| "The behavior of heavy metals was investigated at 22 WWTPs. And the survey of heavy metal balance was conducted in detail at one WWTP. For the measurement, 22 kinds of heavy metals were selected from the chemical materials of PRTR. There were some heavy metals, which were detected not in wastewater but in de-watered sludge. By means of the detail survey at one WWTP, 60% to 80% of some heavy metals, such as “Pb”, “V”, “Cu”, “Ag”, “Cd”, “Sb” and “Ba”, were discharged with ashes. But it was observed that “Se” and “Cr” were circulated between wastewater treatment and sewage sludge treatment in the WWTP. To estimate the behavior of heavy metals in the environment, leaching tests were applied to the products made of biosolids. During a series of leaching tests for building materials, it was observed that the concentration of heavy metals was very small, but the ratio of increase keeps constant value. Products for recycling are requested not only to be produced constantly at WWTP but also to have the durability against climate. So the results of long-term exposure test will be important." |
