Potentials of Local Rock Substrate and Plant Species for an Integrated Treatment of Chromium (Cr) Containing Tannery Wastewater Using Constructed Wetland Systems (CWSs), Bahir Dar, Ethiopia
| dc.contributor.advisor | Lemma, Brook (Prof) | |
| dc.contributor.author | Alemu, Agegnehu | |
| dc.date.accessioned | 2019-12-16T12:02:01Z | |
| dc.date.accessioned | 2023-11-18T08:42:28Z | |
| dc.date.available | 2019-12-16T12:02:01Z | |
| dc.date.available | 2023-11-18T08:42:28Z | |
| dc.date.issued | 2019-06 | |
| dc.description.abstract | Chromium is one of the most important chemical substances widely applicable in various industrial processes both in elemental and compound forms. In developing countries like Ethiopia, industries, like tanneries discharge a large quantity of chromium with little treatment to the environment. Chromium occurs in the environment in two most common oxidation states, Cr (III) and Cr (VI), which have quite different chemical properties. Cr (VI) is extremely toxic compared to Cr (III) and can cause carcinogenic, teratogenic and mutagenic effects according to different studies. In this study, vesicular basalt volcanic rock was obtained in the North West Ethiopia and its applications for adsorption of Cr (VI) and Cr (III) from aqueous solution were investigated. Different physical and chemical properties of the powdered rock was studied using Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction(XRD) and scanning electron microscopy (SEM). A series of batch experiments were carried out to study the effect of various experimental parameters (pH, ionic strength and contact time) on Cr (VI) and Cr (III) adsorption. The concentrations of Cr (III) and Cr (VI) were determined using inductively coupled plasmaoptical emission spectroscopy (ICP-OES) and UV-Vis spectroscopy with 1, 5-diphenyl carbazide respectively. Instrumental investigations of vesicular basalt rock indicated mineral compositions such as plagioclase, pyroxene, olivine, silica, hematite, magnetite and goethite. The major elemental compositions by weight were 48.46 % Oxygen, 17.37 % Silicon and 9.55 % aluminium. Other elements such as iron (Fe), calcium (Ca), sodium (Na), potassium (K) and magnesium (Mg) are also identified in the sample. Batch adsorption experiments of Cr (VI) from aqueous solution onto the vesicular basalt rock indicated that the removal efficiency of Cr (VI) decreased with increasing pH and ionic strength. The maximum adsorption capacity was 79.20 mg kg-1 at pH of 2, initial concentration of 5.0 mg L -1 and adsorbent dosage of 50 g L-1 . In individual adsorption tests, Pseudo-second-order kinetic and Freundlich isotherm models could better describe Cr (VI) adsorption on the vesicular basalt. xix Adsorption studies of Cr (III) onto the VB surface were highly dependent on pH. The maximum adsorption capacity was 0.976 mg g-1 at pH 6, initial concentration of 100 mg L-1 and adsorbent dosage of 50 g L-1 . Kinetic experiments indicated that the pseudo-second-order model displayed the best correlation with adsorption kinetic data. The adsorption mechanism of Cr (III) onto the surface of the vesicular basalt involved film diffusion and intraparticle diffusion during the reaction. Equilibrium studies indicated that Langmuir Isotherm model was found to be in better correlation with experimental data. Adsorption studies of both Cr (VI) and Cr (III) indicated that vesicular basalt, which is abundantly available and low cost, has the potential to remove Cr (VI) and Cr (III) from polluted water. Tannery wastewater is composed of a complex mixture of chromium and other organic and inorganic components from various processes that can critically pollute water bodies, if discharged without treatment. In this study, local emergent plant species were used in a HSSF constructed wetland system filled with vesicular basalt to investigate the removal efficiency of chromium containing tannery wastewater. Four pilot units were vegetated with P.purpureum, T. domingensis, C. latifolius and E. pyramidalis, and a fifth unit was left as an unvegetated (control). The HSSF constructed wetland system was effective in removing Cr, COD and BOD from the inflow tannery wastewater. Its removal efficiency reached up to 99.38 %, 84.03 % and 80.32% for Cr, COD and BOD5 respectively in the 6 days of HRT. The removal efficiency of TSS, TP and NO3 - obtained to a maximum of 70.59 %, 62.32% and 71.23 % respectively. The reduction of TDS, EC and Clin the outlet reached up to a maximum 40.62 %, 34.52% and 25.09 % , respectively. All the plant species used for removal of Cr (III) indicated BCF > 1 and TF < 1. These plants might not be adequate for phytoextraction, since most of the Cr (III) is accumulated in the roots, not in the harvestable parts of plants. Though P. purpureum showed low TF, it might be used to accumulate Cr (III) in its rhizomes, because of its rapid growth and biomass production. The removal of Cr (III) from the inflow tannery wastewater was high during operation, but no significant differences in performance were observed between the vegetated and the control xx units. This might be precipitation of Cr (III) (hydroxides, sulphides, sulphates, and carbonates), and adsorption onto the surface of vesicular basalt bed in the 6 days of retention time. | en_US |
| dc.identifier.uri | http://etd.aau.edu.et/handle/12345678/20379 | |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | Adsorption | en_US |
| dc.subject | Bioconcentration factor | en_US |
| dc.subject | Chromium (III) | en_US |
| dc.subject | Chromium (VI) | en_US |
| dc.subject | Constructed wetland | en_US |
| dc.subject | Tannery wastewater | en_US |
| dc.subject | Translocation factor | en_US |
| dc.subject | Vesicular Basalt | en_US |
| dc.title | Potentials of Local Rock Substrate and Plant Species for an Integrated Treatment of Chromium (Cr) Containing Tannery Wastewater Using Constructed Wetland Systems (CWSs), Bahir Dar, Ethiopia | en_US |
| dc.type | Thesis | en_US |