Conservation Analysis of Food Waste Composting: Insight from the Nutrient Content and Compost Quality Index (CQI) Assessment

. Compost has a critical role in preserving and conserving soil health and increasing soil fertility, both of which are essential for sustainable agricultural systems. The purpose of this research was to evaluate the efficacy of effective microorganisms (EM) in composting vegetable waste (VW), fruit waste (FW), and mixed food waste (MFW) using the Takakura Composting Method. During the 30-day composting period, nutrient content, including total nitrogen (TN), total phosphorus (TP), potassium (K), carbon to nitrogen (C/N) ratio, pH, and phytotoxicity as measured by germination index (GI), were evaluated. The compost quality index (CQI) was also used to evaluate the quality of the compost. The results showed that all VW, FW and MFW had pH values, TN, TP, K and C/N ratios that were within the acceptable range for mature and high-quality compost. The GI of VW and MFW


Introduction
The expansion of the global human population has resulted in a significant increase in the production of municipal solid waste (MSW), which encompasses many forms of waste, including food waste.The global quantity of MSW is projected to reach around 3.4 billion tons by the year 2050 [1] and currently the quantity of food waste daily is around 1.13 million tons, with fruits and vegetables accounting for approximately 38% of this total [2].According to a prior study conducted in Malaysia, it was found that Malaysians generated around 38,000 tons of MSW daily.Out of this total, an estimated 16,688 tons of waste per day consisted of food [3].
Food waste is associated with substantial economic losses, exacerbates food insecurity, and increase pressures on climate, water, and land resources, contributing to natural resource depletion and environmental pollution.In general, a massive amount of food waste is burnt or dumped in landfill sites.Food waste in landfills releases toxic substances in the soil that cause negative consequences for groundwater and also contributes to the development of greenhouse gases (GhG) in landfills.For every 1kg of food thrown at landfill, it is equivalent to 2.5 kg of GhG being emitted [4].Despite the biodegradability of food waste, their decomposition process can be lengthy, resulting in substantial timeframes for complete breakdown.
Therefore, the composting process has consistently been regarded as the optimal solution for disposing of food waste instead of depositing it in landfills.The Takakura composting method is considered a more favourable option due to its cost-effective and has a rapid decomposition rate compared to traditional composting methods through the usage of inoculants rich in effective microorganisms [3].Nevertheless, to ensure the safety of compost as an amendment in degraded soils, it is imperative to meet specific quality standards.Selecting compost type is crucial to reduce environmental impact and ensure high-quality compost recycling.By categorizing compost quality as good, moderate, or bad, can provide us with valuable guidance for selecting the most suitable compost to be used.Therefore, this study aimed to determine the comparative assessment of different types of composted food waste in terms of their maturity and nutrient content, as well as to evaluate the quality of each compost produced by using the Compost Quality Index (CQI).

Materials
Vegetable waste (VW), fruit waste (FW) and mixed food waste (MFW) was collected from the food stalls at Arked UTHM and residential college cafeterias.Takakura Composting Method (TCM) was used in this study, which utilize black soil with rice husk in ratio 2:1 as the decomposing medium.The combination of fermented soybean and brown sugar was used as effective microorganisms (EM) in this composting process to stimulate microorganisms' activity and accelerating the decomposition process of organic materials.3 L of water mixed with 250g of brown sugar and one piece of fermented soybean were fermented for a week before being used along with the decomposing medium.
The conservation analysis of the compost samples was performed in terms of pH level, nutrient content (Total Nitrogen, Total Phosphorus, and Potassium), C/N ratio and microbial counts for 30 days according to the standard method.In addition, the stability-maturity and the quality of compost produced were also be evaluated by using germination index and CQI.

