Comparative analysis of phytotoxicity and compost quality in industrial composting facilities processing different organic wastes

Abstract A comparative analysis of industrial composting facilities processing Vegetal Residues, Sewage Sludge, Municipal Solid Waste, Agri-food Waste or Olive Mill Waste was performed. The evolution of phytotoxicity during composting was analyzed by measuring the germination index. Physico-chemical parameters (pH, electrical conductivity, organic matter, reducing sugars, phenolic compounds, humic substances, soluble organic carbon, N–NH4+ and N–NO3-) and heavy metals content were evaluated in final products. The material became non-phytotoxic at the cooling phase or at the end of composting in facilities processing Olive Mill Waste, Sewage Sludge, and Agri-food Waste. In facilities processing Municipal Solid Waste and Vegetal Residues, the material never lost phytotoxicity. All composts, except Municipal Solid Waste, fulfill requirements of the Spanish legislation for heavy metals content. Phytotoxicity was attributed to the high electrical conductivity and pH of the Vegetal Residues compost and heavy metal content of the Municipal Solid Waste compost. Germination index is recommended to track the performance of industrial composting. This work provides new insights for the better management of composting at the industrial scale.