Compost with High Soil Conditioning Potential Obtained by Composting Using a Portable and Low-Cost System

Abstract

A simple and functional home composting process was investigated. This study consisted of three experiments altering the proportion of manure and sawdust, the former used as a nutrient and the latter as a desiccant. The mass proportions of manure–sawdust added weekly to the composting process were 1:1, 1:3, and 3:1 in the compost bins. The food waste used was provided daily by the IECT/UFVJM restaurant and added in equal parts, approximately 32 kg, to each of the three compost bins for a period of approximately 120 days. The bacterium Bacillus subtilis from the soil’s natural microbiota was added every fortnight to the three compost bins in a fixed volume solution equivalent to 150 mL. In the composting process carried out in compost bin 2, the compost with the highest final yield on a wet basis was obtained, at 39.89%. However, the compost produced in compost bin 3 had the highest compostable organic matter content at 24.66%, only 4.86% of the organic matter resisted composting, and it also had the best organic carbon/nitrogen ratio, at 32/1. Furthermore, this most promising compost, produced in compost bin 3, showed fulvic acid, humic acid, and total humic extract contents of 5.21%, 5.21%, and 10.42%, respectively, with these values being three to four times greater than that required by national legislation. The micro- and macronutrient content is also adequate, and only the NPK value needs to be maximized in this compost product for immediate commercialization. In this sense, we encourage the sustainable production of compost via home composting in the system investigated here for use as a soil conditioner capable of significantly improving its properties for safe development in regenerative agriculture.

1. Introduction

The exponential growth of the human population associated with rapid industrialization and urbanization has triggered enormous waste production. In 2012, the World Bank project estimated that the annual production of solid urban waste should be approximately 1.3 million tons for urban settlements and that this figure will probably double by the end of 2025 [1].

Solid waste management is one of the main parts of an environmental management system that in recent years has seen its approaches constantly modified to become an increasingly efficient and practical option for establishing sustainability based on the principles of 3R։ reduce, reuse, and recycle [2]. The organic fraction of urban waste is responsible for generating numerous environmental impacts, and recycling organic waste is considered a matter of ecological efficiency.

Organic waste is often disposed of improperly and sent to landfills and dumps, where it is a source of pollutants, causing serious health and environmental problems. Proper recycling of this organic waste can prevent impacts on the eutrophication of fresh and marine water, the formation of ozone harmful to human health and terrestrial ecosystems, human carcinogenic toxicity, ecotoxicity of fresh, terrestrial, and marine water, water consumption, and the scarcity of mineral resources [3]. The most common processes for recycling organic waste are composting and biodigestion, which consist of the degradation of waste in the presence and absence of oxygen, respectively.

Composting is a very interesting strategy, since it is a process of controlled decomposition accompanied by the stabilization of solid organic waste. During composting, active fractions of organic substances can be transformed into stable and complex macromolecules such as humins and humic and fulvic acids. These play a very fundamental role in various environmental processes and are crucial for regulating global carbon and nitrogen cycles in various ecosystems [4]. Several studies carried out in recent decades have proven that humins and fulvic and humic acids promote an increase in root biomass and size, inducing the growth of lateral roots and root hairs, allowing the plant to better explore the soil profile and be better able to survive in the event of a water deficit [5,6,7,8]. In this context, food production is expected to increase rapidly by 2025 due to the increase in population on planet Earth, and the use of non-toxic soil conditioning compounds should be encouraged instead of chemical fertilizers that pollute the environment and have a negative impact on biodiversity.

Home composting in cities has gained popularity as a sustainable way to reduce organic waste, but it faces specific challenges due to the urban environment. The main problems include (i) contamination of waste with a mixture of inappropriate materials such as plastics, glass, and other non-biodegradable items; (ii) contaminated organic waste that may include processed food scraps, packaging, or pesticide residues; (iii) unpleasant odors due to poorly managed composting due to an imbalance between carbon- and nitrogen-rich materials and accumulation of anaerobically decomposing organic matter; (iv) pest infestation in food scraps, especially meat or dairy products due to lack of adequate sealing in composters; (v) lack of space as many city dwellers live in apartments or small houses; (vi) lack of technical knowledge of the correct proportion of dry, carbon-rich materials and wet, nitrogen-rich materials; (vii) time for maintenance as the process requires monitoring and attention; (viii) urban climate as high temperatures can accelerate decomposition and, on the other hand, humid or cold places can hinder the process; (ix) integration with the public collection system as there is a lack of initiatives that integrate domestic composting with public waste management; and (x) high cultural and psychological resistance and misinformation because there is prejudice against composting associated with dirt, bad smells, or the idea that it is “something for rural areas” [9].

