World Student Community for Sustainable Development

by Ketan Pednekar , Mahak Sabouri

Developing countries have great opportunities to try new and innovative technologies thereby minimizing the environmental impacts. The experiences of developed countries can be utilized for decisions regarding developmental projects in such countries. The experiences, though, have to be seen in context to the local environmental and social aspects.

India, 7th largest country in the world in terms of size and 2nd largest in terms of population (more than 1 billion) 2, has ample scope to carve its path towards development in sustainable way. The increasingly new affluent middle class in India is raising the material and energy consumptions to higher levels. It is important that the waste generated through these consumption patterns be handled in such a way that their environmental impacts are minimized.

The economic activities in developing countries can be accelerated if cheap and continuous power supply is available. This can be achieved by various conventional means like coal or fossil fuel based power plants. These methods give rise to greenhouse gas emissions, thus leading to global warming and depletion of natural resources.

However, if this power supply is provided with innovative and sustainable methods, we can reduce these undesirable impacts. Current per capita energy consumption in India is 290 kg of oil equivalent. It is much lower as compared to many developed industrialized countries (USA with 8080 kg of oil equivalent).1 It is because the country is in a developing stage and access to cheap power supply is not easily available. An efficient and cheap power infrastructure needs to be developed to overcome this problem. When the cheap power supply is available, the consumption levels are bound to increase. The higher consumption levels will lead to greater environmental effects. ‘Prevention is better than cureâ€^TM makes it a perfect case for adopting sustainable technologies while building new infrastructures than to seek ‘end of the pipe solutionsâ€^TM.

There is already some initiative taken by Indian government for using renewable resources to produce heat and power. The current scenario of power generation through renewable resources in India is as follows:

[Source: Ministry of Non-conventional Energy Sources (MNES) & Planning Commission, India]

As mentioned before, continuous power supply is desired in a developing city to stimulate industrial and entrepreneurial activities. The wind power, and solar power cannot provide continuous power. Hydropower is dependent on the availability of natural resource like river. In this paper, power generation from bio gas produced through bio-methanation of solid waste is considered. As the biogas produced is not in sufficient quantities, it is coupled with natural gas infrastructure.

The complete procedure of the waste management and energy generation of a small city ‘Amalpuramâ€^TM, in southeast part of India is considered as a case study. In India, like many other developing countries, the waste generated by material consumption is increasing. Proper disposal of this waste is an important issue. It is interesting to explore the possibilities of generating energy from waste.

This can help solve the problem of waste disposal as well as energy generation. The energy generation from waste in generally done by two methods:

1. Direct incineration.
2. Burning the biogas produced through digestion process.

Due to high resistance by environmental agencies for direct incineration in India, mainly due to the dioxins produced during the process, bio-digestion process is a preferred operation and is considered in this case study.

Case Introduction

Amalpuram, a small city with a population of 51,000 inhabitants2 is chosen as a case that can be modeled to be a sample for a sustainable city. Amalpuram is a small city in Indian state of Andhra Pradesh in southeast. Not very developed, it presents ample opportunities for introducing innovative technologies to mould it as a sustainable city. As continuous power supply is the main objective of the proposal, the cities connected by natural gas infrastructure were considered.

There is a proposal of natural gas pipeline in this city3, which is a necessary requirement for the case. Purpose of selecting this city is also due to the fact that this is one of the less prosperous amongst the neighboring cities and can be helped towards prosperity. The proposed project can be a tool for accelerated economical growth of the city, and can be a model to be emulated by other similar or bigger cities.

Waste Management

The patterns of material wastes are derived from general patterns prevailing in Indian cities and are not specific to the city. The city specific data can a subject of further research if the project is to be implemented.

The normal waste generation from Amalpuram would be 27 tones per day*. The composition of waste is as follows:

From waste compositions listed in the table2, it is seen that the much of the waste is in the form of biodegradable matters, as well as sand and fine earth materials. The large percentage of ash and fine earth is due to increased construction activities in a growing city. It can be easily separated in source and should not be allowed to mix with other biodegradable waste. The other garbage found in significant amounts is paper and cardboard, and perhaps plastic. Paper, cardboard, plastic and metals are sent to the recycle industry after separation process. Already a section of rag pickers do this job. The operation is not organised and sometimes all the mixed waste ends up the landfill. Normally broken glass pieces are also not picked up by the rag pickers.

