Home Composting: A Sustainable Solution at Community Level

Abstract

Food waste management is a critical environmental challenge, particularly when organic waste ends up in landfills. This study focuses on the Romanian household food model to understand the composition of food waste and the effectiveness of homemade composters in transforming this waste into quality compost. The findings aim to highlight composting as a viable solution for mitigating greenhouse gas emissions and conserving water resources. We start from the issue of food waste in landfills and its environmental implications, and the objective is to evaluate the composition of household food waste in Romania and the efficiency of homemade composters. Two samples, namely P1 and P2, of compost were obtained at home using low-cost materials. P1 compost was obtained starting from five waste materials (potato peels, banana peels, orange peels, sawdust, and water), and P2 was prepared starting from nine waste materials (potato peels, banana peels, orange peels, apple peels, apples, cardboard, paper, dried vine leaves, and water). In order to study their potential to be used as fertilizers, various parameters were investigated: pH, aqueous extract conductivity 1:5 Humidity, Ca (mg/kg), Mg (mg/kg), Na (mg/kg), K (mg/kg), Zn (mg/kg), Mn (mg/kg), Cu (mg/kg), particle size (mm), N, C, H, C/N, C/H, N/H content. The final products can be safely used for various household needs, providing a sustainable solution for food waste management.

1. Introduction

If no garden is available, the compost can also be obtained in small containers such as plastic boxes, where holes are made for ventilation purposes. The containers can be placed on a balcony or even in the corner of a small kitchen. If the composting rules are followed, there will be no problems of unpleasant odours or unwanted insects.

Compost usually smells like forest soil. For composting, it is necessary to choose a shaded, accessible place but also to have good drainage. Thus, the ideal place for the compost box is directly on the ground, to facilitate the access of the organisms responsible for the decomposition of organic matter (bacteria, fungi, earthworms, etc.).

Another suitable location is the corner of a garden or orchard, which protects the compost box from strong air currents. It can also be under a tree with falling leaves, thus being protected from the sun in summer and receiving the heat of the sun in winter. To make compost, you need to set up a special space and follow certain simple steps, as follows:

• Collect all biodegradable household waste in special containers, which can be used to obtain compost.
• If a stationary composter is used, put a 10–15 cm layer of broken branches or other yard debris (sawdust) at its base.
• Place the waste in alternate layers: first, layer of brown ingredients, then a layer of green waste, and, finally, a layer of dry garden soil. Equal amounts of kitchen and yard leftovers are desired.
• Aerate the compost. Once a week, mix in the container, from top to bottom, with a fork, wooden stick, or shovel, so that the compost is loosened.
• Ensure the right temperature. Compost is formed in a range of 30–70 °C. Biodegradable waste ferments and the temperatures rise, which is a very good sign. Temperature can be measured with a garden thermometer. In summer, the container must be protected from strong sun and from frost during winter. If the temperature is too high or too low, or if the smell is very strong, mix the compost well.
• Maintain the right humidity. The compost should always be moist but not bite. If it is too dry, water it more. If it is soaked with water, ventilate it and make sure that rainwater can drain off.

Obtaining compost in the household means, first, the efficient recycling of biodegradable household waste, resulting from domestic work or gardening. Compost is a very nutritious natural fertilizer that can be used for both plants in the home and in the yard.

In Romania, Law no. 181 of 19 August 2020 [1] on the management of compostable non-hazardous waste is applied with small steps in several cities: Tulcea, Bucharest, Iasi, Valcea, etc. In low- and middle-income countries, the recovery rate of municipal solid organic waste is only a small part of that generated at the national level and is a rather astringent problem, especially in areas with large populations; community composting, in schools, for example, or home composting is considered a logical and sustainable alternative for the treatment of household biological waste, thus managing to minimize the difficulties of separate collection and recovery of food waste. High-quality compost is obtained through home composting, since bio secondary products and food waste are separated directly, at source, treated and recovered independently, complying with all composting rules because of directing the processes by raising awareness among the population and the community about the importance of composting. The direct application of the product and home composting result in obtaining a special soil quality at the local level by efficiently eliminating the intersection of biological waste with other waste found in the landfill [2].

For urban or rural areas with a low population, it is a reliable alternative, as the costs of separate collection and transport of distinct waste streams to collection and treatment plants become an important implementation factor. There are also identified disadvantages of the home composting process; namely, the finished compost can vary greatly in terms of composition or can be too heterogeneous. Another drawback is biological degradation, which can produce unwanted odours that make people give up installing composters at home and stop using composting at home. The gaseous pollutants obtained during the process are another substantial environmental concern, the emissions being varied, from methane to nitrous oxide, ammonia, and greenhouse gases, but the efficiency of the process and the successful implementation are closely related to a variety of factors, including the characteristics of the substrate initially used, porosity, oxygen diffusion, mandatory ventilation, ventilation conditions, the size, structure and texture of the substrate particles, the amount of water added, the absorbent material used, etc. The physical properties of the substrate and their control are achieved in most cases by pre-treatment, the most important being crushing, cutting, and granulating, but also by adding suitable bulking agents [3]. The pre-treatment of food waste does not require special training and can be carried out by any adult. In the current study, we obtained two compost samples (P1 and P2) and characterised them from a physicochemical point of view in order to investigate their potential to be used as fertilizers (pH, aqueous extract conductivity 1:5 Humidity, Ca (mg/kg), Mg (mg/kg), Na (mg/kg), K (mg/kg), Zn (mg/kg), Mn (mg/kg), Cu (mg/kg), particle size (mm), N, C, H, C/N, C/H, N/H content. Their characteristic values were compared with some examples of typical compost characteristics for desired ranges. Depending on the intended use, some parameters may be acceptable, or even preferred, outside these ranges. It is found that there is a total fit of compost parameters within the standards set by the Compost Quality Alliance in Ontario, Canada.

P1 compost was obtained from five waste materials (potato peels, banana peels, orange peels, sawdust, and water), and P2 was prepared from nine waste materials (potato peels, banana peels, orange peels, apple peels, apples, cardboard, simple paper with no additives, dried vine leaves, and water).

