COMPARATIVE STUDY OF EFFECTIVE CHEMICAL MODIFICATION OF NOVEL BIOSORBENTS USED FOR HEAVY METALS PHYTOFILTRATION FOR WATER TREATMENT

Abstract

Heavy metal ions water pollution is a crucial issue in wastewater treatment due to their non- biodegradable and bioaccumulative nature. Biosorption is a recent technique used for wastewater treatment using biomass, like algae, fungi, agro-waste, plant waste etc. Phytofiltration is an advancement in this technique, where plant based biomass is applied for biosorption. Plants waste, like: leaves, seeds or fruit shells, is easily available from indigenous sources at very low cost. Their limitation of low biosorption capacity can be easily enhanced by suitable chemical modification, so that they can be effectively used for phytofiltration of heavy metal ions. In this study, four novel biosorbents, i.e. Madhuca longifolia, Polyalthia longifolia, Eugenia jambolana and Alstonia scholaris leaf powder samples were used for the removal of heavy metal ions in batch mode. Biosorbent surface was characterized by different physiochemical methods, like: pH, porosity, moisture content, ash content, iodine value, functional groups, point of zero charge and metal ion analysis. Then they were chemically modified by three types of chemicals for improving their biosorption capacity. The types of chemicals are: (a) acid or base (b) organic solvents (c) chelating agents. Effect of chemical modification was investigated by spectroscopic analysis with Scanning Electron Microscopy (S.E.M) and Fourier Transform Infrared Spectroscopy (FT-IR). Then biosorption studies were carried out separately for Pb (II), Cd (II), Cr (III), Cr (VI) and Ni (II) ions in batch mode using their synthetic wastewater samples. During biosorption studies, first step is the selection of best suitable chemical modification. In second step, different operational parameters were optimized using simple non modified and chemically modified leaf samples in comparative mode. Then optimized conditions were applied for mathematical modeling of equilibrium data. After biosorption, used biosorbent was regenerated by desorption with suitable acid and its recycling was examined for evaluating its biosorption efficiency. The results indicated that chemical modification of biosorbent enhanced the biosorption capacity of Madhuca longifolia, Polyalthia longifolia, Eugenia jambolana and Alstonia scholaris leaf powder samples. Most effective chemicals for modification of biosorption capacity of leaf samples were proved to be the following conditions: (i) base (NaOH), formalin and acetone in case of Pb (II) ions, (ii) base (NaOH), acetone, formalin and thio-urea in case of Cd (II) ions, (iii) base (NaOH), acetone, urea and thio-urea in case of Cr (III) ions, (iv) acid (HCl) citric acid and tartaric acid in case of Cr (VI) ions, (v) base (NaOH), urea and thio-urea in case of Ni (II) ions. This research work indicated that using plant waste materials, heavy metal ions can be easily removed from wastewater in an effective manner. Leaf samples processing was easy to carry out at larger scale. The most effective chemicals found in this study for enhancing biosorption capacity of leaf samples were inexpensive and easily available all over the world. After biosorption, used leaf samples can be easily dumped as soil conditioner after recovering metal ions by desorption using suitable acid and precipitating metal ions from eluted fluid with suitable precipitating agents or chelating agents, if required. So in this way, heavy metal ions water pollution can be controlled in environmentally benign way. Key words: Biosorption, phytofiltration, chemical modification, Madhuca longifolia, Polyalthia longifolia, Eugenia jambolana, Alstonia scholaris, leaf powder samples.