Status of Municipal Solid Waste (MSW) collection and disposal in Kenya
The growth in MSW generation has been rapid, while the capacity to collect and safely dispose of the material for clean environment has been on a general decline.
From a country report R.K. Henry et al. / Waste Management 26 (2006) 92–100
In all the five local authorities studied, it was found that little or no consideration of environmental impacts was taken in the selection of dumpsites, including those currently in use. Convenience took priority in the siting of dumpsites. An example was in Eldoret where an abandoned sand quarry at Mwenderi was used for the disposal of MSW, yet it was clear that the site was a water catchment area for small streams that drain into the Sosiani River. Inspection and monitoring of the dumpsite was not consistent, except for Nairobi which had started occasional inspection of MSW waste in 2001. No sanitary practices such as application of daily soil cover or fencing were practiced in any of the five local authorities studied. None of the dumpsites in Nairobi or the other four local authorities meet the basic requirements in protecting ground water from pollution by leachate as they have no liners.
In the poor suburban zones, indiscriminate disposal of MSW at the river sides, road reserves, etc. In Nakuru an outbreak of diarrhoea was traced to a vegetable farm which was being irrigated by surface water contaminated by MSW dumped upstream. In Lake Victoria, accelerated growth of water hyacinth (Eichhornia crassipes) is partly attributable to illegal disposal of solid and liquid municipal wastes in rivers (for example Kisat river) which drain into the lake. (Eco forum, 2001; World Bank, 1995; UNEP/ACTS, 2001; Obera and Oyier, 2002) (Henry, 2006).
Status of the power sector in Africa
The core sources of electricity in most sub-Saharan African countries are hydropower and oil products the total electricity production for Africa in 2000 was 441TWh. Hydropower contributes about 18% of the total power generation in Africa
A conventional power plant makes electricity by a fairly inefficient process. A fossil fuel such as oil, coal, or natural gas is burned in a giant furnace to release heat energy. The heat is used to boil water and make steam, the steam drives a turbine, the turbine drives a generator, and the generator makes electricity. The trouble with this is that energy is wasted in every step of the process.
For example, the water that’s boiled into steam to drive the steam turbines has to be cooled back down using giant cooling towers in the open air, wasting huge amounts of energy—much of which literally disappears into thin air!
Instead of letting heat escape uselessly up cooling towers, why not simply harness the energy to be part of gasification process?
The solution can be a swap some of our power plants over to a different system called combined heat and power (CHP), also known as cogeneration.
In practice, CHP plants make energy in completely different ways using entirely different heat engines . Smaller CHP plants often use what are essentially internal combustion engines (similar to gasoline engines in cars and diesel engines in trucks) to drive electricity generators, with heat exchangers recovering waste heat in hot water. Larger plants use very efficient gas and steam turbine engines. In future, CHP plants are likely to use fuel cells burning hydrogen gas.
Thermal power station
This is a power station in which heat energy is converted to electric power. Water is heated and turns into steam which spins a steam turbine. Steam turbine in turn drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated a Rankine cycle.
In the design of thermal power station the greatest design is due to the different heat sources where fossil fuel dominates. Nuclear heat energy and solar heat energy can also be used.
Some thermal power stations are also designed to produce heat energy for industrial purposes, district heating, desalination of water, in addition to generating electrical power.
How a micro CHP works:
Below is a greatly simplified unit of the basic components of a typical micro CHP.
In practice, there are multiple heat exchangers, noise silencers, and other components but deliberately omitted for the sake of clarity in this case. © Chris Woodford
Fuel (coal, natural gas, oil, or biomass) is added at one end. The engine burns the fuel by ordinary combustion. An electricity generator is connected to and driven by the engine›s driveshaft. Something like 15kW of electricity is produced, which can be used for conventional power or as an emergency supply. Exhaust gases from the engine flow through one or more heat exchangers, which remove most of their waste heat. A catalytic converter (similar to the one in a car) removes some of the pollution from the gases. The (relatively clean) exhaust emerges through a tailpipe or chimney.
Cold water flowing into the heat exchanger picks up heat from the exhaust gas and exits at a much higher temperature. If it’s hot enough, it can be piped directly into radiators or fed into a conventional central-heating boiler for further heating. A unit like this will produce about 40kW of thermal energy (heat).
Advantages of CHP
CHP has efficiency advantages and environmental benefits too. Results to burning fewer fossil fuels which reduce air pollution and related problems such as water and acid rain.
Replacing huge power plants with more CHP plants that are much smaller makes us less dependent on the centralized energy network and, in theory, major system failures and outages (blackouts).
Just like conventional power plants, CHP plants can run off virtually any fuel, from oil, gas, and oil to methane gas produced in landfill sites or power made by burning trash in municipal incinerators.
Disadvantages of CHP
CHP has few obvious disadvantages:
The technology is currently more expensive and complex, so building CHP plants typically requires greater initial investment.- Energy savings eventually pay back the investment, but more money still has to be spent upfront to begin with.
