*4.1.2 Phase II: adhesion and subsidies*

Once the interest of the municipalities for community composting was demonstrated, the Provincial Council of Pontevedra started a new phase of REVITALIZA at the end of 2016. This phase consists in providing the necessary means for the implementation of the new management model as a global system for the treatment of bio-waste at the municipal level. With this objective, a second phase of REVITALIZA was established. Formally joining the plan was required for the municipalities to guarantee compliance with the legal obligations for the bio-waste treatment through composting. The formal adhesion of the municipalities allows them to benefit from three provincial collaboration lines: training of technical personnel, preparation of a municipal waste management plan and financial aid for composters and other resources supply.

 This second phase has allowed the Provincial Council to begin the implementation of the new management model based on the local composting of bio-waste by home and community composting in five municipalities. These municipalities have decided to change the waste service betting on a decentralized model that will close the cycle of organic matter. These municipalities are Mondariz Balneario, Mondariz, As Neves, Vilaboa and O Grove. These municipal entities are small (between 1000 and 11,000 inhabitants) with a scattered population and few high-rise buildings. This new phase aims to manage 50% of the bio-waste produced in these municipalities through local composting in the next 2 years and reduce at least 25% of the organic fraction that is not reused (animal feed), donated (banks of food), composted or stabilized, within 4 years.

To give continuity to the plan and provide it with more personnel resources, different selective processes have been called and two training courses in composting have been carried out during 2017 and 2018.

#### **4.2 Progress of REVITALIZA**

 Thirty-seven municipalities adhered to REVITALIZA, which represents 60.7% of the municipalities and 50.4% of the total population of the province. These municipalities are implementing the composting plan at different levels, either community composting or a municipal waste plan that includes home and community composting. The training and personnel selection activities have allowed 57 master composters who work at different levels and with different tasks and responsibilities. As part of the educational activities, 158 sessions were taught with 9448 participants, among students and teachers, in 51 educational centres.

The staff of the Provincial Council of Pontevedra actively participates in workshops, meetings, congresses, round tables, etc. that give visibility to REVITALIZA and allow to establish synergy with other institutions. REVITALIZA appears regularly in local and regional media reporting on the different events and activities that take place. These publications make it possible to give visibility to the plan not only at local and regional levels but also at national and international levels. Likewise, the neighbours and small producers who participate in composting serve as an example for the rest of the citizens, which allows to gradually involve more sectors of the municipality.

 Next, the main results and advances of local composting are presented. Regarding the small composting facilities, the Provincial Council staff is making contacts with waste management companies with the aim of assuming the municipal bio-waste that cannot be managed by home and community composting.

### *4.2.1 Home composting*

The first deliveries of individual composters started in the spring of 2018. As can be seen in **Table 3**, 37% of the composters expected delivery have been distributed in the five participating municipalities. The staff of the Provincial Council conducts door-to-door visits to collect data on the residents (address, number of family members, bio-waste management, etc.) in the areas of the municipalities that could manage the bio-waste by means of home composting. It should be pointed out that in more rural communities, traditional recovery of household waste at the household level, home composting and animal feed have diverted a part of bio-waste from municipal waste management system [14]. For this reason, a part of the rural population generates a small amount of bio-waste because of on-site reusing, to which one must add the second homes and the phenomenon of rural depopulation.

The master composters call the interested residents of the neighbourhood in which they are going to carry out the training and the delivery of composters. The training activities have been well received, with a percentage of attendance of 60% and an average of 33 composters delivered in 44 training activities.

During the follow-up visits to the home composters, the staff of the collaborating associations has solved doubts and established the necessary corrective measures related to the development of the composting process. The main incidents observed were the scarce quantity or lack of bulking agent and low moisture conditions of the composting material.

There is currently not enough data available to estimate the amount of bio-waste managed through this line of action. In [15], it has been estimated that in urban areas, where homeowners have access to garden space, home composting could potentially divert 20% of the biodegradable household waste stream from landfill disposal if approximately 20% of the community were actively engaged in home composting. The Provincial Council is studying the methodology to establish the amount of organic fraction treated in composters and, therefore, determine the contribution of home composting in bio-waste recycling.