Composting Process
The flow of the composting process involved 4 main steps; 1) the preparation of EM, 2) the preparation of decomposing medium, 3) the preparation of compost reactor, and finally, 4) the composting process itself.In this study, 2kg of black soil with 1 kg of rice husk were prepared properly before being added with the prepared EM and homogeneously mixed.Three composts reactors were set up in this study, according to the types of food wastes (Table 1).This experiment was carried out in 17.5 L reactors (40.0 cm x 28.5 cm x 23.0 cm) with aeration holes at the all sides, as shown in Fig. 1.The reactors were covered with mosquito net and closed to maintain their temperature and prevent insects or pests from entering.All samples were aerated by turning the pile every day in the first two weeks and once a week for the rest of the study (30 days).

Compost analysis
pH values were observed by using pH meter as done by the previous study [5].For nutrient content, digested compost samples were initially prepared by following the digestion method as suggested by Kadir et al. [6].Total Nitrogen (TN) and Total Phosphorus (TP) were measured and determined according to Method 10072 -Persulfate Digestion Method (2 -150 mg/L N (HR)) and Method 8190 -USEPA PhosVer3 with Acid Persulfate Digestion Method (0.02 -1.10 mg/L P) by using DR6000 UV-Vis Spectrophotometer, respectively.Atomic Absorption Spectroscopy (AAS) was used to determine potassium (K) concentration by following Method 311B, while CHONS analyzer was used to determined C/N ratio.Most Probable Number (MPN) analysis [7] was used to calculate the microbial counts of compost and compost extract test for germination index [8] has been used to measure phytotoxicity level.

pH value
Fig. 1 illustrates the fluctuations in pH values observed in FW, VW, and MFW, exhibiting a comparable trend.The pH values of the VW compost treatment showed a rise, transitioning from an initial pH of 6.8 to a final pH of 7.9.The pH content for FW increased from 6.4 to maximum pH of 8.The initial pH of the MFW compost was measured to be 7.4, and it subsequently increased to a final pH of 8.2.The prior study [9] has shown that the recommended pH range for compost of good quality is between 6 and 8.5, which signifies the stability of organic matter.Upon completion of the composting process, it was seen that the pH values of all compost samples were within the acceptable range.This outcome suggests that the pH levels were conducive to ensuring the compost's good quality and maturity.
The increase in pH levels from acidic to neutral implies that the acids present in the compost were depleted.The initial rise in pH during the composting process can be attributed to the generation and release of ammonia resulting from microbial activities involved in ammonification and mineralization of organic nitrogen [10,11].An effective aeration process could increase the pH level and prevent the growth of anaerobic microbes, which can lead to a decrease in pH levels.The pH values exhibited a declining trend towards the end of the composting period, ultimately reaching a state of stability characterized by alkaline values.This may be attributed to several factors, including the release of carbon dioxide as a by-product of the decomposition process, the volatilization of ammonia, and the generation of organic and inorganic acids.The release of H + from microbial nitrification during the breakdown of organic waste is responsible for the subsequent reduction in pH observed during the later stages of the composting period [11,12].

Nutrient content
Availability of nutrient content which were include total nitrogen (TN), total phosphorus (TP) and potassium (K) in compost is important to produce good quality of compost.Fig. 2 displays the TN values at the end of the composting process for FW, VW, and MFW; 2.734%, 2.875%, and 3.43%, respectively.High-quality compost has a TN concentration between 0.45% to 3.50%, and all compost samples fell within this range.Nitrogen-fixing bacteria thrived in the composting environment, producing a high N content [13].Another possible explanation for the high concentration of N at the completion of the composting process is that N is used by microbes to produce new cells, resulting in a decrease in N, but some of the dead organisms are eventually recycled as N, causing the rise in N concentration [6].
Meanwhile, Fig. 3 displays TP values of FW (0.734%), VW (0.874%), and MFW (1.09%) for the compost samples, all of which fall within the 0.2-1.55%range suggested for highquality compost.High rates of carbon loss from the breakdown of organic materials led to an increase in the concentration of phosphorus.Compost with a high TN content may have an elevated TP content due to increased microbial activity to break down P elements [14].
The chemical parameters of high-quality compost include a K content between 0.4% to 1.5%.Fig. 4 showed K content varies from 1.442% in FW compost to 1.327% in VW compost to 0.981% in MFW compost.As a result, in this scenario, every compost sample possesses the qualities associated with mature compost.The use of rice husk as a decomposing medium may account for the observed elevation in K value [15].Composting using rice husk was effective because it absorbed and held onto moisture.As moisture content is absorbed, the material's structural integrity and porosity are preserved, potentially increasing K's value [16].

