Medium Temperature Research Articles

Factorial experiment to identify two-way interactions between temperature, harvesting period, hydraulic retention time, and light intensity that influence the biomass productivity and phosphorus removal efficiency of a microalgae–bacteria biofilm

ABSTRACT This study evaluated the two-way interaction and main effects of four factors on biomass productivity and phosphorus removal efficiency of a microalgae–bacteria biofilm grown in municipal anaerobic digester centrate, with factor levels and operating conditions selected to mimic a pilot rotating algae biofilm reactor (RABR) at a water resource recovery facility (WRRF) in Utah. The two-way interactions of harvesting period × light intensity (LI), harvesting period × temperature, and LI × hydraulic retention time (HRT) had significant effects on biomass productivity: At high temperature and at low LI, highest biomass productivity was achieved with a 14-day harvesting period (25.5 and 10.9 g AFDW/m2/day, respectively), but at medium temperature and at high LI, highest biomass productivity was achieved with a 7-day harvesting period (16.1 and 16.4 g AFDW/m2/day, respectively). At high HRT, highest biomass productivity occurred at low LI (11.9 g AFDW/m2/day), but at low HRT, highest biomass productivity occurred at high LI (19.3 g AFDW/m2/day). Phosphorus removal was strongly influenced by LI (>70% removal at 1,600 μmol/m2/s) and occurred most rapidly during the first 2 days HRT (e.g. 2,270 TP/m2/day for days 0–2 vs. 217 mg TP/m2/day for days 2–4), which, in combination with chemical equilibrium modeling, suggests precipitation contributed significantly to phosphorus removal in this study.

Improved volatile fatty acid production in anaerobic digestion via simultaneous temperature regulation and persulfate activation by biochar: Chemical and biological response mechanisms

Increasing volatile fatty acid (VFA) production via persulfate activation (i.e., chemical effect) in anaerobic digestion (AD) is an emerging resource utilization method. However, the reaction mechanisms responsible for improving VFA production in AD via simultaneous temperature regulation and persulfate activation by biochar remain unclear. In this study, three PB15 treatment systems of low temperature (15 °C), medium temperature (35 °C) and high temperature (55 °C) were set to explore the relationship between VFAs production and treatment temperature and the influence of temperature on the reaction mechanism. The results show that the improvement of hydrolysis and acidification efficiency of the system in the medium temperature system is the highest. The VFA yield and acid production rate in the treatment group at 35°C were 2.49 and 5.22 times higher than those in the control group, respectively. The chemical effect effectively initiated the anaerobic acid production process and maintained the dominant role of the biological effect. The activity of persulfate is too low at low temperature, and its decomposition is too fast at high temperature. Plenty of free radicals lead to enhanced oxidation of the system, which may kill the fermentation bacteria. The NCM model indicates that microbial stability is reduced in high temperature systems. The SEM model showed that temperature change mainly affected substrate degradation by hydrolytic bacteria and indirectly affected acid production by acid-producing bacteria. This study provides a new strategy for realizing pollutant recycling and increasing VFAs production in cold area.

Sustainable valorisation of cigarette butts waste through pyrolysis: An insight into the pyrolytic products and subsequent aqueous heavy metals removal by pyrolytic char

In this study, cigarette butts (CB) waste was pyrolyzed over a wide temperature range (400–700 °C) using Pyro/GC–MS and slow pyrolysis experiments. The feedstock and char products were extensively investigated using TGA, elemental analysis, surface area and porosity analysis, SEM-EDS, XRD, and FT-IR, and subsequently tested for their ability to remove Ni (II) and Cu (II) from aqueous solutions. The Pyro/GC–MS analysis revealed the presence of several useful compounds including acids, esters and hydrocarbons. Char yields ranged from 26.6 to 20.1 wt%, and carbon contents varied from 65.3 to 60.8 wt%. The chars produced at medium temperatures (500-600 °C) were highly porous, with a specific surface area of 272.9–270.8 m2/g. The heavy metal adsorption studies revealed that CB 500 °C had the highest adsorption capacity of 13.8 mg/g with 53.4 % nickel removal, while CB 600 °C had the highest adsorption capacity of 23.4 mg/g with 94.7 % copper removal.