The method used in obtaining the P2 samples introduces several key innovations that differentiate it from traditional composting techniques.

• Customized Environmental Control: Unlike conventional composting methods, which often rely on ambient environmental conditions, the new method incorporates precise control over key factors such as temperature, humidity, and aeration throughout the composting process. This allows for the optimization of microbial activity, resulting in a more efficient and consistent breakdown of organic materials.
• Use of Mineral Salt Additives: The introduction of mineral salts during the composting process is a novelty for the method. These salts not only help to stabilize the pH levels of the compost but also enhance the nutrient content of the final product, providing a more balanced fertilizer that is rich in essential minerals like potassium, magnesium, and calcium. This contrasts with traditional methods, which may lack this level of nutrient fortification.
• Reduced Processing Time: Traditional composting processes can take several months to produce a mature compost product. The invented method, through optimized environmental control and mineral salt use, significantly reduces the processing time. The composting process is accelerated, yielding usable material in a fraction of the time—typically in weeks rather than months.
• Energy Efficiency: The method incorporates energy-saving techniques, such as low-temperature fermentation, which decreases the need for external heating systems. This contrasts with some traditional methods that may require high-energy inputs for temperature control, especially in large-scale composting operations.
• Waste-to-Resource Efficiency: This new method improves resource utilization by effectively recycling agricultural or industrial waste into high-quality, nutrient-rich compost. The process minimizes waste loss and maximizes the potential for producing a valuable end-product, unlike traditional composting, which may be less efficient in terms of waste-to-resource conversion [4].

This study provides a novel approach to home composting by evaluating its implementation and impact at the community level, which has been relatively underexplored in existing research. While previous studies have primarily concentrated on individual household composting practices or large-scale municipal composting systems, our research bridges this gap by examining the collective benefits and challenges of community-driven composting initiatives. The need for this study stems from increasing global waste management challenges and the urgent demand for sustainable, localized solutions to reduce organic waste. By offering insights into the scalability and efficacy of home composting within communities, this study aims to contribute to sustainable waste management practices and support environmental policy development.

2. Materials and Methods

In this experiment, the biological materials subjected to composting were vegetable waste from the house (potato peels, banana peels, orange peels, apple peels, apples, cardboard, paper). Unsuitable material, such as plastic, metals, paper, cardboard, is very rare and collected separately. The absorbent material used consisted of beech sawdust, dry grass, dried vine leaves and biodegradable plastic. Two composting samples were considered, P1 and P2, as follows:

• P1 was obtained from potato peels, banana peels, orange peels, sawdust, and water;
• P2 was obtained from potato peels, banana peels, orange peels, apple peels, apples, cardboard, paper, dried vine leaves, water.

The materials before use underwent pre-treatment operations (cutting, crushing, grinding), which facilitate subsequent biological processes.

After the inlet material was placed in the inlet, the temperature was measured and increased to 55–70 °C, which signals the beginning of the thermophile phase. Microorganisms act immediately on organic waste (which contains carbon) and decompose it through aerobic respiration, also having an optimal environment for development. The necessary oxygen was introduced by keeping the lid open, and the organic vegetable waste was returned to the composter twice a week.

The entire material was kept inside the composters (plastic boxes) for eight weeks, and they were handled correctly according to the instructions. Following the instructions, it was ensured that the compost was safe to use and free of odours or pathogens. After the eight weeks, vermicompost was added to the compost to complete the maturation phase. The maturation stage involves the temperatures stabilizing, and some fermentation continues, converting the degraded material into humus through condensation and polymerization reactions.

The last objective is to produce a material that is stable and can be judged using the C/N ratio. Well-composted materials have a low C/N ratio; for example, the C/N ratio can drop from 30 at the beginning of the composting process to 15–20 in mature compost.

2.1. Conducting Monitoring and Experiments

In order to optimize and demonstrate the efficiency and viability of the home composting unit, it is necessary to identify the intervals in which each control factor of the composting process has values that do not make it necessary not to diversify, since the composition and properties of the input materials establish the physical, chemical and biological aspects. The decomposition method, decomposition time, and quality of the final product depend largely on the selection of biodegradable solid materials in the household that feed the composter [5]. A series of parameters governing the composting process were monitored, including several physical, chemical, and biological parameters. The analyses were carried out according to SR ISO 11465:1998 Soil quality—Determination of dry matter and water content by mass—Gravimetric method [2], to find the common parameters between compost and soil.

2.2. Measurement of pH and Electrical Conductivity

For each sample, each 10 g of compost was mixed with 50 mL of deionized water in a shaker for 30 min (1:5 soil/water). The compost solutions were then filtered with filter paper. The filtered liquid sample was used to determine pH and electrical conductivity (EC) using a pH meter and an electrical conductivity meter (EC meter).

2.3. Moisture Content Measurement

Compost samples were analysed for moisture content via kiln drying at 105 °C in accordance with the ISO standardised method [1].

2.4. Measurement of Total Cations and Trace Minerals

The compost samples were digested in a TOP wave microwave sample preparation system from Analytik Jena, equipped with closed Teflon vessels. For the acid digestion procedure, a sample, 0.5 ± 0.05 g, was digested and placed in the digestion vessel with clean Teflon. Then, 6.0 mL of concentrated nitric acid (65%) and 1.0 mL of hydrogen peroxide (30%) were added. The vessel was closed and placed in the rotor, followed by digestion. The vessel was closed and introduced into the rotor, followed by digestion using a three-stage temperature program, namely (i) pressure 40 bar, ramp 5 min, temperature 170 °C, time 10 min; (ii) pressure 40 bar, ramp 1 min, temperature 200 °C, time 15 min; and (iii) cooling. The vessels were cooled and carefully opened. After the digestion process, each digested sample was quantitatively transferred with ultrapure water into a 50 mL rated flask. The concentration of the elements (Ca, Mg, K, Na, Mn, Zn, Cu) was determined by the method of flame atomic absorption spectroscopy (NOVAA 300, Analytik Jena, Jena, Germany).

