Solid waste management has been a major issue in many developing countries. In Greece, until late 1980s, solid waste was buried in landfill sites and frequently also seen being thrown in open dumping sites. The lack of systematic facilities, coordination and governance of the concerned institutions has created serious problems in the solid waste disposal [5] . However, later, the legislation and environmental planning of Greece has set the target to implement internal SWM, followed by the ongoing reduction of biodegradable solid waste which is presently steering to landfilling, increasing recycle activities and also the closure of open dumping sites [5] . One of the re- cently proposed ways of waste management is to recover the energy from the waste through high temperature thermal treatment, as waste contains significant amount of biodegradable matters, that is expected be used as renewable energy source [6] .

India is an example of a fast growing country. Rapid growth of industrialization, population and urbanization has caused huge amount of municipal solid waste that lead to environmental degradation [7] . Unfortunately, most of the cities there are not able to cope up with environmental pressure due to lack of facilities. With waste generation per capita of 0.5 kg/day, India is facing a major challenge in municipality solid waste management [2] . Sharholy et al. (2008) has conducted rigorous review on solid waste management in Indian context. Mindsets are changing with the progress of development and education. The price hike in petroleum products and other power have enforced the concerned institutions and investors to make energy recovery projects from waste become more practical (Sharholy cited in [8] ).

In response to Kyoto Protocol and agreement in Marrakech, Korea has been giving serious attention on CO₂ emission reduction. The development of renewable energy is considered as one way to reduce CO₂ emission and socio-economic cost due to environmental pressure. As one of the possible sources of energy alternative, the go- vernment has been promoting the expansion of landfill gas for electricity generation. Shin et al. (2005) had con- ducted economic and environmental analysis to see the prospect of landfill gas to generate electricity, under va- rious scenarios of technology. The result showed that electricity generation from waste using steam turbine was the most economical way. However, there are still uncertainties in utilizing landfill gas and the introduction of it to energy market. The technology, economy and regulations are few to take into account in promoting waste to energy concept in Korea [9] .

Indonesia is the countries in fourth position in the world in its population (UNFPA World Population 2012). Gunamantha has perceived that solid waste management solution is not a straight forward problem. The collection and disposal are not the final answer. Different types of methods are available, but the characteristic of waste which is not homogeneous, has created other hindrances. The life cycle assessment on various ways to recover the energy from solid waste in Yogyakarta province has been conducted to encounter questions such as: anaerobic digestion or landfill, thermal conversion or landfill, loss or benefit to the environment [10] . The study showed that direct gasification was supposed to be the safest method in energy recovery from solid waste. Life cycle assessment was considered the appropriate technique to evaluate diverse waste treatment methods in relation to their environmental impact.

Waste to energy is a process of converting waste into gas or electricity. The sources of waste can be from residence, industries, commerce and institutions (offices). The term “waste” implies a non-usable by product of a production process. The first process noticed in the history is the incineration built in Denmark in 1903 [11] . As the energy consumption keeps on increasing, the concept to transform waste (solid waste, to be more specific) into energy has become one of the core issues in promoting an alternative source of energy. The concern on minimizing environmental pressure and the need of energy for living have created a strong linkage between waste and energy [11] .

So far the solid waste is concerned, recycling and reusing are the most preferred methods in most of waste management program. However, converting waste to energy is viewed as a key aspect in solid waste management. In the previous years, burning solid waste was a method to shrink the volume of solid waste and to reduce its harmful effect to human health. Today, waste incineration is combined with the extraction of energy [12] .

Solid waste can be converted into energy through various conversion processes. The most common techni- ques to convert waste into energy have been identified as thermal conversion, biochemical conversion and landfilling [2] .

Thermal conversion techniques include incineration (combustion), pyrolysis, gasification and refuse derived fuel (RDF). The combustion involves burning organic waste and other components like textile and plastic. The heat resulted from this process is converted into electricity. The emission of toxic gases as a side effect of these process is the main drawback of thermal conversion.

Considered as more environmentally friendly process, biochemical conversion comes as an alternative. Composting, vermicomposting and anaerobic digestion are those under biochemical conversion process. Thermal conversion in this method covers trans-esterification and other processes to convert plants and bio oil into biodiesel (Annepu cited in [2] ); [7] .

Landfilling is the most common method used in developing and least developed countries. The simple landfill is a technique to dispose solid waste in an open space. This method is easy but is not environmentally sound. The waste is usually wide-opened and prone to open burning. Unfortunately, most of landfill sites are not (or minimal) equipped with the facility to remove dust [13] . With low effectiveness in controlling pollution, this method is not the one that can be taken as an appropriate option.

Collection time is one factor that affects the effectiveness of collection and transportation of solid waste into dumping sites. Day time collection is more convenient for the workers, but at the same time it creates problem in traffic and pollution due to improper way of transporting the waste (waste drops as well as unpleasant smell and scene). The collection efficiency also has not been up to the mark. Kathmandu Metropolitan City has the highest collection efficiency of 86.9%, followed by Bhaktapur with 86.5%, while the efficiency in Kirtipur is only 35.3% [4] . Night time or early morning collection could be a challenge for the authority in order to improve the collection efficiency.

