Utilization of Agricultural Waste from Brebeg Cilacap Village Become Biogas Using Cow Manure

Straw is one of the most prevalent agricultural wastes in Indonesia, particularly in Cilacap Regency. One hectare of rice fields can yield 7 – 10 tons of dried straw every growing season. In addition, cow dung in Brebeg Village has not been utilized optimally. Cow dung and straw can be utilized as an alternative energy, one of which is biogas. Biogas is produced through anaerobic fermentation in a biodigester. Methanogenic bacteria first convert straw and cow manure in the biodigester into gas, which is subsequently produced as a high concentration of methane. This technology can be easily applied , especially for farmers and ranchers. These experiments were carried out by varying the ratio of cow dung, straw, distilled water, and the percentage of EM-4 bacteria with fermentation for 30 days in each variation. Based on the result, it is known that factors affecting biogas production are ratio of substrate, temperature, pH, and microorganisms. The best biogas is produced with a cow dung, straw, and distilled water ratio of 8:1:2 and 10% EM-4 bacteria with a flash time of 71-seconds and a blue flame. Although a particular sort of plastic is used in this laboratory-scale investigation to make it more efficient, it is prone to leaking. It is advised to use a fixed dome style of storage while scaling up the digester.


INTRODUCTION
One of the most abundant agricultural wastes in Indonesia is straw [1], especially in Cilacap Regency which is the largest district in Central Java with the average population working as farmers.A rice field with an area of 1 ha can produce about 7-10 tons of dry straw each growing season [2].This research was conducted in Brebeg Village, at a distance of 2 km from the Jeruklegi sub-district.Most residents of Brebeg Village are farmers and ranchers.Brebeg village has a total area of 531,914 hectares, of which 110 hectares are paddy fields, 281,390 hectares are dry land, and 140 hectares are used for residential purposes.Cow dung has not been used to its full potential in Brebeg Village.Breeders only utilize it as manure or even just stack it, so that it has an impact on environmental problems and social problems.Optimal utilization of cow dung and straw can produce renewable energy as biogas [1].
Biogas is a gas produced through the mechanism of decomposition of organic material by anaerobic microorganisms.The production of biogas energy is reasonably simple and has access to a wide range of organic waste raw materials [3].Biogas energy with a calorific value of 1 cubic meter is known to be equivalent 0.6-0.8liters of kerosene [4].It is possible to say that biogas can replace LPG, kerosene, and other fossil fuels.In Brebeg Village in particular, biogas technology is anticipated to be able to assist the locals in coping with the rising cost of fuel.As a result, the objective of this research is to explore the mechanism of biogas generation, assess the contribution of cow dung and straw to the quality of the biogas produced, and recommend the best handling and storage procedures for biogas.
The biogas technology that is intended as a solution to the fuel price escalation is a biodigester.This technology can be implemented immediately, especially for groups of farmers and cattle breeders.The biodigester is a container designed anaerobically (airtight) where cow dung, straw, and distilled waterferment to produce biogas [4].Cow dung and straw will be converted into gas by methanogenic bacteria in the form of methane gas with a relatively high content of 40-70% [5].
EM-4 bacteria (Effective Microorganisms) is a brown liquid with a fresh scent.A variety of microorganisms that are useful in accelerating the degradation of organic materials or waste in biogas production can be found in EM-$ baceteria.EM-4 bacteria consist of 90% Lactobacillus sp. which produce lactic acid to accelerate the decomposition of organic substance such as lignin and cellulose [6].
Biogas production research has advanced significantly, particularly with cow dung and straw as raw materials.According to Basri Katjo's research, when straw, water, and EM 4 bacteria were used to make biogas, the mixture with cow dung produced more methane (68%) than the mixture without cow dung (58%) [1].In Dwi Irawan's research, the highest biogas was produced by adding 10% EM-4 bacteria to cow dung, water, and variations of EM-4 bacteria (8%, 9%, and 10%) [7].
According to Adityawarman's research using cow dung as raw material: water = 2:1, biogas production occurs on the fifth day after the gas is first formed.However, the composition of methane gas is still not optimal.
Maximum methane gas production occurs on day 20.Production is slower because the C/N ratio is not optimal [8].The methane concentration was higher while using EM-4 3 L by 53.6%, while using EM4 bacteria 1.5 L by 46.8%, according to Aria Wicaksono's research utilizing cow manure, water, and various EM4 bacteria (3 L; 1.5 L) [9].
The addition of EM4 bacteria affects methane production.Anaerobic fermentation will degrade cellulose into methane in the presence of EM-4 bacteria.The methane produced may also be tested for the blue flame.Based on previous research, the development was carried out.This study's design included four significant independent variants, including cow dung, straw, water, and EM 4 bacteria, based on the best point from earlier research.The formulation of the problem studied in this research is the process of making biogas from cow manure and straw on a laboratory scale, determining the optimal composition of a mixture of cow manure and straw for biogas yields, and determining efficient and safe storage handling for storing biogas production results.

