Decrease In Removal Efficiency Research Articles

Removal of Cr(VI) from Wastewater Using Acrylonitrile Grafted Cellulose Extracted from Sugarcane Bagasse

A highly efficient low-cost adsorbent was prepared using raw and chemically modified cellulose isolated from sugarcane bagasse for decontamination of Cr(VI) from wastewater. First, cellulose pulp was isolated from sugarcane bagasse by subjecting it to acid hydrolysis, alkaline hydrolysis and bleaching with sodium chlorate (NaClO3). Then, the bleached cellulose pulp was chemically modified with acrylonitrile monomer in the presence Fenton’s reagent (Fe+2/H2O2) to carry out grafting of acrylonitrile onto cellulose by atom transfer radical polymerization. The developed adsorbent (acrylonitrile grafted cellulose) was analyzed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Both raw cellulose and acrylonitrile grafted cellulose were used for chromium removal from wastewater. The effects of metal ion concentration, pH, adsorbent dose and time were studied, and their values were optimized. The optimum conditions for the adsorption of Cr(VI) onto raw and chemically modified cellulose were: metal ion concentration: 50 ppm, adsorbent dose: 1 g, pH: 6, and time: 60 min. The maximum efficiencies of 73% and 94% and adsorption capacities of 125.95 mg/g and 267.93 mg/g were achieved for raw and acrylonitrile grafted cellulose, respectively. High removal efficiency was achieved, owing to high surface area of 79.92 m2/g and functional active binding cites on grafted cellulose. Isotherm and kinetics studies show that the experimental data were fully fitted by the Freundlich isotherm model and pseudo first-order model. The adsorbent (acrylonitrile grafted cellulose) was regenerated using three different types of regenerating reagents and reused thirty times, and there was negligible decrease (19%) in removal efficiency after using it for 30 times. Hence, it is anticipated that acrylonitrile could be utilized as potential candidate material for commercial scale Cr(VI) removal from wastewater.

Treatment of oil sands process-affected water using a semi pilot-scale coalescing filter: Effect of fundamental conditions and water characteristics on filtration performance

The reuse of oil sands process-affected water (OSPW) generated during oil extraction is becoming essential due to oil extraction efficiency and stringent environmental regulations. This study investigates the efficacy of a coalescing filter (CF) in removing oil components from OSPW by exploiting coalescence, which involves merging small oil droplets into larger ones using fibers. Real-time, precise oil measurement systems were employed to evaluate the oil removal efficiency of the CF across synthetic OSPW samples with varying properties. Fundamental conditions and water quality components were systematically adjusted to elucidate the influencing factors on oil removal by the CF. Results showed that despite the diesel having significantly lower viscosity than the oil contents in OSPW, CF achieved a removal efficiency of over 60% within the first 10 min of operation time, regardless of oil concentration. Total suspended solids/turbidity exhibited a decreasing trend as it passed through the filter, indicating fouling occurring within the filter. On the other hands, its increase improved CF performance by 6% compared to baseline conditions, while an increase of alkalinity decreased performance by 10%. When each water quality component exists independently, they do not significantly impact the oil removal efficiency. However, when present together, there is a more decrease in removal efficiency due to the reduced interaction between oil and filter. CF was resistant to changes in water quality. Rather, changes in fundamental factors are more sensitive to CF performance. Filter characteristics and mechanisms make residence time the primary factor affecting oil removal by the CF, with variations exceeding 30% depending on conditions. Therefore, optimizing filter number and flow rate is essential to maximize the filtration performance.

Polypyrrole-encapsulated metal oxide nanocomposite for adsorptive abatement of anionic dye from dye laden wastewater: Cost analysis and scale up design

