Bioremediation Potential of Immobilized Bacillus subtilis in the Treatment of Tannery Industrial Effluent Discharge from Sharada Industrial Estate, Kano State, Nigeria

Abstract

Bioremediation potential of indigenous bacteria (Bacillus subtilis) in the treatment of tannery effluent was investigated. Industrial tannery effluent discharge from Loquant Tannery Industry in Sharada Industrial Estate, Kano State, Nigeria was collected for a period of six months (from August 2017 to January 2018). Bacteria were isolated from the effluents using serial dilution and immobilized on agar-agar; the bacteria were identified to be Bacillus subtilis. Different masses (5 g, 10 g, 15 g, 20 g and 25 g) of the identified bacteria were used in the treatment of 250 ml of the effluents. Temperature, pH, BOD, COD, SS, TDS, nitrate, chloride, sulfate, phosphate, and some heavy metals (Cr, Fe, Mn, Ni, Pb, Zn, Cd and Cu) were determined before and after treatment of the effluents with the bacteria. Before treatment, recorded temperature and pH were 28.25±3.13 ^oC and 9.00±0.78, respectively. For COD, BOD, SS, TDS, nitrate, sulfate, phosphate and chloride, the measured values (in mg/l) were 2513±641, 17.9±3.06, 503±106, 5276±2971, 36.65±17.74, 78.80±28.36, 40.38±25.46 and 22.41±11.84, respectively. The concentrations (mg/l) of the heavy metals before treatment with the bacteria were: Cr (0.183±0.334), Fe (0.074±0.064), Ni (0.013±0.019), Mn (ND), Pb (0.03±0.04), Zn (0.011±0.01), Cd (ND) and Cu (0.011±0.01). The post-treatment analysis showed that the mean levels (mg/l) of BOD ranged from 1.1±0.75−4.32±1.63, COD (744±885−2125±1154); SS (417±109−530±169), TDS (65±17−71±20), NO₃⁻ (15.23±11.51−19.58±6.36), SO₄²⁻ (54.00±42.77-69.23±41.59), PO₄³⁻ (14.99±9.16-27.82±24.17), Cl⁻ (13.34±6.83-18.09±18.09), Cr (0.008±0.01-0.052±0.07), Fe (0.021±0.02-0.061±0.05), Ni (ND), Mn (ND-0.002±0.00), Pb (ND), Zn (ND-0.008±0.00), Cd (ND) and Cu (ND-0.006±0.00). The post-treatment analysis using different masses of the Bacillus subtilis indicates that there is a great decrease in the levels of the physicochemical parameters and the heavy metal concentrations as well when compared with the levels observed at the pre-treatment analysis. The decrease could be attributed not only to the increase in the mass of the bacteria, but also to associated increase in the surface area for remediation. The rather high reduction in the values of these physicochemical parameters and heavy metal concentrations implies that Bacillus subtilis has a high potential for the treatment of effluents from the tannery industries.