# Strategies for the Sustainable Management of the Organic Fraction of Municipal Waste
## 2 Materials and Methods
### Study of Raw Material Mixtures and Composting Process  
A pilot composoting experience was carried out for four months, from 4 November 2019 to 27 February 2020, at the Tomas Ferro Experimental Station of the Polytechnic University of Cartagena, using the composoting area set aside on the farm for this purpose. After studying the bio-waste volumes managed by the municipality, it was suggested as a starting strategy to consider three feedstocks for blending:  
* Biodegradable material from the hospitality industry and private houses: for this test, the biodegradable material was obtained from the dining room of the University Residence of the UPCT, as a representative of the materials obtained in the municipality. The waste was collected daily and taken to the experimental station. The waste was transported in bags, which were removed to avoid fermentation. The waste was crushed prior to composoting, leaving a medium consistency. A total of 9550 t of stabilized biodegradable material from household and hotel waste is separated annually at the Cartagena triage plant.  
Figure 1: Population centers in the Municipality of Cartagena (own elaboration).  
* The pruning waste was provided by the Cartagena City Council's Parks and Gardens Service. The pruning residue taken was a representative sample that contained grass, tree pruning and shrubs in the municipality. The pruning was shredded and deposited in an aerated place, in an extended layer to avoid fermentation. The Cartagena City Council's Parks and Gardens Service registers an annual volume of biodegradable material of 2280 t. If plant raw material is needed, there is a central pruning and biowaste agricultural plant near to El Gorguel.
* _Posidonia oceanica_ (L.) Delile: is commonly known as Neptune grass or Mediterranean tapeweed; it was collected from the beaches of the municipality while cleaning. It was transported to the experimental station and spread in thin layers to avoid fermentation after being shredded into straw consistency, then sifted to remove as much as possible. The council collects 2090 t of _Posidonia oceanica_ (L.) [PERSON] from the beaches of the municipality annually.  
At the Experimental Station, three compost piles of 3.00 \(\times\) 1.50 \(\times\) 1.60 m were formed with these wastes in the shape of a triangular prism. Prior to the establishment of the compost heaps or piles, a characterization of the raw materials was carried out. This information is needed for the definition of the mixtures, since composting requires certain values for its activation. Initially, in the raw materials and in the mixtures during the test, pH, %C (Total organic matter method by calcination. Organic carbon = total organic matter 1.724), and N [18] were analyzed in order to determine compliance with the royal decree 506/2013 of June 28 [18], on fertilizer products. At the end of the trial, N, P, K, Ca, and Mg [18], Cr, Ni, Cu, Zn, Cd, Pb [18], Escherichia coli [19], and Salmonella [20] underwent the same analysis. The samples analyzed from the piles were mixed from three randomly selected areas each time.  
The piles were watered to maintain 55-60% moisture and flipped when they reached temperatures of around 60 \({}^{\circ}\)C, which corresponded to approximately one watering and one flipping per week per pile. Compost is known to be \"ready or done\" when the temperature drops to room temperature, in addition to the appearance of black soil with a loose consistency, no garbage odor, and a damp forest soil smell. Likewise, during the fermentation process, the C/N ratio should decrease to values between 12 and 18 [10].  
If the final obtained material after fermentation has a high C/N value, it indicates that it has not undergone complete decomposition, and if the ratio is very low, it may be due to excessive mineralization, although this depends on the characteristics of the input material, hence, the importance of identifying the volumes of each raw material to comprise the piles.