The aim of this work is to evaluate the physicochemical and microbiological quality indicators of the compost produced by a novel low-cost portable composting system capable of isolating waste from pests and rodents that occupy little internal space in homes and apartments in urban areas.

2. Materials and Methods

2.1. Collection of Organic Matter

The organic food waste was collected daily from the IECT/UFVJM cafeteria over a period of 3 months. In the institution’s Chemistry Laboratory, the raw material was selected, and the dimensions were standardized, with edges varying between 2 and 3 cm approximately, whose total masses over the period are shown in Figure 1.

2.2. Production of Organic Compost

The waste specified in Figure 1 was added daily and simultaneously in equivalent quantities to the C1, C2, and C3 compost bins identified in Figure 2. Each composting system consisted of three high-density polyethylene buckets with a capacity of 20 L, duly stacked. For example, the bucket identified as B1 was fitted with a polyethylene tap at the bottom, used to store compost with a high potential for conditioning the soil in a liquid state which is promising for fertigation. Buckets B2 and B3, on the other hand, were adapted with a side opening containing an “L” shaped polyvinyl chloride tube to allow air to enter and gases generated during the composting or decomposition process to escape and were therefore used as static reactors to produce solid-state soil conditioning compost. In addition, the lid of the intermediate bucket, B2, has small holes for the liquid to drain by gravity into the base bucket, B1. The order of addition was as follows: first filling bucket B2, then bucket B3, and swapping positions when B3 reached a maximum occupancy volume, in fact, in both buckets, equivalent to 70% of the total volume.

The three experiments adopted, as variables, the proportion of manure (free of residues and herbicides picloram, 2.4D, and glyphosate) and sawdust (from wood without chemical treatment), the former being used as a nutrient and the latter as a desiccant. The mass proportions of manure–sawdust added weekly in the composting process were 1։1, 1։3, and 3։1 in the compost bins identified as C1, C2, and C3, respectively, as shown in

Table 1. Bacteria solution, manure, and sawdust proportions used in composters.

Composter	Manure (g)	Sawdust (g)	Bacteria (mL)
1	800	800	150
2	400	1200	150
3	1200	400	150

.

The food waste was added in equal parts, using a semi-analytical scale, and homogenized after each addition to promote the necessary aeration, totaling approximately 52 kg on a wet basis at the end of the process (

Table 2. Mass in grams of the materials fed to the composters.

Composter	Component
	Wet Solid	Dry Solid	Liquid
1	52,145.92	23,318.64	28,827.28
2	52,145.92	22,358.64	29,787.28
3	52,145.92	20,438.64	31,707.28

), in each of the three compost bins for a period of approximately 120 days. The bacterium Bacillus subtilis (Tropical Cultures Collection, number 3131, not genetically modified organisms (GMOs)) from the soil’s natural microbiota was added every fifteen days to the three compost bins in a fixed volume solution equivalent to 150 mL. The temperature of the compound in the process was measured by a Portable Digital Infrared Laser Thermometer (Instrutherm TI 550, São Paulo, Brazil) at non-regular time intervals.

2.3. Mass Balance and Yield

Samples collected from solid and liquid fertilizers from composters identified as C1, C2, and C3 after 240 days were used to perform the mass balance and yield calculation. The gravimetric method was used for moisture analysis until a constant mass was obtained in an oven at 105 °C using a balance (Shimadzu, AUX 220, Marte Científica e Instrumentação Ltda, Santa Rita do Sapucai, Brazil) for masses up to 200 g and a balance, 2096 PP (Toledo do Brasil), for masses up to 200 kg. The mass of the liquid fertilizer was calculated using the density obtained through a 25 mL pycnometer, and the respective volume obtained through successive measurements in a 1 L graduated cylinder.

