Recycling wastes from Douro wine industry by composting
The process of composting winery wastewater sludge with grape stalks as bulking material and the use of the compost as soil amendment to fertilize the grapevines, or as substrate component for growing media, is an alternative to the disposal of these materials. However, there is a need to find out the ideal feedstock ratio for the composting blend to achieve high temperatures long enough for compost sanitation. With this aim, a composting experiment was carried out with sludge (C/N=12) and grape stalks (C/N=46) mixed in the proportion of 3:1, 2:1 and 1:1 (sludge:stalks; w:w), for piles 1, 2 and 3 respectively. The optimum mixing rate was 2:1 with temperatures above 55°C for 19 days. Although with increased N content, pile 1 did not attain 50°C because lower stalk content contributed to hamper aeration. At the end of the composting process (4 months) when pile temperatures were similar to ambient levels, all composts showed a high degree of maturation according to their NH4+-N content below 400 mg kg‑1. However, only pile 3 attained the ratio NH4+-N/NO3--N<0.5 (proposed as maturity index for compost). Nevertheless, the germination index >100% for these composts indicated their lack of phytotoxicity. The balance between average compost N, P, K, Ca and Mg contents close to nutrient requirements for grapevines, the electrical conductivity (0.2-0.6 dS m‑1) below the proposed limit for soil amendment of 3 dS m‑1 and their low levels of heavy metals, indicated good quality compost.
Pinto, R., Brito, L.M., Gonçalves, F., Mourão, I., Torres, L. and Coutinho, J. (2021). Recycling wastes from Douro wine industry by composting. Acta Hortic. 1305, 285-292
composting temperature, compost maturation, compost sanitation, grape stalks, winery wastewater sludge