Adsorption of Selected Heavy Metals Using Modified Pennisetum Purpureum Plant Stalks: A Case Study of River Ruiru, Kiambu County, Kenya
Water pollution is a global problem affecting the welfare of humanity. Availability of clean water is a fundamental prerequisite to public health safety and the survival of the human race as well as animals. However, pollution of river water by heavy metal ions deposition is a grave ecological problem especially in developing countries. Previous research work on analysis of fish, soil sediments and water samples obtained from Nairobi and Ruiru river confirmed the presence of heavy metals. These metal ions which include lead, chromium, and iron are mainly from industrial effluents discharged into the rivers. Presence of the heavy metals in the water, pose a serious health risk particularly to rural populations which rely majorly on the river water for domestic purposes. Several methods for elimination of the heavy metal pollutants from river waters have been previously employed. However, most of these methods have proved to be expensive and cumbersome, hence not sustainable. Simpler methods are, therefore, needed for better sustainability. This research explored the potential of modified Pennisetum purpureum plant adsorbent in eradication of lead (II), manganese (II) and chromium (VI) ions from Ruiru river water by adsorption process. Sampling was done at three different locations along the river, that is, Ruiru Town, Juja Farm and Fourteen Falls. The mean concentration of heavy metal ions was determined before and after the adsorption process in triplicates using Atomic Absorption Spectroscopy (AAS). Effect of changes in pH on adsorption was investigated by conducting adsorption at pH of 5, 7 and 9. Data was organized in excel worksheets before it was transferred into SPSS software for analysis. The results show high chromium and lead pollution of the Ruiru river. Average concentrations of chromium and lead were 1.495±0.09 ppm and 1.610±0.1 ppm respectively. Average Manganese levels were 0.05±0.01 ppm which was within the permissible level (0.5 ppm). Modification of the adsorbent surface improved its adsorption capacity. The modified adsorbent achieved greater % adsorption in all the three metals. Increase in the pH of adsorption from 5 to 9 had a reducing effect on the percent adsorption of metal ions from water samples with significant reductions in % adsorption being recorded for lead and manganese ions but not for chromium ions. These results show the potential of the Pennisetum purpureum plant in the purification and detoxification of river water by adsorption. This adsorbent presents a more readily alternative to many current adsorbents and adsorption methods in use. However further research is needed to ascertain the best set of conditions as well as the most suitable modification treatment for maximum adsorption.