3.1. Profile of Composting Local Stakeholders
Income and space availability are not determining factors for people who make home compost. One of the possible reasons for the low requirement regarding space availability may be the preference for composting in stacked boxes (worm farms or boxes with microorganisms), used by 66% of the respondents’ home composters. The sociodemographic results are in
Supplementary Section S4.
Figure 4 shows the models used by the initiatives surveyed in this study. Some initiatives used more than one composting model, details of which are given in
Table 3.
Community composting uses a greater variety of models, which shows an ability to adapt the practice in different situations, depending on the number of people involved and the physical structure conditions typical for decentralized composting [
46]. Overall, decentralized composting units have a processing capacity of up to 5 t/year [
46], receive waste from nearby generators, and are usually simpler due to the smaller amount of material received [
47].
The mass of waste diverted from the landfill, presented in
Table 2, was calculated considering the respondents who knew how to inform each group. They are 83% (
n = 10) for households, 64% (
n = 7) for community/institutional composting, and 75% (
n = 3) for commercially oriented composting. The per capita PSOW deviation of PSOW from landfill to home initiatives was estimated to range from 5.9 to 8.2 kg/month (calculated based on the number of people who benefit from the income and considering the PSOW density equal to 0.435 kg/L [
48] when estimated by volume).
The compost production estimate (
Table 4) was based on 62% of interviewees who knew how to respond. Only one community initiative weighed the compost produced, and the rest of the interviewees answered based on empirical or academic knowledge.
The estimate of the mass diverted from the landfill and the organic compost produced, based on the perception of the interviewees, are uncertain data since the amount of waste inserted in the systems and the percentage of reduction for the matured compost vary, depending on the type of food consumed [
55].
The use of compost for one’s own benefit is one of the main concerns in the practice of composting. In this survey, 96% of respondents use it personally or at the same composting site, as shown in
Figure 5.
According to the interviewees, compost donations are made to people close to the composting site or within the circle of relationships of those who compost. Not everyone donates the compost produced, but those who do are generally sought after, and none of the interviewees had their product refused. Others prioritize returning the fertilizer to those engaged in the management or segregation of waste to reward their participation.
Home composting had an efficiency of between 42% and 59% deviation concerning the waste generated when considering the estimate of 24.3 kg/month of MSW from the common collection and the percentage of 57.15% of PSOW in the composition of MSW of the municipality studied [
21,
56]. The value is close to other studies that evaluated the efficiency by direct measurements, 47% [
57] and 77% [
53].
Decentralized composting can reduce transportation costs, landfill fees, and the purchase of fertilizers [
58] and increase landfill life. A home composting program expanded to the entire municipality studied would have the potential to save approximately USD 9700 per month in landfill fees or an equivalent to approximately 3% of the total budget expended on it (
). The estimative considers the 10% population participation rate, suggested by Pai et al. [
58], the estimated average deviation of PSOW of the households in this study, and the cost of USD 17.97 per ton with a landfill operation in the municipality studied in 2022 (verbal information (information provided by URBAM employee)).
In this study, 26% (
n = 7) of the interviewees had no expenses with the implementation of composting, as shown in
Figure 6. However, 66% (
n = 8) of the households and 55% (
n = 6) of the community/institutional local stakeholders claimed to have incurred expenses. Three households and one community initiative claimed to have costs of maintenance involving fuel, the purchase of dry matter, and/or a delivery service of material to the home. Expenses are occasional and account for, on average, USD 13.03 per year.
For commercial composting, two companies reported expenses with implementation alone, with an approximate average of USD 121.60. Another company said it spends around USD 485.00 to USD 585.00 monthly, involving maintenance costs.
Table 5 summarizes the implementation expenses for the home and community initiatives measured in this research and presents similar case studies.
The reported costs specifically cover the initial investment in equipment and infrastructure. Due to the diverse range of equipment involved, measuring the time duration proves challenging. To facilitate comparisons, we estimated the average cost per ton of waste diverted from community initiatives, assuming a twelve-month compost production period—which is considered the minimum expected durability. Notably, the lowest cost for compost production in this study is attributed to human labor (voluntary), with no consideration of expenses related to campaigns or government programs (which are non-existent in the municipality under investigation).
The effort encompasses the energy expended on activities directly and indirectly linked to composting, such as source separation, packaging, and handling.
Figure 7 illustrates the perceived effort of interviewees, who provided their insights on a Likert scale, ranging from little to a lot at the extremes.
The greatest perceived effort for community composting activities also involves social issues (these elements configured non-operational difficulties and were detailed in item 3.2.9), as reported by Interviewee 14.
“Even mentally, you have to talk to people more and convince them, and then I think it’s a more exhausting process. It’s not just the day-to-day handling there because that’s not a problem for us, considering the volume we’re there. But we often cannot take a step further because I will depend on another structure.” (Interviewee 14).
