Formation and Characterization of Leaf Waste into Organic Compost

doi:10.21203/rs.3.rs-2376791/v1

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Formation and Characterization of Leaf Waste into Organic Compost

https://doi.org/10.21203/rs.3.rs-2376791/v1

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published 25 May, 2023

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In solid waste management, pollution-free disposal of leaf waste in urban areas is still not standardized and adopted. This project was designed to undertake and understand the composting of leaf waste and characterizing the organic fertilizer formed from it. The composting of the leaf waste was set up through the essential microbe (EM) method to produce compost. Different parameters like pH, electrical conductivity, macronutrients, micronutrients, and heavy metals contents were measured at zero to fifty days of composting using appropriate methods. Leaf waste composting attained its maturity within 21–40 days of composting. The values were used to calculate its fertility index based on six parameters like total carbon, total nitrogen, phosphorus, potassium, and sulfur contents. The Potentially Toxic Elements (PTE) and trace elements in the compost were analyzed through ICP-MS. An analysis was also done on samples of other popular matured composts like Kitchen Waste compost, Vermicompost, Cow dung manure, Municipal Corporation of Delhi (MCD) organic waste compost, and Neem cake compost. Arsenic, Chromium, and Mercury were high in all the compost except the leaf waste compost. The trace elements such as Ba, Be, Se, Ti, Tl, and V concentrations were moderate in all the compost. The PTE values were used to calculate their clean index. It was found that leaf waste compost has very good fertility index only next to Neem Cake Compost and has the best clean index. Leaf waste compost could be categorized as good quality compost.

Leaf Waste

Bio-organic Fertilizer

Clean Index

Fertilizing Index

Potentially Toxic Elements

Good Quality Compost

Solid waste management has become a challenging task for metropolitan cities like New Delhi, in developing countries. According to the Central Pollution Control Board report 2021, India generated 160038.9 tonnes per day (TPD). Of this, only 50% of the waste is treated, and about 18% is landfilled. A large junk of about 32% of the waste generated still remains unaccounted for, which is a significant concern (CPCB, 2021). Delhi alone generated about 10990 TPD of solid waste, and only 5193 TPD (50%) are treated whereas the majority of 5533 TPD are landfilled. Generally, the most common methods adopted for the treatment and disposal of solid wastes are composting, recycling, pyrolysis, mechanical and biological treatment, gasification, waste-to-energy, and landfilling (Psomopoulos et al., 2009). Composting has been adopted as a means of sustainable waste management in developing countries since it can lead to the production of organic fertilizer. This practice can generate income with low operational cost with relatively low air and water pollution (Taiwo, 2011). Over utilization of chemical fertilizers has caused extensive contamination of the environment with hazardous chemical pollutants (Chauhan, 2020). Excessive and disproportionate use of chemical fertilizers led to the depletion of carbon in the soil, soil degradation, compaction, and nutrient leaching. It has also caused nutritional stress in the soil (Hakeem, 2021; Lin et al., 2019). Thus, there is a need to shift towards organic farming to some extent, for sustainable agricultural production with less environmental pollution. The prolonged application of organic fertilizers such as compost and manure has been reported to be associated with replenishing organic matter, nutrients, and microbiomes in the soil (Kaur et al., 2005; Wu et al., 2020). Applying organic fertilizers can prevent nutrient leaching and soil erosion. It also improves the soil structure, texture, aeration, and water-holding capacity (Chen et al., 2021; Tadesse, 2020). It has been reported that the application of organic fertilizers such as compost can bioremediate heavy metal contamination in the soil (Huang et al., 2016; Irfan et al., 2021; Mohkam-Singh, 2022). However, there are some limitations to using organic fertilizers. These are slow starters for plant growth since the nutrients are not immediately available to the plant as the mineral fertilizers. In addition, the preparation of organic fertilizers involves a lengthy period of treatment and a higher cost of production. The distribution of these organic fertilizers in soil is non-uniform and can lead to pathogen contamination (Alegbeleye and Ana, 2020; Rousseaux et al., 2005; Sikora, 1998). Additionally, contamination with potentially toxic elements (PTEs) such as Arsenic, Cadmium, Chromium, Lead, Lithium, Nickel, etc. has been a constant concern about the quality of the compost (Farrell and Jones, 2009; Mariachiara et al., 2005). This PTE contamination of the compost has been primarily attributed to the non-segregation and contamination of the substrates (Malamis et al., 2017). Compost as organic fertilizer should have high fertilizing potential but should not have heavy metals and pathogens contaminations. Production of high-quality compost is a necessity for its application in agriculture. There have been studies to analyze the quality of the composts produced from municipal organic solid wastes and other types of organic waste such as kitchen waste (Devi et al., 2019; Reyes-Torres et al., 2018; Rich et al., 2017). Nevertheless, the comparative analysis of different types of composts qualities has not been comprehensively done and reported. This study is done to perform the comparative qualitative analysis of the Leaf waste compost with other types of compost such as Kitchen Waste compost, Vermicompost, Municipal Organic waste compost, Cowdung manure, and Neem Cake compost. Since Leaf Waste is homogenous and possibly has less contamination, it can be used to produce high-quality compost.

