A critical review on geosmin and 2-methylisoborneol in water: sources, effects, detection, and removal techniques.

The exposure to geosmin (GSM) and 2-methylisoborneol (2-MIB) in water has caused a negative impact on product reputation and customer distrust. The occurrence of these compounds and their metabolites during drinking water treatment processes has caused different health challenges. Conventional treatment techniques such as coagulation, sedimentation, filtration, and chlorination employed in removing these two commonest taste and odor compounds (GSM and 2-MIB) were found to be ineffective and inherent shortcomings. The removal of GSM and MIB were found to be effective using combination of activated carbon and ozonation; however, high treatment cost associated with ozonation technique and poor regeneration efficiency of activated carbon constitute serious setback to the combined system. Other shortcoming of the activated carbon adsorption and ozonation include low adsorption efficiency due to the presence of natural organic matter and humic acid. In light of this background, the review is focused on the sources, effects, environmental pathways, detection, and removal techniques of 2-MIB and GSM from aqueous media. Although advanced oxidation processes (AOPs) were found to be promising to remove the two compounds from water but accompanied with different challenges. Herein, to fill the knowledge gap analysis on these algal metabolites (GSM and 2-MIB), the integration of treatment processes vis-a-viz combination of one or more AOPs with other conventional methods are considered logical to remove these odorous compounds and hence could improve overall water quality.

Photocatalytic degradation of local dyeing wastewater by iodine-phosphorus co-doped tungsten trioxide nanocomposites under natural sunlight irradiation.

In the present work, one-step green synthesis of WO3 based on the interaction of ammonium paratungstate and Spondias mombin leaves extract is reported. Different concentrations of iodine and phosphorus in the range of (2%, 5% and 10%) were firstly incorporated into the prepared WO3 nanoparticles to obtain Iodine doped and Phosphorus doped WO3 nanoparticles respectively. Subsequently, iodine and phosphorus co-doped WO3 nanocomposites was prepared using a wet impregnation method followed by calcination at high temperature. The nanomaterials were characterized by HRSEM, HRTEM, BET, UV-Visible, EDS, XRD and XPS. The photo-oxidation of dyeing wastewater by the synthesized WO3 nanomaterials were tested and assessed using Total organic carbon (TOC) and Chemical oxygen demand (COD) as indicator parameters. XRD and HRSEM analysis demonstrated the formation of only monoclinic phase of WO3 irrespective of the dopants. The UV-Visible diffuse reflectance spectroscopy showed the band gap energy of 2.61 eV for undoped WO3 and 2.02 eV for I-P co-doped WO3 nanocomposites. The surface area of I-P co-doped WO3 (416.18 m2/g) was higher than the undoped WO3 (352.49 m2/g). The XPS demonstrated interstitial and substitution of oxygen (O2-) vacancies in WO3 by I- and P3+ and formed I-P-WO(3-x). The I-P co-doped WO3 exhibited higher catalytic activities (93.4% TOC, 95.1% COD) than the undoped (54.9% TOC, 79.2% COD) due to the synergistic effects between the two dopants. The experimental data better fitted to pseudo-second order than first order and pseudo-first order model. This study demonstrated the enhanced photocatalytic performance of I-P co-doped WO3 nanocomposites under sunlight.

High performance B2O3/MWCNTs and TiB/MWCNTs nano-adsorbents for the co-sorption of cyanide and phenol from refinery wastewater.

