Algae development in rivers with artificially constructed weirs: Dominant influence of discharge over temperature.

Algal blooms contribute to water quality degradation, unpleasant odors, taste issues, and the presence of harmful substances in artificially constructed weirs. Mitigating these adverse effects through effective algal bloom management requires identifying the contributing factors and predicting algal concentrations. This study focused on the upstream region of the Seungchon Weir in Korea, which is characterized by elevated levels of total nitrogen and phosphorus due to a significant influx of water from a sewage treatment plant. We employed four distinct machine learning models to predict chlorophyll-a (Chl-a) concentrations and identified the influential variables linked to local algal bloom events. The gradient boosting model enabled an in-depth exploration of the intricate relationships between algal occurrence and water quality parameters, enabling accurate identification of the causal factors. The models identified the discharge flow rate (D-Flow) and water temperature as the primary determinants of Chl-a levels, with feature importance values of 0.236 and 0.212, respectively. Enhanced model precision was achieved by utilizing daily average D-Flow values, with model accuracy and significance of the D-Flow amplifying as the temporal span of daily averaging increased. Elevated Chl-a concentrations correlated with diminished D-Flow and temperature, highlighting the pivotal role of D-Flow in regulating Chl-a concentration. This trend can be attributed to the constrained discharge of the Seungchon Weir during winter. Calculating the requisite D-Flow to maintain a desirable Chl-a concentration of up to 20 mg/m3 across varying temperatures revealed an escalating demand for D-Flow with rising temperatures. Specific D-Flow ranges, corresponding to each season and temperature condition, were identified as particularly influential on Chl-a concentration. Thus, optimizing Chl-a reduction can be achieved by strategically increasing D-Flow within these specified ranges for each season and temperature variation. This study highlights the importance of maintaining sufficient D-Flow levels to mitigate algal proliferation within river systems featuring weirs.

Value-added application of cattle manure bottom ash for phosphorus recovery from water and replenishment in soil.

This study addresses ways to circulate the flow of phosphorus (P) from water to soil to improve water quality and provide a sustainable supply of P into soil. Here, bottom ash (BA_CCM), the byproduct of the combustion of cattle manure, which is performed for obtaining energy, was used to remove P in wastewater. Next, the P-captured BA_CCM was used as P fertilizer for rice growth. BA_CCM was primarily composed of Ca (49.4%), C (24.0%), and P (9.9%), and the crystalline phases of Ca were calcium carbonate (CaCO3) and hydroxyapatite (Ca5(PO4)3OH). The mechanism of P removal by BA_CCM involves the formation of hydroxyapatite by reacting Ca2+ with PO43-. A reaction time of 3 h was required to achieve P adsorption to BA_CCM, and the maximum P adsorption capacity of BA_CCM was 45.46 mg/g. The increase in solution pH reduced P adsorption. However, at pH > 5, the P adsorption amount was maintained regardless of the pH increase. The presence of 10 mM SO42- and CO32- reduced P adsorption by 28.4% and 21.5%, respectively, and the impact of the presence of Cl- and NO3- was less than 10%. The feasibility of BA_CCM was tested using real wastewater, and 3.33 g/L of BA_CCM dose achieved a P removal ratio of 99.8% and a residual concentration of <0.02 mg/L. The toxicity unit of BA_CCM determined for Daphnia magna (D. magna) was 5.1; however, the BA_CCM after P adsorption (P-BA_CCM) did not show any toxicity to D. magna. BA_CCM after P adsorption was used as an alternative to commercial P fertilizer. Rice fertilized with a medium level of P-BA_CCM showed better agronomic values for most agronomic traits, except root length, than that seen with the commercial P fertilizer. This study suggests that BA_CCM can be used as a value-added product to address environmental issues.

Contamination of typical phthalate acid esters in surface water and sediment of the Pearl River, South China: Occurrence, distribution, and health risk assessment.

