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COMPARISON OF DIFFERENT WASTE TO ENERGY TECHNOLOGIES
INTRODUCTION
India’s urban population of 429 million citizens produces a whopping 62 million tonnes of garbage every year. Out of this, 5.6 million tonnes is the plastic waste, 0.17 million tonnes is the biomedical waste, 7.90 million tonnes is hazardous waste and 15 lakh tonnes is e-waste. A staggering figure of forty-three million tonnes of Solid Waste is collected annually, out of which only 11.9 million that is 22-28% is treated, while about 31 million tonnes of waste is left untreated and dumped at the landfill sites. Globally, there are around 2,200 waste-to-energy plants, of which the European Union has 445, China has 150 and USA has 86. Despite its burgeoning population, India just has eight waste-to-energy plants. If India starts collecting and treating its waste effectively then it can be used to generate a lot of energy. The above statistics, suggests for adopting various other waste to energy technologies, which would help in diverting majority of wastes of value from landfill.
Zonta Infratech has been guiding Municipalities to recognize the ill-effects of such methods practiced in the country and to implement the eco-friendly and affordable solutions for the disposal of wastes.
TYPES OF TECHNOLOGIES
The different types of waste to energy technologies offering a prospective business opportunities and an alternative pathway to avoid the increasing load in landfill are:
- Biological treatment
- Sanitary landfills
- Composting
- Biomethanation plant
- Thermal treatment
- Incineration
- Gasification
- Plasma gasification
- Pyrolysis
- Biological treatment ♦ Sanitary landfills Landfilling is the most common method for MSW disposal, wherein, due to the dumping of waste, the anaerobic process gets initiated. It is the cheapest method available for waste disposal. If most of the waste materials, to be dumped into the landfill are inert, then non-engineered landfill is suitable
Advantages Disadvantages
The specific location of waste makes it easier to monitor.
A landfill, if not designed properly leads to the contamination of the groundwater table
Energy production practices can be adopted.
A landfill, if not designed properly leads to the contamination of the groundwater table After its completion of the period of operation, the land can be reclaimed and used for various recreational activities.
The gas produced should be handled with great care, if not would cause severe destruction The methane produced is used for energy production purposes; hence the emission risk is reduced, when compared with the incineration process.
Landfilling is suitable only for inert waste materials, and not for organic wastes.
♦ Composting Composting process is the most suitable process for organic waste materials. The moisture content in the waste produced in India ranges from 40 to 50 percent. Biodegradation of waste matter in the presence of oxygen and aerobic bacteria produces compost Different technologies for composting are windrow composting, aerated static pile composting, in-vessel composting, vertical composting reactor, horizontal composting reactor. Vermicomposting Vermicomposting is the process of turning organic debris into worm castings. The worm castings are very important to the fertility of the soil. The castings contain high amounts of nitrogen, potassium, phosphorus, calcium, and magnesium. Any types of biodegradable wastes-Crop residues, Weed biomass, Vegetable waste, Leaf litter, Hotel refuse, Waste from agro-industries, Biodegradable portion of urban and rural wastes.
Advantages Disadvantages Composting helps in diverting the organic waste materials from the waste stream
Odor pollution is one of the most frequent problems in the composting process.
Gasification processes convert biomass (mostly, dry garden waste) into combustible gases at a temperature greater than 750 0 C that ideally contain all the energy originally present in the biomass. in practice, gasification can convert 60% to 90% of the energy in the biomass into energy in the gas. Gasification processes can be either direct (using air or oxygen to generate heat through exothermic reactions) or indirect (transferring heat to the reactor from the outside). The gas can be burned to produce industrial or residential heat, to run engines for mechanical or electrical power, or to make synthetic fuels.
Advantages Disadvantages
The technology is suitable and economical for small, decentralized applications
High moisture content waste matter cannot be used as feedstock
Biomass is a CO 2 neutral fuel, which offers
an option in mitigating the adverse effects of climate change.
Obtaining the producer gas in a proper state is a really challenging task.
Producer gas or syn gas can be used for generating electricity.
♦ Plasma gasification Plasma gasification is an emerging technology carried out at a temperature of about 1400 – 1600^0 C which can process landfill waste to extract commodity recyclables and convert carbon-based materials into fuels. It can form an integral component in a system to achieve zero-waste and produce renewable fuels, whilst caring for the environment.
Advantages Disadvantages
It unlocks the greatest amount of energy from waste
Waste gasification and combustion ultimately releases carbon dioxide to the atmosphere instead of sequestering a large fraction of the carbon in a landfill;
Feedstocks can be mixed, such as municipal solid waste, biomass, tires, hazardous waste, and auto shredder waste.
Large capital costs relative to current landfills;
Production of clean alloyed slag which could be used as construction material
Requires large electrical energy input if the waste stream does not contains a large fraction of unoxidized hydrocarbons;
Processing of organic waste into combustible syngas for electric power and thermal energy
The highly corrosive plasma flame may lead to frequent maintenance and component replacement with associated facility down time;
The filters and gas treatment systems are themselves sources of toxic waste, some of which (e.g. acidified water) are poor
candidates for plasma processing.
♦ Pyrolysis Pyrolysis is a thermochemical decomposition of organic material at temperatures between 400 °C and 900 °C without the presence of oxygen. It is applicable to hazardous waste treatment.
Advantages Disadvantages
Relative insensitive to input materials Problem persists over emissions and toxicity of residual products Pyrolysis process does not generate products associated with the burned waste
The problem of cost to treat the waste also matters. Pyrolysis is self-sustainable; i.e. energy is required only for start-up operation.
