Electrification through biogas
The Renewable Energy Policy of Bangladesh, published in 2008, states that renewable energy will take a vital role for off grid electrification in the country. The main renewable energy resources in Bangladesh are biomass, solar, wind and hydropower. The hydropower potential of Bangladesh is low due to the relative flatness of the country. Wind power generation in Bangladesh has certain limitations due to the lack of reliable wind speed data and the remarkable seasonal variation of wind speed. The country has good prospects of utilizing solar photovoltaic (PV) systems for electricity generation, but the high capital investment cost is a big barrier for adopting such systems. Biomass is the major energy source in Bangladesh and biomass utilization systems represent a proven environment-friendly option for small- to medium-scale decentralized electricity generation.
Bangladesh's per capita energy consumption is very low. The 2008 energy consumption value stands at about 250 kgOE(oil equivalent), compared to 550 kgOE for India, 515 kgOE for Pakistan, and 430 kgOE for Sri Lanka. Total primary energy consumption in 2008 was 33.50 MTOE (million ton oil equivalent) and the energy consumption mix was estimated as: indigenous biomass 62%, indigenous natural gas 25%, imported oil 12%, imported coal and hydro together about 1%.
Contribution of biomass in total primary energy consumption of Bangladesh is around 60%. The major sources of traditional biomass are agricultural residues, wood and wood wastes, and animal dung, and their shares in energy supply are approximately 45%, 35% and 20%, respectively. Industrial and commercial use of biomass accounts for 14% of total energy consumption. 63% of energy required in the industrial sector comes from biomass fuel. Natural gas, Liquefied petroleum gas (LPG), electricity, kerosene and biomass fuels are used for cooking. In areas without natural gas and electricity, biomass is used to meet the household cooking needs.
Natural gas is currently the only indigenous non-renewable energy resource of the country, which is being produced and consumed in significant quantities since 1970. Gas, the main source of commercial energy, plays a vital role towards the growth of the economy of Bangladesh. The gas market is dominated by power and fertilizer (using gas as feedstock) sectors, which account for 46.65% and 21.71% of the demand, respectively. According to the 2008 BP Statistical Energy Survey, Bangladesh had 2007 proven natural gas reserves of 0.39 trillion cubic metres. Although the remaining recoverable gas reserve is enough for the time being, it is understood that there is significant field growth potential, as most of the state-owned gas fields have not yet been fully appraised.
Therefore, using biomass energy might be the sustainable option of using renewable energy to electrify the rural Bangladesh in this present context.
The economy of Bangladesh depends principally on agriculture. The main crops produced are rice, sugar cane, vegetables, wheat, jute, pulses, coconut, maize, millet, cotton and groundnut. Agricultural crops generate large quantities of residues. Such residues represent an important source of energy both for domestic as well as industrial purposes. Other sources of biomass in the country are farm-animal waste and poultry droppings produced by the national herds, fuel wood from existing forests, tree residues and saw dust from the forestry industry. The 15 million citizens of Bangladesh produce huge amounts of human waste and municipal solid waste (MSW) annually.
Agricultural residues: There are two types of agricultural crop residues: field residues and processing residues. Not all field residues are recoverable. The percentage of field residues of a crop to be recycled onto the land depends upon the specific local climatic and soil conditions. There is no available specific data concerning the common practices in Bangladesh . However, in developed countries, it has been established that only about 35% of field crop residues can be removed without adverse effects on future yields. Crop processing residues, on the other hand, have a 100% recovery factor. Accordingly, it is estimated that the total annual amount of recoverable agricultural-crop residues in Bangladesh is about 42 Mtonne, of which 63% are field residues and 37% process residues.
Animal waste and poultry droppings: Manure from cattle, goats, buffaloes and sheep are the common animal wastes in Bangladesh. The quantity of waste produced per animal per day varies depending on body size, type of feed and level of nutrition. The average amount of droppings (on air dry basis) produced by broilers and layers are 0.02 and 0.03 kg/bird/day respectively. The recovery/collection factors for animal waste and poultry droppings were reported in many literature to be 60% and 50%, respectively. Accordingly, it is estimated that the total annual amount of recoverable animal waste and poultry droppings in Bangladesh is 20.619 Mtonne.