METHODS
In this experiment, the materials used were cow dung, straw, distilled water, and EM-4 bacteria.The series of biodigester tools is shown in Figure 1.

Biogas Reactor Manufacturing
Preparing the container that will be used as a biodigester involves installing a hose for the biogas storage tank, a valve in the lower column to check the slurry, a thermometer on the biodigester to check the temperature in the biodigester and a plastic biogas storage tube.The biogas installation in this experiment employed a batch system [10].Last, check for leaks in the connecting procedure to ensure that anaerobic fermentation occurs optimally.

Raw Material Preparation
The raw materials were prepared in accordance with the experimental design in Table 1.As Straw that has been prepared is chopped in advance to a size of 3 cm [11].
Fill the reactor tube with cow dung, straw, purified water, and EM-4 bacteria.Determination of cow dung and straw variations used in this experiment is based on the value of the C/N ratio [10].According to the calculated ratio, the chopped straw and cow manure were separately weighed and prepared.

Mixing
Mix the chopped straw with cow dung.The mixture is then diluted with distilled water followed by stirred until it is homogenous.The homogenous mixture is then added to the biodigester.Materials fill the biodigester up to around 3/4 of the total volume.

Fermentation
Fermentation was carried out for 30 days under anaerobic conditions at room temperature (mesophilic).The formation of biogas occurs through several stages consisting of hydrolysis, acidification, and methanogenesis (methane formation) [12][13].Hydrolysis is the process of converting complex biomass into simple glucose.Acidogenesis is the process of converting monomers and oligomers into acetic acid, CO2, short-chain fatty acids, and alcohol.Acetogenesis produces acetic acid, CO2, and H2.While methanogenesis is the process by which compounds are converted into methane gas by methanogenic bacteria [14].Methanogenesis is the most important in the anaerobic fermentation process.Methanogenesis is the slowest biochemical process in it's mechanism.Where this stage is sensitive to the operating conditions of the biodigester and the environment.Part of this process that directly affects the mechanism of methanogenesis includes the composition of raw materials, food ratios, temperature, and pH levels.The factors that result in the cessation of methane production are overloading on the digester, changes in temperature, and the introduction of large amounts of O2 [15].The anaerobic fermentation process for 30 days in this research is illustrated by  The pH measurement during fermentation in this study used a digital pH meter and was carried out every day by opening the faucet at the bottom of the digester, taking an adequate sample into the container, and then measuring it using a digital pH meter

Biogas Calculation and Analysis
The mass of biogas is calculated using the ideal gas equation in Equation 1.
Where P is the pressure of the biogas reactor (Pa); V is the volume of the biogas reactor (m 3 ); n is the mole value of methane gas; T is the biogas reactor temperature (K); and R is the ideal gas constant (8.314Pa.m 3 /mol.K), while biogas analysis includes analysis of the biogas flame test and analysis of methane gas levels through the Gas Chromatography Mass Spectrometry (GCMS) test [16].GCMS analysis was performed at the University of Muhammadiyah Purwokerto's Laboratory of Analytical Chemistry, using gas chromatography-mass spectrometry brand Shimadzu type QP2010 plus.Helium gas is used as the mobile phase in GC.