Lack of practice in waste separation is another issue. Most of domestic solid waste is found not well segregated. Separation of organic waste from other components is required when anaerobic digestion system is used to convert waste into energy. Incineration could be another option that does not required separation of organic waste as it can include plastic and textiles to be incinerated to produce heat. However, this technique has serious environ- mental impacts on air pollution. Emission of toxic gasses is the major disadvantage of this technique. The study on air pollution in Kathmandu Valley revealed that CO (carbon monoxide) emission had reached to 178,570 µg/m³, almost six times higher than the standard published by WHO which is 30,000 µg/m³ [16] .

Open dumping is the major disposal method in Nepal. Among five municipalities, Kathmandu Metropolitan City has produced the highest amount of solid waste, followed by Lalitpur Sub Metropolitan City (Figure 1). The two cities and Bhaktapur have been disposing their solid waste in Sisdole landfill site since 2005. With capacity of holding only 275,000 tons of waste, Sisdole will not be able to cope with the increase of solid waste generation (http://www.gorkhapatra.org.np/detail.php?article_id=9936&cat_id=4). This problem has forced the authority to construct a new one in Bancharedanda and to shut down the Sisdolesite in the near future. Bancharedanda is supposed to be the largest landfill site in Nepal. Nevertheless, many municipalities have been facing the problem of waiting the government decision for the approval of land acquisition [4] . Bureaucracy has creat- ed problem in the availability of space for solid waste final disposal.

In addition to this problem, it may be difficult to find land available for dumping site in the future as population is keep on increasing. Ecologically, it is not wise to continue with landfilling as a technique for solid waste

management for long term. Fear of failure of the landfill’s liner, the pollutant would reach the groundwater system. Consequently, groundwater will carry the pollutant into water body nearby, spreading hazardous toxic effect. The effect can stay up to 25 years after the closure of the landfill site [17] .

Addressing those issues requires a joined-hand between the government, citizens and other related institutions (national and international agencies and private sectors). Several researches and studies on waste management have been conducted by some of them. However, many have not investigated the introduction of waste to energy concept in its study. It is high time to explore other techniques that are more environmentally safe and have potential contribution to solving energy crisis in Nepal, specifically Kathmandu Valley.

Solid waste consists of various components. Assessing the potential energy from solid waste is not simple as dif- ferent materials have different calorific values.It is necessary to know the composition of solid waste to obtain its heat content. The moisture content is also important factor to determine how much heat can be extracted from solid waste. Figure 2 and Figure 3 shows the composition of solid waste from various sectors in Kathmandu Valley.

Determining the heat content of solid waste is done by using the data of heat values of various material consisted in municipal solid waste. Table 1 exhibits the heat value of different type of material on dry basis. Heat content is calculated using the following formula:

Heat content (HC) = f_i * HV_i

where f_i = the fraction of component i

HV_i = Heat Value of component i

In a simple way, the heat content of solid waste of Kathmandu Valley is calculated as follows:

HC = 0.45 * 7.6 + 0.16 * 22.6 + 0.25 * 6.7 + 0.02 * 0.1 + 0.01 * 0.7 + 0.02 * 13.8 + 0.01 * 20.65

= 9.2 million Btu

The analysis shows that each ton of solid waste in Kathmandu Valley has potential to produce 9.2 million Btu. It means that every day, a total of 2.7 MW energy theoretically can be generated from solid waste in Kathmandu Valley. Even if only organic waste is incinerated (as other components can be recycled or reused), it will produce about 3.42 million Btu (1.3 MW), which is enough to light approximately of 1000 households. It is not high amount, but not too less to be neglected.

(Source: http://www.epa.gov/msw/msw99.htm)

The implementation of waste to energy concept requires relatively high initial investment. It needs full support from government. The Government of Nepal has taken foremost step with the ratification of Solid Waste Management Act in 2011, though it has not been successfully turned into actions. Now the government is in the pro- cess of devising new policy in solid waste management under which municipalities are encouraged to developed strategy to improve the carrying out of solid waste management in their respective region [4] .

Moreover, the Alternative Energy and Promotion Center under the Ministry of Science, Technology and Environment, has come up with a Waste to Energy Project called Scaling-Up Renewable Energy Program (SREP) and has been soliciting proposals from interested parties across Nepal. The program intends to commercialize energy recovery from urban waste of various sectors. However, the environmental impact need to be taken into account and for that the government has prepared Environmental Management Framework that will work as a guideline to identify, assess, mitigate and monitor potential environmental impacts/risks of projects and activities targeted under the SREP [18] . This move shows the initiative and awareness of the government of Nepal on the importance of managing solid waste and the production of clean energy. It will motivate private sector as well to take part in providing service to manage solid waste.

The Solid Waste Management Act gives the direction to local bodies (municipalities) to impose the service charge to perform the service. From a survey, it was found that 82% of respondents would be willing to pay given the condition that the service level is improved [4] . Although the fee collection has not been effective, willingness to pay shows that people are prepared for a progress. Most of municipalities in Nepal allocate very small amount of budget for solid waste management. The expenditure usually cannot be recovered from that bu- dget. Financial contribution from service users will surely make the service sustains in the future. Increasing the fee collection coverage shall be the first effort. Gradually, the strategy can be carried on to increase the fee per household.

Moreover, the benefit of implementing waste to energy should not be viewed from financial aspect alone. Converting waste into energy will reduce the air and water pollution level, provide healthier environment and producing substantial energy for the people. These intangible benefits are often overlooked.