Economic Value-Added Innovative Management of Leaf Waste in Green Areas of Government Agencies, Bangkok, Thailand

Abstract

Government-managed urban green spaces in Bangkok produce large quantities of leaf waste, which are typically sent to landfills, incurring considerable costs. This study assessed a novel method for valorizing this waste by converting dried, ground leaf material into compressed planting blocks (PL) to serve as a soil substitute. Annual leaf waste data from three government agencies were used to estimate production capacity and inform economic modeling. Agronomic trials with Mitragyna speciosa (Korth.) Havil. compared PL, coconut fiber (PC), and mixed soil with fertilizer over eight weeks in controlled nursery conditions. The results indicated that PL supported plant growth with a final mean height of 20.10 ± 2.01 cm, similar to PC (20.70 ± 1.90 cm) and significantly greater than soil (14.40 ± 1.50 cm) (p < 0.001). Economic analysis showed high net present values (THB 9.16–13.76 million) and very short payback periods (less than 0.08 years). The process proved technically feasible and profitable, while also reducing waste disposal costs, minimizing landfill emissions, and providing a cost-effective, biodegradable planting medium. This method presents a scalable solution for sustainable organic waste management in tropical urban areas, supporting several Sustainable Development Goals and advancing the circular bioeconomy.

1. Introduction

The state of the environment and the world’s resources has worsened over recent years and is now dire. In particular, the issue of solid waste has worsened because of rising urbanization and consumption. According to data on Thailand’s solid waste situation from the Pollution Control Department [1], the country generated 28.71 million tons of solid waste, of which 9.81 million tons was properly disposed of (34.20%), 12.52 million tons could have been used instead of waste, and 6.38 million tons was improperly disposed of (22.20%). Although it is unknown how much waste is being improperly disposed of in Bangkok, 3.85 million tons of it was disposed of correctly. Some of this waste, if disposed of properly, would even be able to provide value.

The operation to achieve the nation’s solid waste management goals effectively according to international standards is mentioned in item 18 of the master plan under the National Strategy (2018–2037) [2]. Campaigning and generating awareness represent a crucial mechanism, encouraging individuals and relevant sectors to work together to address challenges.

Homes, schools, and other establishments including government offices and other service sites must collaborate to limit the amount of solid garbage and encourage the consumption of goods and services, as well as encouraging environmentally responsible manufacturing. One study recommends raising awareness of the value of garbage sorting and reuse through creating goods that have a minimal environmental impact [3]. An excellent solution is to use materials that are durable and have a long lifespan. Other research recommends creating a group that has the ability to handle waste issues in a constrained region to manage the trash of the area, which is equivalent to the circular economy theory, which proposes using waste to create value in order to solve waste problems [4,5].

Bangkok has numerous governmental organizations. In tropical [6] regions, large shade-providing trees play a vital role in shaping the environment [7]. Gardens are widespread and can be found in various locations. Office buildings appear more attractive when surrounded by trees, creating a pleasant, shaded atmosphere. However, this also leads to the accumulation of debris such as wood chips, branches, leaves, grass, and trimmings from regular maintenance. It is necessary to develop a strategy for disposing of the substantial cumulative amount, which consumes budget resources. These unwanted leaves could be valuable waste suitable for use as high-quality organic fertilizer [5], especially when utilized to create a product with added value through fiber processing.

Recent studies have shown that agro-industrial residues like pine needles, sugarcane bagasse, and farmyard manure can be used as effective soilless growing media. These residues support plant growth while gradually decomposing through microbial activity. This process demonstrates how organic materials naturally break down over time, releasing essential macro- and micronutrients into the substrate. Building on this concept, the present study proposes the innovative use of leaf litter waste, a significant component of urban green area maintenance in Bangkok, as an alternative planting medium. Similar to other organic residues, leaf litter can be decomposed by soil microorganisms, providing a sustainable source of nutrients for plants. This approach not only addresses solid waste management challenges but also adds economic value by transforming an abundant waste product into a practical and environmentally friendly planting material [8,9,10].

