Environmental Technology

Arikal, Dhanya; Kallingal, Aparna

doi: 10.1080/09593330.2019.1701094pmid: 31810416

Textile dyes are very toxic to human beings and environment. TiO2 nanoparticles have been of great interest in treating the organic effluent dyes. While using TiO2 nanoparticles, there is the electron-hole recombination, which decreases the degradation efficiency of photocatalyst. MgO nanoparticle, when used along with TiO2, forming TiO2/MgO nanocomposite act as a barrier for electron-hole recombination. Here, TiO2/MgO nanocomposites have been immobilized in chitosan beads, where chitosan acts as a support for the nanocomposite. The photocatalysts have been characterized by scanning electron microscope, ultraviolet (UV), X-ray diffraction and Fourier transform infrared spectroscopy. Methyl orange (MO) and Alizarin Red S (ARS) were used as model dye compounds. For MO, the experimental data have a better fit with Langmuir adsorption model and for ARS, it has a better fit with Freundlich adsorption model. Photocatalytic degradation efficiency of TiO2/MgO nanocomposite for a reaction time of 90 min towards degrading MO is 83.2% and ARS is 43.8%. Degradation efficiency of TiO2/MgO/chitosan hydrogels towards degrading MO and ARS is 82.4% and 41.8%, respectively. 3 wt.% is found to be the optimum concentration of MgO in TiO2/MgO nanocomposite . Degradation of the dye follows first-order kinetics and Langmuir–Hinshelwood model well suites in describing the kinetics of photocatalytic disappearance of the dyes. First-order rate constants for dye degradation under UV irradiation were calculated. TiO2/MgO/chitosan hydrogels could efficiently degrade MO and ARS dyes with a little lesser efficiency than TiO2/MgO nanocomposite making the process economically and environmentally a very suitable and favourable process for textile dye degradation.

Bisognin, Ramiro Pereira; Wolff, Delmira Beatriz; Carissimi, Elvis; Prestes, Osmar Damian; Zanella, Renato

doi: 10.1080/09593330.2019.1701561pmid: 31810406

A wide variety of pharmaceuticals are discharged in water courses on a daily basis due to their incomplete removal from effluent in treatment plants. The aim of the current study was to assess the occurrence, fate and removal of pharmaceuticals from effluent and sludge samples collected in the biggest sanitary sewer plant in Southern Brazil. In total, 13 pharmaceuticals were detected in the influent through UHPLC-MS/M – paracetamol and caffeine recorded the highest concentrations, 137.98 and 35.29 µg L−1, respectively. The treated effluent presented 11 compounds. Antibiotics were the class recording the widest diversity; metronidazole showed the lowest concentration (0.023 µg L−1) and sulfamethoxazole presented the highest concentration (1.374 µg L−1) in influent samples. Seven pharmaceuticals were absorbed by the sludge; among them, one finds caffeine, ciprofloxacin and ofloxacin, which were quantified both in the effluent and in the sludge. On the other hand, doxycycline, fenbendazole, norfloxacin and tetracycline were only detected in sludge samples – their concentrations ranged from 0.026 to 5.034 mg kg−1. Clindamycin, oxytetracycline, sulfathiazole and trimethoprim concentrations increased throughout the treatment. There were high paracetamol and caffeine removal rates (>97%), and it may have happened due to degradation, photodegradation or chemical reaction. Ciprofloxacin and ofloxacin removal rate exceeded 83% mainly due to their sorption by sludge. Finally, the mass balance analysis highlighted high pharmaceutical loads (511.466 g d−1) discharged into recipient waterbodies. This outcome demands broadening the removal of these pharmaceuticals from sewage.

Yang, Yan-Qin; Cui, Min-Hua; Guo, Jian-Chao; Du, Jing-Jing; Zheng, Zhi-Yong; Liu, He

doi: 10.1080/09593330.2019.1701562pmid: 31810427

In this study, biochars were produced by co-pyrolysis of rice husk and sewage sludge, the environmental risk of heavy metal (Pd and Cd) in the biochars was assessed. Co-pyrolysis resulted in a lower yield but a higher C content compared with sewage sludge pyrolysis alone, the relative contents of Pb and Cd in biochars were declined. Co-pyrolysis process transformed the bioavailable heavy metals into stable speciation. The environmental risk assessment codes of Pb and Cd were reduced by 1–2 grades. The co-pyrolysis technology provides a feasible method for the safe disposal of heavy metal-contaminated sewage sludge.