The refinery industry has witnessed tremendous activity aimed at producing petrochemicals for the benefit of the teeming populace. These activities are accompanied by the discharge of wastewater containing chemical substances and elements that have negative impacts on the ecosystem. The presence of phenol and cyanide contaminants in refinery wastewater poses serious health hazards to humans, necessitating their removal. In this study, boron oxide-doped multi-walled carbon nanotubes (B2O3/MWCNTs) and titanium boride-doped MWCNT (TiB/MWCNTs) nanoadsorbents were prepared via a wet impregnation method and characterized using High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS). HR-TEM images depict the nanostructure of the nanoadsorbent, the presence of doped materials, and the internal, external, and wall thickness of B2O3/MWCNTs and TiB/MWCNTs nanoadsorbents. XRD results indicate that the nanomaterials were monocrystalline with average crystallite sizes of 22.75 nm and 16.79 nm for B2O3/MWCNTs and TiB/MWCNTs, respectively. The formation of B2O3 and TiB was observable in the results obtained from the XPS at the binding energy of 192 and 193.1 eV, respectively. The application of the produced B2O3/MWCNTs and TiB/MWCNTs nanoadsorbents for the removal of phenol and cyanide from refinery wastewater was explored in a batch adsorption system. The effects of contact time, adsorbent dosage, and adsorption temperature were investigated. To the best of our knowledge, the incorporation of B2O3 and TiB in MWCNTs resulted in the highest adsorption capacities for phenol and cyanide from aqueous solutions. The highest percentage removal of 100% for phenol and 99.06% for cyanide was observed for the TiB/MWCNTs nanoadsorbent at a residence time of 70 minutes, a temperature of 60 °C, and 0.3 g of adsorbent. The isotherm models show that cyanide and phenol removal obeyed the Langmuir isotherm, indicating monolayer adsorption over B2O3/MWCNTs nanoadsorbent. Furthermore, cyanide and phenol removal depict multilayer adsorption on the TiB/MWCNT nanoadsorbent. The research shows that B2O3/MWCNTs are proficient in cyanide sorption, while TiB/MWCNT favors phenol sorption due to their respective adsorption capacities.

Optimization of the adsorption of total organic carbon from produced water using functionalized multi-walled carbon nanotubes.

This study investigated the removal of Total Organic Carbon (TOC) from produced water by batch adsorption process using adsorbents developed from Multi-Walled Carbon Nanotubes (MWCNTs). The MWCNTs, synthesized by catalytic chemical vapour deposition method using kaolin-supported tri-metallic (iron-cobalt-nickel) catalyst were purified by H2SO4/HNO3 and then functionalized with 1-pyrenebutanoic acid N-hydroxyl succinimidyl ester (PSE). The raw, purified and functionalized MWCNTs were characterized by High Resolution Scanning Electron Microscopy (HRSEM), High Resolution Transmission Electron Microscopy (HRTEM), Brunauer-Emmett-Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR). In the results, HRSEM/HRTEM revealed the structure, purity and also confirmed the attachment of the PSE molecule onto the nano-adsorbent(s). The BET surface areas of MWCNTs, PMWCNTs and FMWCNTs were 970.17, 869.25 and 831.80 m2/g, respectively while the FTIR established the existence of surface functional groups. The functionalized MWCNTs (FMWCNTs) nano-adsorbent showed superior performance efficiency (93.6%) than the purified MWCNTs (PMWCNTs) (79.2%) as examined under the same batch adsorption condition: 0.02 g adsorbent dosage, 10-90 min contact time and 30 °C solution temperature probably, due the improved wettability resulted from incorporation of PSE. Subsequently, Central Composite Design (CCD) was applied to optimize the process parameters for the sorption of TOC onto FMWCNTs. The CCD in the response surface methodology predicted 260 mg/g adsorption capacity of FMWCNTs in the removal of TOC at the optimum condition of 49.70 min contact time, 34.81 °C solution temperature, and 0.02 g adsorbent dosage. The kinetics data were best described by pseudo-second-order model and thermodynamic parameters suggested that the process was feasible, spontaneous and exothermic. It can be inferred from the various analysis conducted that the developed FMWCNTs nano-adsorbent is effective for removal of TOC from oil-produced water and may be explored for removal of organic contaminants from other industrial wastewater.

Enhanced adsorption of As(V) and Mn(VII) from industrial wastewater using multi-walled carbon nanotubes and carboxylated multi-walled carbon nanotubes.