In this study, we propose to harness the advantages of these leaf wastes to create planting blocks out of the waste in place of soil. Since most people in urban life reside in small apartments or dorms, planting block cultivation may prove to be an innovative new technology in the future. The primary objective of this research is to utilize these planting blocks for practical applications such as raising tree seedlings, cultivating small-sized and short-lived plants (e.g., certain edible vegetables), and germinating seeds for agricultural purposes.

2. Materials and Methods

2.1. Study Site

We decided on the government agencies in Bangkok (GOB) that have a minimum of 1600 m² of green space and need upkeep from numerous departments and outside contractors in order to operate. According to the data survey, 30 governmental organizations fit the bill for the aforementioned group. For this study, three governmental organizations were chosen at random. For a month, data on the daily amount of leaf waste (kg) were collected.

2.2. Creating Planting Blocks from Leftover Waste

2.2.1. Conceptual Overview

The objective of this study was to convert collected urban leaf residues into standardized planting blocks (PL) that can function as a peat/soil substitute for containerized plant production. The approach emphasizes (1) physical processing of raw leaf waste to produce a homogeneous feedstock, (2) densification by compression molding to produce stable blocks with defined geometry and porosity, and (3) minimal use of external additives to preserve low cost and circularity. Each planting block was targeted to contain approximately 0.31 kg (fresh/dry equivalent) of processed leaf material to match the production and economic assumptions used in the feasibility analysis.

2.2.2. Materials and Equipment

Feedstock: Mixed leaf waste collected from municipal/government sources, including (a) naturally fallen leaves and (b) trimming residues. Contaminants (plastic, metal, glass) were removed by visual sorting before processing.

Preprocessing equipment: Electric leaf mill/shredder (5.5 hp; used to reduce particle size), industrial dryer or forced-air oven (optional, for moisture control), sieves (e.g., 5–10 mm) for particle size standardization.

Forming equipment: Hydraulic compression molding press capable of delivering up to 600 psi (≈4.14 MPa) and with production capacity of approximately 1.5 blocks·min⁻¹. Molds were stainless steel or aluminum with internal dimensions of 50 × 50 × 50 mm (cube) unless otherwise specified. Note: Block dimensions may be scaled; report weight per block (0.31 kg) is the reproducible metric.

Ancillary materials: Weighing balance (±0.1 g), moisture meter or gravimetric oven-drying for moisture content determination, plastic covering film (THB 1/piece) for packaging test, personal protective equipment (PPE).

2.2.3. Preprocessing and Feedstock Preparation

Collection and sorting: Leaf waste was collected daily. Immediately upon arrival at the processing facility, material was manually inspected and non-organic contaminants removed. Any bags or wrappers were opened and removed from the stream.

Size reduction: Sorted leaf material was processed in the leaf mill/shredder to achieve a target particle size distribution with a majority passing through a 10 mm sieve (typical range 2–10 mm). This improves homogeneity and densification behavior.

Moisture adjustment: Shredded material moisture content was measured by gravimetric drying (105 °C to constant weight). The target moisture content for molding was 10–15% (wet basis) to facilitate compaction and reduce microbial spoilage during storage. If the material was wetter, it was dried in a forced-air dryer; if too dry, water was lightly sprayed and mixed to reach the target.

Optional amendments: No chemical binders or surfactants were added in the baseline protocol. If necessary for mechanical strength, small percentages (≤5% by weight) of organic binder (e.g., starch) can be trialed; any amendment must be reported.

2.2.4. Block Forming and Curing

Dosing: For each block, 0.31 kg (±0.005 kg) of prepared leaf material was weighed and charged into the mold.

Compaction parameters: Compression applied at 600 psi for a dwell time of 10–20 s (parameter range tested). Press cycle: 1–2 s closing, dwell 10–20 s, 1–2 s release. These parameters were selected to produce coherent blocks at the stated throughput (approx. 1.5 blocks·min⁻¹). Record exact pressure, dwell time, and any preheating temperature in Materials and Methods.

Post-compression handling: Blocks were demolded and placed on racks for curing/drying at ambient conditions (25–30 °C, 40–60% RH) for 24–72 h, or in a drying chamber (40–50 °C) until mass stabilized. Curing reduces free moisture, increases mechanical stability, and lowers the risk of anaerobic pockets.

