Human Waste to Energy: A Focus on LagosBy Ahmed Sodiq and Adetunji Alabi
Published on 19 October 2016
Do you know that waste to energy is an abundant but untapped renewable energy option in Nigeria? The current dominant discussion in the Nigeria's energy circle is diversification and deployment of renewable energy mix into its national grid.
Nigeria, the giant of Africa in terms of population, resources and economic potentials , needs to pave the way for sustainable development in the continent. Since the country's Federal Government introduced Independent Power Projects (IPP), Lagos State, the financial nerve center of Nigeria and arguably the most populous State in the country has been leading in terms of new IPPs for non-domestic consumption . Other Nigerian States' IPPs are either in few Megawatts or in project conception stages.
However, this national lead of Lagos State is not impressive on the global scale as self-sufficiency in energy generation for each State is the least expected. Such urban sustainability can only be achieved with the inclusion of renewables, energy saving practices, energy diversity, and efficient energy conversion of wastes; qualities that are present in mega cities but hardly found in Lagos State. Given the multidimensional nature of sustainable energy pathways, it is easy to neglect the most unobvious, yet very promising option - waste-to-energy. Hence, the current article gives special consideration to the human waste to energy conversion option of Lagos State, with a focus on production of biogas via anaerobic digestion (the conversion of organic matter into biogas and bio-fertilizer by microorganisms in the absence of oxygen).
It is estimated that about 21 million people reside in Lagos State . On the average, an individual produces roughly 1.3 kg of human waste (feces and urine) daily, wherein about 0.2 kg accounts for the average solid content . Assuming 70% of Lagosians use the toilet daily, the quantity of human waste produced in Lagos would amount to about 19,000 tons/day. From process simulation software (SuperPro), treating this quantity of sewage by the anaerobic digestion process yields about 1,700,000 kg of biogas (60% methane) . This quantity of biogas is equivalent to about 33,000,000 MJ and translates to about 380 Megawatts of electricity –enough electricity to power about 303,000 households .
Human wastes collection in Lagos State is currently handled by private businesses. The wastes collection transaction is mostly conducted between the landlords and private septic tank evacuators. To offset the cost of this process, monetary contributions are demanded from tenants when it is obvious that the septic tanks are full. Thereafter, the contents of the tanks are collected and eventually dumped into the open lagoon on Lagos Island. For efficient human wastes collection to feed the proposed bioenergy plant, the current solid wastes collection method (tenants pay money monthly in equal proportion while refuse collectors assign a day of the week to each street or district for collection to be made) in Lagos State can be replicated. Since septic tanks do not get filled as frequently as solid waste bins, the monthly contribution can be rearranged to meet with 6-12 months septic tank evacuation plan. The need for efficient wastes collection is important in order to set up anaerobic digestion plant in Lagos State. To begin with, a collaborative research among the universities in Lagos State, The Ministry of Environment, and other interested parties needs to be embarked upon to corroborate the simulation results outlined in the second paragraph above.
If thorough research is conducted to look into human wastes as a means of energy generation for Lagos State, then the population of the state could turn out to be a potent energy resource. The research can focus on electricity generation through human wastes as part of the plans to arrest the imminent environmental pollution and impending epidemics. Research could also be directed at assessing the prospect of producing Liquefied Biogas for cooking to help reduce the over-reliance of Lagosians on the use of cooking stoves that are powered by kerosene and contribute to air pollution. Furthermore, research could also look at ways in which the residue from the anaerobic digestion process would be put to good use in the production of fertilizer that would be sold to generate revenue for Lagos State.
The proposed anaerobic digestion of sewage stands to provide the following benefits: (1) avert the consequences of the environmentally unfriendly practice of lagoon-dumping; and (2) produce a valuable resource – energy in the form of biogas. Prospects abound for diversified energy generation. All hands must be on deck for the actualization of sustainable energy for all.
 A process simulation software was used to mimic the anaerobic digestion process
 Assuming the biogas is fed into a heat engine with an efficiency of 35%
 Assuming daily electricity household consumption of 30.238 kWh. Estimated from: Winds of change blowing through UK energy as world's biggest offshore wind farm opens