REMOVAL OF METALS FROM AEROBIC SLUDGES BY BIOLOGICAL SOLUBILIZATION IN BATCH REACTORS

Biological solubilization of metals in aerobic sludges was performed in 30-1 batches using thiobacilli bacteria. The use of control batches in this study demonstrated the ability of thiobacilli to acidify the environment and solubilize metals. The controls also identified the presence in sludes of naturally occurring thiobacilli. This study showed that sludges can be sufficiently decontaminated of most metals within two days so as to conform to the guidelines set by the Quebec ministry of the environment for use in agriculture. Chromium was the only metal in this study that could not be solubilized. Control at source would have to be implemented for this metal. The percent metal solubilizations obtained in reactors after 2 d were as follows: Cu, 47-80%; Mn, 81-89%; Ni, 42-60%. A solid-liquid separation study indicated that sludges subjected to the biological solubilization technique were in most cases more easily dehydrated than untreated sludges. Furthermore, no addition of polymer would be required to carry out the dehydration process by means of a plate filter press. Monitoring of the metals from the beginning of the process through the treatment and filtration allowed us to conclude that metals did not reprecipitate into the decontaminated sludge during the filtering process. Batch biological solubilization of metals is simple, and most likely can be applied in small waste water treatment stations.