Zhou, Ming; Zhu, Shufa; Wei, Xuefeng

doi: 10.1080/09593330.2019.1701563pmid: 31795921

Red mud contains high levels of fluorine compounds. Once these fluorides were released, which led to adverse effects on human health and environment. The aim of this study was to investigate the possible use-electrokinetic remediation (EKR) for the removal of fluorine from red mud and explore the effects of different electrolytes on the remediation process. Three runs of EKR experiments were chosen using distilled water (run A), 0.1 mol/L HCl (run B) and 0.1 mol/L NaOH (run C), respectively. Related parameters for EKR, such as electric current, electro-osmotic flow (EOF) and energy consumption, were analysed. Characterisations of red mud were studied by SEM, XRD and FTIR. Experimental results showed that EKR could effectively remove fluorine pollutants from red mud. Electrolyte can obviously affect fluorine removal in EKR. The removal efficiency of run A, B and C was 57.69%, 66.75%, 60.04%, respectively, and run B (adding 0.1 mol HCl) had the best removal efficiency and the lowest residual fluorine in treated red mud after EKR, because of the highest electric current and EOF in all runs. Energy consumption per kilogram dry red mud of run A, B and C was 0.370, 0.726, and 0.506 kWh/kg, respectively. Experimental results showed that electro-osmosis and electromigration were both important removal mechanisms in EKR of fluorine from red mud. After EKR, the proportion of RESF (the residual fraction of fluorine) increased significantly, now fluorine of treated red mud had a good chemical inertness and had a smaller influence on environment.

Song, Yongwei; Yang, Linlin; Wang, Heru; Sun, Xinxin; Bai, Shuangyou; Wang, Ning; Liang, Jianru; Zhou, Lixiang

doi: 10.1080/09593330.2019.1701564pmid: 31797752

The oxidation of Fe2+ by Acidithiobacillus ferrooxidans (A. ferrooxidans) in acid mine drainage (AMD) is often accompanied by formation of iron hydroxysulfate minerals, such as schwertmannite and jarosite. This study reported that 80 mmol L−1 of Fe2+ could be completely oxidized by A. ferrooxidans LX5 within 48 h, but only 27.7% of the resultant Fe3+ precipitated to form schwertmannite. However, the conversion efficiency to jarosite was much higher (54.5%). The formation of jarosite lasted 120 h, while only 24 h when conversed to schwertmannite. By constructing a cyclic process of ‘Cu-reducing coupled with bio-oxidization’, the total Fe in AMD could be fully converted into mineral precipitates. The resultant mineral specie could be regulated simply by control the K+ concentration. Thermodynamically, Fe3+ cannot hydrolyze spontaneously to form schwertmannite due to the positive Gibbs free energy (  = 6.63 kJ mol−1) of the reaction. However, if Fe2+ were biologically oxidized by A. ferrooxidans, the resultant Fe3+ could spontaneously form schwertmannite because the aforementioned coupling reaction has a negative Gibbs free energy (  = −34.12 kJ mol−1). Even though Fe3+ itself could hydrolyze to form jarosite spontaneously with  = −22.20 kJ mol−1, the coupling reaction of Fe2+ bio-oxidation followed by Fe3+ hydrolysis in the presence of K+ could easily promote the formation of jarosite, which exhibited a great negative Gibbs energy (  = −67.45 kJ mol−1).

Domingues, Fernando Santos; Geraldino, Henrique Cesar Lopes; Freitas, Thábata Karoliny Formicoli de Souza; de Almeida, Cibele Andrade; Figueiredo, Franciele França de; Garcia, Juliana Carla

doi: 10.1080/09593330.2019.1701565pmid: 31852357

This work investigated the impregnation of Nb2O5 into carbon black (CB) in different ratios and its effect in photocatalytic degradation of real wastewater from a dyeing factory by advanced oxidative processes (AOP). Synthesized catalysts were characterized regarding their crystalline structure (DRX, micro-Raman), morphology (MEV), textural (BET area) and optical properties (bandgap energy by diffuse reflectance) and pH at the point of zero charge (pHpzc). Preliminary tests showed better photodegradation results in the acidic medium after 5 h of irradiation with NCB-0.5 (Nb2O5:CB 0.5:1). Treatment parameters optimization was carried out using response surface methodology based on Box–Behnken experimental design. Catalyst concentration, solution pH and irradiation time were varied, analysing absorbance reduction (285 and 574 nm), COD and TOC removal after treatment as responses. The composite catalyst showed improved photocatalytic activity, attributed to an increase in adsorption capacity and the bandgap narrowing, redshifting the absorption edge wavelength to the visible region, brought by CB impregnation. Optimal conditions were found at 0.250 g L−1 of catalyst, pH 2.0 and 5 h of irradiation, removing 72.19% and 93.52% of absorbance in 285 and 574 nm, respectively, 51.29% of COD and 70.70% of TOC using NCB-0.5.