2.1. Leaf Composting, Sample Collection and Preparation

The leaf compost was produced from the leaf litter waste at the recycling unit, Daulat Ram College, University of Delhi. The leaf wastes were shredded with mechanical shredders and composted in a bin at ambient temperature using a decomposer (Waste Decomposer from the National Centre of Organic Farming) for 50 days. Samples (0.5kg) of the leaf compost were collected in a zip-lock polybag after every 10 days of composting. Six samples (1 Kg) of other types of bio-composts viz. kitchen waste compost, vermicompost, cowdung manure, neem cake compost, and the composts of Municipal Cooperation of Delhi (MCD compost) produced from municipal organic waste, were collected from different sources in and around Delhi-National Capital Region, India. All the samples were air-dried, gently ground, and sieved through a 1–4 mm sieve. The samples were stored at room temperature or 1 to 4⁰C for further analysis. The physicochemical parameters, nutrient contents, metals and trace elements contamination were analyzed through appropriate methods as given below.

2.2. Analysis

2.2.1. pH and Electrical Conductivity (EC)

The pH of the composts was measured using a pH meter and an EC meter respectively. For the analysis, the samples were dissolved in distilled water in a ratio of 1:5 and thereafter measurements were carried out.

2.2.2. Carbon Nitrogen and Sulfur (CNS)

The macronutrients such as Carbon, Nitrogen, and Sulphur in the composts were analyzed by CHNS analyzer (varioEL cube, Ser.no: 19171021). About 6–10 mg of the samples were weighed and placed in the sample holder of the instrument. The combustion and reduction temperatures were set at 1150⁰ C and 850º C. And the helium pressure was set at 1200 milli-bar.

2.2.3. Micronutrients, Heavy Metals, and Trace elements

The samples were heat-digested using tri acids (Hydrofluoric (HF), Nitric acid (HNO₃), and Per-chloric acid (HClO₄) on a hot plate. For this processing, samples (0.5 g) were taken in a Teflon crucible, and a mixture of 10 ml of concentrated HF, 5 ml of HNO₃ and 2 ml of HClO₄ was added to it. These samples were then heated on the heating plate at 90⁰C for 4 hours with the lid closed. After 4 hours, the lids were opened, and heating continued until it was completely dried. A mixture of 5 ml of concentrated HF, 10 ml of concentrated HNO₃, and 2 ml of HClO₄ were added and continue heating until dryness with the lid open. Again, 10 ml of the concentrated HNO₃ was added and heating continue at 90⁰C with an open lid, to achieve complete dryness. Thereafter, 20 ml of 1N HCL was added and continued heating (90⁰C) for a while to bring the samples into the solution with the lid closed. The solution was then, transfer to the volumetric flask. The Teflon crucible was rinsed 2–3 times with 1N HCL and MilliQ water and poured into the measuring flask to avoid any sample loss. The final volume was made up to 100 by adding the MilliQ water. The diluted solution was filtered using the Whatman paper no.2 or 42. The filtrate was subjected to another filtration using 0.45-micron filter paper under vacuum pressure. Then, the filtered solution was stored at 4⁰C before they were analysed in Inductively Coupled Plasma- Mass Spectrometry (ICP-MS) for the analytical measurements. The filtered solutions were diluted 20 times using 1% HNO₃ before taking the reading. The measurements were carried out using iCAP-Q ICP-MS from thermo Scientific in KED (kinetic energy discrimination) mode. The calibration curve was obtained using serially diluted solutions of certified references material SQC001 (Metal in soil, Sigma) of different concentrations. The measured data were analysed using QTEGRA ISDS software and the reported values are average of three independent measurement runs.

2.2.4. Statistical Analysis

The parameters analysed were subjected to one-way ANOVA analysis using Graphpad Prism 9.0 software to identify the statistically significant variation of the analytical data among the samples.

3.1. Formation and Maturation of Leaf Waste Compost

The compost formation and its maturation from the leaf waste as substrate were analyzed from 0 to 50 days of composting by measuring the parameters such as pH, EC, Total Organic Carbon (TOC), Total Nitrogen (TN), Total Sulfur (TS), and calculating the C: N ratio. The pH of the leaf substrate was neutral before composting, but it turned to a moderately alkaline state after 10 days of composting. By 20 days, it was observed to be slightly acidic, and then it was increased to a moderately alkaline state and stabilized from 30 days to 50 days of composting at pH 7.92. The EC was observed to steadily increase from 0 to 50 days of composting, from 0.662 mS/cm to 1.405 mS/cm. The C: N ratio of the leaf substrate was initially observed to be 35.77 which steadily decreased from 10 to 30 days of composting, and then stabilized at around 15 after 40 days of composting. The stability of the pH, EC, and C: N ratio indicated the onset maturity of the compost formation within 30 to 40 days of composting (Fig. 1.).

