit remarkable characteristics including enhanced porosity, adjustable pore dimensions, superior permeability, optimal conductivity, and robust water stability. Their ability to effectively sequester organic compounds has spurred significant research in this field. This paper introduces methods for enhancing the performance of MOFs and explores their potential applications in water treatment. It delves into the detailed design, synthesis strategies, and fabrication of composite membranes using MOFs. Furthermore, it focuses on the application prospects, challenges, and opportunities associated with MOF composite membranes in water treatment.

The multi-functional system of electrochemical desalination, RhB degradation and Cr (VI) removal

SYNOPSIS

: The single function of salt removal limits the further development of the CDI system. A multi-function CDI device is proposed to achieve electrochemical desalination, organics degradation and dichromate ion removal.

Environmental pollution removal using electrostimulation of microorganisms by alternative current

The entrance of some toxic and hazardous chemical agents such as antibiotics, pesticides, and herbicides into the environment can cause various problems to human health and the environment. In recent years, researchers have considered the use of electrostimulation in the processes of microbial metabolism and biological systems for the treatment of pollutants in the environment. Although several electrostimulation reports have been presented for pollutant removal, little attention has been paid to alternative current (AC) biostimulation. This study presents a systematic review of microbial electrostimulation using bioelectrochemical systems supplied with AC. The utilization of alternating current bioelectrochemical systems (ACBESs) has some advantages such as the provide of appropriate active biofilms in the electrodes due to the cyclical nature of the current and energy transfer in an appropriate manner on the electrode surfaces. Moreover, the ACBESs can reduce hydraulic time (HRT) under optimal conditions and reduce the cost of converting electricity using AC. In microbial electrostimulation, amplitude (AMPL), waveform, C/N, and current have a significant effect on increasing the removal efficiency of the pollutants. The obtained results of the meta-analysis illustrated that various pollutants such as phenol, antibiotics, and nitrate have been removed in an acceptable range of 96% using the ACBESs. Therefore, microbial electrostimulation using AC is a promising technology for the decomposition and removal of various pollutants. Moreover, the ACBESs could provide new opportunities for promoting various bioelectrochemical systems (BESs) for the production of hydrogen or methane.

Using wastewater as a cultivation alternative for microalga Dunaliella salina: Potentials and challenges

Untreated or poorly treated wastewater still represents environmental issues world-widely. Wastewater, especially saline wastewater treatment, is still primarily associated with high costs from physical and chemical processes, as high salinity hinders biological treatment. One favourable way is to find the suitable biological pathways and organisms to improve the biological treatment efficiency. In this context, halophilic microorganisms could be strong candidates to address the economics and effectiveness of the saline wastewater treatment process. Dunaliella salina is a photoautotrophic microalga that grows in saline environments. It is known for producing marketable bio-compounds such as carotenoids, lipids, and proteins. A biological treatment based on D. salina cultivation offers the opportunity to treat saline wastewater, reducing the threat of possible eutrophication from inappropriate discharge. At the same time, D. salina cultivation could yield compounds of industrial relevance to turn saline wastewater treatment into a profitable and sustainable process. Most research on D. salina has primarily focused on bioproduct generation, leaving thorough reviews of its application in wastewater treatment inadequate. This paper discusses the future challenges and opportunities of using D. salina to treat wastewater from different sources. The main conclusions are (1) D. salina effectively recovers some heavy metals (driven by metal binding capacity and exposure time) and nutrients (driven by pH, their bioavailability, and functional groups in the cell); (2) salinity plays a significant role in bioproducts generation, and (3) wastewater can be combined with the generation of bioproducts.

Mycoremediation of Industrial Textile Wastewater Using Ganoderma lucidum Pellets and Activated Dolomite in Batch Bioreactor

In the world of fast fashion, textile industries are blooming rapidly to meet the consumer's demands. However, vast amounts of wastewater have been constantly produced, and it is becoming a serious environmental problem in the waterways. Although the technology for treating textile wastewater has been well reported and established, more sustainable efforts have taken the attention nowadays. Through the use of living Malaysian Ganoderma lucidum mycelial pellets (GL) and activated dolomite (AD) in the treatment system, the study explores the synergy between biosorption and physisorption as alternative treatment for textile wastewater. In the current work, mixture of GL premixed with AD (50:50; v/v) is used to treat industrial textile wastewater. The morphology, adsorption characteristics, and antibacterial activity of the adsorbents were studied. The mixture of adsorbents is capable of removing colours by 77.8% and reducing chemical oxygen demand (COD) by 75% within 48 h contact. Furthermore, the kinetic and adsorption had been studied and follow the pseudo-first-order kinetic model while both adsorption of Langmuir and Freundlich model was deduced from the treatment. In addition, antimicrobial activities from the treatment potentially reduced 10 × 101 CFU/mL after 48 h. The synergistic treatment by Ganoderma lucidum mycelial pellets and activated dolomite has immense potential in future wastewater treatment technology to obtain cleaner water.

