Macroorganism-Assisted Bioconversion of Organic Waste by Mealworm (Tenebrio molitor): An Investigation of Process Efficiency and Sustainability

Organic waste management is still a big challenge that still requires a solution. Currently composting is a method that is commonly used, but ordinary composting takes a long time to reduce the mass of organic waste. Utilization of bioconversion agents is one strategy that can be used in processing organic waste. Mealworm (Tenebrio molitor) is an insect that can be used as bioconversion. This study aims to determine the feed consumption rate, mealworm growth, and the physical and chemical of the compost. The results showed that feed consumption increased during the incubation period with the highest level in reactor 1 with fermented vegetables using EM4 + wheat bran as feed. While the highest weight of mealworm larvae was found in reactor 3 with a weight of 196 g. The values for water content, temperature, colour are in accordance with the Indonesian Compost Standard (SNI: Indonesian National Standard). The pH decreased with the incubation period. The pH of the compost from Reactor 1 and Reactor 2 complies with SNI. Compost content of P and C/N ratio are not in accordance with quality standards, while for K the results obtained are in accordance with SNI. Where the P value obtained ranges from 0.0007 - 0.0032%, K values range from 26 - 45% and C/N ratio values range from 0.55 to 1.99.


Introduction
Every day, 175,000 tons of waste are piled up in Indonesia.Waste is transported and disposed of at the final disposal site in as much as 69%, 10% stockpile (landfill), 5% was burned, 7% was composted, and 7% was not well-managed [1].According to Nugraha et al. [2], garbage is classified as (1) 60% organic waste, 2) 15% plastic, 3) paper (10%), and 15% miscellaneous waste (metal, glass, cloth, leather).Food waste (including animal and vegetable products), vegetables, fruits, and other agricultural waste make up the majority of organic waste.If organic waste is not properly managed, it can produce methane gas, which contributes to global warming, as well as become a source of diseases, an offensive stench, and environmental contamination that can contaminate water, soil, and the air [2].
Waste processing technology is needed to overcome the organic waste problems.Common technology that frequently used is composting method.However, composting only use microorganism that take long time.Another technology is utilization of earthworm that often mention as vermicomposting.Previous studies found that vermicomposting can reduce organic waste but take long time with moderate until less reduce of the organic waste [3,4].The latest trend of reducing the organic waste is the usage 1257 (2023) 012004 IOP Publishing doi:10.1088/1755-1315/1257/1/012004 2 of insect larvae as bioconversion.One effort to increase the effectiveness of organic waste processing is to utilize waste from organic waste through insect bioconversion [5].The use of Hong Kong caterpillars or mealworms (Tenebrio molitor) as organisms that decompose organic waste is an innovation to obtain organic fertilizers that are environmentally safe and produce optimal nutrient content.In helping the bioconversion process to be carried out more quickly, it can be assisted by using the effectiveness of microorganisms 4 (EM4), where EM4 can accelerate fermentation in composting.According to previous study [6] fermentation in composting can take place more quickly with the help of microorganisms.Where, natural composting takes about 2-3 months to 6-12 months.So that EM4 can be used as an activator in composting.
The purpose of this research is utilization mealworms (Tenebrio molitor) as bioconversion to decompose organic waste with assistance by EM.

Location and time of research
The research was carried out at workshop room and environmental quality laboratory, Department Environmental Engineering, Indonesian Islamic University from March to August 2022.

Materials
The material used in this research are vegetable waste, dry leaves, mealworm larvae (Tenebrio molitor) was collected from GG Farms located at Piyungan subdistrict, Bantul Regency, EM4 (Effective Microorganism 4), wheat bran, box and plastic (next will use as reactor), and chemical for further analysis of observed variable.
The waste was prepared several days before added in the reactor.The vegetables waste was collected from small vegetables shop around the university and the leaves waste was collected from inside the university.The waste was collected then fermented using EM4 for treatment R1, R2, R4.The fermentation takes time 1 weeks.The experiment procedure: 1. Prepare the reactor that has been made.2. Put wheat bran 100 g in each reactor.
3. Add mealworm larvae (Tenebrio molitor) 125g in each reactor.4. Add the feedstock (vegetable, fermented vegetable, fermented dried leaves) following the treatment.The feed will add every 5 days.
Fig. 1 The reactor of experiment 3

Observed variable and data analysis
The variable that observed in this research are feed consumption [7], reactor temperature, and compost characteristics such as compost temperature, water content [8] using gravimetry, pH using pH meter, color and smell, C-organic and Phosphor using Spectrofotometri Uv-Vis, Kalium using Atomic Absorption Spectrophotometer (AAS), Nitrogen using Kjehdal method.The data obtained will be discussed descriptively.