The present work demonstrates the fabrication of an organometallic material i.e. polypyrrole-encapsulated zinc oxide (PPy@ZnO) nanocomposite for adsorptive elimination of Eriochrome black-T (EBT) dye from water. The specific surface area and pore volume of the PPy@ZnO nanocomposite were observed to be 28.726 m2/g and 0.086 cc/g, respectively. At optimum experimental conditions of solution pH; 4.0, PPy@ZnO nanocomposite dose: 1.0 g/L, contact time: 30 min and initial EBT dye concentration: 50 mg/L, maximum EBT dye removal efficiency of ∼94±1.86% was obtained. The pseudo-second-order kinetic and Langmuir isotherm model provides the best fit for the adsorption experiments, with maximum EBT dye adsorption capacity of 277.78 mg/g. The prominent adsorption mechanisms include the hydrogen bonding, π–π interactions, and electrostatic attraction. The adsorption study is spontaneous (ΔG° < 0) and endothermic (ΔH° > 0, ΔS° > 0) in nature as indicated by the thermodynamics study. The reduction in EBT dye removal efficiency was insignificant (∼10±0.94%) in surface water as compared to other real water samples. Monovalent anions (i.e., NO3–and Cl–) have minimal impact on EBT removal efficiency with reduction in removal efficiencies in the range of 4.0±1.54% to ∼11.0±1.93%. Regeneration study suggests an overall ∼20±1.45% decrease in the EBT dye removal efficiency after 5th cycle of regeneration. Response surface methodology suggests the maximum adsorption efficacy of 95±1.68% at initial EBT dye concentration of 35 mg/L, PPy@ZnO dose of 0.85 g/L and contact time of 40 min. The estimated synthesis cost of PPy@ZnO nanocomposite was determined to be ∼117 USD/kg. Batch mode scale-up design suggests a minimum of 87.48 g of PPy@ZnO nanocomposite needs to be applied to treat 50 mg/L of EBT dye loaded wastewater (50 L volume) with 95% dye removal efficiency.

Study of the Effect of the Surfactant Linear Alkylbenzene Sulfonate (LAS) on the Coagulation of Aged Microplastic

Objective: Evaluate the effect of linear alkylbenzene sulfonate (LAS) surfactant on the coagulation of aged microplastic.   Theoretical Framework: Chemical coagulation is one of the steps adopted in water treatment that can help remove microplastics. During coagulation, suspended particles agglomerate, increasing the efficiency of removing these particles in the sedimentation stage. However, when coagulation occurs in the presence of surfactants, evidence points to deficits in removal capacity.   Method: Using Jar Test tests, the optimal parameters for microplastic removal were determined with aluminum sulfate as a coagulating agent in the presence and absence of the surfactant linear alkyl benzene sulfonate (LAS). The LAS concentrations studied were in the range of 20 mg/L to 300 mg/L. Microplastic removal efficiency was evaluated by measuring turbidity.   Results and Discussions: The combination of pH and coagulant concentration values that best suited the system were 5.0 and 4.25 mg/L, respectively. Due to the addition of surfactants, a decrease in removal efficiency was observed, with an average value ranging from 94.79% to 76.50% due to the interaction of polyethylene spheres with the surfactant.   Research Implications: As explained, due to the coexistence of microplastics and surfactants in the aqueous environment, studies that describe chemical coagulation under these conditions have great value for optimizing treatment systems and technologies.   Research Originality/Value: The use of aged microplastics aims to approximate their natural occurrence.

The application of synthesized geopolymer for the removal of cationic dye from industrial wastewater

In this study, a low-cost and effective coal fly ash porous geopolymer (CFPG) was prepared through alkali activation and applied as adsorbent for the removal of Rhodamine B (RhB) from real industrial wastewater. Mineral composition, microstructural analysis and surface chemistry were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. The batch experiment was investigated at different CFPG dose (0.4–2 g), RhB concentration (5–30 mg/L), pH (2, 7 and 10) and contact time (30–300 min). The removal efficiency for the adsorption of RhB using CFPG was affected by dosage, concentration, and time. However, removal efficiency of 100 % was achieved at pH (2, 7 and 10) indicating that the adsorbent can be used in wide pH range owing to the zwitterionic nature of RhB. The findings demonstrated that while increasing the initial dye concentration resulted in a decrease in removal efficiency, increasing the CFPG dose and contact time led to an improvement in removal efficiency. Additionally, for specified values of examined parameters, such as CFPG dose of 2 g, initial RhB dye concentration of 5 mg/L, and contact time of 300 min, the maximum efficiency of 100 % was achieved for RhB dye removal. The study on removal efficiency of CFPG on selective dyes showed that it could also be used to remove other cationic dyes such as malachite green and crystal violet in industrial wastewater as removal efficiency of 100 % was obtained for the removal of both dyes. Pseudo-first-order (R2 = 0.985) and Freundlich (R2 = 0.860) models were most suitable for the adsorption process.