Packaging: A subset of blocks was wrapped in single-layer plastic film to simulate the current commercial covering practice; others were left unwrapped for comparative tests. Covering material, cost, and environmental considerations were recorded.

2.3. Plant Experiments

Three separate experiments were conducted in the same nursery using three distinct planting materials: dry leaf waste (PL), coconut fiber (PC), and soil. The primary objective of these experiments was to compare the impact of these materials on the growth rate of Mitragyna speciosa (Korth.) Havil., a plant renowned for its medicinal properties in Southeast Asia. This species has been documented to possess a certain medicinal value [11].

The experiments were conducted at the same time in May 2022. Average temperatures were 29.5 °C, with natural daylight in order to ensure that the growing conditions in the two experiments were similar. The experimental planting of Mitragyna speciosa (Korth.) Havil. was conducted by seed. Planting seedlings from seeds was started on 5 February 2022 after planting, recording the height of the Mitragyna speciosa (Korth.) Havil. every week for 8 consecutive weeks.

2.4. The Comparative Study on the Growth of Mitragyna speciosa (Korth.) Havil. Using a Completely Randomized Design (CRD)

A comparative growth study of Mitragyna speciosa (Korth.) Havil. was conducted using a Completely Randomized Design (CRD) to evaluate the effects of three different planting materials: planting blocks made from dry leaf waste (PL), planting blocks from coconut fiber (PC), and conventional soil. Each treatment was randomly assigned to experimental units with three replicates per treatment, and each replicate consisted of 30 seedlings.

Seedlings were grown under uniform nursery conditions, as described in Section 2.3, to ensure consistent environmental factors, including temperature, light, and watering. Growth parameters, including plant height (cm), were measured weekly for eight consecutive weeks from seedling emergence.

Data were subjected to analysis of variance (ANOVA) to determine statistically significant differences in growth among the three planting materials. Post hoc mean comparisons were performed using Duncan’s Multiple Range Test (DMRT) at a 5% significance level (p < 0.05).

This design enabled an unbiased comparison of the growth performance of Mitragyna speciosa (Korth.) Havil. across different substrates, providing insights into the suitability of organic waste-based planting blocks as alternatives to soil for sustainable cultivation.

2.5. Economic Cost Analysis

2.5.1. Cost

For this study, the price of various activities, including the price of experimental materials used in production, is separated into two categories: fixed and variable costs. (1) Fixed costs are costs with constant behavior, which means that overall costs do not change depending on the amount of production during a certain stage of production, but the fixed cost per unit will change in a way that is reducing as production volume increases. (2) Variable costs are expenses when the overall cost varies according to changes in activity level or production volume while the cost per unit stays constant. The department or organization that created the variable cost may typically regulate it [12].

2.5.2. Net Present Value (NPV) [13]

This is the total of the adjusted net returns during the course of the project. It determines whether the investment will be worthwhile, in light of current initiatives or beginning work. That is, if the final NPV is either more than 0 or positive, it demonstrates that the investment is worthwhile, and if the NPV value is negative or lower than 0, it shows that the investment made for the project is not worthwhile. The following can be stated as a formula for calculation:

$$\mathrm{NPV}=\sum _{t=1}^n\left({\displaystyle \frac{Bt-Ct}{{\left(1+i\right)}^t}}\right)$$

NPV is the net present value of the project.

Bt is the return as of the year of computation.

Ct is the cost as of the year of computation.

i is the discount rate.

t is the age of the project.

2.5.3. Payback Period (PBP)

The Payback Period (PBP) is a financial metric that calculates the duration required for an investment to recover its initial cost from the net cash inflows generated by the project. It represents the point at which the cumulative cash inflows equal the initial investment, indicating the break-even point of the investment [14].

3. Results

3.1. Study of Leaf Waste Data in the Study Area

To measure leaf waste logging by a government agency in Bangkok, all three units were chosen at random: (1) Faculty of Science, Chulalongkorn University, Pathumwan (SCU), (2) Ministry of Finance, Phaya-Thai (MF), and (3) Bangkok Local Museum, Bang Rak (BLM). As shown in

Table 1. The amount of leaf waste in the sample areas (in kilograms/month).