The mass balance allowed for associating the feed masses in the composter with the masses of the final composting products. Equation (1) represents the mass balance for the proposed system.

$$m_{residuo}+m_{manure}+m_{sawdust}+m_{bacteria}=m_{solids}+m_{bottom liquid}+m_{gases}$$

(1)

Here, m represents the mass of each of the components present in the composter system.

Equations (2) and (3) were used to calculate the yield of the products on a wet basis (Y_wet) and the yield of the products on a dry basis (Y_dry), respectively.

$$Y_{wet}=100\times \left({\displaystyle \frac{wet mass ofsolid product}{wet mass of solid in feed }}\right)$$

(2)

$$Y_{dry}=100\times \left({\displaystyle \frac{dry mass ofsolid product}{dry mass of solid in feed }}\right)$$

(3)

2.4. Physical and Chemical Analysis

Solid compost samples were obtained by mixing the material produced in the buckets identified as B2 and B3 from each independent compost bin, identified as C1, C2, and C3 after 120 days and C3 after 240 days. The liquid compost obtained in the bucket identified as B1 in each compost bin was not analyzed.

2.4.1. Sample Preparation

The sample was initially quartered and homogenized for pH analysis. For the other analyses, the sample was spread out and manually crushed. It was then completely dried at a temperature of between 65 and 110 °C in a forced circulation oven for 16 h. The sample was then sieved through a 2 mm mesh sieve. The particles with a smaller particle size were placed in an appropriate container and duly identified.

2.4.2. pH CaCl₂ 0.01 mol.L⁻¹

A total of 10 cm³ of the wet sample was placed in a 50 mL beaker, and 50 mL of 0.01 mol.L⁻¹ CaCl₂ solution was added. It was stirred for 15 min at 220 rpm using a shaker table and after 45 min of rest, it was measured using a PG 2000 photometer, Gehaka, São Paulo, Brazil, duly calibrated [10].

2.4.3. Physicochemical Parameters Associated with Organic Matter

The analyses of total organic matter (combustion), compostable organic matter, organic matter resistant to composting, total carbon (organic and mineral), organic carbon, total nitrogen, humic acid, fulvic acid, and total humic extract were carried out using the Manual of Soil Analysis Methods [10].

2.4.4. Macro- and Micronutrients

Phosphorus (P₂O₅ Total), potassium (K₂O Total), calcium (Ca Total), magnesium (Mg Total), sulfur (S Total), boron (B Total), copper (Cu Total), iron (Fe Total), manganese (Mn Total), and zinc (Zn Total) were analyzed using the Manual of Soil Analysis Methods [10].

2.4.5. Heavy Metals

Analyses to quantify lead (Pb Total), cadmium (Cd Total), and arsenic (As Total) were carried out using the Manual of Soil Analysis Methods [10].

2.4.6. Fecal Coliforms

The most probable number (MPN) technique was used, with a series of 3 tubes. For the presumptive test, lauryl sulfate tryptose broth was used, and for the confirmatory test, brilliant green bile broth. The thermotolerant coliform test was carried out using EC broth [11].

3. Results

The tactile–visual analysis showed that the final product obtained after completing the composting process was a completely disintegrated, moist compost with no unpleasant odor and a very dark color, as shown in Figure 2. The average moisture values obtained for the compost produced in the compost bins identified as C1, C2, and C3 were 69.2%, 71.2%, and 70.4%, respectively.

Table 3. Total mass in grams and percentage yields of the products tested.