Zhang, Huibo; Jing, Guolin; Luo, Jian; Tang, Yuening; Yu, Qiming Jimmy; Zheng, Chen; Wang, Mengqi

doi: 10.1080/09593330.2019.1701566pmid: 31829096

Polyacrylamide (PAM) was studied in two characteristic soils in Daqing City: chernozem and saline soil. 120 mg L−1 of KBr was used as a conservation tracer to estimate diffusion coefficients and pore velocities of chernozem and saline soil by using the breakthrough curves (BTCs) of Br–. Isothermal adsorption equations were coupled with the traditional two-site model to establish the transportation equation of PAM. The results of comparing the simulation curve with the BTCs of PAM at different rates showed that the transportation equation of PAM could simulate the transport process of PAM in soil column accurately. PAM behaved as non-equilibrium adsorption in both soils by calculating the kinetic parameters in this equation. The results of this work not only confirmed the kinetic parameters of PAM in both soils, but also found that there is a good liner relationship between the mass transfer coefficient and pore velocity. The R 2 values of the two linear equations are 0.983 and 0.979. These linear equations provide a good prediction basis for site prediction. In addition, it was found that organic matter is the main influence factor for the adsorption capacity of chernozem causing significantly larger than that of saline soil.

Lu, Binchao; Wang, Liang; Zheng, Xin; Hu, Zhongce; Pan, Zhiyan

doi: 10.1080/09593330.2019.1701567pmid: 31846595

Environmental contamination by 4-chlorophenol (4-CP) is a major concern. Photosynthetic bacteria have the ability to biodegrade 4-CP under dark aerobic conditions. In this study, we found that using different carbon sources (i.e. glucose, sodium acetate, sodium propionate sucrose, and malic acid) as co-metabolic substrates accelerated the biodegradation of 4-CP, and this acceleration was especially pronounced in the glucose treatment. A maximum degradation rate of 96.99% was reached under a concentration of 3.0 g·L−1 after 6 days of culture. The optimum conditions were pH 7.5, a temperature of 30°C, and a rotation speed of 135 rpm. The biodegradation of 4-CP was achieved at a range of salinities (0–3.0% NaCl, w/v). The biodegradation kinetics agreed with the Haldane model, and the kinetic constants were r max = 0.14 d−1, Km  = 33.9 mg·L−1, and Ki  = 159.6 mg·L−1. Additionally, the coexistence of phenol or 2,4-dichlorophenol (2, 4-DCP) had a certain impact on the degradation of 4-CP under dark aerobic conditions. When the coexisting phenol concentration reached 100 mg·L−1, the maximum degradation rate of 4-CP reached 90.20%. The degradation rate of 4-CP decreased as the concentration of coexisting 2, 4-DCP increased.

Vidovix, Taynara Basso; Januário, Eduarda Freitas Diogo; Bergamasco, Rosângela; Vieira, Angélica Marquetotti Salcedo

doi: 10.1080/09593330.2019.1701568pmid: 31801431

Nowadays, the occurrence of microcontaminants in water resources has become a worldwide concern. Among them, it can be mentioned Bisphenol A, a substance widely used in the chemical composition of plastic such as manufacture of packages, bottles, toiletries, among others. Its use may cause adverse effects on human health and the environment. Thus, a treatment is necessary to remove this compound and adsorption is an interesting alternative due to its low cost, operation and high efficiency. The objective of the present study was to evaluate the adsorption capacity of bisphenol in babassu activated carbon. The obtained results were satisfactory and the best experimental conditions were at 318 K temperature, 1 g L−1 adsorbent concentration and 720 min equilibrium time, resulting in the maximum adsorptive capacity of 49.61 mg g−1. The experimental data fit best with the pseudo-second order and Langmuir models for the kinetic and equilibrium studies, respectively. Thermodynamic parameters indicated endothermic, spontaneous and reversible process. The main adsorption mechanisms were hydrogen bonds and π–π interactions. In addition, the material regeneration study allowed to verify its possibility of reuse. Therefore, it was noticed that babassu activated carbon has high potential applicability in the treatment of contaminated water.

Gao, Yudong; Li, Huimin; Tong, Jinfu; Wang, Lu

doi: 10.1080/09593330.2019.1701569pmid: 31823678

A simple voltammetric sensor was first constructed by dripping graphene (GR) on to the glass carbon electrode (GCE) and subsequently electro-polymerizing L-cysteine film. The sensor had a good voltammetric response to amaranth and linear in the range of 1.0 × 10−8–1.0 × 10−6 mol L−1. The detection limit of amaranth was 4.0 × 10−9 mol L−1 (S/N = 3). Using this method, we successfully obtained satisfactory results of amaranth in confectionery wastewater. This work promoted the potential applications of amino acid materials and GR in environmental pollution science.