Although it has not been a task foreseen in this work, some interviewees affirmed that the perceived effort at the start of the practice was more significant or may be related to incorporating the habit and the problems faced at the beginning.
Figure 8 and
Figure 9 show the practice time of two groups of local stakeholders and the time spent with handling, respectively.
No clear correlations were observed between the perceived effort and time spent without handling (r = 0.178), segregated residue (r = −0.084), and years of practice (r = 0.137). According to some interviewees, the time dedicated to handling is often considered a rewarding activity. Notably, there was a correlation between work time, handling duration, and the amount of waste diverted from landfills (r = 0.679). Commercial initiatives engaging in activities that take less time (as depicted in
Figure 8) may indicate the social perception of a potential new market niche.
Approximately 80% of the respondents reported composting or having initiatives in place for at least one year, while limited data were available on the population’s participation time in community projects exceeding two years.
Table 6 contrasts the active time of the initiatives in this study with the population’s participation time in source segregation for community composting and volunteering compared to other initiatives.
Overall, the lowest observed percentage between 6 and 12 months across various studies highlights the fragility in the continuity of composting practices or participation in composting schemes. The higher rate of activities after one year is influenced by project duration and influx, masking dropouts during this period. Given that those who remain over one year are more likely to continue in the project, it is suggested that adhesion campaigns should be consistent within the first 12 months to solidify composting schemes [
60]. Additionally, government incentives and training programs can further encourage and support this practice.
As reported by the interviewees, the composting time varied from 1 to 12 months, with 50% indicating that the process takes 3 to 4 months, aligning with similar findings in other community composting case studies ranging from 2.5 to 5 months [
61,
62,
63]. The processing time aligns with Kiehl’s assertion that compost stabilization occurs between 1 and 2 months, maturing between 3 and 4 months [
36]. Variations depend on the initial conditions like particle size and the carbon/nitrogen ratio [
36], as well as physicochemical parameters throughout the process, such as the pH and moisture content [
64]. However, this study did not delve into verifying these parameters or assessing the quality of matured compost, as it was beyond its scope.
3.2. Influencing Factors
The factors influencing composting are motivators (opportunities) and inhibitors (barriers). Among the motivating factors are the trigger factors, which led to the decision to start composting.
Figure 10 presents the influencing factors and triggers identified in this study and those reported by Pereira and Fiore [
30]. In this study, the factors were centered on the experiences of the social actor and not on the initiative, except when two actors discussed similar factors related to the same initiative. In this case, this factor was considered only once.
Trigger factors (
Table 7) were obtained based on personal experience or the history of the initiative provided by the interviewee. These factors are not necessarily exclusive to the practice and only functioned as a trigger for the decision to compost. In total, 61% of the expertise cases covered two or more trigger factors.
In essence, insights from the interviews revealed three distinct categories—professional issues, social technology, and the impact of the COVID-19 pandemic—adding nuances beyond those previously reported by Pereira and Fiore [
30]. Professional issues pertain to the conditions in which one’s job directly or indirectly fosters a connection with composting. Social technologies, in turn, drive community-based social transformations [
65], encompassing values such as collaboration, sustainability, empowerment, knowledge dissemination, human-nature connection, and community support for projects.
The COVID-19 pandemic, treated separately due to its unique impact, led to changes in people’s routines, resulting in a reduction in food waste [
66]. This reduction was attributed to improved food planning and preparation [
67], increased available time, and a heightened awareness of waste consequences [
68]. However, in community and institutional settings, the overall decrease in people’s movement or the absence of individuals to maintain management adversely affected many initiatives. In this case study, 32% of the discontinued initiatives had to close due to pandemic-related challenges. Descriptions and details of the other influencing factors are in
Supplementary Section S5.
3.3. Operational and Non-Operational Difficulties
The operational difficulties identified in this study, presented in
Figure 11, refer to problems related to system management, which involve infrastructure issues and a lack of technical knowledge.
In the initial stages of home composting, half of the interviewees faced operational challenges, with issues like fruit fly infestations, earthworm escapes, or deaths, and unpleasant odors, all linked to insufficient humidity and oxygenation conditions. Ultimately, 25% of the home composters continue to grapple with the discomfort caused by fruit flies as the lone persisting problem.
Conversely, operational challenges were uncommon for community and commercially oriented initiatives, with only two instances reporting initial problems with flies and rats. Within these groups, primary operational hurdles centered around low maintenance due to time or personnel constraints and employee turnover. Recurrent difficulties in these contexts, identified through interviews, were associated with non-operational factors, including social and socioeconomic challenges.