The Influence of Cow Manure and Straw Mixture Ratio on Biogas Production
The production of methane gas is influenced by the temperature of the digester.A temperature range of 25⁰C to 40⁰C is required for the production of methane gas [17].Figure 3 shows the changing digester temperature conditions.The temperature values obtained in this study fluctuated as a result of changes in ambient temperature and were within 1°C of the ambient temperature.The increase in digester temperature relative to ambient temperature is the result of the anaerobic fermentation process.However, since anaerobic fermentation only produces relatively small energy, the reactions that take place during the decomposition of organic matter do not significantly raise the digester temperature.Moreover, it occurred during Mujdalipah's research [15].As a consequence, temperature changes are mainly influenced by changes in ambient temperature.Change in the digester temperature is due to the anaerobic process depending on the density of microorganisms, while microorganisms are very susceptible to fluctuations in the surrounding air [12].When rainy weather results in low substrate conditions in the digester, methanogenic bacteria that feed on glucose develop more slowly and are sensitive to sudden changes in physical and chemical conditions, and vice versa.In this study, the biogas temperature was also influenced by sampling every day, so fluctuations occurred.This is presumably because the digester material used is not a heatretaining material or a good insulator so the ambient temperature affects the bacteria in the digester.This also happened in the study by Aris Kurnia et al [18].
Based on Figure 4, it can be seen that The ambient temperature in this study is the mesophilic/ no heating conditions (< 35 o C) ranges from 26,8 -27,2 o C [19] [15] and there is no significant difference every week.On the 15 th day the temperature decreased by 0.8°C then rose again on the 30 th to 27,2 °C.In general, the temperature of the biodigester tends to increase due to acidogenic and methanogenic mechanisms [19] [20].The increase in temperature in this process is categorized as exergonic, namely the release of energy during chemical metabolic processes by microorganisms to decompose organic substrates [21].The energy produced by the metabolism of these microorganisms is in the form of heat, which affects the ambient temperature of the biodigester.

The Influence of Cow Manure and Straw Mixture Ratio on Biogas Mass
The results of mass observation in each digester for all substrate variation are shown in Figure 5.In this study, samples 14-16, on the fourth day, experienced the formation of biogas.This phenomenon also occurred in Suyitno's research, which found that biogas generated on the fourth or fifth day after the digester was full [22].The average mass of biogas on day 5 was 1.677 g, with sample 14 having the lowest value at 1.649 g and sample 6 having the greatest amount at 1.714 g.The increase in biogas mass can also be seen on the 10 th day.The increase in biogas mass means an increase in biogas production during the anaerobic fermentation stage.[3].This is presumably due to the content of cow manure and the influence of environmental temperature.The biodigester's temperature is impacted by the outside temperature.This affects how well bacteria break down organic matter, which in turn affects how much biogas is produced.Due to the presence of methane-producing bacteria present in ruminant stomachs, cow dung is thought to be the most ideal substrate for the production of biogas.Ruminant large intestines contain bacteria that aid in fermentation and speed up the production of biogas in the digester [7].
Substrate levels can increase the speed of anaerobic reactions and biogas production capacity.The mass of samples 7, 8, 9, 10, and 15 all decreased, however sample 12's mass remained constant.On the 15 th day, almost all samples experienced a decrease in mass, except for the 15 th sample which experienced a not so significant increase in mass.This is probably because the outside temperature dropped.then influence lowering the digester's temperature, which directly impacts how well the decomposing bacteria perform.All samples had an increase in mass on the 20 th day, which was accompanied by a rise in the ambient temperature.
On the 25 th day, the 16 variations experienced a decrease in mass.The decrease in biogas mass is an indicator of a decrease in biogas production because the raw material for biogas fermentation in the digester has decreased.This phenomenon was also experienced by Suanggana [3] in his research, which found that biogas decreased around the 30 th day.According to the theory, it resulted from a decrease in the substrate or bacterial population, which slowed the anaerobic reaction's rate.According to Irawan's research [7], the amount of bacteria present (8%-10% EM-4 bacteria) is directly correlated with the generation of biogas.