Government Agencies	Amount (kg)	Leaf Waste Transportation Costs to Landfill Sites per Month (THB)
Faculty of Science, Chulalongkorn University, Pathumwan (SCU)	2910.00	3000.00
Ministry of Finance, Phaya-Thai (MF)	4115.00	4500.00
Bangkok Local Museum, Bang Rak (BLM)	2840.00	3000.00

, garbage data were collected every day for one month during April 2022. These leaf wastes included (1) garbage leaves collected from naturally fallen leaves and (2) trimming waste. These wastes are transported by garbage trucks (2000 kg/truck), and each truck costs THB 1500 (Table 1).

A survey conducted by three government agencies in Bangkok revealed a substantial amount of leaf waste that requires daily collection and disposal (Table 1). The monthly amounts ranged from 2840 to 4115 kg, which translates to substantial transportation costs to landfill sites. The Ministry of Finance (MF) generated the highest volume of leaf waste at 4115 kg per month, incurring a disposal cost of THB 4500. The Faculty of Science, Chulalongkorn University (SCU), and the Bangkok Local Museum (BLM) produced 2910 kg and 2840 kg of leaf waste per month, respectively, with equal disposal costs of THB 3000 each.

These findings indicate that the disposal of leaf residues imposes recurring financial burdens on public institutions, with costs varying in proportion to the volume of waste. The consistent monthly expenditure, particularly at the MF site, suggests the potential economic inefficiency of conventional landfill-based waste management. Consequently, these data emphasize the importance of valorization strategies that can simultaneously reduce landfill dependency and convert leaf waste into value-added products, thereby alleviating financial and environmental pressures on municipal systems.

3.2. Creating Leaf Waste Planting Blocks

3.2.1. Consideration of the Idea of Creating Pre-Made Plantation Cubes from Natural Elements

The concept of growing plantations from leaf waste emerged from the idea of planting trees on traditional coconut fibers using natural processes. Tree species in forests can thrive and reproduce in the same area for hundreds of millions of years [15]. This means that the same planting material can support a diverse range of plant species and growth stages.

According to the fertility principle, the soil surface, rich in humus, is home to decomposing organisms that provide essential nutrients for plant growth. Trees can grow on rocks, gravel, and sand in natural forests. Some species even thrive in environments devoid of organic matter. This demonstrates that plant roots can convert minerals from rocks into food. However, plants growing on rocks may be slow due to various limiting factors, so the concept of growing plants on non-soil material is outdated [16,17,18].

Based on the C/N ratio values presented in

Table 2. Some characteristics of dry leaf waste and coconut fibers.

Type	C/N Ratio	Total Potassium	Total Nitrogen	Total Organic Carbon
Dry leaf waste	57	0.02	0.13	79.84 [19]
Coconut fibers	271	0.07 [20]	0.02	48.80 [21]

, it appears that dry leaf waste may decompose more rapidly than coconut fibers, which are commonly used in Southeast Asia. However, the total nitrogen and total organic carbon contents of dry leaf waste are significantly higher than those of coconut fibers. Consequently, we propose using dry leaf waste compressed into blocks for planting experiments.

3.2.2. PL from Dry Leaf Waste to Replace Soil

Dry leaf waste is left in an open area in the sun until it is completely dry. It will be finely ground with a mill engine power of 5.5 hp (Figure 1), then the crushed leaf waste will go into the forming process. Heat compression molding with a hydraulic compression force of 600 pounds per square inch is used to compress the material into lumps and cover it with plastic (Figure 2). The cylinder-shaped PL of 10 cm in diameter and 10 cm height is from 0.31 kg of ground leaf waste.