Human waste and MSW: The total rate of human waste generation by the 138.1 million citizens in Bangladesh has been estimated as 4.537 Mtonne of dry matter/year (corresponding to 0.09 kg/capita/day). The MSW generation rate in urban areas of Bangladesh is between 0.4 and 0.5 kg/capita/day. In rural areas of the country, the generation rate is only 0.15 kg/capita/day. Considering that human waste and MSW are 100% recoverable, the total annual amount of the biomass available from these two sources in Bangladesh is 14.793 Mtonne.
Forests and the forestry industry: Forest biomass includes tree components such as trunk, branches, foliage and roots. Tree trunks and main branches constitute what is commonly known as fuel wood. Twigs, leaves, bark and roots are tree residues. Both wood processing residues (e.g. sawmill off-cuts and sawdust) and recycled wood (e.g. that derived from the demolition of buildings, pallets and packing crates) are important sources of energy. The annual amount of such recycled wood, on a sustainable basis, is, however, not known. It has been estimated that only about 20% of a tree, initially harvested for timber, results in sawn products. The remaining 80% is discarded, in equal proportions, as forest residues and process residues (i.e. bark, slabs, sawdust, trimmings and planer shavings). Ply mills produce about the same amount of residues as sawmills. In 2004, 0.123 Mtonne of sawdust was available for energy purposes. Considering 100% recovery rate, the annual amount of recoverable biomass from forests and forestry industry in Bangladesh is 8.871 Mtonne.
Available for electricity generation
The total annual generation and recoverable rates of biomass in Bangladesh are about 165 and 9 Mtonne/year, respectively. In 2006, the biomass consumption for energy in Bangladesh was reported as about 350 pico-Joule (PJ). At an average annual growth rate of 1.3%, the consumption in 2010 will be about 370 PJ. The total available recoverable biomass energy of the country in 2006 was about 1250 PJ. Accordingly, in 2006, about 820 PJ of biomass energy was available for the generation of electricity. On the other hand, the total biomass energy consumption in 2006 was about 473 PJ. Assuming the same average annual growth rate of 1.3%, the biomass consumption in 2010 will be about 286 PJ. Therefore, the amount of biomass energy available in 2006 was 777 PJ, which is equivalent to 216 terawatt-hour (TWh). According to these two estimates and considering that the consumption of biomass for non-energy purposes is negligible, the annual available biomass energy potential for electricity generation in Bangladesh is in the range of between 216 and 250 TWh.
Prospects for electrification
Therefore, there is a huge possibility to produce electricity using biogas in Bangla desh, if proper research is carried out by research agencies, professionals and the implementing authority, i,e, the government. The government agency Infrastruc-ture Development Company Limited (IDCOL) sources said Bangladesh has 215,000 poultry farms and 15,000 cattle farms. By establishing biogas plants in these farms, electricity could be generated. So far 35,000 biogas plants have been established across the country and these plants are producing gas, which is being used for cooking purposes in the rural areas. The agency has set a target of establishing 60,000 biogas plants by 2012. One plant produces on an average 94.22 square feet gas. At present 33 lakh square feet biogas is being produced in the country daily. If this generated gas can be utilized properly, it can serve to produce about 1,000MW electricity and if the opportunity is utilized the growing shortage of electricity could be greatly met in this power-starved country.
However, the successful application and extension of this option depends on:
* Institutional measures -- close collaboration between sectors involved. This should include, among others, provision of soft term loans and/or subsidization of this technological option as an integral part of total sanitation programme, which currently prevail in Bangladesh;
* Availability of standard design for construction, and maintenance guidelines for the specific site, adopted to local socioeconomic condition;
* Meaningful public involvement -- should have objective to pass relevant information of this technology to the community, to increase awareness to maximize the acceptability of this technology; and,
* Prediction of realistic benefit of this technology.
The writers are faculty members of Civil/ Environmental Engineering Department of Ahsanullah University of Science and Technology.