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Microbial induced calcium precipitation by Zobellella denitrificans sp. LX16 to simultaneously remove ammonia nitrogen, calcium, and chemical oxygen demand in reverse osmosis concentrates

In recent years, with the rapid development of industrial revolution and urbanization, the generation and treatment of a large number of salt-containing industrial wastewater has attracted wide attention. A novel salt-tolerant Zobellella denitrificans sp. LX16 with excellent nitrogen removal and biomineralization capabilities was isolated in this experiment. Kinetic experiments were conducted to determine the optimal condition. Under this condition, chemical oxygen demand (COD) can be entirely removed together with ammonia nitrogen, and the removal efficiency of calcium was 88.09%. Growth curves and nitrogen balance tests showed that strain LX16 not only had good HNAD and MICP capabilities, but also had high nitrite reductase and nitrate reductase activities during this process. Three-dimensional fluorescence results reflected that when external carbon sources were lacking or salinity was high, humic acid could effectively enhance the metabolic activity of heterotrophic nitrifying aerobic denitrifying microorganisms through extracellular electron transfer, and the substances produced in the metabolic process could promote biommineralization. Moreover, combined with SEM, SEM-EDS, XRD and FTIR analysis, it is concluded that the microbial surface can provide nucleation sites to form calcium salts, and with the increase of alkalinity to generate Ca5(PO4)3OH. The theoretical basis for the use of biological treatment in reverse osmosis wastewater have been proved by this experiment.

Ternary Graphene Oxide and Titania Nanoparticles-Based Nanocomposites for Dye Photocatalytic Degradation: A Review

Advanced oxidation processes stand as green alternatives for the decontamination of waste waters. Photocatalysis is an advanced oxidation process in which a semiconductor material absorbs photon energy and triggers redox reactions capable of degrading organic pollutants. Titanium dioxide (TiO2, titania) represents one of the most popular choices of photocatalytic materials, however the UV-activation of its anatase phase and its high charge recombination rate decrease its photocatalytic activity and weaken its potential. Graphene oxide is a 2D carbon nanomaterial consisting of exfoliated sheets of hexagonally arranged carbons decorated with oxygen- and hydrogen- functional groups. Composite nanomaterials consisting of titania nanoparticles and graphene oxide have proven to enhance the photocatalytic activity of pure TiO2. In this review, we present a thorough literature review of ternary nanocomposites based on synthesized or commercial titania nanoparticles and GO (or reduced GO) particularly used for the photodegradation of dyes. GO/TiO2 has been enriched primarily with metals, semiconductors and magnetic nanomaterials, proving a superior dye degradation performance and reusability compared to bare TiO2. Ongoing challenges and perspectives are outlined.

Microbial community structure and functional prediction in five full-scale industrial park wastewater treatment plants

The development of industrial parks has become an important global trend contributing significantly to economic and industrial growth. However, this growth comes at a cost, as the treatment of multisource industrial wastewater generated in these parks can be difficult owing to its complex composition. Microorganisms play a critical role in pollutant removal during industrial park wastewater treatment. Therefore, our study focused on the microbial communities in five full-scale industrial park wastewater treatment plants (WWTPs) with similar treatment processes and capacities. The results showed that denitrifying bacteria were dominant in almost every process section of all the plants, with heterotrophic denitrification being the main pathway. Moreover, autotrophic sulfur denitrification and methane oxidation denitrification may contribute to total nitrogen (TN) removal. In plants where the influent had low levels of COD and TN, dominant bacteria included oligotrophic microorganisms like Prosthecobacter (2.88 % ~ 10.02 %) and hgcI_clade (2.05 % ~ 9.49 %). Heavy metal metabolizing microorganisms, such as Norank_f__PHOS-HE36 (3.96 % ~ 5.36 %) and Sediminibacterium (1.86 % ~ 5.34 %), were prevalent in oxidation ditch and secondary settling tanks in certain plants. Functional Annotation of Prokaryotic Taxa (FAPROTAX) revealed that microbial communities in the regulation and hydrolysis tanks exhibited higher potential activity in the nitrogen (N) and sulfur (S) cycles than those in the oxidation ditch. Sulfate/sulfite reduction was common in most plants, whereas the potential occurrence of sulfide compounds and thiosulfate oxidation tended to be higher in plants with a relatively high sulfate concentration and low COD content in their influent. Our study provides a new understanding of the microbial community in full-scale industrial park WWTPs and highlights the critical role of microorganisms in the treatment of industrial wastewater.

