Assessment and remediation of selected heavy metal contaminants in leather tanning effluents using green banana peels and coffee husks biochar

Abstract

Water is undeniably a vital resource for life and a necessity for chemical, physical, biological and economic activities. However, discharge of untreated tannery effluents into water sources has tremendously contributed to water pollution thereby making environmental protection a core demand. This has further led to accumulation of non-degradable heavy metals such as chromium leading to adverse effects on the environment, human health and the economy. The trend of heavy metal concentration increase was expected with tanneries having large production capacities polluting more, results of the study however showed site 3 with the lowest production capacity (50 hides per day) having Cr (chromium) concentration levels of 6.13±0.44 mg/L and Site 1with a production capacity of 42 tones hides per day , site 2 with a capacity of producing 700 hides and 2500 skins per day containing Cr concentration levels of 0.09±0.18mg/L and 0.06±0.16mg/L respectively. Various existing treatment methods employed are either very expensive, time consuming or inadequate hence this study on the remediation of selected heavy metal contaminants in tannery effluents using biochar from green banana peels and coffee husks biomass wastes. Characterization of biochar using hawk pyrolysis machine to determine Total organic carbon (TOC), carbonated carbon (CC), Hydrogen Index (HI), Oxygen Index (OI), Oil Saturation Index (OSI) parameters and FTIR (Fourier transform infrared spectroscopy) studies for functional groups were performed with the aid of a Shimadzu FTIR spectrophotometer. Comparative studies of treated and untreated biochar showed that using non-treated coffee husks biochar is more effective than other studied biochar. Study results further showed that non-treated coffee husks biochar containing TOC-36.76 (wt.%), HI-260, OI-156, CC-1.69 (wt.%), OSI-94.00 per gram sample and Surface O-H stretching (3362 cm-1), Aliphatic C-H stretching(2930.94 cm-1), Aldehyde C-H stretching(2860.23 cm-1), Aliphatic acid C=O stretching(1734.3 cm-1),Unsaturated group like alkene stretching (1655.14 cm-1), Carboxylate anion C=O stretching(1364.62 cm-1), Si-O stretching(1030 cm-1), and Aromatic C-NO2 stretching (1469.92 cm-1) was the most effective in extracting chromium heavy metal ions from tannery wastewater at a contact time of 60 minutes, remediating 98.3% of chromium. Therefore, tannery industries in Uganda should reconsider taking up this effective alternative as a means of effluent treatment.