Utilization of clam shell waste through circular economy activity in Tangerang Regency coastal area

Tangerang Regency is a coastal district with a substantive potential for marine resources, particularly in Ketapang Village, Mauk District, Tangerang Regency. Significant quantities of fish, shrimp, and shellfish are produced. About 86% of the population makes a living as fishermen. As producers of shellfish, there are several entrepreneurs with daily boiling capacity ranging from 0.5 to 1 ton. Although this business has economic potential, it has a negative influence on the coastal environment. Consequently, circular economy activities are required to address these issues. This study aims to analyze the potential of clam shell waste, the potential alternative for circular economy activity to deal with clam shell waste, and the added value of clam shell waste management. The results indicate that the six shellfish stripping units have the capacity to generate 4.1 tons of clam waste each day. As an alternative, the mollusc shell can be processed commercially into animal feed . Clam shell flour has a potential selling price of Rp. 11,930 per kilogram depending on its Cost of Goods Manufactured (COGM). Optimal management of discarded clam shells can prevent negative environmental impact and give economic value to the community.


Introduction
As a connection between land and ocean, coastal regions play a significant role in national and regional economic development.Coastal lands continue to increase in value along with the rising socio-economic development and population growth.As a result of these activities on the coast, utilization management conflicts develop due to competing interests in the coastal zone [1].
Tangerang Regency has abundant marine resource potential, particularly in Mauk District, particularly Ketapang Village.This area contains one of the prospective marine resource locations.In Ketapang Village, the production of fish, shrimp, and shellfish is substantial.In 2017, Ketapang Village had a population of 6,542, and 86% of the population is supported by fishing.This circumstance renders Ketapang Village a coastal village [2].
Based on initial observations, there were six shellfish boiling businesses, each with a daily boiling capacity at 0.5 -1 ton.This business provides a substantial economic value potential for Ketapang Village.According to this study, one unit of clam boiling business can employ between 10 and 15 people.Each individual receives a per-kilogram wage of Rp 3,000.00.On the other side, the huge economic potential of clam boiling has negative consequences, such as the continued accumulation of clam shell waste.Currently, clam shell waste is either piled on muddy land or thrown into the river.These accumulated shells can be harmful to human health because they contaminate the raw materials of drinking water.Consequently, it is necessary to build a "Circular Economy" in the community to manage clam shell waste.In fisher's settlements, it is necessary to devise a plan for utilizing clam shell waste to promote economic growth and environmental sustainability.
The utilization of clam shell waste has been widespread, including the production of souvenirs, a concrete mixture, animal feed, etc.However, the use rate of clam shell waste in Ketapang Village must become the main factor in its management.This condition is occurred due to the large and rapid production of shellfish waste.
These are the objectives of this study: 1) Calculate the potential of clam shell waste, 2) Identify alternative "circular economy" activities in handling clam shell waste; and 3) Assess the added value of clam shell waste management in Ketapang Village, Mauk District.

Circular economy
The circular economy seeks to maximize the potential of each material to recover those that have reached the end of their final age.The Circular Economy Action Plan is a traditional feature rejection concept for economic growth (e.g., mass production, non-renewable resource usage, production of preserved goods, etc.), but offers innovative solutions to conserve natural capital and enhance social welfare [3].
The circular economy concept is ggoverned by the available resource maximization and waste minimization.The use of resources, waste, emissions and wasted energy are minimized by closing the production and consumption cycle by extending product life, design innovation, maintenance, reuse, remanufacturing, recycling to original products, and recycling into new products (upcycling).