How high salt shock affects performance and membrane fouling characteristics of a halophilic membrane bioreactor used for treating hypersaline wastewater

In the present study, the effect of short-term salt shocks (13% and 20%) on the performance of a halophilic MBR bioreactor used to treat a hypersaline (5% salt) synthetic wastewater was considered. 13% and 20% salt shocks resulted in a transient and permanent decrease in chemical oxygen demand removal efficiency, respectively which could be correlated with soluble microbial products (SMP) concentration and specific oxygen uptake rate values of the halophilic population. DNA leakage tests suggested that both 13% and 20% short-term salt shocks resulted in some cell structural damage. During both 13% and 20% salt shocks mixed liquor SMP, extracellular polymeric substances (EPS), zeta potential and endogenous respiration increased while relative hydrophobicity, EPSp/EPSc and exogenous respiration decreased; in both cases, however, the pre-shock values for these parameters were restored after the removal of the salt shock. 13% salt shock resulted in a transient increase in the membrane fouling rate and a permanent rise in total membrane resistance (Rt). On the other hand, both membrane fouling rate and Rt increased during 20% salt shock. Membrane fouling rate initially reduced after the 20% salt shock removal but after 5 days a “TMP jump” occurred. The latter was caused by the higher steady state SMPc and SMPp concentrations after removal of 20% salt shock compared to pre-shock values. This might have either resulted in a decrease in critical flux or an increase in local flux above critical flux in some parts of the membrane. The contribution of cake layer resistance to overall membrane resistance increased after the 13% and 20% salt shocks. The findings of the present study reveal the robustness of halophilic MBRs against salt shocks in the treatment of hypersaline wastewater. However, in cases of very high salt shocks, appropriate membrane fouling reduction strategies should be carried out during its operation.

Adsorption effects of electron scavengers and inorganic ions on catalysts for catalytic oxidation of sulfamethoxazole in radiation treatment

This study aimed to investigate adsorption effects of electron scavengers (H2O2 and S2O82−) on oxidation performance for mineralization of sulfamethoxazole (SMX) in radiation treatment using catalysts (Al2O3, TiO2). Hydrogen peroxide (H2O2, 1 mM) as an electron scavenger showed weak adsorption onto catalysts (0.012 mmol g−1-Al2O3 and 0.004 mmol g−1-TiO2, respectively), leading to an increase in TOC removal efficiency of SMX within the absorbed dose of 30 kGy by 12.3% with Al2O3 and by 8.0% with TiO2. The weak adsorption of H2O2 onto the catalyst allowed it to act as an electron scavenger, promoting indirect decomposition reactions. However, high adsorption of S2O82− (1 mM) onto Al2O3 (0.266 mmol g−1-Al2O3) showed a decrease in TOC removal efficiency of SMX from 76.2% to 30.2% within the absorbed dose of 30 kGy. The high adsorption of S2O82− onto the catalyst inhibited direct decomposition reaction by reducing adsorption of SMX on catalysts. TOC removal efficiency for Al2O3 without electron scavengers in an acidic condition was higher than that in a neutral or alkaline condition. However, TOC removal efficiency for Al2O3 with S2O82− was higher in a neutral condition than in other pH conditions. This indicates that the pH of a solution plays a critical role in the catalytic oxidation performance by determining surface charges of catalysts and yield of reactive radicals produced from water radiolysis. In the radiocatalytic system, H2O2 enhances the oxidation performance of catalysts (Al2O3 and TiO2) over a wide pH range (3–11). Meanwhile, S2O82− is not suitable with Al2O3 in acidic conditions because of its strong adsorption onto Al2O3 in this study.

