Large-scale Wastewater Treatment Research Articles

Construction of durable superhydrophilic activated carbon fibers based material for highly-efficient oil/water separation and aqueous contaminants degradation

Developing filtering materials with high permeation flux and contaminant removal rate is of great importance for oily wastewater remediation. Herein, a robust three-dimensional (3D) activated carbon fibers (ACFs) based composite with uniformly grown layered double hydroxide (LDH) on the surface was successfully constructed through a feasible hydrothermal strategy. The LDH with a high surface energy and vertically aligned structure could provide superhydrophilicity to ACFs. Systematic investigation confirmed that the 3D material could overcome the size mismatch between the ACFs macropores and tiny emulsified droplets through the combination of size-sieving filtration on the surface and oil droplet coalescence in the fiber network. This process efficiently separated the intractable surfactant-stabilized oil-in-water emulsions with high permeation flux (up to 4.16 × 106 L m−2 h−1 bar−1). Notably, the LDH also had well-dispersed catalytic active sites, which could initiate advanced oxidation processes (AOPs) to efficiently eliminate various types of water-soluble organic pollutants (e.g., pharmaceuticals, phenolic compounds and organic dyes). The resulting modified ACFs exhibited exceptional removal rates for both oil and organic pollutants in the complex sewage during the continuous filtration process. These versatile abilities integrated with the facile preparation method reported herein provide outstanding prospects for the large-scale treatment of oily wastewater.

Synthesis of Magnetic Adsorbents Based Carbon Highly Efficient and Stable for Use in the Removal of Pb(II) and Cd(II) in Aqueous Solution.

In this study, two alternative synthesis routes for magnetic adsorbents were evaluated to remove Pb(II) and Cd(II) in an aqueous solution. First, activated carbon was prepared from argan shells (C). One portion was doped with magnetite (Fe3O4+C) and the other with cobalt ferrite (CoFe2O4+C). Characterization studies showed that C has a high surface area (1635 m2 g−1) due to the development of microporosity. For Fe3O4+C the magnetic particles were nano-sized and penetrated the material’s texture, saturating the micropores. In contrast, CoFe2O4+C conserves the mesoporosity developed because most of the cobalt ferrite particles adhered to the exposed surface of the material. The adsorption capacity for Pb(II) was 389 mg g−1 (1.88 mmol g−1) and 249 mg g−1 (1.20 mmol g−1); while for Cd(II) was 269 mg g−1 (2.39 mmol g−1) and 264 mg g−1 (2.35 mmol g−1) for the Fe3O4+C and CoFe2O4+C, respectively. The predominant adsorption mechanism is the interaction between -FeOH groups with the cations in the solution, which are the main reason these adsorption capacities remain high in repeated adsorption cycles after regeneration with HNO3. The results obtained are superior to studies previously reported in the literature, making these new materials a promising alternative for large-scale wastewater treatment processes using batch-type reactors.

Controllable fabrication of photocatalytic TiO2 brookite thin film by 3D-printing approach for dyes decomposition

An immobilized photocatalytic system is being considered as an advantage for wastewater treatment. The stability and durability of photocatalytic materials in film form strongly depend on both supported materials and immobilization techniques. In this work, the composite of a styrene-acrylate (DC668) polymeric binder and the TiO2 brookite spherical nanoparticles (NPs) was immobilized on the surface of the glass substrate by direct-ink-writing technique using a 3D printer. Physicochemical and photocatalytic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy, respectively. Rose bengal (RB) was used as the target pollutant to investigate the photocatalytic behavior of the obtained TiO2/DC668 composite thin film which was evaluated by UV–VIS absorption spectra. We found that an amount of less than 10% of the industrial DC668 emulsion has significantly improved the dispersion of TiO2 NPs in the polymeric matrix as well as the adhesion of 3D-printed TiO2 thin film to the glass surface. After UV-A light exposure for 300 min, the decomposition rate of RB over TiO2 film was 0.029 min−1 corresponding to the nearly complete decolourization. The reuse tests show that the thin-film photocatalyst was remarkably stable. Its high activity can be maintained after four uses with the RB dyes photodegradation efficiency of 92%. The photo-catalyzing capacity of the thin films with immobilized TiO2 NPs was slightly lower than that of only bare TiO2 NPs, but the thin film can be efficiently reused for more cycles without any further separation. Thereby, the 3D-printed TiO2 brookite thin-film photocatalysts provide the potential for application in large-scale wastewater treatment.

