- 1 Introduction
- 2 Present Solid Waste Management Services and their Drawbacks
- 3 Available technologies for Treatment, Processing and Disposal of Waste
- 4 The Choice of Technology
- 5 BOOT, BOO, and DBO Contracts for Treatment and Disposal of Waste
- 6 Conclusion
With life style changes, rapid urbanization and population growth the waste load increases to alarming levels and its management has become very difficult. In the last six decades the urban population has increased five times to 485.35 million (Indian Census, 2011) increasing the burden on municipal corporation to deal with the solid waste management.
The unsanitary conditions of present waste dumping sites is leading to water pollution, foul odours, high chances of communicable diseases, toxic metabolites release and awful ambience. With prohibition of open dumping sites, overflow of current dumping yards and difficulty in arrangement of new dumping zones waste management has become a matter of deep concern.
Few years back the solid waste comprised only of biodegradable matter which could be easily recycled or reused as manure or assimilated in the environment. With increase in non-biodegradable matter and plastics as solid waste the threat to the environment has increased considerably.
In Indian cities per capita generation of waste ranges from 0.2-0.6 kg per day amounting to 42 million tonnes annually. It is estimated that by 2047 waste generation will exceed 260 million tonnes (The Energy and Resource institute of India, 2011).
There are approaches to SWM (Solid Waste Management) the technological application and social engineering. Ethical aspect of reducing, recovering and reducing waste is social engineering. Improvement of supportive and assimilative capacities of the environment is the technological application. This paper highlights the technological application of the waste management process.
Present Solid Waste Management Services and their Drawbacks
There is no organised and regular process of door to door waste collection. Only sweeping the street is the main mode of collection. However, it is also not a daily process and some important streets and commercial areas are only covered daily on priority basis, thus increasing back log. Street sweeping tools are outdated and inefficient. The vehicles for waste transportation are handcarts, trucks etc with some cities using hydraulic vehicles. For temporary waste storage for bulk transportation masonry bins and cement bins are created at various places.
At times waste often spills during transportation or near temporary storage units which are unhygienic and unsightly. After waste collection the next step is processing and disposal of waste. The most neglected part of the process is disposal. The municipal authorities dump the waste haphazardly at dump yards and do not cover it with inert materials. Hence these dump yards are breeding grounds for flies, rodents etc and water pollution zones with severe environmental threat.
Available technologies for Treatment, Processing and Disposal of Waste
The processing techniques are based on thermal conversion or bio-conversion process. The bio-conversion process works on organic waste and it forms compost and generates bio-gas and residual sludge. Incineration processes are thermal conversion technologies.
A Brief account of the efficiency, impact and applicability of these technologies are illustrated below:
It is the oldest bio-conversion process in India. Composting is the decomposition of organic matter by microorganism in warm, moist, aerobic and anaerobic environment. Compost of heterogeneous urban waste is more nutrient compared to the compost of agro-waste.
Benefits and commercial viability of composting techniques have been demonstrated in several towns and cities of India as it is a simple and low cost methodology. The main advantage of composting is that it recycles the nutrients to the soil, hence improving the soil texture.
Composting is not suitable for wet waste. During rainy season open compost plants have to be dysfunctional. Huge land requirement and lack of awareness of compost usage amongst farmers makes the technique a small scale application. If the organic waste is not properly segregated at source level then chances of toxic materials getting mixed in the soil through compost increases.
It is another bio-conversion process where organic matter is decomposed by worms forming a nutrient rich residue called vermin compost which is a very good natural fertilizer and soil conditioner. If carried out in anaerobic conditions the process creates bad odour and toxic environment for the worms.
Biomethanation and Anaerobic Digestion
It is a process of anaerobic digestion of biodegradable waste material by microorganisms producing biogas and compost (monsal.com, 2007). Biogas is a power supply source. With an enclosed system the collection of gas becomes easy, less land is required, release of bad smell is prevented. However setting up of plants requires huge cost and the quantity of waste has to be huge for processing.
Hence it requires large scale application. Liquid sludge generated in the process can be used as a direct fertilizer. The waste water produced has to be treated for prevention of water pollution, hence increasing the cost. The technology is not suitable for certain organic compounds as oils, yard wastes and grease hence large scale segregation of waste at source is required which makes the process difficult.
Factors like transportation of waste to the plants also have to be taken under consideration for large scale process application. This technology has been commercialised at Lucknow and Vijayawada with Nisarguna Biogas Plant as operational unit.