Long-term effect of microplastics on anammox systems: From macro efficiency to micro metabolic mechanisms and antibiotic resistance genes proliferation

Wastewater treatment plants (WWTPs) are sinks for various types of microplastics (MPs), which have an undeniable impact on anaerobic ammonia oxidation (anammox) systems, yet their differential effects remain elusive. In this study, the long-term effects of non-biodegradable polyvinyl chloride (PVC) MPs and biodegradable polylactic acid (PLA) MPs in anammox systems were investigated from macro efficiency, micro metabolic mechanism, and antibiotic resistance gene proliferation. Results showed that the introduced 0.5 mg L−1 PVC MPs caused a 20.64 % decrease in nitrogen removal efficiency (NRE) compared to the control one, while PLA MPs resulted in a 10.73 % increase in NRE. Accordingly, the relative abundance of Ca. Kuenenia with the introduced PLA MPs was 16.68 % higher than the control group, while it was 10.89 % lower with the introduced PVC MPs. Furthermore, MPs inhibit the reactor performance by inducing intracellular reactive oxygen species (ROS) production in anammox cells. However, PLA MPs, as a slow biodegradable organic, have a reversible negative effect on ROS induction, which further improves nitrogen removal performance and sludge proliferation through dissimilatory nitrate reduction to ammonium (DNRA) and microbial interactions. Nevertheless, this also poses an increased risk of antibiotic resistance genes (ARGs) spread and proliferation in anammox sludge. This study clarified the comprehensive effects of different MPs types in anammox processes, highlighting the feasibility and potential risks in the engineering applications of anammox processes for MPs-contained wastewater treatment.

Unrefined low-grade pyrolusite for elemental mercury removal from flue gas: Experimental and DFT insights

Dual characteristics of oxidation capacity and economic advantage endow the unrefined low-grade pyrolusite (LGP) as a potential adsorbent/catalyst. This paper successfully applied it to remove Hg0 from flue gas, by which 98.6% of removal efficiency was obtained without chemical modification or external oxidant. Effects of various flue gas components on the Hg0 removal were investigated, and the synchronous improvement in efficiency and stability by HCl was revealed. Also, its reusability was evaluated and the decrease in removal efficiency after 5th cycles is less than 6%. Product analysis indicated that over 90% of Hg0 was chemisorbed as HgO without HCl, but the presence of HCl reversed the pathway to form HgCl2 that easily escape from the surface, with a proportion of about 95%. By combing experiments, characterizations and theoretical calculations, the mechanism was preliminarily speculated: (i) without HCl, O2 and the main components of LGP (MnOx, Fe2O3, etc.) involved in the catalytic oxidation according to Mars-Maessen mechanism; (ii) HCl tended to dissociate and adsorb on the MnO2 to form the chlorinated surface, and the mercury removal followed both L-H and E-R mechanism, although E-R was dominant; (iii) the formation of HgCl lowered the energy barrier of HgCl2 desorption, thereby expediting the oxidation-removal of Hg0.

Hydrothermal precipitation of hematite from the model solution of zinc hydrometallurgical extraction

Abstract The effect of temperature and silicon concentration on iron precipitation and morphology of hematite particles was discussed. The results showed that increase of initial silicon centration will lead to the decrease of iron removal efficiency, and the Fe content decreases and S content increases in hematite. Increasing temperature is beneficial to increase iron removal rate and Fe content in hematite, but increasing temperature can not decrease silicon content in hematite. The content of Si in precipitate is proportional to the concentration of silicon in solution. Silicon is adsorbed on the surface of hematite in the form of silicic acid. Hematite particle was agglomerated microsphere. Increasing concentration of silicon will increase the disorder degree of hematite crystallization. With the increase of silicon concentration, the agglomeration of hematite particle was more obvious, and the average particle size of hematite particles increased. At 175 °C, the morphology of iron precipitation particles are composed of flake particles and rhomboid massive particles, but when the temperature rises to 195 °C, the agglomeration phenomenon is obvious, small flake particles agglomerate into microspherical aggregates.

Ofloxacin weakened treatment performance of rural domestic sewage in an aerobic biofilm system by affecting biofilm resistance, bacterial community, and functional genes