Selective catalytic reduction of NO with NH3 over HZSM-5/CeO2 hybrid catalysts: Relationship between acid structure and reaction mechanism

CeO2 is active in the NH3 selective catalytic reduction of NO (NH3-SCR) reaction due to its excellent redox properties. However, the low surface acidity of CeO2 limits its NH3-SCR activity. In this study, highly active HZSM-5-modified HZSM-5/CeO2 (Z/Ce) mixed oxide catalysts were prepared by a simple physical milling method. The HZSM-5 modification stimulated many thermally stable Brønsted-acid structures and high oxygen mobility on the surface of the Z/Ce catalysts, promoting the acid cycling pathways driven by redox macrocycles, and accelerating NO removal. The NO conversion of 25Z/Ce at 200–400 °C is about 34.8 %-62.3 % higher than that of CeO2. A series of physicochemical and in situ interfacial reactions were analyzed to explore the medium- and high-temperature reaction mechanism on the CeO2 surface. The Eley-Rideal reaction mechanism on the Lewis-acid structure with NO(g) as the reactant is deduced. When HZSM-5 modified CeO2, more NO was activated to NO2(g) on the surface of the Z/Ce catalyst at medium and high temperatures (300 °C). This significantly enhanced the Eley-Rideal reaction mechanism with NO2(g) as the main reactant on the Brønsted-acid structure as well as the occurrence of the “Fast-SCR” reaction. This work provides a simple method to improve the performance of CeO2 in the NH3-SCR reaction and elucidates the reaction mechanism.

Unravelling the impact of Al-Ti content on the microstructure-toughness relationship in the coarse-grained heated-affected zone of super-high-strength pipeline steels

This study aims to investigate the role of Al-Ti addition on particle modification in super-high-strength pipeline steels, and its following effect on microstructural evolution and impact toughness in the coarse-grained heated-affected zone (CGHAZ) is also explored. The steel plates with low and high Al-Ti content (0.009 wt-% Al + 0.006 wt-% Ti vs. 0.033 wt-% Al + 0.025 wt-% Ti), respectively, are subjected to gas metal arc welding with 6–7 kJ/cm heat input. The results reveal that the second-phase particles including micron-scale inclusion of Al-Mg oxide covered with CaS and nano-scale precipitate of titanium nitride are obtained in low Al-Ti steel, which are modified to the Al-Mg-Ti oxide core surrounded by CaS and TiN precipitate in high Al-Ti steel. The nano-scale TiN precipitate and micron-scale inclusion can restrict the austenite grain growth at high temperatures and induce acicular ferrite nucleation at medium temperatures, respectively, leading to the fine-grained mixed microstructure of bainite and acicular ferrite in CGHAZ of both steels. Because of the variant selection during the decomposition of austenite to bainite and acicular ferrite, those fine-grain structures with amounts of high-angle grain boundaries exhibit excellent CGHAZ toughness in both specimens. Compared with low Al-Ti steel, more precipitates induce smaller austenite grains, and the inclusions containing titanium increase the ability of inclusion to promote acicular ferrite nucleation in CGHAZ of high Al-Ti steel. Both of them resulted in smaller crystallographic grain and toughness improvement in CGHAZ of high Al-Ti steel than that in low Al-Ti steel.