A commonly used method of developed countries, where biodegradable and non-biodegradable waste such as plastics, paper, pathological wastes and packaging materials are burnt at 1400C above temperature and converted to innocuous materials like ash and steam. The steam generated can be used for energy recovery through steam turbines generating power.
It is a noiseless and hygienic method with minimal land requirements. As the incineration plants can be set up in city limits the waste transportation cost can be cut down. However the establishment, operational and maintenance cost of such plants is very high. The residual ash contains pollutants and toxic substances, alarming environmental concerns. The operation and maintenance of such plants require skilled labour.
Pyrolysis ans Gasification
It is a gasification process where wastes such as biomass and homogeneous organic matter are reacted with controlled amount of oxygen at high temperatures (Middleton, 2005; Marshall & Morris, 2006) producing a synthesis gas called syngas which is a fuel. Syngas can be converted to electric power and it is more efficient than biogas or liquid fuel.
The drawbacks of the process are high power consumption for pre-processing wastes, supply of pure oxygen as a gasification agent, timely closure of service plants for cleanups.
Decomposition of waste material in oxygen-starved environment to gaseous substances using an electric arc gasifier at high temperatures is plasma pyrolysis. The process intends to generate electricity and reduce the slag sent for landfills. It is not suitable for wet wastes as electricity cost is high for processing it. Transportation and burning of pyrolysis oil with high viscosity is problematic and handling of gasifier ash with toxic matter and its disposal is difficult.
Pelletization/Production of Refuse Derived Fuel (RDF)
It is a method for processing mixed municipal solid wastes producing RDF an enriched fuel feed for thermal processes like incineration and industrial furnaces (Chantland, 2006). The RDF pellets can be used as coal substitutes and can be stored or transported to longer distances easily. It is not a feasible process during rainy season or for wet wastes.
If RDF fluff/pellets are contaminated by toxic/hazardous material, the pellets are not safe for burning in the open or for domestic use.
Sanitary Landfills and Landfill Gas Recovery
It is the ultimate method for disposal of all types of wastes such as residual sludge, industrial and commercial waste, inorganic wastes and inert matter which cannot be recycled or reused in the future. The main advantage of this technology is that it is highly cost effective and does not require skilled labour for maintenance.
The landfill gas generated can be utilized for direct thermal applications as domestic fuel. However, transportation of waste to landfill sites, getting land for landfill sites in the cities, pollution of ground water by leacheate pollutants and chances of explosion due to emission of green house gases as carbon dioxide and methane at landfill site are some of its drawbacks. It is mandatory in India to treat the organic waste before disposal as dumping of it is prohibited by law. Hence in India recovery of landfill gas is minimal.
The Choice of Technology
The choice of technology depends on its economic and technical viability, environmental implications and sustainability keeping in view the financial and physical resources.
The key factors are:
- The quality and origin of waste
- Presence of toxic waste components
- Availability of energy producing outlets
- Commercial markets for sale of compost produced
- Land prices and labour costs
- Experience and capabilities of technology providers.
However, compliance of any proposed technology with the Municipal Solid waste (Management and Handling) Rules 2000 issued by the Ministry of Environment and Forests is mandatory.
BOOT, BOO, and DBO Contracts for Treatment and Disposal of Waste
Due to the incapability of municipal authorities in solid waste collection and disposal the relegation of responsibility to private players and their participation is gradually increasing. Build, Own, Operate and Transfer (BOOT) and Build, Own and Operate (BOT) are the popular models.
The municipal authorities provide land on lease for plant set up and garbage at plant sites. According to the BOOT contract the private firm invests money to build, own and operate the plant for 20 to 30 years and then transfer it to the municipal authorities after investment returns.
But in BOT contract the plant is dismantled after the contract period and the land is taken up by municipal authorities. In some cities DBO contracts are adopted where the plant building, ownership and land costs are borne entirely by the municipal authorities with the private firm responsible for only designing, building and operating the plant.
All the technological options are analysed, their salient features and cost implications are taken into consideration. Study of environmental implications and suitability to biophysical environment of India is carried out. The research shows that composting, vermin-composting and biomethanation are the preferred techniques.
Choice of technology depends on the type of waste. Composting and biogas generation is for slaughter house and fish market wastes, Vermi composting for homogeneous wastes such as fruits and vegetable wastes and windrow for heterogeneous wastes. Precaution has to be kept near thermal conversion plants so that the fuel gas emitted does not pollute the environment.
Sanitary land filling is the easiest option. However in India pyrolysis, plasma pyrolysis and pelletization are rare technologies and not in use at large scale. The analysis indicates that no technology is perfect. All of them have merits and demerits. Therefore, the choice of technology has to be done judiciously.