All chemicals and reagents used during this study were of spectroscopic quality; ICP Multi-Element Standard Solution XVI Certipur, with a certified value of 100.0 ± 0.3 mg·L⁻¹ (Merck KGaA Frankfurter, Darmstadt, Germany), was used in the quantitative analysis for the calibration curve. Ultrapure water, with a maximum resistivity of 18.2 MΩ·cm⁻¹, was used for the treatment and dilution of samples. All investigated calibration curves were characterized by a high correlation coefficient (R > 0.995).

3. Results and Discussion

The physicochemical parameters of the two prepared compost samples (P1 and P2) are presented in

Table 1. Parameters of P1 and P2 compost samples.

Physicochemical Parameters	Sample 1	Sample 2
pH extract after 1:5 (upH)	6.9	7.6
Aqueous extract conductivity 1:5 (µS/cm); (ms/cm)	1982; 1.982	2450; 2.450
Humidity (%)	6.57%	61.67%
Ca (mg/kg)	15,313.74	20,569.98
Mg (mg/kg)	1916.60	1909.19
Na (mg/kg)	994.44	1519.68
K (mg/kg)	5249.40	7322.39
Zn (mg/kg)	84.99	137.76
Mn (mg/kg)	279.75	167.81
Cu (mg/kg)	28.65	23.22
Particle size (mm)	25	18

and

Table 2. Results of the elemental analysis of P1 and P2 compost samples.

Physicochemical Parameters	Proba 1	Proba 2
N	1.18%	1.41%
C	13.33%	22.18%
H	2.22%	3.32%
C/N	11.29	15.73
C/H	6.00	6.68
N/H	0.53	0.42

.

We compared some examples of compost characteristics,

Table 3. Compost parameters.

Parameters	Value
Particle size:	<25 mm
Humidity:	40–50%
Total organic matter:	>30% based on dry weight
C/N Report:	<22
pH:	5.5–8.5
Conductivity	<7.39
Sodium (Na):	<2% of dry weight
Soluble salts (of a saturated paste):	<4 mS/cm

, with the typical desired ranges. Depending on the intended use, some parameters may be acceptable, or even preferred, outside these ranges. It is observed that there is a total fit of compost parameters within the standards set by the Compost Quality Alliance in Ontario, Canada.

The composition of the final compost product can vary, particularly in terms of its salt content. Salts, in the form of mineral ions, such as sodium (Na), magnesium (Mg), potassium (K), and calcium (Ca), are naturally present in all composts. During the composting process, these salts tend to concentrate as organic matter breaks down and moisture levels fluctuate. The salt content in compost is an important factor, especially for its application in sensitive environments. Different plants exhibit varying levels of tolerance to soil salinity. For instance, compost intended for use as a seed germination medium should have a soluble salt content of less than 2 mS/cm to avoid adverse effects on seed development. To ensure the suitability of compost for specific agricultural or horticultural purposes, laboratory testing can provide an analysis of soluble salt and sodium content. These services help determine whether the compost meets the required thresholds for its intended use, thereby preventing potential issues such as plant stress or reduced germination rates. Managing moisture levels during composting is crucial, as it influences the concentration of salts. Proper balance ensures that salts do not accumulate to levels that could be detrimental to plant health. Additionally, pre-treatment methods and the selection of appropriate bulking agents can help moderate salt levels in the final product.

The Compost Quality Alliance (C QA) can be a useful resource for determining the appropriate salt content for various intended uses. C QA is a voluntary program, established by the Compost Board of Canada and compost producers, using standardized testing methodologies and uniform operating protocols, to improve customer confidence in the selection and use of compost [3,6,7].

3.1. Effect of C/N Ratio on Compost Composition

Elemental analysis (C, H, N) was performed using gas-coupled combustion and pyrolysis chromatography (Flash EA2000, Thermo Scientific, Waltham, MA, USA) [8]. The C/N ratio is one of the key parameters of the composting process; the availability of nutrients for microbial growth depends entirely on their value. All other necessary nutrients are met in sufficient quantities in almost all biodegradable solid waste. Food waste collected at source is considered free of heavy metals because it has been meticulously prepared for consumption and is taken directly from the pot to the compost.

C is a source of energy and the main building block of organisms, while N is a main element when it comes to building proteins and accounts for 50% of the dry mass of microbes. The elements belong to the main nutrients for microbes that carry out aerobic biodegradation; P, Ca, Mg, Na, and K are the rest of the main nutrients. All these elements are usually found in excess in food waste, but the C/N composition ratio is of profound importance for the composting process, and the nutritional evaluation of feed is established through it. The C/N ratio of the structure of microorganisms falls between 9 and 12, while, during the degradation process, microorganisms assimilate about a third of the metabolized carbon, releasing the rest through emissions, mainly in the form of CO₂. Obtaining an adequate initial C/N requires an appropriate combination of different types of food waste. During aerobic biodegradation, C loss is usually greater than N loss, resulting in a reduced C/N ratio in the final product. From the data obtained experimentally (Figure 1), it is found that in the P1 sample, C values of 13.33% were obtained compared to the P2 sample, where C is 22.18%, which means that a large part of the C was lost through the emission of CO₂. The amount of N in P1 is lower than in P2 because the biological materials used were reduced.

In the case of home composting, for P1 (Figure 2), the C/N ratio of the compost has an initial value of 11.29, and for the P2 sample, it is 15.73, which falls within the C/N ≈ 15–20 values, obtaining quality compost.

The C/N ratio is an important factor in the composting process as it influences microbial activity and the decomposition rate. A balanced C/N ratio is key for producing quality compost. An interpretation of the provided values for the P1 and P2 samples is as follows:

• P1 (C/N = 11.29): This value is slightly lower than the ideal C/N ratio (around 15:1). While still within a reasonable range, it may indicate that the compost has a relatively higher nitrogen content. Nitrogen-rich compost can decompose faster but might have a higher risk of odour problems due to excessive ammonia release if not balanced properly with carbon.
• P2 (C/N = 15.73): This value falls within the ideal C/N ratio range of 15–20, which is considered optimal for composting. At this ratio, the decomposition process is balanced, providing the right nutrients for microorganisms without excessive nitrogen that could cause odour issues or a slower process.