The maturation of the leaf waste composting was attained within 30 to 40 days of composting as observed from the stability of the analytical values of the pH, EC, C: N ratio, and total organic carbon. The pH of the leaf waste compost became stabilized at a moderately alkaline state after 30 days of composting till 50 days, which is an indication of the compost maturity (Cayuela et al., 2008). The EC of the leaf waste compost steadily increased till 50 days of composting from 0.661 to 1.405 mS/cm. The EC of the leaf waste compost was well below the recommended level of the quality control limit of 4 mS/cm according to the Fertilizer Control Order (FCO) Standard 2013, Government of India. The EC of the leaf waste compost stabilized between 30 to 40 days of composting at about 0.9 mS/cm, which indicated that the stability of the compost could be achieved after 30 days of composting (Avnimelech et al., 1996). The total organic carbon content of the leaf waste compost decreased as the composting progressed from 0 to 50 days of composting, but became stabilized after 30 days of composting at about 32 to 33%. A decrease in the organic carbon content and its stabilization indicated that the process of composting was undergoing maturation (Goyal et al., 2005).

The C: N ratio is another indicator of compost maturity and stability. The C: N ratio of the leaf waste compost decreased as the composting progressed from the initial value of 35 to 15 at the end of the composting. The C: N ratio of the leaf waste compost became stabilized after 40 days of composting. The C: N ratio of 10 to 15 is considered the ideally matured and stabilized compost, also the C: N ratio ranging from 15 to 20 has also been commonly accepted (Rashwan et al., 2021). According to the FCO guidelines, the compost used as organic fertilizer should have a C: N of less than 20.

Depending on the type of substrate, composting organic waste to produce matured compost could take different periods or a number of days (Mahapatra et al., 2022). Microbial degradation of the organic matter into matured compost generally involves four phases. The initial phase is the mesophilic phase in which mesophilic microbiome actively involved in the decomposition, followed by thermophilic phase in which the temperature is increased above 45⁰C due to the increased activity of the microbiome. In this phase, thermophilic bacteria become active and the temperature sensitive bacteria began to die off. In the third cooling phase, when the organic matters are almost degraded, the temperature began to drop and return to the mesophilic phase where the mesophilic bacteria began to re-emerge again. The final phase is the maturation or curing phase in which the compost are allowed to mitigate from any pathogens (Biyada et al., 2021; Meena et al., 2021; Nemet et al., 2021).

3.2. Comparison of Mature Leaf Waste Compost with other types of Organic Composts

3.2.1. pH and EC

The pH of the composts was uniquely different in all the compost, although mostly alkaline except for the Neem Cake compost, which was acidic. The Kitchen Waste compost (pH − 9.16) was highly alkaline. The Vermicompost (pH – 7.97), MCD Organic waste compost (pH – 8.13), Leaf compost (pH – 8.26), and Cow Dung manure (pH – 8.40) were moderately alkaline. Whereas, the Neem Cake compost (pH – 5.51) was the only compost that had an acidic pH value. The analysis of variance showed that the variation of the pH among the different types of composts was statistically highly significant. The pH of the compost could be moderately acidic or alkaline, depending on the properties of the substrates used to produce the compost. The compost that is to be used in agriculture should have a pH ranging from 6–8.5, which is an indication of their relative stability (Crohn, 2016). The lower pH value of the compost is not desirable since organic acids can be phytotoxic to the plants.

The electrical conductivity (EC) of the composts was observed to be within the recommended value of less than 4 mS/cm. The Neem Cake compost and Kitchen Waste compost have the highest EC values of 1.07 and 1.06 mS/cm respectively. The Vermicompost has the lowest EC of 0.56 mS/cm. The Leaf compost and Cowdung manure have similar EC values of 0.66 mS/cm. The MCD Organic Waste organic compost has an EC value of 0.97 mS/cm. The variation of the EC among the composts was statistically significant. The high EC value indicates a high nutrient content in the compost. If EC is too high, then it can have a non-specific and specific impact on crop development. High nutrient content can generate a high osmotic gradient that prevents plants from obtaining the nutrients and water they require. Alternatively, by absorbing specific non-nutritive ions in excess that can be toxic to plants and directly affect crop development. It can also indirectly affect plant growth by displacing more vital nutrients in the plant with non-nutritional ions (Morales and Urrestarazu, 2013). As per the FCO guideline 2013, the EC of the compost should not be more than 4 mS/cm for an ideal compost (Table 1).

