Removal of methylene blue dye using nano zerovalent iron, nanoclay and iron impregnated nanoclay - a comparative study.

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry. The sorption process is one conventionally used method. In this study, nanoclay, nano zero valent iron (nZVI), and iron impregnated nanoclay were prepared and studied for the removal of MB dye in batch mode. The effects of operating parameters like pH, dye concentration, sorbent dosage, and contact time were investigated and optimized. The nZVI, nanoclay, and iron impregnated nanoclay sorbents showed zeta potentials of -32.1, -53.4, and -40.7 mV, respectively. All the nano adsorbents were crystalline. The nanoclay was characterized by an average surface area, pore volume and pore diameter of 43.49 m2 g-1, 0.104 cm3 g-1 and 2.806 nm, respectively. nZVI showed a surface area of 47.125 m2 g-1, pore volume of 0.119 cm3 g-1, and pore diameter of 3.291 nm. And iron impregnated nanoclay showed a surface area of 73.110 m2 g-1 with a pore volume of 15 cm3 g-1 and a pore diameter size of 3.83 nm. A Langmuir EXT nitrogen gas adsorption isotherm (R 2 ∼ 0.99) was the best fit. The thermodynamics parameters, such as ΔG° (-12.64 to -0.63 kJ mol-1), ΔH° (+0.1 to +62.15 kJ mol-1) and ΔS° (+0.10 to +0.22 kJ mol-1), confirmed that a spontaneous and endothermic adsorption process took place at a high rate of disorder. Iron impregnated nanoclay showed higher negative Gibbs free energy (-12.64 kJ mol-1), higher enthalpy change (+62.5 kJ mol-1) and entropy (+0.22 kJ mol-1) and gave a better MB removal performance. In addition, the lower negative heat of enthalpy for all adsorptions proved the dominance of physisorption. The methylene blue adsorption isotherm on nZVI and nanoclay showed the best fit with the Freundlich isotherm model with correlation coefficients (R 2) ∼0.98 and 0.99, respectively. Whereas the Langmuir adsorption isotherm was the best fit for iron impregnated nanoclay (R 2 ∼ 0.98). The adsorption activities of nZVI, nanoclay and iron impregnated nanoclay were fitted to a pseudo-second-order kinetic model with correlation coefficients (R 2) of 0.999, 0.997 and 0.983, respectively. The optimal pH 7.0 (RE: 99.1 ± 0.73%), initial MB concentration 40 ppm (RE: 99.9 ± 0.03%), contact time 120 min (RE: 99.9 ± 0.9%), and adsorbent dose 80 (99.9 ± 0.03%) were obtained for iron impregnated nanoclay. The optimal operational parameters of nanoclay and nZVI, respectively, were pH 11.0 and 13.0, initial MB concentration 20 and 20 ppm, adsorbent dose 100 and 140 mg, and contact time 120 and 140 min. In general, iron impregnated nanoclay has shown promising cationic dye adsorbance for industrial applications; but a recyclability test is suggested before scale-up.

Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd2+, Cu2+ and Pb2+) from aqueous solutions.

For the past 15 years, nanoscale metallic iron (nZVI) has been investigated as a new tool for the treatment of heavy metal contaminated water. The removal mechanisms depend on the type of heavy metals and their thermodynamic properties. A metal whose redox potential is more negative or close to the reduction potential of Fe(0) is removed by the reduction process, while the others will be mediated by precipitation, complexation or other sorption processes. This review summarises our contemporary knowledge of nZVI aqueous chemistry, synthesis methods, mechanisms and actions (practical experiences) of heavy metal (Cd, Cu and Pb) removal and challenges of nZVI practical applications. Its inner core (iron(0)) has reducing ability towards pollutants, while the iron oxide (FeO) outer shell provides reaction sites for chemisorption and electrostatic interactions with heavy metals. Emerging studies highlighted that nZVI surfaces will have negatively charged species at higher pH and have good affinity for the removal of positively charged species such as heavy metals. Different sizes, shapes and properties of nZVI have been produced using various methods. Ferric salt reduction methods are the most common methods to produce stable and fine graded nZVI. Higher uptake of copper(ii), lead(ii) and cadmium(ii) has also been reported by various scholars. Practical pilot tests have been conducted to remove heavy metals, which gave highly satisfactory results. Challenges such as agglomeration, sedimentation, magnetic susceptibility, sorption to other fine materials in aqueous solution and toxicity of microbiomes have been reported. Emerging studies have highlighted the prospects of industrial level application of nano zero valent particles for the remediation of heavy metals and other pollutants from various industries.