Step Towards Enzymatic Bioelectrorefinery: Design of a Ligninolytic Hybrid Air‐Breathing Biocathode

AbstractLignins, abundant aromatic biopolymers and one of the major components of lignocellulosic biomass, remain the most underutilized renewable bioresources of aromatics and hydrocarbons on the Earth. Numerous physical and chemical processes have been developed for lignin valorization; however, they generally suffer from environmentally unfriendly, harsh conditions and lack reaction specificity. On the other hand, milder methods involving biocatalysts exist but are impeded by many limitations, such as cofactor regeneration, deleterious enzyme–lignin interactions, and low stability. In this work, we attempt to eliminate the constrains encountered in enzyme‐based lignin valorization processes through the development of a novel electrochemically assisted bioprocess. This “all‐in‐one” biocathode incorporates a hybrid electrocatalytic interface combining a hydrogen peroxide‐generating passive air‐breathing gas diffusion electrode with an immobilized hydrogen peroxide‐consuming lignin peroxidase on a single surface and catalyzing the depolymerization of lignins. The ligninolytic potential of this bioelectrochemical device is demonstrated using both lignin models (veratryl alcohol and veratrylglycerol β‐guaiacyl ether) and a technical lignin at room temperature in aqueous media with the reaction efficiency of 14.9% per hour.

A Machine-Learning Approach to Biosignature Exploration on Early Earth and Mars Using Sulfur Isotope and Trace Element Data in Pyrite.

We propose a novel approach to identify the origin of pyrite grains and distinguish biologically influenced sedimentary pyrite using combined in situ sulfur isotope (δ34S) and trace element (TE) analyses. To classify and predict the origin of individual pyrite grains, we applied multiple machine-learning algorithms to coupled δ34S and TE data from pyrite grains formed from diverse sedimentary, hydrothermal, and metasomatic processes across geologic time. Our unsupervised classification algorithm, K-means++ cluster analysis, yielded six classes based on the formation environment of the pyrite: sedimentary, low temperature hydrothermal, medium temperature, polymetallic hydrothermal, high temperature, and large euhedral. We tested three supervised models (random forest [RF], Naïve Bayes, k-nearest neighbors), and RF outperformed the others in predicting pyrite formation type, achieving a precision (area under the ROC curve) of 0.979 ± 0.005 and an overall average class accuracy of 0.878 ± 0.005. Moreover, we found that coupling TE and δ34S data significantly improved the performance of the RF model compared with using either TE or δ34S data alone. Our data provide a novel framework for exploring sedimentary rocks that have undergone multiple hydrothermal, magmatic, and metamorphic alterations. Most significant, however, is the demonstrated potential for distinguishing between biogenic and abiotic pyrite in samples from early Earth. This approach could also be applied to the search for potential biosignatures in samples returned from Mars.

Impacts of long-term different fertilization regimes on microbial utilization of straw-derived carbon in greenhouse vegetable soils: insights from its ecophysiological roles and temperature responses

As the largest organic carbon input in the agroecosystems, crop residues can increase soil carbon sequestration and crop production in greenhouse vegetable fields (GVFs). However, the soil microbiological mechanisms driving straw decomposition in GVFs under different incubation temperatures and fertilization treatments are not clear. Thus, soil samples were collected from a long-term field experiment included chemical fertilizer application alone (CF), 2/4 fertilizer N+2/4 organic fertilizer N (CM), 2/4 fertilizer N+1/4 organic fertilizer N+1/4 straw N (CMS), 2/4 fertilizer N+2/4 straw N (CS), and incubated with 13C-labeled straw at different temperatures (15, 25, and 35°C) for 60 days. Organic-amended treatments (CM, CMS, and CS), especially CMS treatment, increased soil bacterial Alpha diversity before and after straw addition. Straw decomposition process was dominated by soil Proteobacteria, Actinobacteria, and Firmicutes for each treatments. The effect of incubation temperature on soil microbial community composition was higher than that of fertilization treatments. Soil Alphaproteobacteria and Actinomycetia were the most predominant class involved in straw decomposition. Gammaproteobacteria (Pseudomonas, Steroidobacter, Acidibacter, and Arenimonas) were the unique and predominant class involved in straw decomposition at medium and high temperatures as well as in the straw-amended treatments. Organic-amended treatments, especially straw-amended treatments, increased the relative abundance of glycosyl transferases (GT) and auxiliary activities (AA). Alphaproteobacteria, Actinomycetia, and Gammaproteobacteria had higher relative contribution to carbohydrase genes. In summary, the long-term organic-amended treatments altered the structure of soil microbial communities and increased soil bacterial diversity, with the CMS having a greater potential to enhance resistance to external environmental changes. Soil Alphaproteobacteria and Actinomycetia were responsible for the dominance of straw decomposition, and Gammaproteobacteria may be responsible for the acceleration of straw decomposition. Fertilization treatments promote straw decomposition by increasing the abundance of indicator bacterial groups involved in straw decomposition, which is important for isolating key microbial species involved in straw decomposition under global warming.