Table 1

**The pH, EC, and macronutrient contents of different composts**: This table gives the observed values of pH, EC, C, N, P, K, and S in different types of composts. The comparison of significant variations of the parameters in the leaf waste compost with other types of composts was done through multiple comparisons of one-way ANOVA. * indicates the level of significance, *(P < 0.01); **(P < 0.001); ***(P < 0.0001); ****(P < 0.00001).
Parameter/ Compost Type	Kitchen Waste Compost	Vermi Compost	Cowdung manure	Neem Cake Compost	MCD Organic Waste Compost	Leaf Waste Compost	Safety limits (FCO 2013)
pH	9.16 ± 0.52*	7.97 ± 0.48	8.40 ± 0.66	5.50 ± 0.36****	8.13 ± 0.06	8.26 ± 0.27	6.5–7.5
EC (mS/cm)	1.06 ± 0.40	0.56 ± 0.204	0.66 ± 0.255	1.07 ± 0.093 **	0.97 ± 0.082 **	0.66 ± 0.11	> 4.0
Total C (%)	22.09 ± 3.95 *	15.26 ± 2.08****	10.51 ± 3.58 ***	29.94 ± 3.26	13.87 ± 1.40***	31.75 ± 2.24	< 14
Total N (%)	2.67 ± 0.45	1.24 ± 0.15***	0.98 ± 0.23 ***	2.86 ± 0.18 **	1.60 ± 0.13 **	2.23 ± 0.10	< 0.5
C: N ratio	8.28 ± 0.61***	10.3 ± 1.52 **	0.73 ± 2.04 *	10.46 ± 0.90 **	8.71 ± 0.74 ****	14.26 ± 0.57	< 20
P (%)	0.14 ± .00 *	0.13 00	0.12 ± 0.00	0.16 ± 0.00 *	0.11 0.00	0.071 ± .00	< 0.5
K (%)	0.07 ± 0.0 ***	04 ± 0.0 **0	0.09 ± 0.0 ***	0.16 ± 0.0 ***	0.15 ± 0.0 ***	0.14 ± 0.0	< 0.5
S (%)	0.59 ± 0.09	0.49 ± 0.13	0.40 ± 0.10	0.67 ± 0.04	0.88 ± 0.14 *	0.38 ± 0.17	< 0.5

3.2.2. Macronutrients

The Leaf Waste compost has the highest total carbon content at 31.75%, which could be used as a good amendment for the soil. The Neem cake compost has the second highest total carbon content at 29.94%, followed by Kitchen Waste compost (22.09%), Vermicompost (15.26%), and MCD Organic Waste compost (13.87%). Cow dung manure has the lowest total carbon content at 10.51%. The variation of the total carbon content among the composts was statistically very significant. The total organic carbon content in the compost should not be less than 14 per cent by weight. The organic carbon promotes soil structure with excellent stability, enhancing soil aeration and water retention and preventing nutrient leaching and erosion. The organic carbon content is also crucial for chemical composition and biological productivity of the soil (Corning et al., 2016).

The total nitrogen contents were detected to be high in all the composts, and their variation among the composts was statistically very significant. The neem cake compost has the highest total nitrogen content at 2.86% and the cow dung has the lowest value at 0.98%. Nitrogen is an essential macronutrient for plant growth and development, which is critically involved in many important functions such as the photosynthetic process, phyto-hormone activities, and plant biomass production (Crawford and Forde, 2002). Insufficient nitrogen availability to the plant can significantly hinder its growth and development. Nitrogen has a significantly important role in the improvement of root growth, which can ultimately enhance the nutrient uptake, nutrient balance and dry mass production of the plant (Diaz et al., 2006).

The Leaf Waste compost has the highest value of the C: N ratio of 14.26, whereas the Kitchen Waste compost and MCD Organic Waste compost have the lowest C: N ratio of 8.28 and 8.71 respectively. The other composts have a C: N ratio of about 10. The variation of the C: N ratio among the compost was statistically very significant. The C: N ratio is essential in determining compost maturity and quality. The compost used as soil amendment should have a C: N ratio of less than 20 (Crohn, 2016). The higher C: N ratio leads to the immobilisation of the nitrogen, which rendered it unavailable to the plant, whereas, the lower C: N ratio stimulates the gradual mineralization of nitrogen made available for the plant (Bruun et al., 2006). All the composts analyzed in this study have a C: N ratio of less than 20, which is suitable for soil amendment.

