| Author | Wu, Zhiping |
| Call Number | AIT Thesis no.EV-95-42 |
| Subject(s) | Sewage|xPurification--Heavy metals removal
|
| Note | A thesis submitted in partial fulfilment of the requirement for the degree of Master of Science. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-95-42 |
| Abstract | The presence of heavy metals in sludge limits the application of sludge to agricultural land. Reduction of heavy metal content in sludge to an acceptable level is a necessity since applying sludge to agricultural land is an economical and environmentally friendly final. disposal mode. In this work, forms of heavy metals in anaerobically digested sludge and undigested sludge cake were investigated by using sequential extraction method. The effectiveness of ferric ion and ozone in oxidizing sulfides was studied based on the finding that major form of heavy metals in anaerobically digested sludge was sulfide. Leaching from anaerobically digested sludge by ozone was also studied. The effect of pH, solid content and ferric ion dosage in leaching was investigated for anaerobically digested sludge. Leaching of heavy metals from undigested sludge cake by FeC13 was also studied. Sulfide was found to be the major form of heavy metals in anaerobically digested sludge. But undigested sludge cake had fewer metals in oxidizable form than anaerobically digested sludge. Ozone was found not effective in leaching 'of heavy metals from sulfides and anaerobically digested sludge. For sulfides, it was due to the ineffective contact between gaseous ozone and very insoluble sulfides. For anaerobically digested sludge, it was due to the ineffective contact and strong scavenging capacity of the sludge. Ferric ion was found effective in leaching of heavy metals from anaerobically digested sludge and undigested sludge . .,~ cake. For anaerobically digested sludge, lower pH, lower solid content and higher ferric ion dosage were in favor of leaching. Better leaching effect was obser-ved at lower solid content because viscous nature. of the. sludge decreased reactants' activity at high solid content. After 4 days leaching by ferric ion at 1 % solid content, 1/3 FeC13 .6H~O to dry solid ratio and pH3, 13.5% Cr, 30% Cu, 59% Mn, 39% Ni, 14.5% Pb and 92% Zn were leached. For undigested sludge cake, its weak buffer capacity resulted in drastic drop of sample pH when ferric salt was added, then acid soluble heavy metals were dissolved and oxidizable heavy metal compounds might also be oxidized. After 7 days leaching by ferric ion at 1 % solid content and 1/6 FeC13.6H20 to dry solid ratio and pH3, 46% Cu, 51% Mn, 51% Ni, and 65% Zn were leached. |
| Year | 1995 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. EV-95-42 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Umita, Teruyuki; |
| Examination Committee(s) | Visvanathan, C.;Stoll, Uwe; |
| Scholarship Donor(s) | Government of Japan; |
| Degree | Thesis (M. Sc.) - Asian Institute of Technology, 1995 |