| Author | Kanatip Ratanachoo |
| Call Number | AIT Thesis no. EV-95-14 |
| Subject(s) | Sewage|xPurification--Heavy metals removal
|
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-95-14 |
| Abstract | Heavy metal removal from sewage sludge by biological method was carried out in a continuous stirred tank reactor(CSTR) with and without sludge recirculation and the factors affecting the process were investigated in order to determine the optimum operational conditions for maximum heavy metal removal. During settling periods in sedimentation tank, heavy metals were easily adsorbed by sludge solids especially at first 30 minutes of settling . Physical adsorption was the major mechanism of this event. The optimum settling time would be 60 minutes and pH of sludge should be less than 2.5 . Sequential extraction was performed to find out exchangeable, adsorbed, organic, carbonate and residual forms of the metal in sludge. Each metal showed binding characteristics of its own. Most of heavy metal associated mainly with organic fraction except Ni which retained mainly in residual form. Chemical leaching were carried out in batch system at pH 2.0 and 3.0 showed that solubilization percentage became high as the pH of sludge decreased. Cr very low leaching (0.7%) while Pb did not leached at pH 2.0. Exchangeable form of all metals increased whereas adsorbed, organic, carbonate and residual forms decreased after leaching. The factors affecting the continuous flow of bioleaching process under this consideration were HRTs, sludge recirculation and ferrous sulfate concentrations . For HRT, it is evident that solubilization percentage was slightly higher with longer HRT e.g. Cu, 72.91% at HRT 3 day and 63.78% at HRT 0.5 day . Especially, HRT increased solubilization percentage of Cu, Mn and Ni but not for Cr, Pb and Zn. 20% sludge recirculation increased solubilization percentage of Cr, Cu and Mn in a small amount at HRT 0.5 and 1 day, also Ni and Pb at HRT 1 day but not at HRT 0.5 day. No affect was observed for Zn at both HRTs. Increase of ferrous sulfate concentration made solubilization percentage increased in a considerable amount for Cu, Mn, Ni and Zn while slightly increased with Cr and Pb. After bacterial leaching, exchangeable form of Cu, Ni and Zn decreased and no change was found with Mn while Pb and Cr increased . Also carbonate form of Pb and Cr increased in a considerable amount. Organic form showed the most dominant decrease . The optimum operational conditions was obtained at HRT 1 day with 20% recirculation and 4 g/l of Fe804 • 7H20 resulted in the following metal solubilization : 6.78% Cr, 73 .78% Cu, 66.94% Mn, 52.72% Ni, 2 . 89% Pb and 86.49% Zn and leached sludge can be used in agriculture according to U.S.EPA standards, 1992. |
| Year | 1995 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. EV-95-14 |
| 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 (EV) |
| Chairperson(s) | Umita, Teruyuki |
| Examination Committee(s) | Stoll, Uwe;Yang, Byung-So |
| Scholarship Donor(s) | Petroleum Authority of Thailand (PTT) |
| Degree | Thesis (M. Sc.) - Asian Institute of Technology, 1995 |