In summary, the P2 sample with a C/N ratio of 15.73 is ideal for high-quality compost production, while the P1 sample with a C/N ratio of 11.29 could still yield good compost, but adjustments might be needed to ensure a balanced decomposition process, possibly by adding more carbon-rich materials like dry leaves or straw.

3.2. Effect of the Evolution of Humidity

Moisture content is a parameter of significant importance in the composting process [9]. Optimal moisture levels ensure proper microbial activity and efficient decomposition. A low moisture content, typically between 35 and 40%, can hinder biological processes by limiting microbial activity and slowing down decomposition. If the moisture content falls below 30%, microbial activity can cease entirely, effectively halting the composting process. The recommendation to maintain an optimal humidity level of 45–65% in compost is frequently made by various authoritative sources, including the U.S. Environmental Protection Agency (EPA). The EPA provides guidelines for composting, emphasizing that maintaining moisture levels within a range of 45–65% is crucial for effective microbial activity and decomposition. This range helps ensure that the compost remains moist enough to support microbial life but not so wet that it becomes anaerobic [10,11].

Conversely, excessive moisture levels, above 65%, often lead to anaerobic conditions. A high moisture content reduces the porosity of the substrate, limiting oxygen availability and encouraging anaerobic microbial activity, which can result in unpleasant odours and the production of methane, a potent greenhouse gas. Managing the moisture content of the substrate is crucial for maintaining aerobic conditions and preventing anaerobic breakdown. The ideal moisture range for composting is between 50 and 60%, which promotes microbial activity without compromising porosity or oxygen diffusion. Effective moisture management can be achieved by adjusting the mix of dry (carbon-rich) and wet (nitrogen-rich) materials and by monitoring water addition throughout the process. In conclusion, the optimal values of moisture content are those in a range of 45% to 65% according to the standards. The humidity of the two samples is clearly different: P1 has a humidity of 6.57% and P2 61.67, which means that P1 complies with the technical norms and can only be used after adding water necessary to balance the humidity of the compost. In all cases, the raw materials used for composting initially had a moisture content exceeding the optimal upper limit of 65%, primarily due to the nature of household food waste. This is particularly true in southern European countries, where food waste is often composed of fruits and vegetables, resulting in moisture levels of 70% or higher. Such a high moisture content can reduce substrate porosity, leading to anaerobic conditions and hindering the composting process.

To address the challenges posed by excessive moisture, regular manual aeration was implemented. During the first 7 days of the composting cycle, aeration was performed twice daily, followed by weekly aeration thereafter. This practice ensured adequate oxygen levels, promoting aerobic conditions and facilitating the evolution of the composting process. Manual aeration helped prevent anaerobic conditions and maintained the aerobic biodegradation essential for producing quality compost. Regular testing of the moisture content, along with soluble salt and C/N ratio assessments, helps maintain the balance necessary for effective composting. By managing these parameters, the composting process can proceed efficiently, producing a high-quality, stable final product.

Effective management of the moisture content is critical, especially in cases where the initial moisture levels are high due to the nature of the raw materials. Regular manual aeration, particularly during the early stages of the composting cycle, helps maintain aerobic conditions by ensuring adequate oxygen levels and preventing excess moisture from creating anaerobic environments. This practice is essential for optimizing microbial activity and ensuring the successful decomposition of organic matter. The addition of sawdust, cardboard, and paper led to an increase in the porosity of substrates and improved aeration, preventing the establishment of anaerobic conditions. The P1 sample was far too dry due to the temperature of the outside environment and the addition of a larger amount of sawdust at the end. A graphic representation of the evolution of humidity in the case of compost samples can be seen in Figure 3, noting a very large difference in the last 3 months.

In the case of the P2 compost sample, the humidity is at first extremely high because a quantity of water equal to the amount of each vegetable raw material used is introduced. The humidity is 90%, which is due to the composition of the vegetable waste in the water. Along the way, the humidity decreases, reaching 61.73% in the maturation phase. During the thermophilic phase, wood sawdust was added to stabilize the moisture.

3.3. Effect and pH Profile

Acidity is a significant parameter in composting, as it determines the types of microorganisms that can thrive and decompose the organic materials in the substrate. Initially, the substrate tends to be slightly acidic, particularly due to the nature of Mediterranean food waste, which often includes high amounts of fruits and vegetables. This acidity influences the microbial species capable of initiating the decomposition process. Regular testing of the pH, alongside moisture content, soluble salt levels, and C/N ratio, ensures that the composting process remains balanced. Monitoring these parameters allows for adjustments that optimize microbial activity and decomposition rates, leading to a nutrient-rich final product. Managing pH levels is critical for the composting process, particularly during the initial stages. A slightly acidic environment is typical at the start due to the composition of the raw materials, especially in Romanian food waste. Over time, the production of ammonia and the decomposition of organic acids contribute to a gradual increase in pH, fostering conditions that support the growth of diverse microbial populations essential for efficient composting.

During the first two days of composting, the pH remains relatively stable, showing a slight increase. This initial stability can be attributed to the delayed decomposition of organic acids. Although metabolic processes begin immediately, leading to the production of ammonia from the degradation of nitrogen compounds, the breakdown of organic acids proceeds at a slower rate. This delayed decomposition results in a gradual pH increase rather than a sharp rise, allowing for the establishment of microbial communities suited to these conditions.

While the pH of mature compost is expected to be close to 7, when the process is supposed to have ended, it varies for P1, pH = 6.9 and for P2, pH = 7.6, which indicates that the product is stable, being in the stage of maturation and stabilization. Wood sawdust has an important role in stabilizing the pH. It is at first acidic, 4–4.5, and reaches neutral, 6.9 and 7.6, respectively, and by adding sawdust, it becomes slightly alkaline. Figure 4a,b show the evolution over time of the pH from the values of 4.5 to 6.9 in the case of P1 and 7.6 in the case of P2, noting stabilization, starting with the introduction of vermicompost and sawdust, respectively, at month 3.

