Persistent Organic Pollutants In Wastewater Research Articles

Heterogeneous photocatalytic degradation of antiviral drug didanosine mediated by rose bengal and TiO2 nanoparticles.

There is a great concern among the researcher to remove the problem of the persistent organic pollutants in wastewater. Pharmaceutical agrochemical and personal care products are generally considered Persistent organic pollutants. Therefore, it is a matter of concern to develop new techniques how to remove these pollutants safely at low cost. This study mainly focuses on the commonly used antiviral drug didanosine and one most commonly used dye rose bengal. In this study, an organic dye rose bengal and TiO2 nanoparticles have been used in combination with UV light to achieve the photodegradation of selected pharmaceutical products and the dye was also degraded by using TiO2 Nanoparticles. The formation of three oxidation products was detected by using a very popular separation technique thin layer and column chromatography. The isolated photoproduct was characterized by using advanced characterization techniques like FTIR (Fourier transform infrared spectroscopy), UV Spectroscopy, and Proton and 13C NMR (Nuclear Magnetic Resonance spectroscopy). The role of singlet oxygen as an active species in this reaction was confirmed by using D2O as a reaction medium. The role of singlet oxygen in this photochemical reaction was also established by the addition of sodium azide. The TiO2 nanophotocatalyst efficiently degrade the didanosine and rose bengal in the presence of the UV light. In the TiO2-induced photocatalytic degradation of didanosine and dyes, the hydroxyl and superoxide radical anion play a prominent role. The finding of this manuscript is very useful to develop an efficient low-cost method for the treatment of wastewater contaminated by antiviral drugs, similar pharmaceutical products and dyes. This study was also very helpful to establish a plausible mechanism behind the phototoxicity of the didanosine.

A Theoretical Study of the Interactions between Persistent Organic Pollutants and Graphene Oxide.

Persistent organic pollutants (POPs) have adverse effects on the human health and ecosystem functioning. Graphene oxide (GO) has been developed to remove trace levels of POPs from wastewater samples. However, many questions involved in these processes are still unresolved (e.g., the role of π–π interaction, the effect of GO on the degradation of POPs, and so on). Revealing the microscopic interactions between GO and POPs is of benefit to resolve these questions. In the present study, a quantum chemical calculation was used to calculate the molecular doping and adsorption energy between eight representative POPs and GO. The influences of GO on the thermodynamic parameters, such as the Gibbs free energy and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, were also reported. We found the molecular doping is dependent on the species of POPs. The adsorption energy of the majority of POPs on GO is between 7 and 8 kJ/mol. Consequently, the GO may make degradation of POPs in wastewater more productive and lead to a change of kinetics of the degradation of POPs.

Investigating crystal plane effect of Co3O4 with various morphologies on catalytic activation of monopersulfate for degradation of phenol in water

As phenol represents as the most typical persistent organic pollutants in wastewater, SO4•−-involved chemical oxidation techniques using monopersulfate (MPS) have been regarded as a promising method to eliminate phenol. Since Co3O4 is the benchmark heterogeneous catalyst for activating MPS, it is highly critical to investigate shape-varied Co3O4 catalysts with well-defined crystal planes for activating MPS to degrade phenol. Thus, the aim of this study is to elucidate how different Co3O4 catalysts with various well-defined planes would influence catalytic activities for MPS activation. Specifically, three Co3O4 nanocrystals are fabricated: nanoplate (NP), nanobundle (NB), and nanocube (NC) with different dominant exposed facets of {1 1 2}, {1 1 0}, and {1 0 0}, respectively. As the facets of {1 1 2} and {1 1 0} consist of more abundant Co2+/Co3+, Co3O4-NP and Co3O4-NB exhibit noticeably higher catalytic activities then Co3O4-NC for activating MPS to degrade phenol. Nevertheless, since Co3O4-NP shows a much higher surface area than Co3O4-NB, Co3O4-NP could exhibit a relatively high catalytic activity in comparison to Co3O4-NB. In addition, Co3O4-NP also exhibits much faster degradation kinetics with a rate constant of 0.061 min−1 at 30 °C, and more resistance towards pH variation, with much stable reaction stoichiometric efficiencies (RSE) ranging from 0.034 to 0.039 at pH = 3 ~ 9, than the other two Co3O4 nanocrystals, making Co3O4-NP with the {1 1 2} facet a more outstanding Co3O4 for activating MPS to degrade phenol.

Succinic anhydride-based chemical modification making laccase@Cu3(PO4)2 hybrid nanoflowers robust in removing bisphenol A in wastewater.

