Abstract:

In order to investigate the variations of contents and chemical forms of heavy metals in the municipal sewage sludge during the alternative aerobic and anaerobic composting, municipal sewage sludge was mixed with municipal organic garbage to carry out a 602day alternative aerobic and anaerobic composting tryout. In the experiment, the moisture content and the C /N ratio were respectively controlled at about 60% and 30～40. The results indicate that (1) the contents of Cu, Ni, Cd, Cr and Pb all decrease, while the content of Zn slightly increases; (2) the contents of these metals are all lower than the sewage sludge indices set by the state for agronomic use; (3) the distributions of chemical forms of these heavy metals greatly change after the composting, especially, the proportions and contents of Cu, Ni, Cd, Cr and Pb in changeable form decrease obviously; and (4) the proportion of Zn in changeable form decreases, while the content slightly increases. These results indicate that the alternative aerobic and anaerobic composting can p revent the soil and water from being contaminated by heavy metals when municipal sewage sludge and organic garbage are adop ted for in agronomic use.

Key words: heavy metal, municipal sewage sludge, composting