The occurrence and distribution of six phthalate acid esters (PAEs) in surface water and sediment of the Pearl River were investigated, including Xijiang River (XR), Beijiang River (BR), Lingdingyang Estuary (LE), and Guangzhou River (GR) in South China. Six target PAEs were identified in surface water and sediment at almost all sites in the Pearl River, with di(2-ethyl-ethyl) phthalate (DEHP) and dibutyl phthalate (DBP) as dominant PAEs. Total 6 PAEs (ΣPAEs) in surface water and sediment ranged from 1,797.5 to 4,968.5 ng L-1 and 95.24 to 3,677.26 ng g-1 dw, respectively. In addition, the contamination levels of PAEs in the Pearl River are in the following order: XR > BR > GR > LE for surface water and BR > XR > GR for sediment. Local agricultural activities, industrial production, water confluence, and seawater intrusion are the probable sources of PAEs in the Pearl River. Based on correlation analysis, the possible collocation patterns of different PAEs were revealed. The risk assessment indicates that residual PAEs in the Pearl River pose a serious threat to the ecological environment. According to risk characterization of fish living in the Pearl River, the decreasing order of health risks was: GR > LE > XR > BR.

As(III) adsorption onto Fe-impregnated food waste biochar: experimental investigation, modeling, and optimization using response surface methodology.

Biochar derived from food waste was modified with Fe to enhance its adsorption capacity for As(III), which is the most toxic form of As. The synthesis of Fe-impregnated food waste biochar (Fe-FWB) was optimized using response surface methodology (RSM), and the pyrolysis time (1.0, 2.5, and 4.0 h), temperature (300, 450, and 600 °C), and Fe concentration (0.1, 0.3, and 0.5 M) were set as independent variables. The pyrolysis temperature and Fe concentration significantly influenced the As(III) removal, but the effect of pyrolysis time was insignificant. The optimum conditions for the synthesis of Fe-FWB were 1 h and 300 °C with a 0.42-M Fe concentration. Both physical and chemical properties of the optimized Fe-FWB were studied. They were also used for kinetic, equilibrium, thermodynamic, pH, and competing anion studies. Kinetic adsorption experiments demonstrated that the pseudo-second-order model had a superior fit for As(III) adsorption than the pseudo-first-order model. The maximum adsorption capacity derived from the Langmuir model was 119.5 mg/g, which surpassed that of other adsorbents published in the literature. Maximum As(III) adsorption occurred at an elevated pH in the range from 3 to 11 owing to the presence of As(III) as H2AsO3- above a pH of 9.2. A slight reduction in As(III) adsorption was observed in the existence of bicarbonate, hydrogen phosphate, nitrate, and sulfate even at a high concentration of 10 mM. This study demonstrates that aqueous solutions can be treated using Fe-FWB, which is an affordable and readily available resource for As(III) removal.

Use of calcined sepiolite in removing phosphate from water and returning phosphate to soil as phosphorus fertilizer.

We investigated the application of cheap but efficient sepiolite for the removal of phosphate and the use of phosphate-adsorbed sepiolite for rice cultivation. Sepiolite was calcined under different temperatures to improve its phosphate adsorption capacity; the sepiolite calcined at 950 °C (950-SPL) was found to have highest adsorption capacity. As the calcination temperature increased, the amount of Ca eluted from sepiolite also increased, resulting in the formation of Ca-P precipitates. Phosphate adsorption on 950-SPL reached equilibrium within 12 h. Both the Langmuir and Freudlich models were not well-fitted to the equilibrium adsorption model because phosphate at initial concentration was fully removed by 950-SPL. The maximum adsorption capacity of 950-SPL with respect to phosphate was 172.34 mg/g. The phosphate adsorption of 950-SPL was endothermic and spontaneous. Phosphate adsorption at pH 3 was two times higher than at pH 11. The presence of bicarbonate significantly influenced the decrease of phosphate by 950-SPL. A breakthrough of column packed with 950-SPL/sand was not observed during >200 h. The phosphate fraction in 950-SPL was mainly composed of apatite-P and residual fraction. A toxicity test using Daphnia magna showed that the toxic units of 950-SPL corresponded to no acute toxicity. Tiller number, shoot height, shoot dry weight and total dry weight were significantly higher in P-adsorbed 950-SPL application than control. It can be concluded that calcined sepiolite can be effective in the removal of phosphate and that the sepiolite after phosphate adsorption can be used as a P fertilizer in soil.

