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Sustainable Management of Fish Gut Waste Through

Transesterification

R.T.A.J.K.L. Rathnasekara, I.B. Wjethunga, E.R.J.M.D.D.P. Wijesekara, A.M.P.C. Amarasinghe and E.P.R.H.H.W.

Nilmalgoda

Department of Biosystems Technology, Faculty of Technology, Sabaragamuwa University of Sri Lanka, Belihuloya, 70140

boiling. The extracted fish oil was then converted into biodiesel through a transesterification reaction with methanol in the

presence of potassium hydroxide (KOH) as a catalyst. Two optimization experiments were conducted to determine the best

methanol concentration (15%, 20%, and 25%) and KOH concentration (1g, 2g, and 3g). The results showed that the highest

biodiesel yield was obtained using 20% methanol (producing 10.71g of biodiesel) and 1g of KOH as a catalyst, yielding a

biodiesel production of 8.66g for 15% methanol and 6.89g for 25% methanol. The biodiesel produced exhibited promising fuel

properties, with a flashpoint of 127.5°C, a calorific value of 39.248 MJ/kg, kinematic viscosity of 4.4107 mm²/s, and density of

0.8766 g/cm³, all of which were within the acceptable limits set by ASTM standards. Additionally, the FFA content of the

extracted fish oil was initially 7%, which was reduced through a saponification process, making the oil suitable for biodiesel

production. The study estimated that approximately 237 metric tons of biodiesel could be produced per month from the fish waste

in Sri Lanka, based on the average monthly fish waste generated (50% of total fish production). The biodiesel production from

higher quality of life. Global energy demand has increased by 2.9% in 2018, and current predictions indicate that consumption

will be increased by 30% to 740 million TJ by 2040 [3] [4] . The primary sources of global energy consumption are fossil fuels

such as coal, oil, and natural gas and these fuels account for more than 80% of the world's energy consumption [5].

Traditional sources have a finite availability, and their extraction, transportation and use cause significant environmental impacts

[6][7]. Moreover, the growing global demand for energy, driven by population growth and increased industrialization, has led to a

global energy crisis, marked by price volatility, supply disruption, and environmental degradation [8] [3] [9]. Presently, the global

warming effect, depletion of fossil fuel reserves, and higher petroleum prices are the main issues driving worldwide interest in the

development of alternative biofuels. Biodiesel is an alternative resource that is sustainable, affordable, and environmentally

friendly [5] [10] [11].

Biodiesel is a mixture of long-chain mono alkylic esters from fatty acids derived from renewable resources [12] [13]. It has

sources provides sustainability to the process providing a solution to the generated waste [22] [23] [24]. In this regard, waste

cooking oil and waste animal fat have been used as feedstock for biodiesel since it does not have a conflict with food security

especially when it is impossible to commit land to produce biodiesel as the world population grows denser [25] [26].

The oil from discards of marine fish which is a first generation biofuel source has been found to be a plentiful, affordable source

of biodiesel [27] [28] [29]. Sri Lanka, being an island country has a long history of fish consumption dating back many centuries

and its per capita fish consumption rates are one of the highest in the world [19]. Sri Lanka’s per capita fish consumption was 13

kg as of 2015 and the government of Sri Lanka have taken many initiatives to increase the per capita fish consumption to 22 kg

by 2020 [30] [31]. Although the fish production is rising, 40% to 50% of it is lost in handling and processing [32]. Fish waste is

high in protein, low in saturated fat, and contains fatty acids that are well-known for their numerous health benefits. Sri Lanka

caught 486170 MT of fish are in 2012, of which only 40–60% was utilized for production. Fish markets and fish processing

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utilized the transesterification process where the lipid reacts with the alcohol in the presence of a catalyst. On the other hand, this

study serves as a sustainable waste management solution for the fishing community that faces numerous health issues due to

unsustainable fish waste handling.

II. Methodology

Fish waste sample preparation

The fish waste used in this current study was collected from the Negombo fish market (7⁰12’36” N 79⁰49’52 E) where less

valuable nonedible parts of fish, like heads, tails, fins, and organs, were taken as fish waste to produce biodiesel (Figure 1.).

Additionally, chemicals like sodium hydroxide, methanol, and potassium hydroxide were used for the experiment.

Fig 1. Fish viscera waste

Oil extraction procedure

Oil extraction from the fish waste was done using wet boiling extraction method. Firstly, 6 kilograms of fish waste was boiled for

1 hour at 100

C. Then the mixture was kept for 24 hours to settle after which the upper layer was collected for further processing.

Analysis of fatty acid methyl ester (FAME) composition of oil

Titration method was used to analyze the FAME of the extracted soil to ensure that it is at an optimum range to continue the

100ml of 0.1M NaOH solution. If high amount of free fatty acids (FFA) was observed, it was reduced using saponification

Transesterification process

Transesterification reaction process was done where fish oil was mixed with methanol and 1% w/w (KOH) to act as a catalyst.

