Evaluation of the coagulation properties of magnesium hydroxide for removal combined contamination of reactive dyes and microfibers.

Microfibers are a new type of pollutants that are widely distributed in water bodies. And the simultaneous removal of pollutants in water is popular research in the field of water treatment. In this study, magnesium hydroxide was used as coagulant to investigate the performance and mechanism of coagulation and removal of dyes (reactive orange) and microfibers (MFs). The presence of dyestuff in the composite system promoted the removal of microfibers, and the maximum removal efficiency of both could reach 95.55% and 95.35%. The coagulation mechanism was explored by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential. The removal of reactive orange and microfibers relied on electrical neutralization, sweep flocculation, and adsorption mechanisms. Turbidity can enhance the removal efficiency of both. Boosting the rotational speed can increase the removal efficiency of microfibers. This study provides an important theoretical support for an in-depth understanding of the characteristics and mechanisms of coagulation for the removal of complex pollutants from printing and dyeing wastewater.

Coagulation properties of magnetic magnesium hydroxide for removal of microplastics in the presence of kaolin and humic acid.

Microplastics (MPs) is one of the most concerned emerging pollutants in recent years. Its widespread distribution has been shown to have potentially adverse effects on human health and ecosystems. Therefore, in this study, magnetic magnesium hydroxide coagulant (MMHC) was prepared by adding Fe3O4 magnetic micron particles in the Mg(OH)2 generation process, and it was used with PAM, a polymer flocculant, to remove polyethylene microplastics (≤270 µm) from water by coagulation. The removal efficiency of microplastics by MMHC reached 87.1%, which was 14.7% higher than that of traditional magnesium hydroxide coagulant (MHC). However, the Zeta potential of MMHC was lower than that of MHC, only 17.3 mV. In addition, the surface morphology of MMHC showed bubble-like clusters. The effect of PAM adding time on the microplastic removal efficiency was investigated. The best adding time of non-ionic PAM was 15s before the slow mixing started. The removal efficiency of organic matter and suspended particles in water by MMHC was determined by turbidity, ultraviolet spectrophotometry and three-dimensional fluorescence. The maximum removal efficiency was 98.5% and 93.3%, respectively. With the increase of the concentration of humic acid and kaolin in water, the removal efficiency of microplastics was basically not affected. MMHC can be reused after recycle, but it was found that the electrical neutralization mechanism was affected due to the transformation of its Zeta potential, and the adsorption effect of humic acid and kaolin particles in water became worse, the removal efficiency of microplastics, turbidity and UV254 decreased to 20.2%, 17.5% and 30%, respectively.

Formation of anaerobic granular sludge (AnGS) to treat high-strength perchlorate wastewater via anaerobic baffled reactor (ABR) system: Electron transfer characteristic, bacterial community and positive feedback mechanism.

Anaerobic granular sludge (AnGS) was cultured to treat high-strength perchlorate (reaching to 4800 mg/L) wastewater by an anaerobic baffled reactor (ABR) system with five equal-volume compartments (C1-C5 compartments). Inoculated sludge completely granulated on day 104 with granule size of 0.50-0.75 mm and perchlorate removal efficiency reaching to 97% (influent perchlorate of 2000-4800 mg/L). The Cyclic voltammetry (CV) capacitance increased from 487.5, 465.8 and 407.8 µF to 576.5, 552.4, 549.6 µF in C1, C3 and C5 compartments of ABR system, respectively, suggesting the electron transfer capacity was enhanced under high-strength perchlorate stress. Meanwhile, adenosine triphosphate (ATP) value and electron transport system activity (ETSA) increased to 25.05, 22.87, 20.43 and 6.22, 4.87, 3.95 of C1, C3 and C5 compartments, respectively. The results suggested that high-strength perchlorate stress improved the microbial metabolic activity, which promoted secretion of extracellular polymeric substances (EPS). The more EPS could facilitate the formation and stability of AnGS under high-strength perchlorate stress. In addition, more reasonable metabolic division of labor in functional bacterial (Thauera and Comamonas) was beneficial to AnGS formation, which achieved high-strength perchlorate efficient removal. Finally, a positive feedback mechanism between AnGS formation and high-strength perchlorate removal was established through EPS, microbial metabolic activity and electron transfer characteristic in ABR system. However, excessive perchlorate (5800 mg/L) would exceed the treatment capacity of AnGS, which resulted in the deterioration of removal performance. This work provided an effective information for AnGS application to treat high-strength perchlorate wastewater.

Floc formation and growth mechanism during magnesium hydroxide and polyacrylamide coagulation process for reactive orange removal.