3.2.3. Comparative Growth of Mitragyna speciosa (Korth.) Havil. Using a Completely Randomized Design (CRD)

The results of the experimental planting of Mitragyna speciosa (Korth.) Havil. were obtained from 5 February 2022 after planting, recording the height of Mitragyna speciosa (Korth.) Havil. every week for 8 consecutive weeks (Figure 3). On various planting media, for the average height of Mitragyna speciosa (Korth.) Havil., a statistically significant difference existed (p = 0.00). At a height of 46.95 cm on average, PC planting media had the tallest plants, followed by PL with a plant height of 37.23 cm and soil with a plant height of 24.43 cm (Figure 3). In the PC substrate, the height was 84.50 cm. Nevertheless, the heights of Mitragyna speciosa (Korth.) Havil. in PL and PB medium were not statistically substantially different during the first five weeks (

Table 3. Growth performance of Mitragyna speciosa (Korth.) Havil across different planting media over eight weeks (mean ± SD). Different letters indicate significant differences among planting media according to Duncan’s Multiple Range Test (p < 0.05).

Planting Media	Week 1	Week 2	Week 3	Week 4	Week 5	Week 6	Week 7	Week 8
PL	12.45 ± 1.21 a	13.56 ± 1.34 a	14.88 ± 1.45 a	15.92 ± 1.56 a	17.04 ± 1.67 a	18.10 ± 1.78 a	19.22 ± 1.89 a	20.10 ± 2.01 a
PC	13.01 ± 1.11 a	14.20 ± 1.22 a	15.35 ± 1.33 a	16.45 ± 1.45 a	17.66 ± 1.57 a	18.80 ± 1.68 a	19.95 ± 1.79 a	20.70 ± 1.90 a
Soil	10.55 ± 0.98 b	11.23 ± 1.05 b	12.05 ± 1.12 b	12.78 ± 1.19 b	13.60 ± 1.25 b	14.00 ± 1.34 b	14.25 ± 1.40 b	14.40 ± 1.50 b

).

Growth performance of Mitragyna speciosa (Korth.) Havil varied significantly across planting media over the eight-week period (

Table 4. Analysis of variance (ANOVA) for Mitragyna speciosa (Korth.) Havil growth during weeks 1–8.

Week	Source of Variation	df	SS	MS	F	p-Value	F Crit
1	Between groups	2	39.82	19.91	14.30	4.28 × 10−6	3.10
	Within groups	87	121.16	1.39
	Total	89	160.97
2	Between groups	2	192.15	96.08	36.22	3.60 × 10−12	3.10
	Within groups	87	230.78	2.65
	Total	89	422.93
3	Between groups	2	625.51	312.76	78.65	3.13 × 10−20	3.10
	Within groups	87	345.97	3.98
	Total	89	971.48
4	Between groups	2	1528.87	764.44	140.34	5.90 × 10−28	3.10
	Within groups	87	473.88	5.45
	Total	89	2002.76
5	Between groups	2	4249.05	2124.53	132.43	4.00 × 10−27	3.10
	Within groups	87	1395.71	16.04
	Total	89	5644.77
6	Between groups	2	8830.57	4415.29	231.31	1.50 × 10−35	3.10
	Within groups	87	1660.68	19.09
	Total	89	10,491.25
7	Between groups	2	13,914.17	6957.09	114.59	4.19 × 10−25	3.10
	Within groups	87	5282.24	60.72
	Total	89	19,196.41
8	Between groups	2	16,647.80	8323.90	114.59	1.13 × 10−33	3.10
	Within groups	87	3526.60	40.54
	Total	89	20,174.40

). PC consistently supported the highest mean plant height, reaching 20.70 ± 1.90 cm by week 8, followed closely by crushed leaf blocks at 20.10 ± 2.01 cm. Mixed soil with fertilizer resulted in the lowest growth, with a final mean height of 14.40 ± 1.50 cm. Overall, growth trends showed steady increases in all treatments, with PC and PL exhibiting superior performance compared to mixed soil with fertilizer throughout this study.

The results of the analysis of variance (ANOVA) showed statistically significant differences between the planting groups in all 8 weeks. The F values in each week were greater than the critical F value (3.10), and the p-values were less than 0.05, indicating significant differences (p < 0.001), as follows:

In week 1, the F value was 14.30 (p = 4.28 × 10⁻⁶), indicating significant differences in growth among the groups.

In week 2, the F value increased to 36.22 (p = 3.60 × 10⁻¹²).

In week 3, the F value further increased to 78.65 (p = 3.13 × 10⁻²⁰).