Catalytic enhancement of water gas shift reaction with Cu/ZnO/ZSM-5: Overcoming challenges of CO2 and H2 rich feeds

Water gas shift (WGS) reaction commonly converts CO to CO2 using H2O and produces H2 and CO2 in a catalytic fixed bed reactor. This study aims to develop a Cu/ZnO/ZSM-5 catalyst loaded in water gas shift reactor for converting typical synthesis gas produced from dry reforming of methane (DRM) at medium temperature shift (MTS, 200–350 oC) conditions and for preventing reverse reaction due to high feed concentrations of CO2 and H2. The Cu/ZnO/ZSM-5 catalyst was prepared by impregnation method with lower Cu metal loading of 5, 10, and 15 wt%, respectively, compared to commercial catalysts. The synthesized catalyst was characterized using XRF, XRD, SEM, H2-TPR, NH3-TPD, and TGA. The catalyst activity and stability for the WGS reaction were tested in the fixed bed reactor at atmospheric pressure and temperature of 325 °C. The experimental results show that CO conversion increases with increasing Cu loading. The 15 wt% Cu/ZnO/ZSM-5 catalyst showed the best results with a CO conversion of 35% and a yield of H2 of 36% and showed good stability for 32 h. Based on the TGA, the 15 wt% Cu/ZnO/ZSM-5 catalyst forms a 0.04 g carbon/g catalyst, which is much lower when compared to commercial catalyst (0.105 g carbon/g catalyst). The relative activity of the synthesized catalyst indicates 2.4 times better when compared to commercial catalysts. High concentrations of H2 and CO2 in the feed may initiate side reactions, including reverse WGS, methanation, and carbon formation, which will decrease H2 yield.

Numerical Study on the Variable-Temperature Drying and Rehydration of Shiitake

Variable-temperature convective drying (VTCD) is a promising technology for obtaining high-quality dried mushrooms, particularly when considering rehydration capacity. However, accurate numerical models for variable-temperature convective drying and rehydration of shiitake mushrooms are lacking. This study addresses this gap by employing a model with thermo–hydro and mechanical bidirectional coupling to investigate five dehydration characteristics (moisture ratio, drying rate, temperature, evaporation rate, and volume shrinkage ratio) and a drying load characteristic (enthalpy difference) during VTCD. Additionally, a mathematical model combining drying and rehydration is proposed to analyze the effect of VTCD processes on the rehydration performance of shiitake mushrooms. The results demonstrate that, compared to constant-temperature drying, VTCD-dried mushrooms exhibit moderate shrinkage rates and drying time (16.89 h), along with reduced temperature variation and evaporation rate gradient (Max. 1.50 mol/(m3·s)). VTCD also improves enthalpy stability, reducing the maximum drying load by 58.84% compared to 338.15 K constant-temperature drying. Furthermore, drying time at medium temperatures (318.15–328.15 K) greatly influences rehydration performance. This study quantitatively highlights the superiority of variable-temperature convective drying, offering valuable insights for optimizing the shiitake mushroom drying processes.