Environmental hazard assessment and metal contamination in coastal sediments

In order to reduce contamination levels from diverse sources, it is important to understand the factors affecting the natural ecosystems that are impacted by coastal and marine pollution. In this study, we used GIS and remote sensing techniques to investigate and evaluate the distribution of heavy metals (Fe, Mn, Zn, Cr, Pb, Co, and Cu) in surface sediments along Tamil Nadu's East Coast (from Besant Nagar to Sathurangapattinam). The CF and Igeo of metals indicate that sediments contain no evidence of Fe, Mn, or Zn metal pollution in the sediments, with only mild contamination from Co, Cu, and Pb. In contrast, the sediment samples were found to be significantly contaminated with Cr. Heavy metal contamination occurs in the following order, according to our research: Cr > Pb > Cu > Co > Mn > Zn > Fe. Except for sites 8, 10, 11, and 13, where PLI>1 implies that there is no pollution in this area, the PLI values show that most of the locations are contaminated. The ecological risk index (ERI) values for five metals in the study areas are as follows: Cr > Pb > Cu > Mn > Zn. The sediment samples fall into the low-risk and highly polluted to dangerous sediment categories for SPI, according to the Risk index (RI). Based on the Mean Effect Range-Median Quotient (M-ERM-Q), Cu, Pb, Zn, and Cr metals in the research region have a 9-21% probability of being harmful. Statistical approaches show that the majority of heavy metals in sediments are of natural origin. The spatial distribution of heavy metals in surface sediments provides the conceptual framework for practical strategies to protect coastal areas. Many shreds of evidence indicate that anthropogenic inputs from the surrounding land area are primarily responsible for the deposition of these heavy metals in the coastal zone.

Water-Floating Hydrogel Polymer Microsphere Composites for Application in Hydrological Mining of Cu(II) Ions

Innovative materials and technologies capable of extraction and recovery of technologically relevant metal ions from various water sources, such as lakes, oceans, ponds, or wastewater reservoirs, are in great demand. Polymer beads are among the most well-known solid-phase adsorbents and ion exchangers employed in metal ion recovery. On the other hand, hydrogels are an emerging platform for producing innovative adsorbents, which are environmentally friendly and biocompatible materials. In this work, we take advantage of both technologies and produce a new type of material by loading nanostructured polymer microsphere adsorbent into a PVA matrix to obtain a hydrogel polymer microsphere (HPM) composite in the form of a block. The main role of the poly(4-vinylpyrridine-co-methacrylic acid) microspheres is to adsorb metal ions, such as Cu(II), from model water samples. The secondary role of these microspheres in the hydrogel is to change the hydrogel morphology by softening it and stabilizing it under a foam-like morphology. The foam-like morphology endows these composites with the capability of floating on water surfaces. In this work, we report, for the first time, an HPM composite capable of floating on water surfaces and extracting Cu(II) ions from model water samples. This could enable more environmentally friendly hydrological mining technologies by simply deploying adsorbents on water surfaces for metal ion extraction and recovery, thus eliminating the need for water pumping and mechanical processing steps.