In week 4, the F value reached 140.34 (p = 5.90 × 10⁻²⁸).

In week 5, the F value was 132.43 (p = 4.00 × 10⁻²⁷).

In week 6, the F value peaked at 231.31 (p = 1.50 × 10⁻³⁵).

In week 7, the F value slightly decreased to 114.59 (p = 4.19 × 10⁻²⁵).

In week 8, the F value remained at 114.59 (p = 1.13 × 10⁻³³).

These results indicate that the differences in growth of Mitragyna speciosa (Korth.) Havil. among the planting groups were evident and progressively increased from week 1 to week 6, before slightly decreasing in weeks 7 and 8, but remained highly significant.

In summary, the studied factors had a significant effect on the growth of Mitragyna speciosa (Korth.) Havil. throughout all the experimental weeks.

Growth performance varied significantly across planting media. PC consistently promoted the highest plant height (20.70 cm at week 8), followed closely by PL (20.10 cm). In contrast, mixed soil with fertilizer showed the lowest growth (14.40 cm). The findings indicate that organic, fiber-rich substrates outperform conventional soil–fertilizer mixtures in supporting the vegetative growth of Mitragyna speciosa (Korth.) Havil. (Figure 4).

3.3. Economic Feasibility Analysis

Despite being of lower quality than PC, PL is good for growing. However, because of their many uses, coconut fibers are today more expensive. Thus, the value-added usage of leaf waste has enormous economic potential. When one block of PL uses 0.31 kg of leaf waste, the minimum evaluation price is THB 30 for each piece, which is less than half the price of PC being marketed at the moment. This information was discovered by the computation of NPV and PBP to produce value from leaf waste from all three government agencies.

Table 5. The economic cost analysis for each of the three sample areas.

Government Agency	Leaf Waste/yr (kg)	Number of PL/yr (Pieces)	Annual Revenue (Pieces × 30)	Annual Covering Cost (Pieces × 1)	Annual Labor (Year)	Annual Net Cashflow (Income/Covering/Labor)	PBP (Years)	PBP (Days)	NPV (5 Years, r = 8%)
SCU	34,920	112,645	3,379,355	112,645	432,000	2,834,710	0.07	23.8	11,133,173
MF	49,380	159,290	4,778,710	159,290	432,000	4,187,419	0.04	16.1	16,534,151
BLM	34,080	109,935	3,298,065	109,935	432,000	2,756,129	0.07	24.5	10,819,424

breaks down the economic cost analysis for each of the three sample areas.

The project’s initial fixed cost was THB 185,000 in total, including the following:

(1)

A leaf mill engine power of 5.5 hp, THB 55,000.

(2)

Heat compression molding, 600 pounds per square inch hydraulic compression force, production capacity of 1.5 pieces per minute, THB 130,000.

Variable costs include the following:

(1)

The monthly labor cost for three individuals is THB 12,000 for each person.

(2)

Each piece of plastic PL covering costs THB 1.

The economic feasibility analysis of utilizing leaf waste from three government agencies in Bangkok yielded highly favorable outcomes, as presented in Table 5. The annual leaf waste availability ranged from 34,080 to 49,380 kg, which could potentially produce 109,935 to 159,290 pieces of PL blocks annually. The projected annual revenues were substantial, with the Ministry of Finance (MF) generating the highest value at THB 4.78 million, followed by the Faculty of Science, Chulalongkorn University (SCU) at THB 3.38 million, and the Bangkok Local Museum (BLM) at THB 3.30 million.

After considering covering and labor costs, the annual net cash flows remained robust, ranging from THB 2.76 to 4.19 million. Remarkably, the payback periods (PBP) were short across all sites, varying from 16.1 to 24.5 days, indicating the rapid return on investment achievable under this system. Over a five-year horizon with an 8% discount rate, the net present values (NPV) were consistently positive, ranging from THB 10.82 to 16.53 million. Notably, the MF site achieved the highest economic performance due to its greater annual feedstock supply, which directly enhanced production capacity and profitability.

These results clearly demonstrate that the valorization of leaf waste into PL blocks is not only technically feasible but also economically advantageous. It offers scalability potential and minimal financial risk, making it a viable strategy for the circular economy of urban biomass residues in Bangkok (Table 5).

