Environmental Engineering

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Browsing Environmental Engineering by Subject "Adsorption"

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    Adsorption of Heavy Metal from Constituent Waste Water by Tea Waste Adsorbent
    (Addis Ababa University, 2016-06) Oljira, Lalise; Kiros, Solomon (PhD)
    Most industries such as electroplating, textile, fertilizer, batteries, leather, and others in less developed countries discharge huge volumes of untreated wastewater into water bodies. The industrial wastewater may contain toxic chemicals in excess of the threshold level when released into the environment, particularly to the aqueous environment and soil; significantly degrade the quality of the water thereby affecting river health substantially and subsequently human health. There are several techniques for removing toxic chemicals such as ion exchange, membrane filtration, adsorption, irradiation and chemical and biological treatments. However, the adsorption method is believed to be the better option because it is cost-effective, efficient, simple and easy to operate, and environmentally friendly according to many studies. Accordingly, this method can be a preferable option for developing countries like Ethiopia, where advanced treatment technologies for high volumes of toxic industrial waste water are unaffordable. The aim of this work was to determine the potential of tea waste (TW) as a useful adsorbent for the removal of copper and zinc ions from aqueous systems. The study was conducted using batch experiments with constituted wastewater having copper and zinc ion concentration of 1000 mg·L-1. The effects of initial concentration, contact time and pH on adsorption efficiency were investigated. Adsorption isotherm was also studied. Generally, the result showed an increase in removal efficiency with increase in contact time, pH and decrease of initial concentration. The adsorption equilibrium data correlate well with Freundlich model and Langmuir model respectively for zinc removal and copper removal with regression coefficient (R2=0.9913, R2=0.981). The results showed that efficiencies of (TW) for the removal of copper and zinc ion were 95.98% and 99.80% respectively at optimum point of 5pH, 10ppm, and 120min. These results clearly indicate the efficiency of tea waste (TW) as a low-cost adsorbent for treatment of wastewater containing copper and zinc ions. Therefore, it is recommended that tea waste can be used, as a low cost and abundant source for the removal of heavy metals as an alternative to more costly materials. KEY WORDS: Copper, zinc, toxicology, adsorption, tea waste, batch study, atomic adsorption spectrometer.
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    Adsorption of Methylene Blue Dye from Synthetic Wastewater using Chitosan/graphite Composite Adsorbent; Statistical Optimization
    (Addis Ababa University, 2023-11) Soliyana Teshome; Shimelis Kebede (PhD)
    The study aimed to synthesize a chitosan/graphite composite (CGC) for methylene blue dye removal from synthetic wastewater using the impregnation method. Expanded graphite was prepared by reacting graphite with H2SO4 and H2O2 at room temperature, then washed, dried, and heated. The specific surface area of graphite increased from 1193.75m2/g to 1223.648m2/g. The composite adsorbent material was synthesized using the impregnation method, with chitosan to expanded graphite ratio of 75:25. The CGC was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller (BET) method, scanning electron microscope (SEM), and point of zero charge analysis. The optimized experimental design resulted in 98.61% removal efficiency at initial concentration of 5.24 mg/L, pH of 9.98 and contact time of 95.43. The adsorption of methylene blue dye onto CGC was best fitted with Langmuir isotherm, with an R2 value of 0.9974 and adsorption capacity of 98g/g. The kinetics of adsorption were best fitted to pseudo-second order with an R2=99.39.
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    Biopolymer Based Hydrogel for Adsorption of Heavy Metal Ions from Aqueous Solution: Experimental and Theoretical Investigation
    (Addis Ababa University, 2024-04) Leta Lemma; Zebene Kiflie (Prof.)
