Livestock waste as alternative energy for rural households: A review

Most livestock businesses in Indonesia are still small-scale farms located in rural areas with ruminants and poultry. BPS data for 2023, ruminant livestock and poultry amount to 63 million and 4,119 million, respectively. Ruminant livestock waste averages 15 kg/day, producing 946 million livestock waste/day. Livestock waste is used as raw material for organic fertilizer and alternative energy (biogas) for rural households. Biogas comes from gas produced through an anaerobic process from organic materials, namely human and animal waste, organic waste, household waste, and other biodegradable waste. Biogas has potential as an alternative energy source for rural households. The energy produced is environmentally friendly; biogas slurry is used as organic fertilizer, reduces carbon emissions, reduces the fossil fuel crisis, and reduces environmental pollution. However, the development of utilization of livestock waste into biogas faces obstacles, namely limited human and capital resources, as well as the number of livestock owners. Therefore, a more practical alternative energy (biogas) development strategy needs to be carried out by the government and farmers through the utilization and development of farmer groups, expanding the socialization of biogas technology, increasing the knowledge of farmers with non-formal education, and providing biogas installations in rural areas.


Introduction
Most of the livestock businesses in Indonesia are still small-scale farms located in rural areas with ruminants and poultry.The livestock population shows an increase with the demand for meat increasing from year to year [1,2] due to increasing population and increasing demand for high protein food derived from animal products [3,4].An increase in the livestock population will increase the amount of waste which will harm the environment if it is not further processed.
Livestock waste increases global warming from animal manure and extraction [5].Livestock waste can be used as organic fertilizer or an alternative energy source, biogas [6,7], to reduce global warming.
Livestock waste as an alternative energy source has many advantages, such as an odorless fuel and reducing soil and air pollution [5].
Organic waste is often ignored and has no economic value, even though anaerobic processing of this waste can be used as bio.Therefore organic waste, which is processed into biogas, is an effort to obtain alternative energy sources for rural households [8].Utilizing livestock waste as biogas in rural areas makes the environment healthier, reduces carbon emissions, and is integrated and sustainable [9].
The potential for biogas development in rural areas is enormous because most rural people work in the livestock and agricultural sectors.However, livestock and agricultural waste have yet to be utilized optimally due to socioeconomic constraints in rural communities.Therefore, this paper aims to determine the livestock population in Indonesia, the potential and utilization of livestock waste as 1292 (2024) 012002 IOP Publishing doi:10.1088/1755-1315/1292/1/012002 2 biogas, the use of biogas in rural households, and identify obstacles to biogas development at the household level in rural areas.

Livestock population development in Indonesia
The ruminant livestock population in Indonesia is smaller (63 million heads) than the poultry population, especially broiler chickens (3.168 million heads).However, the development of the ruminant livestock population in Indonesia over the last six years (2017-2022) has fluctuated, decreasing from 3.32 %/year to 2.64 %/year.The highest population increase occurred in the beef cattle population, with a rise of 2.64 %/year, followed by dairy cattle (1.35 %/year), goats (1.21 %/year), and buffalo (1.41 %/year).In contrast, cattle experienced a decrease in population, such as pigs (3.32%/year), sheep (2.40%/year), and horses (0.36%/year).This phenomenon occurs because Indonesians consume more meat from ruminants, cows, and goats.Meanwhile, the study's results [10] predict that the dairy cattle and buffalo population will decline from 2010-2020.The development of the livestock population is presented in Figure 1.Source: [11] An increase in the livestock population, especially beef cattle, is suspected of increasing the demand for meat every year [2; 12].Improving people's income, awareness of fulfilling nutrition, and changes in consumption patterns of animal protein have caused people's demand for meat to increase [13].

