Abstract: Bulking agent is important in the process of sewage sludge composting. A reasonable proportion of bulking agent added in the pile could improve the structure， and reduce costs of composting process. Sawdust was used as compost bulking agent in the present study to explore the influence of different sawdust addition ratios on the temperature and oxygen change during the process of sludge composting. The results showed that the amount of sawdust had a significant impact on temperature， oxygen and dehydration. Compared to the treatment with ratios of 3∶1 （m/m） and 5∶1 （m/m）， the treatment with ratios of 3.5∶1 （m/m） and 4∶1 （m/m） in sludge and sawdust showed higher heating rate， higher temperature， and longer thermophilic phase. The oxygen content at the end of blast and the minimum oxygen content before blast increased along with the compost process， and the oxygen consumption rate decreased. The oxygen consumption rate was higher when the ratios were 35∶1 （m/m） and 4∶1 （m/m）， and microbial activity was greater. The moisture content in compost material decreased with composting， and water removal was larger when the ratio was 3.5∶1 （m/m） or 4∶1 （m/m） than that of 3∶1 （m/m） and 5∶1 （m/m）. Taking the cost into account， the 4∶1 （m/m） ratio of sludge to sawdust was suggested for the sludge composting.

Key words: sewage sludge, composting, bulking agent, temperature, oxygen