A Feasibility Study of Bio-Briquettes Production from the Skin and Epidermis Layer of Cassava ( Manihot esculenta ) as An Alternative Energy

: Unprocessed leftover cassava wastes from the home industries in Pomahan Village in Bojonegoro, East Java, has become a serious problem as a pollutant to the environment. This study examined the quality of bio-briquettes made from cassava skin waste with its epidermis starch as an adhesive agent, or binder. The aim is to assess the quality of the bio-briquettes for alternative energy sources and their suitability from an economic point of view. The utilized research method was a descriptive quantitative approach by measuring water and ash content, calorific value test, and economic feasibility calculation. The results indicated that the highest calorific value of 5337.83 cal/g was obtained from a bio-briquette mix of 50 g cassava skin with 5% epidermis starch binder. This bio-briquette also possesses the lowest water and ash contents of 2.75 and 8%, respectively, compared to other mixtures. The economic feasibility calculation showed a BEP value of 423 kg/ month, B/C Ratio of 6.14-fold, ROI of 30%, and PBI of 0.2 years. In conclusion, cassava-based bio-briquettes are economically promising and environmentally friendly due to their biomass property and help to tackle the environmental problem due to the cassava waste.


Introduction
Organic waste in Indonesia has become a big problem that needs serious handling and management efforts (Gerda, 2023).Based on the Sistem Informasi Pengelolaan Sampah Nasional (SIPSN), an information system of national waste management of the Ministry of Environment and Forestry of Indonesia (KLHK) in 2022, there are 19.45 million tons of organic waste pile in Indonesia.Organic waste is commonly found from leftover foods, vegetables, peels, and fruit seeds (Prarikeslan et al., 2023, Taqiyyah et al., 2023), and as a byproduct of domestic activities such as Usaha Mikro Kecil dan Menengah (UMKM) or home industries that use paddy rice, cassava, corn, and other crops (Nugrahani & Listyarini, 2023).
Pomahan Village is a village situated in Baureno District.This district is in the easternmost part of Bojonegoro Regency, on the close border with the Babat District of Lamongan Regency.Both regencies are in the East Java Province of Indonesia.In Pomahan Village, 15 craftsmen of the UMKM made processed food products with cassava (Manihot esculenta) as the main ingredient.Each craftsman can use 50 kg of cassava to produce tape, a traditional fermented cassava-based food (Herminingrum, 2019;Anggayasti et al., 2022).Thus, all craftsmen utilize an average of 750 kg of cassava to make tape.Such process will result in 150 kg of cassava skin waste.However, the cassava skin waste from tape production usually gets dumped anywhere near the village's housing area, leading to air pollution due to the decomposition process (Linggi & Pawarangan, 2018) and taking up free spaces.
Cassava skin has high levels of carbohydrates that reach 72.49-85.99% of its total mass (White et al., 2022) possibly in form of linamarin (Anggayasti et al., 2022).This property makes it likely to be an alternative energy source candidate.Therefore, this study will attempt to process cassava skin waste as bioenergy to avoid burdening the environment, as previously reviewed in cases of African countries (Oghenejoboh et al., 2021;Veiga et al., 2016).The increasing popularity of bioenergy is considering the growth of the human population, which is inversely proportional to the existence of fossil energy (Setyono & Purnomo, 2022).The use of organic wastes as bioenergy becomes one of the solutions both to provide eco-friendly energy as well as to reduce environmental pollution (Akam et al., 2024).
The choice of cassava as a renewable energy source becomes increasingly popular worldwide, be it in form of substrate for ethanol fermentation (Akaracharanya et al., 2011) or biogas, bioethanol (Ridwan et al., 2023), and biohydrogen (Andrade et al., 2022).Cassava skin wastes that are appropriately managed will become a commodity with high economic value (Rohimah & Kurnia, 2021;Azzahra et al., 2023).Organic waste from tape production could even be used as a biomass for efficient and economically profitable alternative fuel (Utami et al., 2021), which is also environmentally friendly (Obi et al., 2022).
Briquettes are alternative fuels made from organic wastes, which may have different calorific values depending on the biomass used (Sulmiyati & Said, 2017).Besides that, the addition of a suitable binder will increase the briquette's hardiness against outer pressure and add its calorific potential (Yuliati et al., 2021).The choice of adhesive agent or binder also plays an important role in holding ash particles together (Jannah et al., 2022;Obi et al., 2022).
For the first time, this study will generate cassava skin-based briquettes by using the epidermis layer starch of the cassava tuber as binder.Previous studies elaborated the benefits of cassava skin for bio-briquettes; however, tapioca powder was used as binder for both cases (Puri et al., 2022;Berlian et al., 2023).Hence, this study aims to analyse the feasibility of cassava skinepidermis starch combination for making bio-briquette from the economical point of view and the quality assessment.These assessments will help to determine the bio-briquette quality and potential as a substitute for fossil energy, as well as solving the environmental problem caused by cassava waste in Pomahan Village, Bojonegoro Regency.