Galactomannans for Entrapment of Gliomastix murorum Laccase and Their Use in Reactive Blue 2 Decolorization

In the present study, a novel laccase from ascomycete Gliomastix murorum was produced in agro-industrial wastes and entrapped in galactomannan beads for Reactive Blue 2 (Rb-2) decolorization. The maximum laccase production in agave bagasse-based medium occurred at 72 h (1798.6 UL−1). Entrapped laccase decolorized ˃80% of 0.5 mM Rb-2 in 2 h without the addition of redox mediator. Km for Rb-2 substrate was 1.42 mM, with a Vmax of 1.19 µmol min−1 for entrapped laccase. Galactomannan matrices produce stability to acid pH (2–5) and temperatures from 20–70 °C. Reusability assays showed that entrapped laccase could retain efficient Rb-2 decolorization of ˃80% six times. In general, galactomannan used for entrapment of laccase provides economic advantages in large-scale wastewater treatment due to its natural origin and efficient results.

Polyoxometalates for bifunctional applications: Catalytic dye degradation and anticancer activity

Improving the efficiencies of organic compound degradations by catalytic materials is a challenging materials research field. In our research, we successfully synthesized cobalt-based polyoxometalates (CoV-POMs) via a simple crystallization-driven self-assembly method. The incorporation of the newly synthesized CoV-POMs into peroxymonosulphate (PMS), forming a mixture, greatly enhancing the catalytic activation for a complete degradation of dye solution. The positive synergic effect between CoV-POMs and PMS was substantiated by a relatively meager degradation of less than 10% in the system without CoV-POMs, in which CoV-POMs played a vital role to activate PMS towards free radicals generation for dye degradation. Methylene blue (MB) and rhodamine B (RB) dyes were completely decolorized under 60 min with the presence of 40 mg/L CoV-POMs and 150 mg/L PMS. The CoV-POMs/PMS system was pH dependance with a lower dye degradation efficiency at elevated pH. The effect of pH was more prominent in RB dye, in which the degradation efficiency dropped drastically from 93.3% to 41.12% with the increase in the solution pH from 7 to 11. The quenching tests suggested that sulfate radicals were the dominant active species involving in the dye degradation reaction. Besides MB and RB dyes, CoV-POMs/PMS system also showed significant activity towards the degradation of phenol red (PR) and methyl orange (MO) dyes. In the biological test, CoV-POMs exhibited non-toxic behavior towards normal cells that reduced safety concern for the large-scale wastewater treatment application. In addition, the testing divulged the anticancer property of CoV-POMs with more than 35 % of A549 lung adenocarcinoma and MDA-MB-231 breast adenocarcinoma were killed with 250 mg/L CoV-POMs. The selective lethality of CoV-POMs towards cancer cells was found to be caused by different extents of cellular apoptosis. In overall, the synthesized bifunctional CoV-POMs manifested superior activities in the examined applications, specifically dye degradation and anticancer.

“Small amount for multiple times” of H2O2 feeding way in MoS2-Fex heterogeneous fenton for enhancing sulfadiazine degradation

In recent years, MoS2 catalyzed/cocatalyzed Fenton/Fenton-like systems have attracted wide attention in the field of pollution control, but there are few studies on the effect of H2O2 feeding way on the whole Fenton process. Here, we report a new type of composite catalyst (MoS2-Fex) prepared in a simple way with highly dispersed iron to provide more active sites. MoS2-Fex was proved to possess selectivity for singlet oxygen (1O2) in effectively degrading sulfadiazine with a wide pH adaptability (4.0∼10.0). Importantly, the mechanism of the interaction between H2O2 and MoS2 on the Fenton reaction activity was revealed through the combination of experiment and density functional theory (DFT) calculations. Compared to the traditional “a large amount for one time” feeding way of H2O2, the “small amount for multiple times” of H2O2 feeding way can increase the degradation rate of sulfadiazine from 36.9% to 91.1% in the MoS2-Fex heterogeneous Fenton system. It is demonstrated that the “small amount for multiple times” of H2O2 feeding way can reduce the side reaction of decomposition of H2O2 by MoS2 and effectively improve the utilization rate of H2O2 and the stability of MoS2-Fex. Compared with Fe2O3-based Fenton system, MoS2-Fex can significantly save the amount of H2O2. Compared with nano-iron powder, the formation of iron sludge in MoS2-Fex system was significantly reduced. Furthermore, long-term degradation test showed that the MoS2-Fe75/H2O2 system could maintain the effectiveness of degrading organic pollutants for 10 days (or even longer). This study has a guiding significance for the large-scale treatment of industrial wastewater by improved Fenton technology in the future.