#### *4.2.2 Community composting*

In November 2018, 76 CCCs formed by 535 modular units were in operation, spread over 28 municipalities in the province of Pontevedra. The master composters regularly visit CCCs, record the process parameters, such as temperature and changes in volume over time, and proceed to mix and turn the material between modular units, among other activities.

As previously mentioned, the work method allows the development of the composting process in three modular units. **Figure 5** shows the temperature profile of a


#### **Table 3.**

*Results of home composting in the five participating municipalities during 2018.* 

### *Towards the Recycling of Bio-Waste: The Case of Pontevedra, Spain (REVITALIZA) DOI: http://dx.doi.org/10.5772/intechopen.83576*

 neighbourhood CCC and a small producer CCC, already settled in the population, during the monitoring of the process in the three units. The temperature profiles of both CCCs showed patterns typical of the composting process, in other words, temperatures increasing to thermophilic levels (>45°C) followed by maintaining said temperature and a subsequent decline in temperature until reaching mesophilic levels. Thermophilic temperatures were maintained for 65 days and 50 days in the neighbouhood CCC and small producer CCC, respectively. Despite these differences, compost hygienization was ensured by continuously maintaining temperatures above 55°C for more than 15 days [16]. In general, all CCCs reach high temperatures in the bio-waste input unit, although the development of the process will depend on numerous factors. Although, material in community composters are more isolated than the material present in home composters, the environmental changes can affect temperature development (periodic access for bio-waste input and for process control tasks). Another factor that affects the process is the type of bio-waste: uncooked and cooked waste. The biodegradation of recalcitrant compounds accelerates after the cooking process. On the other hand, [17] observed that when large amounts of waste were added at each feeding, compost temperature and maturity increased.

 In the case of small producer CCC, it is observed that, after the turning of material from modular unit 1 (bio-waste input) to module 2 (homogenization), there was

#### **Figure 5.**

*Evolution of maximum temperature, fill level and turning during composting in the three modular units of (A) a neighbourhood CCC and (B) a small bio-waste producer CCC.* 

 a rise in temperature. The master composters perform deep or superficial mixing of the composting material according to the conditions of the process. Although, the transfer of material from one module to another allows greater aeration and homogenization, which can facilitate an increase in temperature. In both temperature profiles, the phases or stages discussed above are distinguished: intensive degradation and temperature rise to thermophilic conditions (stage 1), less intense decomposition with maintenance and/or decrease in temperature (stage 2) and progressive decrease in temperature and maturation of the compost (stage 3). After the process, the compost presents homogeneous appearance (soil-like material), dark brown colour and a pleasant earthy smell (**Figure 4**). To facilitate the use of the product as fertilizer, potting soil or organic amendment, it is necessary to sift it.

Next, the analysis data of 76 composts sampled during the years 2017–2018 are presented (**Table 4**).

 In general, composts showed high contents of organic matter, although the self-heating tests showed stability values indicative of mature compost. Important variabilities were observed among the compost for some parameters, such as electrical conductivity, ammonium and nutrients. The quality of municipal waste compost is dependent on many sources of variation including the composting facility design, feedstock source and proportions used, composting procedure, and length of maturation [18]. The different composition of the bio-waste affects the physicochemical characteristics of the compost. The high ammonium content could be a consequence of problems of degradation of the organic matter during the composting process due to a lack of moisture. However, only one sample had higher ammonium values than those considered suitable for compost 400 mg kg<sup>−</sup><sup>1</sup> [19]. Regarding electrical conductivity, high values were detected (78% of the samples with a conductivity higher than 2 dS m<sup>−</sup><sup>1</sup> ). The use of compost must be controlled so as not to have negative effect on plant growth, although the compost of municipal waste usually presents electrical conductivity values between 4 and 8 dS m<sup>−</sup><sup>1</sup> [18]. As for pathogen content, 7.9% of the samples presented values higher than that established by the legislation for *E. coli* while *Salmonella* spp fulfilled the required level in all the samples.


