Recycling of Water Hyacinth biomass as bio sorbent to sequester heavy metal from industrial effluent

Introduction: Water is an essential commodity, disposal of industrial and urban wastes into them beyond its self cleaning capacity causes serious threat. The most prominent threat to the environment through anthropogenic activities is the heavy metal pollution. Among that, chromium contamination is a significant obstacle worldwide because of its utilization in wide range of industrial processes. With respect to industries, the tanning industry ranked as one of the most polluting industry with the release of Cr in considerable quantities. Though many chemical methods are involved in Cr removal, their exorbitant nature and toxic sludge generation call for the viable and environmentally friendly technology (1). Realizing this, the present investigation was planned, exploring the potentials of water hyacinth to remove chromium from the tannery effluent through biosorption process. Methods: The water hyacinth biomass and biochar were utilized as adsorbents. A batch experiment was formulated for evolving the optimum strategies such as solution pH, biosorbent size, dosage, solute concentration and contact time were optimized for Cr (III & VI) adsorption onto water hyacinth biomass and biochar. Utilizing the optimized solution pH and adsorbent size, a column experiment was conducted with adsorbate concentration of 500 mg L-1 for optimizing the flow rate (0.5, 1.0, 1.5 ml minute-1) of the solute. The efficiency of the desorbing agents was also tested (2). Results & Discussions: The solution pH (2.0-Cr(VI) and 5.0-Cr(III)), biosorbent size (0.2mm), dosage (2.0 g 100ml-1 solute), solute concentration (100mg L-1) and contact time (24 hrs (Cr(III)) and 18 hrs (Cr(VI)) were found to be the optimum for Cr (III & VI) adsorption onto water hyacinth biomass. The solution pH (2.0-Cr(VI) and 4.0-Cr(III)), biosorbent size (0.2mm), dosage (2.5g 100ml-1 solute), solute concentration (100mg L-1) and contact time (12hrs (Cr(III)) and 36hrs (Cr(VI)) were found to be the optimum for Cr (III & VI) adsorption onto water hyacinth biochar. Similar trend was also observed by (3). Utilizing the optimized solution pH and adsorbent size, a column experiment was conducted with adsorbate concentration of 500 mg L-1 for optimizing the flow rate (0.5, 1.0, 1.5 ml minute-1) of the solute. Higher unit adsorption of Cr(III & VI), % adsorption and prominent S- shaped breakthrough curve was noticed at lower flow rate of 0.5ml minute-1 whereas sharper and steeper breakthrough curves were noticed in higher flow rate of 1.5ml minute-1. With the optimized flow rate of the solute (0.5 ml minute-1), a column study was conducted to assess the Cr adsorption capacity of the adsorbents utilizing the tannery effluent as adsorbate. Among the adsorbents, water hyacinth biomass recorded higher unit adsorption and percent removal originally compared to the water hyacinth biochar. But due to higher percent Cr desorption from water hyacinth biochar, the percent adsorption was higher in water hyacinth biochar than the biomass in successive cycles. The efficiency of the desorbing agents were in the order of 0.1M HCl > 0.5M HCl > 0.1MH2SO4> 0.5M H2SO4. Conclusions: Water hyacinth based biosorbent will play a significant role in adsorption of both Cr (III & VI) in industrial effluent and with effective desorption potential. This will play a dual role of Cr management and Keywords: Water hyacinth biomass, biochar, biosorbent, chromium, adsorption References Parameswari, E. (2009). Impact of agricultural drainage water on crops under sequential biological concentration system and use of nanoparticles for wastewater treatment. Tamil Nadu Agricultural University, Coimbatore, India. Premalatha, R. P., Parameswari, E., Davamani, V., Malarvizhi, P., & Avudainayagam, S. (2019). Biosorption of chromium (III) from Aqueous Solution by Water Hyacinth Biomass. Madras Agricultural Journal, 106. Avudainayagam, S., Megharaj, M., Owens, G., Kookana, R. S., Chittleborough, D., & Naidu, R. (2003). Chemistry of chromium in soils with emphasis on tannery waste sites. Reviews of Environmental Contamination and Toxicology 53-91