To prepare a robust biocatalyst and enhance the removal of bisphenol A in wastewater, succinic anhydride was reacted with laccase to obtain succinic anhydride-modified laccase (SA-laccase) and then co-crystallized with Cu3(PO4)2 to form SA-laccase@Cu3(PO4)2 hybrid nanoflowers (hNFs). The activity of SA-laccase@Cu3(PO4)2 reached 5.27 U/mg, 1.86-, 2.88- and 2.15-fold those of bare laccase@Cu3(PO4)2, laccase@Ca3(PO4)2 and laccase@epoxy resin, respectively. Compared with free laccase, the obtained hNFs present enhanced activity and tolerance to pH and high temperature in the removal of BPA. Under the optimum conditions of pH 6.0 and 35 °C, BPA removal reached 93.2% using SA-laccase@Cu3(PO4)2 hNFs, which was 1.21-fold of that using free laccase. In addition, the obtained SA-laccase@Cu3(PO4)2 hNFs retained nearly 90% of their initial catalytic activity for BPA removal after 8 consecutive batch cycles. This efficient method for preparing immobilized laccase can also be further developed and improved to acquire green biocatalysts for removing persistent organic pollutants in wastewater.

Understanding the active sites of boron nitride for CWPO: An experimental and computational approach

Hexagonal boron nitride (h-BN) has been explored as a catalyst for degrading persistent organic pollutants in wastewater by Catalytic Wet Peroxide Oxidation (CWPO). Herein, the superior activity of the h-BN on the phenol degradation (model pollutant) compared to other metal-free catalysts, such as carbon-based ones, and the lower selectivity to CO encourage the potential application of h-BN catalysts in CWPO processes. Through a combined density functional theory calculations, experimental reactions and catalyst characterization approach, a comprehensive study on the reaction mechanism has been conducted. According to this, only defected B atoms in the h-BN layer, protonated as B-(OH2)+, decompose the hydrogen peroxide into highly reactive hydroxyl radicals. The radical species diffuse towards inner h-BN regions and react with the phenol adsorbed by π-π interaction on the h-BN surface. Oxidation by-products cause carbonaceous deposits and progressive deactivation of the h-BN catalyst that can be directly regenerated by burning off in air.

Heterogeneous photo-Fenton system of novel ternary Bi2WO6/BiFeO3/g-C3N4 heterojunctions for highly efficient degrading persistent organic pollutants in wastewater

In this study, novel ternary Bi2WO6/BiFeO3/g-C3N heterojunctions with enhanced photocatalytic activity were synthesized and its heterogeneous photo-Fenton system was construct for highly effectively degrading persistent organic wastes, namely rhodamine B (RhB) and tetracycline hydrochloride (TH). Furthermore, the mechanism of generated free radicals in this heterogeneous photo-Fenton system was explored. The characteristics of the as-prepared photocatalysts were investigated in detail by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectra (FT-IR), UV–vis diffuse reflectance spectra (UV-DRS), Photoluminescence spectra (PL), Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky curves. The results demonstrated that the heterojunction between Bi2WO6, BiFeO3 and g-C3N has formed, which can narrow the band gap to improve separation and migration of photogenerated electrons-hole pairs. In addition, it has been suggested that the recombination of photogenerated electron-holes can be inhibited due to the good conductivity of BiFeO3 and g-C3N4. Hence, Bi2WO6/BiFeO3/g-C3N possessed enhanced photocatalytic activity, which can further enhance photo-Fenton activity to effectively degrade RhB (99.85 % in 30 min) and TH (83.68 % in 45 min). In addition, it has been determined that Bi2WO6/BiFeO3/g-C3N mainly produce O2− and e+ played the main roles in the photo-Fenton activity, rather than OH−. This study not only confirmed the feasibility of heterogeneous photo-Fenton system of Bi2WO6/BiFeO3/g-C3N4 for highly efficient degradation of persistent organic pollutants in wastewater, but also provided a mothed to synthesized the novel heterojunction of Bi2WO6/BiFeO3/g-C3N4 with enhanced photocatalytic activity.

Photo-catalytic membrane reactors for the remediation of persistent organic pollutants – A review

A major problem that is worldwide prominent is limited access to clean water. The process of catalysis coupled with the separation process carried by catalytically active membranes, takes place in device known as a catalytic membrane reactor (CMR). In this paper, CMRs that are driven by light as external stimuli known as photo-catalytic membrane reactors (PCMRs) are comprehensively described and compared on the basis of their performance to remediate persistent organic pollutants (POPs) in the wastewater. There is rapid development in the PCMR technology in the past decade, and this review gives an overview of conventional methods employed in treatment of selected POPs and progress in the types, configuration, and operational parameters of PCMRs. The split and integrated types of photocatalytic membrane reactors, their construction techniques and properties of photo-catalytically active membranes are discussed. The PCMRs are compared on basis of degradation rate of common POPs in wastewater. Additionally, a discussion on practical application is presented with regard to major challenges and gaps in the development and up-scalability of PCMR technology.

