Assessment of Surface Water Pollution Caused by Tannery Effluents and Its Mitigation Strategies in Bangladesh

Abstract

Wastewater from leather processing industries generally contain high amount of toxic metal ions, organic and inorganic pollutants, which poses high risk to the ecosystem and human civilization. This thesis focuses on the assessment of pollution level of surface water collected from the river adjacent to the leather processing industries. The research also focuses on the use of peanut shell, Bagasse, and potato peel for the treatment of prepared wastewater and tannery effluents. First of all, various physico-chemical properties including pH, temperature, TDS, EC, NaCl %, BOD, and COD along with heavy metals (Cr, Ni, Cu, Cd, and Pb) of the surface water samples were analyzed. These sample were collected from three layers at three different locations of Dhaleshwari, Buriganga, Bhairab and Karnaphuli rivers nearby the tannery where the effluents were discharged. In the next step, chemically activated pyrolyzed peanut shell (PNS), chemically activated peanut shell (NS), and chemically activated pyrolyzed bagasse (PB) were prepared to remove Cr(III) from Cr2(SO4)3.6H2O aqueous solution and from chrome tanning effluents. Adsorbent PNS, NS and PB was characterized through EDX, FTIR, SEM, XRD and BET analysis. The adsorption capacity of PNS, NS, and PB were 104.82 mg/g, 58.28 mg/g and 74.63 mg/g respectively for removal of Cr(III) from aqueous solution at pH 5.0, while, it was 72.79 mg/g, 58.11 mg/g, and 72.45 mg/g respectively for removal of chromium from chrome tanning effluents. In this research, another adsorbent was prepared from potato peel powder (PP) and characterized through EDX, FTIR, SEM, XRD and BET analysis. The PP was applied for removal of leather dye C.I. Acid Red 73 (AR73) from aqueous solution and dyeing effluent. The adsorption capacity of PP was 258.39 mg/g for removal of AR73 from aqueous solution at pH 2.0, and 137.39 mg/g for removal of AR73 dye from dyeing effluent. The Langmuir and Freundlich isotherm model were applied to explain the distribution of adsorbate (Cr3+ and dye) on adsorbents (PNS, NS, PB and PP) surface. The values signify that the adsorption of Cr3+ on adsorbents comply both Langmuir and Freundlich isotherm model, preferably the Langmuir model. Pseudo-first-order and pseudo-second-order kinetic models were employed to justify the adsorption process. It was observed that pseudo-secondorder kinetic models provide better correlation for all adsorbents. The thermodynamic analyses were also carried out for all adsorbents and it was revealed that the adsorption process was spontaneous at low temperature. The regeneration was studied for the spent PNS, NS, PB and PP, and it was found that the used adsorbents could be regenerated and reused.