Porous Electrospun Fibers Embedding TiO2 for Adsorption and Photocatalytic Degradation of Water Pollutants.

Using a bipolymer system consisting of polyvinylpyrrolidone (PVP) and poly(vinylidene fluoride) (PVDF), P25-TiO2 was immobilized into thin film mats of porous electrospun fibers. Pores were introduced by dissolving sacrificial PVP to increase surface area and enhance access to TiO2. The highest photocatalytic activity was achieved using a PVDF:PVP weight ratio of 2:1. Methylene blue (MB) was used to visualize contaminant removal, assess the sorption capacity (5.93 ± 0.23 mg/g) and demonstrate stable removal kinetics ( kMB > 0.045 min-1) under UVA irradiation (3.64 × 10-9 einstein/cm2/s) over 10 cycles. Treatment was also accomplished via sequential MB sorption in the dark and subsequent photocatalytic degradation under UVA irradiation, to illustrate that these processes could be uncoupled to overcome limited light penetration. The photocatalytic mat degraded bisphenol A and 17α-ethynylestradiol in secondary wastewater effluent (17 mg TOC/L), and (relative to TiO2 slurry) immobilization of TiO2 in the mat mitigated performance inhibition by co-occurring organics that scavenge oxidation capacity. This significantly lowered the electrical energy-per-order of reaction (EEO) needed to remove such endocrine disruptors in the presence of oxidant scavenging/inhibitory organics. Thus, effective TiO2 immobilization into polymers with affinity toward specific priority pollutants could both increase the efficiency and reduce energy requirements of photocatalytic water treatment.

Cr(VI) Adsorption to Magnetic Iron Oxide Nanoparticle-Multi-Walled Carbon Nanotube Adsorbents.

The aim of this study was to investigate the Cr(VI) adsorption to magnetic iron oxide(MIO) nanoparticle- multi-walled carbon nanotubes (MWCNTs) in aqueous solutions using batch experiments. Results show that the maximum adsorption capacity of Cr(VI) to MIO-MWCNTs was 11.256 mg/g. Kinetic model analysis demonstrates that the pseudo-second-order model and Elovich model are suitable for describing the kinetic data. Thermodynamic analysis indicates that Cr(VI) adsorption to MIO-MWCNTs decreased with increasing temperature from 5-60 °C, indicating the spontaneous and exothermic nature of the sorption process. Equilibrium isotherm analysis demonstrates that the Redlich-Peterson model suitably describes the equilibrium data. In the pH experiments, Cr(VI) adsorption to MIO-MWCNTs decreased gradually from 5.70-2.13 mg/g with increasing pH from 3.0-7.3. Sequential extraction indicates that, among the five binding forms of Cr(VI) associated with MIO-MWCNTs, the predominant contributions are the fraction bound to Fe-Mn oxides (57.82%) and the residual (23.38%).

Adsorption of bacteriophage MS2 to magnetic iron oxide nanoparticles in aqueous solutions.

The aim of this study was to investigate the adsorption of bacteriophage MS2 by magnetic iron oxide nanoparticles in aqueous solutions. The characteristics of synthetic nanoparticles were analyzed using various techniques. The adsorption of MS2 to the nanoparticles was examined under various conditions using batch experiments. The results showed that the nanoparticles were mainly composed of maghemite along with goethite. The nanoparticles had a specific surface area of 82.2 m(2) g(-1), with an average pore diameter of 13.2 nm and total pore volume of 0.2703 cm(3) g(-1). The results demonstrated that the removal of MS2 by the nanoparticles was very fast. A 3.15 log removal (99.93%) was achieved within 60 min (adsorbent dose = 2 g L(-1); MS2 concentration = 2.94 × 10(6) pfu mL(-1)). The log removal decreased from 3.52 to 0.36 with increasing MS2 concentration from 1.59 × 10(4) to 5.01 × 10(7) pfu mL(-1). Also, the effect of solution pH on MS2 removal was minimal at pH 4.2-8.4. The removal of MS2 decreased in the presence of anions such as carbonate and phosphate, with the latter showing a greater hindrance effect on removal. This study demonstrated that magnetic iron oxide nanoparticles are very effective in the removal of MS2 from aqueous solutions.

