4. Municipal solid waste treatment and disposal
The disposal methods and techniques vary from material to material. We will be discussing the different types of treatments and methods involved in this part of the module.
As we learnt earlier, the disposal methods and techniques vary from material to material. And the challenges faced by municipalities include locating new waste disposal sites and determining what waste materials were disposed of overtime in a dumping site. The integrated waste management system aims to reduce the amount of waste being disposed of while maximizing resource recovery and efficiency. However, solid waste dumping and open burning are some common practices of disposal in developing nations.
Let’s take a look at some waste management strategies typically practiced for municipal solid waste [13]
1. Waste to Compost
Composting is an aerobic method of decomposing organic solid wastes that can be converted into compost/manure. Compost is defined as an organic material that can be added to soil to enhance plant growth[14]. Making compost keeps these materials out of landfills where they take up space and avoids the release of methane, a potent greenhouse gas.
2. Recycling of waste
Waste is a subjective term, as it could be of value for another person or industry under different circumstances.
A product which is considered a waste for one, is valued as a material for another.
Waste materials such as plastic, paper, metal and glass are recyclable in nature and can be recycled. The next preferred alternative is the recovery of recyclable material resources and strengthening a waste recycling chain through segregation, collection, and reprocessing to create new products.[15]
3. Waste to Energy
In cases where material recovery from waste is not possible, energy recovery from waste through production of heat, electricity, or fuel is preferred. Pyrolysis, gasification, waste incineration, production of refuse derived fuel (RDF), and co-processing of the sorted dry rejects from (MSW) are commonly adopted waste to energy technologies. Wet waste can be converted to biogas by the process of biomethanation or anaerobic digestion.
The end products of Waste-to-Energy include: Biomass, Biofuels, Biogas, Bio-plastics, Biochemicals, Bioenergy.
The waste materials can be utilized as a source of energy by the following methods:
Anaerobic digestion/Biomethanation :
An anaerobic digestion is the process where the organic fraction of the waste, typically food waste is segregated and fed into a closed container (biogas digester) producing methane-rich biogas and effluent.
Combustion/Incineration :
It is a waste burning process which converts material to hot air/steam and hot water. The steam generated in turn can be used in steam turbines to generate power.
Pyrolysis/Gasification :
Pyrolysis is a common technique used to convert plastic waste or any material containing carbon—such as coal, petroleum or biomass—into synthesis gas (syngas) composed of hydrogen and carbon monoxide.
4. Landfilling
Rejects and Inerts which cannot be recycled or used for energy recovery are disposed of in a landfill. Disposing waste in landfills is one part of an integrated waste management system. Landfills cannot be built in environmentally-sensitive areas and are engineered so that they donot affect ground water and air quality.