Holistic assessment of solid wastes and their environmental impacts in Osogbo city, Southwestern Nigeria with the application of GaBi6 modeling tool

Abstract

Environmental impacts and attendant nuisance of solid wastes escalate in the 21st Century. Effective management of the wastes in a holistic manner is a proven way out of the menace. This research focuses on accessing the life cycle of solid wastes in Osogbo. The main objective is to evaluate the physical and chemical constituents of the wastes and determine their best disposal method in the study area. In the study, wastes were collected over a period of 2 weeks, wastes composition was determined for the randomly selected residential buildings, and the per capital waste generation rate was evaluated for the area. Potable gas detectors were used to detect and measure the gases present at this dumpsite. The emission of gases and energy consumption was evaluated using the methodology of life cycle in calculating life cycle inventory of the waste strategies. The measured gases include; Sulphur (IV) oxide (SO2), carbon monoxide (CO), carbon (iv) oxide (CO2), ammonia (NH4). The Tool for the Reduction and Assessment of Chemical and other Environmental Impacts (TRACI) of the United States Environmental Protection Agency and the Methodology of the Centre for Environmental Studies (CML) of the University of Leiden are the two approaches applied as provided for in the GaBi6 (Holistic Balancing) Life Cycle Assessment (LCA) software database, to classify and characterize environmental impacts of municipal wastes in Osogbo. The Impact Indices measured from both scenarios were: Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP) and Ozone Layer Depletion Potential (ODP). For the Life Cycle Impact Assessment (LCIA), two waste management scenarios were developed and compared using GaBi6 software. Scenario one involves collection, transportation and incineration, while Scenario 2 ends with landfilling. Findings showed that the overall mean percent (%) wastes composition for paper, biodegradable, plastic, glass, metal, wood and textile were respectively found to be 4.32, 67.53, 5.07, 4.90, 6.54, 8.74 and 2.90. The per capita waste generation in the study area was found to be 1.09 kg/capita/day. From the results of LCIA methods studied using the ODP index, Scenario one with the TRACI method gives the total values for GWP, AP, EP, ODP as 4.18, 1.08, 1.392E-4, 3.147E-8 respectively. With the CML method, the values are 4.18, 1.3E-3, 3.771E-4, 2.878E-8 respectively. The respective results from scenario two with the TRACI method and CML methods showed total values for GWP, AP, EP, ODP as 9.64, 0.112, 3.108E-3, 1.447E-11 and 9.64, 1.77E-3, 7.247E-3, 1.361E-11. It is concluded that of the two management scenarios considered, landfilling of wastes is more environmentally friendly as compared to incineration, and is therefore recommended for use in the study area.