In Figure 4a, the pH levels for both P1 (6.9) and P2 (7.6) indicate that the compost has reached a stage of maturation and stabilization. While a pH close to 7 is expected in mature compost, the slight variation between the two samples suggests different stabilization dynamics, influenced by the materials and processes used.

Wood sawdust, initially acidic (pH 4–4.5), plays a crucial role in buffering and stabilizing the compost’s pH. As decomposition progresses, the acidic nature of sawdust diminishes, helping the compost reach more neutral to slightly alkaline pH levels. The shift to a more neutral pH (6.9 for P1) or slightly alkaline (7.6 for P2) highlights the effectiveness of sawdust in balancing the pH, especially when combined with vermicompost. The introduction of these materials appears to be critical in achieving pH stability by the third month, as shown in Figure 4b. The observed pH stabilization, especially starting from the third month, indicates that both composts are entering a mature phase. This stability is key for compost usability, as mature compost with a stable pH is beneficial for soil application, improving nutrient availability and reducing the risk of plant stress. The differences in final pH (6.9 vs. 7.6) suggest that the specific composting conditions or material proportions (like the amount of sawdust and vermicomposting) may influence the end product’s characteristics. P2’s slightly higher pH could be due to a greater influence of alkaline components or less acidic initial materials.

3.4. Effect of Conductivity on Composting

Conductivity serves as an index of soluble salts, providing valuable insight into the nutrient content of the compost. Conductivity measures the ability of a solution to conduct electricity, which directly correlates with the concentration of soluble salts in the compost. A higher conductivity indicates a higher concentration of soluble salts, which can be beneficial for certain plants by providing essential nutrients. However, excessive salt concentrations can be harmful to plants, especially those that are sensitive to salinity.

While moderate levels of soluble salts in compost may enhance its nutritional value, an excessive salt content can lead to plant stress, reduced water absorption, and inhibited growth. This is particularly important for sensitive plants or for compost used in seed germination, where salt levels should be kept within a safe range to avoid adverse effects. Routine testing of conductivity, along with other parameters such as pH, moisture content, and the C/N ratio, ensures balanced and high-quality compost. Monitoring soluble salt levels helps prevent potential issues with salinity, ensuring that the compost is appropriate for plant growth and does not harm sensitive species. The conductivity values are initially low, ranging from 1.43 mS/cm in the case of potato peels, slowly increasing to 1.98 mS/cm in the case of the P1 sample and a maximum of 2.45 mS/cm in the case of the P2 sample. This is in line with the reported conductivity profiles for compost processes [10,12,13]. The increase in conductivity is attributed to the decomposition of organic substances that increases the salt content in the substrate. The final conductivity is within the expected range for compost (up to 7.39 mS/cm). Conductivity can be improved by adding salts. Figure 5 shows the evolution of conductivity starting from creating a lower value in the case of potato peels to the optimal value of 7.39 mS/cm.

3.5. The Effect of Volatile Solids

Volatile solids represent the organic content of the substrate, which is key for microbial growth and the overall composting process. Volatile solids are readily absorbed and digested by the microbial flora in the compost. These organic materials are the primary food source for the microbes responsible for breaking down the compost. As the microbes degrade volatile solids, they produce the heat and activity that drive the composting process forward. The percentage of volatile solids in the substrate is a key indicator of the compost’s organic content and provides insight into the progress of decomposition.

The reduction in volatile solids is a critical part of the composting process. This reduction typically occurs most vigorously in the first days of composting, with significant microbial activity taking place during the early stages. The graph of volatile solids over time serves as a useful visual tool for tracking the progress of decomposition and can help indicate when the composting process is nearing completion.

The thermophilic phase of composting, which is marked by higher temperatures (typically above 45 °C), plays a crucial role in the breakdown of volatile solids. This phase is particularly important for a rapid reduction in organic matter and the stabilization of the compost. The temperature profile during composting can often be used to deduce the intensity of the thermophilic phase and, consequently, the rate at which volatile solids are being reduced. Managing the reduction in volatile solids is essential for a successful composting process. As organic materials are broken down by microbial activity, the decrease in volatile solids reflects the decomposition progress. The early stages of composting and the thermophilic phase are particularly critical for the rapid reduction in volatile solids, which contributes to the overall stability and maturity of the compost. Adding only wood chips to the substrate resulted in a significant reduction in volatile solids. For both samples, a value of solid salts in the composition of a saturated paste of less than 4 mS/cm was determined, in accordance with the international technical norms in force.

3.6. Compost Testing and Quality Grade Determination

Compost testing is mandatory after the end of the ripening period and before it is launched on the market. While composting is a valuable process for recycling organic materials, ensuring the quality of the end-product is crucial. One key factor in compost quality is the concentration of metals, particularly regulated metals. Low concentrations of certain metals, such as copper, zinc, or iron, can be beneficial or even necessary for plant growth and development. However, excessive concentrations of these metals can be harmful to plants and the environment, leading to soil contamination and bioaccumulation. Maximum limits for metal concentrations in compost are established to prevent harmful effects on plant growth and to avoid the accumulation of metals in the soil over time. These limits are critical to ensure the compost remains safe and effective for agricultural or horticultural applications. If the compost does not meet the established metal concentration standards for a specific category, it will not qualify for use in that category.

To safeguard environmental health and promote sustainable agricultural practices, compost quality is monitored for specific regulated metals. This includes metals, such as cadmium, lead, mercury, and others, whose excessive presence can pose a significant risk to both soil and plant health. This study outlines some of the key limits on metal concentrations in compost, as established by regulatory bodies [3,14,15,16].

Regular testing and adherence to established metal concentration standards help prevent contamination and ensure that compost remains a sustainable resource for plant growth. The compost will be tested for those parameters listed in

Table 4. Maximum concentration for metals in compost [5].