Mobilizing new participants poses a significant challenge, particularly among those perceiving the activity as ‘dirty’ or resisting direct contact, associating composting with handling inconveniences like odor and undesirable animals. Another hurdle lies in the lack of recognition of post-segregated organic waste (PSOW) collection and treatment as a service subject to payment, leading to the disregard and undervaluing of the logistical and composting process costs.
Additional reported problems include material theft in public spaces, challenges in assigning responsibilities to individuals already occupied with other primary duties in institutions, and difficulties in composting all generated waste due to the volumetric limitations of compost bins. Trust in the system is also questioned due to insufficient investments, support, and dialogue between the government and the population, along with the organization of one-off events or initiatives lacking continuity with ongoing efforts.
3.4. Textual Statistics Analysis
Descending hierarchical classification (DHC), shown in
Figure 12, was performed in the respondents’ native languages with a correspondent translation in
Supplementary Section S6. For the interpretation of the classes, the first most relevant words resulting from each class were considered.
The analysis of word classes allows us to infer the most prevalent factors in this study, namely education, infrastructure, and social influence, without delving into their intricacies. Reading begins with the upper row, forming two major groups: classes 2 and 3, pertaining to education and social issues, and classes 1, 4, and 5, relating to operational concerns.
Class 2 is linked to environmental education, encompassing the experiences tied to educational spaces and individuals. The represented actions involving verbs delineate processes of knowledge exchange, dissemination, and the associated energy costs. The educational environment emerges as a pivotal space in individual development, contributing to the construction of pro-environmental behavior and fostering social influence. It also serves as a crucial avenue for driving the social and cultural changes necessary for ensuring the viability of the system.
Class 3 encapsulates education in terms of awareness-raising and infrastructure, underscoring the role of public authorities in waste management and the performance of the private sector. This class also evidences the acknowledgment of local stakeholders with the mention of them, emphasizing their vital role in collaboratively constructing a composting system.
Class 4 revolves around handling activities and composted materials, standing out as the class with the highest number of verbs, with the most relevant word being an action verb. Class 1 represents the phase following waste processing, also interpretable as the perceived benefit. Class 5 addresses the operational challenges in the process, encompassing the control and parameters of composting. It holds the highest frequency of occurrence, underscoring its significance compared to other themes in the study.
3.5. Local Market
Out of the 50 potential trading establishments identified, 32% were found to retail some types of organic agricultural inputs. Concerning these establishments, 4% lacked a responsible person available for an interview during the data collection phase of this research. Consequently, information on product packaging was consulted. Furthermore, 34% of the establishments asserted that they did not sell the product under scrutiny in the study, and an additional 32% were not accessible for survey purposes.
The organic-based agricultural inputs identified in the study area were classified by the establishment and/or suppliers as topsoil, earthworm humus, cattle manure, chicken manure, substrate, soil conditioner, organic fertilizer, organic compost, and peat. Among the establishments consulted, those not selling topsoil offered organic compost. According to Brazilian legislation, organic fertilizers are considered as manure, peat, earthworm humus [
69], and organic compost [
70], which can also be used as a soil conditioner and substrate ([
71] apud [
70]).
Interviewees mentioned the number of sales only for the most commercialized products, emphasizing topsoil.
Table 8 presents the characteristics of the most recurrent products in the researched establishments.
The average weekly sale for the 10 kg package was 17.25 units, and for the 20 to 25 kg package, 45 units. However, this was reported as one of the most sought after; the most offered by the establishments were 5 kg and 10 kg. This difference is probably because small establishments without larger packages are available for selling the product.
Figure 13 presents the average price per kilo of products sold in packages of 2 kg to 5 kg and sold in 80% of the establishments covered in this study.
Companies providing post-segregated organic waste (PSOW) collection and treatment services, with plans to sell organic compost in the future, propose an average price approximately 30% higher than soil conditioner and organic compost and 60% higher than local topsoil prices. To enhance the chances of local market acceptance, the PSOW organic compost needs to be perceived by the population as offering greater added value compared to competing products or priced more competitively against substitute products available in the local market.
Studies indicate there is a low acceptance of organic compost by peri-urban farmers in São José dos Campos, who prefer agricultural inputs or any other types of fertilization to those made through composting [
72]. In the metropolitan region of Vale do Paraíba (MRVP), 69% of farmers use chemical fertilizer, 68% animal manure, 28% vegetable compost, and 4% humus [
73]. Promoting home composting emerges as a viable strategy to boost population acceptance. Home composting offers local use without the need for extensive logistical infrastructure, and users have insight into the production process, making it feasible, even in confined spaces.
Agriculture assumes a central role in any local circular economy strategy. Its practice in urban environments can contribute to a low-carbon economy and enhanced food safety, provided precautions are taken to prevent contamination by pollutants [
74]. Additionally, access to locally produced food proves strategically valuable during crises [
75], such as the COVID-19 pandemic. According to [
73], the MRVP exhibits areas with good or moderate suitability for olive cultivation.
