Abstract
Composting is a process of exothermic oxidative microbial degradation and stabilization of organic residues. The microorganisms driving the process, which are determined by temperature, change during the different phases. The main objective of this research was to study both physicochemical and microbiological dynamics during the composting process of wine industry residues composed by exhausted grape pomace and stalks supplemented by sludge from a winery wastewater treatment plant. Three composting windrows of 41 m3 were constructed with 0, 10 and 20% sludge addition. Physical–chemical parameters were assessed following the Test Method for the Examination of Composting and Compost (TMECC), and the diversity and dynamics of bacterial and fungal communities involved in this process were assessed by a high-throughput sequencing metabarcoding approach. After six months of aerated turned windrow composting, it was observed that the addition of sludge increased moisture, bulk density, and pH. No effect of the sludge on the macronutrient composition of compost was observed. Bacterial and fungal dynamics showed significant differences depending on the addition of sludge and a high amount of beneficial microorganisms and a low presence of potentially pathogenic microorganisms in the final compost. Beneficial fungal phosphorus solubilizers, such as Aspergillus and Talaromyces, were found. Streptomyces and Mycobacterium were the most abundant beneficial bacteria. Finally, the addition of sludge results in a significant increase in the percentage of beneficial microorganisms in the final products.