Immobilized Microalgae using Alginate for Wastewater Treatment

Organic and inorganic substances are released into the environment because of domestic, agricultural, and industrial activities which contribute to the pollution of water bodies. Removal of these substances from wastewater using conventional treatment involves high energy cost for mechanical aeration to provide oxygen for aerobic digestion system. During this process, the aerobic bacteria rapidly consume the organic matter and convert it into single cell proteins, water, and carbon dioxide. Alternatively, this biological treatment step can be accomplished by growing microalgae in the wastewater. Chlorella vulgaris immobilized in calcium alginate was used to study the removal efficiency of main nutrients in wastewater such as ammonium and phosphate that act as an important factor in microalgae growth. The immobilized cells demonstrated higher percentage of ammonium and phosphate removal of 83% and 79% respectively, compared to free-suspended cells (76% and 56%). COD removal recorded was 89% and 83% for immobilized cells and free-suspended cells, respectively. The kinetics parameters of nutrients removal for immobilized C. vulgaris in synthetic wastewater were also determined. The specific ammonium removal rates (RA) and phosphate removal rates (RP) for Chlorella vulgaris in synthetic wastewater were 8.3 mg.L-1day-1 and 7.9 mg.L-1day-1, respectively. On the other hand, the kinetic coefficient for each nutrient removal determined were kA = 0.0462 L.mg-1 day-1 NH4 and kP = 0.0352 L.mg-1 day-1 PO43-. This study proves the application of immobilized microalgae cells is advantageous to the wastewater treatment efficiency. Furthermore, optimization on the immobilization process can be conducted to further improve the nutrients removal rates which potentially can be applied in the large-scale wastewater treatment process.

Degradation of organophosphorus pesticide diazinon by hydrodynamic cavitation: Parameters optimization and mechanism investigation

Diazinon (DZN), a broad-spectrum and highly effective organophosphorus pesticide, is widely being used in agricultural production and household environments. However, massive DZN effluent can be generated during the DZN production process, which will cause devastating effects on the ecosystem and damage human health due to the improper dispose of pesticide effluent before discharging. In this work, hydrodynamic cavitation (HC), a new advanced oxidation technology, was used to degrade DZN in wastewater for the first time. The influences of DZN initial concentration (5.0–15 mg/L), solution pH (4.0–10), temperature (30–50 °C) and some orifice plate geometric parameters (orifice numbers and orifice half angles) on the degradation effect of DZN were investigated. It can be observed that the DZN in solution can be effectively degraded in orifice plate HC system based on three orifices with 45° convergent half angle and the degradation ratio can reach 50.52 % under the operation conditions of 150 min treatment time, 30 °C temperature and pH = 4.0 acidity. Subsequently, the studies of intensifying DZN degradation were also carried out through adding different inorganic oxidants such as potassium peroxodisulfate (K2S2O8), potassium periodate (KIO4) and sodium perchlorate (NaClO4). The maximum DZN HC degradation extent (81.92 %) can be achieved in the presence of K2S2O8 under the optimized conditions. The generated intermediate products in DZN HC degradation process are some low-toxic and low-active substances. And that, these intermediate products can be further mineralized to H2O, CO2 and inorganic ions. On the basis of cavitational yield, the energy consumption analysis has been performed. Overall, this work demonstrates that the HC combined with oxidant K2S2O8 may be a promising strategy for the large-scale treatment of organophosphorus pesticide wastewater.

The Effect of Sodium Hydroxide Concentration on the Structure of Iron Oxides@Bacterial Cellulose and their Catalytic Activity for Methylene Blue Degradation in Solution

Heterogeneous fenton , although offering promises for large scale wastewater treatment, is still hindered in its practicality due to its modest catalytic activity. The usage of catalyst supportas been demonstrated previously toecrease the overall particle size to improve its catalytic performance. In this demonstration, fenton catalysts were prepared using the sol-gel method and bacterial cellulose (BC) as catalyst support, with varying sodium hydroxide (NaOH) concentrations (0.01; 0.1 and 1 M). NaCl impurities' presence was successfully eliminated by reducing NaOH concentration relative to the previous 4 M concentration. Lower NaOH concentration leads to a more favorable condition for the formation of smaller non-agglomerated particles and magnetite (Fe3O4) as its main crystalline phase. It was found that the best performing catalyst was produced using 1 M NaOH and was able to degrade Methylene blue solution up to 53.8% remaining dye concentration within two hours.