Shellfish flour
Shellfish are soft invertebrates belonging to the Bivalvia or Pelecypods of the Mollusca phylum.In general, the five body sections of clams are the foot byssus, head, digestive and reproductive organs, membrane (mantle) and shell.
Mouth and sensory nerve organs are located on the head.The color and shape of the shell varies greatly depending on the species, location and nutrition.Shellfish typically exhibit bilateral symmetry with a mantle resembling lobes or earlobes and a symmetrical shell.Several muscles that leave the curved traces are known as mantle lines, that attach the mantle to the shell.The outer surface of the mantle serves to exude organic matter from the shell and deposit calcite or lime crystals.The shell has three layers, namely: 1) A thin, protective exterior layer termed periostracum; 2) A thick second layer composed of calcium carbonate; and 3) An inner layer of mother-of-pearl generated by the mantle in the shape of a thin layer.As the animal ages, this thin layer causes the shell to thicken [4].
Clamshell flour is a mineral source material that typically originates from marine animals in the form of milled shells with high carbonate and calcium content [13].
Shellfish is a source of protein rich in calcium, essential amino acids, especially arginine, leucine, and lysine.In addition to the meat, the shell can also be utilized in the preparation of shellfish.Therefore, shellfish shells can be utilized as animal feed due to their high calcium content.However, people prefer to use shellfish and marine organisms just for their meat and have not exploited them for other highvalue commodities such as ornamental items, handicrafts, and animal/fish feed (Kartono et al, 2021).
The shells of shellfish can be ground into flour, which is the the primary component of animal/fish feed.Shellfish flour is a mineral source material that often derives from marine animals in the form of milled shells that are rich in carbonate and calcium [4].

Methodology
This study was located in Ketapang Village, Mauk District, Tangerang Regency, as the epicenter of the clam-boiling industry, which has the potential to generate shellfish waste.Primary data are utilized to address the goal of this study.Field observation, survey gathering, and in-depth interviews provided the primary data on the business of boiling clam shells in Ketapang Village, Mauk District.

Analysis method
3.1.1.The potential of clam shell waste.This study determined the length of the shells, the whole weight, the weight of the contents, and the weight of the shells on 200 shellfish samples.Then, the proportion of bulk weight to the whole weight and the proportion of bulk weight to the shell weight were calculated.The high potential of shells from shell stripping production in Ketapang Village, Mauk District, Tangerang Province was utilized to determine the potential for waste formation.
Bulk weight to the whole weight proportion (%) = Bulk weight (Gram) Whole weight (Gram) x 100% (1) Bulk weight to shell weight proportion (%) = Bulk weight (Gram) Shell weight (Gram) x 100% (2) Clam shell waste per day (gram) = shell weight per unit per day (gram) x numbers of shell stripping unit (3) 3.1.2.Circular economy in clam shell waste handling.This study highlights the economic value of using clam shell waste to create a circular economy for the community by identifying the type of business that can utilize clam shell waste.One of the economic activities associated with the utilization of clam shell waste is its transformation into animal feed.Through the sale of high-quality animal feed, the usage of clam shell as animal feed can enhance the household's financial situation.Additionally, it can reduce the animal feed cost, which is more expensive than average on the market.Animal feed nutrition derived from shellfish can improve the quality of livestock.
In this investigation, animal feed formulae derived from clam shell waste were identified.Alternative feed formulas are created by identifying the available raw materials in the community, so that feed can be produced at a reasonable cost without sacrificing the required nutrients.The prepared diet refers to the requirements of the animals throughout the layering period (egg-laying phase).The composition of the ration is based on the feed provided.Using Microsoft Excel and a solver, the rations were calculated based on the premise of a general linear model using the trial-and-error method.The diet is developed in accordance with SNI 2017, whereas Table 1 presents the composition of feed ingredients and the nutrient content of the ration for laying ducks.
Table 1.The composition of feed ingredients and nutrient content of feeding ration for laying ducks.

Clam shell waste
After the calculations of 200 green mussels, the average length of the shells was 6.2 cm and the average intact weight was 9 g.The whole weight of the clam consisted of 3 g of meat and 6 g of shell.Thus, it can be deduced that the entire weight of the shellfish is only about 31.98% of the overall weight.Also, it indicates that when clams are stripped, more shell waste will be collected than the weight of the shell contents.The weight of the clam shell is around 68.02%.In addition, the average weight ratio of the contents to the shell is approximately 48.05%.This calculation is displayed in Table 2. Source: primary data, 2021 (processed) In Ketapang Village, Mauk District, Tangerang Regency, there are six shellfish stripping business that produce around a ton of shellfish every day.Thus, the resultant shell weight per business unit each day is 684 kg, if multiplied by six business units of shellfish peeling, the daily production of clam shell waste is around 4.1 ton.Each month, there will be 123,09 tons of shellfish waste.The creation of clam shell waste in Ketapang Village can result in environmental problems.