C/N ratio
Table 2 represents the final ratio for all the compost samples.Compost maturity might be determined throughout the process of decomposition by measuring the C/N ratio.All of the compost samples ended up with a lower C/N ratio than they had at the beginning of the process.On day 30 of the composting period, the C/N ratio for VW compost was 18.3, 19.7 for FW compost, and 15 for MFW compost.According to Jusoh et al. [9], the final C/N ratio of compost must be less than 20 for complete decomposition to occur.However, as stated by Bernal et al. [18], a C/N ratio of 15 or less indicates that the compost has reached the proper level of maturity.These statements suggest that all the compost samples were mature and ready to be used as intended.

Microbial counts
Microbial counts in the VW, FW, and MFW were 1.53×1012 cfu/g, 1.47×1011 cfu/g, and 2.34×1012 cfu/g, respectively.The total microbial counts of MFW are the highest compared to VW and FW.Besides, total number of bacteria is far higher than that of fungi and actinomycetes, as seen in Table 3. Bacteria are essential in composting due to their nutritional value and capacity to initiate decomposition and produce heat and carbon dioxide, thus accelerating the process [19].According to Pathak et al. [20], bacteria are most active and multiply during the thermophilic phase (40°C to 60°C) as organic materials are readily available as a food

Germination index
Compost maturity and phytotoxicity may be measured with the germination index (GI).
When compost has a GI greater than 80%, it will be labelled as phytotoxin-free [21][22][23].The absence of phytotoxicity indicates that the compost is matured enough for use.As shown in Fig. 5, the compost's GI increased as the process progressed, indicating that the phytotoxicity component in the compost pile was gradually eradicated.VW and MFW completed composting with GI values of 89.1% and 82.1%, respectively, whereas 79.3% of GI value was recorded for FW.This shown that the phytotoxicity levels were slightly higher in the compost treatment for FW than in the other two.

Germination index
The following equation ( 1) represents the Compost Quality Index (CQI), which was developed using analysis parameters (Table 4) to categorize the different categories of composts quality [24].

Conclusion
The conservation analysis from the study above showed that that the pH level, nutrient content (TN, TP, and K), and C/N ratio of VW, FW, and MFW compost were all within the acceptable range for high-quality compost.The total microbial counts showed that many more bacteria than fungi actinomycetes were present, indicating that bacteria were actively growing during the thermophilic phase of composting to ensure a complete decomposition process of organic materials.In terms of the GI, VW and MFW have exceeded 80% signifies their phytotoxin free and achieved maturity level, while FW was only slightly phytotoxic with 79.3% of GI.Based on the CQI values, MFW was in very good quality compost sample, following by VW which is in good quality classification and lastly compost sample FW was moderate quality compost.In conclusion, the study demonstrates that EM may help improve and produce high-quality food waste compost within 30 days of composting.

Table 1 .
Reactors prepared in the experimental work

Table 2 .
C/N ratio of compost samples

Table 3 .
Microbial counts of compost samples

Table 4 .
Compost quality classification , we can see from Table5that the VW compost sample has a CQI of 4.24, indicating good quality compost, while the FW compost sample has a CQI of 2.92, indicating moderate quality of compost.The CQI value of 7.05 for the MFW compost sample indicates very good quality of compost.

Table 5 .
CQI of compost samples