Method
This study utilized experimental methods with descriptive quantitative data analysis based on briquette quality assays and economic analysis.Raw material collection was done in Pomahan Village, Baureno District, Bojonegoro Regency.Laboratory experiments were done in the Laboratory of Entrepreneurship, Faculty of Agricultural Technology, and the Laboratory of Combustion Engine, Faculty of Engineering, both in Universitas Brawijaya Malang.

Data Collection
The main ingredients used in this study were cassava skin and epidermis layer starch.The types of equipment used were drum, sitting scales, machetes, 40mesh sieves, pounders, buckets, stainless steel blades, measuring cups, stoves, and ovens.The equipment for product analysis included platinum or porcelain plates, digital balance, desiccators, and weigh bottles.The research flow chart is presented in Figure 1.The Production of Bio-Briquette Bio-briquette production generally initiated by waste collection from home industries and moulding (Masyruroh & Rahmawati, 2021).For this study, firstly, cassava skin waste collected from Pomahan Village was weighed.After that, the collected waste was dried under direct sunlight for three days.The dried skin waste is shown in the upper part of the flowchart of Figure 1.The collected waste was then processed in a pyrolysis machine for 2 h.Lastly, the output product was ground and sifted with a 40-mesh sieve.
The epidermis layer of cassava root was collected by scratching the peeled cassava root with a knife until as many as 25-30 grams of epidermis starch was collected.The starch was dried with direct sunlight for three days before being ground and sifted.The pyrolyzed cassava skin waste in form of biochar (Figure 1) was mixed with the epidermis starch binder.The percentages of the starch used were 5, 10, 15, and 20% (g/g) of the total mass of 50 g.The mixtures were moulded with a briquette press machine at 20-30 MPa.The produced bio-briquette has a diameter of 2.2 cm with a thickness of 4 cm.Lastly, the bio-briquettes were dried under direct sunlight for three days, as illustrated at the end of flowchart in Figure 1.

Measurement of Water Content
The calculation of water content was conducted according to the formula and procedure described previously (Meiliyadi, 2017).The formula used is as follows.
Whereby: m1 = the weight of empty container m2 = the weight of container with sample m3 = the weight of container with sample after drying

Measurement of Ash Content
The ash content of the produced bio-briquette was estimated with the protocol and formula described in a previous study by Triantoro et al. (2019).

Economic Analysis
This analysis is aimed to assess the economic feasibility of a business form to be done (Rusdianto et al., 2020).The practical aspects considered in this study are the estimation of profit and loss and the business feasibility analysis.The latter consists of the Break Event Point (BEP), B/C Ratio, the rate of Return on Investment (ROI), and Pay Back Period (PBP) (Yusniati et al., 2021;Kasmi et al., 2023).The last parameter calculates the expected period for the business investment to be returned.