Circular economy in clam shell waste handling
The circular economy approach relies on the product innovation and management systems to ensure that the materials are as long as possible.The circular economy is not only associated with environmental added value, but also with the creation of new economic and social added values, such as community empowerment.As there is an absence of community awareness regarding the management and utilization of clam shell waste, the adoption of a circular economy for the management of clam shell waste is necessary.
Utilizing clam shell waste can alleviate the shell waste problem and make it more efficient.In addition, it can provide alternative solutions for the economic well-being of the community through the utilization and management of clam shell waste and dissemination of further knowledge about the management of clam shell waste.
The nutritional value of clam shell can be used to boost the added value.It is vital to diversify goods that can be utilized as a natural calcium supply because clam shell nutrients contain minerals, most notably calcium.According to Prawirohartono [5], the clam shell is composed of three layers of lime: 1. Periotraktum (outermost layer), which is the thinnest, darkest, and composed of horny substance; 2. Prismatic, a thick middle layer composed of prismatic CaCO 3 crystals; and 3.The pancreas (the deepest layer), also known as the pearl layer, is composed of CaCO3 crystals that are fine and distinct from the crystals in the prismatic layer.
According to Basri et al. [6], shellfish waste can be used as animal feed, which can be converted into a meal via direct milling or combustion.Shells can be milled into a variety of forms, including coarse (grit) and fine (flour) mills, making the milling method advantageous for shell processing.In addition to being a source of nutrients, grit from clam shells can also aid the digestion process in the gizzard.Meanwhile, the meal-based products can be administered to ruminants as licking blocks or mineral blocks.The combustion approach can improve the concentration of Ca minerals during processing.The combustion process also serves as a sterilizer and grinding agent [6].
In addition, Agustini et al. [7] revealed that the optimal usage of clam shell in the food processing process has not been achieved.They determined how clam shell flour could affect the quality of cookie items.Calcium was extracted from clam shell through protein hydrolysis method with hydrochloric acid (HCl) solution.The concentrations of 0%, 5%, and 7.5% clam shell flour in cookie dough varied throughout the treatments.Increasing the concentration of clam shell flour had a significant (α = 0.01) impact on the cookie's moisture content, ash, fat, protein, calcium, phosphorus, and hardness.The (hedonic) preference test was insubstantially affected (α = 0.01) by this therapy.The addition of 7.5% shell flour yielded cookies with the highest calcium content (6.57%), phosphorus content (1.58%), ash content (6.95%), carbohydrate content (52.31%), and cookie hardness value (1.06 kg).The panellists preferred the addition of shell flour at 5% concentration.
Based on Ridho et al. [8], only mussel meat is consumed by the community, while the shells are considered as waste and unutilized properly.For the exploitation of mussel shell waste rich in calcium carbonate, an adequate waste management strategy is required to become more economically valuable.For example, this product can be utilized as the ingredient part of various cosmetic goods.This activity was successful in raising the economic added value of mussel shell waste with beneficial impact on the local economy by increasing the income of entrepreneurial cadres.
According to Kurniasih et al. [9], the grit content of mussel shells contains Calcium (Ca) at 30-40%, Phosphorus (P) at 1%, and protein at 3-4%, which can become an excellent supplement for livestock and pets, including laying ducks, broilers, native or broiler chickens, laying hens, plunge chickens, ornamental chickens, fighting chickens,, and grain-eating birds such as wench and walnut.In addition to providing appropriate calcium, phosphorus, and protein, clam flour functions, this product can also be used as a mechanical decomposer of chicken food in the gizzard.Moreover, clam flour has a great deal of potential for animal production and growth.Using a grinding process, shellfish shells are turned into shellfish grit grains rich in calcium, phosphorus, and protein.Furthermore, this shellfish grit can raise stamina, improve egg quality, prevent paralysis, reduce anemia, prevent nail and beak deformities, etc.This project will highlight the economic value of clam shell waste utilization as animal feed for the Tangerang community by adapting the past studies.It is anticipated that selling high-quality animal feed will increase the household's income.In addition, it can reduce the market's reliance on expensive livestock rations and increase the quality of livestock.