Adsorptive removal of acid blue dye 113 using three agricultural waste biomasses: The possibility of valorization by activation and carbonization - A comparative analysis

The presence of various organic and inorganic contaminants in wastewater leads to serious health effects on humans and ecosystems. Industrial effluents have been considered as noticeable sources of contaminating water streams. These effluents directly liberate the pollutants such as dye molecules and heavy metal ions into the environment. In the present study, three biowaste materials (groundnut shell powder, coconut coir powder and activated corn leaf carbon) were utilized and compared for the removal of acid blue dye 113 from aqueous solutions. The characterization study of newly prepared sorbent material (H3PO4-activated corn leaf carbon) and the other utilized sorbents was carried out by Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrophotometer (FTIR), along with Energy Dispersive X-Ray (EDX) Analysis. The influence of experimental conditions such as pH, initial dye concentration, temperature, contact time, and sorbent dosage on the removal efficiency of the dye were appraised. The adsorption isotherm and kinetic result of acid blue dye 113 adsorption onto the sorbents best obeyed from Sips and pseudo-second-order kinetic model. Overall, the outcomes confirmed that the newly synthesized sorbent material (carbonized H3PO4-activated corn leaf) has superior adsorption capacity, rapid adsorption, and higher suitability for the removal of toxic dyes from the contaminated waters.

Visible light photocatalysis: efficient Z-scheme LaFeO3/g-C3N4/ZnO photocatalyst for phenol degradation

In this work, a Z-scheme LaFeO3/g-C3N4/ZnO heterojunction photocatalyst with large specific surface (68.758 m2/g) and low cost (0.00035 times the cost of per gram of Au) was easily synthesized by glucose-assisted hydrothermal method. The structure, surface morphology, and optical properties of the photocatalyst were investigated. The constructed Z-scheme heterojunction catalysts can enhance the visible light absorption and carrier separation efficiency. Among these photocatalysts, the 10%-LaFeO3/g-C3N4/ZnO composite possesses the premium performance for efficient degrading 97.43% of phenol within 120 min. Even after 5 cycles, it still sustains an excellent photocatalytic stability (92.13% phenol degradation). According to the XPS surface states and the capture of active species on LaFeO3/g-C3N4/ZnO, the electrons would be transferred from ZnO and LaFeO3 to g-C3N4. In addition, ·OH plays an important role in photocatalytic reactions for phenol degradation. Thus, the proposed possible photocatalytic reaction mechanism of Z-scheme LaFeO3/g-C3N4/ZnO can provide a more economical and efficient conception for phenol degradation.

Highly Efficient Solar-Light-Active Ag-Decorated g-C3N4 Composite Photocatalysts for the Degradation of Methyl Orange Dye

In this study, we utilized calcination and simple impregnation methods to successfully fabricate bare g-C₃N₄ (GCN) and x% Ag/g-C₃N₄ (x% AgGCN) composite photocatalysts with various weight percentages (x = 1, 3, 5, and 7 wt.%). The synthesized bare and composite photocatalysts were analyzed to illustrate their phase formation, functional group, morphology, and optical properties utilizing XRD, FT-IR, UV-Vis DRS, PL, FE-SEM, and the EDS. The photodegradation rate of MO under solar light irradiation was measured, and the 5% AgGCN composite photocatalyst showed higher photocatalytic activity (99%), which is very high compared to other bare and composite photocatalysts. The MO dye degradation rate constant with the 5% AgGCN photocatalyst exhibits 14.83 times better photocatalytic activity compared to the bare GCN catalyst. This photocatalyst showed good efficiency in the degradation of MO dye and demonstrated cycling stability even in the 5th successive photocatalytic reaction cycle. The higher photocatalytic activity of the 5% AgGCN composite catalyst for the degradation of MO dye is due to the interaction of Ag with GCN and the localized surface plasmon resonance (SPR) effect of Ag. The scavenger study results indicate that O₂^●- radicals play a major role in MO dye degradation. A possible charge-transfer mechanism is proposed to explain the solar-light-driven photocatalyst of GCN.

Decreasing lactate input for cost-effective sulfidogenic metal removal in sulfate-rich effluents: Mechanistic insights from (bio)chemical kinetics to microbiome response

High material cost is the biggest barrier for the industrial use of low-molecular-weight organics (i.e. lactate) as external carbon and electron source for sulfidogenic metal removal in sulfate-rich effluents. This study aims to provide mechanistic evidence from kinetics to microbiome analysis by batch modeling to support the possibility of decreasing the lactate input to achieve cost-effective application. The results showed that gradient COD/SO42- ratios at a low level had promising treatment performance, reaching neutralized pH with nearly total elimination of COD (91%-99%), SO42- (85%-99%), metals (80%-99%) including Cu, Zn, and Mn. First-order kinetics exhibited the best fit (R2 = 0.81-0.98) to (bio)chemical reactions, and the simulation results revealed that higher COD/SO42- accelerated the reaction rate of SO42- and COD but not suitable to that of metals. On the other hand, we found that the decreasing COD/SO42- ratio increased average path distance but decreased clustering coefficient and heterogeneity in microbial interaction network. Genetic prediction found that the sulfate-reduction-related functions were significantly correlated with the reaction kinetics changed with COD/SO42- ratios. Our study, combining reaction kinetics with microbiome analysis, demonstrates that the use of lactate as a carbon source under low COD/SO42- ratios entails significant efficiency of metal removal in sulfate-rich effluent using SRB-based technology. However, further studies should be carried out, including parameter-driven optimization and life cycle assessments are necessary, for its practical application.

