Use of Algae for Removing Heavy Metal Ions from Industrial Wastewater

Abstract

The presence of heavy metal ions in the environment has been a big challenge facing the world due to its harmful effect on the health of humans even at low concentrations. There are various treatment techniques that can be used to remove heavy metals from wastewater such as chemical, physical, and biological processes. However, the practical application of chemical and physical techniques is limited due to high cost, process complications and the need for well-trained personnel. Therefore, it is necessary to develop new, low cost, highly efficient and eco-friendly wastewater treatment methods that can be effectively eliminate and remove heavy metals from contaminated water solutions. Biological processes are considered the most economical alternative for the treatment of wastewater if compared with other processes in which its adsorbents are widely available. Thus, the main aim of this research work is to utilize microalgal species for removing heavy metal from industrial wastewater. The ability of non-living and living local algae strains to remove different heavy metal ions such as Nickel, Aluminum, and Copper from industrial wastewater samples was investigated. The secondary wastewater sample was modified in the laboratory by adding a specific concentrations of heavy metal ions to conduct the experiment. Batch experiments were conducted to find the optimal operating conditions and the most suitable material to remove Nickel, Aluminum, and Copper via adsorption. pH, initial metal concentration, biomass dosage, and contact time were tested. Therefore, it was found that the optimum pH, biosorbent dosage, and the initial metal concentration are 5.5, 0.5 g/L, and 10 mg/L, respectively. The maximum removal% of heavy metals from industrial wastewater by non-living spirulina sp. biomass was found to be 57.38% for Nickel, 38.24% for Copper, and 93.46% for Aluminum within 4 hours. In order to fit the experimental data, Adsorption isotherms (Langmuir and Freundlich) have been used, then the process kinetics can be obtained. The results showed that the Langmuir isotherm was much better able to fit the linearized data points than the Freundlich isotherm with all metal; Nickel, Copper, and Aluminum based on the value of correlation coefficient (R2). It was concluded that all metals have the same optimal operating conditions, although, all operating conditions showed positive results. Preliminary screening was conducted on 12 different living algae strains, in order so select the top 5 algae strains that abled to growth with 10 mg/L of the initial concentration of Aluminum ions. The results showed that the best growth of algae was with Mychonastes, Chlorella, Chlorophyta, Desmodesmus, and Scenedesmus that have the highest optical density @750nm. These algae species were used to conduct different experiment with different initial concentration of Aluminum 5, 10, and 15 mg/L. During these experiment OD@750 nm, pH values, and the percentage removal of Aluminum were reported. Chlorophyta showed the highest percentage removal of Aluminum at all the initial concentrations; 58%, 69%, and 45% at 5, 10, and 15 mg/L of Aluminum ions. However, in order to obtain new results on the other different parameters (i.e. agitation speed, temperature, adsorbent particle size, light), further investigations may be needed.