Distribution of antibiotic resistance genes and their association with bacteria and viruses in decentralized sewage treatment facilities.

The distribution of antibiotic resistance genes (ARGs) has been intensively studied in large-scale wastewater treatment plants and livestock sources. However, small-scale decentralized sewage treatment facilities must also be explored due to their possible direct exposure to residents. In this study, six wastewater treatment facilities in developed rural areas in eastern China were investigated to understand their risks of spreading ARGs. Using metagenomics and network analysis tools, ARGs and bacterial and viral communities were identified in the influent (INF) and effluent (EFF) samples. The dominant ARGs belonged to the bacitracin class, which are different from most of municipal wastewater treatment plants (WWTPs). The dominant hosts of ARGs are Acidovorax in bacterial communities and Prymnesiovirus in viral communities. Furthermore, a positive relationship was found between ARGs and phages. The ARGs significantly correlated with phages were all hosted by specific genera of bacteria, indicating that phages had contributed to the ARG’s proliferation in sewage treatment facilities. Paying significant concern on the possible enhanced risks caused by bacteria, viruses and their related ARGs in decentralized sewage treatment facilities is necessary.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s11783-021-1469-4 and is accessible for authorized users.

Asparagine functionalized MWCNTs for adsorptive removal of hazardous cationic dyes: Exploring kinetics, isotherm and mechanism

In present work, a novel asparagine functionalized multiwalled carbon nanotube (Asp-CNT) was synthesized and characterized by SEM-EDX, and FTIR spectroscopy. Synthesized nanomaterial was used as an effective adsorbent for removal of hazardous cationic dyes like Malachite green (MG) and Methylene blue (MB) from water in single and binary system. The adsorption parameters like contact time (0-90 min), stirring speed (200-800 rpm), pH (2-9), adsorbent dosage (5-25 mg), initial dye concentration (10-350 mg L−1) and the temperature (25-55°C) were optimized. The adsorption capacities obtained under optimum conditions were 637 mg g−1 and 500 mg g−1 for MG & MB respectively. The kinetic and equilibrium studies were performed using different models. The active investigation of kinetic and equilibrium studies demonstrated that the adsorption process followed pseudo second order and Langmuir model (R2 > 0.99) for both dyes, which infers monolayer adsorption occurred via chemisorption. The simultaneous adsorption study of MG and MB in a binary system showed that MB has faster adsorption rate than MG which can be explained on the basis of structure of dyes. The high adsorption capacity of Asp-CNT for both dyes was explained with the help of adsorption mechanism and further confirmed by FTIR spectra of dyes saturated Asp-CNT. Desorption study of both dyes was conducted using various eluents. It was observed that the adsorbent could be easily regenerated by mixture of acid and ethanol and reused for 3 cycles without altering the adsorption efficiency. Hence, it is concluded from adsorption studies that the synthesized nanomaterial has a great potential to be used for large scale wastewater treatment.

Life cycle assessment of prospective sewage sludge treatment paths in Germany

Due to the amendment of the sewage sludge ordinance, both a thermal post-treatment and a phosphorous recovery from sewage sludge will become mandatory for large-scale wastewater treatment plants in Germany. This study analyzed four prospective treatment paths for sewage sludge by means of life cycle assessment. In the realm of a gate-to-cradle approach, environmental impacts were quantified for all compartments of the ReCiPe Midpoint (H) 2016 method.The spreading of digested sludge on agricultural soils was considered as the base case (system: AD + spreading). It was compared to the centralized incineration of sludge (system: AD + I), a decentralized hydrothermal carbonization followed by centralized incineration (system: AD + HTC + I) and a decentralized pyrolysis of sludge followed by centralized incineration (system: AD + P + I). For all cases, phosphorous recovery from the ash was included. A comparative evaluation showed that AD + spreading resulted in least environmental impacts in most categories but was subject to a high local immission potential due to sewage sludge spreading. It was found to be only justifiable, if toxicity and eutrophication were not compromised. Alternatively, a thermal post-treatment step is required. Hereby, AD + I and AD + HTC + I showed the overall least environmental impacts, while AD + P + I was characterized by similar or higher environmental impacts throughout all impact categories.Alongside the comparative analysis, a hotspot analysis was carried out and mitigation potentials were identified. For all thermochemical post-treatment paths, it was derived that (i) the share of fossil external energy must be kept to a minimum, (ii) primary or secondary measures to control N2O emissions during the incineration and pyrolysis should be implemented and (iii) the technological approach to recover phosphorous must be carefully selected.