No.	Metal	Category AA Compost (mg/kg Dry Weight)	Category A Compost (mg/kg Dry Weight)	Category B Compost (mg/kg mg/kg Dry Weight)	P1 (mg/kg Dry Weight)	P2 (mg/kg Dry Weight)
1.	Calcium	25,000	8000	5000	15,313.74	20,569.98
2.	Magnesium	2000	1500	800	1916.60	1909.19
3.	Sodium	25,000	5000	2000	994.44	1519.68
4.	Potassium	10,000	4000	3000	5249.40	7322.39
5.	Copper	100	400	760	28.65	23.22
6.	Manganese	250	500	700	279.75	167.81
11.	Zinc	500	700	1850	84.99	137.76

and will be classified according to the concentrations listed for each metal, calculated based on dry weight. To maintain compost quality and protect environmental and plant health, different categories of compost are defined based on the concentration of metals. These categories and their respective metal limits are as follows:

• Category AA compost must not contain controlled metals at concentrations exceeding any of the limits set out in column 2 of Table 4. This category is typically the highest-quality compost, with stringent standards for metal content, ensuring the compost is suitable for a wide range of applications, including sensitive uses such as seed germination and soil amendment for high-value crops.
• Category A compost must not exceed the controlled metal concentrations listed in column 3 of Table 4. This category is commonly used in agricultural and horticultural applications, where moderate levels of metals may be acceptable but still need to stay within safe and regulated limits.
• Category B compost must not exceed the limits for regulated metals specified in column 4 of Table 4.

This category is typically intended for use in less sensitive applications, such as landscaping and general soil conditioning, where higher metal concentrations may be tolerated.

Microelements (Fe, Mn, Cu, Zn, B, Mo, etc.) have a detached classification in the classification of fertilizer elements. This category is distinguished by low concentrations in vegetable dry matter (s.u.), not exceeding 0.01% of the s.u., within the limits of variation of N × 10⁻²–N × 10⁻⁶% of the s.u. As a supply in ppm: Fe—400–1000 ppm, Mn—25–100 ppm, Cu—15–50 ppm, Zn—12–60 ppm, B—12–80 ppm, Mo—2–4 ppm [17,18,19].

Essential roles as macroelements (N, P, K, S, Na, Ca, Mg), but less plastic, constitute plant matter, but they are mainly enzymatic and catalytic in the vital metabolic processes of plants. The exception here may be B, which, in addition to enzymatic effects, can be found in cell and tissue membranes, along with Ca, with a plastic role. It is applied in much lower doses than macroelements and effectively manifests itself with roles on the background of soil fertilization (sometimes complemented by foliation), with essential macroelements. By comparing the results obtained with the values specific to the compost categories, samples P1 and P2 fall under compost type AA (Category I) and A (Category II), respectively.

In the composting process, temperature plays a crucial role in determining the intensity and efficiency of microbial activity. In the experiment, the composting process begins vigorously, particularly due to the absence of temperature control. Environmental conditions have a minimal impact on the substrate during the initial stages, allowing microbial activity to dominate.

The process enters the thermophile phase around day 7, particularly in cases where simple composting is performed at 18 °C. During this phase, the temperature increases significantly, typically above 45 °C, promoting the rapid microbial degradation of organic matter. This high-temperature phase is critical for the reduction of organic carbon and the stabilization of the compost.

As composting progresses, the porosity of the substrate becomes an essential factor in maintaining microbial activity. The incorporation of materials like wood chips helps to enhance porosity, improving airflow and oxygen diffusion throughout the compost pile. The increase in porosity plays a significant role in sustaining aerobic conditions, which are essential for the efficient breakdown of organic materials.

In the thermophile phase, the reduction of organic carbon is most pronounced. The high temperatures encourage the activity of thermophile microorganisms, which break down complex organic materials, reducing the overall organic carbon content in the compost. This phase is particularly effective in speeding up the decomposition process, contributing to the rapid conversion of volatile solids and the overall progress of composting. While temperature control is not a major factor in this specific experiment, the CQA emphasizes the importance of maintaining optimal temperatures during composting. In industrial or larger-scale composting systems, temperature management is crucial for maximizing microbial activity and ensuring the production of high-quality compost [3,6,7]. During the thermophile phase of composting, the pH of the substrate increases significantly. This is primarily due to the rapid consumption of organic acids by the thermophile microorganisms, which are highly active in this high-temperature environment. As organic acids are broken down, the pH shifts towards a more alkaline state. Additionally, the decomposition of organic nitrogen compounds results in the increased concentration of ammonia, which further raises the pH. This increase in pH is a natural byproduct of microbial activity and reflects the progress of decomposition during the thermophile phase.

The moisture content of the substrate is a critical factor in maintaining optimal conditions for microbial growth. In this study, the amounts of sawdust and water used were found to be adequate for regulating substrate moisture to acceptable levels. Proper moisture levels are essential for maintaining the activity of microorganisms and promoting efficient aerobic decomposition. The moisture content was kept within a range that facilitated microbial growth and prevented excessive dehydration or anaerobic conditions [20,21].

Porosity is essential for ensuring proper aeration within the compost pile. Mineral additives played a key role in improving the substrate’s porosity, which helped maintain adequate oxygen levels and allowed for proper airflow throughout the pile. The addition of materials such as sawdust enhanced the structure of the compost, ensuring that oxygen could diffuse effectively to support aerobic microbial activity.

Frequent stirring (2–3 times per day) of the compost was essential for maintaining optimal conditions throughout the process. Manual aeration helped control both humidity and oxygen levels, preventing the pile from becoming too compact or wet, which could lead to anaerobic conditions. The consistent stirring ensured that the substrate remained well mixed and that microorganisms had access to sufficient oxygen, facilitating efficient aerobic decomposition. Effective composting requires careful management of moisture, pH, and aeration. The thermophile phase contributes to increased pH as organic acids are consumed and ammonia is released, but maintaining optimal moisture levels through manual aeration and the addition of materials like sawdust ensures the process remains aerobic and efficient. Regular stirring helps maintain the ideal balance of oxygen and moisture, promoting microbial activity and decomposition. Porosity is a vital component in the composting process, as it influences aeration and moisture retention. The addition of mineral additives and sawdust enhances porosity, which, in turn, improves oxygen diffusion and prevents the pile from becoming too compact, ensuring that aerobic conditions are maintained throughout the composting process.

