###### Abstract  
Municipal green waste (MGW) has significantly increased with the development of urban green areas, and its utilization by composting is a good alternative to solve the problem. This paper presents the results from the quality assessment of two industrial composts (from the composting facility of a regional nonhazardous waste landfill) based on their physicochemical properties, hygienic safety (microbiological parameters), fertilizing potential (by fertilizing index, FI) and heavy metal polluting potential (by clean index, CI). Composot 1 (C1) was made from MGW (100%) and Composot 2 (C2) was made from MGW (75%) and discarded green peppers (25%). The evaluation of physicochemical parameters was conducted according to Bulgarian Standards (BDS) methods and microbiological analysis using selective, chromogenic detection systems. It was found that the EC, P, K, Mg, Cu, Cr and Ni were lower for C1 (\(p\) < 0.05-0.001). On the other hand, Pb concentration was higher compared to C2 (\(p\) < 0.001); the concentrations of Cd, Hg and the _E. coli_ were very low for both composts; presence of _Salmonella_ was not detected. The estimated quality indexes (FI and CI) classified C1 as Class B compost (very-good-quality compost with medium fertilizing potential) and C2 as Class A compost (best-quality compost with high soil fertility potential and low heavy metal content). The C1 and C2 composts meet the requirements of EU and Bulgarian legislation and can be used as soil fertilizers. green waste; industrial composting; compost; clean index; fertilizing index; quality +
Footnote †: journal: Applied  
matter into circulation while maintaining the waste-soil-plant production continuum [9]. In addition, GW management is a key issue due to its high production rate and the variety of physical properties and chemical composition, making composting a promising alternative for GW treatment and valorization [10]. It should be also borne in mind that composts produced from different types of substrates have different characteristics and properties as soil fertilizers, and different potential markets and areas of application [11; 12]. Some reports [13; 14; 15; 16] have outlined the positive aspects related to the composting of biodegradable wastes: the reduced amount of waste to be disposed in landfills; reduced emissions of greenhouse gases, as the compost can sequester carbon and decrease net CO\({}_{2}\) emissions to the atmosphere; the presence of readily available compounds in the organic matter of biowaste that immediately can be used by the composting microbiota. Despite the positive aspects of GW composting and its application, some disadvantages should also be noted: GW compost quality strongly depends on the different compound patterns, which are highly variable and determined by the predominant vegetation in the area, the season and the local collection policy [17; 18]; its slow mineralization and the resulting sluggish progress of nutrient release diminish the agricultural value of composts [9]. During the past 20 years, extensive research on composting municipal green waste, either alone [17; 18; 19; 20; 21; 22; 4] or cocomposing with other organic wastes--food waste [5; 8; 10; 25], MSW [7], woody biomass [26], sewage sludge [9], agricultural plant residues [9; 27] and animal manure [28; 29], as well as with other additives, such as biomass ash [30], mushroom compost and biochar [31], sugarcane bagasse and grape marc [32], bean dress and crab shell powder [33], etc.--was performed worldwide. Simultaneously, technologies and facilities/plants for MGW composting/cocomposting were also developed. For example, in thirty-six states of the USA, 3474 GW composting facilities are in operation [34]. Green waste management by composting facilities was reported also from Spain (Madrid [35] and Catalonia [17; 29]), Lithuania [19] and Italy [27]. At Sofia University, Bulgaria, a pilot facility for garden waste composting was created to perform research and educational activity [36].