The Phosphorus (P) contents in all the composts ranged from 0.071 to 0.162%, which was not statistically significant. The Neem Cake compost has the highest phosphorus content at 0.162%, and the Leaf Waste compost has the lowest value at 0.071%. The Neem Cake compost has the highest Potassium (K) content at a concentration of 0.161%, and the Vermicompost has the lowest potassium content at 0.036%. The Sulphur (S) content was high in all the composts, with statistically very significant variation. The Leaf Waste compost has the lowest S content, and the MCD Organic Waste compost has the highest S content at a concentration of 0.387% and 0.886%, respectively. According to the FCO guidelines, the P and K contents in the compost that are used as organic fertilizer should not be less than 0.5% of the dry matter. The composts analyzed in this study have P and K less than the recommended levels. The deficiencies in P and K can have many adverse effects to plant growth and development, such as seedling growth impairment, chlorosis, reduced plant biomass production, delayed maturity and fruit development (D.Atkinson, 1973; Thornburg et al., 2020). Such nutrients must be fortified and enriched in the compost to be used as bio-organic fertilizer. Sulfur is another essential nutrient for plant growth and development. To supplement the sulfur content in the soil, the compost should have a sulfur content of not less than 0.25% of the dry matter (Dan M. Sullivan, 2018). The sulfur contents in the composts analyzed were well within the optimal level of 0.25–0.8%, according to the FCO recommendation (Table I).

3.2.3. Micronutrients

The composts analysed has a sufficient amount of micronutrients such as Boron, Manganese, Cobalt, Molybdenum, and Zinc. Neem cake compost has the highest B content (53.01mg/kg) whereas Kitchen Waste compost has the lowest B content (10.16mg/kg). The Cow Dung manure has the highest Mn content at 482.68 mg per kg, and the leaf compost has the lowest Mn content at 184.03 mg per kg. The MCD Organic Waste compost has the highest contents of Co, Cu, and Mo at a level of 4.03, 298.46, and 10.63 mg per kg, respectively. The Leaf Waste compost has the lowest content of the said elements at the concentration of 1.10, 25.90 and 2.32 mg per kg, respectively. The Kitchen Waste compost has the highest Zn content at 504.15 mg /kg, and the Neem Cake compost has the lowest Zn content at 45.64 mg/kg.

The optimal concentration of the micronutrients such as B, Mn, Co, Cu, Mo, and Zn in the compost is essential for the compost if used as a soil amendment. A high concentration of such elements could be harmful to the plant, and a very low concentration could hinder the plant's growth and development. According to the FCO guidelines, the maximum concentration of Cu and Zn in the compost to be used as bio-organic fertilizer should be 300 and 1000 mg/kg of the dry matter, respectively. All the composts analyzed have CU and Zn contents below the permissible limits, although MCD organic waste compost has maximal Cu content near the maximum permissible limit (Fig. 2.).

3.2.4. Potentially Toxic Elements (PTEs) and Trace Elements

The contamination of the composts with the PTEs such as Arsenic (As), Cadmium (Cd), Chromium (Cr), Mercury (Hg), Lead (Pb), Lithium (Li), and Nickel (Ni) was analyzed. It was observed that the Leaf Waste compost has the least contamination with PTEs, as their contents were all below the permissible limits according to the FCO guidelines. The Arsenic content was observed to be high in the Cow Dung manure, Kitchen Waste compost, Vermicompost, Neem cake compost, and MCD Organic Waste compost. The Leaf Waste compost has the least Arsenics content at 3.76 mg/kg. The variation of Arsenic contents in the different groups of the compost was not statistically significant.

Table 2: The content (in mg/kg) of Potentially Toxic Elements (PTE) in the composts: This table gives the observed values of the PTEs in different types of composts. The comparison of variation of the PTEs content in the leaf waste compost with other types of composts was done through multiple comparisons of one-way ANOVA. *(P < 0.01); **(P < 0.001).

Element	Kitchen Waste Compost	Vermi Compost	Cowdung Manure	Neem Cake Compost	MCD Organic Waste Compost	Leaf Waste Compost	Safety limits (FCO 2013)
As	15.14 ± 0.30	13.52 ± 0.25	23.71 ± 0.50	13.18 ± 0.20	9.70 ± 0.27	3.76 ± 0.08	10.0
Cd	1.36 ± 0.07	0.63 ± 0.10	1.17 ± 0.03	0.26 ± 0.00	3.29 ± 0.09 *	0.20 ± 0.00	5.0
Cr	86.74 ± 1.23	70.99 ± 0.67	88.98 ± 0.93	72.99 ± 0.08	318.52 ± 6.04	39.71 ± 0.90	50.0
Hg	0.12 ± 0.00	0.12 ± 0.00	0.15 ± 0.02	0.18 ± 0.00	0.37 ± 0.05	0.07 ± 0.00	0.15
Pb	33.78 ± 0.68	28.57 ± 0.38	20.45 ± 0.33	12.40 ± 0.16 **	77.29 ± 0.72	17.85 ± 0.23
Li	7.00 ± 0.68	6.01 ± 1.15	7.37 ± 0.83	6.64 ± 0.33	15.88 ± 0.52	2.85 ± 0.40
Ni	7.49 ± 0.10	7.29 ± 0.12	8.94 ± 0.12	5.40 ± 0.07	29.39 ± 0.41	3.15 ± 0.10	50.0