Ofloxacin (OFL) is a typical fluoroquinolone antibiotic widely detected in rural domestic sewage, however, its effects on the performance of aerobic biofilm systems during sewage treatment process remain poorly understood. We carried out an aerobic biofilm experiment to explore how the OFL with different concentrations affects the pollutant removal efficiency of rural domestic sewage. Results demonstrated that the OFL negatively affected pollutant removal in aerobic biofilm systems. High OFL levels resulted in a decrease in removal efficiency: 9.33% for chemical oxygen demand (COD), 18.57% for ammonium (NH4+-N), and 8.49% for total phosphorus (TP) after 35 days. The findings related to the chemical and biological properties of the biofilm revealed that the OFL exposure triggered oxidative stress and SOS responses, decreased the live cell number and extracellular polymeric substance content of biofilm, and altered bacterial community composition. More specifically, the relative abundance of key genera linked to COD (e.g., Rhodobacter), NH4+-N (e.g., Nitrosomonas), and TP (e.g., Dechlorimonas) removal was decreased. Such the OFL-induced decrease of these genera might result in the down-regulation of carbon degradation (amyA), ammonia oxidation (hao), and phosphorus adsorption (ppx) functional genes. The conventional pollutants (COD, NH4+-N, and TP) removal was directly affected by biofilm resistance, functional genes, and bacterial community under OFL exposure, and the bacterial community played a more dominant role based on partial least-squares path model analysis. These findings will provide valuable insights into understanding how antibiotics impact the performance of aerobic biofilm systems during rural domestic sewage treatment.

Comparison of aluminum formate and traditional aluminum coagulants in structure, hydrolysates, coagulation behavior, and its corrosion resistance advantage

Aluminum formate (AF) has been considered as a superior coagulant that can decompose under the UV light without causing equipment corrosion during water treatment. The main components of the aluminum formate coagulant are aluminum formate (C3H3AlO6), aluminum formate hydrate (C3H3AlO6·3H2O), and aluminum hydrogen formate (C3H3AlO6·2H2O2). Analysis of the hydrolyzed products revealed that the content of added formic acid during the synthesis of aluminum formate is a crucial factor influencing its coagulation effectiveness. Increasing the HCOOH/Al ratio from 1.5 to 4.0 resulted in smaller mass-to-charge ratio (m/z) and higher positive charge for AF hydrolysates, with fewer undetected aluminum species present. Hydrolysates of AF 1.5 exhibited similar characteristics to those of aluminum polychloride, while AF 3.0 demonstrated optimal glucan removal efficiency (>55 %) through physical absorption rather than chemical bond bridging as the primary coagulation mechanism. The jar test results for bovine serum albumin (BSA) coagulation removal indicated a decrease in removal efficiency as the HCOOH/Al molar ratio increased from 1.5 to 4.0, accompanied by a decrease in pH conditions from 6.35 to 7.27. The highest BSA removal efficiency (58 %) was achieved using AF 1.5 at pH 6.35, suggesting that BSA molecules were captured by aluminum formate through chemical bonds such as NO-Al-, Al2(SO4)3, unlike the physical absorption effect observed in glucan coagulation process. Furthermore, it should be noted that compared to traditional aluminum salt coagulants, aluminum formate exhibits excellent pipeline corrosion resistance properties.

Deactivation of internal recirculation in a full-scale Biological Nutrient Removal (BNR) Wastewater Treatment Plant (WWTP) reveals outstanding microeukaryotic bioindicators

The bioindicator potential of the microeukaryotic community in a full-scale A2O wastewater treatment process was assessed after deactivating the internal recirculation in one of the two parallel treatment lines of the plant. The deactivation of the internal recirculation in one of the lines (NIR-line), led to a strong decrease in nitrogen removal efficiency (53 % ammonia-uptake in the NIR-line versus 97 % in the unaltered line or IR-line), as well as to a lower organic matter removal (95 % BOD5 removal versus 97 % in the IR-line). The microeukaryote community structure changed greatly confirming trends observed in experimental studies and showed a decrease in abundance and richness in the NIR-line. However, this line showed a significant higher abundance of certain ciliate species, such as Epistylis camprubii and Vorticellides infusionum, which are common species in conventional activated sludge. Conversely, the IR-line showed useful indicators of internal recirculation, associated with much higher ammonium and BOD5 removal. These results show that identification to ciliate species level provides a more reliable bioindication in nutrient removal systems, supporting the importance of research on biological parameters, mainly protists, as simple and useful tools for plant operators to manage nutrient removal processes. These observations extend the current boundaries of bioindication.