Smaller-scale CHP plants produce electricity more expensively than larger-scale ones
Fossil-fuelled CHP plants reinforce our dependency on the very fuels we should be trying to eliminate (though it is possible to run them on greener fuels such as biomass
Gasification is a process that converts organic- or fossil fuel-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel. The power derived from gasification and combustion of the resultant gas is considered to be a source of renewable energy if the gasified compounds were obtained from biomass (Chris Higman and Maarten van der Burgt, 2008).
This is an extreme thermal process using plasma which converts organic matter into a syngas (synthesis gas) which is primarily made up of hydrogen and carbon monoxide. A plasma torch powered by an electric arc, is used to ionize gas and catalyse organic matter into syngas with slag remaining as a by-product. It is used commercially as a form of waste treatment and has been tested for the gasification of municipal solid waste, biomass, industrial waste, hazardous waste, and solid hydrocarbons, such as coal, oil sands, pet-coke and oil shale (Moustakasa, Fattab, Malamisa, & Haralambousa, 2005-08-31)
How Gasification Works:
Gasification is made up for five discrete thermal processes: Drying, Pyrolysis, Combustion, Cracking, and Reduction. (Kalinenko, Kuznetsov, Levitsky, & Messerle, 1993)
The main advantages of plasma torch technologies for waste treatment are:
- Clean destruction of hazardous waste
- Preventing hazardous waste from reaching landfills
- Some processes are designed to recover fly ash, bottom ash, and most other particulates, for 95% or better diversion from landfills, and no harmful emissions of toxic waste
- Potential production of vitrified slag which could be used as construction material
- Processing of organic waste into combustible syngas for electric power and thermal energy
- Production of value-added products (metals) from slag
- Safe means to destroy both medical and many hazardous wastes.
- Gasification with starved combustion and rapid quenching of syngas from elevated temperatures can avoid the production of dioxins and furans that are common to incinerators
- Air emissions can be cleaner than landfills and some incinerators.
Main disadvantages of plasma torch technologies for waste treatment are:
- Large initial investment costs relative to that of alternatives, including landfill and incineration.
- Operational costs are high relative to that of incineration.
- Little or even negative net energy production.
- Wet feed stock results in less syngas production and higher energy consumption.
- Frequent maintenance and limited plant availability.
In our data analysis we focus on municipal waste which is the problem being analysed with the aim of getting an effective disposal method. From available information the data justifies a disposal system that is not effective and also confirms a need that requires a solution. Our case study majorly is Kenya – Nairobi city which is a replica of the scenarios in most of the towns in African countries.
Solid waste management challenge
All countries have regulations and policies which dictate how waste should be managed. Responsibilities especially in the areas of health, environmental management and planning expected by law are well spelt out. One major challenge of MSW in Africa is the creation of enough capacity not only limited to monetary terms but also in technological and infrastructural advancement (Bello IA, 2016).
This is required so as to drive at an environmentally sound waste management wherein recovery and recycling of waste streams across Africa will be achieved. There is need to have access to finance and technical knowledge and this will go a long way in assisting the waste management municipalities who are most times ill-equipped to deal with prompt collection and disposal of waste.
Furthermore, private sectors that have the means and are willing to go into waste management have been prevented by certain by-laws which gives all waste management responsibilities to government bodies. In addition, lack of transparency, bad governance and prevalence of corruption in most African countries are major problems militating against efficient MSW management. Importation of substandard products and non-operational laws and policies have also contributed to rapid increase in waste generation (Wilson D, 2006)
Our paper suggests establishment of gasification power plants alongside the power plants already in existence.
This is with a motive of supplementing electricity to the national grid and also as a form of technical solution for disposal of MSW.Heat being lost from the power plants to cooling systems can be used in pre-treatment of biomass feedstock which is generally the first step in gasification. Pre-treatment involves drying, pulverizing, and screening.
From our review, failure of gasification plants is majorly attributed to wet feed stock which results in less syngas production .If we effectively utilize the heat lost from power plants then this will greatly solve the challenge for us.
Another disadvantage of gasification plants is high operation cost, maintenance cost and high initial investment cost. By integration of the plants with already in existence power plants will directly or indirectly slightly lower the cost.
Little or even negative net energy production for gasification plants is also a major drawback.
By siting these plants together with already existing older power plants where the gasification plants main aim will be MSW management justifies an economic viability. The plants will remain useful even with little energy production.
Gasification plants have an advantage of producing cleaner air emissions’ to the atmosphere and by- product wastes from this process – vitrified slag could be used as construction material. This stands out as an environmental friendly process.
We also believe that this integration will be a milestone breakthrough transition as we phase out the dirty fossil fuels which are accelerating the problem of global warming and majorly threatening climate change. Gasification plants can also be modified to use oil as raw material producing lesser emissions’.
For the case of solar, hydro, wind energy, tide energy etc. which keep on fluctuating the system can be modified to enable harvest of excess electricity produced during peak time. This can be stored in large scale heat pumps and thermal storage facilities for use in electricity production by gasification to supplement the main energy sources at times of low production.
The paper successfully presents an idea inform of a concept to the future of our energy sector in Africa . We also suggest a solution to Municipal Solid Waste Management (MSW) which remains a serious environmental concern.
The African governments and all stakeholders should adopt this idea since it is environmentally friendly and also directly offers a solution to Municipal Solid Waste Management (MSW) which has been a puzzle in Africa.