Bioprocessing for renewable energy production from Municipal and industrial wet wastes in Zambia

Abstract

The poor management of wastewater causes loss of environmental quality. Biomethanation, a biogas-producing technique, as an attractive solution to the problem, was investigated. Biogas, a greenhouse gas, is a mixture of methane and carbon dioxide. While carbon dioxide is returned into the environment in the carbon cycle, methane can be burned as a fuel in existing types of power conversion technology namely, Internal combustion engines or microturbines to produce electric power and heat. This technique has the added incentive of accessing the carbon credit facility of the Kyoto Protocol's Clean Development Mechanism, COM.Laplace transformation was used to develop a mathematical model to predict process behavior applicable for municipal and industrial waste water produced, by way of example, respectively,Lusaka Water and Sewerage Company at Manchinchi treatment plant and Kembe Meat Products Limited, at their bovine meat processing plant. Experiments were used to both investigate biodegradability of the wastewater and validate the model developed. Characterizing the waste included determination of Biochemical Oxygen Demand, (BOD),Total Solid (TS), Volatile Solids (VS), biogas yield and determination of n coefficient in the model calibration. Apparatus used to determine biogas production included a 5-litre mild steel bioreactor where gas was collected by water displacement.Computing the energy content in the biogas, where 62 percent was methane, the potential of the available power from the wastewater was determined. By using Homer micro-power simulation software, a 350 kW micro turbine was suitable for Manchinchi. This would meet the operating load for in-house energy saving. Where commercialization was considered, a power output of 1 MW with grid sales would be available using gas generator and ancillary equipment. For Kembe, 40 to 60 kW Power can be accessed with a sound waste management system in place.Due to the smaller footprint, biomethanation is recommended to support financially strapped organizations in their waste management matters. Besides the economic investigations of the application of biogas in energy supply, estimation of the carbon credits of the Kyoto protocol's Clean Development Mechanism, (COM) represents a key incentive for organizations to adopt Anaerobic Digestion, (AD), where applicable, and therefore address the current global environmental concerns with benefits. Selecting a gas engine generator and 3x 3,500m3anaerobic digesters, gas handling and storage equipment and exhaust heat recovery facility for process heating, can produce a revenue-generating plant adding benefits to the core business. The operating load at Manchinchi during this investigation was valued at 55kW.In monetary terms, supposing that the carbon trade facility or the CDM arrangement was accessed, a value of US$ 107,489.5 could be realized annually over seven years. In meeting the demands for emission reduction, it was estimated that 26,872.37 tons of carbon dioxide would fall for mitigation by implementing the energy recovery scheme. The carbon dioxide content measured by a Dansensor gas detector was 37 percent. The remaining 1 percent was other trace gases including hydrogen sulfide. Economic and financial appraisal showed that the NPV was US$ 484,939.89 and IRR 23 percent in the case that the plant was equipped with biogas recovery and energy conversion technology to produce heat and power with the renovation of existing anaerobic digestion tanks.