Enhanced biological phosphorus removal from wastewater and dynamics of microbial population in dual PAOs symbiosis system

Low level of volatile fatty acids (VFAs) is a key factor limiting the performance of enhanced biological phosphorus removal (EBPR) by traditional polyphosphate accumulating organisms (PAOs). A newly discovered PAOs capable of fermenting macromolecular organic matter into short-chain VFAs could solve the problem. However, the roles of traditional and fermented PAOs in wastewater treatment processes and the collaboration between functional microorganisms remain unknown. In this study, a sequencing batch reactor (SBR) was operated with alternating anaerobic oxic (An/O) mode to investigate the effect of mixed carbon source ratios, namely, acetate (NaAc):casein hydrolysate (Cas aa) = 4:0, 3:1, 1:1, 1:3 and 0:4, on EBPR performance and microbial community structure. The results showed that the phosphorus removal efficiency remained stable as NaAc was the sole carbon source. When NaAc:Cas aa varied from 3:1 to 1:3, the recovery of system performance took less time compared to the last Run, implying an adaptation of PAOs to Cas aa. Moreover, the anaerobic phosphorus release time was found to increase with the increasing amount of VFAs from Cas aa degradation, indicating the enrichment of fermented bacteria and the utilization of VFAs by traditional PAOs. Increasing the dose of Cas aa also generated more NH4+-N, owing to the reaction of the groups in the amino acids with water, causing a drastic decrease of ammonium removal efficiency from 88.9 % to 15.2 %. The ideal process performance implied that EBPR by dual PAOs synergistic symbiosis occurred in the system with NaAc:Cas aa = 1:1. Meanwhile, the results of 16S ribosomal RNA (16S rRNA) genes-Illumina MiSeq high-throughput sequencing showed that the abundance of traditional PAOs decreased from 22.4 % (4:0) to 11.6 % (1:1) and to 4.9 % (0:4), but fermented PAOs increased from 9.9 % to 19.5 %, then decreased to 17.3 %. Dual PAOs synergistic symbiosis could be of great potential for EBPR in treating low VFAs wastewater.

Integrated bipolar electrocoagulation and PVC-based ultrafiltration membrane process for palm oil mill effluent (POME) treatment

In this study, the effectiveness of integrating electrocoagulation (EC) and ultrafiltration (UF) membranes for palm oil mill effluent (POME) wastewater treatment was investigated. The impact of various parameters on contaminant removal efficiency, including electrode configuration (monopolar and bipolar), number of anodes, agitation rate, and current density, was studied. The findings demonstrated that using bipolar (BP) electrodes in the EC reactor improved coagulation efficiency. However, an increase in agitation rate led to a decrease in removal efficiency. The electrode configuration of 2A-2C–2B achieved high contaminant removal with a lower electrode consumption compared to the 4A-2C and 4A-2C–2B configurations. The removal efficiencies for total dissolved solids (TDS), total suspended solids (TSS), chemical oxygen demand (COD), and biological oxygen demand (BOD) were 59.1%, 99.9%, 96.8%, and 96%, respectively. The operating cost for the electrode configuration of 2A-2C–2B was estimated to be 2.71 US$ m−3 at an effluent capacity of 50 m3 d−1 and 20 h d−1 of operating time, while the energy requirement was 6.20 kWh m−3. An increase in operating time from 5 to 24 h d−1 raised the specific operating cost from 2.17 to 2.85 US$ m−3. This study provides valuable insights into optimizing EC and UF processes for POME wastewater treatment, which could have significant implications for sustainable industrial practices.

Electro-oxidation of persistent organic contaminants at graphene sponge electrodes using intermittent current

Borophene (Bph) and hexagonal boron nitride (hBN)-modified graphene sponge anode coupled to N-doped graphene sponge cathode were applied for electrochemical degradation of persistent organic contaminants using intermittent current. Three different ON-OFF pulse cycles were tested using low-conductivity supporting electrolyte in flow-through mode. Functionalization of the reduced graphene oxide (RGO) with Bph and hBN improved the ability of the double layer to store electrical charge, thus maintaining the generation of H2O2, O3, and ·OH even during the OFF cycles. Both anodes tested showed enhanced contaminant removal during shorter OFF periods (e.g. 52.5 s/52.s and 75 s/30 s ON/OFF), due to the improved retention of anode charge during the shorter OFF stages. Electrochemical removal of the target contaminants required 24 kWh m−3 in continuous current mode for both hBN-RGO and Bph-RGO anodes at 231 A/m−2, which was lowered to 11.7 and 13.5 kWh m−3 respectively, using ON-OFF pulse cycles. Electrochemical degradation pathways were elucidated in both systems using carbamazepine as a representative persistent contaminant. Flow-through reactors with both Bph- and hBN-RGO anodes removed ≥60 % of the target contaminants in a single pass using continuous current, whereas intermittent current led to somewhat decreased removal efficiencies (43–58 %) due to the scavenging effect of the wastewater matrix. Thus, halving the current ON time led to less than 20 % decrease in the removal efficiencies due to the capacitive properties of RGO. Given that switching to intermittent current decreased the energy consumption from 9.3 kWh m−3 to 4.4 kWh m−3 (Bph-RGO anode) and from 6.9 kWh m−3 to 3.6 kWh m−3 (hBN-RGO anode), higher removal of the target contaminants can be achieved by coupling sequential reactors in the intermittent current mode.