The cadmium content was seen to be above the permissible limit in the MCD Organic Waste compost. The Neem Cake and Leaf Waste compost were observed with the lowest Cd content. The variation of Cd content in different composts was statistically significant. The Cr contents in all the compost were high except the Leaf Waste compost. The MCD Organic waste compost has the highest Cr content at 318.52 mg/kg. The variation of the Cr content in composts was not statistically significant. Mercury was observed to be high in the MCD Organic waste compost, Neem Cake compost, and Cow Dung manure. The MCD Organic Waste compost has the highest contamination with Pb, Li, and Ni whereas, Neem Cake compost has the lowest Pb (Table 2).

In this study, leaf compost was seen with the least contamination with PTEs such as As, Cd, Cr, Hg, Li, and Ni, as their concentration was well below the maximum permissible limits according to the FCO guidelines. Due to the homogeneity and purity of the leaf substrate, the compost produced from leaf waste is reported to be less contaminated with PTEs (Dmuchowski and Baczewska, 2011). Most of the composts analyzed were found to be contaminated with arsenic and chromium. Arsenic and chromium are toxic to plants affecting various processes from root growth, germination and biomass production to fertility and fruit production (Finnegan and Chen, 2012; Shanker et al., 2005). Mercury is another toxic element found high in all the composts analyzed except the leaf compost. It was detected to be above the maximum permissible limit in the MCD organic waste compost and neem cake compost and just near the permissible limit in the kitchen waste compost and vermicompost. Mercury contamination could cause deformities in the seedling, nodules and ultra-structural development in the plant (Mondal et al., 2015). MCD compost was also seen to be high in Lead, which is toxic to plants, affecting root development (Fahr et al., 2013). Contamination of the compost with potentially toxic elements is a significant concern for its application in agriculture. Many municipal solid waste composts produced in different Indian cities, the United States and European countries have been reported to be contaminated with PTEs (He et al., 1992; Herity, 2003; Saha et al., 2010). The compost used as bio-organic fertilizer should not be contaminated with the PTEs, since they can drastically affect plant growth and development. Such toxic elements should be remediated from the compost before their application in agriculture, or the compost contaminated with toxic elements should not be used for agricultural purposes.

The trace elements such as Barium, Beryllium, Selenium, Strontium, Antimony, Tin, Titanium, Thallium, and Vanadium are observed to be moderately high in all the composts analyzed (Fig. 3.). The trace elements should not be too high since it can be toxic to plant at high concentration. However, their concentration should not be too low since they have potential role in the biological function of plant development.

3.3. Fertilizing Index and Clean Index of different types of composts

The Fertilizing Index (FI) and Clean Index (CI) were calculated based on the modified model as reported by Saha (Saha et al., 2010). The Fertilizing Index was calculated based on the score values and weightage factors of six parameters as given in Table 3. The FI was computed based on the given formula,

\(Fertiling Index= ƩSiWi/ƩWi\) --------- (i)

Where, ‘Si’ is the score value of the analytical data and ‘Wi’ is the weightage factor of the ‘i’th fertility parameter.

The Clean Index was calculated based on the score values and weightage factors of 22 metal contents in the composts instead of 6 metals as used by Saha et al 2010, as given in Table 4. The CI was computed based on the given formula,

\(Clean Index= ƩSjWj/Wj\) -------------- (ii)

Where ‘Sj’ is the score value of the analytical data and ‘Wj’ is the weightage factor of the ‘j’th heavy metal.

Table 3

**The score values and weightage factor assigned to each fertility parameter**: The score values were given based on the analytical values of the parameters analyzed. The higher the analytical value, the higher the score value was assigned. The weightage factor was given based on the biological importance and function of the parameter. The parameter observed to be having higher biological function was given the higher weighting factor.
Parameters	Score value (Si)					Weightage factor (Wi)
	5	4	3	2	1
Total Carbon (%)	> 25.0	20.1–25	15.1–20	9.1–15.0	< 9.1	5
Total Nitrogen (%)	> 1.25	1.01–1.25	0.81-1.00	0.51–0.80	< 0.51	3
C: N	< 10.1	10.1–15	15.1–20	20.1–25	> 25	3
Phosphorus (% )	> 0.60	0.41–0.60	0.21–0.40	0.11–0.20	< 0.11	3
Potassium (%)	> 0.1	0.076-0.1	0.051–0.075	0.026–0.050	< 0.026	1
Sulfur (%)	> 0.5	0.5 − 0.4	0.4 − 0.3	0.3 − 0.2	< 0.2	1