Formulation of animal feeds from clam shell waste as a circular economy activity
Duck cultivation is a system for obtaining outcomes from ducks to fulfill the human requirements.The organizational structure pertains to the notion of the livestock triangle, which includes breeding, feeding management, and environmental management [10].Ducks are raised for meat production, egg production, and meat and egg production (hybrid), depending on their roles.
Most of the duck farming is devoted to egg-laying ducks because farmers rely on their products for daily income.Egg-laying ducks are females that have been in the layer phase for 20 to 22 weeks and have a production span of 15 months.Efficiency is the primary factor that must be considered in duck farming.If seeds, feed, the environment, and animal health are correctly maintained, it is possible to attain maximum efficiency.Indicators of poultry efficiency can be quantified by the FCR (Feed Conversion Ratio), as the ratio of feed to egg production.
The feed formulation was based on the requirements of laying ducks in the layer phase (egg production phase).The feed is produced from the mixed ingredients provided as meal.Four alternative feed formulations tailored to the availability of feed ingredients in Ketapang Village, Mauk District, and Tangerang Regency are shown to ensure the availability of feed ingredients.Table 3 presents the composition of the ration and the nutrient content of layer alternative 1.This ration was created with rice bran and Aking rice as the energy supply, shrimp waste, trash fish, and maggots as the protein source, and clam shell flour as a mineral source.The price of this ration is Rp 3067.30per kilogram, or Rp 46,009.50 per day (consumption of 15 kg per day for 100 ducks).Alternative feed 1 can be used if trash fish can be obtained to limit the amount of shrimp and maggot waste.With fluctuating prices, the inconsistent availability of waste fish will affect feed production.If trash fish is difficult to find, alternative feed 2 might be utilized.However, it is hypothesized that the quality of feed 2 is worse than feed 1 (the protein content is somewhat lower), as the constituent elements are less diverse.The cost of alternative 2's benefits is less remarkable.Table 4 presents the composition and nutrient content of layer alternative 2 ration.Alternative 2 rations are prepared without trash fish, hence increasing the utilization of maggot and shrimp waste.The cost of alternative feed 2 is Rp 3007.30per kilogram of feed, or Rp 45,109.50 per day (100 ducks consume 15 kg of feed per day).The downside of alternative feeds 1 and 2 is high dose of rice bran.By incorporating nutrient-rich bean sprouts into the diet, it is possible to reduce the usage of rice bran.Rice bran is a highly susceptible ingredient material to adulteration with husks or sawdust; therefore, if bean sprouts waste feed sources are available, superior diets can be prepared at a reduced cost.Table 5 presents the composition of the ration and the nutrient content of layer alternative 3. Alternative 3 rations are created in anticipation of the excessive usage of rice bran susceptible to adulteration, which is difficult for farmers to verify its quality.In this proportion, a cheaper price is reached at IDR 2,972.30per kilogram of feed or Rp 44,584.50 per day (consumption of 100 ducks 15 kg per day).This ration boosts the crude protein level while decreasing the crude fiber content.According to several studies, the presence of up to 20% crude fiber in ducks does not impair their digestive health or significantly diminish their performance.Adding trash fish as an available alternative feed can reduce the crude fiber content and improve protein content, resulting in the feed cost increase.The composition and nutrient content of the ration for layer duck feed alternative 4 is presented in Table 6.
Table 6.The composition and nutrient content of the ration for laying ducks as alternative 4. Alternative feed is composed of all basic ingredients by notifying the nutrient balance improvement.Alternative 4 feed has a greater feed cost than alternative 3 and 2 feed, but is still less expensive than alternative 1 feed.The feed cost in the fourth ration formulation is Rp 3032.30per kilogram of feed, or Rp 45,484.50 per day (consumed by 100 ducks per day with 15 kg of feed).Alternative 4 feed is optimally administered to ducks on the condition that feed ingredients are always available.