Efficient cadmium removal from industrial wastewater generated from smelter using chemical precipitation and oxidation assistance.

The effective treatment of cadmium (Cd) in smelting wastewater is of great industrial importance. This study investigates the efficient removal of Cd from real industrial smelting wastewater via chemical precipitation using a series of experiments. In particular, the effects of different precipitants, agitation conditions, and the addition of NaOCl on Cd removal and pH variation are investigated. CaO (3.75 g/L), NaOH (3.50 g/L), and Ca(OH)2 (3.75 g/L) are found to be effective in elevating the wastewater pH and achieving high Cd removal rates (>99.9%), while the use of NaOH as a precipitant maintains a high Cd removal rate even at low agitation intensities. The properties of the produced sludge and supernatant are also determined using moisture content, particle size, and sludge leaching analyses due to the importance of economic and environmental sustainability in filtration, dewatering, and waste disposal processes. In addition, the addition of 2% NaOCl is tested, revealing that it can improve the Cd removal efficiency of Ca(OH)2, thus potentially reducing processing costs and enhancing the environmental benefits. Overall, these findings offer valuable insights into the removal of Cd from smelting wastewater, with potential implications for both environmental sustainability and economic viability. PRACTITIONER POINTS: CaO, NaOH, and Ca(OH)2 effectively remove Cd (>99.9%) from smelting wastewater. The use of NaOH leads to high Cd removal rates even at low agitation speeds. Adding 2% NaOCl can reduce the Ca(OH)2 dose for more economical Cd removal.

Feasibility study of Aesculus turbinata fruit shell-derived biochar for ammonia removal in wastewater and its subsequent use as nitrogen fertilizer.

In the face of increasing nitrogen demand for crop cultivation driven by population growth, this study presents a sustainable solution to address both the heightened demand and the energy-intensive process of nitrogen removal from wastewater. Our approach involves the removal of nitrogen from wastewater and its subsequent return to the soil as a fertilizer. Using biochar derived from Aesculus turbinata fruit shells (ATFS), a by-product of post-medical use, we investigated the effect of pyrolysis temperature on the NH4-N adsorption capacity of ATFS biochar (ATFS-BC). Notably, the ATFS-BC pyrolyzed at 300 °C (ATFS-BC300) exhibited the highest NH4-N adsorption capacity of 15.61 mg/g. The superior performance of ATFS-BC300 was attributed to its higher number of oxygen functional groups and more negatively charged surface, which contributed to the enhanced NH4-N adsorption. The removal of NH4-N by ATFS-BC300 involved both physical diffusion and chemisorption, with NH4-N forming a robust multilayer adsorption on the biochar. Alkaline conditions favored NH4-N adsorption by ATFS-BC300; however, the presence of trivalent and divalent ions hindered this process. Rice plants were cultivated to assess the potential of NH4-N adsorbed ATFS-BC300 (NH4-ATFS-BC300) as a nitrogen fertilizer. Remarkably, medium doses of NH4-ATFS-BC300 (594.5 kg/ha) exhibited key agronomic traits similar to those of the commercial nitrogen fertilizer in rice seedlings. Furthermore, high doses of NH4-ATFS-BC300 demonstrated superior agronomic traits compared to the commercial fertilizer. This study establishes the viability of utilizing ATFS-BC300 as a dual-purpose solution for wastewater treatment and nitrogen fertilizer supply, presenting a promising avenue for addressing environmental challenges.

Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow.

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Magnetic alginate-layered double hydroxide composites for phosphate removal.