Table 4

**The score values and weightage factors assigned to each element**: The score values were given based on the analytical values of the parameters analyzed. The higher the analytical value, the lower the score value was given since these elements could become toxic to the plant at a higher concentration. The weightage factor was given based on the biological function and toxicity of the parameter analyzed. The parameter observed to be having higher toxicity was given the higher weightage factor.
Element	Score Value (Sj)						Weightage factor (Wj)
	5	4	3	2	1	0
Mn	< 300	301–900	901–1200	1201–1500	1201–1400	> 1500	1
B	< 30	30.1–50	50.1–70	70.1–90	90.1–110	> 110	1
Zn	< 151	151–300	301–500	501–700	701–900	> 900	1
Ti	< 15	15.1–20	20.1–25	25.1–30	35.1–40	> 40	1
Sn	< 2	2.1-3	3.1-4	4.1-5	5.1-6	> 6	1
Sr	< 1	1.1–10	10.1–20	20.1–30	30.1–40	> 40	1
Sb	< 1	1.1-2	2.1-3	3.1-4	4.1-5	> 5	2
Ba	< 100	100–200	200–300	300–400	400–500	> 500	2
Be	< 1	1.1–5	5.1–10	10.1–15	15.1–20	> 20	2
Co	< 10	10.0–20.0	20.1–30.0	30.1–40.0	40.1–50.0	> 50	2
Li	< 2	2.1-4.0	4.1-.6.0	6.1-8.0	8.1–10.1	> 10.1	2
Mo	< 2	2.1-4.0	4.1-6.0	6.1-8.0	8.1–10.	> 10	2
Cu	< 51	51–100	101–200	201–400	401–600	> 600	2
V	< 10	10.1–30	30.1–50	50.1–70	70.1–90	> 90	2
Ni	< 21	21–40	41–80	81–120	121–160	> 160	2
Tl	< 0.15	0.15–0.25	0.26–0.35	0.36–0.55	0.56–0.75	> 0.75	2
Se	< 0.5	0.5–1.5	1.6–2.5	2.6–3.5	3.6–7.5	> 7.5	3
Pb	< 51	51–100	101–150	151–250	251–400	> 400	3
Cr	< 51	51–100	101–150	151–250	251–350	> 350	3
Cd	< 0.3	0.3–0.6	0.7-1.0	1.1-2	2.0–4.0	> 4.0	5
As	< 4	4.0–8.0	8.1–12	12.1–16.0	16.1–22.0	> 22	5
Hg	< 0.025	0.025-1.0	0.1–0.2	0.21–0.3	0.31–0.4	> 0.4	5

The Neem Cake compost has the highest fertilizing index, followed by Leaf Waste compost and Kitchen Waste compost. The MCD Organic Waste compost and Vermicompost have a medium-range fertilizing index value, whereas Cow Dung manure has the lowest fertilizing index value. The Leaf Waste Compost has the highest clean index value which means, it was least contaminated with heavy metals. The Neem Cake compost has the second highest clean index value followed by Vermicompost and Kitchen Waste compost. The MCD Organic Waste compost has the least clean index value followed by Cow Dung manure.

Based on the values of the FI and CI, composts could be categorized into different quality compost (Table 5). The Neem Cake compost and Leaf Waste compost could be categorized as compost having very good quality with high fertilizing potential and low metal contamination. The Kitchen Waste compost and Vermicompost could also be categorized as good quality compost. The Cow Dung manure and MCD Organic Waste compost could be classified as medium-quality compost, having a medium fertilizing potential with some metals contamination. The compost having either a low fertilizing index or a low clean index should not be used for agricultural purpose but only as a soil conditioner (Mandal et al., 2014). Various organic waste composts could be an excellent soil amendment and biocontrol agent that can act as organic fertilizer and are more eco-friendly than chemical fertilizers (Joshi et al., 2015). Applying organic waste composts could effectively promote plant growth and fruit quality compared with other fertilizer treatments in the greenhouse study. It could also improve the quality of the soil (Wang et al., 2017).

Table 5

**Classification of the compost quality based on Fertilizing Index (FI) and Clean Index (CI).** *The different compost was classified based on the Fertilizing Index and Clean Index as very good quality compost, good quality compost, medium quality compost, and low quality compost.*
Compost	Fertilizing Index (FI)	Clean Index (CI)	Category
Kitchen Waste Compost	4.06	3.23	Good quality
Vermi Compost	3.19	3.75	Medium quality
Cowdung Manure	2.81	3.10	Low quality
MCD Organic Waste Compost	3.63	2.35	Low quality
Neem Cake Compost	4.44	4.15	Very good compost
Leaf Waste Compost	4.06	4.38	Very good compost

3.4. ANOVA analysis

One-way ANOVA analysis of all the parameters was performed to determine the statistical significance of the variation among the different groups of the composts. The P values less than 0.05 (P < 0.05) is considered statistically significance. The results indicated that there is no statistically significant variation among the groups of the composts with respect to the total P, Mn, B, Sn, Ba, Li, Be, Co, Mo, V, Ni, Se, Cr, and As. The parameters such as pH, total carbon, total nitrogen, sulphur, and zinc have very high statistically significant (P < 0.0001) variation among the groups of the different types of compost. The other parameters analyzed such as electrical conductivity, C:N ratio, Ti, Sr, Sb, Cu, Tl, Cd, Hg, and Pb also have statistically significant (P < 0.05) variation among the groups of the different types of compost (Table 6).