Magnetic graphene oxide prepared via ammonia coprecipitation method: The effects of preserved functional groups on adsorption property

Chromium (Cr) has become one of the main pollutants in tannery wastewater, which causes great harm to human health and environment, especially after being oxidized. Herein, the magnetic graphene oxide composite (GO/Fe3O4) is synthesized via coprecipitation method with NH3·H2O. In this way, the self-functional group of graphene oxide (GO) are greatly reserved when Fe3O4 nanoparticles grown on GO sheets, confirming by characterizations, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman. Up to 90% Cr3+ could be adsorbed by resulted GO/Fe3O4 within 140 min, and the maximum adsorption capacity is 279.62 mg g−1. Furthermore, Cr3+ is mainly absorbed by chemical adsorption, according with quasi-second-order kinetic model and Langmuir isotherm. Most importantly, the external magnetic field can effectively recycle the adsorbents from the aqueous solution, facilitating its application in large-scale treatment of tannery wastewater.

A pilot-scale sulfur-based sulfidogenic system for the treatment of Cu-laden electroplating wastewater using real domestic sewage as electron donor

Elemental sulfur (S0) reduction process has been demonstrated as an attractive and cost-efficient approach for metal-laden wastewater treatment in lab-scale studies. However, the system performance and stability have not been evaluated in pilot- or large-scale wastewater treatment. Especially, the sulfide production rate and microbial community structure may significantly vary from lab-scale system to pilot- or large-scale systems using real domestic sewage as carbon source, which brings questions to this novel technology. In this study, therefore, a pilot-scale sulfur-based sulfidogenic treatment system was newly developed and applied for the treatment of Cu-laden electroplating wastewaters using domestic sewage as carbon source. During the 175-d operation, >99.9% of Cu2+ (i.e., 5580 and 1187 mg Cu/L for two types of electroplating wastewaters) was efficiently removed by the biogenic hydrogen sulfide that produced through S0 reduction. Relatively high level of sulfide production (200 mg S/L) can be achieved by utilizing organics in raw domestic sewage, which was easily affected by the organic content and pH value of the domestic sewage. The long-term feeding of domestic sewage significantly re-shaped the microbial community in sulfur-reducing bioreactors. Compared to the reported lab-scale bioreactors, higher microbial community diversity was found in our pilot-scale bioreactors. The presence of hydrolytic, fermentative and sulfur-reducing bacteria was the critical factor for system stability. Accordingly, a two-step ecological interaction among fermentative and sulfur-reducing bacteria was newly proposed for sulfide production: biodegradable particulate organic carbon (BPOC) was firstly degraded to dissolved organic carbon (DOC) by the hydrolytic and fermentative bacteria. Then, sulfur-reducing bacteria utilized the total DOC (both DOC degraded from BPOC and the original DOC present in domestic sewage) as electron donor and reduced the S0 to sulfide. Afterwards, the sulfide precipitated Cu2+ in the post sedimentation tank. Compared with other reported technologies, the sulfur-based treatment system remarkable reduced the total chemical cost by 87.5‒99.6% for the same level of Cu2+ removal. Therefore, this pilot-scale study demonstrated that S0 reduction process can be a sustainable technology to generate sulfide for the co-treatment of Cu-laden electroplating wastewater and domestic sewage, achieving higher Cu2+removal and higher cost-effectiveness than the conventional technologies.

What removals of pathogen indicators can be expected within large-scale wastewater treatment facilities in the context of wastewater reuse in Paris conurbation?

