Understanding Leaching Behaviour of Landfill Leachate in Benin-City, Edo State, Nigeria through Dumpsite Monitoring

Indiscriminate disposal of solid waste in unauthorized places has become an increasing problem for most cities in Nigeria, especially Benin-City, Edo state. Benin-City one of the largest city in Nigerian is experiencing the problem of solid waste management despite the best attempt of waste avoidance, reduction, reuse and recovery. Use of dumpsites is still the ultimate disposal method of domestic and industrial wastes in Benin-City. Three dumpsites in Benin-City and environs were selected randomly to evaluate their leachates characteristics. Leachate samples were collected from the dumpsites at three months interval and were assessed for their quality through physico-chemical and elemental examination using standard methods for examination of water and wastewater. Physico-chemical analysis result showed pH range of 6.76±0.08 –7.49±0.02, EC (55212.0±2028.43 – 64344.33±1131.22 μS/cm), Temperature (26.03±0.25 – 26.60±0.35OC), Cyanide (0.08±0.04 – 0.46±0.01 mg/L), Sulphide (12.30±1.21 – 14.90±2.26 mg/L), BOD5 (61.23±1.39 – 98.60±3.41mg/L), COD (92.11±2.14 – 140.00±4.19 mg/L), NO3-N 0.41±0.03 – 0.75±0.09 mg/L), NO2-N (0.09±0.01– 0.30±0.03mg/L), TOC (506.67±230.94 – 573.33±370.05 mg/L). Metals with consequential environmental significance determined in the leachate samples recorded concentration in mg/L as: Cd(0.02±0.01 – 0.240.31), Cr(0.04±0.00 – 0.06±0.01), Cu(0.49±0.07 - 0.61±0.05), Hg(0.03±0.01 – 0.06±0.01), Mn(0.27±0.07 - 0.38±0.03), Ni(0.05 ± 0.01- 0.07 ± 0.01), Pb(0.05±0.01 – 0.12±0.010) and Zn(0.37±0.04 - 0.65±0.03). The physiologic and metabolic roles of the elements detected in the leachate are discussed. The concentrations of the elements detected were below the toxicity limits recommended by Federal Environmental Protection Agency (FEPA) limits. On the overall, the physico-chemical and elemental characteristics of leachates obtained in this study revealed that the three waste dumpsites generated leachates that were not as contaminated as those reported in some other parts of the world.