#### **Table 4.**

*Physicochemical parameters in compost from community composters (N = 76) during 2017 and 2018.* 

*Towards the Recycling of Bio-Waste: The Case of Pontevedra, Spain (REVITALIZA) DOI: http://dx.doi.org/10.5772/intechopen.83576* 

**Figure 6.** 

*Box plots of concentration data for six heavy metals in 76 samples of compost from community composting centres (CCC).* 

 The Spanish legislation on compost [20] classifies compost into three categories according to the heavy metal content: Class A, B and C. **Figure 6** provides information on the variability in the heavy metals concentration indicating the respective classification categories. The atypical data observed for Zn, Pb and Cd correspond to different compost samples with a metal concentration 4 times (Zn), 7 times (Cu) and 52 times (Pb) above the mean values and, hence, they are considered outliers from analytical errors. Without taking into account samples with outliers, it is observed that 17.81% of compost belongs to Class A, 75.34% to Class B and 6.85% to Class C. For the last class, the metals Zn (4 samples) and Cd (1 sample) are those that exceed the thresholds of the regulations. There is a consensus in the scientific literature that aerobic composting processes increase the complexation of heavy metals in organic waste residuals and that metals are strongly bound to the compost matrix and organic matter, limiting their solubility and potential bioavailability in soil [21].

If we consider heavy metals separately, all samples belong to Class A for Hg (<0.4 mg kg<sup>−</sup><sup>1</sup> in all samples), Cr and Ni, while more than 96% of samples meet the levels for Class A in Cu and Pb concentrations. In 66.07% of Class B compost, Zn levels determine its classification. The presence of these heavy metals in the final compost may have different sources. In [22], it was concluded that the heavy metal content of the compost can be affected by the pollution of diverse exogenous sources and their origin can be found in the auxiliary materials used, the environment, the process or the storage method used. The possible sources of Zn are being evaluated to determine the necessary actions that reduce its content in the compost.

In **Figure 7**, the estimation of bio-waste treated in the CCCs of the province of Pontevedra is presented since the implantation of the first centres until the first semester of the year 2018. The quantities of treated bio-waste were calculated from the data of filling level of the CCCs, percentage of volume reduction over time

#### **Figure 7.**

*Estimation by semester of the amount of bio-waste (including the vegetal fraction used as bulking agent) and the total amount accumulated in the CCC implemented in the province of Pontevedra.* 

and densities of the different materials. The bulking agent: food waste ratio 1:1 in volume was considered.

 Finally, it should be noted that community composting have transformed, through a biological and aerobic process, about 1459 tonnes of organic waste and vegetable remains, into a biologically stable material that can be used as a soil amendment. This reduces the impact of bio-waste on the environment and makes possible the use of the resources that it contains.

## **5. Conclusions**

 The Provincial Council of Pontevedra promotes a change of model of waste management through the implementation of composting as treatment of the organic fraction generated in the municipalities, reducing the collection and transport services and the environmental and economic problems associated with them.

 The new model has been designed to respond to the particularities of the province and the municipalities that compose it, so that it adapts to the population distribution characterized by dispersion in rural areas. This fact, together with the priority of compliance with the principle of proximity in the waste management, has made it possible to move towards a decentralized model based on the local composting of bio-waste at the municipal level. The provision of personal resources, and not only material resources, presented by REVITALIZA is a fundamental and necessary axis that demonstrates that the waste management projects developed by the administrative entities must be accompanied by training and raising of awareness to be accepted by the citizens.

Local composting allows the treatment of the bio-waste of the household and small producers on site. Bio-waste ceases to be part of the collection, transport and treatment line of the mixed fraction, thus reducing the environmental implications caused by its centralized management.

## **Acknowledgements**

The authors thank the staff of the Provincial Council of Pontevedra for the technical support and the data provided.

*Towards the Recycling of Bio-Waste: The Case of Pontevedra, Spain (REVITALIZA) DOI: http://dx.doi.org/10.5772/intechopen.83576* 