Preparation and Characterization of di- and Tricarboxylic Acids-Modified Arabinogalactan Plasticized Composite Films

To ensure the high quality of water, it is necessary to remove toxic pollutants. At present, purification of water is implemented using various sorbents. The efficient sorption materials are modified polysaccharides. In this study, we report on a new environmentally friendly method for modifying larch hemicellulose-arabinogalactan (AG)-with polybasic carboxylic acids (citric, succinic, oxalic, and adipic) to obtain composite materials. The synthesized AG derivatives have been explored by a complex of physicochemical methods, including gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), and sorption capacity investigations. It is shown that the heat treatment results in the formation of additional inter- and intramolecular bonds between carboxylic acids and polysaccharide molecules. The formation of ester bonds has been confirmed by the appearance of absorption bands in the IR spectra in the range of 1750-1690 cm^-1. It has been found, using the TGA study, that the most thermally stable (up to 190 °C) sample is arabinogalactan oxalate obtained under heat treatment. The SEM study of the synthesized AG films has shown that the modified samples have the homogeneous film surface ensured by cross-linking. It has been established, when studying the sorption properties of the AG derivatives, that AG succinate (82.52%) obtained by lyophilization has the highest sorption capacity, due to the developed mesoporous surface, which, in turn, makes the synthesized films promising eco-friendly materials for use as drug carriers, sorbents, and water treatment agents.

Current overview and future perspective in fungal biorecovery of metals from secondary sources

Microorganisms are intimately involved in many biogeochemical processes that underpin the transformation of metals and cycling of related substances, such as metalloids and radionuclides. Many processes determine the mobility and bioavailability of metals, thereby influencing their transfer to the environment and living organisms. These processes are closely related to global phenomena such as soil formation and bioweathering. In addition to environmental significance, microbial metal transformations play an essential role in both in situ and ex situ bioremediation processes for solid and liquid wastes. The solubilization of heavy metals from industrial waste and soil is commonly used in bioremediation. Moreover, immobilization processes are applicable to bioremediation of metals and radionuclides from aqueous solutions. This review provides an overview of critical metal extraction and recovery from secondary sources, applied microorganisms and methods, metal-microbe interactions, as well as a detailed description of known metal recovery mechanisms.

A study on the efficiency of the sequential batch reactor on the reduction of wastewater pollution from oil washing

Industrial pollution discharges from washing fuel oils pose severe problems for the environment, particularly for the marine environment receiving these discharges. This work evaluates the biological treatment performance of wastewater (90 m³/h) rich in organic matter with low biodegradability using a sequential batch reactor (SBR) on a laboratory scale. The test using SBR was carried out for 25 days on a continuous cycle of 24 h (30 min of filling, 17 h of aeration, 4 h of anoxia, 2 h of settling, and 30 min of emptying). The feasibility of alternative sources of microorganisms from urban wastewater. The performance of the batch sequencing reactor was evaluated using turbidity, total suspended solids, chemical oxygen demand (COD), biological oxygen demand (BOD), ammonium, nitrate, and phenol as indicators. The results obtained showed that the COD/BOD ratio and the pollutant load vary from one campaign to another. The removal efficiency of COD, BOD, TSS (Total suspended solids), ammonium, nitrate, and phenol varies from 81%, 91%, 72%, 100%, 52%, and 63%. Thus, SBR-type treatment could be an interesting way to reduce pollution due to its simplicity, less space occupation, low energy consumption, and not requiring highly qualified personnel.