Component
Composter	Wet Solid	Dry Solid	Bottom Liquid	Net Total	Gases
1	18,450.00	5685.91	14,261.20	27,025.29	4868.64
2	20,800.00	5986.62	11,564.50	26,377.88	1558.64
3	19,300.00	5706.42	12,857.30	26,450.88	1138.64
Yield Considering Wet Feed
Composter	Wet Solid	Dry Solid	Bottom Liquid	Net Total	Gases
1	35.38	10.90	27.35	51.83	9.34
2	39.89	11.48	22.18	50.58	2.99
3	37.01	10.94	24.66	50.72	2.18
Yield Considering Dry Food
Composter	Wet Solid	Dry Solid	Bottom Liquid	Net Total	Gases
1	79.12	24.38	61.16	115.90	20.88
2	93.03	26.78	51.72	117.98	6.97
3	94.43	27.92	62.91	129.42	5.57

shows the results obtained from the mass balance for the composters identified as C1, C2, and C3.

Table 4. Organic matter parameters obtained for organic compost produced by composting for 120 days.

Analysis/Dry Basis	Unit	Composter 1	Composter 2	Composter 3
pH CaCl2 0.01 M (Ref. 1:2.5)	pH	8.10	8.20	8.40
Total Organic Matter (Combustion)	%	21.58	26.98	29.52
Compostable Organic Matter (Titration)	%	16.55	20.93	24.66
Organic Matter Resistant to Compost	%	5.03	6.05	4.86
Total Carbon (Organic and Mineral)	%	11.99	14.99	16.4
Organic Carbon	%	9.19	11.63	13.7
Total Nitrogen	%	0.67	0.82	0.43
C/N Ratio (Total C and Total N)	-	18/01	18/1	38/1
C/N Ratio (Organic and Total N)	-	14/01	14/1	32/1
Humic Acids (120 days)	%	0.82	2.46	1.64
Fulvic Acid (120 days)	%	4.10	1.64	3.28
Total Humic Extract (120 days)	%	4.92	4.10	4.92
Humic Acids (240 days)	%	-	-	5.21
Fulvic Acid (240 days)	%	-	-	5.21
Total Humic Extract (240 days)	%	-	-	10.42

and

Table 5. Micro- and macronutrient parameters obtained for organic compost produced by composting for 120 days.

Analysis/Dry Basis	Unit	Composter 1	Composter 2	Composter 3
Phosphorous (P2O5 Total)	%	0.32	0.3	0.31
Potassium (K2O Total)	%	0.20	0.16	0.21
Calcium (Ca Total)	%	12.39	13.04	10.52
Magnesium (Mg Total)	%	2.05	1.89	1.68
Sulfur (S Total)	%	0.13	0.12	0.14
Boron (B Total)	mg.Kg−1	3	3	5
Iron (Fe Total)	mg.Kg−1	1936	1244	1121
Copper (Cu Total)	mg.Kg−1	9	7	8
Manganese (Mn Total)	mg.Kg−1	301	222	244
Zinc (Zn Total)	mg.Kg−1	19	13	15
Sodium (Na Total)	mg.Kg−1	2	2	2

show the results obtained for the main parameters analyzed in the quality control of the industries that produce organo-mineral fertilizers. Table 4 shows the results obtained for the physical–chemical parameters associated with organic matter, while Table 5 shows the results obtained for macro- and micronutrients.

Table 5 shows the fractions of humic and fulvic acids and their sum, expressed as a total humic extract, which also includes the humin content found in the compost samples after 120 and 240 days of composting, respectively. The results obtained for macro- and micronutrients, except for the carbon and nitrogen available in Table 4, are shown in Table 5 and indicate that the composts produced have good chemical conditions to be used as soil conditioners [12].

Table 6. Toxicity parameters obtained for organic compounds produced by composting for 120 days.

Analysis/Dry Basis	Unit	Composter 1	Composter 2	Composter 3
Lead (Pb)	mg.Kg−1	12.6	13.6	18.9
Arsenic (As)	mg.Kg−1	NQ	NQ	NQ
Cadmium (Cd)	mg.Kg−1	NQ	NQ	NQ
Fecal Coliforms	(NMP/Kg.MS)	ND	ND	ND

NQ—Not Quantified; ND—Not Detected.

shows the toxicity results obtained by quantifying the heavy metals lead, arsenic, and cadmium. In addition, the results of the microbiological experiments carried out on the samples can be used to check the phytosanitary conditions through fecal coliform analysis.