Table 6

**One-way ANOVA analysis of the parameters among different types of compost**: Sixteen parameters such as pH, EC, TN, C: N, S, Zn, Ti, Sr, Sb, Cu, Tl, Pb, Cd, Hg, and K were statistically significant, whereas fourteen parameters such as P, Mn, B, Sn, Ba, Li, Be, Co, Mo, V, Ni, Se, Cr, and As were not statistically significant among different types of compost.
Parameter	P value	Statistically Significant?	Parameter	P value	Statistically Significant?
pH	< 0.0001	****/Yes	P	0.0441	No
EC	0.0441	*/Yes	Mn	0.2345	No
TC	< 0.0001	****/Yes	B	0.2117	No
TN	< 0.0001	**** /Yes	Sn	0.1062	No
C: N	0.0003	***/Yes	Ba	0.237	No
S	< 0.0001	****/Yes	Li	0.1576	No
Zn	< 0.0001	****/Yes	Be	0.0583	No
Ti	0.0094	**/Yes	Co	0.4498	No
Sr	0.0056	**/Yes	Mo	0.0881	No
Sb	0.022	*/Yes	V	0.5275	No
Cu	0.0154	*/Yes	Ni	0.1656	No
Tl	0.0018	**/Yes	Se	0.187	No
Pb	0.0199	*/Yes	Cr	0.1057	No
Cd	0.0139	*/Yes	As	0.2409	No
Hg	0.0033	*/Yes
K	0.0026	**/Yes

Leaf waste could be suitable for producing good quality compost. This study showed that leaf waste compost has high fertilizing potential with low PTEs contamination. All the composts analysed are alkaline except the neem cake composts. They were rich in macronutrients (C, N, S), but P and K were lower than recommended. The micronutrients (B, Mn, Co, Cu, Mo, and Zn) were adequate. However, some PTEs contamination could be observed in all the compost analysed except the leaf waste compost. The leaf waste compost has the most negligible PTEs contamination with no elements above the maximum permissible limits, whereas MCD organic waste compost has the highest PTEs contamination. It can be stated that leaf waste can be used as substrate for the production of high quality organic fertilizer with less PTEs contamination through the process of compost

Acknowledgement

Authors are thankful to Inter University Accelerator Centre (IUAC) for extending Q-ICPMS, established under National Geochronology Facility funded by the Ministry of Earth Science (MoES) with project reference number MoES/P.O.(Seismic)8(09)-Geochron/2012. We also thank the University Science Instrumentation Centre (USIC), University of Delhi for extending the CNS analyser.

Funding Source

The authors did not receive support from any organization for the submitted work

Conflict of Interests

The authors have no relevant financial or non-financial interests to disclose.

Ethics Approval: Ethics approval is not required

Consent: All the authors have given consent to participate and publish this article in your journal

Data: Is provided in the manuscript

Material or Code Availability: Not applicable

Authors Contribution

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by [Sophayo Mahongnao], [Pooja Sharma], [Darshan Singh] ,[Arif Ahamad], [Pankaj Kumar], [Pavitra V Kumar] and [Sarita Nanda}. The first draft of the manuscript was written by [Sophayo Mahongnao] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript

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Formation and Characterization of Leaf Waste into Organic Compost

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Journal Publication

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Abstract

Figures

Introduction

Materials And Methods

2.1. Leaf Composting, Sample Collection and Preparation

2.2. Analysis

2.2.1. pH and Electrical Conductivity (EC)

2.2.2. Carbon Nitrogen and Sulfur (CNS)

2.2.3. Micronutrients, Heavy Metals, and Trace elements

2.2.4. Statistical Analysis

Results And Discussions

3.1. Formation and Maturation of Leaf Waste Compost

3.2. Comparison of Mature Leaf Waste Compost with other types of Organic Composts

3.2.1. pH and EC

3.2.2. Macronutrients

3.2.3. Micronutrients

3.2.4. Potentially Toxic Elements (PTEs) and Trace Elements

3.3. Fertilizing Index and Clean Index of different types of composts

3.4. ANOVA analysis

Conclusion

Declarations

References

Status:

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