A review on recovery processes of metals from E-waste: A green perspective

E-waste management has become a global concern because of the enormous rise in the rate of end-of-life electrical and electronic equipment's (EEEs). Disposal of waste EEE directly into the environment leads to adverse effects on the environment as well as on human health. For the management of E-waste, numerous studies have been carried out for extracting metals (base, precious, and rare earth) following pyrometallurgy, hydrometallurgy, and biometallurgy. Irrespective of the advantages of these processes, certain limitations still exist with each of these options in terms of their adoption as treatment techniques. Several journal publications regarding the different processes have been made which aids in future research in the field of E-waste management. This review provides a comprehensive summary of the various metal recovery processes (pyrometallurgy, hydrometallurgy, and biometallurgy) from E-waste, along with their advantages and limitations. A bibliometric study based on the published articles using different keywords in Scopus has been provided for a complete idea about E-waste with green technology perspective like bioleaching, biosorption, etc. The present study also focussed on the circular economic approach towards sustainable E-waste management along with its socio-economic aspects and the economic growth of the country. The present study would provide valuable knowledge in understanding E-waste and its different treatment processes to the students, researchers, industrialists, and policymakers of the country.

The role of biomass elemental composition and ion-exchange in metal sorption by algae

The use of macroalgae, microalgae and cyanobacteria for metal sorption has been widely reported. Still, there are no studies allowing a direct comparison of the performance of these biomasses, especially while evaluating metal competition. The simultaneous sorption of Co²⁺, Cu²⁺, Ni²⁺ and Zn²⁺ present in a multi-elemental solution by six macroalgae, two microalgae and three cyanobacteria was evaluated. Brown macroalgae were shown to be the most promising biosorbent, with Undaria pinnatifida having a total metal sorption capacity of 0.6 mmol g^-1. Overall, macroalgae performed better than microalgae, followed by cyanobacteria. Carboxyl groups were identified as being the main functional groups involved in metal sorption, and all biomass samples were found to be selective to Cu²⁺. This was linked not only to its higher complexation constant value with relevant functional groups when compared to the remaining metals, but also the Irving-Williams series. The release of K⁺ and Ca²⁺ to the aqueous solution during the metal sorption was followed. The obtained results suggest they are readily exchanged with metals in the solution, indicating the occurrence of an ion-exchange mechanism in metal sorption by most biomass. Red macroalgae are an exception to the reported trends, suggesting that their metal sorption mechanism may differ from the other biomass types.

Applied novel functionality in separation procedure from leaching solution of zinc plant residue by using non-aqueous solvent extraction

Traditional solvent extraction (SX) procedures limit metal separation and purification, which consist of the organic and aqueous phases. Because differences in metal ion solvation lead to distinct distribution properties, non-aqueous solvent extraction (NASX) considerably expands the scope of solvent extraction by replacing the aqueous phase with alternate polar solvents. In this study, an experimental design approach used non-aqueous solvent extraction to extract cobalt from zinc plant residue. The aqueous phase comprises ethylene glycol (EG), LiCl and metal ions. In kerosene, D2EHPA, Cyanex272, Cyanex301, and Cyanex302 extractants were used as a less polar organic phase. Various factors were investigated to see how they affected extraction, including solvent type, extractant type and phase ratio, pH, Co(II) concentration, and temperature. The results revealed that at a concentration of 0.05 M, the Cyanex301 extractant could achieve the requisite extraction efficiency in kerosene. The optimal conditions were chosen as the concentration of Cyanex 301 (0.05 M), the concentration of cobalt (833 ppm), the pH (3.5), and the percent of EG (80%). As a result, during the leaching process, these systems are advised for extracting and separating a combination of various metal ions.

Efficient catalytic degradation of methylene blue by a novel Fe3+-TiO2@CGS three-dimensional photoelectric system

In this study, a novel three-dimensional photoelectric system was designed and constructed for the degradation of methylene blue (MB) via photocatalysis, electrocatalysis, and photoelectric catalysis. To this end, a Ti/RuO₂-IrO₂-SnO₂-CeO₂ electrode was prepared via a thermal oxidation coating method and used as a dimensionally-stable anode (DSA). The cathode was made of a titanium sheet with Fe³⁺-doped TiO₂ loaded on coal gasification slag (CGS) (Fe³⁺-TiO₂@CGS) as a photocatalyst. The factors affecting the degradation efficiency, such as the supporting electrolyte, current density, and initial pH were systematically investigated. The results revealed Fe³⁺-TiO₂@CGS three-dimensional photoelectric system exhibiting efficient synergistic performance of photocatalysis and electrocatalysis with a synergistic factor of 1.11. Photo-generated holes (h⁺) were generated by light irradiation and direct anodic oxidation. Furthermore, hydroxyl radicals (HO·) radicals were induced via other pathways. Such active species showed highly-oxidizing abilities, beneficial to the degradation of methylene blue (MB). The representative Fe³⁺-TiO₂@CGS three-dimensional photoelectric system showed super high degradation efficiency at pH 11 and current density of 18.76 mA cm^-2. Using NaCl as a supporting electrolyte, the degradation yield reached 99.98% after 60 min of photoelectrical treatment. Overall, the novel Fe³⁺-TiO₂@CGS three-dimensional photoelectrical system looks very promising for the highly efficient catalytic degradation of organic contaminants.

