Abstract:
Hexavalent chromium is well recognized as an element of environmental and public health
concern. Numerous commercially available activated carbons have been used for chromium
adsorption, both as-received and after chemical modifications. To ensure sound application on
the mitigation of chromium, chemically activated carbon from coffee husk was utilized by
considering partly the existence of substantial amount of by product coffee husks in Ethiopia.
The adsorbents surface was characterized by XRD.The different physicochemical properties
such as bulk density, moisture content, volatile matter, ash content, pore volume, pH and
electrical conductivity were determined. The adsorption of hexavalent chromium from aqueous
solution by chemically activated carbon prepared from coffee husk and its application to real
wastewater was studied. The extent of adsorption was studied as a function of pH, contact time,
adsorbent dose, and initial adsorbate concentration. Optimum conditions studied were found to
be 60 minutes, 80 mg/l, 2, 2.5 g/100 ml and 150 rpm for contact time, concentration of
adsorbate, pH, adsorbent dose and stirring speed, respectively. The adsorption efficiency of
activated coffee husk was found to be 99.6% at optimal conditions. The adsorption process has
best fitted pseudo-second order kinetic model than pseudo-first order kinetic model. Langmuir
and Freundlich adsorption isotherm models were applied to analyze adsorption data, and
Langmuir adsorption isotherm model was found to be best fitted to this adsorption process. The
study showed that activated carbon from coffee husk is a good candidate for the removal of
hexavalent chromium from contaminated water.