In the experiment, the moisture content and alkalinity of the finished compost are important indicators of compost quality. For the P2 sample, the moisture content and alkalinity were found to be satisfactory, meaning it was ready for use without additional adjustments. However, for compost derived from the P1 process, there were some challenges. The compost produced from the P1 process required a period of wetting before it could be used effectively, as its moisture content initially fell outside the optimal range. In addition, the compost from this process needed enrichment with a series of mineral salts to bring it to an acceptable nutritional level for plant use.

Given that the feedstock for the composting process was derived from human food waste, the total concentration of heavy metals in the compost is considered negligible. Food waste, especially when it is sourced directly from kitchens and prepared foods, is generally free from heavy metals, which ensures that the final compost product is safe and suitable for use in gardening and agriculture [11].

The process improvement was achieved by adding wood chips, which played a critical role in enhancing the porosity of the compost pile. This increase in porosity helps maintain proper aeration and moisture retention, both of which are crucial for supporting aerobic microbial activity. The addition of wood chips also helps balance the moisture content and temperature fluctuations, resulting in a more efficient decomposition process. Therefore, the incorporation of wood chips into the in situ composting process has been deemed a promising improvement, enhancing both the quality and efficiency of the final product [20,21].

The physicochemical characteristics support the stated technical advantages of the ecological P2 compost obtained according to the invention, as follows:

• It is synergistic through the complementarity of the three biologically active components;
• It has high stability in terms of physicochemical parameters (time and light) due to the complex mixture of the three residual biomasses;
• It presents fertilizing complexity due to the presence of both organic (humus) and inorganic components represented by macronutrients in forms accessible to plants (soluble forms of nitrogen and potassium), soluble salts of Na, Ca, Mg, K and micronutrients (Mn, Zn, Cu);
• Reduces soil acidity to low basic, from pH 5 to pH 6.9–7.6;
• It has major properties of absorption and retention of water in the soil due to the presence of sawdust biomass;
• Due to the presence of humic acids in the composition (which have the role of chelating the metal ions Ca, Mg, Fe, Mn, Zn, Co, Cu), they help to fix mineral salts in the soil, which leads to the vigorous growth of plants (roots, stems, fruits, flowers), completing the properties of the soils on which they are grown;
• By using vegetable waste from the household environment as raw materials in the compost composition, a new method of their recovery is identified, thus participating in a reduction in the harmful effects on the environment generated by the old method of their disposal through simple storage [22].
• Compost can be used directly but also incorporated into the soil, because compost, due to its composition, maintains its fertilizing qualities for 2 years, a period in which it is no longer necessary to use any other fertilizer;
• It is low cost because it uses only organic waste as raw materials.

4. Conclusions

This study demonstrates that households in Romania can efficiently manage and exploit food waste by composting at home, through an innovative simple compost unit, even if the substrate has a low C/N ratio. The composting process can be successfully carried out on a small scale, at room temperature, and with minimal costs, making it an accessible and practical solution for households.

The research highlights the feasibility of implementing composting on a small scale at home, where families can manage food waste efficiently without significant financial investment. By using basic materials and equipment, households can produce quality compost for domestic use, which can be utilized in gardening or landscaping, reducing the need for chemical fertilizers.

The findings suggest that this home composting process could be adopted more widely, not only in Romania but also in other regions with similar conditions. Even with a low C/N ratio in the substrate, regular manual aeration and the use of bulking agents like wood chips can optimize the composting process, leading to the successful production of compost for household needs.

This low-cost, small-scale approach to composting offers significant environmental benefits, including a reduction in the food waste sent to landfills, a reduction in greenhouse gas emissions, and the creation of valuable organic compost that can enhance soil health. The economic advantages are equally compelling, as households can save money by reducing waste disposal fees and decreasing their dependence on commercial fertilizers.

Given the positive results of this study, further research and experimentation could refine the composting process to enhance its efficiency and ensure broader adoption in households. With the right knowledge, training, and support, home composting could become a standard practice in Romania and beyond, contributing to more sustainable waste management and resource utilization.

Composting is a significant innovation due to its ability to transform organic waste into a valuable product, reducing negative environmental impacts, supporting sustainable agriculture, and integrating waste into the circular economy. Continuous technological and procedural innovations improve the efficiency and accessibility of composting, amplifying its benefits [23]. Two compost samples were obtained as follows: P1 compost was obtained starting from five waste materials (potato peels, banana peels, orange peels, sawdust, and water), and P2 was prepared starting from nine waste materials (potato peels, banana peels, orange peels, apple peels, apples, cardboard, paper, dried vine leaves, and water). In order to investigate their potential to be used as fertilizers, various parameters were investigated: pH, aqueous extract conductivity 1:5 Humidity, Ca (mg/kg), Mg (mg/kg), Na (mg/kg), K (mg/kg), Zn (mg/kg), Mn (mg/kg), Cu (mg/kg), particle size (mm), N, C, H, C/N, C/H, N/H content. The physicochemical characteristics of the P2 compost support the technical advantages of this ecological composting method. The optimal moisture content, alkalinity, and nutrient levels observed in the P2 compost sample indicate the successful management of the composting process, leading to a high-quality finished product. These properties align with the desired outcomes for home composting, proving that it is possible to achieve a stable, effective composting process with minimal costs and effort.

The low humidity observed in sample P1 can be attributed to several factors. First, the raw materials used in the preparation of sample P1 might have had a lower initial moisture content compared to standard requirements. This could be due to the sourcing of materials from arid regions or insufficient pre-treatment processes. Additionally, the processing conditions, such as extended drying times or higher temperatures, may have inadvertently reduced the moisture content beyond the desired levels. Environmental factors, such as low ambient humidity during storage or handling, could also have contributed to the moisture loss [22].