The objective of this study was to investigate phosphate removal using magnetic alginate-layered double hydroxide (LDH) composites. The magnetic composites were prepared by entrapping synthetic magnetic iron oxide and calcined Mg-Al LDH in polymer matrix (alginate). Results showed that the magnetic composites (2% magnetic iron oxide and 6% calcined Mg-Al LDH) were effective in the removal of phosphate with the sorption capacity of 5.0 +/- 0.1 mgP/g under given experimental conditions (adsorbent dose = 0.05 g in 30 ml solution; initial phosphate concentration = 10 mgP/l; reaction time = 24 h). Both magnetic iron oxide and calcined Mg-Al LDH have the ability to adsorb phosphate, with the latter having much higher sorption capacity. In the magnetic composites, calcined Mg-Al LDH functions as a phosphate adsorbent while magnetic iron oxide provides both magnetic and sorption properties. Results also demonstrated that phosphate sorption to the magnetic composites reached equilibrium at 24 h. The maximum phosphate sorption capacity was determined to be 39.1 mgP/g. In addition, phosphate removal was not sensitive to initial solution pH between 4.1 and 10.2. Only 9% of the phosphate sorption capacity was reduced as the solution pH increased from 4.1 to 10.2. This study demonstrated that magnetic alginate-LDH composites could be used for phosphate removal in combination with magnetic separation.

Adhesion of bacteria to pyrophyllite clay in aqueous solution.

The aim of this study was to investigate the adhesion of bacteria (Escherichia coli) to pyrophyllite clay using batch and flow-through column experiments. Batch results demonstrated that pyrophyllite was effective in removing bacteria (94.5 +/- 2.0%) from aqueous solution (1 mM NaCl solution; pyrophyllite dose of 1 g/ml). At solution pH 7.1, negatively-charged bacteria could be removed due to their adhesion to positively-charged surfaces of pyrophyllite (point of zero charge = 9.2). Column results showed that pyrophyllite (per cent removal of 94.1 +/- 2.3%) was far more effective in bacterial adhesion than quartz sand (53.6 +/- 5.3%) under the given experimental conditions (flow rate of 0.3 ml/min; solution of 1 mM NaCl + 0.1 mM NaHCO3). Bacterial removal in pyrophyllite columns increased from 90 to 100% with decreasing flow rate from 0.6 to 0.15 ml/min due to increasing contact time between bacteria and filter materials. In addition, bacterial removal remained relatively constant at 94-97% even though NaHCO3 concentration increased from 0.1 to 10 mM (flow rate of 0.3 ml/min). This could be related to the fact that pyrophyllite remained positively-charged even though the solution conditions changed. This study demonstrates that pyrophyllite could be used as adsorptive filter materials in the removal of bacteria.

Efficient removal of dyes from aqueous solutions using short-length bimodal mesoporous carbon adsorbents.

Ordered mesoporous carbons (OMCs) with controlled mesopore lengths and volumes were synthesized and investigated to remove the model dye methylene blue (MB) from aqueous solutions. The pore size, specific surface area, pore volume, and pore length of OMCs (CMK-3, sCMK-3, and sCMK-5) were analyzed and benchmarked against commercial activated carbon (AC). CMK-3 and sCMK-3 had narrow pore size distributions (PSDs) centered at ∼4.4 nm, whereas the PSD of sCMK-5 was bimodal, derived from the same pores as CMK-3 (∼4.4 nm) and the inner diameter of the carbon nanotubes (∼5.8 nm). The pore length decreased from 743 nm for CMK-3 to 173 nm for sCMK-3 and 169 nm for sCMK-5, facilitating the MB accessibility and efficient utilization of internal mesopores. The MB adsorption on the prepared adsorbents was well described by a pseudo-second-order kinetic model (R2 > 0.999), and the initial adsorption rate (h) on sCMK-5 was 34.07-fold faster than that on commercial AC. The Langmuir model adequately explained the equilibrium adsorption data, and the increase in the Langmuir maximal adsorption capacity (qm) of the OMCs was proportional to the specific surface area. The MB adsorption on sCMK-5 was endothermic and spontaneous, and proceeded primarily through physical adsorption as well as chemisorption reacting with oxygen atoms in hydroxyl groups. The prepared adsorbents were also suitable for polishing textile wastewater containing color-causing substances along with the background organic matter. These OMCs are promising for treating wastewater as efficient adsorbents for large molecular pollutants such as dyes.

Exploring the viability of a floating photocatalyst in a continuous stirred tank reactor system for continuous water treatment.