The fate of pathogen indicators (Escherichia coli - EC, intestinal enterococci - IE, RNA-F bacteriophages and spores of sulfite reducing bacteria - SSR) was extensively studied in Parisian large-scale wastewater treatment plants (WWTPs), based on conventional activated sludge, biofiltration or membrane bioreactor (MBR) processes. Between 14 and 87 campaigns were performed between 2014 and 2018 in five WWTPs. High removals of 3 log for both EC and IE, and lower removals of 1-2 log for SSR and RNA-F bacteriophages, were observed in conventional activated sludge and biofiltration WWTPs. The MBR WWTP achieves notably greater removals of 4.5-5.5 log for faecal bacteria and 3-4 log for SSR and RNA-F bacteriophages. This WWTP is the only one already in compliance with reuse standards, the other ones being non-compliant because of SSR and RNA-F bacteriophages. The implementation of a micro-grain activated carbon process would increase the WWTP removals of 0.8 log for faecal bacteria, due to particles retention, with no significant effect on both other pathogens. Ozonation (0.9-1.3 g O3/g dissolved organic carbon) or performic acid (0.8-1.2 ppm) would have greater benefits with additional removals of 1.5-2.5 log for EC, 1-2 log for IE and 0.5-1 log for SSR and RNA-F bacteriophages. Correlations between pathogen indicator removals and initial concentrations were found, as well as a significant decrease of RNA-F bacteriophage concentrations in Parisian raw wastewater, below 2 log. Thus, RNA-F bacteriophages could be a real issue to evaluate the compliance of Parisian wastewater with reuse. The time evolution of removals demonstrated that SSR is the most problematic parameter regarding reuse in conventional activated sludge and biofiltration WWTPs, as its initial concentration is high (5 log) but removals insufficient (<2 log). In contrast, removals of RNA-F bacteriophages greater than 2 log can be obtained within WWTPs completed or not with a tertiary treatment when the initial concentration in raw wastewater is sufficient. Correlations were also found between the removals of pathogen indicators and the removals of physico-chemical parameters, but they are not good enough to allow performance predictions.

Biomass-Derived Adsorbents for Dye and Heavy Metal Removal from Wastewater

Wastewater has a high concentration of dyes and heavy metals, which are the two most significant contaminants. Due to their high toxicity and vulnerability, they possess a potential threat to human health as well as the ecosystem. There are many ways to eliminate these pollutants from water but adsorption has attained much interest because of its low cost, easy application, and no secondary pollutants. Biomass is considered an ecological burden and a reason for the reduction in the earth’s carrying capacity. These materials may be used as cost-effective adsorbents to remove dyes and heavy metals from wastewater. This paper highlights recent advances made in dye and heavy metal adsorption in the last 10 years. The prime focus of this review paper is on the direct application of these biomasses without any chemical or physical alteration. The removal efficiencies and adsorption capabilities of different biomass-derived adsorbents for the removal of dyes and heavy metals from wastewater are summarised in this study. Additionally, the adsorption mechanisms underlying the removal of dyes and heavy metals using biomass-derived adsorbents have been discussed, with a focus on two kinetic models: pseudofirst-order and pseudosecond-order. Furthermore, the Langmuir and Freundlich isotherms were utilised to verify the experimental findings and to quantify the amount and degree of adsorption favorability. Based on what has been covered in the literature, the conclusion has been drawn. The future research needs are proposed in the area of biomass-derived adsorbent development, their modification for improved efficiencies, and application on large-scale wastewater treatment plants.

Degradation of norfloxacin in aqueous solution using hydrodynamic cavitation: Optimization of geometric and operation parameters and investigations on mechanism

