As tons of solid waste are being generated each minute, environmental practitioners and municipal managers struggle with ways to sustainably treat it. Solid waste has by-products which are detrimental to the health of both flora and fauna as well as posing a risk of contamination and pollution to environmental bodies. The most common methods that have been used and emphasized across the globe include recycling, reusing as well as composting. However, what then happens to the residual waste that cannot be recycled, reused or sent through for composting?
Landfilling has been an option but there are some disadvantages associated with this process. This include the possibility of leachate contamination of underground water sources and the production of methane with contributes to global warming. Another major disadvantage to consider is that of land coverage. The fear therefore, is that if not managed properly, most arable or habitable lands could end up posing as landfills or illegal dumpsites.
Pyrolysis and gasification are 2 processes that can be used to deal with residual waste. There are more than 100 facilities operating around the world, capable of processing over 4 million tonnes of waste per year. The two processes are options that can be used to recover value from waste by thermal treatment. They are used on carbon-based waste products such as paper, petroleum-based wastes like plastics, and organic materials such as food scraps and they turn wastes into energy rich fuels by heating the waste under controlled conditions.
Pyrolysis and gasification use high temperatures and little oxygen to break down waste containing carbon. Pyrolysis degrades waste to produce char, pyrolysis oil and synthetic gas also termed syngas. The gasification process then breaks down the hydrocarbons left into a syngas using a controlled amount of oxygen. Syngas constitutes of carbon monoxide and 85% hydrogen, with small amounts of carbon dioxide and methane. It has a calorific value and can be used as a fuel to generate electricity or steam. It can also be used as a basic chemical in the petrochemical and refining industries. The gasification process requires the use of small amounts of oxygen whilst pyrolysis uses none.
There are a number of advantages associated with the 2 processes. These stand in as a few reasons why pyrolysis and gasification should be considered as waste treatment methods despite the high costs of plant set up. There are increased possibilities for recycling associated with the process. The processes offer more scope for recovering products from waste compared to other waste treatment process such as incineration. The gases, oils and solid char from pyrolysis and gasification are not only used as fuel but can also be purified and used as a feedstock for petro-chemicals. The by-products can be sold to allow for revenue inflow or used onsite and reduce expenditure rates thus making the processes economically viable.
The processes also offer better energy efficiency and contribute to the reduction global warming. This can help achieve renewable energy targets, address concerns about global warming and contribute to achieving Kyoto Protocol commitments. The research for the Community Recycling Network argues however that, it is important to identify which fuel is being displaced by using waste to produce energy. If coal, a greenhouse gas emitter is being replaced then gasification and pyrolysis become viable processes in the context of climate change. However, if a cleaner fuel such as gas and renewable energy sources such as wind and solar is to be displaced, then pyrolysis and gasification would be labelled poor options in terms of climate change. In terms of climate change mitigation, pyrolysis and gasification should be avoided because they divert energy from true renewable sources like wind and wave energy but there still are cases where coal and firewood are still being used as sources of energy. One has to weigh the pros and cons and make an informed decision when it comes to employing the different waste management treatment method.