4. Discussion

The excellent disintegration of the compost can be attributed to the size control of the pieces of organic waste in the feed, whose edges varied between 2 and 3 cm approximately. It is important to note that feeding too much particulate material can cause excessive compaction and impair aeration. On the other hand, waste made up of very large pieces ends up retaining little moisture and hinders the reproduction of the microorganisms responsible for fermentation, significantly slowing down decomposition time. Barrena and Sánchez investigated several home composting systems in a review and came to the conclusion that in terms of weight, yield, temperature, respiration rate, and organic matter reduction, the best results were obtained in aerated systems [13].

Moisture content results are consistent with the fruit and vegetable waste fed into the IECT, which also had high moisture values, except for the eggshells made of calcium carbonate. The optimum humidity range for maximum decomposition rates is 50 to 60% and in this sense, the composting process investigated here took place under unfavorable conditions that probably influenced the decrease in decomposition kinetics [14]. This is because water occupies the empty spaces in the reaction medium, restricting the occupation of air and the diffusion of oxygen needed to oxidize organic matter.

Another unfavorable condition that influenced the increase in decomposition time was temperature, since the Chemistry Laboratory at the IECT is air-conditioned to 20 ± 2 °C and the home composting system here is preferably designed for use outdoors, which, due to the climate in the north of Minas Gerais, reaches average temperatures of between 28 °C and 35 °C practically all year round. In fact, the estimated time of 90 days for active degradation was initially postponed to 120 days under these conditions. The temperature measurements carried out demonstrated that the compound in the initial phase (approximate period of 30 days) remained in a range between 30 and 40 °C. In the intermediate period (between 30 and 90 days), the temperature increased, reaching values of 60 °C. Measurements at the end of the process showed that the temperature of the compound decreased drastically, remaining close to the laboratory room temperature.

The mass of gases is associated with the loss of moisture by evaporation and the volatile material formed and released during the degradation of residues, mainly water and carbon dioxide, and depending on the residue, it can also generate gases such as ammonia, methane, and hydrogen sulfide, among others, such as in the composting of pig manure [15]. The analysis of Table 3 suggests that the best solid yield values for the compost in both wet and dry basis calculations are a reflection of the high moisture content of the residues fed into the system at the beginning of composting. Considering the final wet product, the final composting yield considering wet basis feeding is between 35.38% and 39.89% of the initial mass, with the compost produced in compost bin 2 showing the highest final yield. The yield considering dry basis feeding reaches considerable values ranging from 79.12% to 94.43%.

The pH in composting is self-regulating and is useful for identifying the phase of composting food waste [16]. The initial phase is acidic, around 5 and 6, due to the formation of mineral acids and carbon dioxide, and then increases as the organic acids neutralize with the bases released during the decomposition of the organic matter, finally stabilizing at neutral or slightly alkaline values, usually between 7 and 8 [17].

In this context, the analysis of Table 4 shows that the compound produced in this research had a pH measured between 8.1 and 8.4, showing that after 120 days it was at an advanced stage of biodegradation. Vázquez and collaborators verified the physicochemical and biological characteristics of compost produced by decentralized composting programs using canteen waste and obtained pH values ranging from 7.4 to 8.34 and a C/N ratio between 11.6 and 22.6 in their samples [18]. The ratio of (organic) carbon to (total) nitrogen (C/N) should normally be close to 24/1, which is considered the ideal value for demonstrating the efficient evolution of the composting process [14]. If the C/N ratio is much lower than 24/1, there could be a large loss of nitrogen in the ammoniacal form, damaging the quality of the compost produced, especially in relation to macronutrients. On the other hand, a C/N ratio much higher than 24/1 induces a decrease in the rate of decomposition, resulting in compost with low levels of organic matter, since decomposing microorganisms need nitrogen to act as receptors and donors of electrons in metabolic reactions [14]. Table 4 shows that the C/N ratio is 14/1 for both compost samples produced in compost bins 1 and 2, while the compost sample from compost bin 3 showed a better C/N ratio of 32/1.