Ionic liquid/polybenzimidazole/SiO2 composite membranes for medium temperature operating

Fuel cells (FC) with proton exchange membranes (PEMs) are seen as an alternative energy source due to their efficiency, power density, low emissions, and reliable energy supply. Proton exchange membranes based on polybenzimidazole have shown potential for operating at high and medium temperatures to enhance FCs performance. New composite membranes made from m-PBI and diethylammonium mesylate [DEAH/MsO] ionic liquid were prepared trough a solution casting method. Silica nanopowder (SiO2) was used as an inorganic filler at varying concentrations (0.5–20 wt%). The ionic liquid content in the membranes ranged from 1 to 2.5 mol per mole of PBI monomer units. Our study is focused on the thermal properties, such as thermal stability and phase transition temperatures, morphology, conductivity, and electrochemical stability of the membranes. The influence of the inorganic filler on these properties was also discussed.

Low and intermediate temperature fracture performance of hot mix asphalt (HMA) reinforced with nano-reduced graphene oxide (NRGO) under freeze-thaw cycles and aging conditions

ABSTRACT This study evaluates the effect of nano-reduced graphene oxide (NRGO) and conditions of short- and long-term (three freeze-thaw cycles (3 FTC)) failure and six days of ageing (6 AM) on bituminous mixtures from the viewpoint of fracture toughness (KIIC and KIIIC) and fracture energy (FEII and FEIII) at ±15 °C. The results showed the fracture stiffness was improved at ±15 °C (under three conditioning states). However, the fracture flexibility was decreased and increased at low and medium temperatures, respectively. At low temperatures, the results indicated that FEIII and KIIC had the lowest resistance under unconditioned and AM conditions, while FEII and KIIC had the lowest resistance under FTC. At intermediate temperatures, FEIII and KIIC under non-conditioned and FTC conditions and FEII and KIIC under AM conditions obtained the lowest resistance. Therefore, it was recommended to check both loading states in determining the shear performance (in-plane and out-of-plane) of asphalt mixtures. Finally, by providing the minimum short- and long-term properties required to control shear and tear cracks, reinforced mixtures lead to increased service life, reduced maintenance costs and improved road safety in cold and tropical regions.

Test of Mechanical Properties of Composite Recycled Concrete After Medium and High Temperature

Compressive strength is one of the important indexes to test the mechanical properties of concrete. The compressive strength of recycled composite concrete after high temperature is studied by single factor experimental analysis and double factor experimental analysis. Combined with variance analysis, the influence of replacement rate of recycled aggregate, volume incorporation amount of polypropylene fiber and volume incorporation amount of nani CaCO3 on compressive strength of recycled concrete after high temperature was systematically studied. The results show that when the replacement rate of recycled aggregate is 50%, the volume incorporation amount of polypropylene fiber is 0.08%, and nani CaCO3 is 1.2%, the compressive strength of composite recycled concrete reaches the maximum value. Nano CaCO3 is the most significant factor affecting the compressive strength of recycled concrete after high temperature. The significant influencing factors are the incorporation amount of polypropylene fiber and the replacement rate of recycled aggregate.

Heat Transfer in Double Pipe Heat Exchangers with Small Tube Spacing

Abstract In this current work, the heat transfer in double pipe heat exchangers with small tube spacing is analysed. This type of heat transfer is generally described in many literary sources, however, in laminar flow, the resulting values of the theoretical equations differ. Moreover, the small spacing of the pipes can affect the fluid flow and subsequent heat transfer. The suitability of using available theoretical methods for the design of double pipe heat exchangers (the Stephan, VDI and Baehr methods) was evaluated. A series of experiments was carried out on a double pipe heat exchanger with a tube spacing of 1.4 mm. The experimentally determined value of the heat transfer coefficient was up to two times higher in comparison with the values calculated according to theoretical methods. The relative increase was more significant for the lower Reynolds number values. At the same time, the difference of the wall temperature along the circumference of the outer tube was detected. This phenomenon was theoretically analysed and can be explained by tube misalignment in the small tube spacing. The procedure of quantification of this effect was proposed. This effect may cause an inhomogeneity of the media flow and temperature distribution and, as a result, increase the performance of the heat exchanger by tens of percent.