The value-added of clam shell handling
Clam shells can be ground as animal feed ingredient meal.Based on the experimental results, 1 kilogram of clam shells may generate the same amount of meal as 1 kilogram.Thus, the potential for clam shells in Mauk Village, Ketapang District, is sufficient to 4,103 ton of clam shell meal.
The added-value generated by the sale of this clam shell flour can be estimated.It is possible to calculate the cost of goods manufactured (COGM) by summing all parts of production expenses.In addition, COGM is calculated by dividing the total production cost by the quantity of products or expected products.The determination of COGM is essential for external reporting in inventory value and profit determination, and it can also be used to inform decisions regarding product selling prices and pricing strategies.
Mulyadi [11] stated that the COGM determination method determines the production-based cost elements.There are two methods for determining the production elements: full costing and variable costing.Full costing is an estimation method that takes into account all parts of production costs into COGM, including the costs of raw materials, direct labor, and production.According to full costing, factory overhead expenses are both variable and fixed; hence, COGM is comprised of production cost parts.According to Mulyadi [11], variable costing is a method for calculating COGM that solely considers production expenses that apply internal variables (COGM), such as raw materials, direct labor costs, and factory overhead costs.
Consequently, it can be concluded that the objectives and benefits of determining the COGM are a basis for determining the selling price, assessing the production process efficiency, monitoring the realization of production costs, and determining the profit or loss on a periodic basis.In determining the production cost, it must be appropriately and clearly categorised.The result of calculating the production cost of clam shell meal is shown in Table 1.
Table 7 presents the production costs for animal feed at Rp 19,750,000,000.The COGM/kg of the clam shell meal is Rp 19,175,000 / 2,250 = Rp 8,522 per kilogram.This calculation is obtained from available data that 75 kg meal is produced per day, followed by 30 productions that are carried out per month, then 75 kg meal is multiplied by 30 equals 2,250 kilograms of meal per month.The COGM of clam shell meal is computed by dividing the total production cost by the quantity of flour produced.In addition, determining the optimal selling price is a technique to entice consumers to purchase clam shell flour.The selling price of a product or service is comprised of the company's production expenses plus the desired profit margin.The following factors will affect the selling price per kilogram of clam shell flour.In Ketapang Village, the added value of processing clam shell waste into animal feed is Rp 7,668,000 per month.According to the calculation results, animal feed from clam shell waste has the potential to generate a profit, as the selling price can be less than the market price, hence attracting buyers to pay less.

Conclusion
The following are the findings of this investigation: 1) The bulk weight of the shells is only about 31.98% of the whole weight;.In Ketapang Village, Mauk District, Tangerang Regency, there are six shellfish stripping businesses with a potential daily waste output at 4.1 tons.2) Circular economic activities highlight the economic worth of utilizing clam shell waste as animal feed for the community by enhancing the family economy through the sale of excellent animal feed.Additionally, it can reduce the cost of rations for livestock, if purchased on the market, and can increase the cattle quality.3) Based on four alternative formulas for duck feed, the alternative 4 has the most nutritionallybalanced feed ingredients.4) The sale price of clam shell meal indicates that the added-value (profit margin) of clam shell is Rp 3,408 per kilogram.

Figure 3 .
Figure 3. utilization of clam shell waste into animal feed.
Value-added in clam shell waste handling.Quantitative and qualitative descriptive analysis was utilized.The quantitative points are: 1) Possibility analysis for minimizing clam shell waste 2) Added value analysis of clam shells based on the estimation of clam shell meal production cost (COGM).

Table 2 .
Generation of clam shell waste in Ketapang Village, Mauk District, Tangerang Regency.

weight of shellfish (Gr) The length of shellfish (Cm)
6Source: primary data, 2021 (processed) Figure 2. Correlation of length and whole weight, content length and weight, length and clam shell weight.

Table 3 .
Composition and nutrient content of the ration for laying duck feed as alternative 1.

Table 4 .
The composition and nutrient content of the ration for laying ducks as alternative 2.
Note: laying ducks were able to produce up to 100 heads with a daily feed intake of 15 kg.

Table 5 .
The composition and nutrient content of the ration for laying ducks as alternative 3

Table 7 .
Production cost of clam shell meal.

Table 8 .
Selling price of shellfish meal.According toTable 8, the selling price per kilogram of shell mealr is Rp 11,930.If the expected profit is 40%, then the selling price per kilogram of clam shell meal is calculated as: (40% * Rp 8,522) + Rp 8,522 = Rp 11,930 per kilogram.The profit margin on the sale of clam meal is Rp 3,408 per kilogram.