Technological viability of coffee husk ash, soil rich in koalinite-ferrinatrite and koalinite-geothite for the adsorptive removal of chromium (VI) from industrial wastewater.
Samuel, Zerihun Asmelash.
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Most industries in developing countries discharge a high amount of untreated wastewater, containing toxic chemicals, into nearby water bodies. Heavy metals and chemicals above permissible levels can be emitted to the environment as wastewater effluents from industries such as leather, electroplating, tanning, metal, fertilizer, and other industries. When these are discharged into the environment, they significantly pollute the quality of the water bodies and the environment, thereby substantially affecting river and human health. The safe and effective purification of polluted water containing heavy metals is always a challenge in many parts of the world, because cost-effective treatments are not readily available. Various methods are used for removing heavy metals, such as irradiation, chemical precipitation, ion exchange, adsorption, biological and chemical treatment. However, the adsorption technique is the best option due to easy to operate, simple, cheap, efficient, and suitable for the environment. The adsorption method is a suitable technique for developing countries like Ethiopia, where the advanced wastewater treatment technologies for high amount of toxic industrial wastewater are unaffordable. Locally-available adsorbent materials reasonably meet the criteria that have been established for the wastewater treatment process, due to their natural availability as adsorbents, their high natural porosity, their very low price, easy design, operation and maintenance, as well as their suitability for pollutant adsorption. The applicability of low-cost, locally-available adsorbent materials for the adsorptive removal of heavy metals from industrial wastewater is important. This study investigated the technological viability of low-cost materials, such as coffee husk ash, soil that is rich in kaolinite (40.4%) and ferrinatrite (59.6%), and soil that is rich in kaolinite (29.4%) and goethite (70.6%), for the adsorptive removal of chromium from industrial wastewater. The physical properties and elemental composition of the three adsorbents (soil rich in kaolinite-ferrinatrite, coffee husk ash and kaolinite-geothite) were characterized. The experiments were conducted under batch adsorption set-ups to assess the effect of different parameters and their optimum removal efficiency. The optimum adsorption of Cr(VI) on the three adsorbents used were observed at 40 minutes and two pH values and their doses of adsorbent, shaker speed, and initial Cr (VI) ion concentration were different in the batch adsorption experiments. The adsorption of Cr(VI) followed pseudo second-order kinetics, with a coefficient of determination r2 > 0.99 for the three-adsorbent media. Results of the adsorption isotherm show that Freundlich adsorption isotherm model better described Cr(VI) adsorption into soil rich in kaolinite-ferrinatrite (SRKF), soil rich in kaolinite-geothite (SRKG) and coffee husk ash (CHA) with coefficients of determination; r2 > 0.93. The adsorption capacity of the adsorbent followed the decreasing order CHA >SRKF > SRKG. The findings on the adsorption characteristics of batch system from this work suggests that soil rich in kaolinite-ferrinatrite, coffee husk ash and soil rich in kaolinite-goethite could represent an interesting low-cost naturally available adsorbent material that could be used for the chromium (VI) removal from wastewater. The empirical data and models developed in the study were used to establish theoretical design analysis of adsorptive treatment plant for industry emits such wastewater. However, further investigations will be required for the practical application of these locally-available adsorbent materials for the removal of chromium from wastewater.