In addition, the compost sample produced in compost bin 3 showed higher total organic matter levels than the compost samples produced in compost bins 1 and 2, reaching a value of 29.52%. Furthermore, at the end of the active biodegradation process, this sample had the highest rate of compostable organic matter and the lowest rate of organic matter resistant to composting, at 24.66% and 4.86%, respectively. The sawdust used to control humidity is mainly made up of lignocellulosic materials which normally slow down the decomposition factor, thus explaining the higher rates of compost-resistant organic matter obtained in the compost produced in compost bins 1 and 2 [19]. We can see that the compost samples produced in compost bins 1 and 3 after 120 days had a higher total humic extract content than the compost sample produced in compost bin 2, as shown in Table 4. In addition, the compost produced in compost bin 3, because it had the best characteristics discussed above, was kept for another 120 days in the composting system without the addition of organic waste, manure, sawdust, and bacteria solution.

The content of fulvic and humic acids and total humic extract was measured again after this period and, remarkably, after 240 days, it rose from 4.92% to 10.42%, totaling an increase of almost 112%. Generally speaking, these figures show that under the experimental conditions, 120 days was not enough to complete all the composting stages. In fact, for the next 120 days, the degradation of organic matter continued the process of biostabilization through humification. A careful evaluation of the literature and current standards allows us to say with certainty that there is no Brazilian legislation that determines the maximum and minimum content of total humic extract in composts and fertilizers. However, companies generally offer their products on the market with a total humic extract content of between 7 and 8%. Adequate humic and fulvic acid content in compost is essential for improving the soil’s physical and biological characteristics [20]. In this sense, plants will be promoted due to high cell growth rates, as well as having greater resistance to diseases and pests. Humic acids originate from lignin and therefore have a high content of carboxylic acids. They have great water retention potential and are essential for high root growth [21]. Fulvic acids, on the other hand, have a lower molecular weight, a greater amount of phenolic compounds, and a smaller amount of aromatic structures, and these characteristics make them the most responsible for the high cation exchange capacity. The Ministry of Agriculture requires that organo-mineral fertilizers for soil application and fertigation have at least 3% and 6% organic carbon, respectively. The composts produced in the system proposed here and investigated as a potential soil conditioner showed organic carbon percentage values that exceeded the legal requirement by more than four times, such as the one produced in compost bin 3, which showed the equivalent of 13.7%.

In relation to the other macronutrients, nitrogen, phosphorus, and potassium (NPK) are considered the most important for plant development. The NPK content of organo-mineral fertilizers must exceed 3%, and in this context, the products obtained in this study are interesting for marketing as compost, but not as fertilizers, as they fall short of expectations since the NPK results are around 1.1 ± 0.1%, as shown in Table 5. Vázquez and collaborators obtained NPK values ranging between 2.17 and 6.88% in the composting of organic canteen waste and also in community composting. These higher values may be associated with the raw material used in the study, which, in this case, as reported, was a mixture of green and food waste, including leftover raw fruits and vegetables, food scraps, raw fish or meat, and other similar waste [18]. In addition to nitrogen, phosphorus, and potassium, calcium, magnesium, and sulfur are also essential macronutrients. The levels of these elements found for the three samples did not differ significantly from each other, but the high calcium content for the three samples can be explained by the large amount of eggshells, made up of calcium carbonate, used in the compost. Brazilian soil has an average pH of 5.8 and needs to be corrected in many agricultural regions, so this high calcium content could be interesting for marketing this compost as a conditioner for very acidic soils. Some micronutrients were quantified in the samples, including boron, iron, manganese, zinc, copper, and sodium, whose values are also available in Table 5. The same behavior of the macronutrient content is observed for the micronutrients, since there were no significant differences between the samples; however, the iron content seems to be above the average values found in this class of materials. Although it is an important micronutrient, as it plays a fundamental role in the redox reactions of photosynthesis and in metabolic processes such as chlorophyll synthesis, excessive concentrations of iron ions can reach toxic levels and promote oxidative stress in most plants, visually characterized by leaf tanning [22].

In Table 6, the results obtained for heavy metals showed that the compost was free of arsenic and cadmium, but lead ions were quantified in all the samples, with results ranging from 12.6 to 18.9 mg.Kg⁻¹ commonly found in slurry manure.

