CHARACTERISATION AND TREATMENT OF LEACHATE FROM A MUNICIPAL SOLID WASTE LANDFILL SITE IN IBADAN

Abstract

A study on characterisation and treatment of leachates from a Municipal Solid Waste(MSW) landfill site was carried out at Aba-Eku, in Ona Ara Local Government area of Ibadan. The site was an upgraded open-dump site being used since 1994 when refuse dumping at Ring road in Ibadan was abruptly stopped. In 1998 this site was upgraded into a MSW landfill under the Ibadan urban project. It is owned and operated by Ibadan Waste Management Authority (IWMA) for disposal of solid wastes generated in Ibadan Metropolis. It is the major repository and the only landfill site available in Ibadan beside the other two approved dumpsites in Awotan and Lapite, which were opened for disposal in 1998. Leachates, the waste water emanating principally from landfills are a major source of surface and groundwater pollution and contribute to adverse environmental and health risks to communities in the vicinity. The leachates generated at this site are discharged directly into Omi stream, a major source of water serving about 16 communities in the area, without regard for the environment and health impacts. Although leachate management is a worldwide issue, a dearth of information exists to date in Nigeria. The study was experimental and analytical in design. It was conducted to assess the physical and chemical composition of leachates from Aba-Eku landfill site, and to find appropriate and sustainable solutions to its final disposal into the environment through laboratory methods. Sample of 12 integrated raw leaches were collected during drying and wet periods and 64 effluent samples obtained from laboratory-scale treatment experiments were analysed for their physico-chemical characteristics using Standard Methods (APHA, 1998). Leachate treatment with various methods: Physical (sedimentation, soil filtration and charcoal filtration), Chemical (neutalization, alum, lime and hydrogen peroxide) and Biological (sand filtration (SF), sequencing batch reactor (SBR), and reed bed (RB, an artificially constructed wetland) were conducted singly and in combination to produce treated effluents to meet approved national and international discharge standards. The physical and chemical characteristics determined include: temperature, colour, turbidity, total solids, suspended solids, total dissolved solids, conductivity, pH, alkalinity, chloride, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), ammonia, nitrate, phosphate, sulphate, lead, cadmium, zinc, nickel, iron and manganese. Flow rates were also measured. Analytical results showed that mean generation of raw leachates was 45.15± 48.3m³/day and ranged between 2.63 and 181.44m³/day. Raw leachates were yellow (426±68.96 HU) in colour and alkaline with a mean pH of 8.2±0.4. The suspended solids (SS) and turbidity values respectively were 176 ± 77.91mg/l and 114.25 ± 42.40 FTU while those of DO, BOD, COD and ammonia were 1.94 ± 0.24, 795.83 ± 419.56, 2914.50 ± 1016 and 688.46 ± 286.84mg/l, respectively. In addition, mean values for lead, zinc, iron and manganese were 1.49 ± 0.78, 1.96 ± 1.07, 148.53 ±76.35 and 22.63 ± 10.65mg/l, respectively which were above permissible limits. The mean values (mg/l) for cadium (0.33 ± 0.34), nickel (0.815 ± 0.38), nitrate (0.58 ± 0.29), sulphate (84.86 ± 42.79) and phosphate (2.2 ± 1.56) were within national permissible limits (FEPA, 1991). Optimum treatment dosage using hydrogen peroxide (30%w/v), alum and lime were found to be 10ml/l, 1g/l, respectively. A setting time of 30 minutes was adequate for clarification of the effluents. The best physical chemical and biological methods were soil filtration, alum and application of RB, respectively. These treatments respectively produced effluents with significant reductions in SS: 85.82%, 68.17%, 81.01% and COD: 28.86%, 61.37%, 72.94%. Chemical treatment, however produced better effluents than physical treatment while biological treatment using RB gave the best results in the laboratory studies with significant reductions in BOD, by 86.03%, and NH by 99.77%. Treatment combinations involving SBR or RB, alum and SF produced effluents with BOD, COD and NH, reductions respectively ranging from (%) 79.65-97.17, 85.88-96.46 and 92.42-97.73. The treatment sequences involving RB, alum and SF proved to be ideal in obtaining effluents whose values were within the permissible limits set by FEPA. In conclusion, a combination of RB, alum coagulation and SF is a cost-effective treatment method for leachates at the study site in Ibadan. It is recommended for implementation at the site to reduce the potential impacts of unsanity, off-site disposal of leachates into the environment of Aba-Eku.