Co-composting a grape marc: An influence of grape stalks and different biowastes presence on the physical - chemical parameters of the mixture

Grape pomace (GP) represents a solid residue generated after the wine-making process and includes grape marc (GM) and it contains skins, seeds, pulp and grape stalks (GS). In this work, eight different mixtures of GM and organic wastes, was observed with an aim to investigate the effect of co-supstrate and GS presence. In the first experiment, GM and co-substrates was co-composted together, in mixture M1, GM was mixed with food waste (FW), in mixture M2, GM mixed with poultry manure (PM), in M3, GM mixed with wheat straw (WS) and GM mixed with FW, PM and WS in M4. In the second experiment, in M5, GM, FW mixed with GS, in M6, GM, PM mixed with GS, in M7, GM, WS mixed with GS, and GM, FW, PM, WS mixed with GS in M8. During the co- composting, the all mixtures achieved two temperature peaks and the acidic phase lasted 10-23 days in first experiment and 6-16 days in second experiment. The loss of total OM and total C was recorded, and a total N increased from 0.58 % to 91.5% in both experiments. The four mixtures from the both experiments showed the bigger change, reaching the C/N ratio around 15 which is characteristic of the end of process, while in the other mixtures, the C/N was higher than 20. The analyses of biodegradability showed that the six mixtures has a higher biodegradability rate (from 15.03 % to 25%). A slight decrease in the biodegradability when is WS co-substrate (5.66 % and 5.23 %) was found. Thus, co-composting process might be suitable treatment for GM, especially when the co-subtracts are PM and FW, and GS as the bulking agent. In this way, the recycling and velarization of those wastes can be achieved, with positive environmental effects.