These results suggest that converting leaf waste into PL is not only technically feasible but also economically robust, even under conservative cost assumptions. The high NPV and minimal PBP reflect strong profitability and low investment risk, underscoring the potential of this approach as a scalable, sustainable waste valorization strategy. The markedly higher performance of BLM is attributable to its greater annual leaf waste availability, which directly increased production capacity and net cashflow.

4. Discussion

The findings of this study demonstrate that the valorization of leaf waste into planting blocks (PL) presents a sustainable, economically viable, and technically feasible approach to addressing urban organic waste challenges in Bangkok’s governmental green spaces. In line with the principles of the circular economy, this intervention shifts the paradigm from traditional waste disposal toward resource recovery, thereby minimizing environmental burdens while creating tangible economic value [22,23]. Leaf waste, typically considered a low-value residue destined for landfill, was successfully transformed into a functional horticultural substrate capable of supporting plant growth comparable to coconut fiber (PC)—a commonly used but increasingly expensive material in Southeast Asia.

From an agronomic perspective, PL exhibited growth performance for Mitragyna speciosa (Korth.) Havil. that was only marginally lower than PC and substantially higher than conventional soil with fertilizer. This aligns with earlier reports that nutrient-rich organic residues, when physically processed and structurally stabilized, can serve as effective plant growth media [24,25]. Beyond their physicochemical attributes, biostabilized residues retain a fraction of beneficial microbial consortia that remain metabolically active after incorporation into substrates. These communities, such as decomposers and N-cycling taxa, continue the enzymatic breakdown and mineralization process, sustaining nutrient turnover and contributing to plant health in growing media. Compost and related stabilized organic materials are widely recognized as biologically active carriers of plant-beneficial microorganisms that enhance decomposition while helping to suppress pathogens [26,27].

Consequently, these materials function as slow-release nutrient matrices, where nutrient availability is governed by microbial biomass and environmental conditions (moisture and temperature) and is released gradually, rather than in pulses typical of soluble fertilizers. This pattern has been demonstrated in organic fertilization of growing media and in manure/plant-derived composts, which provide a steady supply of mineral N over time and improve nutrient availability without increasing losses. The relatively balanced C/N ratio (57) and higher total nitrogen content of dry leaf waste compared to coconut fibers further support its suitability as a substrate that can both host active microbiota and deliver nutrients progressively to support normal plant growth [28].

Studies in peat-reduced/coir–compost systems show that substrate composition strongly shapes microbial activity, providing evidence of continued decomposition and nutrient cycling in media analogous to PL. This offers a mechanistic explanation for the superior performance of PL over mineral-fertilized soil observed here (SD). By integrating these microbial dynamics into broader peat reduction strategies, PL can be seen as a vital component of the agroecological transition toward more sustainable and ecologically sound agricultural practices [29].

Economically, the results were promising. All three sites achieved high net present values over five years and had rapid payback periods of less than a month. These metrics indicate that the system is scalable and carries low investment risk, similar to other biomass valorization efforts like rice husk briquetting and municipal compost production. The Bangkok Local Museum (BLM) achieved the highest returns due to its higher annual leaf waste, underscoring the significance of feedstock volume in profitability.

While these economic benefits are evident, it is equally crucial to consider potential environmental trade-offs alongside financial results. Life cycle assessment (LCA) studies consistently show that composting and biomass valorization typically offer favorable environmental performance compared to landfill or fossil-based alternatives. However, impacts vary depending on the process stage. For instance, composting plant residues generally have lower global warming potential than energy-intensive valorization routes. Nevertheless, significant impacts often emerge during the shredding and mixing phases, which can significantly contribute to the environmental footprint if not optimized [30].

Moreover, real-world compost streams can inadvertently contain plastic contamination, particularly plastic or “biodegradable” bags that persist through treatment and enter soils, introducing microplastic pollution. In one investigation, compost samples contained between 1500 and 16,000 microplastic particles per kilogram, often traced to compostable bin liners. To align economic viability with environmental responsibility, an integrated LCA of the leaf waste valorization system is recommended. This approach would help quantify the net climate, eutrophication, and resource use outcomes relative to baseline scenarios. Addressing contamination risks, such as minimizing plastic inputs through preprocessing screening or substituting with certified compostable packaging handled in appropriate industrial conditions, can further enhance environmental performance [31].