Treatment of persistent organic pollutants in wastewater using hydrodynamic cavitation in synergy with advanced oxidation process.

Persistent organic pollutants (POPs) are very tenacious wastewater contaminants. The consequences of their existence have been acknowledged for negatively affecting the ecosystem with specific impact upon endocrine disruption and hormonal diseases in humans. Their recalcitrance and circumvention of nearly all the known wastewater treatment procedures are also well documented. The reported successes of POPs treatment using various advanced technologies are not without setbacks such as low degradation efficiency, generation of toxic intermediates, massive sludge production, and high energy expenditure and operational cost. However, advanced oxidation processes (AOPs) have recently recorded successes in the treatment of POPs in wastewater. AOPs are technologies which involve the generation of OH radicals for the purpose of oxidising recalcitrant organic contaminants to their inert end products. This review provides information on the existence of POPs and their effects on humans. Besides, the merits and demerits of various advanced treatment technologies as well as the synergistic efficiency of combined AOPs in the treatment of wastewater containing POPs was reported. A concise review of recently published studies on successful treatment of POPs in wastewater using hydrodynamic cavitation technology in combination with other advanced oxidation processes is presented with the highlight of direction for future research focus.

Microporous carbon fibers prepared from cellulose as efficient sorbents for removal of chlorinated phenols

Cellulose-based microporous carbon fibers (CFs) were evaluated for the adsorption of 2-Chlorophenol (CP), 2,4-Dichlorophenol (DCP), and 2,4,6-Trichlorophenol (TCP), which are persistent organic pollutants in wastewater. CFs with different surface area values were prepared by using ZnCl2 as a chemical activator, and the samples were characterized by BET, FTIR, SEM, PALS, Zeta potential, and pH titration analysis. The point of zero charge values for CF-1, CF-2, and CF-3 were found as 8.14, 6.79, and 7.01, respectively. The surface area of CFs were determined as 454 m2/g (CF-1), 760 m2/g (CF-2), and 1217 m2/g (CF-3), and PALS measurements at ambient temperature and vacuum indicated the effective pore diameter of about 0.6 nm for all samples. The adsorption of chlorophenols was examined at different solution pH, temperature, and contact time. At the optimum pH of 6.0, the DCP adsorption capacities of CFs, namely, CF-1, CF-2, and CF-3 were calculated as 29.27, 229.81, and 244.09 mg/g, respectively. The adsorption capacity of the CF-3 sample was found to be an ideal adsorbent for CPs removal from aqueous solutions. A comparison of the adsorption kinetic data was best described by the pseudo second-order and particle diffusion models. For the CF-2 sample, the initial sorption rates of CP, DCP, and TCP were found in the increasing order as 2.084, 32.23, and 43.63 mg/g min. Similar order of the sorption rates were also observed for CF-1 and CF-3 samples. The obtained results demonstrated the fact that among the CP homologues, TCP showed both a higher affinity and a higher diffusion rate for all CFs. The adsorption process was found to be exothermic, and the entropy values were positive, depicting that CPs were randomly distributed at the solid/solution interface.

Effects of Advanced Oxidation Processes on the Decomposition Properties of Organic Compounds with Different Molecular Structures in Water

Studies to decompose persistent organic pollutants in wastewater from chemical factories by using Advanced Oxidation Processes (AOPs) have recently been performed. Oxidation reactions involving ozone and •OH radicals and cleavage caused by UV are the main decomposition reactions that occur in AOPs using ozone and UV. The mechanisms through which organic compounds are decomposed in AOPs are complicated and difficult to understand because various decomposition reactions occur simultaneously. The Total Organic Carbon (TOC) removal efficiencies achieved in several different AOPs were evaluated in this study. The TOC removal efficiencies were different for organic compounds with different chemical structures. The TOC was more effectively removed when aromatic compounds were treated using the O3-UV-TiO2 process than when using the other AOPs, and the TOC was removed more effectively by the O3-UV process than by the UV-TiO2 process. However, the TOC was removed more effectively when open-chain compounds were treated using the UV-TiO2 process than using the O3-UV process, and the UV-TiO2 and O3-UV-TiO2 processes resulted in similar TOC removal efficiencies. Therefore, it is necessary to use the O3-UV-TiO2 process to decompose aromatic compounds as quickly as possible. On the other hand, the UV-TiO2 process degraded the open-chain compounds most effectively, and the O3-UV-TiO2 process did not need to decompose open-chain compounds. Moreover, the TOC of aromatic compounds was removed more slowly than that of open-chain compounds. The TOC removal efficiency increased with decreasing the number of carbon atoms in the molecule. The TOC removal efficiencies increased in order of the organic compounds containing methyl groups, aldehyde groups and carboxyl groups. The removal of the TOC when organic compounds were treated using the O3-UV-TiO2 process followed pseudo-zero-order kinetics.