Potential and utilization of livestock waste as biogas
One form of alternative energy that is suitable to be developed and used by people in rural areas is biogas.Rural areas are agricultural and livestock areas, where crop and livestock waste can be obtained from agriculture and livestock.If this waste is not utilized, it will produce relatively high methane gas, especially waste from livestock, namely feces and urine.Methane gas is a potent greenhouse gas and causes global warming and climate change [14].According to [15], methane is a potent GHG and accumulates in the atmosphere at 1% per year.Agriculture and land use change contribute 22% of global GHG emissions [16].Over the past 150 years, methane levels have more than doubled due to human use of fossil fuels and intensive agriculture.
On the other hand, methane gas can be used as an energy source to replace diminishing fossil fuels.One renewable energy that can be produced is biogas, which has an excellent opportunity to be developed in rural areas in Indonesia.Agricultural and livestock production centers are in rural areas.Therefore, rural areas are a source of raw materials for alternative energy (biogas).Biomass-rich agricultural waste is livestock waste, especially livestock manure, and agricultural waste, especially rice -2,000,000 4,000,000 6,000,000 8,000,000 10,000,000 12,000,000 straw.A farming system integrated with livestock will create a symbiotic mutualism between plants and livestock by utilizing plant waste as feed and livestock waste (feces and urine) as organic matter for plants; it can also be used as a material for producing biogas [17].
In addition to livestock waste, biogas can be obtained from other organic raw materials, such as food waste, agriculture, and humans [18].Biogas has flammable properties because it comes from the fermentation process of organic matter.In fermentation, anaerobic bacteria live in airtight conditions to produce methane, carbon dioxide, and water [19,20].Biogas production is obtained through an anaerobic digestion process, namely hydrolysis, acetogenesis, and methanogenesis [21].The number of sizeable ruminant livestock (cows and buffaloes) in Indonesia in 2021 is 19.8 million heads [11].Assuming that one ruminant livestock produces 15 kg of manure day -1 , the manure that can be obtained is 297 million kg day -1 .Each cow can produce 0.023-0.040m3 of biogas [22], so the biogas potential that can be made from livestock manure is 6.83-11.88m3 day -1 .[23] has summarized several potential biogas sources obtained from several livestock types, as shown in Table 1.Source: [23] Table 1 illustrates the biogas potential that can be obtained from certain types of animals based on the coefficient of animal manure availability for the selected species (AC) and biogas yield per kilogram of total solids (BY).The most significant biogas potential is obtained from sizeable ruminant manure (cattle, buffalo, camel, horse, donkey, and mule), which is between 0.6 -0.8 m3 kg -1 TS, and the minor biogas potential is obtained from poultry manure, which is between 0.2 -0.8 m3 kg -1 TS.The potential for biogas from poultry is relatively minor because the amount of waste produced is less than that of ruminants.

Utilization of biogas in the household
Farmers can utilize biogas obtained from livestock waste as a substitute for LPG gas for household needs [18] because biogas is a combination of CH4 gas (± 60%), CO2 (± 38%), and others, such as N2, O2, H2, and H2S (± 2%) which can be burned such as LPG which is often used for cooking and lighting [24].Waste disposal, sanitation, environmental concerns, and the high cost of fossil fuels make biogas production a better option in line with the opinion [14] that the use of biogas as alternative energy that shifts wood fuel in rural households for cooking activities can reduce air pollution in the house and reduce respiratory diseases.Some of the advantages of biogas production from agricultural waste, especially from cow dung, are that the energy produced is very environmentally friendly because, in addition to utilizing waste from livestock, the rest of the process (biogas slurry) can be used as organic fertilizer which is rich in the elements needed by plants [25], reduce consumption of fossil fuels, carbon emissions, and avoid largescale deforestation, reduce waste hazards, and increase fertile soils [20].Research [14] shows that two types of energy used by households in rural areas, namely wood fuel, release higher methane emissions than households using biogas fuel (Figure 2).The maximum methane emissions obtained from households using wood stoves and biogas stoves are 2048.05and 956.23 kg Coe HH -1 year -1 , respectively.There is a difference in methane emissions of 1091.82 kg Coe HH -1 year -1 between households using wood stoves and households using biogas stoves.Besides being used as alternative energy as household fuel, biogas can also be used as a householdscale power plant [26].According to [5], biogas is used for cooking and lighting for people in Boyolali Regency.Farmers in Magelang Regency have used livestock waste to produce biogas as a substitute for gas stoves and wood stoves [27].Although biogas can be used as a substitute for fuel and lighting, its use still needs to be improved [28] and has yet to spread widely to rural areas.

