Abstract:
Heavy metal contamination has become a severe problem all over the world due to its adverse impact on the environment and human health. Heavy metal, particularly chromium, is a major contaminant discharged by the tannery industry. Under natural environmental conditions, chromium is frequently found in the trivalent Cr (III) and hexavalent Cr (VI) forms. Chromium in its hexavalent state is extremely poisonous and carcinogenic. Although there have been technological breakthroughs in heavy metal removal in wastewater, traditional technologies are costly to employ, especially in developing nations. The use of low-cost adsorbent materials to remove chromium metals from tannery wastewater has been the subject of research.
This research study investigated the use and effectiveness of Neem leaves, Sojne leaves, Chhatim leaves, Banana peels, and Peanut shells as bio-sorbents in green (raw) and ash (carbonized) form to remove chromium from tannery wastewater samples in batch experiments. The five adsorbents were prepared by rinsing and drying in an oven before use, and for ash form, these were carbonized in a muffle furnace. Batch experiments were conducted to evaluate the effect of dosage, pH, and contact time on chromium removal by the five adsorbents.
The initial Cr concentration of collected tannery wastewater was 3534 mg/l and the five adsorbent materials showed moderate chromium removal in green form with a range of 94-99% at optimum experimental conditions. For ash-formed biosorbents, the batch studies were performed on Neem leaves, Sojne leaves, and Chhatim leaves and the removal percentage were 100% at optimum experimental condition, showing excellent improvement after carbonization, especially Chhatim leaves. High Cr removal was observed to be effective at pH 8 with an optimum dosage of 10 to 12 g for 100ml of wastewater with green biosorbents and 2.5 to 3 gm for 100 ml of wastewater with ash biosorbents. Adsorption equilibrium times for green biosorbents were observed at 120-180 min for Neem, Sojne, Chhatim leaves, and 60 min for Banana peel and Peanut shell. While that of ash-formed biosorbents were observed at 120-180 min. The adsorption of chromium increased with an increase in contact time till equilibrium is attained.
Adsorption results were modeled using Langmuir and Freundlich isotherm models. Experimental data indicated that chromium adsorption by all the five adsorbents in green form fitted well with Freundlich isotherm models than Langmuir model, with regression coefficient value, R2 closer to 1. The three biosorbents in ash form were observed to fit well with both Langmuir and Freundlich isotherm model, with separation factor (RL<1) and n values (n>1) showing favorability for the adsorption of chromium. Physico-chemical characterization by Fourier-Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscope (SEM) showed the three ash biosorbents have high potentiality to remove chromium from tannery effluent.