Furthermore, the formulation of sample P1 might lack hygroscopic components that help retain moisture, making it more prone to drying out. Understanding these factors highlights the need for adjustments in raw material selection, processing parameters, and storage conditions to maintain appropriate humidity levels in future batches.

This study confirms that a low-cost and efficient composting process can be achieved on a small scale, using simple equipment and materials. The P2 compost was able to meet the necessary conditions for domestic use, indicating the viability of such systems for individual households. The simplicity of the process ensures accessibility for households, making it a practical and sustainable solution for food waste management.

Sample P2 demonstrates several key advantages due to its satisfactory moisture content and balanced alkalinity, making it highly suitable for practical agricultural applications. The optimal humidity content shows that the fertilizer remains easily spreadable and reduces the risk of clumping during storage and application. This consistency enhances the efficiency of application machinery, leading to more uniform distribution across fields.

Moreover, the balanced alkalinity of sample P2 plays a crucial role in soil health. It helps to neutralize acidic soils, promoting better nutrient availability and uptake by plants. This can lead to improved crop yields and healthier plant growth. The stable alkalinity also minimizes the risk of over-alkalization, which could otherwise harm the soil structure and microbial activity.

The use of ecological P2 compost demonstrates significant environmental benefits by reducing food waste sent to landfills and mitigating the greenhouse effect. Additionally, the compost produced can enrich soil, thus reducing the need for chemical fertilizers and improving agricultural practices. The process offers economic benefits as well, as households can lower waste disposal costs and cultivate their own compost for gardening or other purposes.

In practical terms, these properties mean that farmers using sample P2 can expect more reliable results, reduced application effort, and improved long-term soil management. These factors make sample P2 a valuable option for enhancing agricultural productivity and sustainability. We note the high stability and fertilizer complexity of P2 samples, and these properties could be beneficial in practical agricultural production. The potential effects and advantages of using P2 samples in real-world agricultural applications could involve improvements to crop yield, soil health, or sustainability practices for various culture. A farmer in a region with slightly acidic soil could use sample P2 as a fertilizer for their wheat crop. The soil tests reveal that the pH is around 7,6, which is below the optimal range for wheat growth. Given that sample P2 has a balanced alkalinity, it is chosen for its ability to raise the soil pH to a more suitable level, improving nutrient availability.

Step 1: Application Preparation. Before applying, the farmer checks that the moisture content of the fertilizer is within the ideal range, ensuring the product will be easy to spread and will not clump during the process. The farmer mixes the P2 fertilizer with the appropriate amount of water to achieve the desired consistency for even application.

Step 2: Fertilizer Application. The farmer uses a modern fertilizer spreader to distribute the P2 fertilizer across the fields. Because of its stable moisture content, P2 spreads evenly, and the farmer can achieve consistent coverage without overapplying or wasting fertilizer.

Step 3: Soil pH Adjustment and Nutrient Availability. After applying the fertilizer, the farmer observes that the slightly alkaline nature of P2 begins to neutralize the acidic soil, gradually raising the pH towards a more favourable range (around 6.0 to 6.5). This adjustment unlocks key nutrients such as phosphorus, magnesium, and calcium, making them more available to the wheat plants.

Step 4: Improved Plant Growth. Over the growing season, the wheat plants begin to show signs of healthier growth, with stronger root systems and more vibrant green leaves. The nutrients released from the fertilized soil contribute to improved crop vigour, leading to better overall yields.

Step 5: Cost Savings and Sustainability. Thanks to the efficient application of sample P2, the farmer notices that the need for additional soil amendments and fertilizers decreases. The stable alkalinity of P2 ensures that the soil remains in good condition for subsequent planting seasons, reducing the long-term cost of fertilizer inputs and contributing to more sustainable agricultural practices [4,23].

With the success of the P2 composting method, further research into optimizing the process and enhancing its efficiency could lead to the widespread adoption of home composting practices. In Romania and other regions with similar household conditions, small-scale composting offers a sustainable approach to waste management, contributing to a circular economy and a reduction in environmental impacts. This conclusion reflects this study’s findings on the feasibility and effectiveness of home composting in Romania, highlighting its potential for small-scale, low-cost implementation with environmental and economic benefits.

The scientific discourse on composting has evolved from early investigations of small-scale household systems to more complex analyses of community-level initiatives. In the early 2000s, some studies concentrated on the biochemical processes and efficiency of individual home composting systems. These foundational works provided essential insights into composting dynamics, including optimal conditions for decomposition and nutrient cycling [11].

In contrast, more recent research has begun to explore the broader implications of composting at the community scale. For example, researchers have investigated the environmental benefits of decentralized composting, such as reduced greenhouse gas emissions and the diversion of organic waste from landfills. However, these studies primarily focus on environmental outcomes, often neglecting the socio-economic and infrastructural challenges associated with scaling composting practices [4].

In the context of the circular economy, researchers have advanced the field by examining the socio-economic impacts of community composting projects, highlighting the potential for job creation and local economic benefits. Yet, their work did not fully address the long-term sustainability and scalability of such initiatives in diverse urban and rural contexts [23].

Our study builds upon this body of literature by offering a comprehensive assessment that integrates the environmental, social, and economic dimensions of community-level home composting. By addressing the gaps in current research, particularly in the scalability and community engagement aspects, our work provides critical insights into the feasibility and broader impacts of sustainable waste management practices. This holistic approach not only contributes to the scientific understanding of community composting but also offers practical recommendations for policy and implementation.

This study adds valuable knowledge to the field of home composting by analysing the decomposition process and its effectiveness under different conditions. In the future, we shall take a more comprehensive approach that addresses the limits of other parameters and explores other variables that influence composting results. By improving these aspects, this field helps us better understand how to optimize home composting for sustainability and waste reduction at the community level.