Any materials that can be decomposed are regarded as biodegradable. Maximum of the waste generated in household level is usually biodegradable, and therefore has the potential of getting converted into energy instead of getting lost as solid waste. Even in the case of Kathmandu, Solid waste management is a huge problem and over 70% of the waste generated is organic waste. The landfill site is a mess because of unmanaged waste disposal and has resulted in problems of leachate infiltration to odour to outbreaks of diseases. Instead of having problems like these, if we were to take up a more sustainable approach to convert the waste into energy, it would help in reusing these wastes, reducing dependency on the fossil fuels, more managed waste disposal to name a few.
According to the Baseline and Feasibility Assessment of the Waste to Energy Report, 2015, submitted to the AEPC, (Alternative Energy Promotion Center,) the available biodegradable waste produced per day for the community biogas plant from cattle dung, night soil and kitchen are 8.5 per cattle, 0.86 kg per person and 0.34 kg per person respectively. The waste produced per day for the commercial level biogas plant from cattle farm, night soil, kitchen waste are 45.83 kg per buffalo, 7.91 kg per cattle, 0.48 kg person and 0.38 kg per person respectively. The waste produced for the institutional level biogas plant from night soil and kitchen waste are 0.46 kg per person and 0.36 kg per person respectively. Similarly, for municipal level biogas plants, organic solid waste generated is 0.51 kg per capita. Community biogas plant for 4-5 family of 15 m3 size will reduce 9940 kg fuel wood and 10.46 ton CO2 emission per year. Commercial and Institutional biogas plant of 35 m3 size will reduce 1873 kg LPG and 5.59 ton CO2 emission per year. Municipal solid waste of 136 ton per day for Kathmandu, Bhaktapur and Lalitpur districts will reduce 18,764 tonne CO2 per year.
The breakdown of organic matter by anaerobic bacteria produces a mixture of different gases like the methane and carbon dioxide which is referred to as the biogas. The wastes coming from variety of sources like animal manure, plant material, sewage, municipal waste, food waste can be turned into biogas this way. This biogas can then be used as an alternative energy, after converting it into heat or electrical energy. It also exerts far less carbon footprint than the fossil fuels while also managing the wastes in a more sustainable way. The main microorganisms that breaks down these wastes are Psychrophillic bacteria, Mesophilic bacteria and Thermophilic bacteria. According to studies, the gas production potential of cattle is about 0.023-0.040 m3 gas production per kg, that of pig is 0.040-0.059 m3 and that of human excreta is 0.020-0.028 m3.
The subsidy policy of Nepal (2069) recognizes broadly four different types f waste to energy projects. They are commercial, institutional, community and municipal. The municipal solid waste based biogas plant converts municipal waste to energy. The community based biogas plant has a common gas grid system and is built to help convert all the community wastes accumulation to energy. The produced slurry is also shared among the community people for farming fertilization purpose or can be sold to the market too. The plants installed in commercial institutions like firms, farms, hotels, industries are referred to as commercial biogas plant and they are of higher capacity than the household ones. The bio digesters established in institutional places like academic institutions, religious institutions, farms, etc, are referred to as institutional biogas plant.
Because of the ongoing climate crisis, reducing the green house gases emission has become a major concern of the present, and one of the best ways to do that is through the renewable energy technology. The first Clean Development Mechanism was also prepared for the biogas technology and registered with the UNFCCC. The Centre for Rural Technology has also implemented CDM-GS prject in six districts in Terai of Nepal and certified emission reductions have been issued. The Netherlands Development Organization has also initiated ICS carbon projects in seven district of Far-Western region to promote 150,000 improved stoves. But still, according to a study by the Ministry of Finance in 2015, the consumption of traditional, commercial and renewable energy has been 77%, 20% and 3%, which shows how much dependent we are on the traditional energy system. But, the potential of biogas in Nepal is huge, and Nepali farming system is heavily dependent on livestock, and according to the same report, there is technical biogas potential for at least one million household size plants, 57% located in the Terai plains, 37% in the hills and 6% in remote hills. There are about 200 community and institutional biogas plants in Nepal which range from 6-75 m3 and are normally fed from kitchen wastes, toilet waste and livestock manure.