The influence of the C: N ratio on the composting rate

Sewage sludge was composted with the addition of straw and sawdust to modify the C: N ratio of dry matter.The experiment was conducted in closed and insulated bioreactors, at four C: N ratios: 9.2, 12.1, 17.0 and 26.4.The following parameters were measured during the composting process: temperature inside the bioreactor, aeration rate, ammonia and carbon dioxide emissions from the bioreactor.The composting process lasted 25 days.Temperature was measured after the end of composting, up to day 33 of the experiment.The measured parameters were used to calculate accumulated temperature and composting rate.The results indicate that the C:N ratio significantly influenced the temperature inside the bioreactor (the higher the C:N ratio, the higher the temperature and composting rate) as well as cumulative emissions of CO 2 , H 2 S and NH 3 .The lowest cumulative gas emissions were noted in bioreactor R2 where the C: N ratio was very low at 12. Our results suggest that sewage sludge can be effectively composted with the addition of only 40% of straw / sawdust as bulking agents which increase substrate porosity and improve the C: N ratio.The substrate was effectively sanitized in all four bioreactors.