Magnesium hydroxide is commonly used as a coagulant for treating reactive dyes wastewater. However, the flocs are relatively small and coagulation process needs longer sedimentation time. Large flocs and short operation time are important for good coagulation performance. Coagulation floc formation and growth processes using magnesium hydroxide and polyacrylamide (PAM) dual-coagulant were investigated with controlled experiments through flocculation index (FI), floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. The final average floc size reached 58.5 and 4.96 µm with and absence of PAM addition during slow mixing periods. PAM feeding time and magnesium hydroxide formation time can affect the floc formation and growth processes. The results showed that floc formed rapidly during magnesium hydroxide generation within 90 s and flocs aggregated together by PAM bridging function. Reactive orange removal efficiency reached 99.3% with rapid mixing 250 rpm at 90 s during 100 mg/L magnesium ion addition, then adding 6 mg/L PAM at the beginning of slow mixing period in dual-coagulant system.

Rational design of biogenic PdxAuy nanoparticles with enhanced catalytic performance for electrocatalysis and azo dyes degradation.

The green biogenic PdAu nanoparticles (bio-PdAu NPs) exhibits remarkable catalytic performance in hydrogenation, which is highly desired. However, the catalytic principles and effectiveness of bio-PdxAuy NPs in response to various catalytic systems (electrocatalysis and suspension-catalysis) are unclear. Herein, a facile synthetic strategy for bio-PdxAuy NPs synthesis with controlled size and the catalytic principles for hydrogen evolution reaction (HER) and azo dye degradation is reported. In the biosynthetic process, the size and composition of the bio-PdxAuy NPs could be precisely controlled by predesigning the precursor mass ratio of Pd/Au, and the Au proportion showed a linear relationship with the size of NPs (R2 = 0.92). The obtained bio-PdxAuy NPs exhibit variable activity in electrocatalysis (HER) and suspension-catalysis (azo dye degradation). For electrocatalysis, the formation of conductive networks that facilitates the extracellular electron transfer is crucial. It was revealed that the bio-Pd2Au8 exhibited superior electrocatalytic performance in HER/toward hydrogen evolution, with a maximum current density of 1.65 mA cm-2, which was 1.54 times higher than that commercial Pd/C (1.07 mA cm-2). The high electrocatalytic activity was attributed to its appropriate size (81.38 ± 6.14 nm) and uniform distribution on the cell surface, which promoted the extracellular electron transfer by constructing a conductive network between catalyst and electrode. However, for suspension-catalysis, the size effect and synergistic effect of bimetallic NPs have a more prominent effect on the degradation of azo dyes. As the increase of Au proportion the particle size decreases, and the catalytic activity of bio-PdxAuy improved significantly. The response principles of bio-PdxAuy proposed in this study provide a reliable reference for the rational design of bio-based bimetallic catalysts with enhanced catalytic performance.

Preparation of composite adsorbents of activated carbon supported MgO/MnO2 and adsorption of Rhodamine B.

Activated carbon (AC) was modified by MgO and MnO2 through an impregnation-precipitation-calcination procedure. The batch experiments of adsorption of Rhodamine B (RB) by a modified adsorption material, an MgO-MnO2-AC composite, were carried out and the characteristics of the composite adsorbent were evaluated. The results showed that manganese/magnesium loading changed the surface area, pore volume and increased the number of active adsorption sites of AC. The highest Brunauer-Emmett-Teller (BET) surface area (1,036.18 m2·g-1) was obtained for MgO-MnO2-AC compared with AC. The content of AC loaded with magnesium and manganese was 34.24 and 5.51 mg·g-1 respectively. The adsorption of RB on MgO-MnO2-AC was significantly improved. The maximum adsorption capacity of RB on MgO-MnO2-AC was 16.19 mg·g-1 at 25 °C under the RB concentration of 50 mg·L-1. The adsorption of RB by AC and MgO-MnO2-AC increased with the initial concentration of RB. The adsorption of RB increased first and then decreased when pH was between 3 and 11. The results indicated that the pseudo-second-order kinetic equation and Langmuir equation can be used to describe the adsorption of RB on MgO-MnO2-AC.

Effect of kaolin on floc properties for reactive orange removal in continuous coagulation process.

Magnesium hydroxide was used as a coagulant for treating reactive orange wastewater in a real continuous process. Effects of kaolin on coagulation performance and floc properties were investigated with controlled experiments through floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. Kaolin had significant influence on magnesium hydroxide-reactive orange floc formation and growth. The results showed that average floc size reached 16.31, 12.88 and 20.50 µm, respectively, in the rapid mixer, flocculation basin and sedimentation tank when kaolin concentration was 10 mg/L and reactive orange initial concentration was 0.25 g/L. The floc size tended to increase with the increase of kaolin suspension to 10 mg/L. All of the flocs under investigation showed that floc breakage led to decreased average floc size and remained stable in the flocculation basin. Reactive orange and kaolin could be removed effectively in the continuous coagulation process. Reactive orange was adsorbed in the surface of magnesium hydroxide through charge neutralization and adsorption.

Coagulation-adsorption of reactive orange from aqueous solution by freshly formed magnesium hydroxide: mixing time and mechanistic study.