Correction: Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd2+, Cu2+ and Pb2+) from aqueous solutions.

[This corrects the article DOI: 10.1039/D1RA01427G.].

Assessment of Dioxin and Furan Emission Levels and Management Practices in Addis Ababa, Ethiopia.

INTRODUCTION: An increase in population and related increased demand for health services, expansion of industries, and increasing transportation demands have increased the emission of dioxin and furan persistent organic pollutants (POPs) in Addis Ababa, Ethiopia. OBJECTIVE: This study aimed to identify sources of dioxin and furan emissions, quantify their release into various environmental medias and assess related management practices. METHODS: The standard United Nations Environmental Programme (UNEP) (2005) toolkit guide and default emission factor were used to identify the main anthropogenic sources and to quantify the amount of released dioxin and furan. Stratified random sampling techniques were applied to assess current management practices. RESULTS: Nine main groups of dioxin and furan emission sources were identified. The emission of each source group was calculated by the activity rate data multiplied by an emission factor. The results found that about 138.85 g toxic equivalent(TEQ)/a(TEQ/year)of dioxin and furan were released to air, water, residue (materials remaining as sludge after sewage treatment or in the form of ash after incineration activity) and soil. Waste disposal activities recorded the largest release of dioxin and furan, accounting for 68.30 g TEQ/a of dioxin and furan to water and residue, 34.00 g TEQ/a to air and 0.64 g TEQ/a emitted into soil. CONCLUSIONS: Several sources of dioxin and furan emission were identified and the present study found that their management is inadequate. Waste disposal services are especially inadequate and generate higher amounts of dioxin and furan gasses. In addition, the organizations that are responsible for the release of dioxin and furan have no awareness of their release and inadequate management practices. The present study points to the need for reformulation of the national legal management framework, adoption of best available technology for disposal services such as incinerators with flue gas management, increasing public and stakeholders' awareness and participation and capacitating the responsible government organizations.

Biodegradation of Methanol Using Thiosulphate as an Electron Acceptor Under Anaerobic Conditions.

BACKGROUND: Methanol is a volatile organic compound commonly found in the effluent of the pulp and paper industries. Because of its toxicity, methanol can cause metabolic acidosis, neurologic sequelae, and even death when ingested. Information on biokinetic activity such as biodegradation rate of methanol and thiosulphate, biomass growth rate and biomass yield coefficient is limited in the literature. OBJECTIVES: To study the biomass growth rate and biomass yield coefficients of methanol and thiosulphate biodegradation. This research aims to increase knowledge of how to reduce the emission of toxic gas to the environment. METHODS: The biodegradation trends of both methanol and thiosulphate were studied under anaerobic conditions using batch experiments at ambient temperature and alkaline conditions. Both supplement each other for their degradation. Methanol is an electron donor, whereas thiosulphate acts as an electron acceptor. A mixed culture from a previously used biomass in a biotrickling filter reactor from theUnited Nations Educational, Scientific and Cultural Organization (UNESCO), International Graduate Water Education Facility and fresh activated sludge from the Harnaschpolder wastewater treatment plant were used as a biomass source. RESULTS: A specific biomass growth rate of biomass ranging from 0.04 to 1.7g per day was observed. The thiosulphate is biologically degraded by the biomass grown inside the reactor. The biodegradation rate of thiosulphate in the reactor varied from 0.02 to 0.80g per unit gram of biomass per day. A biodegradation rate of methanol in the reactor was observed in the range between 0.04 to 3.9g per unit gram of biomass per day. Bacterial biomass was grown as per the amount of methanol present inside the reactor. A maximum biomass yield coefficient of 0.7g biomass per gram of methanol was recorded. Thiosulphate was converted to sulphate that indirectly served as an electron acceptor for methanol degradation. Both degradation of methanol and thiosulphate in this experiment were in the range of the degradation rate shown for sulphate and organic compounds in other studies. CONCLUSION: Simultaneous removal of thiosulphate and methanol using an anaerobic bioreactor is promising and can be applied on an industrial scale. This finding is an important contribution to public health as it reduces the emission of toxic gas to the environment.