Valorization of waste: energy and nutrient recovery from solid waste in Jimma town, Ethiopia

Abstract

Solid waste, which is a consequence of day-to-day activity of human kind, needs to be managed properly. Jimma, like other towns in the country, faces problems associated with poorly managed solid waste operation. This poor solid waste management and urban growth are posing a threat on sustainable development, which results in human health problem and environmental pollution. This study deals with evaluating the quantity, composition, energy potential and nutrient value. A cross-sectional study design was used to assess the composition as well as the physical and chemical properties of the residential solid waste. The daily solid waste generation and composition of household solid wastes were determined following standard protocols. Estimates of the energy content were made results using bomb calorimeter and models developed on physical composition and proximate analysis. Physical characterization showed that food, yard, textile, leather, rubber, wood, yard, metal, plastic and paper waste were the constituents of all collected waste samples in the study area, but in varying proportions. Proximate analysis showed household solid waste characteristics as: moisture, volatile matter, fixed carbon, and ash content, being 49.38, 41.21, 6.10, and 3.31%, respectively. The total solid waste generated daily from Jimma town household was estimated to be 77,364.46 kg, and the average per capita generation rate was 0.50 ± 0.08 kg/capita/day. The energy content of household solid waste was estimated to be 17.50 MJ/kg for gross heating value (HHV), and 9.54 MJ/kg for net heating value (LHV). Such difference between HHV and LHV is due to high portion of water content of solid waste. Results from selected models showed higher heating values, but still equivalent with the experimental value of 17.5 MJ/kg and fit the minimum level of 7 MJ/Kg net heating value required for incineration projects. Further analysis showed that biodegradable organic waste constituted 62.75% by weight with an average moisture content of 49.38% and good nutrient contents suggest the applicability of household solid waste stream for implementing composting operations. In conclusion we suggest that the residential solid waste can be used as a valuable resource for recycling in the form of organic fertilizer and energy recovery. As such, an economic benefit can be obtained from this waste while avoiding the cost of treatments and disposal. Further study is required with detail analysis of solid waste to optimize its use for both nutrient and energy recovery