    Contamination of water by heavy metal ions, in particular, hexavalent chromium (Cr6+) ion, lead (Pb2+) ion and cadmium (Cd2+) ion, has become one of the most serious issues threatening human health and thus remedial measure have to be taken. Adsorption–based research toward biodegradable polymers for heavy metal ions remediation has received much attention in recent years due to environmental concerns. Polysaccharides in this domain are interesting starting materials for the preparation of novel adsorbents. In this work, novel type of biopolymer–based hybrid hydrogel such as PPSgCG, PCCFG, and CZVI–CS–PVA were designed for removal of Cr6+, Pb2+, and Cd2+ ions from aqueous solution. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), acrylamide–grafted native starch (Coccinia abyssinica) (S–g–AAm), chitosan (CS), and graphene oxide (GO) were used to prepare PVA–PVP–S–g–AAm–CS–GO (PPSgCG) hydrogel. L-cysteine–functionalized graphene oxide (CFG), chitosan, and polyvinyl alcohol were used to synthesis polyvinyl alcohol–chitosan–cysteine–functionalized graphene oxide (PCCFG) hydrogel. L–cysteine stabilized zero–valent iron (CZVI), chitosan, and polyvinyl alcohol were used to prepare L–cysteine–zero–valent iron–chitosan–polyvinyl alcohol (CZVI–CS–PVA) hydrogel. Physiochemical properties of freeze–dried hydrogel were characterized by Fourier transform infrared spectroscopy (FTIR; Spectrum 65, PerkinElmer), zetasizer (3000HS), scanning electron microscopy (SEM; JCM-6000 Plus, Japan), energy dispersive X–ray spectroscopy (EDX; JSM–IT 100, JEOL), X-Ray Diffractometer (XRD; XRD–7000, Shimadzu, Japan), and thermogravimetric analysis (TGA/DTA; HCT–1, China). Adsorptions of Cr6+ ion onto PPSgCG and CZVI–CS–PVA hydrogel, and Pb2+ and Cd2+ ions onto PCCFG hydrogel as functions of initial heavy metal ion concentration, pH, time, hydrogel dose, and temperature have been studied by following a one–factor–at–a–time approach. The Cr6+ ions concentration in solution was determined by UV–vis spectrophotometer (Human, X–ma 1200). The Pb2+, Cd2+, and Cu2+ ions concentration in the solution after adsorption was determined by atomic adsorption spectroscopy (AAS; ZEEnit 700p, Analytikajena). The adsorption of Cr6+ onto PPSgCG hydrogel, at optimum conditions: 2, 100 mg l-1, 120 minutes, 3 g l-1, and 25oC of pH, initial Cr6+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The adsorption data agree with Langmuir (R2 = 0.99) isotherm at 25°C and follow pseudo–second–order kinetic model (R2 = 0.999) at pH of 2. The maximum adsorption capacity of the PPSgCG hydrogel towards to Cr6+ was 93 mg g−1. The obtained negative standard Gibb‟s free energy (ΔG°= – 1.120 kJ mol−1) and negative enthalpy (ΔH°= – 2.360 kJ mol−1) reveal the spontaneity and exothermic nature of Cr6+ ion adsorption onto the hydrogel. Moreover, the adsorption thermodynamics shows enthalpically favoring host–guest complexion along with decrease in entropy. Furthermore, the effect of common competing ions such as sulfate (SO32-), phosphate (PO43-), nitrate (NO3−), and chloride (Cal−) ions on adsorption efficiency and selectivity of Cr6+ ion on the hydrogel were investigated and the result shows that sulfate ion has a significant effect on the Cr6+ ion adsorption, which might be related to identical chemical properties and geometrical configuration. The adsorption of Cr6+ onto CZVI–CS–PVA hydrogel, at optimum conditions: 3, 45 mg l-1, 90 minutes, 4 g l-1, and 25oC of pH, initial Cr6+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The adsorption data agree with Langmuir isotherm (R2 = 0.99) at 25°C and follow pseudo–second order (R2 = 0.999) model at pH of 3. The maximum adsorption capacity of the PPSgCG hydrogel towards to Cr6+ was 15.86 mg g−1. The adsorption of Pb2+ and Cd2+ onto PCCFG hydrogel, at optimum conditions: 5, 225 mg l-1, 50 minutes, 2 g l-1, and 25oC of pH, initial Pb2+ and Cd2+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The experimental data well described by a pseudo–second–order kinetic model (R2 = 0.99 for Pb2+ and R2 = 0.98 for Cd2+) and Langmuir isotherm (R2 = 0.980 for Pb2+ & R2 = 0.978) with maximum adsorption capacities of 250 and 192 mg g−1 at 25°C for Pb2+ and Cd2+, respectively. The adsorption capacity of the PCCFG hydrogel increased with the increase in temperature. The value of ΔG° was negative, which shows the spontaneity of the reaction (electron exchange or ion exchange) between the metal ion and electron–rich atoms (–N, –S, –O). The positive ΔH° shows that the adsorption reaction consumes energy and the positive ΔS° shows the strong affinity of PCCFG toward the Pb2+ and Cd2+ ions. Pb2+ had better affinity and less spontaneity than Cd2+. The effect of competing ions was studied in batch adsorption experiments in the solution containing the three metal ions (Pb2+, Cd2+, and Cu2+) and the result shows that the coexistence of metal ions in the solution inhibits the adsorption capacity of the hydrogel compared to solutions containing a single metal ion.Theoretical investigation of adsorption mechanism of Cr6+ and Pb2+: Gauss View 6.0.16 interface were employed to construct the modeled system. The ground state geometry optimization of modeled system were first optimized by Molecular Mechanics (MM) method with aid of Universal Force Field (UFF) followed by Hartree fock (HF) and Density Functional Theory (DFT) method, using Gaussian 09 software package. Moreover, frequency, Natural Bond Orbital (NBO), and energy calculation were done by DFT method with aid of Gaussian 09. Hybrid–generalized gradient approximation (hybrid–GGA), B3PW91–D3 level of theory, where D3 denotes the third–generation dispersion correction by Grimme and basis set, the Stuttgart–Dresden–Boon (SDD) basis set was employed for heavy metal ions, and the 6–31G(d) basis were used for C, N, O, S, and H atoms during geometry optimization, frequency and NBO calculation. Single–point energy calculations were performed using the ωB97XD functional where basis set 6-311+G (d, p) was employed for C, N, O, S, and H atoms, and SDD basis set was employed for heavy metal ions. Solvation effect (H2O) was evaluated with polarizable continuum model (PCM) to mimic the real aqueous solution. The Gaussian simulation result shows that mainly the –N and –O atoms of amine (–NH2), amide (–CONH2), and carboxyl (–COOH) functional group of the hydrogel were responsible for binding of heavy metal ions via electron sharing/covalent bonding.
