Physico-chemical changes and maturity evaluation of composts from wood residue mixed with sewage sludge and chicken manure

Purpose: Using the effective approaches for modifying the recycled wood as a novel bulky agent improves the quality of soil amendment. This study aimed to compare the stability and maturity of the soil amendments produced by the compostation of forest industrial waste and sewage sludge on seed germination. Method: Three materials, namely sawdust, sewage sludge, and chicken manure were mixed at different ratios (dry weight basis) to reach the initial bulk density of 0.40 Kg.L^-1, the temperature of 30 °C, the C/N ratio of 25, and the moisture content of 60 %. A pilot-scale composting process was applied to monitor the aeration rate, temperature, and moisture contents during the process over time. The comparison of physico-chemical, phytotoxicity, and germination indices among the samples was performed in three repetitions. Results: The results of this study indicated that the sustainable conditions (i.e., the temperature of 70 °C, aeration rate of 0.30 L.Kg^-1DM.min^-1, and moisture content of 50-60 %) can have a significant effect on the thermophilic stage for compost curing without any inhibitory repercussion. Increasing the germination index of cress (Lepidium sativum) up to 79 % proved that the toxicity of industrial sewage sludge was declined through the elimination of heavy metals. Conclusion: This study revealed that the availability of bulky agents such as wood residue can reinforce the microbial activity by continuously decreasing the C/N ratio to the minimum value of 13.2.