Activation of the process of layer combustion of bitter coal with iron nitrate and waste of metal rolling production

The influence of metal-rolling production waste and iron nitrate on the characteristics of the process of layer combustion of coal is investigated. As a solid fuel, coal of the T grade was used. Metal scale and iron nitrate were introduced into the fuel by mechanical mixing. According to XRD data, phases of iron oxides Fe3O4 and manganese Mn3O4 were identified in the metal scale. The characteristics of the combustion process of the studied samples were studied using high-speed video with the use of a combustion chamber at a heating medium temperature of 700°C. Combustion Also, the process of activated layer combustion coal was scaled using a solid fuel boiler unit. It has been experimentally established that the use of metal scale and iron nitrate leads to an increase in the reactivity of the fuel, as evidenced by a decrease in the ignition delay time. Due to the intensification of the combustion process, the fuel underburning and the concentration of CO formed in the composition of gas-phase combustion products were reduced.

Medium and high temperature H2S removal via phosphazene polyoxometalate ionic liquids: Performance evaluation and mechanism exploration

The development of non-aqueous solvent desulfurizer is crucial to addressing the challenges associated with traditional liquid-phase wet desulfurization technologies. Based on this, we prepared a series of phosphazene polyoxometalate ionic liquids (PPILs) based of 1-butyl-3-methylimidazolium chloride using different kinds of phosphazenes (PNs) combined with polyoxometalate (POM), and used for hydrogen sulfide (H2S) dynamic absorption experiments. The effects of PN type and ratio, temperature and desulfurizer concentration on the desulfurization performance of different PPILs were explored. Among them, PPILs@IBuPN-9 as the optimal desulfurizer could keep almost 100 % desulfurization efficiency in the medium and high temperature range (100–200 °C). The results showed that the combination of PNs with POM significantly improved and widened the H2S removal performance and the operational temperature window of the desulfurizer. Besides, PPILs@IBuPN-9 required only air regeneration to maintain relatively stable cycle performance for at least four times and the sulfur capacity could be efficiently increased during multiple regenerations. It was found that the hydrogen bonding sites on IBuPN network formed significantly enhanced the H2S capture ability of PPILs and the sulfur capacity was substantially improved by S2− substitution of oxygen atoms in the POM according to the characterization results and density functional theory calculations. This study promotes the deep integration of polyoxometalate chemistry with ionic liquids in the field of gas purification and promotes the development of non-aqueous phase desulfurization process.

Computational prediction of Thermo-Elastic and charge carriers transport properties of Ba2MnReO6, Ba2NiReO6, and Sr2MnReO6 double Perovskite compounds

The present work involves a computational investigation of the elastic, thermal, and thermoelectric characteristics of Ba2MnReO6, Ba2NiReO6, and Sr2MnReO6 from the Double Perovskite family. The study verified the mechanical stability of the three compounds and investigated Young’s modulus, Poisson, bulk, and shear modulusin various stress orientations. We were also able to compute longitudinal, transverse, and average sound velocities (Vl, Vt, and Vm, in m/s), and the findings revealed that Sr2MnReO6 had a greater longitudinal velocity than the other two compounds. Thermodynamic characteristics revealed that Ba2MnReO6, Ba2NiReO6, and Sr2MnReO6exhibit low lattice thermal conductivity (Kl) at medium temperatures, strong heat absorption, and a moderate coefficient of thermal expansion.The analysis of the electron and hole charge carriers’ transport characteristics revealed that, when doped with an electron concentration close to 1020 cm−3, the two materials, Ba2MnReO6 and Sr2MnReO6, may have an excellent figure of merit surpassing 0.6 at temperatures over 600 K.