The Influence of Cow Manure and Straw Mixture Ratio on the pH
The fermentation process's control variable in this study is pH.pH is one aspect that determines the success of biogas production [23] [24].To assess the condition of the substrate in the digester, pH is evaluated daily during sampling.The ideal pH range must be maintained, which is 6.8-7.9 [25][26] [27].The amount of biogas produced will be decreased if the substrate's pH drops since it will become difficult to convert the substrate into biogas.An acidic pH is incompatible with methanogenic bacteria, which are methane-producing bacteria during the methanogenesis stage [28].A decrease in methane production means a decrease in biogas obtained.Moreover, high pH values must be avoided.As a result, there will be an increase in CO2 output.An increase in CO2 production means a decrease in methane production [29] [28].The degree of acidity in this research can be seen in Figure 6.
Figure 6 demonstrates that the biogas's pH on the first day of formation tends to be normal, or about 7. Afterwards, all variations gradually start to reduce.On the tenth day, the pH decreased from approximately 7.1 to 5.9.The average pH was between 6 and 5 on day 15.Samples 1, 6, 15, and 16 had a pH reduction on day 20, while samples 4, 5, 7, 8, 11, 12, 13, and 14 had an increase and other samples remains constant.Similar to the previous week, no samples pH changed significantly on the 25 th day.The pH of the samples increased differently on day 30 than it had the week -0,2 0,2 0,6 before.The anaerobic fermentation process has increased, which includes the stages of hydrolysis, acidification, and methanogenic processes that play a role in raising the pH [26] to a certain peak, causing a change in the pH of the biodigester.The acidogenic and methanogenic bacteria groups are the most important groups of bacteria in the formation of biogas because these bacteria thrive and multiply in alkaline pH conditions (6.8-8.0)[27].This pH is associated with several stages of bacterial growth, beginning with the log phase, when the bacteria are adapting to the growing media and preparing to multiply through cell division, which occurs on the first day of the fermentation process.On the 2 nd -10 th day of the fermentation process, the bacteria have adapted to the media and divided themselves so that the number of bacterial populations increases very quickly and remains constant.Then it enters the stationary phase, which occurs on days 11-25 of the fermentation process, because the nutrients have been depleted and the metabolic products are toxic, resulting in the death of the bacteria.The death phase is denoted by a descending line that represents the increasing number of dead bacterial cells; this phase begins on the 26th day and continues indefinitely.
Based on Figure 6, it is shown that the anaerobic processes that occur in the digester are all under acidic conditions.This condition is difficult to avoid because the rate of reaction involving acid-forming bacteria is higher (faster) than the rate of reaction involving methanogenic bacteria.When the digester is given a starter for the first time, acid-forming bacteria will produce acid very quickly.Methanogenic populations may be less amenable to consuming the acid produced, so they are unable to maintain or achieve a neutral pH.If the pH is less than 6.5, the methanogenic population will begin to die off, and the overall bacterial population will become increasingly unstable [30].A decrease in pH indicates that the fermentation is sour due to the processes of acidogenesis and acetogenesis, where acids are formed as a result of the conversion, causing a decrease in pH and instability in the methanogenesis process [31].Instability in the methanogenesis process will then affect the rate of methane production.
To counteract the acidic conditions in the digester, an alkaline solution or a buffer solution can be added, depending on the needs.Khaerunnisa's research has shown that the addition of NH4HCO3 buffer solution can keep the pH of the digester neutral, whereas the pH of the digester without the addition of buffer is below 5 If a scale-up is required, this suggestion can be considered for further research on digester design.

