## 2 Materials and Methods  
### Starting Materials and Mixtures  
Among the different raw materials selected, only two were conventional virgins: a local ferruginous (around 8 wt% of Fe\({}_{2}\)O\({}_{3}\)) red clay (used as ceramic matrix for lightweight aggregates) and reagent grade K\({}_{2}\)CO\({}_{3}\) (put in some compositions as potassium carrier). The other are residues, post-consumer products, or sub-products. Packaging glass cullet or quarry scrap pumice were used as vitriying agents in the realization of glasses or ceramic aggregates. Spent coffee grounds (SCG), thanks to their high LoI, 98%, and with a C content around 50 wt% were used as pouring agent for aggregates; cattle bone flour ash (41 wt% of P\({}_{2}\)O\({}_{5}\)) and vegetable biomass ash (60 wt% of K\({}_{2}\)O) (in some case this last substituted by reagent grade K\({}_{2}\)CO\({}_{3}\)) were considered alternative raw materials for the supply of the two main nutrients, phosphorus and potassium, respectively. The third main nutrient, nitrogen, was applied on a selected composition of aggregate using an organic nitrogen-based coating (average N content ranging from 8 to 9 wt%) extracted from black soldier fly (BSF) prepupae reared on poultry dejections and compared to a commercial organic nitrogen fertilizer of blood derivation. The volcanic scrap (pumice) is a natural porous silico-aluminous mineral containing 57 wt% SiO\({}_{2}\) (determined by XRF analysis, here not reported), and it is a good substituent of local clay as a silicon source. The mineralogical analysis highlighted that only a small amount of SiO\({}_{2}\) is in the crystalline phase constituted by sanidine (11%), quartz (1%), anorthite (3%), muscovite (4%), and traces of feldsparoids, the rest is in the composition of the amorphous phase (80%). A deep characterization of the other raw materials was provided in the previous publication of the authors [12].  
Two series of samples were prepared and studied: the first constituted by glasses and the second by aggregates, as shown in Table 1. Three glasses (FG1, FG2, and FG3) were obtained by melting in electric furnace at 1450 \({}^{\circ}\)C, varying both the vitriying component (packaging glass cullet or pumice scrap) and the potassium carrier (reagent grade K\({}_{2}\)CO\({}_{3}\) or vegetable biomass ash), but keeping fixed the introduction of P\({}_{2}\)O\({}_{5}\) in the form of cattle bone flour ash. All the fertilizer glasses produced were tailored to have the following amounts of the main oxides: SiO\({}_{2}\) (30-32 wt%), Al\({}_{2}\)O\({}_{3}\) (1-4 wt%), K\({}_{2}\)O (-15 wt%), Na\({}_{2}\)O (-6 wt%), CaO (24-26 wt%), MgO (-1.50 wt%), P\({}_{2}\)O\({}_{5}\) (-15 wt%).  
Eight aggregates were tailored and obtained by fast powder sintering at 1000 \({}^{\circ}\)C. A first series was constituted starting from a formulation of 85 wt% of clay and 15 wt% of spent coffee grounds alone (C) and addition of 50 wt% of P, K nutrients vitrified by packaging glass cullet (CFG2) or non-vitrified (CNUT2). A second series was represented by aggregates of half part of clay and half part of pumice (volcanic inert) for a total of 85 wt%, plus 15 wt% of spent coffee grounds alone (CP) and addition of 50 wt% of P, K nutrients vitrified by pumice scrap (CPFG3) or non-vitrified (CPNUT3). Finally, a third series was represented by the specimens with half part of clay and half part of pumice as matrix and FG3 glass and coated by a nitrogen-containing layer of degreased from biomass of soldier fly prepupas (CPFG3N1) compared to a commercial product based on animal blood (CPFG3N2).