Efficient visible-light-driven photocatalytic degradation of tetracycline by rod-like CoFe2O4/MWCNTs nanocomposite as a recyclable photocatalyst: a comprehensive study

ABSTRACT Tetracycline (TC), a common antibiotic used to study bacterial illnesses in living organisms, is also exceedingly dangerous to the aquatic environment. Numerous traditional techniques are applied to remove the TC antibiotics from the water solution. However, these procedures have not helped to get rid of TC antibiotics. So, in this work, photocatalytic TC degradation has been considered. Hydrothermal synthesis was used to create the CoFe2O4 /MWCNTs nano-composite, and various techniques were used to characterise it. The characterisation experiments revealed that multi-walled carbon nanotubes (MWCNTs) are successfully incorporated into cobalt ferrite spinel (CoFe2O4) nanoparticles and this limits the rate at which charge carriers recombine after combining with MWCNTs. The effectiveness of the catalyst was then evaluated in a batch reactor using the weight percentage variation of the nano-composite, specifically TC 0.5, TC 01, TC 02, TC 03, and TC 04, with constant pH 7, with TC concentration of 0.05 g/L and nano-composite dosage of 0.6 g/L for 120 min under 120 W/m2 of visible light. The same operational settings were used to study the TC degradation using CoFe2O4 and MWCNTs as individual pure materials. According to the findings, using CoFe2O4 /MWCNTs with a weight percentage ratio of 1:4 (TC 04) increased the photocatalytic degradation efficiency to 90.00% compared to pure materials. After being utilised three times in a row, the photocatalysts were as-produced, and it was discovered that there was an approximate 2.7% decrease in removal efficiency. As a result of its comparatively straightforward synthesis, high stability, and high potential for recycling, CoFe2O4 /MWCNTs nano-composite, specifically, TC 04, demonstrated a respectable efficiency in the TC degradation. Therefore, this material will make it possible to eliminate and degrade pharmaceutical organic contaminants.

Fabrication of polyaniline based calcium ferrite nanocomposite and its application in sequestration of Victoria blue dye from wastewater

Fabrication of a novel nanocomposite named calcium ferrite/polyaniline (CaFe2O4-PANI) was reported and its potential for adsorption of toxic cationic dye named Victoria blue (VB) was studied in this work. The CaFe2O4-PANI has showcased improved adsorptive potential for VB dye with approximately 95.35 (±1.48)% of removal efficiency at solution pH 8.0, CaFe2O4-PANI dose of 0.5 g/L, contact time of 20 min and initial VB dye concentration of 50 mg/L. The adsorption process follows pseudo-second-order kinetic model and Freundlich isotherm model with a maximum uptake capacity of 266.67 mg/g. The adsorbent was also tested against surface and ground water sample loaded with VB dye and in presence of several ions. It was found that surface water has caused less interference (∼2 (±0.85)% reduction in VB dye removal efficiency) followed by ground water (∼4 (±0.91)% reduction) and wastewater (∼8 (±1.24)% reduction) and also the removal efficiencies are affected the most by bicarbonate ions (∼12 (±1.39)%–14 (±1.62)% reduction in VB dye removal efficiency). The experimental process was optimized utilizing a five level, three factor based response surface methodology (RSM) approach and the experimental parameters were optimized to CaFe2O4-PANI dosage = 0.5 g/L, contact time = 65 min and initial VB dye conc. = 60 mg/L, using the developed quadratic model to achieve a maximum VB removal efficiency of 98.63 (±2.13)%. Regeneration study suggests that the fabricated adsorbent can be reused up to five cycles with ∼10 (±1.13)% decrease in the VB dye removal efficiency.