Removal of heavy metals from wastewater using synthetic chelating agents

The issue of heavy metal water pollution is one that concerns everyone. Both plants and humans are negatively impacted by heavy metals. Consequently, the environment and water resources require an efficient heavy metal remediation technique. In this context, a series of compounds were investigated as potential chelating agents for the removal of Cu, Zn, Cd, and Pb cations from water. By solvent extraction, it was shown that the chelating ligands’ affinity for Cu, Zn, Cd, and Pb as indicated by the extraction performance was in the following order: Cu > Zn > Cd > Pb. The size and electrical characteristics of the metal as well as the ligand structure affect how well L1–L6 extracts that metal.

Valorization of wastewater: A paradigm shift towards circular bioeconomy and sustainability

Limitation in the availability of natural resources like water is the main drive for focussing on resource recovery from wastewater. Rapid urbanization with increased consumption of natural resources has severely affected its management and security. The application of biotechnological processes offers a feasible approach to concentrating and transforming wastewater for resource recovery and a step towards a circular economy. Wastewater generally contains high organic materials, nutrients, metals and chemicals, which have economic value. Hence, its management can be a valuable resource through the implementation of a paradigm transformation for value-added product recovery. This review focuses on the circular economy of "close loop" process by wastewater reuse and energy recovery identifying the emerging technologies for recovering resources across the wastewater treatment phase. Conventional wastewater treatment technologies have been discussed along with the advanced treatment technologies such as algal treatment, anammox technology, microbial fuel cells (MFC). Apart from recovering energy in the form of biogas and biohydrogen, second and third-generation biofuels as well as biohythane and electricity generation have been deliberated. Other options for resource recovery are single-cell protein (SCP), biopolymers as well as recovery of metals and nutrients. The paper also highlights the applications of treated wastewater in agriculture, aquaponics, fisheries and algal cultivation. The concept of Partitions-release-recover (PRR) has been discussed for a better understanding of the filtration treatment coupled with anaerobic digestion. The review provides a critical evaluation on the importance of adopting a circular economy and their role in achieving sustainable development goals (SDGs). Thus, it is imperative that such initiatives towards resource recovery from wastewater through integration of concepts can aid in providing wastewater treatment system with resource efficiency.

Hydrophobic plasmonic silver membrane as SERS-active catcher for rapid and ultrasensitive Cu(II) detection

The rapid and selective identification of heavy metal ions is crucial for environmental water safety. In this study, a novel surface-enhanced Raman scattering (SERS)-active catcher was designed for Cu(II) detection using a hydrophobic hydroxyoxime-mediated plasmonic silver membrane (HOX@Ag-PVDF). Uniformly dispersed Ag nanoparticles (ca. 80 nm) and hydroxyoxime molecules were synchronously decorated on the skeleton of the polyvinylidene fluoride membrane via an in situ interfacial assembly strategy. HOX@Ag-PVDF shows excellent SERS activity (EF = 2.5 × 10⁷), high reproducibility (~8% RSD), and long-term stability (50 days) for detecting 4-nitrothiophenol (4-NTP). Moreover, HOX@Ag-PVDF can serve as a new platform for rapid and dry-free SERS detection of Cu(II) owing to its strong affinity and surface hydrophobicity. Cu(II) ions can be rapidly captured in 5 s and selectively recognized by SERS signals without interference from other metal ions. HOX@Ag-PVDF exhibits linear SERS response signals at low concentrations ranging from 10^-6 to 10^-10 mol/L Cu(II) (R² = 0.9893) with a low detection limit (LOD) of 52.0 pmol/L. This hydrophobic plasmonic membrane, with its simple sampling and rapid SERS response characteristics, provides ultrasensitive recognition and heavy metal detection for practical applications.