The use of photocatalysts in continuous stirred tank reactor (CSTR) systems allows for efficient and continuous water treatment, thus meeting the demand for scalable technology and comparative data in large-scale implementations. Hence, this study aims to explore the feasibility of a floating photocatalyst within a CSTR system for continuous water treatment. An expanded polystyrene (EPS)-TiO2 composite was synthesized following established methodologies, and their efficacy in removing the water pollutant methylene blue (MB) was compared for both batch and CSTR systems. A nonlinear first-order model was identified as the most suitable approach to accurately simulate MB degradation under experimental conditions, and the calculated pseudo-first-order degradation rate constant (k') for the CSTR system (0.0126-0.0172/min) was found to be superior to that observed for the batch system (0.0113/min). In addition, an increase in the flow rate reduced the retention time, leading to lower MB removal efficiency for the CSTR system. In addition, the EPS-TiO2/UV system with a CSTR configuration was found to efficiently use light and energy based on the calculated quantum yield (Φ = 2.86 × 10-4) and electrical energy per order (EEO = 857.46 kWh/m3/order). The findings of this study contribute to the development of sustainable and efficient water treatment strategies, offering valuable insight into the implementation of practical water treatment processes.

Use of thermally activated Fenton sludge for Cd removal in zinc smelter wastewater: Mechanism and feasibility of Cd removal.

Fenton sludge is a byproduct of the Fenton process that contains large amounts of Fe and Ca. Because of the secondary contamination generated during the disposal of this byproduct, ecofriendly treatment methods are needed. In this study, we used Fenton sludge to remove the Cd discharged from a zinc smelter factory, using thermal activation to enhance the Cd adsorption capacity. Among the various temperatures considered (300-900 °C), the Fenton sludge that was thermally activated at 900 °C (TA-FS-900) adsorbed the highest amount of Cd because of its high specific surface area and high Fe content. Cd was adsorbed onto TA-FS-900 via complexation with C-OH, C-COOH, FeO-, and FeOH and cation exchange with Ca2+. The maximum adsorption of TA-FS-900 was 260.2 mg/g, indicating that TA-FS-900 is an efficient adsorbent, comparable to those reported in the literature. The initial Cd concentration in the zinc smelter wastewater discharged was 105.7 mg/L, 98.4% of which was removed by applying TA-FS-900, suggesting the applicability of TA-FS-900 for real wastewater containing high concentrations of various cations and anions. The leaching of heavy metals from TA-FS-900 was within the EPA standard limits. We concluded that the environmental impact of Fenton sludge disposal can be reduced, and the use of Fenton sludge can add value to the treatment of industrial wastewater in terms of the circular economy and environment.

Effect of water filtration infrared-A (wIRA) sauna on inorganic ions excreted through sweat from the human body.

Sweat discharged as a result of exposure to sauna plays an important role in removing inorganic ions accumulated in the body, including heavy metals. In this study, inorganic ions (toxic and nutrient elements) excreted in the form of sweat from the body using a water-filtered infrared-A (wIRA) sauna were determined using inductively coupled plasma sector field mass spectrometry. The analyzed elements included eight toxic elements (Al, As, Be, Cd, Ni, Pb, Ti, and Hg) and 10 nutrient elements (Ca, Co, Cr, Cu, Fe, Mg, Mn, Se, V, and Zn), and their correlations were determined. Analysis of the sweat obtained from 22 people using the wIRA sauna showed a higher inorganic ion concentration than that obtained from conventional activities, such as exercise or the use of wet sauna, and the concentration of toxic elements in sweat was higher in females than in males. Correlation analysis of the ions revealed a correlation between the discharge of toxic elements, such as As, Be, Cd, and Ni, and discharge of Se and V, and Ni was only correlated with Mn. This study provides fundamental information on nutritional element supplementation when using wIRA sauna for detoxification.

Facile synthesis of N vacancy g-C3N4 using Mg-induced defect on the amine groups for enhanced photocatalytic •OH generation.

