Chromium is one of the most important chemical substances widely applicable in variousrnindustrial processes both in elemental and compound forms. In developing countries likernEthiopia, industries, like tanneries discharge a large quantity of chromium with little treatment tornthe environment. Chromium occurs in the environment in two most common oxidation states, Crrn(III) and Cr (VI), which have quite different chemical properties. Cr (VI) is extremely toxicrncompared to Cr (III) and can cause carcinogenic, teratogenic and mutagenic effects according torndifferent studies.rnIn this study, vesicular basalt volcanic rock was obtained in the North West Ethiopia and itsrnapplications for adsorption of Cr (VI) and Cr (III) from aqueous solution were investigated.rnDifferent physical and chemical properties of the powdered rock was studied using Fourierrntransform infrared spectroscopy (FT-IR), Powder X-ray diffraction(XRD) and scanning electronrnmicroscopy (SEM). A series of batch experiments were carried out to study the effect of variousrnexperimental parameters (pH, ionic strength and contact time) on Cr (VI) and Cr (III) adsorption.rnThe 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 carbazidernrespectively.rnInstrumental investigations of vesicular basalt rock indicated mineral compositions such asrnplagioclase, pyroxene, olivine, silica, hematite, magnetite and goethite. The major elementalrncompositions by weight were 48.46 % Oxygen, 17.37 % Silicon and 9.55 % aluminium. Otherrnelements such as iron (Fe), calcium (Ca), sodium (Na), potassium (K) and magnesium (Mg) arernalso identified in the sample.rnBatch adsorption experiments of Cr (VI) from aqueous solution onto the vesicular basalt rockrnindicated that the removal efficiency of Cr (VI) decreased with increasing pH and ionic strength.rnThe maximum adsorption capacity was 79.20 mg kg-1rnat pH of 2, initial concentration of 5.0 mgrnLrn-1rnand adsorbent dosage of 50 g L-1rn. In individual adsorption tests, Pseudo-second-order kineticrnand Freundlich isotherm models could better describe Cr (VI) adsorption on the vesicular basalt. rnxixrnAdsorption studies of Cr (III) onto the VB surface were highly dependent on pH. The maximumrnadsorption capacity was 0.976 mg g-1rnat pH 6, initial concentration of 100 mg L-1rnand adsorbentrndosage of 50 g L-1rn. Kinetic experiments indicated that the pseudo-second-order model displayedrnthe best correlation with adsorption kinetic data. The adsorption mechanism of Cr (III) onto thernsurface of the vesicular basalt involved film diffusion and intraparticle diffusion during thernreaction. Equilibrium studies indicated that Langmuir Isotherm model was found to be in betterrncorrelation with experimental data.rnAdsorption studies of both Cr (VI) and Cr (III) indicated that vesicular basalt, which isrnabundantly available and low cost, has the potential to remove Cr (VI) and Cr (III) from pollutedrnwater.rnTannery wastewater is composed of a complex mixture of chromium and other organic andrninorganic components from various processes that can critically pollute water bodies, ifrndischarged without treatment. In this study, local emergent plant species were used in a HSSFrnconstructed wetland system filled with vesicular basalt to investigate the removal efficiency ofrnchromium containing tannery wastewater. Four pilot units were vegetated with P.purpureum, T.rndomingensis, C. latifolius and E. pyramidalis, and a fifth unit was left as an unvegetatedrn(control). The HSSF constructed wetland system was effective in removing Cr, COD and BODrnfrom the inflow tannery wastewater. Its removal efficiency reached up to 99.38 %, 84.03 % andrn80.32% for Cr, COD and BOD5 respectively in the 6 days of HRT. The removal efficiency ofrnTSS, TP and NO3rn-rnobtained to a maximum of 70.59 %, 62.32% and 71.23 % respectively. Thernreduction of TDS, EC and Clin the outlet reached up to a maximum 40.62 %, 34.52% and 25.09rn% , respectively.rnAll the plant species used for removal of Cr (III) indicated BCF > 1 and TF < 1. These plantsrnmight not be adequate for phytoextraction, since most of the Cr (III) is accumulated in the roots,rnnot in the harvestable parts of plants. Though P. purpureum showed low TF, it might be used tornaccumulate Cr (III) in its rhizomes, because of its rapid growth and biomass production. Thernremoval of Cr (III) from the inflow tannery wastewater was high during operation, but nornsignificant differences in performance were observed between the vegetated and the control rnxxrnunits. This might be precipitation of Cr (III) (hydroxides, sulphides, sulphates, and carbonates),rnand adsorption onto the surface of vesicular basalt bed in the 6 days of retention time.