Removal of polymethyl methacrylate nanoplastics and silver nanoparticles by a novel ferrofluid-COF-aminated natural cotton-based hydrogel nanosorbent

In this work, an innovative nanosorbent is assembled based on the combination of Fe2VO6 ferrofluid, silane covalent organic frameworks (COFs) and gelatin/aminated natural cotton/chitosan hydrogel (FF-SiCOF@Gel-ANC@Ch.Hgel). The developed nanomaterial was fully identified using several characterization techniques such as FTIR, electron microscopy, XRD and XPS; and was then studied as an effective nanosorbent for removal of organic nanopollutants such as polymethyl methacrylate nanoplastics (PMMA) and inorganic nanopollutants such as silver nanoparticles from water. Optimization of experimental parameters such as reaction duration, nanosorbent mass, nanopollutant concentration, solution pH, temperature and medium ionic strength revealed promising removal efficiencies towards both nanopollutants with 98.3% and 99.2% recovery for Ag and PMMA nanopollutants, respectively. Kinetic studies confirmed that the adsorptive removal of both nanosorbent followed via a pseudo-second order chemisorption process. Thermodynamic investigations highlighted that spontaneity of the chemisorption process in terms of negative ΔG° values. Industrial scale applicability was confirmed with interestingly high removal efficiencies toward both nanopollutants (99.45% and 96.80% for Ag and PMMA, respectively) in industrial wastewater. Furthermore, proposed nanosorbent showed appreciable recyclability with little decrease in removal efficiencies (from 95.30% to 91.00% and from 97.20% to 93.00% for Ag and PMMA respectively) after 5 adsorption/regeneration cycles. Considering nanosorbent comparatively high adsorption capacities, together with its industrial applicability and reusability, it was proposed as a promising candidate for wastewater treatment applications. The green aspects in this study were investigated in terms of reusing the recovered Ag@FF-SiCOF@Gel-ANC@Ch.Hgel as a potential nanocatalyst in reductive degradation of sulfasalazine drug, a potentially hazardous pollutant. High degradation rates were deduced at optimal conditions providing 2.3 min−1pseudo-first order rate constant with only 3.18% drop in the catalytic activity after 5 successive reduction/regeneration cycles. This accounts for the promising potential of recycled Ag@FF-SiCOF@Gel-ANC@Ch.Hgel as reductive degradation catalyst for targeted water treatment applications.

Enhanced photocatalytic performance of milkvetch-derived biochar via ZnO–Ce nanoparticle decoration for reactive blue 19 dye removal

In this research, the photocatalytic removal of reactive blue 19 (RB19) dye is investigated employing zinc oxide/cerium (ZnO@Ce) nanoparticles decorated with biochar under LED irradiation. Synthesis of ZnO@Ce nanoparticles decorated with biochar was performed utilizing the co-precipitation procedure and, then, the texture and morphology of the fabricated nanocomposite were analyzed using energy dispersive X-ray (EDX), field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and Fourier transform infrared (FTIR) spectroscopy techniques. Moreover, FE-SEM images demonstrate that ZnO–Ce nanoparticles were successfully decorated on the surface of biochar. The specific surface areas of biochar and biochar/ZnO–Ce were 519.75 and 636.52 m2/g, respectively. To achieve the maximum yield in the removal of RB19 dye, the effects of operating variables including dye concentration, LED lamp power, biochar@ZnO–Ce catalyst dose, pH and H2O2 dose were explored. Besides, the maximum percentage of RB19 dye removal was 96.47% under optimal conditions, i.e. catalyst dosage of 100 mg, H2O2 dosage of 1 mL, pH of 9, initial dye concentration of 5 ppm, LED power of 50 W, and reaction time of 140 min. Furthermore, the kinetic analysis reveals that the removal of RB19 dye follows the pseudo-first order kinetic model, with calculated values of a reaction rate constant of 0.045 min−1 and a correlation coefficient of R2 = 0.99, respectively. Moreover, the reusability and recyclability of biochar@ZnO/Ce nanocatalyst was promising over five runs, with only a 6.08% decrease in RB19 dye removal efficiency. Therefore, it can be concluded that the biochar @ZnO/Ce photocatalyst can be promisingly applied for the removal of azo dyes in aqueous solutions.