Effect of Comparison of Cow Manure and Straw on Flame Test
The flame test can be observed by adding or flowing the gas from the biogas storage into the biodigester.After that, release the hose and get the candle ready for the lighter.In addition to performing the flame test, a stopwatch was also used to calculate the flame time.The calculation of the flame test begins when the methane flow interval is open and shows the flame and ends when the flame is extinguished.The flame test time is calculated for all variations.This tests for the presence of methane gas during the biogas fermentation process [33].The methane content is critical in the production of biogas because it can make the biogas flammable [34].The flame indicates the success or failure of the biogas fermentation process.The biogas process is expected to produce a blue flame, which will benefit the user when used in everyday life [33].The biogas flame test in this research is presented in Figure 7 and Table 2.It can be seen that all the gas produced by each digester can start a fire.The color of the flame indicates the heat level of the fire as well as the contents of the burning gas [35].This is evidence of the presence of methane gas that is formed [36], although in some biodigesters, the flame test is still short.A qualitative test of the biogas composition was carried out through a flame test to determine the quality of the gas produced by each variation by looking at the color of the flame during combustion during the flame test.If the color of the flame is blue and the gas produced burns immediately, the resulting gas is of good quality, similar to LPG gas [37].If the color of the flame shown is reddish, the biogas may contains more impurity gases.If the flame is barely visible (not burning), it proves that the methane content in the biogas that is formed is not much [36].
This was demonstrated in Indriani's research through the results of the gas chromatography test, where the sample with a methane concentration of 76.37% area and CO2 concentration of 0,997% area produces a red flame color, indicating the least amount of methane in the gas.While the sample with a methane concentration of 78.66% area and CO2 concentration of 0,887% area produces a dominant blue color, indicating a high methane content [4].The results of this flame are also consistent with Fairuz's research, which states that a blue flame indicates a high methane content when compared to the content of other gases besides methane [38].
Table 2 shows that 15 of the 16 variations produced blue flames, while sample 16 produced red flames.So it was concluded that 93.75% of this research resulted in a good level of fire heat and methane gas content.Brebeg locals may be able to use this renewable energy for daily purposes like cooking if the flame period of biogas with a blue flame can be extended utilizing a scale-up digester.

GCMS Analysis Results
The expected component of biogas is methane.The sample with the largest mass according to earlier computations is the variation that was evaluated by GCMS in this study.The analysis of the GCMS test of variation 4 with an 8:1:2 ratio of cow dung, straw, and distilled water and 10% EM-4 bacteria findings are shown in Figure 8.
The GCMS results in Figure 8 show the existence of methanol, which is detectable at the peak of 522 m/z region and is 0.07%, rather than the presence of methane.This methanol is the result of the oxidation of methane produced during the biogas fermentation process [39], and it is unavoidable that oxygen will enter the liquid since the liquid must first be filtered to remove any slurry or solids before it can be evaluated.Equation 2 illustrates the oxidation of methane to methanol.

CH4 + O2 →CH3OH
(2) [39] Despite calculations and flame tests indicating that there should be methane content, there is no visible methane content in the GCMS test, which only shows methanol.It is intended that the sampling procedure to be evaluated would receive more consideration in subsequent study to prevent the same error from happening.
Biogas storage is recommended in fixed dome-type storage because it is more adequate to be used as biogas storage.Storage can be chosen from materials that are rust-resistant and have minimal leakage [22].As for this research, this was a household/small-scale study, so storage

CONCLUSION
This study found that the substrate ratio, ambient temperature, pH, the proportion of EM4 bacteria, and the anaerobic digester conditions all significantly affect the biogas production process.In this study, the optimal conditions for biogas production were shown in sample 4 with a ratio of 8:1:2 cow dung: straw: distilled water and 10% wt EM-4 bacteria.This is demonstrated by the calculation of the highest mass of biogas and the results of the 71-seconds blue flame test indicating the presence of methane gas (CH4).A methanol level of 0.07% was discovered by the GCMS test.This is suspected to be methane which has undergone oxidation due to errors in the sampling process.Plastic storage was employed in this study.Given the small production size/lab scale, this is aimed at the economic worth of research, although this storage is prone to leakage.Thus, fixed dome storage is recommended if biogas production in Brebeg village is expanded.

Figure 5 .
Figure 5. Trends of Mass Observation Resultsin each Digester

Figure 7 .
Figure 7. Biogas Flame Test Graph the form of 2.5 L balloons/plastic.This is intended to be more efficient in handling and changing places but has the disadvantage of leaking easily because the storage used is made of plastic.

Table 1 .
Experimental Design

Table 2 .
Flame Color Test