In Brazil, establishments that sell or produce fertilizers, correctives, or substrates for plants must be registered with the Brazilian Ministry of Agriculture, Livestock and Food Supply (MAPA). In this study, only 52% of suppliers and 25% of establishments were registered in May 2022.
Table 9 shows the price per kilogram, verified in this study, of products based on suppliers with and without MAPA registration.
This research reveals that, in the local market, products lacking registration with the MAPA are, on average, about 50% cheaper than registered products. It is important to highlight that registration ensures that a product has undergone an agronomic efficiency assessment process and meets the quality conditions required by MAPA [
76]. However, no studies explored the impact of MAPA registration on the product’s competitiveness in the market.
Vermicompost presents an opportunity to enhance the value of post-segregated organic waste (PSOW) in the local market, as evidenced by this research, which indicates that the price of earthworm humus ranks among those with the highest added value. Furthermore, as per national legislation, humus generated and processed naturally, without the addition of chemical products, may be exempt from registration when used for personal purposes or sold directly to the final consumer, provided it adheres to specific legislation regarding the usage requirements and safe application [
77,
78].
Compared with organic compost, vermicompost offers greater moisture retention capacity in the soil [
43], improves the diversity and stability of the bacterial community in the ground [
79], provides higher levels of nutrients [
80,
81], with higher percentages of total nitrogen and phosphorus [
82], has better availability quality [
83], and can reduce GHG emissions by 23 to 48% if feeding under ideal conditions [
84]. Vermicomposting can reduce levels of toxic metals and break them down into non-toxic forms [
85]. Furthermore, humus generated through vermicomposting can be used immediately after production [
84], and the process is adaptable for small spaces, making it suitable for home contexts.
Despite the potentialities compared with compost, vermicomposting is ten times less studied than composting for treating PSOW [
82]. There are few studies on the viability and sustainability of vermicomposting for urban waste management and the socioeconomic impact of the practice and use of the product in agriculture [
86]. Research investigating such issues can contribute to the appreciation of PSOW.
This research identifies 21 suppliers of various organic inputs, along with 2 others not identified. Only two suppliers are headquartered in the municipality of São José dos Campos, while eighteen are scattered across other cities in the state of São Paulo, and one is located in the state of Minas Gerais, as indicated in
Figure 14.
This research found that 80% of the suppliers are located within a radius of 200 km from São José dos Campos, and the longest route is approximately 670 km. Given the low value of agricultural products relative to their volume, transportation costs exert a significant impact on the overall price [
88], making traveling long distances unfeasible. For mineral fertilizers, the transportation cost represents around 60% of the price composition [
89]. There are no available estimates regarding the maximum economically viable distance for transporting organic fertilizers in the Brazilian market.
3.6. Opportunities and Barriers
The yet-unexplored potential of PSOW compost production in Brazil holds significant promise for urban and peri-urban food production across Brazilian municipalities [
90]. Gathering local information on the availability of waste, strategic locations for processing the material, and potential consumers is crucial for consolidating this market and the segregation at the source of the PSOW.
Figure 15 presents a SWOT matrix outlining the primary opportunities and barriers to composting in a municipal context, as identified in this study, categorized into social, economic, and environmental dimensions.
The matrix mainly explores the social and economic aspects since the panorama reached is limited to the vision of the sectors of the PSOW chain consulted in this study, the local stakeholders that carry out the composting, the market offer, and the secondary data from peri-urban farmers. Although the environmental dimension is rarely mentioned, it is already well explored in LCA studies [
91,
92] and circular economy studies of PSOW [
93]. In the same way, the technical aspect was not a previous intention for this work, which focused only on the three dimensions of sustainability, highlighting that the technical aspect is equally important. Future studies may explore the quality of the compost produced in a local context to complement this topic.
The findings from this study suggest a profile akin to that of developing countries, where initiatives are spearheaded by local stakeholders [
94] that persist even with low institutional support [
95] and limited collaborative interaction among the intersectoral actors involved in the PSOW chain [
94]. Hence, it is reasonable to extrapolate the main observations to similar territorial contexts, emphasizing the importance of considering local specificities.
This study also highlights the need to create mechanisms that ensure the effective contribution of the local stakeholders involved in the composting chain in the participatory processes of waste management. This strategy may enhance consistent cultural changes supporting the transition from the current linear chain to a circular chain, as reported by Ddiba et al. [
94]. Despite the current low participation, it is understood that the local government can serve as a catalyst for structuring the network of local stakeholders in composting. This can be achieved through strategies that not only ensure the chain’s continued operation but also minimize the need for long-term government intervention.