Constraints and efforts to develop biogas
Biogas technology is vital in supporting government programs and policies as an alternative energy provider for households and other networks in several developed countries and continents.Germany is an example of a leading country on the European continent that has advanced large-scale biogas technology, namely by building 8,005 of a total of 17,240 biogas plants in the agricultural sector in Europe [29].China is also a pioneer in developing biogas technology, focusing mainly on household biogas digesters, with 111,000 biogas generators in 2015 [30].The development of biogas in these countries is also growing rapidly, as reported by [32] regarding the adoption of biogas technology in rural areas in Pakistan; it is influenced by the age and education level of the head of the family, household income, land assets, and the number of livestock owned by the farmer; [33] explained that biogas adoption in India is influenced by physical capital (home and land ownership), as well as human capital (education); [34] found that male household heads tend to adopt more biogas technology than female household heads, farmer education, number of livestock, household income, convenience for farmers to obtain credit, distance from house to farm, and the number of trees planted are factors influencing household decisions in adopting biogas technology in Ethiopia.
Biogas technology in Indonesia began in the 1970s, and starting in the 1981s, waste processing technology with biogas installations has been developed in several provinces through financial support from the Food and Agriculture Organization (FAO).In the 2000s, household-scale biogas reactors were designed with simple construction using materials made from ready-to-install plastic at relatively affordable prices [24].However, until now, biogas technology has not developed significantly [31].
Biogas technology has not yet developed in Indonesia because the agricultural and livestock waste produced cannot yet be utilized because the human resources of rural farmers are not yet able to process livestock waste into biogas due to technical, economic, and social factors [38].Research [24] found that farmer education, distance from house to barn, disease, and number of livestock, as well as the price of LPG subsidized by the government are considered factors inhibiting the development of biogas technology.Apart from that, the livestock business at the farm level is still small-scale and managed traditionally.Extensive rearing systems (grazing) are one of the obstacles to obtaining manure and other livestock waste [35,39].From an economic perspective, high initial investment/capital costs and a relatively long payback period and the low purchasing power of farming households are obstacles to the development of biogas at the household level [40,41].A number of studies reveal that the perspectives of Indonesian society are diverse due to culture and traditions.As a result, biogas adoption varies greatly from one region to another, lacking government support to promote biogas technology [38].Another study found that farmer literacy and education were still low in using biogas [42].
The Indonesian government has made various efforts to disseminate biogas technology, starting from access to capital, dissemination of biogas technology, coordination with relevant governments, sustainable agricultural development, improved governance, investment, and policy support, all of which are efforts and challenges as well as opportunities for the Indonesian government in developing biogas.Efforts to build biogas by empowering communities through the government and private sector, and other institutions to utilize livestock waste into energy potential [36], as well as increasing awareness about the use and utilization of biogas [37].Government support is very important in increasing the diffusion of biogas technology in developing countries like Indonesia; this dependence can create dependence, a sense of ownership and low maintenance of the technology.One of the approaches developed by the Home Biogas Program (BIRU) is a scheme where farmers can access credit at various interest rates to pay for small-scale biogas through collaboration with the private sector [38].Therefore, it is a more effective biogas development strategy.The government needs to do this through the use and development of farmer groups, more extensive socialization of biogas technology, increasing farmer knowledge with non-formal education, optimizing the use of biogas, and making it easier for farmers to access biogas technology in rural areas.

Concluding remarks
The increased livestock population in Indonesia has led to improved livestock waste.This waste will cause environmental pollution if it is not treated further.Animal and other organic wastes can be processed anaerobically into alternative energy, namely biogas.
Farmers in several regions in Indonesia have used livestock waste to turn into biogas as a substitute for gas stoves and wood stoves, as well as a source of lighting.However, until now, the utilization of livestock waste as alternative energy has not developed significantly due to several obstacles, especially human resources in rural areas, which on average have low formal education, are no longer productive, have limited capital, a small number of livestock, and the existence of LPG price subsidies from the Government.Nevertheless, efforts to reduce livestock waste that the Government has carried out are through the utilization and development of farmer groups, expanding the socialization of biogas technology, increasing farmers' knowledge with non-formal education, as well as optimizing the use of biogas and facilitating farmers' access to biogas technology in rural areas.

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Biogas cook stove with regulator (red in color)Clay-lined wood stove.

Table 1 .
Amount of manure and biogas from several types of livestock