The utilization of magnesium hydroxide was successfully carried out to remove reactive orange by coagulation-adsorption from aqueous solution. The coagulation-adsorption mechanisms and magnesium hydroxide-reactive orange floc property were analyzed through zeta potential, scanning electron microscope (SEM), X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Flocculation Index was then discussed with controlled experiments using intelligent Particle Dispersion Analyzer (iPDA) and optimum rapid mixing time of 90 s was obtained for pH 12. The results of this study indicate that charge neutralization and adsorption are proposed to be the main coagulation mechanisms. The FT-IR spectra and SEM showed that reactive orange was adsorbed on the magnesium hydroxide surface during coagulation and adsorption. Freshly generated magnesium hydroxide can effectively remove reactive orange and the removal efficiency can reach 96.7% and 46.3% for coagulation and adsorption, respectively. Adsorption process accounts for 48% of the whole coagulation experiment. The removal efficiency decreased significantly with increasing magnesium hydroxide formation time.

Prevalence of serum neutralizing antibodies to adenovirus type 5 (Ad5) and 41 (Ad41) in children is associated with age and sanitary conditions.

Neutralizing antibody (NAb) can dampen the immunogenicity of adenovirus (Ad) vector-based vaccine. Vector systems based on human adenovirus type 41 (Ad41) have been constructed and used to develop recombinant vaccines. Here, we attempted to study the seroprevalence of NAbs to Ad5 and Ad41 among children and adults in Qinghai province, China. The positive rates (titer⩾40) of Ad5 and Ad41 NAb in adults from Xining city were 75.7% and 94.7%, respectively. The moderate/high-positive rates (titer⩾160) of NAb were quite close between the two viruses in adults (70.4% for Ad5 and 73.5% for Ad41). Age-dependent increase of NAb seroprevalence was observed for both viruses in children. NAb-positive rate of Ad41 reached 50% at 3.3-4.6years of age for children from Chengxi district, Xining city, approximately 1.5years earlier than that of Ad5 did. Interestingly, NAb level was also associated with sanitary conditions among young children. For Ad5, 8-15% children (0.2-3.0years of age) from city or town, where the sanitations were relatively better, had moderate/high-positive NAb, while the same rate was 62% for children from villages. For Ad41, 22% children from city, 47% from town and 88% from villages possessed moderate/high-positive NAb. The possible influence of NAb titer distributions on the application of Ad41-vectored vaccines was discussed in detail. Our results suggested that children from places with poor sanitations should be included for comprehensive Ad NAb seroprevalence studies, and provided insights to the applications of Ad41 vectors.

Magnesium hydroxide coagulation performance and floc properties in treating high pH reactive orange wastewater.

Application of magnesium hydroxide as a coagulant for treating high pH reactive orange wastewater was studied. The coagulation performance and magnesium hydroxide-reactive orange floc properties were investigated under different dosages, feeding modes and pH values. Flocculation index (FI) was then discussed with controlled experiments using an intelligent particle dispersion analyzer and optimum coagulant dose of 150 mg/L (magnesium ion) was obtained for pH value 12. The results showed that the optimum magnesium ion dose tended to decrease with the increase of initial pH value. One time addition feeding mode led to relatively large FI value and higher removal efficiency compared with other addition modes. All of the flocs under investigation showed a limited capacity for re-growth when they had been previously broken. Based on the changes of zeta potential and floc properties, charge neutralization and precipitate enmeshment were proposed to be the main coagulation mechanisms.

[Study on the probability of hepatitis B virus infection at public service places].

OBJECTIVE: To provide data for the control and prevention of hepatitis B and HBV surface antigen (HBsAg) status among the appliances and practitioners working in the public service places. METHODS: 63 beauty parlors, barber shops and bathing centers selected under stratified randomization sampling method and 682 workers were investigated through questionnaire. HBsAg from th e appliances of the public service places and employee was detected by RIA. RESULTS: Two main sanitizing modes that including alcohol cleaning (34.60%) and ultraviolet light disinfection (30.79%) were used. The rates of testing on HBsAg among the appliances were 2.13% at the public service places, and were 0.63%, 2.67% and 3.70% in large-, medium- and small-sized appliances respectively. The rate of testing on HBsAg on large-, medium- and small- sized appliances were statistically different (chi2 = 6.68, P < 0.05). The positive rates of HBsAg on the appliances of beauty parlors, barbering shops and footbath inns were 2.97%, 0.61% and 3.42% respectively. People working in different service sites had different rates of HBsAg: those who worked at the 'acne needle' and the forceps were 5.13% and 4.17%. The positive rate of HBsAg among the workers in the public service places was 7.13%. The rates of HBsAgamong the workers in large-, medium- and small-sized public service places were 7.34%, 8.33% and 2.94% respectively. The rates of HBsAg among the workers in beauty parlors, barbering shops, footbath inns and bathing centers were 9.01%, 6.37%, 4.35% and 7.29% respectively. HBsAg positive rates were different among the workers working at different service sites: 13.33% at tattoo business, 12.68% in pedicles workers and 8.03% in massagists. CONCLUSION: It is important to improve the sanitizing management of the appliances used in the public service places and to improve the knowledge, attitude, as well as practice of vaccination on hepatitis B among those populations.