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 degrees C for more than 3d, but the period with temperature above 55 degrees 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 3000microScm(-1) for stable composts. Only the final NH(4)(+)-N of composting mixture with an initial C/N ratio of 28 did not exceed the limit value of 400mgkg(-1) to be considered a stable compost. The NO(3)(-) 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, 0.70mgh(-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%.