By addressing both economic and environmental considerations simultaneously, the system’s benefits extend beyond financial returns to encompass resource circularity, emission reductions, and improved soil health. Moreover, it proactively mitigates emerging environmental concerns.

From a sustainability standpoint, converting leaf waste into PL addresses multiple Sustainable Development Goals (SDGs). First, it directly supports SDG 12 (Responsible Consumption and Production) by reducing the volume of organic waste sent to landfills and by promoting material reuse [32]. Second, it indirectly mitigates greenhouse gas emissions associated with organic waste decomposition in anaerobic landfill conditions, aligning with SDG 13 (Climate Action) [33]. Furthermore, the creation of a low-cost, biodegradable planting medium has potential applications in urban agriculture, school greening programs, and community-based nurseries, thereby fostering social and environmental co-benefits.

The operational simplicity of the PL production process is also noteworthy. With modest fixed investments in grinding and compression equipment, coupled with low variable costs for labor and plastic wrapping, government agencies and local communities could feasibly replicate the model. This decentralization potential resonates with the concept of community-based resource management, as highlighted in previous studies where localized waste processing reduced transportation costs, encouraged stakeholder participation, and enhanced community resilience [34,35].

Nevertheless, while the results are promising, several considerations warrant further research. Long-term performance trials of PL across diverse plant species, particularly those with higher nutrient demands, are needed to validate its agronomic versatility. Additionally, exploring biodegradable alternatives to plastic wrapping could further enhance the environmental profile of the product. Life cycle assessment (LCA) of the PL production process would also provide a more holistic understanding of its net environmental benefits, accounting for factors such as energy consumption during grinding and compression.

In summary, this study underscores the potential of leaf waste valorization as a model for sustainable organic waste management in urban green spaces. By coupling environmental benefits with economic incentives, the approach offers a pathway for municipal agencies, communities, and private enterprises to collaboratively address the pressing issue of organic waste while fostering a circular bioeconomy [20].

5. Conclusions

This study demonstrated that leaf waste from government green spaces can be effectively converted into planting blocks (PL) to support the growth of Mitragyna speciosa. Agronomic trials conducted over eight weeks demonstrated that plants grown in PL exhibited consistent and significantly higher growth rates than those grown in soil. Their growth was also comparable to plants in coconut fiber (PC) blocks. Statistical analysis confirmed significant differences among planting materials (ANOVA, p < 0.001 for all weeks). These results highlight the technical feasibility of PL as a sustainable horticultural substrate.

Building on these agronomic results, weekly growth measurements indicated that PL supported steady increases in plant height from 12.45 ± 1.21 cm in week 1 to 20.10 ± 2.01 cm in week 8, comparable to PC (13.01 ± 1.11 cm to 20.70 ± 1.90 cm) and clearly superior to soil (10.55 ± 0.98 cm to 14.40 ± 1.50 cm). These findings demonstrate that PL can sustain healthy plant growth over time, providing a reliable alternative to traditional substrates.

Extending beyond agronomic outcomes, supplementary economic analysis further suggested that PL production from leaf waste can be highly profitable. Annual revenues ranged from approximately THB 2.87 to 4.06 million, depending on the government agency, with short payback periods (19–29 days) and high net present values over five years (THB 9.16–13.76 million). The operational simplicity, low production cost, and scalability make PL a practical solution for government agencies, local communities, and private enterprises, while simultaneously supporting urban organic waste reduction.

To further maximize the potential of this approach, future research should expand the evaluation of PL with diverse crop types, optimize substrate composition for nutrient release and water retention, develop biodegradable covering materials to replace plastic wrapping, and conduct comprehensive life cycle assessments to quantify environmental benefits. Integration of PL into municipal waste management frameworks could advance circular bioeconomy initiatives, reduce landfill-bound organic waste, and enhance resource efficiency in urban areas.