Result and Discussion
As many as four bio-briquettes were successfully produced in this study.These types were categorized based on the percentages of cassava's epidermis layer starch used in the mixture, namely 5, 10, 15, and 20%.The resulting bio-briquettes are presented in Figure 2. The visibly highest consistency and firmness were reported for the binder percentage of 5%.Further, the quality of the four bio-briquette types was examined by water content, ash content, and calorific value tests.The lower the water content of a biobriquette, the easier it is to ignite (Akbari et al., 2022).In contrast, higher water content means that the biobriquette will not be easily used for combustion (Akbari et al., 2022), increasing risk for decay, and unwanted chemical reactions (Fauzana et al., 2023).The determination of the water content is meant to measure the ability of the bio-briquette to absorb moisture in each composition.The water content will significantly affect the calorific value (Tira et al., 2023).The result of the biobriquette water content calculated with formula (1) can be seen in Table 1.The numbers indicated that each briquette with 5, 10, 15, and 20% binder had water contents of 2.75, 3.20, 2.95, and 3.31%, respectively.All water content percentages are deemed satisfactory because it is less than the Indonesian national standard (SNI) value of 8% (Aziz et al., 2019).However, as can be seen in the data, the increasing amount of adhesive may cause the moisture content of the adhesive to bind with the ash.The water moisture becomes difficult to evaporate due to the higher density of the bio-briquette (Aziz et al., 2019).The next quality parameter is the ash content, as calculated with formula (2).Ash is an easily combustible material, although the inorganic content is not (Cholilie & Zuari, 2021).The result of the ash content test can be seen in Table 2. Table 2 showed that the highest ash content of 12% is in sample B and D, which used the binder mixture of 10% and 20%.Meanwhile, the lowest ash content of 8% can be found in sample A which had 5% of adhesive.Similar with water content, the ash content will crucially determine the calorific value.Lastly, calorific value is an indicator to measure the heat produced by a biobriquette as a fuel.The higher calorific value of a briquette, the higher the quality of the briquette (Haliza & Saroso, 2023).The test results as calculated with formula (3) can be seen in Table 3.Based on the results in Table 3, it is known that the highest calorific value is produced by the bio-briquette with 5% binder, which is 5337.83cal/g.In contrast, the lowest value is that of the bio-briquette with 20% binder, which is 4162.26cal/g; since the higher amount of binder is used, the higher the density of the bio-briquette (Nasrul et al., 2021).Therefore, the calorific value gets reduced, which explains why the lowest percentage of adhesive, which results in lesser density, exhibits the highest calorific value.
In comparison with calorific value of the previous studies, the value obtained for the mixture with 5% cassava starch adhesive in this study (5337.83cal/g) is higher than that of cassava peel briquette with 5% tapioca binder at 2680 cal/g (Berlian et al., 2023), with lower water and ash contents.It is also higher than the calorific value of 90 : 10 mixture of corn husk and cassava peel at roughly 3186 cal/g (Waheed et al., 2019).The calorific value in this study is about the same as 5771 cal/g value obtained by durian peel briquette with 10% tapioca binder (Jannah et al., 2022).It is suspected that the use of cassava starch binder promotes higher calorific value, as pointed out by another study using durian peel mixture with 10% cassava starch binder, which gained 5880 cal/g (Suppalakpanya et al., 2020).However, this hypothesis needs further testing.
Other than the quality parameters of the biobriquettes, this study also reviewed the economic feasibility of the bio-briquette production.The first component to be counted is the production cost, where the amount of the cassava skin waste was calculated based on the cost being paid.There are two categories: production cost (Table 4) and fixed cost (Table 5).The next observation is the estimation of profit and loss which is based on: (1) the main ingredient, namely the cassava skin waste; (2) the binder, namely the epidermis layer starch; (3) the cassava skin waste used daily in form of 100 bio-briquettes; and (4) effective production period which was 26 days in a month.With the assumption that the price of the bio-briquette is Rp.7,800/kg, therefore: Income = 100 kg x 26 days x Rp. 7,800 = Rp.20,280,000 /month Profit = total income-total production cost (Table 4) = Rp.20,280,000 -Rp.3,300,000 = 16,980,000 /month The last component is the analysis of business feasibility, with the calculations as follows.
Break Event Point (BEP) BEP = Total production cost/price per kg =Rp.3,300,000 /Rp.7,800 = 423 kg/month Thus, it can be said that the business will reach an impasse if as many as 423 kg of biobriquette can be sold per month.
B/C Ratio B/C Ratio = Total income/Total production cost = Rp.20,280.000/Rp.3,300,000 = 6.14 From the above estimation, it is understood that in each modal unit being used, the obtained income will be 6.14-fold of the modal unit.Based on the results, the production of biobriquettes from cassava skin waste with epidermis layer starch as adhesive has a potential for mass-production and can be deemed profitable in terms of economically valuable waste management (Septianingrum et al., 2023).The payback period is also especially faster compared to other study (Kasmi et al., 2023).As this study represents the first attempt to assess the quality of cassava-based bio-briquettes with cassava epidermis layer, it adds the economical values of cassava wastes itself as potential renewable energy.

Conclusion
The best mixture of bio-briquette in this study is 50 g cassava skin waste with 5% epidermis starch binder.This type of biobriquette had the highest calorific value of 5337.83 cal/g and the lowest water and ash content.If the adhesive amount exceeds 5%, the calorific value will get lower.It is thought that the starch binder may play a role in increasing the calorific value, which warrants further study.Based on the analysis of production economic feasibility, the capital will be returned if 423 kg of bio-briquettes are made and sold per month, with an expected profit of 30%.Thus, the income generated will be 6.14 times the production cost of Rp. 54,975,000.This capital return is estimated to happen within 0.2 years, or about 2-3 months.Therefore, the production of this cassava-based bio-briquette is profitable as an alternative, renewable energy source.From the environmental point of view, the production of cassavabased bio-briquettes does not emit high levels of pollutants.Using cassava skin as main ingredient for bio-briquette will help to reduce organic waste especially in Pomahan Village of Bojonegoro Regency, thus keeping the sustainability and hygiene of the environment.

Figure 1 .
Figure 1.Research flowchart weight of empty container m2 = the weight of container with sample m3 = the weight of container with sample after dryingMeasurement of Calorific ValueCalorific values were counted using the formula stated in a current research(Setiawan & Nurhidayah, 2021) as following.

Table 1 .
The Water Content of Each Bio-briquette

Table 2 .
The Ash Content of Each Bio-briquette

Table 3 .
The Calorific Value of Each Bio-briquette

Table 4 .
The Bio-briquette Production

Table 5 .
The Fixed Cost of Bio-briquette Production

Table 6 .
Results of Economic Feasibility Calculations