Evaluation of advanced oxidation processes (AOP) using O3, UV, and TiO2 for the degradation of phenol in water

The treatment of persistent organic pollutants in wastewater from chemical factories by decomposition using advanced oxidation processes (AOPs) has recently been studied. However, the AOPs studied to date suffer from problems such as high running costs for ozone generation and difficulties with operational parameters in the addition of hydrogen peroxide. In this study, a compact AOP reactor that generates ozone by UV irradiation was developed. Ozone was generated using the Chapman method, i.e., by irradiating oxygen with UV light; the use of this method saves energy. The decomposition activity of the designed reactor and the effects of a combination of ozone, UV, and TiO2 were examined. The results showed that 100% decomposition of 50mg/dm3 phenol was reached within 120min using an O3–UV–TiO2 process, and COD removal reached 100% within 240min. COD analysis confirmed that a synergistic effect was obtained using ozone, UV, and TiO2 simultaneously.

Determination of selected persistent organic pollutants in wastewater from landfill leachates, using an amperometric biosensor

Landfill leachates that contain persistent organic pollutants (POPs) are a big threat to groundwater systems and are projected to have hazardous effects in the long term if proper management strategies of the landfills are not put in place by those responsible. Monitoring the levels of POPs in landfill leachates is very crucial. This work presents an amperometric biosensor for determination of selected POPs in landfill leachates. The biosensor is based on kinetic inhibition of horseradish peroxidase (HRP). The enzyme was immobilised by electrostatic attachment on a polyaniline-modified Pt electrode surface. Selected POPs inhibited HRP enzyme activity and the decrease in the enzyme activity was used to determine these environmental pollutants. Selected polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) were the analytes of choice because they are commonly found in South Africa water systems. Limits of detection for the amperometric biosensor were established as 0.014, 0.018, 0.022, 0.016 and 0.019μgl−1 for BDE-100, PBB-1, PCB-1, PCB-28 and PCB-101, respectively. The HRP biosensor system gave different linear ranges for; BDE-100 (0.424–25.8μgl−1), PBB-1 (0.862–13.4μgl−1), PCB-1 (0.930–18.1μgl−1), PCB-28 (0.730–15.7μgl−1) and PCB-101 (0.930–27.1μgl−1). Inhibition studies on HRP biosensor response toward the reduction of H2O2 in the absence and presence of the selected POPs were carried out to investigate the inhibition kinetics and its mechanism. The results obtained indicated that the inhibition mechanism was competitive for PBDEs and non-competitive for biphenyls (PCBs and PBBs). The application of the biosensor was tested on wastewater samples obtained from landfill leachate for determination of selected POPs. The leachate samples were found to contain PCB-28 (0.28±0.03μgl−1) and PCB-101 (0.31±0.02μgl−1). The samples were also analysed by GC–MS as a cross-check method and the two sets of results were in close agreement.

Chemical coupling of photocatalysis with flocculation and adsorption in the removal of organic matter

An experimental investigation was made to study the effects of chemical coupling of flocculation and adsorption with photocatalysis in treating persistent organic pollutants in wastewater. The photocatalysis alone showed initial reverse reaction when titanium oxide (TiO 2) was used in catalysis. The effect of the pretreatment of adsorption with powdered activated carbon (PAC) on photocatalysis was studied. The results showed that PAC adsorption followed by photocatalysis was not effective in alleviating reverse reaction. On the other hand, when PAC and TiO 2 were added simultaneously, the reverse reaction was eliminated. Further, the organic removal was also improved by simultaneous PAC and TiO 2 additions. When flocculation with ferric chloride (FeCl 3) was used as pretreatment, the organic removal efficiency was superior. The initial reverse reaction was also eliminated/minimized. However, inadequate doses of FeCl 3 (less than 30 mg l −1) resulted in initial reverse reaction and inferior DOC removal.