Photocatalysis offers opportunities to degrade recalcitrant organic pollutants without adding treatment chemicals. Nitrogen (N) vacancy is an effective point-defect engineering strategy to mitigate electron-hole recombination and facilitate hydroxyl radical (•OH) production via superoxide radical (O2•-) generation during photocatalytic application of graphitic carbon nitride (g-C3N4). Here, we report a novel strategy for fabrication of N-vacancy-rich g-C3N4 (NvrCN) via post-solvothermal treatment of Mg-doped g-C3N4. The addition of the Mg precursor during the polycondensation of urea created abundant amine sites in the g-C3N4 framework, which facilitates formation of N vacancies during post-solvothermal treatment. Elemental analysis and electron paramagnetic resonance spectra confirmed a higher abundance of N vacancies in the resultant NvrCN. Further optical and electronic analyses revealed the beneficial role of N vacancies in light-harvesting capacity, electron-hole separation, and charge transfer. N vacancies also provide specific reaction centers for O2 molecules, promoting oxygen reduction reaction (ORR). Therefore, •OH generation increased via enhanced formation of H2O2 under visible light irradiation, and NvrCN photocatalytically degraded oxytetracycline 4-fold faster with degradation rate constant of 1.85 × 10-2 min-1 (light intensity = 1.03 mW/cm2, catalyst concentration = 0.6 g/L, oxytetracycline concentration = 20 mg/L) than pristine g-C3N4. Overall, this study provides a facile method for synthesizing N-vacancy-rich g-C3N4 and elucidates the role of the defect structure in enhancing the photocatalytic activity of g-C3N4.

Cycling of phosphorus from wastewater to fertilizer using wood ash after energy production.

Quercus wood was used for thermal energy production, and wood bottom ash (WDBA) was used as a medium for water purification and soil fertilizer in accordance with the recently proposed food-water-energy nexus concept. The wood contained a gross calorific value of 14.83 MJ kg-1, and the gas generated during thermal energy production has the advantage of not requiring a desulfurization unit due to its low sulfur content. Wood-fired boilers emit less CO2 and SOX than coal boilers. The WDBA had a Ca content of 66.0%, and Ca existed in the forms of CaCO3 and Ca(OH)2. WDBA absorbed P by reacting with Ca in the form of Ca5(PO4)3OH. Kinetic and isotherm models revealed that the results of the experimental work were in good agreement with the pseudo-second-order and Langmuir models, respectively. The maximum P adsorption capacity of WDBA was 76.8 mg g-1, and 6.67 g L-1 of WDBA dose could completely remove P in water. The toxic units of WDBA tested using Daphnia magna were 6.1, and P adsorbed WDBA (P-WDBA) showed no toxicity. P-WDBA was used as an alternative P fertilizer for rice growth. P-WDBA application resulted in significantly greater rice growth in terms of all agronomic values compared to N and K treatments without P. This study proposed the utilization of WDBA, obtained from thermal energy production, to remove P from wastewater and replenish P in the soil for rice growth.

Bacterial removal in flow-through columns packed with iron-manganese bimetallic oxide-coated sand.

The objective of this study was to investigate the performance of iron-manganese bimetallic oxide-coated sand (IMCS) in the removal of bacteria (Escherichia coli ATCC 11105) using small-scale (length = 20 cm, inner diameter = 2.5 cm) and 30-day long-term (length = 50 cm, inner diameter = 2.5 cm) column experiments. Results indicated that the bacterial removal capacity of IMCS (q(eq) = 0.66 g/g) was slightly lower than that of iron oxide-coated sand (ICS) (q(eq) = 0.69 g/g) but about two times greater than those of manganese oxide-coated sand (MCS, q(eq) = 0.30 g/g) and dual media containing ICS and MCS (q(eq) = 0.35 g/g). In IMCS, increasing the flow rate from 0.5 to 3.0 mL/min decreased the removal capacity from 1.14 to 0.64 g/g. Nitrate showed an enhancement effect on the removal capacity of IMCS at 1 and 10 mM, while phosphate and bicarbonate had both hindrance (1 mM) and enhancement (10 mM) effects, depending on their concentrations. The long-term column experiment (bacterial injection conc. = 4.2 × 10(6) CFU/mL) showed that IMCS could remove more than 99.9 % of bacteria within 13 days (effluent conc. = 1.6 × 10(2) CFU/mL). This study demonstrated that IMCS could be used as an adsorptive filter medium for bacterial removal in water treatment.