Reactor temperature, feed consumption rate and mealworm weight
Temperature is one of factor that influence the organism growth.Where every organism has an optimum temperature preference to support its life.Observation of the reactor temperature is needed to find out whether the temperature is in accordance with the optimum conditions for the growth of mealworms (Fig. 2) Reactor 1 Reactor 2 Reactor 3 Reactor 4 Fig. 2 The reactor appearance Fig. 3 The reactor temperature Fig. 3 shows the temperature in the reactor which was observed for 5 days in the first week.The initial temperature ranged from 29-30 °C on the first day and fell on the second day and rose again the next day.This decrease was influenced by changes in ambient temperature where the second day it rained which caused the ambient temperature to drop.Based on previous research [9], the optimum temperature for mealworm growth ranges from 26.5-27.5 °C with 75.5% humidity.In this study the reactor temperature was higher than the optimum temperature for mealworm growth, but mealworms could grow.Based on the data, the temperature in reactor 1 (R1) is consistently higher than other reactors.It is suspected that the activity of mealworm larvae in R1 is the most active compared to other 1257 (2023) 012004 IOP Publishing doi:10.1088/1755-1315/1257/1/0120044 reactors.This is shown from the feed consumption data in R1 which is always higher than in other reactors.Where the feeding activity carried out by the larvae will release heat in the reactor Feed consumption measurements are carried out every 5 days, together with the adding of new feed.The waste (feed) given has been consumed and drastically reduced, leaving only the bones of leaves and pieces of vegetable waste.The highest feed consumption value was in R1 by feeding EM4 fermented vegetables and wheat bran while the lowest feed consumption value was in R4 by feeding EM4 fermented leaves, vegetable waste and polar (Fig. 4).

Fig. 4 Feed consumption of mealworm
The vegetable waste fed to the mealworms serves as additional water and nutrition.Based on Fig. 4, the feed consumption graph shows a decrease on the 10th day then an increase until the 25th day.The decrease in the level of feed consumption is thought to be influenced by the water content of the compost (feed that has turned into compost) where on the 10th day the compost water content increases and this high-water content reduces the feeding activity of the larvae.The average feed consumption value obtained based on Figure 3 on R1 is 99.4%, R2 is 97.4%, R3 is 97.7% and R4 is 95.7%.The increase in the feed consumption graph from day 15 to day 25 indicates the condition of the mealworm larvae which are approaching the end of their larval stage.Maha et al (2021) explained that larvae that have entered the old larval phase experience an increase in feed consumption [10].This occurs because the larvae will go to the pupal phase.Where when mealworms have reached the pupal phase, they do not eat but still can meet nutritional needs.
Observation of mealworm weight is done every 5 days for 25 days.The weight of the mealworm weighed at the beginning of the study was 125 grams in each reactor.The weight of mealworm as presented in Fig. 5. Mealworm weight will continue to increase along with incubation time.The average weight of mealworm larvae obtained in each reactor was 186 grams (R1), 182 grams (R2), 196 grams (R3) and 177 grams (R4) respectively.
Mealworms fed vegetable and wheat bran on R3 produced the highest weight of 196 grams.This is because the raw materials used have good nutritional content for the growth of mealworms larvae.In R1, the nutrients from vegetables have been reduced due to fermentation, while R2 and R4 contain dry leaves which are less nutritious so that the weight of larvae in R2 and R4 is low.In each process of observing the weight of the mealworm that was carried out, there were several larvae that experienced molting.

According to Wiglesworth (1792) [11] in Hapsari et al (2018) [12]
Molting is a process of changing the skin which is included in the growth process of insects which is conditioned by the cuticle.Mealworms that have molted will experience an increase in weight.Mealworms have a fairly hard body wall that will later change their skin or molt.

Compost characteristic 3.2.1 Compost weight
After conducting research for 25 days, the compost weight data was obtained which is shown in Figure 6.The compost weight looks unstable with increases and decreases.

Fig. 6 Compost weight
On day 5 to day 10 there was an increase experienced by R1 and R2 where the initial compost weight of 28 g and 24 g changed to 60 g and 65 g.Then on the 15th day the weight of the compost obtained was quite stable compared to the 10th day.On the 20th day, R1, R2 and R3 experienced a successive increase in weight of 63 g, 66 g and 65 g while for R4 it decreased from 67g to 63g.Then on day 25 all indicators decreased.Fluctuations in compost weight can be caused by mealworm and death mealworm consumption patterns so that the pattern produced fluctuates.

Compost temperature
On day 5 to day 10 in all reactors the temperature decreased from 25.9°C to 25.5°C (Fig. 7), then it increased again on day 15.The decrease and increase that occurred was said to be quite stable because the changes in numbers that occurred were not too far.According to Nurdini (2016) [13] the process of decreasing or increasing temperature occurs due to a reduction in the activity carried out by microorganisms in decomposing organic matter.In addition to the decomposition process by microorganisms, the temperature around the reactor also affects the temperature of the compost.The results of temperature measurements at the four reactors averaged 25.4-26°C, this indicated that the compost temperature complied with the criteria of SNI 19-7030-2004, i.e. ground water temperature of <30°C.