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    Removal of chromium hexavalent (Cr(VI) from aqueous solution using activated carbon prepared from Prosopis Juliflora Plant and find the optimal operating condition for adsorption process.
    (Addis Ababa University, 2015-02) Emirie, Molalign; Tekola, Beteley(Assistant Professor)
    In the present study adsorption of chromium (VI) ions from aqueous solution by activated carbon prepared from Prosopis Juliflora plant was investigated under batch mode. The removal of hexavalent chromium was optimized by using response surface methodology. The influence of various process parameters such as initial chromium (VI) concentration, solution pH, sorbent dose and contact time on the removal process were investigated. A total of 30 sorption experimental runs were carried out employing the detailed conditions designed by response surface methodology based on the Central Composite Design. The analysis of variance (ANOVA) depicted that the quadratic model was suitable for the responses. Contour and response surface plots were used to determine the interaction effects of main factors and optimum conditions of process, respectively. From the experimental result, maximum chromium (VI) removal of 99.23 % was obtained at the optimum condition of initial chromium (VI) concentration (80 mg/L), pH (1.5), adsorbent dose (10g/L) and contact time (106.79 min). The experimental removal efficiency (99.23 %) agreed very well with the predicted one (99.27 %), indicating the suitability of the model employed and the success of response surface methodology in optimizing the conditions of the removal of chromium (VI) ions from aqueous solution. Keywords: Response surface methodology; Prosopis Juliflora; adsorption; ANOVA; Contour
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    Removal of Some Selected Heavy Metal Using Modified Bagasse and Eucalyptus Bark from Gold Mining Waste Water: Case Study of Ezana (Meli) Gold Mining Development Plc Industries
    (Addis Ababa University, 2018-06) Mebrahtom, Hagos; Abubeker, Yimam (PhD)
    This study investigated the potential use of modified bagasse (MSB) and eucalyptus Bark (EB) treated from sample wastewater in batch mode experiments. The discharge of untreated gold mining wastewater contaminates with heavy metals such as Cu (II) and Pb (II), which is threatening ecosystems, carcinogenic to the human & hinder development of plants. Since the removal by adsorption is cost effective, not time consuming and environmentally friendly, it has been widely studied by many scholars for remediation of heavy metals. Characterization of bagasse and eucalyptus bark were analyzed using proximate analysis like MC (%), Ash value (%), ƍ b (g/cm 3 ), VM (%), fixed carbon (%) and % (C, N 2 ). FTIR analysis revealed the presence of multiple functional groups in the adsorbent, some of which were involved in the sorption process and x-ray diffraction (XRD) used to measure the crystalline content of adsorbent materials. The result indicated that the effluents discharged from Ezana Gold extraction were mainly contains the following: TSS (ppm), turbidity (NTU), EC (µs/cm), TDS (ppm), COD (ppm), temperature(°C), pH, cyanide WAD with <11°C (ppm) and heavy metals such as Fe > Cu >Pb >Mn > Cr (VI) >Zn > Co > Ni > Cd (ppm). They were determined by atomic absorption spectroscopy. The major pollutants selected from the process effluent were Cu 2+ and Pb 2+ due to exceeded standard discharge limits. The objective of the study was removal of Cu 2+ and Pb 2+ from rich Ezana wastewater using modified sugarcane bagasse and eucalyptus bark powder as an adsorbent. The selected parameters were pH, adsorbent dose and time. A maximum removal of (Cu 2+ , Pb 2+ ) by modified bagasse (88.45%, 94%) and eucalyptus bark (92%, 99%) respectively was achieved. The adsorption data were well fitted to the Langmuir isotherm model and pseudo-second order kinetic model for both modified bagasse (Cu, Pb) and eucalyptus bark (Cu, Pb). This indicated that Eucalyptus bark powder was more effective than modified bagasse (MSB) and it can be used as an alternative low cost adsorbent for the removal of copper and lead from Ezana mining wastewater.