Evaluation of stability and maturity during forced-aeration composting of chicken manure and sawdust at different C/N ratios

We examined physicochemical and biological parameters in order to assess their effectiveness as stability and maturity indicators during the forced-aeration composting process of chicken manure mixed with different amounts of sawdust, yielding initial C/N ratios of 12, 18 and 28. The composting mixture with initial C/N ratio of 28 maintained the temperature exceeding 55 °C for more than 3 d, but the period with temperature above 55 °C in the bottom layer of the composting mixtures with initial C/N ratios of 12 and 18 did not meet the requirement of pathogen destruction. The final electrical conductivity in three composting mixtures did not exceed the limit value of 3000 μS cm−1 for stable composts. Only the final NH4+-N of composting mixture with an initial C/N ratio of 28 did not exceed the limit value of 400 mg kg−1 to be considered a stable compost. The NO3- content in the three composting mixtures increased with the composting time, and a more pronounced increase was found in the composting mixture with an initial C/N ratio of 28. The final specific oxygen uptake rate was 2.38, 2.35, 0.70 mg h−1 g−1 organic matter for composting mixtures of initial C/N ratio of 12, 18 and 28, respectively, which suggested a higher stability in composting mixture of initial C/N ratio of 28. The final germination index in composting mixture of initial C/N ratio of 28 was 94%; however, the germination indices in the composting mixtures of initial C/N ratio of 12, 18 were never over 80%.