Ujj and collaborators carried out a quality analysis of a compound produced with yard waste and found between 5.13 and 11.76 ppm of lead [23]. In addition, using the most probable number methodology, all the samples were found to be free of fecal coliforms, which is very important since fecal coliforms are considered to be the most abundant environmental contaminants and can interfere with and compromise the quality of the product. In this investigation, the compost produced could be classified as “Class C”, which allows a maximum lead content of 150 mg.kg⁻¹ and tolerates up to 1,000,000 MPN/Kg.MS of thermotolerant coliforms [24,25]. An alternative to control the amount of lead ions would be to compost on spent mushroom substrate (SMS) as it improves the physicochemical properties of the compound such as slightly alkaline pH, greater hydrophilicity, and cation exchange capacity, facilitating the precipitation and biosorption processes for its removal [26]. In addition, this classification is related to a composting process originating from any amount of raw material from household waste that results in a product that is safe to use in agriculture.

An analytical reflection on the characteristics of the three samples from the composting systems investigated here leads us to understand that the mass proportion of manure–sawdust of 3։1 is the most suitable, as it provides a more efficient composting process in kinetic terms. This can be explained by the greater amount of nutrients in mass for the microorganisms involved coming from manure, coupled with the lower amount of lignocellulosic materials coming from sawdust, which are resistant to composting but sufficient to control humidity during the process.

Home composting, when properly monitored in terms of nutrients, granulometry, humidity, temperature, and aeration, proved to be viable for recycling solid organic waste, and can be extrapolated, expanded, and applied in various environments, such as schools, restaurants, and town halls, among others, as long as there is awareness on the part of the managers and members of these institutions. Composting pig waste has proven to be economically viable, in addition to the environmental benefits related to reducing pollution of water resources, soil, and the atmosphere [27].

In fact, environmentally correct disposal associated with appropriate composting technology proved capable of producing compost in this study, with a high content of organic carbon and fulvic and humic acids and good macro- and micronutrient content, which can reach a market value of between USD 40.00 and 50.00/tonne. This compost can also have its value-added property if we add a mixture of simple superphosphate and rock dust rich in water-soluble potassium and phosphorus at the end of the composting process, as demonstrated for yellow passion fruit seedlings grown in the north of Minas Gerais [28].

This strategy is intended to give the commercial product a greater capacity to remineralize the soil and it is estimated that the compost from the composting process described here, enriched with a mixture of superphosphate and sawdust, will reach values of USD 100.00/tonne as long as the NPK levels are maximized to between 3 and 5%. It is worth mentioning that the estimated social bias could lead to marketing strategies in small volume packaging for gardening and/or flower shops, adding value and reaching the amount of USD 1400.00/tonne. This strategy is even more relevant considering that Brazil is one of the world’s largest fertilizer importers.

It is worth noting that reconditioning the soil with organic compost instead of synthetic fertilizers can be three to four times more economical [29].

5. Conclusions

It was demonstrated in the system developed here that home composting of organic waste such as fruit and vegetable peels, eggs, and coffee powder is quite viable and can be carried out by non-specialized people in a safe process, free from pests and rodents and bad smells since that waste is properly reduced into small pieces and aerated daily. This is possible and promising from an environmental, social, and economic point of view as long as people are motivated and informed about the collective benefits for the population through advertising campaigns and demonstration of practical results.

The physicochemical and microbiological characteristics obtained for the produced compound demonstrate that the material is promising for commercialization. The micro- and macronutrient indexes are consistent with products sold in Brazil. Furthermore, humic and fulvic acids and humins are three to four times higher than products commonly sold for fertilization and soil conditioning. Only the NPK index was below that required by legislation, and this parameter can be overcome by adding sawdust with an appropriate composition.

In this context, the compost produced is promising for restructuring and conditioning the soil, including in the north of Minas Gerais and in many other regions of Brazil where the soil is weathered, often acidic, and deficient in organic matter. It is important to note that this practice of composting using a portable, low-cost system can be included in the concept of regenerative agriculture, which aims to develop practices for restoring productive areas that lead to the health of the environment as a whole, establishing the tripod of sustainability, i.e., social, economic, and environmental.