The presence of As(V) and Mn(VII) in water beyond the permissible concentration allowed by World Health Organization (WHO) standard affects human beings, animals and the environment adversely. Hence, there is need for an efficient material to remove these potentially toxic elements from wastewater prior to discharge into water bodies. This research focused on the application of response surface method (RSM) assisted optimization of Fe-Ni/Activated carbon (AC) catalyst for the synthesis of MWCNTs. Also, the MWCNTs was carboxylated and the adsorption behaviors of both nano-adsorbents in the removal of As(V) and Mn(VII) from industrial wastewater was investigated through experimental and computational techniques. The prepared Fe-Ni/AC, MWCNTs and MWCNTs-OCH2CO2H were characterized using BET, TGA, FTIR, HRSEM, HRTEM, XRD and XPS. The result showed the BET surface area of Fe-Ni/AC, MWCNTs and MWCNTs-OCH2CO2H were obtained as 1100, 1250 and 1172 m2/g, respectively. Due to the enhanced impact of carboxylation, the adsorption capacity of As(V) and Mn(VII) removal increased from 200 to 192 mg/g for MWCNTs to 250 and 298 mg/g for MWCNTs-OCH2CO2H. The isotherm and kinetic models were best fitted by Langmuir and pseudo-second order kinetics, while the thermodynamic investigation found that the adsorption process was endothermic, spontaneous and chemisorptions controlled. The regeneration potential of MWCNTs and MWCNTs-OCH2CO2H after six repeated applications revealed good stability of adsorption efficiency. The study demonstrated optimization importance of Fe-Ni/AC catalyst design for MWCNTs adsorbents and the potentials of utilizing both MWCNTs and MWCNTs-OCH2CO2H in the removal of selected heavy metals from water and soil.

Potential of using kaolin as a natural adsorbent for the removal of pollutants from tannery wastewater.

In the present work, kaolin sample from Gbako Local Government, Niger State, Nigeria was used as an adsorbent for the removal chloride, COD, BOD, sulphate, chromium, cadmium, zinc and the reduction of total alkalinity in tannery wastewater. The kaolin sample was pretreated to enhance its adsorption capacity and then characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Electron Microscopy (HRSEM), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive Spectroscopy (EDX), Selective Area Electron Diffraction (SAED) and Brunauer Emmett-Teller (BET). The specific surface area, pore volume and pore diameter of the kaolin were 17 m2/g, 0.018 cm3/g and 3.587 nm, respectively. The adsorption methods of the parameters onto the kaolin were investigated as functions of contact time, adsorbent dosage and temperature. Equilibrium isotherms for the adsorption parameters were carried out experimentally and the adsorption data correlated very well with Jovanovic and Redlich-Peterson models. Furthermore, the adsorption kinetics followed the Avrami model. From the results of the study it was established that kaolin from Gbako, Nigeria can serve as an economic, safe and effective natural adsorbent for the pollutants removal from tannery wastewater.

Synthesis of carbon nanotubes by swirled floating catalyst chemical vapour deposition method.

A series of developments have been made in synthesizing Carbon Nanotubes (CNTs) by Catalytic Vapour Deposition (CVD) methods since its discovery as a possible route to the large scale and high quality production of CNTs. In this study, CNTs were synthesized continuously in a swirled floating catalytic chemical vapour deposition reactor using acetylene as carbon source, ferrocene as catalyst, with argon and hydrogen as carrier gases within the temperature range of 900-1050 degrees C. The effects of pyrolysis temperature, acetylene flow rate, hydrogen flow rate, and ratio of flow of acetylene to hydrogen on the rate of production of CNTs were investigated. The CNTs produced were purified with dilute nitric acid and the nature and quality of the CNTs were analysed by TEM, Raman spectrometer, EDX, and TGA. Results obtained revealed that a mixture of single and multi wall carbon nanotubes were produced continuously with a maximum yield rate of 0.31 g/min at 1000 degrees C and a flow ratio of acetylene to hydrogen of one to five.