Compost water content
In general, the compost water content in all reactors has the same pattern (Fig. 8), where the compost water content decreases with the length of incubation time.Compost ware content on day 25 was in the range of 12-13%.

Fig. 8 Water content of compost
Diaz et al (2007) explained that when the composting process takes place the efficient water content is in the range of 45% -50%, water content must be maintained so that the microbes can function properly [14].The reduced water content of the compost is caused by the activity of microorganisms and the activity of mealworms which generate heat energy as a result of which the compost evaporates the waters and then the water content decreases.Apart from functioning to stimulate the activity of microorganisms, the water content in the compost serves to maintain the compost temperature as the compost temperature increases during the decomposition process [15].The water content obtained in this study when compared with SNI 19-7030-2004 is in accordance with the quality standards, namely below 50%.

Compost acidity
The compost pH was decrease following the time of composting (Fig. 9).The initial pH of compost was in base condition, However, in the end of composting period the compost pH in neutral condition (R1, R2) and acid condition for R3 and R4.The high pH in the initial of decomposition because of microorganism activities.Composting relies on the activity of various microorganisms, including bacteria and fungi.These microorganisms play a crucial role in breaking down organic matter.As they decompose the organic materials, they consume the available carbon and release metabolic byproducts, including carbon dioxide (CO 2 ) and water (H 2 O).This process of respiration by microorganisms leads to the production of hydroxide ions (OH -) as a byproduct.Where producing OH-will increase pH [16].In other hand, compost pH decreaseing following the time this caused by the treatment of microorganisms on waste which causes the temperature to increase and finally produces organic acids which trigger the pH value to decrease [17].

Compost colour
Based on the observations that have good compost quality are R1 and R2 because the colors produced are brown and dark brown, this is in accordance with SNI 19-7030-2004 which states that good compost has a black colour.According to Setyaningsih et al., (2017) [18] stated that black-brown compost is triggered by a fairly high water content, whereas when brightly colored compost is triggered by a low water content.This explains the value of the water content that has been obtained shows that R1 has the highest water content every week, so R1 has a darker compost color than the other reactors, namely dark brown.

C-organic, N-Total and C/N ratio of compost
Based on Fig. 10, show that C-organic was increasing in 5 day to 25 day.In the 5-day C-organic in the range 3.7-47%, meanwhile in 25 days C-organic in range 5.6-9.2,The highest C-organic was consistently found in R4.The N-total was observed on day 25, where the observations showed that the highest N-total was in Reactor 2 of 10.64%.Based on Fig. 11 The C/N ratio obtained from compost is quite small and below the SNI standard.
Factors that affect the size or size of the C/N ratio can be caused by the condition of the raw material.
If the concentration of the C/N ratio is low, the excess nitrogen that is not used up by the microorganisms cannot be incorporated.This is due to the limited carbon content in the compost, so it cannot bind free nitrogen.Then nitrogen will be released in the form of ammonia and low quality compost.The optimal concentration of the C/N ratio will be close to the C/N ratio of the soil of 12.Where this value is the best condition that can affect the efficiency of the utilization of nutrients contained on fertilizer [19].

Potassium and Phosphor content of compost
Potassium has a function in plant metabolism such as plant growth, hardening of roots and stems.In SNI 19-7030-2004 the minimum standard for potassium in compost is 0.2% and there is no maximum limit.Based on the observations that have been made, the results of potassium on day 5 and 25 are quite similar.Potassium measurement on the 25th day there was an increase in potassium levels compared to the 5th day with an average increase of 4% for each rector.This explains that the observed value of potassium in all reactors meets SNI standards.The condition of increased potassium is caused by the decomposition of organic matter assisted by K-solvent bacteria in compost which proves that the presence of microorganisms greatly affects the levels of potassium produced [20].On the 5th day, phosphorus results were obtained with a range of 0.0007% -0.0008%.This shows that the use of fermented and unfermented types of feed does not affect composting results because feed that enters the digestive system of caterpillars containing phosphate will be changed by enzymes (phosphatase) and excreted in the form of feces [21].Whereas on the 25th day the results were obtained in the range of 0.0027% -0.0032%.This said that the value of phosphorus contained in all reactors did not meet the SNI standards.on R1 the dominant phosphorus value was greater on day 5 and day 25 compared to other reactors.This is caused by the feed ingredients given in the form of vegetable waste.Vegetable waste has a high phosphorus content.This is because phosphorus is needed by plants.Plants need phosphorus for root growth and protein formation [22].Dietary manipulation can be conducted to enhance the phosporus content by adjusting the mealworms' diet to include phosphorus-rich food sources.In previous study found that frass content produce by mealworms will varies according to the insect's diet [23].

Fig. 10 C
Fig. 10 C-organic of compost