## 3 Results and Discussion
### Evolution of the Physico-Chemical and Chemical Parameters  
Table 4 shows the evolution of the most relevant parameters in the sets during the composting process. The initial pH values in the set mixtures (Table 4) were within the optimal range (5.0-8.0) for the suitable development of the bacteria and fungi typical of the composting process [23].  
During the process, a progressive increase in pH was observed in the sets, up to values in the alkali range of 8.1 to 8.9 at the end of the composting period (Table 4), values that are in line with those previously observed in composting experiments using similar organic wastes [25; 28; 36]. The EC showed a similar trend to pH with initial values range from 3.6 to 5.8 dS m\({}^{-1}\) and an increase to final values between 4.6 to 7.5 dS m\({}^{-1}\). This increase could be associated with the observed organic matter degradation (Figure 4) and the subsequent concentration of soluble salts in the composting mass, as well as due to the absence of excessive irrigation, since the process was carried out in closed  
Figure 4: Organic matter (OM) losses (%) in the composting sets. Lines represent the curve fitting for each set.  
In general, the final composts showed high EC values, mainly due to the mineralization processes associated to the composting process, but especially due to the initial EC values showed by the FW, with EC initial values higher than 5 dS m\({}^{-1}\) (Tables 2 and 3). Salt concentrations in the final composts above 4 dS m\({}^{-1}\) can be detrimental to crops [38; 39], so it would be advisable to mix such materials with others prior to their use to reduce their salt content [4].  
On the other hand, OM concentrations were high at the beginning of the process in all the sets, with values of 92.0, 93.4, 87.6, and 92.1% for sets 1 to 4, respectively (Table 4). These values decreased with the composting process to final values of 76.7, 78.5, 75.3, and 78.9% for sets 1 to 4, respectively, with these values widely fulfilling EU regulations, which stipulate that a compost must contain a minimum of 15% organic matter calculated on a dry matter basis following the composting process [31].  
As a consequence of the loss of the composting mass due to the decomposition of the raw materials, the TN concentration increased in sets 1, 2 and 4. In contrast, this parameter exhibited a slight decline in set 3 during the composting process, which showed the highest value at the beginning of the process (Table 4). This decline could be attributed to the lower proportion of bulking material in the mixture, which avoids N losses by volatilization. [PERSON] et al. [40] also reported in a review about gaseous emissions during organic waste management the significant effect of the bulking agent in the reduction of N losses during composting. In this sense, the minimization of the N losses during composting not only increases the N contents of the compost obtained but also reduces odor emissions and thus environmental impacts, providing both economically and agronomically added value to the final compost, which can be used as a substitute for inorganic fertilizers in agriculture [3].