*3.2.1.2 Stage 2: homogenization*

When the bio-waste input module is full, approximately in 4 weeks, the master composters move the material to the second module. The modular units are assembled together but have slide-out panels on all sides. This allows easy access on all sides and

#### **Figure 3.**

*(A) Community composting centre with six modular units and bulking agent bags and (B) details of the modules during the composting process.* 

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

#### **Figure 4.**

*(A) Bio-waste feeding in the first modular unit, (B) transfer of the material from the first module to the second to continue the composting process, (C) compost screening and (D) details of the physical aspect of the compost.* 

the movement of the material from one unit to another. Turning the material to the second module allows a more intense homogenization by mixing the most recent biowaste inputs with degraded materials of the bottom. At this stage, the material might be too dry and the degradation process can stall; so, moisture control is important.

#### *3.2.1.3 Stage 3: maturation*

 The material of the second unit is turned towards the third unit where the compost maturation takes place. The temperature drops progressively and more complex compounds are formed. The finished material has lost its original appearance. Compost is a soil-like material, dark with a pleasant earthy smell. Master composters sift the compost to facilitate its use as a fertilizer product or organic amendment. The compost can be distributed to citizens who have participated or can be employed by the municipal staff in the gardens and public areas.

As far as possible, the installation of urban or community gardens associated with CCC is promoted, so that the produced compost goes to the garden itself. The neighbours or small producers, instead of taking the compost produced for private use, would distribute the products of the garden. In [13], it has been proposed that the shift of municipal waste management systems from landfill disposal to resource recovery requires, among other aspects, sufficient urban gardens to divert the compost produced.

Throughout the process, master composters carry out the monitoring and control of composting and its key parameters (taking of temperature, filling level measurement, correction of incidents, etc.) and the necessary physical work required by the process (bulking agent addition, mixing, rewetting, turning, screening, etc.)

#### **3.3 Small composting facility**

The small composting facilities will manage bio-waste that cannot be treated through the other lines of action due to technical or operational causes. As has been described, local composting, both home and community composting, presents requirements for its implementation. In the case of high population densities

distributed in buildings of various heights, local composting cannot assume all biowaste generated. Therefore, it is necessary to implement a collection and transport service and bio-waste treatment in composting facilities. Following the principle of proximity, these facilities should be located close to the waste-production centres, so that the bio-waste transport is minimized and the treatment in areas near the point of generation is prioritized. These facilities must be small scale, handle between 1000 and 3000 tonnes year<sup>−</sup><sup>1</sup> . These will have limited mechanization given that the input waste cannot contain non-biodegradable materials or impurities (maximum allowed 10%). Medium-scale facilities could be established in the case of the two cities with the largest population of the province: Pontevedra and Vigo.