The separation can be managed more effectively if most of the citizens contribute to separation process. A lack of public awareness is the primary problem. It is important to raise environmental awareness in the area so as to help manage the waste. This can be implemented by the government support and education. Two major groups to be educated for waste minimization are householders and children. They also play a big role in producing waste. So, in this regard we can also enjoy the advantages of public media training to accelerate this process. Long-term program of training children in school is also required to make the process sustainable. This can be done by teaching some courses in this regard and by making them responsible for their own environment. The penalties levied for improper waste handling and garbage dumping can also help in collecting the waste in a systematic way.

Biological Treatment

Anaerobic digestion is proposed to be used for treatment of typical Amalpuram biodegradable solid waste. It involves biological decomposition of organic materials without the presence of oxygen, accompanying with production of methane and carbon dioxide. Bio-methanation process operates under ambient temperature and pressure. The process itself comprises refuse separation, blending, anaerobic digestion, gas cleaning, and liquid and solid effluent removal.

Although several companies have been working with this waste treatment technique in India, the present technologies are still for homogenous waste. Hence, the cleaning and separating costs for mixed municipal waste are likely to be high. A good way to deal with the problem is to intercept the appropriate wastes, e.g. kitchen rubbish, at the generating points before they are mixed with other wastes. Also, combining the solid and liquid waste treatment in an integrated plant would appear to be an interesting alternative, since the solid waste needs dilution with liquid stream for this method. This would reduce capital and operational cost of the plant compared to an individual treatment plant. The proposed process uses a typical continuous bio digester as shown in the figure1.

Energy Generation

The simple flow diagram of the proposed process for power generation is shown in figure2. The separated biodegradable waste is first taken to the continuous digester. The unit consists of a pre-mixing area or tank, a digester vessel(s), a system for using the biogas, and a system for distributing or spreading the effluent (the remaining digested material). In a continuous digester, organic material is constantly or regularly fed into the digester.6 The solid remains after digester is an excellent fertilizer and can be used in the farms surrounding Amalpuram. The gas generated has H2S as a product of sulfur decomposition during digestion process. This corrosive sulfur compounds have to be removed before the gas can be fired in a gas turbine. This can be done by using an amine absorption unit and a small sulfur unit with Claus process. The basic reaction in the Claus process is

H2S + 1/2 O2 → H2O + S°

The clean gas after sulfur removal is sent to gas turbine. The turndown of the gas turbine is maintained by controlling the auxiliary natural gas flow.

As the gas is burned in gas turbine, electric power is produced. The hot gases going out from turbine are used to produce steam in the waste heat boiler. The steam produced from the waste heat boiler can be used in steam turbine producing more electric power. Some of the steam is sent to amine unit for regeneration purposes. Considering 40% of the waste material is biodegradable (table 2), the estimated biogas generation from continuous digester is 1944 m3/day (1kg of biodegradable waste generates 0.18 m3 of biogas, Kura and Lea(1995)). Since the population of the town and the gas produced is quite low, the small gas turbine producing 5MW electricity can be used.4 Even in this case, most of the gas for turbine is supplied by the natural gas auxiliary firing. The hot exhaust gases from gas turbine are passed through a waste heat boiler where high pressure steam is produced and is sent to condensing steam turbine. Therefore total electric power produced will be higher.

Future Visions

More biogas can be produced if higher amounts of wastes are handled. As the city is growing, amount of waste generated will increase. This plant can be a center for processing wastes from neighboring villages and cities. The efficiency of digesters can be increased by adapting to the new technological advances as they come through. The waste water can also be treated in a nearby premises and the bio gas produced from the same can be integrated to the system. The water needed for solid waste treatment can be taken from the waste water plant.

Conclusion

The solid waste management utilizing the energy potential of solid waste is considered in the proposal. Although the solid waste and the biogas produced is low, the energy potential inherent in the solid waste is tried to be utilized.

The proper waste collection and separation system coupled with bio-methanation and energy recovery will help reduce the environmental impacts and energy loss inherent in the current system(landfill). The power generation also is expected to drive Amalpuram to prosperity.

The paper writes a general proposal for Amalpuram. More specific research with respect to local conditions and specific area statistics need to be done.

- Ketan Pednekar and Mahak Sabouri, Chalmers University of Technology, Sweden

References

1. Energy scenario in India, V. Raghuraman, confederation of Indian Industry.
2. Data from Census India, 2001
3. Hindu Business Line Friday, January 10, 2003
4. Data from the General Electric online catalogue for gas turbines.
5. Evaluation of energy from waste investment opportunities in India, Department of Trade and Industry, UK
6. http://www.eere.energy.gov/consumerinfo/refbriefs/ab5.html