Potassium hydroxide (1g) was dissolved in a beaker containing methanol (8.7g -20% by the amount of fish oil) and agitated

continuously in a magnetic stirrer till the potassium hydroxide dissolved completely and formed potassium methoxide, a strong

caustic. The above-formed potassium methoxide was mixed with 45g of fish fat under agitation the fish oil is heated until it

reaches 60˚C for 1 hour. Then the mixture was transferred to a separating funnel and the contents were allowed to settle down,

and the two distinct layers the top layer being bio-diesel and the bottom layer of glycerol were separated. After separating the

glycerol, the methyl ester was washed twice with a 1:1 volume of water for 1 hour to remove excess methanol. Using this

transesterification method, two experiments were done. First experiment was to analyze biodiesel production yield using different

amounts of methanol percentages (15%,20% and 25%) and the second experiment analyzed biodiesel production yield using

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sample within the bomb. After that the sample was ignited completely in the presence of oxygen, releasing heat that was absorbed

by the bomb calorimeter, typically filled with a known quantity of water. The temperature of the water within the calorimeter was

monitored throughout the combustion process. The change in temperature of the water within the calorimeter was recorded as the

sample burned. This temperature change was used to calculate the heat released during combustion. The Calorific Value (CV) of

fish oil biodiesel was automatically displayed. CV is usually expressed in joules per gram (J/g) or, more commonly, in kilojoules

per gram (kJ/g).

Density and viscosity

The viscosity is a liquid measurement of its resistance to flow due to internal friction and it is an essential feature of diesel fuel

since it affects the engine's fuel injection system when it is cold. The kinematic and dynamic viscosity and density of the biodiesel

samples were measured by Anton Paar SVM 3001 viscometers. The viscometer underwent thorough cleaning with an ample

amount of toluene, ensuring the removal of any residues from previous analysis. Then the viscometer was calibrated meticulously

present, it should be noted that the biodiesel component must pass a flash point test before blending. In the present study,

flashpoint of the biodiesel sample was measured by PMA 500 Pensky - Matens flash point tester. Initially, a 50ml volume of fish

oil biodiesel was introduced into a test cup, which was then positioned within the apparatus. This equipment featured a heating

mechanism that progressively elevated the sample's temperature. Simultaneously, a flame ignition source was applied to the

sample's surface at regular intervals. With the rising temperature, vapors emanating from the sample had the potential to form an

ignitable mixture with air. The flashpoint denoted the lowest temperature at which this ignition process occurred.

The Pensky-Martens apparatus incorporated a detection system designed to identify the flashpoint by recognizing the presence of

a flame or other indicators of ignition. The entire procedure adhered meticulously to the ASTM-D93B standard, ensuring both

consistency and accuracy in flashpoint determination. The PMA 500 tester, distinguished by its Pensky-Martens design, delivered

a trustworthy and standardized approach for evaluating the flashpoint of fish oil biodiesel. While biodiesel has a higher flash

indicated that the initial FFA content was 7%. According to the literature, maximum biodiesel production could be achieved with

a FFA content of 2.2%. The FFA content was reduced using saponification to get an optimum FFA value for the process.

Calculation of FFA

Amount of NaOH consumption

FFA mass

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waste.

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The key properties measured were kinematic viscosity, calorific value (CV), flashpoint, and density. The biodiesel exhibited a

kinematic viscosity of 4.4107 mm²/s, which falls within the ASTM standard range of 1.90–6.00 mm²/s, indicating that it is fluid

enough for proper engine injection and combustion. The calorific value of the biodiesel was 39.248 MJ/kg, which aligns with the

ASTM standard range of 35–43 MJ/kg, confirming that the fuel provides adequate energy content similar to conventional diesel.

The flashpoint was measured at 127.5°C, well above the ASTM minimum of 93°C, ensuring that the biodiesel is safe to handle

and transport, with a reduced risk of ignition under normal conditions. Lastly, the density of the biodiesel was 0.8766 g/cm³,

which is within the ASTM range of 0.860–0.900 g/cm³, indicating that the fuel has an appropriate energy density for effective

combustion. Overall, the biodiesel from fish oil produced in this study met the essential ASTM standards, demonstrating that it is

a viable and safe alternative to fossil fuels, with suitable properties for use in diesel engines.

The monthly biodiesel production potential in Sri Lanka was calculated using the data obtained through the experiment and the

available literature data. According to the calculation, approximately 237 MT of biodiesel can be produced per month using the

fish waste in Sri Lanka as presented in the Table 4.

Table 4. Calculation of monthly biodiesel production potential

and yield. Its properties like Flash point (127.5℃), CV (39.248MJ/kg), Viscosity (4.410 mm

2

/sec), and Density (0.876 g/cm

3

)

were in the close range to the ASTM standards which proves the efficiency of the produced biodiesel. The significance of this

research extends beyond mere biodiesel production as a solution to the fuel shortage but also to find an effective solution to the

waste management aspect of fish waste within the community. However, it is vital to conduct comprehensive compatibility

studies of fish waste oil biodiesel blends and existing boat engines to ensure adherence to standards to avoid negative impacts on

the environment and performance. Moreover, optimization of the blending methods is important to enhance fuel characteristics,

combustion efficiency and stability

Author Contributions: E.P.R.H.H.W.: Conceptualization, methodology; R.T.A.J.K.L.: formal analysis, writing—original draft;

E.P.R.H.H.W., A.M.P.C. and E.R.J.M.D.D.P: supervision, project administration; I.B.: writing—review and editing. All authors

Amount of fish waste generated per month (50% of the production)

Amount of biodiesel produced per 1 Kg of fish waste

Sample

1

2

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