Hydrodynamic cavitation (HC), as one of novel advanced oxidation processes (AOPs), is considered to be a promising technology for wastewater treatment because it has the advantages of wide application range, simple operation and no secondary pollution. In this work, the effects of different orifice plate geometric parameters such as orifice shape (circle, square and triangle), orifice plate thickness (2.00–6.00 mm), orifice number (n = 1–5) and orifice divergence angle (α = 0° and ± 45°) on the norfloxacin degradation by using HC were studied to obtain a strong HC effect. And the effects of various operating parameters such as solution pH (3.0–9.0) and initial norfloxacin concentrations (5.0–15 mg/L) on the norfloxacin degradation by using HC were discussed. The trapping experiments of free radicals (OH and O2−) were also carried out for exploring the mechanism of norfloxacin degradation. In addition, adopting the designed orifice plates with optimized geometric parameters, the norfloxacin degradation efficiencies by using HC combined with some added oxidants (H2O2, K2S2O8 and NaClO) were investigated. The Total Organic Carbon (TOC) analysis at the optimum conditions was also performed to identify the mineralization extent. The intermediate products during the norfloxacin degradation were detected by using Liquid Chromatograph-Mass Spectrometer (LC-MS). The experimental results indicated that, under 5.0 bar inlet pressure for 10 mg/L initial norfloxacin concentration at 40 °C operating temperature in pH = 3.0 solution, the degradation ratio of norfloxacin can reach up to 84.20% in the HC system and can reach up to 96.45% in the HC + H2O2 system by using the orifice plate with 4.00 mm thickness, three square orifices and α = 0° orifice divergence angle. The TOC test results show that the mineralization ratio can reach 71.57% in the HC system for 150 min successive cycling, which demonstrated that the HC can effectively mineralize norfloxacin. In addition, the LC-MS results manifested that norfloxacin moleculars can be degraded into a series of organic compounds with low molecular weight and further be oxidized into CO2, H2O and some inorganic ions during the HC process. Overall, the work has demonstrated that the HC is an effective strategy for a large-scale treatment of antibiotics wastewater.

Tough dual-network GAMAAX hydrogel for the efficient removal of cadmium and nickle ions in wastewater treatment applications

A dual network Poly(Acrylamide-co-Acrylic Acid)/Xanthan Gum (XG) hydrogel incorporated with graphene oxide (GAMAAX) was synthesized through free radical polymerization method for the removal of heavy metal ions. The GAMAAX hydrogel was characterized by Fourier transform infrared spectrum (FTIR), environmental scanning electron microscope (ESEM), energy dispersive X-ray spectroscopy (EDS) and rheology tests. The adsorption capacity and electrical conductivity of GAMAAX hydrogel was investigated for varying pH range and adsorption dosage by central composite design (CCD) method. The results indicated that the heavy metal ion adsorption followed the pseudo-second-order kinetic model, and conformed Freundlich adsorption model with substantial adsorption capacities of 312.15 mg/g and 185.0 mg/g for Cd2+ and Ni2+, respectively. In addition to a great single-ion affinity for Cd2+ and Ni2+ ions, it also proved a remarkable dual-ion adsorption capability with the adsorption of 259.25 mg/g and 80.75 mg/g Cd2+ and Ni2+, respectively. Moreover, less than 20% reduction in the adsorption capacity after four adsorption–desorption cycles, verified the reusability of the GAMAAX hydrogel for the practical and large-scale wastewater treatment applications.

Metal-free n/n-junctioned graphitic carbon nitride (g-C3N4): a study to elucidate its charge transfer mechanism and application for environmental remediation.

Graphitic carbon nitride (g-C3N4) has been regarded as a promising visible light-driven photocatalyst ascribable to its tailorable structures, thermal stability and chemical inertness. Enhanced photocatalytic activity is achievable by the construction of homojunction nanocomposites to reduce the undesired recombination of photogenerated charge carriers. In the present work, a novel g-C3N4/g-C3N4 metal-free homojunction photocatalyst was synthesized via hydrothermal polymerization. The g-C3N4/g-C3N4 derived from urea and thiourea demonstrated admirable photocatalytic activity towards rhodamine B (RhB) degradation upon irradiation of an 18 W LED light. The viability of the photoreaction with a low-powered excitation source highlighted the economic and environmental benefits of the process. The optimal g-C3N4/g-C3N4 homojunction photocatalyst exhibited a 2- and 1.8-fold increase in efficiency in relative to pristine g-C3N4 derived from urea and thiourea respectively. The enhanced photocatalytic performance is credited to the improved interfacial transfer and separation of electron-hole pairs across the homojunction interface. Furthermore, an excellent photochemical stability and durability is displayed by g-C3N4/g-C3N4 after three consecutive cycles. In addition, a plausible photocatalytic mechanism was proposed based on various scavenging tests. Overall, experimental results generated from this study is expected to intrigue novel research inspirations in developing metal-free homojunction photocatalysts to be feasible for large-scale wastewater treatment without compromising economically. Graphical abstract.

Greenhouse Gas Emission Mitigation of Large-Scale Wastewater Treatment Plants (WWTPs ): Optimization of Sludge Treatment and Disposal

Greenhouse Gas Emission Mitigation of Large-Scale Wastewater Treatment Plants (WWTPs ): Optimization of Sludge Treatment and Disposal