Modeling and Analysis of Droplet Evaporation at the Interface of a Coupled Free-Flow–Porous Medium System

AbstractEvaporation of droplets formed at the interface of a coupled free-flow–porous medium system enormously affects the exchange of mass, momentum, and energy between the two domains. In this work, we develop a model to describe multiple droplets’ evaporation at the interface, in which new sets of coupling conditions including the evaporating droplets are developed to describe the interactions between the free flow and the porous medium. Employing pore-network modeling to describe the porous medium, we take the exchanges occurring on the droplet–pore and droplet–free-flow interfaces into account. In this model, we describe the droplet evaporation as a diffusion-driven process, where vapor from the droplet surface diffuses into the surrounding free flow due to the concentration gradient. To validate the model, we compare the simulation results for the evaporation of a single droplet in a channel with experimental data, demonstrating that our model accurately describes the evaporation process. Then, we examine the impact of free-flow and porous medium properties on droplet evaporation. The results show that, among other factors, velocity and relative humidity in the free-flow domain, as well as pore temperature in the porous medium, play key roles in the droplet evaporation process.

Seasonal Rise in the Contents of Microcystin-LR and Odorous Substances Due to Cyanobacterial Blooms in a Drinking Water Reservoir Supplying Xinyang City, China.

Cyanobacterial blooms have become a serious water pollution problem in many parts of the world, and the monitoring and study of the impacts of biotoxins on human health are of vital importance. In this study, the contents of microcystin-LR, 2-methylisoborneol, and geosmin were measured in water and sediment samples from Nanwan Reservoir, China, by means of bimonthly sampling between February and December 2023. The physicochemical and hydrochemical factors and phytoplankton dynamics in the reservoir were also investigated. The results showed that the overall mean concentration of microcystin-LR (0.729 μg/L) in summer approached the guiding standard (1 μg/L) set by the WHO for drinking water. Furthermore, the content of 2-methylisoborneol (143.5 ng/L) was 14 times higher than the national standard (10 ng/L). The results of laboratory cultures showed that lower light levels and medium temperatures were suitable for the growth of Microcystis and Planktothricoides but higher temperatures promoted the synthesis and release of microcystin-LR and 2-methylisoborneol. In addition, the results of co-cultures showed that the growth of Planktothricoides was inhibited by Microcystis. Our results suggest that cyanobacterial bloom and the presence of the metabolites 2-methylisoborneol and microcystin-LR can decrease the drinking water quality of Nanwan Reservoir.

Preparation of grafted starch‐based cationic flocculants and its removal of reactive and disperse dyes

AbstractIn this paper, a starch‐based flocculant (ADSt) with medium and low temperature solubility and enhanced flocculation effect was synthesized using corn starch, acrylamide, and dimethyldiallyl ammonium chloride as main materials by the ethanol‐alkali method and grafting method. The main mechanism of ADSt's flocculation was electrical neutralization and bridging. The flocculation performance of ADSt was verified by using it along with polymeric aluminum chloride (PAC) as coagulant/flocculant, dispersible dye (dispersible yellow RGFL), and reactive dye (active trimeric blue KN‐G) to simulate dye wastewater. For the dispersed yellow water sample and active emerald blue water sample, the dosage of PAC was 40 and 35 mg/L respectively. When the dosage of ADSt was 10 mg/L with a dye content of 100 mg/L, the decolorization rates for both dyes reached up to 96.2% and 94.4% respectively. The properties of the flocs such as size and two‐dimensional fractal structure were described. The prepared ADSt maintained a good flocculation effect in the pH range of 5–9 due to its excellent water solubility achieved through the ethanol‐alkali preparation process, where its solubility reached 86.7% at 30°C. Overall, the preparation process for ADSt is simple, cost‐effective, while providing an effective solution for treating printing and dyeing wastewater.