## 3 Results and Discussion
### Assessment of Compost Quality  
The quality assessment of the produced composts was made in three aspects: (a) fertilizing potential and heavy metal polluting potential, and appropriateness as soil fertilizers according to (b) the Bulgarian legislation and (c) the EU legislation. The evaluation through the fertilizing index (FI) and the clean index (CI) [42; 54] used the equality-based parameters for determining compost's agronomic value in terms of fertilizing potential and heavy metal polluting potential. The results showed that the FI value of C2 was higher than that of C1, namely 4.33 vs. 3.40 (Table 3). According to the suggested classification [42], these values classified C1 as Class B compost (FI = 3.1-3.5) and C2 as Class A compost (FI \(>\) 3.5). The C2 compost prepared from the mixture of GW (75%) and discarded green peppers (25%) was a better soil fertilizer than the C1 compost prepared from GW only (100%). The fertilizing index reported for GW compost (FI = 4.47) and for compost made from green and food wastes (50-60%:50-40%) (FI = 4.27-5.0) was close to the FI value of C2 and higher than that of C1 [5]. Regarding the CI, the values were comparatively high and very similar for the two composts: CI = 4.26 (C1) and CI = 4.13 (C2). Based on the scores, the tested composts were classified as Class A (CI \(>\) 4.0), the highest class in the above-mentioned classification [42], corresponding to minimum heavy metal levels as well as minimum pollution threat to the environment [54]. FI and CI values of the two composts were comparable to--and in some cases were even higher than--those of composts produced by municipal solid wastes: FI = 1.8-4.2; CI = 0.5-5.0 [42]; FI = 4.47-4.6; CI = 2.33-2.38 [54]; FI = 3.5-3.6; CI = 4.0-5.0 [88]. Therefore, the composts produced from green biodegradable wastes were equally valuable soil fertilizers as composts produced from solid municipal organic waste. The final classification of both composts on the basis of the two indexes (FI and CI) classified C2 as Class A compost (FI \(>\) 3.5, CI \(>\) 4.0) and C1 as Class B compost (FI = 3.1-3.5,CI \(>\) 4.0). Class A determined C2 as a GW compost of best quality with high soil fertility potential and low heavy metal content, which could be used for high-value crops, such as in organic farming. Class B characterized C1 as a GW compost with very good quality with medium fertilizing potential and low heavy metal content [42]. Regardless of the established high fertilizing potential and low heavy metal polluting potential of the produced GW composts, they can be used as soil fertilizers only if they meet the requirements of Bulgarian and EU legislation in terms of environmental and human health protection. The national-level compost quality assessment, carried out through three physicochemical parameters (moisture content, pH and EC), seven heavy metals (Zn, Cu, Pb, Cr, Ni, Cd and Hg) and two microbiological parameters (_E. coli_ and _Salmonella_ spp.) showed that all monitored parameters for both composts (C1 and C2) were below the limits of the relevant standard [55] (Table 3). Only the moisture content was above the permissible standard limit (10%)--2.18 times for C1 and 1.79 times for C2. Unlike the other evaluated parameters, excess compost moisture could be relatively easily removed and brought to the standard limit, for example, by better aeration of stored compost batches. On the EU level, the assessment based on the seven above-mentioned heavy metals revealed that the concentrations of all elements in the produced composts were under the permissible limits according to Commission Regulation (EC) No 889/2008 [56] (Table 3). The only exception was the Cd content, which exceeded the permissible limit of the standard 1.28 times.