BIOSORPTION OF SELECTED HEAVY METAL IONS FROM TEST SOLUTIONS USING GREEN ALGAE BIOSORBENT

Abstract

Human activities such as agricultural and industrial operations have led to the accumulation of pollutants for example, heavy metals in the environment since they do not break down. When this occurs over a long period of time, it can cause both pollution and health risks. Consequently, there is need to remove these heavy metals from environmental matrices. The different conventional ways of removing heavy metals from the environment are expensive and mostly ineffective. Among these methods, biosorption has been proved to be efficient and cheap in heavy metal removal. Most common marine weeds have been found to be potent biosorbents. This study aimed at examining the capability of green algae in the biosorption of heavy metals from waste waters. The green algae were sampled from the University of Eldoret fish ponds, washed, dried and ground using pestle and mortar. Four selected heavy metal test solutions of Ni2+, Zn2+, Cu2+ and Cd2+ were used in the study. A 5 gram mass of the algae sample powder was transferred into 250 ml beaker containing a 100 mL solution of specific heavy metal at pH values 4, 7 and 9, and stirred for ten minutes. Ten ml samples were then taken from the reacting vessel at time intervals of 10, 20, 30, 40, 50 and 60 minutes and metal levels measured by the atomic absorption spectrophotometer. The results showed that for each of the four selected metals, the levels significantly increased in the biosorbent faster in the first 10 minutes, while the equilibrium reached after 50 minutes. For Cu2+ the maximum biosorption was found to occur at pH 9, Zn2+ pH 7, Ni2+ pH 7, and Cd2+ pH 7,while the least biosorption occurred at pH 4 for Cu2+., Zn2+ pH 4, Cd2+ pH 9 and Ni2+ pH 9. The isotherm data fitted Langmuir better than Freundlich from the values of R2. The R2 values for pH 4, 7 and 9 ranges, were found to be tending to one, indicating a strong positive relationship between the equilibrium heavy metal ions concentration (Ce) and the metal uptake (Qe). Freundlich, the correlation coefficients, R2, were found to be less than 0.900, indicating a weak positive relationship between the equilibrium heavy metal ions concentration (Ce) and the metal uptake (Qe). Pseudo second order kinetics agreed most strongly with the four metals, the correlation coefficient of the metals were calculated and the second order kinetics, R2, equaled to almost 1.000, the accepted parameter in biosorption. Thus green algae are effective biosorbents for the removal of Ni2+, Zn2+, Cu2+ and Cd2+ from aqueous solutions. Further studies should be done for other heavy metals by the different algae species at different pH ranges.